I've seen a few articles suggesting wider tyres are quicker or have lower rolling resistance.
I came across this website
[url= http://www.bicyclerollingresistance.com/mtb-reviews ]rolling resistance site for tyres[/url]
The tyre with the lowest rolling resistance is a 2.35
Can anyone help me understand? This is something discussed on GCN to for road bikes.
Yet it goes against everything I know.
Surely this can be sorted empirically?
2.8 tyres running at 15psi were unnaturally fast.
They also punctured remarkably easily so swings and roundabouts.
Why though. All I can see is a big sloppy tyre grabbing the floor?
(I'm about to suit up with 2.8s on a new + bike)
It depends. Supple tyres conform to the ground better so there is less vibration and the bike "flows" over the ground faster. Same as having suspension vs. rigid on rough terrain. If the tyre is stiff or really high pressure you don't get the advantage. Read Jan Heines blog, he explains it way better than me!
Think it depends on road surface too. A bigger tyre will roll smoother on a rough surface, is my understanding. A bigger tyre is also heavier and potentially less aerodynamic, so there's more to consider than the rolling resistance itself.
Yes, it depends. Having ridden a stony rough trail downhill on 2.35s at 35psi with someone on 3.0s at 15psi, he was rolling straight past me as I was pedalling, the difference was astonishing.
Probably slower on smooth surfaces though.
Okay I'm with this - but the GCN was referring to road cycling.
Something to do with contact patch shape?
There are two main factors - the friction between the tyre and the ground, in particular the contact patch and the energy losses created by the tyre carcass deflecting. Wider tyres have a wider, shorter contact area which is smaller than a skinny tyre i.e. less friction. A wider tyre also doesn't distort as much as a skinny tyre for the same pressure, so the energy losses are less. Off road, there are also losses due to the tyre distorting the soft surface - a wide tyre often doesn't leave as big an imprint. Wider tyres are heavier, so lose during acceleration, but once up to speed its in the favour of the wider tyre. Wide tyres can also be run safely at lower pressures, so offroad give you more grip on rocks and roots which really helps on climbs. Aerodynamics has negligible impact on the road - makers starting to look at 28mm tyres for road racing
The part of the tyre having to deform to the flat road surface is less ceived on a wider tyre so deforms less, which uses less energy
Mass spread over a larger tyre area equalling less kg per square mm? Would that not mean less friction?
Probably wrong! 🙂
Hysteresis innit???????
The point that many many miss is that the wider tyres only have lower RR if they are at the same pressure. In reality most people ride wider tyres at lower pressure so are used to thinking of them as slow. Plus, fatter tyres have more aero resistance as well.
You referring to me, molgrips? If so, I remember that myself, and was as astonished as you.
rone - Member
...The tyre with the lowest rolling resistance is a 2.35Can anyone help me understand? This is something discussed on GCN to for road bikes.
Yet it goes against everything I know.
It's true. I've been preaching this for over 50 years.
The reason it never caught on earlier is because racing doesn't improve the breed, but fashion follows racing, and therefore wheels got thinner and thinner as roads tended towards smoother.
The end result is that road bikes were not able to fit wide tyres. Also wide tyres tended to be more for industrial uses - eg trade bicycles had 26" tyres with 2" section, but they were coarse with thick sidewalls, the very opposite of supple.
For several years I've been running converted 29ers as road bikes using Big Apple 2.35" tyres. Freewheeling downhill beside other road bikes I have to trail my brakes to keep level.
In cycling magazines of the 1920s there would occasionally be an old hand bemoaning the lack of 2" tyres since WW1.
The tyre manufacturers are starting to recognise this and produce suitable tyres so it's easy enough to try if you have a 29er handy.
All you need is a supple tyre and a lower pressure than you'd think.
Comfort is much improved too.
However if you're an actual racer I suspect 2.35" may be a handicap at speeds where aerodynamics are critical.
You're comparing apples and oranges. Yes the rolling resistance is lowest for a 2.35, but thats also a tyre with no tread. If you look at the numbers you'll see that construction of the tyre has a much bigger effect than size. Unfortunately while I like the site, its also limited to its sample set, so not so useful as to draw a conclusion about how size etc. effects rolling resistance (at least off road - I must confess Ive never checked out the data for the dark side). I actually offered to send the guy that runs the site a free box full of tyres to test in various sizes and compounds to get a more useful data set, but he never got back to me 🙁
To a point I believe it, certainly never noticed any difference moving from 23 to 25 to 28, other than more comfort/confidence on descents.
However, DEFINITELY noticed the difference going from a 40 to a 32 on my commuter, even having fitted mudguards at the same time as the 32s it still feels faster. So I reckon the effect tops out somewhere.
[url= https://www.schwalbe.com/en/balloonbikes.html ]I think this mob have a suitably wide choice of tyres to pick from....[/url]
Feeling faster isn't necessarily the same as actually being faster though.
singletrackmind - Member
Hysteresis innit???????
It's not THAT funny.
singletrackmind - Member
Hysteresis innit???????
Laugh! I nearly bought one
As I understand it, it will depend on the surface. A perfectly smooth, perfectly hard road surface would give lowest rolling resistance with a very narrow, hard tyre at very high pressure.
In the real world, the rougher the surface, the lower the ideal pressure, and the wider the ideal tyre. At the same pressure, a wide tyre and a narrow tyre will have the same contact areas, so a wider tyre will have less sidewall deflection at the same pressure.
On a soft surface, you need a tyre pressure low enough that the road surface doesn't deform, so a wide tyre at low pressure will roll much faster.
On road, aerodynamic drag is much more important than rolling resistance, so narrow rims and tyres are faster.
On the subject and a bit more, these are worth a read...
https://janheine.wordpress.com/2014/01/01/tires-how-wide-is-too-wide/
https://janheine.wordpress.com/2014/01/05/wide-and-fast-tires/
https://janheine.wordpress.com/2015/02/17/tire-pressure-data-and-details/
https://janheine.wordpress.com/2010/10/18/science-and-bicycles-1-tires-and-pressure/
higher pressures result in more vertical change in direction.. having your bike and body going up and down over rocks and roots results in a change (decrease) in your forward speed. More control to boot.
Softer tyres deform to trail imperfections and require less vertical bike deflection.
According to a pinkbike article on the topic which I cant find.
For me, 2.4" tires at 20psi and a dad bod result in much quicker trail/race times than my old 2.0" @40+psi back when I was fitter, lighter and riding much more.
I understand that wider road tyres are also gaining traction for their aero improvements
The trend for wide road bike tyres is BS to sell you something new..
If wider tyres offered less rolling resistance on smooth roads I doubt the car manufacturers would be fitting super narrow high pressure tyres to cars when they game the pollution tests.
If you want to believe overwise carry on, by the way your helmet will aso explode after two years and any bike without discs is a danger to humanity.
The trend for wide road bike tyres is BS to sell you something new.
But if you've got to replace tyres anyway then you'd be buying something irrespective?
The trend for wide road bike tyres is BS to sell you something new..
A wider tyre is more comfortable, has more grip and is marginally faster and is marginally less likely to puncture. Why wouldn't you use one?
If you think you can compare a car and it's tyres to a bike and it's tyres you may want to do a bit of research....
I doubt the car manufacturers would be fitting super narrow high pressure tyres to cars when they game the pollution tests
Passenger car tyres are generally inflated to 30 to 35 PSI. Skinny bike tyres are often twice that, despite carrying less than 10% of the weight. Even narrow, low rolling resistance car tyres run much lower tyre pressures than most road bikes. Also, a narrower wheel and tyre will lower a car's aerodynamic drag enough to improve fuel consumption at highway speeds.
I've seen a few articles suggesting wider tyres are quicker or have lower rolling resistance.I came across this website
rolling resistance site for tyres
The tyre with the lowest rolling resistance is a 2.35
That test uses a flawed method though. What it's checking for is the lowest amount of resistance to sidewall and tread flex. That will be related to actual road/trail rolling resistance in part but to be fully representative you wouldn't use a smooth drum. Rolling resistance in the real world is related to a tyre's ability to do what many above have described, provide the micro-suspension that stops your bike and body weight being bounced over bumps and keeps you moving forward efficiently.
Once you factor in pressures needed to prevent pinch flats, a larger tyre with less pressure and a flexible casing does that very well.
Roads aren't generally that smooth, road bikes are light and easily deflected and the speeds are high so those vibrations and small impacts are happening with a fair bit of force. Any gain in ability to manage the road surface via the tyre deformation will mean a gain in efficiency. The difference is more easily noticed off-road but the gain is there for roadies too.Okay I'm with this - but the GCN was referring to road cycling.
This is worth a listen:
Hmm doesn't see very clear as usual.
Maybe letting my own bike roll down a hill with different tyres on may shed some light as I pass the speed indicator at the bottom.
As for the rolling resistance test site no being very accurate, do we have an alternative? Not that I've seen.
I tried a test off the back of that podcast with some 28mm Gatorskins at 200w. 120,100 and 80 psi. All three were 16.7mph. The difference in comfort was night and day though.
Non of the reasons given explain why car manufacturers with all their resources choose narrow tyres over wide tyres to significantly reduce rolling resistance.
Because we're talking about bicycles, not cars.
hols2 - Member
As I understand it, it will depend on the surface. A perfectly smooth, perfectly hard road surface would give lowest rolling resistance with a very narrow, hard tyre at very high pressure...
That's the nub of it. The ideal is a steel wheel on a steel surface, ie rails. They have the lowest rolling resistance. SImilarly a very hard narrow tyre on smooth concrete is pretty good.
However most of us live in a real world of roads with exposed aggregate, lumpy surfaces, slightly raised manhole covers, potholes, etc etc.
I wonder how many of the naysayers have actually ridden a bike with proper wide tyres.
BTW 28mm isn't wide. 🙂
Non of the reasons given explain why car manufacturers with all their resources choose narrow tyres over wide tyres to significantly reduce rolling resistance.
A fairly narrow car tyre is 175mm wide. A wide car tyre is twice that. They have a flat contact patch because the wheel stays close to vertical all of the time, so the contact patch is wide, hence they run fairly low pressures. A narrow bike tyre is less than 25mm wide. A wide bike for on-road is still less than 50mm wide. They have a round profile because the bike leans over massively when cornering, hence they run much higher pressures than cars. The considerations in a car tyre and bike tyre are completely different.
Too many variables in MTB imo.
With road I have the suspicion that its the 'tallness' of the tyre that makes the difference. ie a 28mm tyre is 5mm wider but also 5mm (ish) taller. So epicyclo when riding downhill your bigger tyres are faster because the circumference of the wheel is bigger not because of the width of tyre.
I was very disappointed when my Vittoria Corsa 25c tyres measured 23mm and with a 'tallness' to match the 23c Contis they replaced.
Non of the reasons given explain why car manufacturers with all their resources choose narrow tyres over wide tyres to significantly reduce rolling resistance.
Because modern cars do not use narrow tyres, they are all on wide tyres when you compare across the 150 years of motor vehicles. Road bicycles are still on skinny tyres compared to the whole history of bikes.
Here's a modern eco car and its tyres:
[img] 
[/img]
Here's a 1930s racing car (and racing cars tend to have wide tyres for grip) and its tyres
[img] 
[/img]
Also, much of the efficiency loss when car tyres go past their optimum width for efficiency is due to increased aerodynamic drag, not rolling resistance.
I think comfort has a big part to play too.
You're more efficient when you're comfortable, you don't tense up as much and you pedal much more smoothly, for longer.
Less mentally tiring too, which makes you happier as well as faster.
Not when they are cheating efficiency tests. The manufacturers take a car that woyld normally have wide tyres and reduce its rolling resistance by fitting narroe tyres at above normal pressures.
If wide tyres dont add to rolling resistance why would rhey go to the trouble. Its not for aero fains because much of the testing is in a rolling road or low speed.
We also know that much wider tyres on the road offer considerably more rolling resistance but we are saying marginally wider offers less? Thats illogical.
I get it for comfort and grip off road or broken roads but on normal roads I dont think you'll reduce the rolling resistance over 23/25mm 100psi tyres by going wider or lower pressure.
I have no empirical data to bring to this debate 😉 However, I lent a mate of mine my Solaris Max running 2.8 tyres at 12 PSI last night. I'm normally a quicker climber than him, but he beasted me. Many other variables suggest this might not be statistically significant!
What was interesting tho - as this was his first ever ride on chubby tyres - was his insistence (and my refusal) they needed more air when he first sat on it, and his perception of how much quicker they climbed on the rooty/loamy trails we have here and how much trouble he had slowing the bike down once it got up to speed compared to his 650b bike shod with 2.3 tyres.
I was riding 29x2.35s. First time after riding 2.8s for five months. They certainly spun up to speed faster, but didn't seem to roll better when I was chasing on the descents.
Still in other news, how fantastic are tyres compared to what we had a few years ago.
cars != bicycles, stop comparing them.
I don't think you'll reduce the rolling resistance over 23/25mm 100psi tyres by going wider or lower pressure.
There is significant evidence that says otherwise [i]for real world road conditions[/i].
We also know that much wider tyres on the road offer considerably more rolling resistance but we are saying marginally wider offers less? Thats illogical.
It's not illogical at all, there's an inflection point, you don't/can't just extrapolate in one direction and assume everything follows that trend forever.
Too narrow and high pressure = greater suspension losses, and carcass deformation.
Too wide = greater losses to aerordynamics, weight and friction
In the middle is the variable zone where the optimum depends on the exact conditions in terms of surface, speed, pressure, and specific tyre casing construction.
The fastest tyres will be lightweight, supple casing tyres, of a size and pressure that allow you to minimise hysteresis losses and minimise suspension losses, while balanced against rolling friction losses and aerodynamic losses. It's that balance point in the middle, too far either way and you lose out.
One of the things that has clouded opinion over the years is that mostly 'big' road tyres were also sturdy overbuilt touring style tyres, whihc would never be quick due to their casings and compounds, so people equated big with slow, when it was actually that [i]type [/i]of tyre that was slow.
Build 30-40+mm tyres with the same casings as proper racing tyres and it's a whole differnt ball game. The crazy thing is that these tyres were available in the early half of the 20th century, and were being used to great effect, it's the weird 30+ year blip in the 70s(ish)-80s-90s and 00's where everything went super narrow for no good reason*.
Those kinds of tyres are now starting to become available again, although in limited ways, it's almost as if we're having to re-capture lost knowledge.
*mostly driven by racing and bad testing conditions. At high speeds aero has a much higher impact than for 'normal' road conditions,so they went narrower and narrower, fashion followed. Made worse by rolling resistance testing that doesn't replicate real world conditions**.
** smooth rollers are a terrible approximation of a road, they tried bumpy rollers to improve matters, but they're still a poor approximation, and the one thing NONE of the 'official' rolling resistance tests actually include is the 70kg jump of meat on top of the bicycle and how jiggling that around impacts speeds in the real world.
If wide tyres dont add to rolling resistance why would rhey go to the trouble. Its not for aero fains because much of the testing is in a rolling road or low speed
You answered your own question. Rolling roads are very smooth, so narrow tyres are indeed lower RR. See also track bikes.
However in the real world the advantages that a wide tyre can offer on rough surfaces outweigh the effect of the width.
Hysterical losses is really complicated to think about. It is not just the tyre that passes through the contact patch that gets hysterical. The sidewalls will bulge as they go past the contact patch. Plus probably some squirm resulting in road/tyre friction energy loss. With a wider tyre and a narrower tyre at the same pressure, I think more bits of the wider tyre will get hysterical, but they will deform less. The data suggest that the latter effect outweighs the former (up to a point).
Measured rolling resistance of GP4000S in 23, 25 and 28 sizes...
http://www.bicyclerollingresistance.com/specials/conti-gp4000s-ii-23-25-28
Not when they are cheating efficiency tests. The manufacturers take a car that woyld normally have wide tyres and reduce its rolling resistance by fitting narroe tyres at above normal pressures.
I don't know how these efficiency tests are done but if they're not on a normal road surface with all its imperfections then it is a deeply flawed test.
Make an essentially perfectly smooth surface and then the minimum rolling resistance comes from very high ground pressure - that's how railways work. As cars and bikes do not run on rails then the optimum pressure is lower. The lower the optimum pressure then the wider the tyre needs to be ensure you don't end up with increasing hysteresis looses due to sidewall flex.
Note that radial tyre construction allows increased sidewall flex for a given hysteresis loss so you can run lower pressures without being penalised.
then it is a deeply flawed test
We all know they are deeply flawed, just look at the results!
Incidentally, VW's specs for my Passat are quite a bit higher than the charts the tyre companies get sent out - 38psi vs 33psi. Car is more comfortable at 33 as you'd expect, but I do lose maybe one or two mpg although it's difficult to detect in the noise.
Too narrow and high pressure = greater suspension losses, and carcass deformation.Too wide = greater losses to aerordynamics, weight and friction
In the middle is the variable zone where the optimum depends on the exact conditions in terms of surface, speed, pressure, and specific tyre casing construction.
The fastest tyres will be lightweight, supple casing tyres, of a size and pressure that allow you to minimise hysteresis losses and minimise suspension losses, while balanced against rolling friction losses and aerodynamic losses. It's that balance point in the middle, too far either way and you lose out.
I think you've made sense of it there.
What I have learnt thought is just pumping up a narrow mountain bike tyre doesn't necessarily make it faster because of all the variables to take into account.
I just assumed it was a given.
This is worth a listen:
That is a great listen and covers most of the stuff discussed.
I get it for comfort and grip off road or broken roads but on normal roads I dont think you'll reduce the rolling resistance over 23/25mm 100psi tyres by going wider or lower pressure.
And you are basing this on?
It was the early-mid 80s when 'aero' was all the rage for road bikes and the introduction of super-skinny 18-20 tyres and rims - not supported by any scientific data and it's taken a long time for folks to change their views - particularly believing a 1-2mm difference in tyre width has any aerodynamic impact. Another factor is the impact of riding skinny, hard tyres is increased rider fatigue. The advent of super-stiff, 'aero' carbon frames and deep-rim wheels don't help either - they often give you a complete battering.
mrblobby - Member
Measured rolling resistance of GP4000S in 23, 25 and 28 sizes...http://www.bicyclerollingresistance.com/specials/conti-gp4000s-ii-23-25-28
And more importantly, that's on a smooth(ish) drum, so it's only influenced by the shape of the contact patch and they carcass deformation to achieve it. On a real road you get all those added benefits of vibration absorption.
Basicly you could go as wide as you like until you start to trade off against weight (impacting acceleration) and aero drag (influencing top speed). So track sprinters are unlikely to ever stray into bigger tyres, but everyone else will probably find their optimum with wider tyres.
Car tyres are a red herring.
1) Their contact patch is rectangular, not round. So you have to balance load against construction and pressure, you can't just swap to a wide tyre and low pressure and get similar performance.
3) A car tyre has very different construction to a bike tyre. A bike tyre looks very similar inside all the way bead to bead (additional reinforcements aside). A car tyre has completely different constructions to achieve vertical sidewalls, the tread area, and even under the different areas of the tread.
4) Car tyres have to prevent aquaplaning, a lightweight car needs narrow tyres to maintain grip in the wet. A 2ton Range Rover doesn't quite have the same problem when fitted with 280 section tyres! It also needs those big tyres to dissipate the heat generated keeping all that weight on the road in the dry!
And it's still a compromise, a wide tyre has more of every other type of 'drag', so you still have to compromise. A car that does 70mph obviously has a different optimum to a road cyclist on a 15-20mph club run.
And you are basing this on?
Its what 99.9% of the millions of people who want to go fast on a bicycle use.
http://www.bicyclerollingresistance.com/specials/conti-gp4000s-ii-23-25-28
/p>
Looking at that page. I run 23mm GP4000S at 100R/90F. If I go to 25mm I'm going to gain approx 0.2 watts per wheel (if it doubles up like that). The tyre will be heavier and less aero so I am guessing these will all just about equal out and there'll be no real world benefit.
BUT, I wouldn't run 25mm tyres at the same pressure, so now the 25mm tyres at a lower pressure are heavier, less aero and more draggy.
I accept there's better grip due to an improved contact patch shape, better comfort due to the larger volume tyre and lower pressure, but I'm still to be convinced you can have both of these AND lower rolling resistance / more speed.
wilburt - Member
And you are basing this on?
Its what 99.9% of the millions of people who want to go fast on a bicycle use.
So your argument is based on hearsay rather than maths and science?
Which way did you vote on Brexit?
BUT, I wouldn't run 25mm tyres at the same pressure, so now the 25mm tyres at a lower pressure are heavier, less aero and more draggy.
I'd hazard that the incremental aero losses of the tyre are relatively small, especially when aero wheels are getting wider too. And the 25 is a whole 11g heavier, so ~1% of the wheel.
At some point it becomes self defeating going bigger, but I doubt it's 24mm.
Otherwise, why run 23mm? Why not 21, or 19?
What this thread needs is a conveyor belt.
Its what 99.9% of the millions of people who[i] want [/i][b]to go fast on a bicycle use.
Yes, but do they actually go faster...?
Do a bit of reading, some links already posted on here, plenty more out there.
The evidence shows that narrow and high pressure does not equal faster except under artificial conditions.
Just because millions of people are doing it, doesn't mean it's right 😉
Also, as a few of us have already mentioned, before everyone was running thin and hard to go fast, people used to go wide and soft to go fast*.
If you look at this in pure isolation it means one of those groups of people got it wrong. Or possibly they were both right but didn't fully understand the situation.
if you come back with a counter argument that the early group were wrong and revised/better understanding lead to a change (thin and narrow) then why can you not accept that same process is at work now as we further our understanding even more?
*on handmade cotton casing lightweight supple tyres, it's important to compare tyres of similar construction and not just size.
ie: a 38mm touring tyre (eg. marathon plus) won't be quicker than a 25mm racing tyre. But it will be quicker than 30mm marathon plus at the same pressure.
Now translate that back to your racing tyre... a 30mm tyre of eqaal construction can/will be quicker than it's 25mm counterpart.
(Until you reach a point at which aero drag dominates the losses.)
so now the 25mm tyres at a lower pressure are heavier, less aero and more draggy.
But aren't people saying that lower pressures isn't less draggy due to roughness in the road surface?
I accept there's better grip to due an improved contact patch shape, better comfort due to the larger volume tyre and lower pressure, but I'm still to be convinced you can have both of these AND lower rolling resistance / more speed.
You can't really. You can either run them both at same pressure and have less rolling resistance with the wider tyre. Or you can run the wider tyre at a lower pressure and have roughly the same rolling resistance but a bit more comfort (which may well allow you to ride harder.)
Basicly you could go as wide as you like until you start to trade off against weight (impacting acceleration) and aero drag (influencing top speed).
The higher the speeds the more significant small aero gains become. A quick bit of googling suggests that a 22mm turbo cotton has a CdA about 0.002 better than a 24mm turbo cotton on a HED Jet 6 rim (0.020 vs 0.018). Plug this into the drag/speed/power equations and it's easy enough to work out the tipping point.
The higher the speeds the more significant small aero gains become. A quick bit of googling suggests that a 22mm turbo cotton has a CdA about 0.002 better than a 24mm turbo cotton on a HED Jet 6 rim (0.020 vs 0.018). Plug this into the drag/speed/power equations and it's easy enough to work out the tipping point.
In isolation yes, but when the aero drag of the system as a whole is dominated by the lump on top of the bike, and then the whirly bits disturbing the flow, the small (but significant in isolation) change from tyre size alone isn't as important.
BUT, I wouldn't run 25mm tyres at the same pressure, so now the 25mm tyres at a lower pressure are heavier, less aero and more draggy.I accept there's better grip due to an improved contact patch shape, better comfort due to the larger volume tyre and lower pressure, but I'm still to be convinced you can have both of these AND lower rolling resistance / more speed.
There is some data (limited but increasing, mostly because not well tested yet) out there about how changes in pressure have very low effect on RR for decent lightweight supple tyres. Certainly less variation than for heavier casing tyres.
ie: the penalty for a lower pressure on a decent supple tyre is a lot less than the penalty on a stiffer carcass tyre, in some cases to the point where the reduced RR from the increase in size can then be 'used' to lower the pressure and bring you back to a net zero change in RR at the road, but with increased grip and comfort.
This obviously isn't always the case, and can be very condition specific, but again the thing that repeatedly gets ignored is the effect of jiggling a 70kg human around on top of the bike.
So even in cases where you might have a small increase in actual RR at the road, you end up with an net overall speed gain due to reduced suspension losses and reduced fatigue/better ability to apply power. And the longer the ride the more relevant that becomes. A straight out track sprint is a different ball game to a few hundred kilometres on rough roads.
When you look at the system as a whole 'speed' is about more than just the RR.
It really is a fascinating area to look into and research, but does require leaving some preconceptions at the door (from both sides of the argument!)
But aren't people saying that lower pressures isn't less draggy due to roughness in the road surface?
Yes, they're saying that. I'm saying I'm not convinced they're any faster.
If the numbers on that site are to be believed then the bigger tyre is draggier albeit on a smoothish drum. Lets say for the sake of argument the bigger tyre is less draggy on a rough surface than it is on the drum
So you're back where you started with your narrow tyre at a higher pressure, but with slightly better grip, and a little bit more comfort, but no faster.
In isolation yes, but when the aero drag of the system as a whole is dominated by the lump on top of the bike, and then the whirly bits disturbing the flow, the small (but significant in isolation) change from tyre size alone isn't as important.
Tell that to a tester who spends thousands on aero testing 🙂 Tiny gains wherever you can find them add up.
So you're back where you started with your narrow tyre at a higher pressure, but with slightly better grip, and a little bit more comfort, but no faster.
Or...your bigger tyre at the same pressure and faster. There are choices as to whether you jsut go bigger and run the same pressure, or go bigger and drop pressure.
Or as with my post above, "it's complicated" due to other factors, and the mixed terminology when talking about 'speed'
ie:
speed, as in on a drum/in a test due to lower measurable RR
vs
speed, as in actually faster over a given course with a human prioviding the power.
the two are not necessarily the same.
Tell that to a tester who spends thousands on aero testing Tiny gains wherever you can find them add up.
I don't disagree at all, I'm just saying that for the majority of riders the reduced drag of a thinner tyre is mostly irrelevant compared to other factors. And as we all know you attack the big factors first, before going after the marginal gains. And what is lacking is a proper evaluation of RR vs Aero and the point at which they inflect for any given tyre choice in [i]real world[/i] conditions.
For example, if it could be shown that a gain in reduced RR was larger than the aero loss of the increased size it would make sense to take the aero hit for an overall improvement, especially if it increased comfort and allowed you to power the bike for longer or at higher output. You'd obviously also have to know at what speeds the crossover happened, the faster you go the more the aero factors dominate.
Likewise if it could be proven that smaller tyres always netted an aero gain bigger than any increase in RR you'd be mad to run the bigger tyres for that kind of use, even if you had to put up with increased fatigue or reduced grip, for a tester it'd be worth it.
The problem is we don't actually have a reliable and accurate enough data set (yet) to prove that either way because we don't have decent real world RR data that takes the entire system into account.
[b]amedia[/b], I think we are saying the same thing, ie it's not as straight forward as a bigger tyre = faster and better grip and increased comfort and less fatigue. You can't have them all, you have to choose the ones that are important to you and your riding.
amedia, I think we are saying the same thing, ie it's not as straight forward as a bigger tyre = faster and better grip and increased comfort and less fatigue. You can't have them all, you have to choose the ones that are important to you and your riding.
Kind of, and absolutely it's not straight forward, that's why it's so poorly understood!
The thing to take away though is that you can have benefits and mostly it's an overall benefit either a big one in one area, or a balance in multiple areas.
The downsides are increased weight and increased aero drag, the point being that neither of those are big factors overall.
Even if as you say you end up with no net improvement in RR overall, you will end up with an increase in grip and comfort (which is no bad thing 😀 ) and that might lead to an increase in actual speed between point A and point B, even if that's not measurable on the drum.
Another piece of empirical information - try riding crits in the wet on a 23mm @ 100psi vs 25mm @ 80psi and see who can get around the corner faster?
So you're back where you started with your narrow tyre at a higher pressure, but with slightly better grip, and a little bit more comfort, but no faster.
Not sure I quite understand what you are saying but:
On a smooth road, narrow tyres are faster. On a rough road, BOTH tyres are slower, but the wider one slows down by less than the smooth one. So you are better off on wider tyres if it's less than perfectly smooth.
Rolling resistance does reduce with tyre width, but at ~15mph+ the aero drag of the tyre surface area and how well the tyre blends in with the wheel rim become increasingly important with increased speed and also in increasingly windy conditions.
My Wazoo's main roll is commuting, in "full fat" wheelset mode with 4" JJs the ride is very comfy and on still days or days with a tailwind they are surprisingly quick. I normally use my FatNotFat 29er wheelset, where the 2.25" G-Ones are faster but still quite comfy; the 700x38 Marathon Cross are probably quicker still with a little less comfort; but only recently using 700x28 Grand Sport Races have I done the ~4.5 mile journey to work in under 15 minutes.
Rolling resistance does reduce with tyre width, but at ~15mph+ the aero drag of the tyre surface area and how well the tyre blends in with the wheel rim become increasingly important with increased speed and also in increasingly windy conditions.
My Wazoo's main roll is commuting, in "full fat" wheelset mode with 4" JJs the ride is very comfy and on still days or days with a tailwind they are surprisingly quick. I normally use my FatNotFat 29er wheelset, where the 2.25" G-Ones are faster but still quite comfy; the 700x38 Marathon Cross are probably quicker still with a little less comfort; but only recently using 700x28 Grand Sport Races have I done the ~4.5 mile journey to work in under 15 minutes.
The downsides are increased weight and increased aero drag, the point being that neither of those are big factors overall.
To be fair the increases in grip, comfort or RR are going to be small too. Not many people are going to notice sub 1 watt gains.
Narrow tyres need to be run at high pressures so they kind of dictate the comfort and grip you'll get. Wider tyres give you some wiggle room with pressure allowing you to pick how your want your bike to ride. You can opt for grip, comfort or less RR, which is an advantage.
BOTH tyres are slower, but the wider one slows down by less than the smooth one
But if the narrower one had less RR to begin, could its RR increase more as a percentage and still end up the same RR as the wide tyre?
My Wazoo's main roll is commuting, in "full fat" wheelset mode with 4" JJs the ride is very comfy and on still days or days with a tailwind they are surprisingly quick. I normally use my FatNotFat 29er wheelset, where the 2.25" G-Ones are faster but still quite comfy; the 700x38 Marathon Cross are probably quicker still with a little less comfort; but only recently using 700x28 Grand Sport Races have I done the ~4.5 mile journey to work in under 15 minutes.
comparing 28mm with 4inch tyres isn;t really what this is about though is it!
And you've fallen right into the trap with comparing 38mm Marathon Cross with 28mm Grand Sport Races, they are not in any way comparable in terms of construction. You're comparing big tyres of one type with smaller tyres of another type.
Rolling resistance does reduce with tyre width, but at ~15mph+ the aero drag of the tyre surface area and how well the tyre blends in with the wheel rim become increasingly important
Yes, when compared in isolation, but the aero drag of the tyres is still small in comparison to the rest of the system. Even if the drag from 25mm to 28mm doubled that's still only a very small %age overall as the bulk of the thing in the way is the rider.
But if the narrower one had less RR to begin, could its RR increase more as a percentage and still end up the same RR as the wide tyre?
Possibly, possibly not, that's why more testing in real world conditions is needed, but current experimental data suggests that the wider tyre still gets you a net benefit overall.
And I know I keep banging this drum but it's important... NONE of the testing so far takes into account the effect on the human on top. It's all very well having the fastest tyres in the world on paper, but if the rider is impacted by vibration to the point where they either can't apply the same power or fatigue earlier it's an overall net loss.
I'm not saying that that definitely is the case, I'm saying that it's an unknown factor that needs consideration and further investigation, as there is plenty of anecdotal and situational (but not rigorous scientific) evidence that suspension losses at the rider/overall can outweigh RR changes.
ie: (purely mad up numbers but) if your tyres of size X are 8Watts faster than tyres of size Y, but impact the rider to the point where their sustained output is reduced by 10Watts then it's a net loss.
The elephant in the room is the tyre choice itself though...
The difference between the best tyres and worst tyres in any given type/size can be in the region of 10s of Watts.
It's silly arguing over 25mm vs 28mm if you're buying crap tyres in either size 😀
epicyclo - Member
For several years I've been running converted 29ers as road bikes using Big Apple 2.35" tyres. Freewheeling downhill beside other road bikes I have to trail my brakes to keep level.
That's F=MA, not rolling resistance. Your tyres have over 3lbs of additional rotating weight, once they've overcome intertia and are upto speed, their momentum is huge compared to road wheels and tyres.
But if the narrower one had less RR to begin, could its RR increase more as a percentage and still end up the same RR as the wide tyre?
No, the theory is that it increases much more, beyond that of the wider tyre.
It's hard to detect on the road but it's starkly obvious off-road, comparing 2.3s against 3.0s on a rough trail. You'd be getting the same effect on road but it would be a case of cumulative fatigue and lost minutes over longer rides.
I have two road bikes - a reasonably nice if old carbon racy bike on 23s and a cheap commuter on 32s. You know that feeling when you hit a rough crappy bit of road surface and it all gets harder work, like a headwind? That is far less apparent on the 32s.
NONE of the testing so far takes into account the effect on the human on top.
I think some of the testing that Jan Heine/Bicycle Quarterly have done talks about how thin tyres can [i]feel[/i] faster, because of the extra vibration going into the rider. While having wide supple tyres feel slower but leave the rider feeling a lot fresher at the end of a long ride.
[url= https://janheine.wordpress.com/2016/08/08/the-missing-piece-suspension-losses/ ]The article is here[/url] if people haven't already checked it out. I do think the BQ testing is slightly more relevant to average riders than many others, because they concentrate on real world testing, rather than wind tunnels, rollers, etc.
The BQ stuff is the only testing I'm aware of that has attempted to include it, the problem is it doesn't (nor attempt to) [b]quantify [/b]it very well and although his tests are well executed they aren't as easy to repeat away form their own testing environment to actually start gathering meaningful data to compare with other test results.
I do think the BQ testing is slightly more relevant to average riders than many others, because they concentrate on real world testing, rather than wind tunnels, rollers, etc.
This is simultaneously both the best and worst thing about their tests. They are focused on the real world and testing things under normal conditions, which means when their results go against the accepted wisdom people are quick to dismiss them as non-scientific or inaccurate, when actually the opposite is true, they are very scientific (controlled, repeatable, in some cases double-blind) they're just not [i]idealised [/i]like many lab tests, which is exactly the downfall of the lab testing!
I like JH and have read most of his stuff, but his passion is easily mistaken for arrogance and I've been wary of pointing people towards his articles as when I've done it before most people have scoffed and not taken it seriously, or been put off by his particular quirks, which is a shame as he has probably done more for the wide tyre re-revolution on road bikes than most in the industry in recent years 🙁
But for anyone who does want to read and has an open mind I can wholeheartedly recommend spending a few hours reading through the last few years of his blogs, some very interesting stuff on there and not just about tyres.
..which is a shame as he has probably done more for the wide tyre re-revolution on road bikes than most in the industry in recent years
Agreed. Jan Haine and Jeff Jones have been saying the same thing for a long time from 2 quite different view points. Jeff threw out the old Bontrager rim light-is-right thing, 'got' 29ers early on and inspired what became plus bikes, Jan knew all along that when it came to randonneuring the French were right from the start and those expensive 650B tyres were worth it.
I'm not fully convinced by many of the points Jan makes about bikes, or at least don't prioritise the same things, but have a lot of time and respect for anyone that investigates the what and why of bikes to that extent.
NONE of the testing so far takes into account the effect on the human on top.
It takes into account the weight of the human, which is all that's really required if you want to eliminate variables from the testing process.
Its what 99.9% of the millions of people who want to [s]go[/s] [b]feel like they're going[/b] fast on a bicycle use.
How many riders do any useful testing beyond feel and maybe strava? [i]Feeling[/i] fast is why we have 120 psi in skinny tyres, 73.5 or 74 head angles and overly stiff frames. Feedback loop of feels fast - reacts fast - I go fast.
But
How long can you ride that stiff, skittish, fast-responding bike for? A crit bike can be that way, a 6hr plus classics or endurance bike, probably not.NONE of the testing so far takes into account the effect on the human on top.
Correct if you're looking at an absolute figure, if you're looking at what goes fast over a period of time it's probably less correct, gets a bit more complex then.It takes into account the weight of the human, which is all that's really required if you want to eliminate variables from the testing process.
Are these tyres on a conveyor belt?
It takes into account the weight of the human, which is all that's really required if you want to eliminate variables from the testing process.
It really isn't. It tells you the effect that that static* weight has on the tyre. It gets you 'a' metric, but not a meaningful one if you want to look at the effect on the system as a whole. It doesn't tell you what effect that tyre has on the human over a long ride, or it's impact on that humans ability to power** the bike over dodgy surfaces***.
I know that my fastest bike over 1 or 2hrs on decent roads is not my fastest bike over 8-10hours on mixed/crappy roads. The crappy roads one is 7lb heavier and has 32/35mm tyres vs 25mm, but it's quicker overall on the longer rides.
Same with MTB, for 1-1.5hr XCO races I can deal with getting beaten up a bit, but on 12/24hr races I need the comfort to stay fresh...
In extremis this is just like rigid/hardtail Vs suspension arguments, and most people have pretty much cottoned on to the fact that suspension, whether delivered by big floaty tyres, or springs, allows you to go faster for longer, it's the same principles at work on the road just the terrain is micro-bumps and the battering is vibrations rather than big hits, but overall it's the same principles at work in different levels of effect.
*this may or may not be important too, a static weight test doesn't tell you much about how a moving/bouncing lump affects the tyre. When hysteresis and carcass behaviour is so important to a tyres performance you also need to consider the loads form above as well as from the road, and a static weight doesn't replicate a human very well.
**same here, to my knowledge none of the testing attempts to replicate human power delivery, they just spin a wheel at constant speed with controlled power input, again, not a great approximation of real world.
***this really bugs me too, surely they can do a better job of actually replicating a road surface rather than just a poor approximation with a slightly bumpy roller (of a different material!)
The tests are great at describing what is fastest in a lab, with a static rider and power delivered in a smooth constant way, not so great at describing what is fastest in real life and as we are seeing you can't necessarily extrapolate the lab behaviour.