Now my groad is up and running, I’ve been having a bit of a thought experiment. While riding the bike on in gravel mode (40mm tyres) on a particularly bad section of road between bridleways, I was struck by how much smoother the ride was and how I hardly noticed the poor surface.
This led me towards the idea of trying some 32s or even 35s as slicks for the road. The road surfaces round here (especially on the quieter country roads) are often indifferent at best, not getting any better, and even 28s in tubeless are not always the most comfortable.
Now, let me be clear, I don’t race, and while I do some fast-ish group rides and have target times in mind for a few forthcoming sportives, absolute speed isn’t everything for me (just as well really). So with that in mind, losing a little pace shouldn’t really bother me.
But… I work quite hard for my current fitness and speed, indifferent as it is, and I’m loathe materially to sabotage that.
My gut and research seems to suggest that at 30mm, any speed losses would be trivial, and perhaps even at 32, but at 35 I’d expect to notice a fall-off.
So what I’m asking is this: has anyone in a similar position actually put wider (over 30mm) tyres on their road bike, and how did you find the experience? How much, if any, speed did you lose? If it helps, I’m not quite 4w/kg, tend to average 27-29kph over 2-4hrs riding solo on fairly lumpy terrain, 1-2kph faster in a group, and ride Aeolus Pro 37 wheels (28mm external width).
Larger tires do more poorly with rims due to poor aerodynamics at the tire/rim interface at high speeds. If you aren’t spending much time above 23 mph, though, the difference is probably negligible (2 maybe 3 watts at “lower” speeds). What ISN’T negligible is the freshness you feel and the ability for your core to assist in laying down power when it isn’t exhausted from getting bounced around all over the place. Specialized made a similar argument when comparing the Tarmac SL6 and Venge - the more compliant bike was faster for more people due to reducing fatigue than the sheer aero gains of the Venge.
An interesting corollary is the fast “feel” of narrow tires that many will insist on that has been thoroughly debunked; people associate getting jarred around and feeling every road surface imperfection in their hands and neck with speed when actually it is the perception of speed that is changing.
That’s exactly what I was thinking. I am unlikely, in honesty, ever to average over 23mph over the course of any ride longer than 30-40 minutes on a road bike, and 2-3 watts isn’t material to me. 20-30 watts would be. That’s useful, thanks.
Those numbers are what ENVE gave me when I was trying to decide between two wheel choices, so they may not be exact translations, but they are pretty dang close.
We have old road surfaces with a lot of broken pavement, some sections are so bad I jokingly call them pave.
On my Tarmac SL7 I’ve got about 6 weeks experience swapping between:
Enve 5.6 Disc
28mm external width Enve 5.6 Disc
26c road tires (currently Pirelli Cinturato TL) that measure just under 28mm
tires fairly well matched to rim width, for aero gains
rims are around 60mm deep
only rolling with Enve on Wed night worlds
Bontrager Aeolus Pro 3V TLR
32mm external width
32c road tires (Conti 5000 TL) that measure close to 34mm
tires wider than rim, not as aero in theory
rims are about 35mm deep
daily setup on bike
The Pirelli have almost 2000 miles and I plan to replace soon with my low mileage 5000 TL (25c). Those Pirelli are puncture resistant training tires, about 9W more rolling resistance vs 5000 TL (on a smooth drum according to Bicycle Rolling Resistance).
I’m not feeling like there is much speed differences on longish ~24mph / 39kph tempo tailwind surfing here in flatland.
Most would say the Enve wheels should carry speed better above ~20mph / 32kph, but I haven’t put my 26c 5000 TLs on them and done A/B comparison testing.
The Enve look better on my bike. Its a little goofy running Trek wheels on a Specialized bike, however I prefer the wider tires in the mountains and on the bad roads I train on in flatland.
Eventually I’ll drive out on a windy evening and do A/B comparison with 5000 TL tires on both wheels to get a rough estimate of difference at 24mph / 230W.
Ok, so I’m a data guy and going to give data on imperfect comparison over last month…
Two different nights on SL7, pulled up a Strava segment that has constant wind (no houses, no trees, no obstructions). Its a bumpy old road heading almost due east with tailwind. Strava segment is 1.12 miles / 1.8km.
Date
Wheels
Wind
Power (average)
speed
time
August 11
Aeolus Pro 3V / 5000TL / 32/34mm
SW 10mph gusting 17
steady 245W
24.4mph / 39.3kph
2:46
July 14
Enve 5.6 / Pirelli / 28/27.5mm
WSW 9mph gusting 15
intervals 244W average
24.2mph / 39.0kph
2:48
rim and tire widths are approximate.
hard to draw a conclusion. On paper the Pirelli give up 18W, but the wind was different. No power data on impact of different tire widths on SL7. And I was doing intervals on the Enve and steady effort on Aeolus.
I really need to drive out and do a comparison on same night in same wind conditions.
This is what Specialized puts on the top-end S-Works SL7 (Roval Rapidx CLX):
The fastest guy on Wed night keeps telling me to put the Aeolus on the front (wider and shallower for stability in cross winds) and Enve on rear (deeper at 63mm for more ‘disc’ like aero), which is consistent with the pic above. I tell him to go back to college and finish his Aerospace Engineering degree and I’ll believe him
From ENVE marketing, the tire/rim interface becomes more and more important at greater yaw angles, making the tire width selection more important for windy days.
Still doesn’t change the fatigue/aero calculation IMHO but to each his own
Not scientific but I got between my road bike with 28s tubed and gravel bike with 650b 47s. On the same routes at similar power I would say I lose <1 mph. The PMs are pretty closely calibrated and my position on the bike is the same, other than wider handlebars.
My sense is I am losing speed due to aero and weight rather than say rolling resistance. I will say both bikes are pretty smooth though (Canyon Endurace and Felt Breed) - one produces smoothness from the frame/seatpost and the other from the tires. I wish both of them had more compliance up front.
I’m running Rene herse bon John extralight tires that plump out to 38mm on my bonty Aeolus 3V rims. Frame is a 2020 trek domane. 50 psi. Super duper comfy. About 2 mph slower than my 2011 specialized shiv and 3 mph slower than my premier tactical. I’m a fan of the fat tire road bike.
I do most of my outdoor rides these days on my gravelish bike that is outfitted with 650b wtb horizons (47 mm wide). 90% of my riding is on roads (of various quality). And this includes a lot of training focused rides. I love how comfortable they are and I love how much more connected with the road surface I feel. It doesn’t really answer your question, cuz these tires are wider than what you’re considering (and I certainly do give up a few mph compared to my TT bike), but I’ve gone fat and I’ll never go back. Fwiw, I do some outdoor rides on my TT bike, but reluctantly (usually only races).
You should have no issues keeping up in group rides and sportives with fatter tires. Getting a good draft saves way more watts than skinny tires. If you do get dropped in a sportive, you can just fall back to the next group not too far down the road.
I moved to 32mm tubeless tires and it’s a much smoother ride than before. French roads aren’t great, and it makes a substantial difference in comfort. For me it’s great because I don’t race and enjoy centuries/sportives. FWIW, the bike shop informed that recreational riders won’t lose speed with wider tires.
Thanks all for the contributions. My sense is that I am generally slightly below the threshold speed at which aerodynamics makes a real difference (roughly 32kph) and given my goals/preferences, wider tyres are worth a shot.
While I won’t be able to collect anything like scientific data, I may invest in some 32s and compare them to 28s and report back.
I’d go with a quality 30mm (measured tyre). When I say quality, I mean a high TPI cotton side-walled open tubular style tyre like the Vittoria corsa control or similar (in whatever size will mate with your rim to create that 30mm width).
Having tried 28mm, 30mm, 32mm I reckon 30mm is the sweet spot. It’ll be just as comfortable as a 35-38mm vulcanised tyre, lighter (really does feel better to accelerate), more aero (when at high speeds). Will also give you better contact with the ground than 28mm for good grip while also being more comfortable.
I think in due course, 30mm will become the standard road tyre, with 35-40mm being for gravel/cross and >40 for more specialist stuff.
I don’t think the depth matters when talking tire width. The important match-up is the external rim width and the width of the inflated tire. The rim should be just slightly wider than the tire. The aerodynamics of wheel depth are related to average speed, not tire width.
