[Closed] This wider tyres being quicker

They're testing the rolling resistance of a tyre.

Yes I get that, but the discussion is about the speed of the entire system, not just the tyre. Sure you can try to quantify the difference between individual tyres under controlled lab conditions but the speed of the rider and bike overall require a more in depth and complete analysis.

Looking at individual metrics is fine, but we need to look at all the individual metrics and how they interact, as always the problem is that it's complicated and actually quite difficult to model anything more than the individual elements.

I wouldn't be surprised to find that with the right tyre/rim combo that 28-32mm is about the sweet spot when considering rolling resistance, fatigue, grip, aero and weight

I think you're probably right there but that's still a lot bigger than conventional wisdom would have said 5 or 10 years ago. I'm intrigued to see if that is the sweet spot or not, especially since a lot of the aero performance of tyres is do closely linked to the rim it's mounted on and we're only just beginning to see people experimenting in that area too.

Daffy - Member
They never will, because at the speed they're moving on the flat and downhill, aerodynamic drag on the trailing edge of the 40mm tyre will more than eliminate any gains from rolling resistance...

However most STWers I have met aren't quite as lean (cough, cough) so if they're concerned about aerodynamics it's not their tyres they should be worrying about improving for aerodynamic efficiency...

Yesterday I did a 120 mile loop around Wester Ross on my trusty 3 speed Pompino which has 38mm tyres. The roads are rough up here.

By the end my wrists and hands were screaming, unlike when I do the same loop with 60mm tyres at lower pressures. (My posterior was fine because I fitted a triple sprung Brooks because I know what to expect on those roads).

It certainly didn't feel as free rolling on the rough downhill exposed aggregate sections.

But it did set my mind to wondering who makes a 38mm roadster tubular, because tubs tend to be more compliant so can be run at lower pressures.

It's compliance that's the secret, not necessarily the big tyre, but the big tyres can afford to run low pressures without damaging the rims on bumps, so for them compliance is a given.

But it did set my mind to wondering who makes a 38mm roadster tubular,

have you had a look at Compass Barlow Pass? not tubs, but a very supple open clincher in 700c 38mm, they are ace, and I believe tehres a 44mm version too now, Snoqualmie Pass?

amedias - Member
have you had a look at Compass Barlow Pass? not tubs, but a very supple open clincher in 700c 38mm, they are ace, and I believe tehres a 44mm version too now, Snoqualmie Pass?

When I got home yesterday I started checking the frame, I reckon I could cut the chainstays and move them over a tad to squeeze in up to about a 45mm though. That's the nice thing about cheap steel bikes built out of obtanium. 🙂

Also I'll investigate going tubeless which is probably simpler and more achievable.

Unfortunately 38mm is pushing it for the Pompino or I would have bigger tyres in it

[s]650B and 48mm?[/s]

scrap that, I thought the Pomp was disc

but...

Campag Mexico Olympic tubular rims sitting unused

It'd be a shame not to put them to use!

It really is. They're testing the rolling resistance of a tyre. A metric for each tyre on a slightly lumpen surface (it's not a smooth wheel), under the same load, at the same speed, on the same hardware means that comparisons can be drawn. Mechanical drag on the system is measured, translated and compared. The test tells you how much energy is lost as a result of normal rolling resistance. It doesn't try to compute all losses and their subjective feel, but accounts for a large percentage of energy lost directly as a result of tyre compound, construction etc.

Yes, that makes a lot of sense. Meaning if you picked the tyres at the extremes of RR you should have some sort of difference in the real world.

In fact I'm going to do it. I have a power meter and a few tyre combinations.

Meaning if you picked the tyres at the extremes of RR you should have some sort of difference in the real world.

Yes, useful for when comparing tyres of similar size and type to find the 'fastest' at size X for example. As Daffy says, it's a useful metric for comparing like for like for RR, but it's not necessarily an indicator of 'speed' in the real world.

Where you need to be careful, and the whole point of this thread is say looking at a 25mm tyres and seeing they have lower RR than some other 35mm tyre so assuming the 25mm will be quicker, when reality says it might not depending on the road/surface conditions and length of ride.

Plus all the other stuff that the tests don't take into account, which means that simple extrapolation/assumption that the tyre with the lowest RR will be the fastest over a route from A to B is not always the case.

In fact I'm going to do it. I have a power meter and a few tyre combinations.

This is a great approach, if you have a mix of tyres, and a power meter you're already pretty well equipped to find out which tyres are going to work best for your and your riding. Remember to look at the other factors less easy to measure, like level of fatigue and discomfort rather than just raw power, and tailor your tests/results to your riding. A crit rider will have a different set of requirements to an Audaxer, and XCO racer different to Marathon etc. Its no good making a XWatt saving on your tyres if you're too beat up to carry on putting that power out to the end of the race/ride for example.

Experimentation and evaluation of your own experiences trumps someone elses lab test, crack on and have some fun 🙂

^ more of this required please, in all aspects, I wish people would be more willing to try things out and evaluate in the real world for themselves rather than trust magazines and 'the figures' all the time.

Your not doing the credibility of your argument any favours by being a *.

Ahhh, but my position and credibility as a * is unimpeachable.

[b]You're[/b] not doing the credibility of [b]your[/b] argument any favours with poor grammar though.

Talk about a can of worms!

My understanding is - on a flat surface, as you can run higher pressures in a smaller tyre of the same construction, you can achieve similar pressures. And aero and weight are better for a smaller tyre, however if you look at the data on bicyclerollingresistance.com, the Schwalbe big one is lower rolling resistance thatn the Schwalbe one, even at less than half the pressure - so for most practical purposes, it'll be faster. This probably stops applying at some point between bimble and pro race speeds as the aero penalty increases with the cube of speed - and a lighter weight narrower tyre will give the bike a lighter, more responsive feel.

However, as you get further into the real potholed, bumpy world, fatter tyres give more of an advantage as at reasonable pressures for their size and typical construction you have more cushioning so roll over things rather than bouncing off them. I probably should run far bigger tyres on the commute (and run tubeless to allow a really supple construction with puncture protection), but would need a new frame and forks (and hauuuuge mudguards) for this, and I can't imagine the tyres would be easy to source. So yeah, fashion stops me from running what probably would be the best option.

[url= https://janheine.wordpress.com/2016/03/09/tire-pressure-take-home/ ]Following the link to Compass that amedias gave, I ended up here, and this probably sums it up.[/url]

[i]Higher pressure decreases the energy required to flex the tire. Less energy is lost due to internal deformation (hysteresis). But higher pressure increases the losses due to the vibrations of bike and rider. More energy goes to suspension losses. The two effects cancel each other. Whether you pump up your supple tires super-hard or ride them squishy-soft, they have the same resistance.[/i]

To me the important feature is compliance to irregularities on the surface you're riding on. On yesterday's ride with all the exposed aggregate the highest irregularity probably wasn't more than 15mm, but spaced at distances where it caused considerable vibration.

So for that presumably I want a tyre that can easily deform that much without instant rebound (ie hysteresis comes in to it).

There's no reason a suitably compliant 38mm tyre couldn't handle that, but you're getting perilously close to the rim at those deflections if you're running a pressure low enough. That's because you also have to allow for the amount of sag in the tyre from the rider's weight.

Also to protect your rim you may need to run a higher pressure for the less usual lumps on the road - eg the edges of cattle grids. I crossed several yesterday at speed and quite a few were proud of the road surface.

It's the sort of thing you can get away with when you have tubulars because the shape of the rim means no snakebites, and they also they are extremely strong (probably not so much more these days). I've done a weeks outback tour on rough dirt roads in Oz with 32mm tubs with no problems despite several crunches.

BTW just realised those Compass tyres are actually tubeless, not tubulars. Duh, slaps forehead. 🙂

Tldr:
I'm on 2.8 front and rear now... Seems quicker ... Not sure if it's rolling resistance as such, possibly the tyres ability to soak up most of the surface noise instead if sending it up through the bike.
I've also hardly ridden in 3 months due to injury, so I hope they really are easier rolling once I'm back out doing 50 - 70 miles again.

I can't scientifically prove it, but going 'half-fat' on my 29er (a 2.8 up front) has sped things up for me.

Might be due to the increased circumference.

Brilliant fun too! No going back

Afaik, the rolling resistance figures for the fat-b-nimble 29er were crazy low, lower than those for a 700*23 roadie tyre.

And their ability to absorb bumps makes them handy around town.

But, once you hit 17mph, aerodynamics really kick in and on any unmodified bike you have to double your power output for every mph achieved.

I can't scientifically prove it, but going 'half-fat' on my 29er (a 2.8 up front) has sped things up for me.

Thanks for reminding me I want a plus front wheel.

I was wondering if it'd be slower on road though?

I've experimented with 25-40mm on the roads.
Is it just me that doesn't notice much difference?

Tyre construction seems to have far more effect than width.

I run Schwalbe Marathon Supreme (not the heavy, solid touring version) 32mm tyres on my commuter 'cross bike.

I generally run them at 80psi and have used up to 95psi

I've been really impressed by combination of rolling speed and comfort on normal (i.e rough and potholed) roads and on farm tracks. They certainly don't feel draggy and I've taken the 'cross bike for a few longer road rides whilst my road bike has been set up for TTs.

The previous tyres on the cross bike were Schwalbe Durano 28mm, which were not actually that much smaller, although didn't feel quite as supple when run at similar pressures.

I have sets of 23mm tyres and 25mm tyres for my road bike, but the 23mm tyres don't appear to offer me any noticeable advantages and give a fairly harsh ride. I'll probably go for 28mm for the road bike when I replace them.

@spoonboy

So you still havent got anything productive to say? The best youve got is personal abuse with someone who disagrees with you in a discussion about tyre size.

Awesome.