So I switched to tubs 6 months ago and have been tinkering around with tyre pressure. I did a bit of research, but that just totally confused me. People I train with and on forums saying they run their tubs anything from 80 psi up to 160 psi. An ex Olympian cyclist, Matt Illingworth mentioned he used to run his at 160, but 140 psi would be OK, with my Vittoria Corsa Speed G+. So I’ve been racing with them between 130 and 140 and they’ve felt good. The road surfaces are generally good. I had a chat with Jack Bobridge (Olympian & TDF) after a race (OD, he did the duathlon) and mentioned what tyre pressure I was running, he looked at me like I was mad! Anyway I had a sprint at the weekend and decided to stick them up to 150psi, excellent roads, but I was very sluggish on the bike. I really struggled. I could have just had an off day, but bike didn’t feel right. I’m thinking of dropping them down to 120ish but not sure. So what’s the science behind tyre pressure? How can I find optimum tyre pressure for me? I’m 160 lbs. All the roads I ride are on pretty good quality and I never feel like I’ve getting bounced around.
Note - I’m aware inflating to 150psi was probably a dumb ass move, a bit of an experiment if you like.
I’m running 23mm Vittoria Corsa Speed G+ tubs on Zipp 900 disc and 808 front
Wow, if you ride those sorts of pressures on roads that are anything less than truely spectacular and have never felt you’ve been bounced around, it’s because your comfort calibration is way out of whack!
The good news is that you should be able to dramatically drop your pressure without any significant increase in resistance, and quite possibly an decrease. And, the comfort difference should be a revelation. I know no reason to run at anywhere near those pressures (unless perhaps you’re on 18mm tyres).
I weigh quite a bit more than you, typical range 80-83kg. I ride 23mm tyres at 80-85 front / 95-105 rear on narrow rims. I ride 25mm tyres at 75-80 front / 85-95 rear on narrow rims and about 5psi lower on wide rims. I could go a bit lower but don’t like them to feel squishy when climbing out of the saddle.
Based on Tom A and Silca’s testing I believe you’re much better off to err low than high. There is a small reduction in RR with increased pressure until a certain point beyond which it increases dramatically with additional pressure. It seems very likely that you’re beyond this point and losing speed due to excessive pressure.
So just to join those dots in case it isn’t obvious.The method is to start with a high pressure and test that you feel that bouncing. A bike with too much high pressure in the tires will skip up or to side of every small obstruction. obviously you can’t do this on the whole course so it’s up to you where you do it but that’s another question. Then you reduce the pressure in small increments and test ride until that skittering feeling goes away. That should be where you want to be. You aren’t losing energy skipping and jumping over stuff but also the pressure isn’t any lower than it needs to be and you aren’t losing energy dragging a tire around that’s too soft. At least that’s how I see it. My brother just puts as much air in as he can and hopefully not blow up the tire.
I think that method will likely leave you with higher than optimum pressure.
Have a look for the graphs on the Silca website. Links have been posted fairly frequently in various discussions here but I don’t have it handy. Tom A has also discussed this topic quite frequently.
The plot of their findings shows a gradually reducing RR as pressure increases until a very defined break point where the RR starts increasing again. The lowest RR is therefore right at the break point. However, since the slope is much steeper after the breakpoint, it makes sense to err on the low side. The method you’ve outlined in the quote above depends on interpreting “bounce” by feel. I really don’t think that’s terribly useful. Everyone will interpret the feel differently and I expect those who’ve previously used very high pressures will end up remaining with excessive pressures.
If you weigh 70-80kg and use 23mm tyres, I’d be saying you should have figures like 85-105psi in mind for the rear and I always go about 10-15% lower at the front. If you weigh less, you should be able to go lower. If in doubt, try 90psi for a few training rides and see what you think. Don’t forget, there’s a difference between being fast and feeling fast!
