As per the subject. I’m looking for some input from the techno geeks, engineers and scientists on here. I was just about to place my annual order for tyres and I had a thought…
Running a 25mm GP TT on the rear wheel is a given but is it worth running a 23mm conti GP TT on the front wheel? Does the increased rolling resistance of a higher pressure 23mm tyre get offset by the improved aerodynamics of a narrower profile? Do yaw angles and and the quality of the road surface come into play or is the difference so small I should just order whats cheapest.
23mm. The 23mm TT already isn’t exactly a great aero performer. The 25mm would be a disaster and, contrary to popular belief, the 25mm tire will not have a lower crr.
I switched to 25 front and back on my 404s a couple weeks ago after riding 23 for a couple years. I don’t have any objective data on the change, but I enjoy the ride so much more that I don’t really care if I fall from 52nd to 55th in my age group.
contrary to popular belief, the 25mm tire will not have a lower crr.
Really? Did they screw up the GPTT25 they way they appear to have scewed up the SS23?
OP, the best option for the front if you want some puncture resistance and and low Crr is probably the Attack23. It has “aero grooves” oriented the right way now.
I switched to 25 front and back on my 404s a couple weeks ago after riding 23 for a couple years. I don’t have any objective data on the change, but I enjoy the ride so much more that I don’t really care if I fall from 52nd to 55th in my age group.
Pressure? The spring rate of the tire is dominated by pressure. The lower limit is set by pinch flat worries… and if you use latex tubes, you can run low pressure. If you hit something hard enough to pinch flat you are probably wrecking the rims (or about to). I once hit a pothole hard enough to dent both rims, but the tubes were fine.
I was just going to make a point along these lines. The roads in my area have deteriorated so badly that I can’t be confident running 23 mm tires much anymore. Running larger tires and lowering the pressure makes a lot of difference in how much I get beat up. The OP might want to take that aspect into account if they know their courses. Aero and RR might not necessarily be the top considerations if the pavement is less than optimal.
contrary to popular belief, the 25mm tire will not have a lower crr.
Really? Did they screw up the GPTT25 they way they appear to have scewed up the SS23?
OP, the best option for the front if you want some puncture resistance and and low Crr is probably the Attack23. It has “aero grooves” oriented the right way now.
Nope, crr is primarily driven by compound and tire construction. The whole “wider is faster” myth is because CRR tests are normalized around tire pressure instead of casing tension. As a result, wider tires have a higher “spring rate” by default. You wouldn’t run a 29x2.0 MTB tire at 90psi (it would be rock hard) so why would you run a 25mm tire at the same pressure as a 23mm tire? You wouldn’t (or shouldn’t). Once you adjust for pressure, the size of the contact patch and the amount the tire deforms does not change meaningfully. As a result, crr is driven primarily by compound and casing (“spring material” if you will).
Wide tires ≠more comfort either. Wide tires allow you to obtain a more comfortable ride by running a lower pressure with less risk of a rim strike on account of having more volume.
Nope, crr is primarily driven by compound and tire construction. The whole “wider is faster” myth is because CRR tests are normalized around tire pressure instead of casing tension. As a result, wider tires have a higher “spring rate” by default.
A narrow tire and a wide tire of the some construction will have the same spring rate at the same pressure. I think Josh Poertner and Damon Rinard have both measured this. If you run them both at 100 psi, they’ll ride about the same and the wide tire will have lower Crr. If you run the wide tire with less pressure, the Crr may be the same, but then you gain more comfort with the larger tire.
Still experimenting with pressure. Happy to get any recommendations. I weigh 175. 85psi felt a little low. 90 felt pretty good. Ran 105 on my 23s. I ride in Florida in midday heat so I am a little skittish on putting too much air in the tires, whether justified or not.
90 psi should be plenty for 23s. You could probably get by with 80 or even less if you use latex tubes.
Nope, crr is primarily driven by compound and tire construction. The whole “wider is faster” myth is because CRR tests are normalized around tire pressure instead of casing tension. As a result, wider tires have a higher “spring rate” by default.
A narrow tire and a wide tire of the some construction will have the same spring rate at the same pressure. I think Josh Poertner and Damon Rinard have both measured this. If you run them both at 100 psi, they’ll ride about the same and the wide tire will have lower Crr. If you run the wide tire with less pressure, the Crr may be the same, but then you gain more comfort with the larger tire.
The casing tension of the wider tire will be higher and thus its “spring rate†(not a 100% accurate term here but close enough) will be higher. Damon chimed in on this last year when Flo released their preliminary casing tension study saying that normalizing for casing tension was indeed the correct approach. TomA has mentioned this as well. Hopefully he joins this thread. I’ll find and link Damon’s comment when I’m back in front of my laptop.
Casing tension has been missed by most in the industry because 1.) its difficult to measure and 2.) humans are wonderfully prone to placebo effect. BikeRadar has a story last year where they compared the GP4000S II in three different widths. Even though they ran all three tires at the same pressure (95psi if memory serves) they stated that the 28mm tire was “smoother†and all the other usual marketing gibberish.