I haven’t kept up with changes for at least 5 if not 10 years. My “current” race bike is a P3SL - maybe circa 2005? I have old HED race wheels that are likely also circa 2005. I’m trying to get fit, race again, and may look into getting a new bike at some point in the near future. I’ve done some searching but would like more info on the benefits/role of wider tires. I reviewed the low PSI recommendations from the HED site and they seem crazy low.
What are the benefits of racing with wider race wheels? What is “wide”? Downsides?
Experience racing the wider race wheels with the lower PSIs?
Any of the more popular superbikes (speed concept/cervelo/QR/canyon/others) not allow/easily accomodate wider race wheels?
Just trying to learn more and start wrapping my head around some of the changes.
What are the benefits of racing with wider race wheels? What is “wide”? Downsides?
Experience racing the wider race wheels with the lower PSIs?
Any of the more popular superbikes (speed concept/cervelo/QR/canyon/others) not allow/easily accomodate wider race wheels?
Just trying to learn more and start wrapping my head around some of the changes.
Thanks -
Wider tires allow a smaller contact patch, which reduces deformation of the tire material, which reduces rolling resistance. We only all *thought *that narrower tires pumped to 120psi were faster, probably because they felt harsher and we associated that with faster. Certainly when you get a run-flat and are down in the 10psi range, it feels smushy and slow, and I certainly associated “soft” with slow so much that when I run optimal PSI’s I often find myself thinking “surely this can’t be right.”
Wider wheels allow for wider tires with less of an aerodynamic penalty.
Almost all (maybe all) new bikes since 2019 allow at least 28mm tires, even if those nominally 28mm tires inflate out to a measured 30mm. I believe this includes TT bikes. The trend is definitely continuing to be more accepting of wide tires.
Advantages other than rolling resistance: better traction, less skipping around during sprints, lower tread puncture risk maybe…
I used to race on 23mm tires exclusively. I now race on 25’s or 28’s depending on how much I value aerodynamics. If I had better wheels to suit 28mm tires, I’d just run those exclusively but the aero penalty grows a bit if you’re using wheels optimized for 20-23mm tires.
I used this calculator by Silca for my wife’s 5th place at US Pro Nationals in the TT, and it seemed to work alright. Certainly not so far off that there was any hit to performance and she loves the way her bike rides when I use that calculator to set pressures.
Wider tires at lower pressures absorb more of the road buzz, rather than transmitting it to the rider’s body. On rough roads, not only are wider tires more comfortable and less fatiguing, they are actually faster. And on anything less than freshly laid hotmix, most roads are rougher than you think. Wider tires allow lower pressures to be used without the risk of pinch flatting.
In terms of aero, it is the wheel/tire system that matters. To maintain a smooth flow of air over the wheel and keep the aero benefits of deeper wheels, the external width of the rim should be slightly wider than the tire. Known as the rule of 105 (rim width should be at least 105% of the MEASURED WIDTH of the tire).
Most modern (released in the last 3-4 years) rims are now 26-27mm externally, meaning they are designed around 25mm tires. However, many of the latest rims are 29-31 mm externally, and are designed with 28mm tires in mind - but you can still run a 25mm tire on a wider rim and remain aero.
Along with external width, internal rim width has also grown - where 13-15 mm internal width used to be standard, 17-19 is more prevalent, with the latest rims typically around 20-21 mm internally. And many gravel/all-road wheels are 23-25mm internally.
Of course, a tire installed on an internally wider rim is going to measure wider. Many nominally “25mm tires” will actually measure 27-28mm when installed on a modern internally wider rim, thus unintentionally breaking the rule of 105. So you need to be looking at the measured width of the rim as installed, not just what is printed on the sidewall. This installed width (and height) on a wider rim may mean frame clearance issues on an older bike, which was intended for 21-23 mm tires on a narrow rim. Measure and check carefully the tires and clearance on your current bike, before thinking on new wheels.
On the plus side of wider rims, this allows a more rounded trailing edge to the rim (a U shaped rim), which means modern deep section wheels retain more of their aero benefits and are easier to handle in strong cross-winds than earlier V shaped rims.
Minor correction on the first paragraph. 120psi tires on narrower tires actually does have a smaller contact patch. But it’s slower because it basically bounces/vibrates on an imperfect surface while a softer tire rolls over it.
Contact patch size is directly correlated to pressure. A 120lbs rider riding on any tires at 120psi will have 1 sq-in of contact patch while riding at 60psi will lead to 2 sq-in patch. This is regardless of tire width. But the wider tire will have a wider contact patch while the narrow tire has a longer one (in the axis of travel). The latter involves greater deformation of rubber, making it less efficient.
Minor correction on the first paragraph. 120psi tires on narrower tires actually does have a smaller contact patch. But it’s slower because it basically bounces/vibrates on an imperfect surface while a softer tire rolls over it.
Contact patch size is directly correlated to pressure. A 120lbs rider riding on any tires at 120psi will have 1 sq-in of contact patch while riding at 60psi will lead to 2 sq-in patch. This is regardless of tire width. But the wider tire will have a wider contact patch while the narrow tire has a longer one (in the axis of travel). The latter involves greater deformation of rubber, making it less efficient.
Touche! You are correct. Thank you for correcting that. The tire’s ability to deform over the variable surface underneath is an important consideration which underpins the math in that calculator I linked. I better step out of this conversation before we go any further though, because we’ve officially reached the extent of my understanding. Heading back into carbohydrate-land.
“Wider tires have a lower rolling resistant” is a bit of a false narrative. Yes, a 25mm tire vs the same 23 mm tire on the same wheel at the same exact pressures will measure a lower crr on a steel drum. Assuming your 23mm tire pressure has been optimized for a given road surface, you shouldn’t run a 25mm at the same pressure due to impedance losses on actual road conditions. If you optimize your tire pressure for the 25mm, you will end up with a lower pressure vs the 23 mm and ultimately the same rolling resistance (crr).
Tom A said it best, rolling resistance makes up for a lot of aero sins.
This is true EXCEPT that wider tires run at proper pressures (i.e., pressures that take advantage of wider tires’ bump compliance) DO NOT have lower rolling resistance than identical narrow tires.
So aero ends up being king for racing. And narrow tires/wheels (all other things being equal) are far more aero than identical wide ones.
i am curious about the trade offs … crr scales linearly whereas cda is exponential, correct? so at itt speeds i’d expect aero to matter more.
I don’t look at it that way. It all matters.
Ignore nothing, no stones unturned.
I echo the above about TRUE pressures and CRR for wider tires. The gain isn’t necessarily a contact patch one. Because to get that, you’re having to pump up the larger tire to a similar pressure to get a gain. But the gain of not bouncing along the road inefficiently at that lower pressure on a larger tire makes up for it.
Lots of weird summer expansion crack bumps out in eastern NC. On 25’s at lower pressure they’re tolerable versus a 23mm. I started out years back on a 21mm on old wheels on an old bike, that was torture sometimes on bumps.
If I could go 28 for training tire fitting well on my aero wheels, sure I’d do it. For racing, nah. 23 front and 25 rear. I’m light enough that works.
I’m toying with using the Notio with constant equipment and position to get info on CRR at differing tire pressures. CDA would change, then I can calculate the equivalent delta in CRR. I could do that even better probably for gravel bike.
Wider tires do not have lower rolling resistance at proper inflation pressures.
Using the same drop percentage for two tires of differing width for the same use case does not make much sense. It means you’re inflating the wider tire much squishier.
The old 15% rule of thumb was intended to adjust the tire setup for different use cases. A 50mm tire gets inflated much squishier than a 25mm tire because it’s assumed that the 50mm tire is being used in rougher riding. But if you’re using the 50mm tire on a smooth road ride, that assumption is false.
Even BRR’s later test using absolute drop distance doesn’t make much sense to me, since a tire’s spring rate with respect to a flat surface is different than with respect to road irregularities. In particular, if the dynamic situation tracks the static one, this study appears to imply that the wider tires were still being inflated to greater compliance.
It seems to me that the way to answer the question usefully would be measure and characterize how breakpoint pressure changes with tire width, and compare crrs at those pressures. This makes the question more complex, but it’s unclear to me that the proxy methods being used by BRR are actually answering it at all.
Didn’t see it called out, but there’s a weight penalty to consider.
All these wider wheelsets and corresponding 28mm+ tires are heavier than the old low profile wheels mounted with 23’s, or 21’s and even19mm tires that folks used to race on.
Tom A said it best, rolling resistance makes up for a lot of aero sins.
This is true EXCEPT that wider tires run at proper pressures (i.e., pressures that take advantage of wider tires’ bump compliance) DO NOT have lower rolling resistance than identical narrow tires.
So aero ends up being king for racing. And narrow tires/wheels (all other things being equal) are far more aero than identical wide ones.
Is there not a relationship between width and depth of the airfoil. Example leading edge of a 747 wing is wide, but the wing is deep. So narror means you can get to the same drag with a less deep wheel whereas wide you need a much deeper wheel to get to low aero drag.
So narrow means you can get to the same drag with a less deep wheel whereas wide you need a much deeper wheel to get to low aero drag.
Yes, this is absolutely correct.
Plus, simply the smaller frontal area of a narrower wheel/tire will always (other things being equal) create less drag than the bigger frontal area of a wider wheel/tire.
My rules: for training, ride the most comfortable tire that you possibly can. For gravel, I ride 3"/76mm wide tires on my training tank. For most TT training, fast or slow does not matter much, but comfort certainly does; and lots of comfort means you’ll probably ride more, which in itself will make you faster. But for racing, if speed matters, ride the narrowest aero wheel/tire combo that you can, considering the best and narrowest tire width and type that would be suitable for the road surface and conditions expected.
I’m pretty sure TomA meant that in the narrow context of asking “which is the best tire on this wheel” … where often tiny differences in cda were offset by larger differences in crr.
Vs “should i get a wide wheel with a wide well-fitting tire or a more narrow wheel with a more narrow well-fitting tire”
I’m pretty sure TomA meant that in the narrow context of asking “which is the best tire on this wheel” … where often tiny differences in cda were offset by larger differences in crr.
Vs “should i get a wide wheel with a wide well-fitting tire or a more narrow wheel with a more narrow well-fitting tire”
