I had a marketing email from a seller of carbon wheels yesterday. I've forgotten who it was from, but it was claiming that wider rims and tyres are more aero.
In my own very limited experience, my road bike with marketing 25mm tyres (i.e. 23mm) is noticeably quicker than my cross bike with 32mm tyres. And my mountain bike is just the least aero of all of them.
Are wider tyres really more aero, or is this marketing cobblers dressed up as science?
I don't know about bikes...
...but I do know that when 'we' test our cars for CO2 emissions there is a noticeable increase in drag when the car has wider tyres fitted.
The optimum aero wheel profile is created by the proportion of width and depth - something like 3:1 and a depth of about 90mm (before the wheel rim gets too heavy and depth impacts handling) and therefore a wider tyre like 28mm helps create the optimum aerofoil shape.
Likewise, with modern tyre construction, a 28mm tyre had lower rolling resistance than a 23mm once of similar construction.
Well, they may be more "aero" when measured in a lab. But dont forget, when you sit a MAMIL ontop of the bike, all that nice smooth aero on the bike / wheels etc becomes pretty pointless.
Still, there will be some who lap up any sort of marketing claims, BS or not. Remember, some things can be measured in the lab, but not felt in the real world.
MAMIL ontop of the bike, all that nice smooth aero on the bike / wheels etc becomes pretty pointless.
Quoi? Surely the fat amateur cyclist is the one who needs all the help they can get?
I used to think I had no need for aero kit as my position is massively un-aero (handlebars level with saddle) but given my litany of tedious lower back issues, it would be much better and easier just to buy as much aero kit as possible to make up for my 45 degree torso, than it would bevto try and force my spine into a position it just doesn't want to adopt...
Basically your average office worker can only get so fit and flexible, after which it should be open season on high end performance kit!
Lab testing says otherwise. Hambini et al.
Like drag cars - big ass fat rear tires and nice skinny front.
Tyres
This guidance is uniform across the board. It is vitally important to install tyres that are slightly narrower or inline with the brake track of the wheel rim. A ballooning tyre will impact the drag significantly.There has been a trend towards wider tyres on bikes of late. From an aerodynamic perspective, the width of the rear tyre has little effect but the width of the front tyre has much more impact and therefore a 23mm front tyre is recommended irrespective of whether the wheel was designed for 25mm tyres. At speeds above 30km/h, it is more beneficial to have 23mm tyres than 25mm front tyres for aerodynamic benefit.
that said i have 25s on my propel. because its what it came with and i refuse to waste tires just because they are not flavour of the month
that said i have 25s on my propel. because its what it came with and i refuse to waste tires just because they are not flavour of the month
He's also seemingly not taking rolling resistance into account there, with the bigger tyre handling non-billiard table roads far better than the 23c
Well, they may be more “aero” when measured in a lab. But dont forget, when you sit a MAMIL ontop of the bike, all that nice smooth aero on the bike / wheels etc becomes pretty pointless.
Surely a beautifully rotund torso clad in close fitting lycra has the potential to present quite an Aero dynamic (low turbulence) shape?
Conversely a Slab chested, rippling six packed Gym bunny could well be less aero while a 62kg anorexic pro-cyclist will only slide through the air efficiently if his kit actually fits, flappy jerseys are an aero-no-no surely?
You might actually be trying to 'Fat shame' the ultimate Aero weapon...
he is simply talking aero.
aero is nothing to do with the surface
aero is air flow across an object.
yes there are other influences at play...... but the OPs statement is wide rims = aero.
* edit does this place have its own autocorrect ? i always blamed my phones autocorrect for the random word inserts..... maybe its this place as i'm at a computer with no autocorrect on it....
Wheels on my tt bike are ridiculously wide, to the point i can't run a 25 mm tyre as it blows it out to 30mm..too big for the fork.
Whether it's faster or not who knows.. apparently it's been tested in a wind tunnel.
Lab testing says otherwise. Hambini et al.
Tyres
This guidance is uniform across the board. It is vitally important to install tyres that are slightly narrower or inline with the brake track of the wheel rim. A ballooning tyre will impact the drag significantly.There has been a trend towards wider tyres on bikes of late. From an aerodynamic perspective, the width of the rear tyre has little effect but the width of the front tyre has much more impact and therefore a 23mm front tyre is recommended irrespective of whether the wheel was designed for 25mm tyres. At speeds above 30km/h, it is more beneficial to have 23mm tyres than 25mm front tyres for aerodynamic benefit.
I don't disagree with his conclusion, it makes sense, you could guess that without a wind tunnel.
Smooth shapes have lower Cd, narrower tyres have lower area, put the two together, lower CdA. You don't need a wind tunnel to figure that out, although it obviously doesn't do your youtube viewing figures any harm. What a wind tunnel might do (although CFD would be more useful, but again less watchable) is tell you which manufacturers profiles worked best under what conditions.
His testing had holes in it you could push a 26x5.25" Vee Snowshoe through. Using a real rider for half the test (which is never likely to be repeatable) then a dummy for the second half.
cookeaa
Surely a beautifully rotund torso clad in close fitting lycra has the potential to present quite an Aero dynamic (low turbulence) shape?
I like your thinking... 🙂
It does seem to me that the aero zone is more often occupied by the likes of trail_rat, a lean mean cycling machine, than the likes of me. Except downhill of course, but that's free energy.
I'll plump for the comfort of the wider tyre regardless of any aero benefits.
It does seem to me that the aero zone is more often occupied by the likes of trail_rat, a lean mean cycling machine
seems somewhat pointless having an aero roadbike and towing the little one behind me in the trailer......do i care ? 😀
I used to think I had no need for aero kit as my position is massively un-aero (handlebars level with saddle) but given my litany of tedious lower back issues, it would be much better and easier just to buy as much aero kit as possible to make up for my 45 degree torso, than it would bevto try and force my spine into a position it just doesn’t want to adopt…
Basically your average office worker can only get so fit and flexible, after which it should be open season on high end performance kit!
Firstly did you go faster?
My hunch is you didn't
My back is like yours and i probably weigh more and put out less power
For some one like me aero isn't that important. If your body isn't in an aero position and your not putting out much power your not going fast enough for the bits of the bike to make that much difference. The slower you are the bigger the % of your effort that goes on rolling resistance bearing friction etc.
You've got me, I haven't actually spent a penny on aero kit, but in theory I think I'm entirely entitled to, I don't agree with the sneery 'anyone slower than a pro shouldn't buy fast kit' philosophy.
Actually the philosophy I buy into is that nice kit doesn't make you much faster by dint of aero or weight saving, but by the sheer motivational force of a having a nice light fast feeling bike beneath you. So I still do worry about weight savings on my nice bike, and would go more aero but as I understand it aero wheels often feel a bit 'dead' so I'd rather stick with shallow, stiff lightweight wheels.
Anyway, massive digression, apologies OP!
Basically your average office worker can only get so fit and flexible, after which it should be open season on high end performance kit!
The two aren't mutually exclusive, I'm nowhere near anything that could be described as a racing weight, but can quite happily adopt and hold a position where my knees are banging into my chest. It's a position I've honed over years of mid group club run mediocrity, being able to hide from the wind and suffer through the last hour when the coffee and cakes long ago worn off is a cycling skill worth having.
I thought the whole reason for wider rims being more aero is that it changes the shape of the tyre. With a narrower rim, the tyre is shaped more like a lightbulb, whereas with a wider rim, the tyre is more 'U' shaped. This shape change is more aerodynamic.
Other things are more important and more noticable.
Buy what you like and it will make you happy. A happy rider is a faster rider. Wider tyres will be more comfy and a comfy rider will also be a happy rider.......................it goes on and on.
Oh, and dont forget, a bike in your favorite colour is also faster.
If your not carefull you end up chasing smaller and smaller numbers instead of chasing good memories.
I have a road bike with a power meter and all the gear, but the best rides are the ones on my mountainbike where there is nothing to measure.
wider rims are less aero if the tyre fits properly. There is, however a shortage of really narrow tyres. I run 21c tyres on y original HED3s to match the narrow rim. They are the most aero option.
Surprised tyre manufacturers havent gotten more involved in it.
Theyre a 3d shape, so the shape of the sidewalls isnt just down to the width of the rim, they can ve tall and skinny, short and stout, rounded, square etc. Maxxis made their 'wide trail' tyres for mtb, but ive not heard of road tyres being more optimised yet?
I've had a set of wider Hunt wheels (34 aero wide disc) for a couple of weeks now and set them up tubeless with Continental GP5000tl 25mm tyres. Very unscientific, but my average speeds for my rides since I've had this set up are generally at least 1mph average faster and the power numbers are basically the same. At first I thought it was just that new parts placebo...but it definitely isn't. Trouble is, I can't say if it's the wheels or the tyres that are making the most difference so I should probably go back to my older tyres and tubes to test again. I'm enjoying the free speed though so I probably won't 🙂
Zipp sold aero tyres for a while. They were a more aero, but the aero shape increased rolling resistance cancelling out the benefit.
I was thinking just making them U shaped rather than bulb shaped would be a good start, and a more accurate measuring system.
I was mulling this over while Yohandsome was deliberating which chinese rims to get. Lightbike do some really wide aero rims, would something like a 60-70mm deep but ~28mm (external) wide rear rim with a 25mm tyres (which is inevitably 28mm on a wider rim these days) out back with a ~45mm deep 25mm wide front wheel with a 23mm tyre be the best combination?
My thought process was that with tubeless tyre pressure Vs width isn't so critical, so you can run the 23mm tyre as soft as you would the 25mm one anyway.
And any MTBer knows that the rear tyre has a much bigger impact on the rolling resistance, so best to take advantage of that at the rear.
I've only got Hunt Aero Light Disc wheels (17mm internal rim width, 28mm deep rim), but I've just bought 23/25mm GP5000s with a pair of Supersonic tubes, to experiment with aero benefits at the cost of comfort.
This will mean riding outside, rather than on Zwift. 😮
and therefore a wider tyre like 28mm helps create the optimum aerofoil shape.
Likewise, with modern tyre construction, a 28mm tyre had lower rolling resistance than a 23mm once of similar construction.
This. They will be more aero and faster than your 23mm tyres. But don't forget, the least aerodynamic thing about cycling is the shape of the human body.
don’t forget, the least aerodynamic thing about cycling is the shape of the human body.
True, but watts are watts whether it's loosing weight off your body, the bike, getting either more aero or spending time on the turbo trainer. It's still a simple (ish) equation of speed = watts in - watts wasted through excess drag or weight.
And who doesnt like new bike bits?
The human body shape is the most consistant thing about any particular bike and rider combo.
In that you cannot pay money to lose weight or get drastically more aero between rides unless you have been doing it very wrong ....
Why aren't super aero bike frames and forks dimpled like golf balls?
Mattyfez, some light reading for you and a short video....
https://forum.slowtwitch.com/forum/Slowtwitch_Forums_C1/Triathlon_Forum_F1/Hambin i's_take_on_Zipp_Dimples_ROFL_P7086307/#p7086307
Of course its marketing BS but that doesn't necessarily mean its not correct. You can't really say the wheel on its own is more aerodynamic..it might very well be or not, but the reality is the wheel works within a larger system so it's not just about the wheel, its about how the air interacts with the wheel and then with the rest of the bike down stream of the wheel. So it is unlikely a wider wheel on its own will be more aerodynamic than a narrower one, but when put into a frame the downstream interaction of the airflow coming off the wheel with the frame and rider behind it might very well have a net positive impact on the overall aerodynamics.
So I think that it is the case that a slightly wider tyre and wheel does have a positive overall benefit...but of course you can always take things to the extreme until there comes a point that it no longer has a net beneficial effect...just like tyre pressures and the often misunderstood thing about lower tyre pressures having less rolling resistance. It's not that simple.
So I think a 28mm tyre on a deeper rim is more aerodynamic than a narrower tyre, especially if it is mounted on a shallower rim. But clearly if you go wider then any benefit will start to reduce and that will ultimately depend on what's behind the wheel. I think the 28mm wide tyre on a typical road bike seems to be the sweet spot width...any wider or narrower and the benefit drops off. But on a TT bike with a narrower and more aero frame then a narrower tyre might be the sweet spot...then you bring the variable of rim depth and geometry into it and you have a whole different situation etc. and so it goes on. These things are sometimes a balance of many variables and therefore not always intuitive.
True, but watts are watts whether it’s loosing weight off your body, the bike, getting either more aero or spending time on the turbo trainer. It’s still a simple (ish) equation of speed = watts in – watts wasted through excess drag or weight.
And who doesnt like new bike bits?
I'm not denying your right to buy whatever you want.
Watts are Watts. But the numbers quoted are small as they are. But they are all calculated at pro speed. A new Specialized rise bike might save Cavendish 24w. It might save me under a quarter of that. Down at the is it measurable level
Oh and no I don't like new bikes and bits. Much happier 6 months on when outs my tried and tested bike