I imagine most have now read the recent Cyclingnews lab test, which found that 40mm road tyres are faster for nearly everyone.
Given there aren’t that many road frames or wheelsets designed to run 40mm road tyres (nor that many 40mm road tyres currently available!), I’m just curious what the widest tyre width people here have tried and use on their road bikes on a daily basis, and what type of wheelset (internal/external width) the tyres are mounted on. TIA
My own experience is not very scientific and my 35mm GP5000AS TR’s won’t be on the most optimised rims, but my rides are consistently slower when I ride using these. By 1-2 km/hr. So I’m rather sceptical. I’m bought into 30mm tyres being as quick as narrower tyres, but 40mm is still a big leap of faith.
Thanks. I’m concerned about them being slower as well. The lab test indicates the rougher the road surface the greater the energy saving by running wider tyres. What is the road surface/condition like where you are?
Also, is your wheelset optimised for a slightly wider tyre? My wheelset is an older style 20mm ID, which is optimised for 26-28mm tyres, so I imagine if I put on some 34-36mm tyres, it would impact the wheel/tyre aerodynamics
I can guarantee that theyd be slower for me. They’d stick in my frames. The biggest I’ve had is a 32mm and the commuter/ winter bike only has clearance under the full front mud guard for a 23mm.
That’s the problem right there. My gen 1 3T Strada was early when it came to wide tires. Just that at that time, 28 mm was considered wider and 30 mm wide. My current 28 mm-labelled tires measure about 29 mm and clearance is so small that I don’t dare to put in anything wider.
But I’d go wider if I could. We have bad cobblestones here, and 29 mm wide tires are uncomfortable. I had a very nasty flat last season, the tire was unfixable even with patches.
The tricky thing is that road surface conditions and other factors like comfort will play a significant role.
We see a similar revolution in the gravel space where some MTB tires are as fast or faster than narrower gravel tires for reasons that are quite complicated.
Yeah, so generally, I don’t think the roughness of roads round here really warrants such wide tyres. Theres the odd stretch of really coarse tarmac. The potholes are getting worse but I’d be wanting to dodge potholes regardless unless I was on mountain bike width tyres and perhaps suspension.
I’m running them on a few gravel bikes with the clearance for wider tyres. Specialized Roubaix 32mm are utter life sucking dogs. The GP5000 35mm are slightly less life sucking. But swap on a set of schwalbe pro ones 25mm, which actually measure 30mm on the gravel wheels, and it is back to what I would class as my typical riding speeds. Been running these set ups for a good while and regular as clockwork, regardless of conditions or the routes I choose, the 32mm and 35mm wide tyres are slower.
Might well be that 32mm and 35mm tyres aren’t truly wide enough to give step change noticeable benefits on cobble/pothole/rough tarmac, whereas 40mm could be?
I’ve been riding a GRoad setup for the past 2.5 years. I use Rene Herse 44mm Snoqualmie Pass tires with extralight casing on 25mm id wheels. It’s one of the fastest rolling “Gravel Tire” there is and I’ve been really happy without any incident this whole time (no flats, no slow leaks, no sidewall cuts). I have a second (deep) wheelset for this bike and going from one to the other changes the feel of the bike - but I don’t have any scientific data to say whether wheelset is faster - I’m simply not going fast enough for this to matter probably.
I’d agree that a good chunk of people would be better off running a wider tire as it improves comfort and extends the roads you can ride. I’m a fan of big road tires and my GRoadbike has become the bike I ride on 90% of the solo rides.
The only thing I’d change is going 2x instead of 1x but that comes down to personal taste.
I can be n=2 with these tires. My Cannondale SuperSix Evo fit the 35mm GP500 AS TR, which measured just over 36mm on my 24int wheels. Ran them for about 6 months in a new location (had just moved). They were comfortable, but not fast. I just swapped back to my normal race tires (GP5000 S TR in 28/30mm) and literally every ride since has been segment PRs left and right. So those segments only had me riding either the AS TR in 35mm vs the S TR in 28/30.
Remember the days when running 28’s in the winter was putting on “the fat” tires, LOL!
Pepperidge Farm remembers.
But 40’s? I can’t wrap my head around how they’d be faster. I’m imaginging a beach cruiser sized tire and it doesn’t equal fast. But what do I know, I’m just an old guy trying to be faster than I was last year. Maybe I need a carbon-aero-beach cruiser with 45’s!
I’ve been using 28mm tyres on my road bike for a few years now and have found I’m faster (on average) for the same sort of power - not by much but certainly enough to feel it, compared to the original 25mm setup.
I’ve since moved to wider internal diameter wheels with a deeper profile (51mm Bontrager) as opposed to the original mavic wheels (2017 specification Cannondale synapse) and again, this made a minor yet noticeable improvement with the existing 28mm tyres (using tubes).
Then moving to tubeless of the same brand (Conti GP5000) and width again, you guessed it, a small but noticeable improvement - also more noticeable was a comfort benefit, I suspect due to lower pressures.
I’m now about to experiment with running a 30mm on the rear whilst keeping the 28mm on the front.
Hoping to gain some comfort - I’d be surprised if I was able to discern a noticeable speed improvement.
Frame will probably take a 32mm at the most, so no way I can experiment with anything much more substantial.
I’m also a little sceptical that even if the frame could accommodate 40mm, that in the real world environment of average UK tarmac, that it would prove faster.
I think the issue would be the wheel tyre combination - I’d imagine I’d need a wider rim to make the most of the extra tyre width.
Also, although I’m the first to bemoan the state of the UK roads in my area, they are for the most part still relatively smooth, so I’d suspect any benefit cited wouldn’t manifest consistently or frequently enough to make an overall net positive difference?
Would certainly be more comfy and forgiving though on the rough stuff and enable a bit of anxiety-free off roading. 
Interesting concept though. I’d imagine where the roads a consistently rough enough, the benefit would be stronger.
For my riding, a 25 mm on the front is still the fastest. But I ride TTs so that makes sense. I’d go to a 28 mm front for general road riding. For the rear I will go as wide as I can once the 28 mm I am using is finished. Will be a 30 or 32 mm.
Swisside still think a 25 mm front with a larger rear is the best option.
I bought the article and they do make a big assumption to assume everyone will be better on a 40 mm wide tyre. Something like British roads are nearly as bad as cobbles. Which is part true, but when I organise rides, I try not to go on the bad roads. Non competitive people can probably ride a 40 mm tyre and be fine. I spend all winter on a 45 mm gravel tyre on the roads and it never stopped me riding with road bikes. I even took my gravel bike to Mallorca because my integrated road bike wouldn’t fit in the bike box I hired (silly mistake).
Color me skeptical
Nice to have someone else confirm my thoughts! 
The difficulty here is that you are comparing vastly different tires. Modern tire technology (construction and especially rubber compounds) have made leaps and bounds, and the differences can be vast. The GP5000s are a good choice as an excellent allrounder tire, so I would compare those across bikes.
Personally, I’d look towards the pros to get an idea of the minimum tire width we should run these days. And that seems to be 30–33 mm, if the frame allows it. As a non-pro I’d err on the larger side and opt for a 32–33 mm tire.
So discounting the Roubaix, which have been around for years, the GP5000AS TR are relatively recent tyres. They are reportedly pretty low rolling resistance but I just find them sluggish compared to every other narrower tyre that I own.
Or are you suggesting I should be comparing my slimmer Schwalbe Pro One tyres with a similar “race” orientated 35-40mm tyre rather than even the modern All Season GP5000? Cos I wouldn’t want to try a narrower all season GP5000 if they’re slower! (Their normal GP5000’s are excellent tho!)
I can feel a purchase coming on 
I would caution against feel. E. g. if you watch Dylan Johnson’s video on measuring the speed of tires for gravel, one of his points is that MTB tires “feel” the slowest, but often are as fast or faster than gravel tires.
Much in the same way that slimmer tires at higher pressures often “feel” faster than wider tires (or even the same tires) at lower pressures.
I would suggest you really have a look at data instead of relying on feel, and that you are aware of the fact that you might be comparing apples and oranges.
Honestly, given what the pros are riding now and how conservative they tend to be, I’d be looking at the 30–35 mm range if you want to be quick and 35–40 mm range if speed is not as important as (long-distance) comfort.
Feeling isn’t always an accurate measure of speed. But comparing a GP5000 AS TR 35mm to a 25mm Schwalbe Pro One is a bit of apples to oranges. Since the 5000 AS is like 150g per tire heavier and is designed to be more puncture resistant. I rode the 5000 AS’s in a 28 for a bit last year and they definitely do feel a bit slower than a Pirelli P Zero in 28. I think it’s down to a bit of extra weight as well as a stiffer construction for durability.
But yeah I think for better comparison you’d want to compare to maybe the newer Pirelli P Zero in a 40mm (which without buying the article it looks like the tire the linked article is referring to) or some other similar ‘race’ tire in a larger size since casing design has a huge impact on tire performance. But I agree that it’s hard testing to do cause it’s such a faff to swap tires on and off and it gets real expensive real quick.
It is one test so far, and the claimed watts savings only serve to heighten my skepticism.
I’m waiting for more data before I start looking for a frame capable of accommodating 40’s.
I’m not saying narrower is faster or anything of the sort…I am planning on running 2.1’s for my gravel races this year. But, just as with Dylan’s tests that showed the Lauf fork is “more aero” or that his USWE pack was more aero than no pack, I think you need to be cautious before accepting any single set of tests as gospel.
This would be one for the Ask Josh Anything version of the Silca podcast because it could probably use a revisit in light of the article.
That said I want to say he’s addressed this before. If I remember correctly his co-hosts have joked about WT riders eventually riding 40s or larger to which Josh responded by saying something along the lines of advantages of wider tires start dropping off over 35c.
Call me skeptical, but when their testing suggests that a 40mm tire saves over 70w @ 40kph compared to a 26mm tire, my impression is that they’ve either made these numbers up, or really screwed up their testing.
I mean, I’ve done this. I was out riding at 40kph yesterday on a 12min segment on my road bike and my average power was 291w.
Putting 40mm slicks on that bike would not have allowed me to go 40kph @ 210-220w. Im not suddenly capable of doing a 1h 40k TT at low endurance pace just because I put wider tires on.
I have a pair of 38c slicks that I played around with once. They were very obviously slower than the 28s I had, even at endurance pace.
