Using different tyre pressure in front/rear


#1

On a Scientific Triathlon podcast I listened to the other day it suggested putting different tyre pressures in front/rear depending on weight distribution.

  • On a road bike the distribution is typically 60%-40%, with more weight on the rear wheel. So 60% of the total tire pressure should be in the rear tire and 40% in the front.

  • The pressure that you put in the tire should take that into account to maximize the relationship between the function and rolling resistance.​

Until then I’d always used the same pressure in both tyres without really thinking about it.

Here’s the calculator they reference:
http://www.dorkypantsr.us/bike-tire-pressure-calculator.html

The calculator gives me the following:

That’s quite a bit lower in the front than I’ve used before.

Here’s the podcast show notes:

The calculator is based on this white paper:


#2

Does this take into account when out of the saddle?

Do you know how the weight distributes when stood up?


#3

I’ve not had chance to look at my weight distribution in any detail yet.

I assume you’re best setting the tyre pressures based on the weight distribution of the position you’ll be spending most of your time in.


#4

For the last year or so I’ve been doing that after reading about pressure distribution. I was running around 95-100 PSI on the TT bike but last season I started using around 90-95 in the front and 95-100 PSI in the rear. 20mm Conti Supersonics FWIW.

Along with the information on the Silca website regarding pressures and CRR which suggest there is a ‘break point’ where at higher pressures the RR dramatically increases on road surfaces which doesn’t show up in CRR tyre testing on rollers I’ve gradually edged the pressures I use down.


#5

Thanks for the link @JulianM, nice article. The graphic showing Crr versus tyre pressure is real interesting.

Riding at 110 psi instead of 100 psi could actually lose 6 watts :open_mouth: Based on the state of most of the roads I ride on it looks like around 95 psi should be the highest pressure I use.


#6

The whole series is well worth a read if you are that way inclined! It certainly seems that it’s better to err on the lower side because the penalty if you’re just the other side of the break point can be significant.

The balance of rolling resistance, tyre pressure and the aero dynamic relationship between the tyre and rim width is very nuanced.


#7

Have you measured your weight distribution on the TT bike, or just an estimate?

That article suggests 50/50 for a TT bike:

A TT bike also has nearly 50/50 weight distribution, so equivalent front and rear tires pressures were used.

I might have to get the scales out to check mine when I get chance :slight_smile:


#8

No, just an estimate on my part. For the reasons you say about weight distribution on TT bikes I just try to put a little more in the rear than the front rather than look for a significant difference.


#9

I believe FLO had the first info on this that I saw (not saying they were the first, but what I came across first) and I’ve been running about the same 5PSI difference between from and rear and pressures on my Tri/TT as @JulianM as well. Whether it makes a difference… :man_shrugging::joy:


#10

Cyclocross riders typically use 1 psi lower in the front tire than in the rear. At 24 or 25 psi, that 1 psi is roughly a 4% difference.