15 years of riding 23-25’s on rim brake bikes. Had started to go 25 on everything due to appalling roads. 2 years ago I bought a new winter bike with discs and room for 30s with mudguards. It was transformational - soooooo much smoother and more comfortable. Every time I jumped on that bike after any time I had been riding one of the others in the stable, I would vow to myself that I would NEVER buy another bike that wouldnt run 30’s, whether that be a winter or ‘best’ summer bike. I run G-One Speeds at about 62-65psi tubeless and after some initial nervousness about speed loss etc I never noticed any issues and certainly never had any challenges riding with friends on the usual 25s etc.
Fast forward to 10 days ago…I collected my new Domane SL7 complete with 32mm Bontrager R3’s. I will admit to being nervous when I collected it and had a long conversation at the LBS about possibly changing them to something slightly smaller, as they look huge on the 31mm rims and my brain just kept telling me they would be slooooow! I have now ridden about 300 miles on it and the comfort is incredible, and Strava tells me I have several PB’s on segments despite not doing anything other than steady endurance and tempo rides so far. I’m completely sold. The difference over the 30’s is noticeable and the additional confidence on gnarly descents and corners on bad tarmac is very real. On this bike the uber wide rims mean the pairing of rim and tyre is pretty aero while my winter bike has slightly narrower rims (25/26 I think?) and there is more of a ‘lightbulb’ profile of tyre and rim - but on a winter bike, who really cares that much?
The only question in my mind is about future trips to the mountains - I amy swap over to some 28’s just to save weight on trips with thousands of meters of climbing day after day. At some point I’ll weight the R3’s and see if thats even worthwhile, but for now, 32s will be the way ahead for me.
While this sounds like common sense, I don’t believe this is correct. A lot of these aerodynamic considerations have turned out to be simply false assumptions, such as riding with hands in the drops vs on the hoods. My understanding is that with a mismatched tire/rim combo, you might as well be running box-section rims.
I’m not an aerodynamicist but it has to do with flow separation and reattachment. The wider the tire, the longer the minimum chord length requirement.
As for the hands on the drops vs hoods, it’s not cut and dry. They’re comparing hands on the hoods with bent arms vs hands in the drops with straight arms. Reality is that riding with bent arms is a lot more strenuous over time.
Nope, I have no data, this is what I have been told by ENVE when talking to them about buying wheels. My understanding is that yes, when you have straight-on airflow, things are pretty linear, but when the attack angle changes to anything other than 0 degrees (i.e. real-world conditions), the rim/tire matchup becomes hugely important. If you get a detachment of the laminar airflow after it hits the tire and transitions to the wheel external width, then the advantage of the deeper wheels is lost…and you may as well be running a box section rim like I said
Also this Aeroweenie.com - Aero Data Compendium is not really helpful, I don’t see any comparisons of what we are discussing. There are comparisons of wheelsets and different tire sets, but this ignores the whole point - that different tire widths will be more aero with different wheel external widths, and that the match-up is the key
Whether a rider has the ability to hold the position or not does not affect whether the aerodynamic savings are there or not. They will either be there or not. A rider might have to make aero sacrifices in the interest of more power (which may or may not lead to more speed), but it doesn’t change the watt savings calculations
I don’t know either, but I’m going point on running a staggered wheel/brand setup and reporting back. Shallow Bontrager 32mm external width in the front, and Enve mid-aero depth at 28mm external width in the back. Is that considered a reverse mullet setup?
I’m really close to buying these from Germany…how do they compare to GP5000 TL? Those have been my go to road tires, but not going to lie, the tan wall would look amazing on my black bike
Pro Ones tried in 2018 and moved on. I had a lot of punctures and tubeless sealing problems. They don’t seem to have a protective belt. Look at reviews on Amazon or BicycleRollingResistance and you’ll see what I’m talking about.
That’s been the gist of what I’ve seen in some reviews, but there are also people who hate the GP5000TL which has in my experience been a fantastic tire. Sometimes I wonder how much if it is that bad experiences get broadcast more readily that good/meh ones! Maybe I’m just too worried about tan walls and should stay with GP5000TL
My three primary road bikes (training, climbing, aero) have 32s, 25s, and 28 respectively.
I would love to do a comparison between the three of them over the exact same course, but only one of them has a power meter so I can’t do a full detailed dive. As with most of you, a lot of the roads around here look more like a rock climbing gym than an actual surface so in theory it would be good to test.
The surface dictates what tire pressure you should run; larger tires support lower pressures. https://blog.silca.cc/part-4b-rolling-resistance-and-impedance
Running too much pressure for a given surface will kill your aero gains easily. For “Naples, FL” perfect but realistic pavement with a equipped 160lb rider, that pressure is ~90-110psi; for a common brushed concrete sidewalk ~60psi, and a weathered country road is probably ~80-95psi.
A larger tire costs about .15w per size increment 25,28,32,35… for a given tire at the right pressure.
Ok… you’re rolling… what about aero
3) If you’re tire is too wide for the aero rim, you’re not aero. The 28mm wide bontrager was made for a 25c tire. Larger than 25c, you won’t get any benefit. This really only matter for the front tire. The right size tire on a regular rim is faster than the wrong one.
you can make big tires aero with the right rim. remember that the tire size counts in crosswinds though. A 35c tire automatically add 10mm of crosssection over a 25c in gusty winds. I think Hunt, 3T, and DT Swiss make a wheel that can make a 32-35c tire aero.
Comfort:
6) Tire pressure and spring rate - It’s pretty linear. As pressure decreases, the ride gets more compliant, but there is a diminishing return. Moving from 110psi to 90 is huge, but 90 to 70 not so much… until the surface calls for it. Moving from 60 to 40psi on a gravel trail is HUGE.
Underpressure is not good - you’ll bounce and your body will bounce on the saddle or you’ll strike the rim , in which case spring rate goes put to whatever the wheel/bike spring rate is.
Same pressure, different size - 90psi rides like 90psi no matter what size tire you’re using.
Tires themselves - road tires are not built for durability and will ride better than gravel tires. A fast rolling gravel tire will cost you about 2w over a comparable road tire (the prior Schwalbe g-One Speed vs Pro v-guard)
So, figure out the appropriate pressure for the surface you’re riding and work from there.
On that rim going from 25c to 32c on a GP5000 tire would cost you (22mph, perfect road):
+.5w rolling watts
+2.1 tire watts + 7w wheel aero
So, 9.6w - that’s 1mph loss on perfect road. Judging the road wrong (10psi too high, new asphalt vs country road) would cost you 6w. On smooth pavement 85psi is just as comfortable as 50psi, so you’re better off on the 25c/28c( f/r) setup. As soon as you hit some surface that’s not asphalt, you should be 30c+. As soon as that surface is dirt and not perfectly smooth, you want to be under 45psi meaning 35c+.
The cost of running a smooth gravel tire on the road is about (BWR California scenario) - 25c @85psi 12.1rolling vs 38c @ 45psi 18w & 4.2w tire aero & 7w wheel benefit = 17.2w road penalty and about 20w on-road advantage (minimum, that’s on bumpy trail but doesn’t account for irregular bumps, sand pits, climbing traction/braking downhill).
That’s a really interesting way of looking at it. Thanks for doing the calculations.
So, given I’m not going to be averaging 22mph (more like 18 on a longer solo ride) a wild guesstimate would be a real world loss of 5w going from 28 to 32? If so, that sounds like a no-brainer to me.
After a while running 28s, I recently installed a GP5000TL 32 on the rear (my current 28 on the front refuses to die). I am running this on Hunt Limitless 48’s which have an external width of 34mm. I haven’t measured the installed width, but visually the rim is still slightly wider than the tire. So according to the rule of 105, this should still be aero.
What I did notice straight up was that the ride definitely felt more plush.
As for speed, that’s always dependent on power and conditions. And I haven’t been obsessive about comparing speeds with before on calm days. Anecdotally, on my favorite training loop , I have been accumulating a number of new PR’s with the same power output (200W), although possibly that is due to becoming better at holding the aero position at about the same time as I moved to the wider tire.
Not sure yet whether I will install a 32 on the front, but will definitely keep it on the rear.
Probably the same as the 22mph wind tunnel numbers given that the ambient air is going to have some wind. I don’t think you’ll see any real comfort gains out of it though. A good case for 32+ road tires would be travel bikes, winter training bikes, flat prevention, cobble/bricks/concrete/groomed gravel,or BWR.
There is some leakage thru the sidewall, yeah. But I read that that was an early production issue and they use a little more rubber (?) to make them “water tight” now.
