That really depends on the all up weight of rider and bike.
Yeah, that used to be me. 110kg plus bike needed 85psi on 28mm tires. Now I weigh the same, but run my 44mm Snoqualmie Pass slicks at 43psi and my speeds are as fast, or maybe faster, than they were before because the tires are really absorbing more of the bumps.
As I lose weight, I’ll probably eventually drop down to 38mm for the road. I think. Those 44mm are sooooo comfortable…
tell it to silca! 
Just trying to pick the closest BRR data point to the closest Silca pressure calculator rec.
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No it doesn’t. Hit the reload button. Or contact their customer support.
And if you want to know whether 28mm tires or 30mm tires are better…go with the 28’s. The data clearly support that choice and, as this thread demonstrates, the only argument for the 30mm tire is that you will ‘feel better’ after riding for a ‘long time’. That’s subjective, not evidence.
Good luck with the Silca widget!
Just for fun I just checked this
Now, as I said, the closest BRR data point is 80 psi. Glad I could help! Good luck with that Silca widget.
Atta boy! Laugh it off!
As detailed earlier in this thread:
rolling resistance: no measurable difference. Maybe 150mW advantage to the 30s.
weight: 60g advantage to 28s
aerodynamics: Enve doesn’t recommend the 30’s. At higher yaw angles, 2-4 watts lost
Yes, that’s correct. And when you refer to the 2nd graphic that I posted…also note there that the BRR data is for 28mm vs 32mm. So not a 1:1 comparison.
But, but, a 30mm GP 5k is only going to be closer to the 28. So at 80psi crr difference between the 28 and the 32 is 200 milliWatts…the difference will only be smaller between a 28 and a 30. So I’m being generous when I say it might be 150mW. More likely it’s less than 100mW difference. de minimis.
But the weight advantage is measureable. Not large but clear avantage to the 28’s.
And the aero disadvantage at yaw is also material. Which is a big part of the reason Enve don’t recommend tires that wide for that wheelset. But, as I said, if you know you ride a moderate distance on 28s and experience a 20W decrement in performance vs riding a moderate distrance on 30mm tires…well, I think you should consider other wheels and capture both gains. Other wheel options are available, as they say.
@Junk_Miles, I know you asked what data supported the notion that 28’s are the clear choice…so just to reiterate:
1.) The rolling resistance between 28’s and 30’s is going to be at best mW. No material difference.
2.) There is a clear weight advantage to the 28’s.
3.) There is a clear aerodynamic advantage to the 28’s. Especially at yaw. Which is probably why the manufacturer don’t recommend larger tires on that wheelset.
Some posters in this thread have said that if they ride a moderate distance on 28mm tires they will experience a 20W decrement in performance vs riding a moderate distance on 30mm tires. If you are in this cohort, it’s probably a good idea to go with a different wheelset that has greater aerodynamic performance at yaw with wider tires.
Silca calculator suggestions are useless, because they don’t take the rim width into account. The pressure for a tyre installed on some old 17 mm rim is totally different than for a tyre on 25 mm rim.
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A 25 mm tyre will measure just over 27 mm on the Enve foundation wheel. The 28 will be closer to 30 mm.
I use a 25 mm front and 28 mm rear as I also like to do time trials on my road bike where I’ll average 42 km/h+ so aero is important.
I’m not ready yet to buy wide wheels (mine are only a year old) and I refuse to give up aero so will be sticking to this. I don’t find it uncomfortable and it is still massively better compared to the 23 and 25 mm I used to run on rim brakes.
For you the safe choice is 28 mm front and 30 mm rear if you are worried about aero. I like the odd tyre sizes and it makes sense in my head.
I may not have adequately explained my points.
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Subjective: For many riders, the reduction in fatigue that comes from a wider tire at lower pressures will materially affect power output over long distances. I’m sure many racers and pointy-end people are much more durable than the majority of cyclists, but for MANY people this is a real consideration.
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Objective: Your argument ignores power losses on the narrower, higher-pressure tires due to suspension effects as the tire’s reduced compliance increases the bike’s “bouncing” (for lack of a better word) over road imperfections where a wider, lower-pressure tire will absorb some of that impact and allow the bike to travel in a more consistent path with less vertical displacement. Those effects are substantial and increasingly well-documented.
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Objective: There is a visible trend even in the fastest pro pelotons for wider tires and lower pressures. That is real-world DATA, even though it’s neither research-derived nor -intended. When even the 2023 Tour de France saw mostly 28’s (and 30’s for Paris-Roubaix), the rest of us are likely best served by running at least the 30mm tire.
I think your position was solidly supported by the best available data around 2015, maybe 2020. But today, I think your argument is missing key pieces that do change the answer.
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No I’m not ignoring it. I just know what it actually is.
I haven’t done a tire bake off on my wheels, but these guys did at two representative powers on nearby roads:
32 tires for the win, on my wheels.
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Your communication does not make that clear. Your graph is about the reduction in rolling resistance, which has nothing to do with suspension losses. Rolling resistance and suspension losses are both components of the total resistance in the system… but they are not the same and they are not too closely related.
Note that suspension losses increase with pressure. This is an entirely different subject from rolling resistance. Read the nicely-explained article about “Why Wide Tires Are NOT Slower” for more details (posted just above by @Junk_Miles). There are plenty of other sources agreeing with that.
Your attitude is that there is a CLEARLY RIGHT answer favoring the narrower tire. What I’m saying is that the world agreed with you 10 years ago, but that there is, at the very least, much less agreement on that today… and I think it’s fair to say that the preponderance of experts will now recommend the wider tire.
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And given how close the times were, I’d have personally chosen the 34mm tires for greater comfort… especially for “longer gran fondo type events” where the OP wants to balance performance with comfort.
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The chart he posted included impedance loses. Did you look at the graph?
Nobody going to resolve differences until you take your wheels and tires outside and test.
That’s not the correct interpretation of that graph. See these tests for example:
I’m just going to link the post so I don’t add anything in my own words.
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Of course I looked at it. But I noted the “Crr” Y axis and didn’t realize/remember that Josh uses impedance as synonymous with suspension, so I missed what he was saying. My mistake.
However… having reviewed it, I’ll note that his graph comes from the Silca blog’s Part 4B: Rolling Resistance and Impedance, where @Brennus has nicely picked the graph most favorable to his/her argument.
Further down the page is a graph clearly showing how increasing the surface imperfections favors lower pressures:
He also shows the breakpoint where “…we learned that Tom Anhalt’s data was repeatable, and impedance does in fact dominate the rolling resistance beyond the breakpoint pressure” (emphasis mine).
I very clearly do NOT see any mention of impedance in the initial arguments by @Brennus and the “I’m not ignoring it, I just know what it is” response clearly indicates a dismissal of its importance. But the same data source indicates its significant importance.
AND, this is all on 25mm tires which had a WAM of 25.8mm. Josh’s “breakpoint pressures” are between 70psi and 95psi depending on surface… but that’s on a pretty narrow tire. The breakpoint pressures where impedance dominates the rolling resistance would be much lower on a 28mm or 30mm tire.
Wider tires at lower pressures are KNOWN to have lower impedance losses since they flex more.
More supple tires are KNOWN to have lower total resistance (again, see graph on same page with caption “Tires with More Supple Casings Have Lower Rolling Resistance Everywhere and are More Forgiving of Over/Under Pressure”).
Links to two really great articles from the SILCA blog on all this:
I see NOTHING to indicate that “the data clearly support that choice [the 28mm tires] and […] the only argument for the 30mm tire is that you will ‘feel better’ after riding for a ‘long time’.”
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Well, that’s just ridiculous. I’d have to ride my bike which is not part of my training program for getting faster by optimizing equipment in hypothetical scenarios.
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There is no weight difference I have GP5000 in 28 and 30c and they weigh exactly the same.
Also on my regular route my fastest time was done on 30mm tyres
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Any of you guys been outside for a ride today? Cabin fever abounds.
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