To start, as a light 130lbs/60kg rider i have opted for 25mm tires, measuring 26mm at 90psi.

90psi considered low?

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90psi considered low?

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Crazy high

Wider tires having lower rolling resistance is only true if the results aren't normalized for casing tension.

right road conditions = track? 130 is off the chart too high

It is widely accepted/proven that wider tires allow for lower rolling resistance, and (maybe less publicised) lower pressures cope better with impedance losses from rough surfaces. It is also well accepted, that wider tires take an aero hit at zero yaw, and do so even more at yaw if you go over the width of the rim.

Disc brakes are allowing tire sizes like 28mm (measuring even larger) to become a reality with minimal low yaw aero losses, offset by improved rolling resistance, and impedance losses, as the roads i frequent are not great.

Many of us are limited in tire choice due to our frames, and/or rim brakes.

It is all give an take, and your average speed, wind strength/direction, rider weight, and road surface factor in.

What combo have you opted for, and why?

To start, as a light 130lbs/60kg rider i have opted for 25mm tires, measuring 26mm at 90psi, on rims that are 25mm at the brake track, and 27mm at the widest. My reasoning is that i want to follow the 105% rule for optimal aerodynamics of my wheel, and i keep the pressures low(er) to prevent tire size from getting too large, and hurting aero. What i lose in rolling resistance with lower pressures is partly offset by my low weight, and gains in comfort, aero, and minimizing impedance.

Given the pressures i run, i estimate marginal gain scaling up to 28cc tires, wider rims (requiring disc brakes).

Why would i run lower?

"It is widely accepted/proven that wider tires allow for lower rolling resistance"


Really?

I tried 75ish psi on jet+ rims with 23c tires(4000k) and got a rash of pinch flats that week. at 75kg. I don't go lower than 85 any more. the 75psi ride felt nicer and wasn't slower, but who the hell want to stop every other ride to fix a pinch flat??

I tried 75ish psi on jet+ rims with 23c tires(4000k) and got a rash of pinch flats that week. at 75kg. I don't go lower than 85 any more. the 75psi ride felt nicer and wasn't slower, but who the hell want to stop every other ride to fix a pinch flat??

90psi is too high for you.
I'm planning to ride the following combo this season:

HED jet plus black / disc combo (25mm width) with Supersonic 20mm front, Supersonic 23mm rear at 75-80psi and latex. I'm 71kg.

I tried 75ish psi on jet+ rims with 23c tires(4000k) and got a rash of pinch flats that week. at 75kg. I don't go lower than 85 any more. the 75psi ride felt nicer and wasn't slower, but who the hell want to stop every other ride to fix a pinch flat??

Pretty much. 19cc tires are pretty dead for example. 8 years ago, 23cc was called “wide.” The debate is more about, for a given rider, at what width do gains become offset by losses? Given the multitude of factors at play to generate a “correct” answer... the answer becomes hazy.

Very interesting. It would be interesting to see wind tunnel data of a 20 on those wheels vs 23. If you could preserve the aero performance of those wheels (not exceeding 25mm) with a 23cc tire, would you swap to achieve lower rr, and less impedance losses?

Also interesting is that conti suggests 145-170 for your front. I assume they print their numbers to account for possible high cornering loads (not typically seen in tri). I tend to ignore lower pressure advice as i figure i am both lighter than the typical test rider the numbers are besed on, and i am not cornering hard in a crit race.

Finally, would you consiter gp4000/5000 if they increased your wheel aero performance at yaw? (Smooth tire profiles are not as good at keeping the air flow attached to the wheel). The data seems to be there if you believe people like swissside.

Traction, comfort, and because you should not be so damn dogmatic.

Also interesting is that conti suggests 145-170 for your front. I assume they print their numbers to account for possible high cornering loads (not typically seen in tri). I tend to ignore lower pressure advice as i figure i am both lighter than the typical test rider the numbers are besed on, and i am not cornering hard in a crit race.