Who's done the wider tyre road experiment?

Equipment
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Peak Torque on YouTube has interesting findings on this topic in this recent video

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The GP 5000 TR S seems to be one of the fastest tires and the effects on aerodynamics by going wider or narrower will be affected by the rim width. He then went on and tested the Corsa Next on the same setup and it was 19 Watts slower than the GP5K, much more than the either going 28 or 32 on the wide or narrow rim. Consensus to me seems to be: choose the fastest tire and the appropriate width for your wheel. If your wheel is 30mm wide chances are a true 30mm tire will be fastest. Rear wheel has probably no measurable effect. So 28 front 30 or even 32 in the back would be both fast and comfortable.

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Don’t have a great before/after comparison because I went from alloy wheels with 38mm gravel tires to a wide carbon wheelset with 32mm GP5000 S TR and the difference was incredible.

The external width of my wheels (hookless x-wide hunt carbon gravel) is 31mm and the tires were basically flush. They looked great, felt amazing in comparison to the stock wheels and tires that came with my gravel bike, and they gave me a lot of confidence on descents. I still get a little worried above 35mph but that is just my lack of long term experience and a general desire to preserve my skin and collar bones. I rode them outside 4-5 days a week for four or five months and never had a flat or excessive loss of pressure in the tubeless setup.

I will say it’s much easier to keep up with the racey business park group with the high-end 32mm tires than it is with the 42mm Pathfinder Pro on the same wheels but that is probably obvious.

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“Just thinking the 5000str might blow up above 30mm on the 303, so a 28c front could give a noticeable aero advantage.”

I have fiddled around quite a bit with the aerodynamics of tire width vs rim width. While the rule of 105 is real, you have to consider it in conjuction with your yaw distribution. For your setup, I would almost always choose the 30mm.

Rule of 105 matters at greater yaw angle. If we’re talking about the difference between a spec 28mm and a spec 30mm tire on a 30mm rim I almost never ride under conditions where the 28mm would win out. When rolling resistance+impedance+aero are summed the 30mm almost always comes out on top.

Now, if you know you’re going to be slugging it out in wicked crosswinds all day, pick the 28mm. Especially if it’s a hilly course.

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“Why would the 30mm have a lower aero penalty?”

At low yaw angles the AERODYNAMIC difference between that rim with a 28mm spec tire and that rim with a 30mm spec tire is de minimis. The rolling resistance + impedance advantage of the 30mm tire is more than the aero advantage of the 28mm tire…AT LOW YAW ANGLES.

If it was a climbing road race I’d pick the 28mm tires, no question. That’s going to save you >100grams.

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When my current 28 P-Zeros wear out, I’ll be going with GP5000S TR on the ‘fast’ bike. The question will be 30 or 32 mm. I’m running 303FC, so a 25m inner and 30mm outer. Maybe a 32 rear/30 front is the sweetspot… decisions, decisions.

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Been on 32mm a few years now, it’s like going back to the width in the 1980s for the UK at least. I don’t race, and my average speeds have not declined from when I ran narrower. It requires so much less energy to ride when you have that extra volume air cushion. Narrow higher pressure tyres feel faster but in reality on the road are not. Leave that to velodromes.

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I’ve just acquired some GP5000 S TR in 32 and will be fitting them tonight for a test tomorrow. They’re going on 303 Firecrest, so I’m guessing they’ll run to 34 or so. I’m hitting 110km tomorrow so that’ll be a decent run out. Will report back!

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Fitted. One went on very simply (1 tyre lever used, but stronger thumbs than mine wouldn’t have needed it, and inflated first time with a track pump), while the other was a little harder to inflate, but after a little fiddling with the bead it was fine.

Weight difference vs the Pirelli P-zero race tlr in a 28 is very unscientifically ~20g; the whole wheel unit has come up c.40g heavier, but I’ve topped up each wheel with an extra 20ml sealant. This corresponds pretty accurately to Pirelli’s claimed weight of 295g and Conti’s claimed 320. In any case, they’re trivially heavier.

They’ve come up just shy of 34. Just over 5mm clearance left up front, just about 4 at the back. I probably wouldn’t want to chance anything bigger at the back - the seat tube gap is the narrow point.

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Have fun on those balloons tomorrow

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Ok, so that was interesting. First, the GP5000S TR is a fast tyre. It has that really zippy feeling that only real race tyres have. It seems (stress ‘seems’) a faster tyre than the P zero race. That, though, is probably a function of the tyre more than the width.

I also experienced a bit more confidence and grip descending, but perhaps that’s partly due to the slightly warmer and drier roads we’re now getting in the Chilterns after a run of fairly warm and dry weather (for February). I did hit a PR down a hill I’ve ridden dozens of times, mind you, and that’s surprising for winter.

Comfort is definitely slightly improved but I don’t think it was a game changer. I set the pressure to 48 psi rear, 45 front, and actually think the sweetspot might be 2-4 psi below that (for reference, I’m 70kg/154lbs, and the tyres are mounted on Zipp 303 Firecrests).

For those interested, today’s numbers:

98.6km, 28.6 kph av speed, 198w av power, 219 NP, av HR 143, weather impact 1.3%. The objective of today was (after getting warm) to try and ride 3 solid hours right on my perceived VT1 and really minimise coasting.

Last long ride: 103km, 26.0 av speed, 188 av power, 202NP, av HR 135, weather impact 5.8%. This was a 60km potter with a friend followed by 40km solo ‘pressing on’ (low tempo).

In other words, the rides are too different to compare the data.

I’ll keep posting in here with reflections as I get more miles out of the tyres.

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How much climbing on each of those rides?

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~950m today, ~1100m last week.

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Isnt there a trade off here in lower pressure higher rolling resistance?
Here is a tire tested at various sizes.

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I just bought a new bike and was going to be going to 32s… was previously on 28s…is it really worth dropping air pressure so low if you are riding on the road? It just seems like we can get some more comfort in going to a larger tire size regardless. I cant ride outside yet to test…too much snow. Will test eventually.

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Sensible question. My view is that I’m not racing (semi-competitive sportives are as close as I’ll likely get), so a handful of watts doesn’t matter, and if I can get more comfort and grip and still have a fast tyre, it’s a win/win.

At 44psi, BRR puts the GP5000S TR (in 32) at 12.8w. That’s just below the pressure recommended for me by the SRAM tyre pressure calculator (and as established earlier, 48/45 is probably a bit high). At 60psi (the calculator recommends 62/58), BRR has the P Zero Race TLR at 16.9W.

Now while the absolute numbers don’t matter, (and I couldn’t run the 26 on the 303FC anyway) that does seem to corroborate the idea at the GP5000S TR in a 30/32 will be faster, grippier and more comfortable than a 26-28 P Zero.

If I were at the sharp end of racing I’d probably put 28 on the front and 30 on the back, but for my current use, 32s (or 30/32) seem right. But it’s very early days.

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Don’t forget the trade off in aero and size.

I also didn’t find larger tires to be a game changer. I’ve tried 26-35mm width as measured tires. Road feel is more important.

Higher volume tires (32c) does appear to reduce flats on rear tire.

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My plan is to try 44/41 next week and go from there. 48/45 didn’t seem way off, just a bit high.

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Does anyone have tire width measurements for 32mm GP5k TR on ~22mm internal width hooked rims? I suspect they’ll inflate true to size since 22mm isn’t really out of the ordinary anymore.

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:popcorn:

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I’m currently of the train of thought that better surfaces and faster speeds exert a downward pressure on the optimum tyre size, while poorer surfaces and slower speeds point towards wider ones.

In my case, the semi-rural roads of Herts, Beds, Bucks and Oxfordshire are often quite poor in quality. In the summer, I might average 35-37kph if I join the A group for some evening loops, but most of my riding is going to be in the 28-32kph range. My understanding of the current thinking is that in that 28-32 range, there is likely to be little to no speed difference between a 28 and a 32 (probably even a 35 if it would fit), but there will be advantages to the wider tyre in grip, comfort and puncture resistance. In the paceline, there probably are small aero losses, but it’s such a small part of my riding, it’s not worth worrying about.

Others may have different views and that’s totally cool, but IMO when you’re quick enough to worry about these kind of differences (like the AXS 10t argument), you’re probably quick enough to be riding what your sponsor gives you (or at least heavily subsidises). Even on that note, the fastest rider I know is planning to be on 30s this year…

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I wouldnt mind hearing how you find it. I typically wont get to ride outside till late April so lots of time for me to dwell on it.