ASK COACH FRED

What Pressures are Appropriate for 28s?

Question:

Back in Issue 548 you addressed the topic of wider vs. narrower tires and RBR ran a question asking what size tires we ride. I noted that you said you had switched to 28mm tires from 25mm without suffering performance problems and found them more comfortable. I had then recently switched to 25s from 23 with the same result and the idea of switching to 28 has stuck in my head. I am going to do so and went back to read the old issues to get an idea of recommended tire pressure for that size tire. I read in interesting article at http://www.bikequarterly.com/images/TireDrop.pdf. Using their chart and assuming a 40/60 front/rear weight distribution came up with optimal pressure of 72psi rear and 55 front. That seems way too low. What do you guys recommend? -- Richard Z.

Coach Fred Matheny Responds:

Good question, Richard. A lot of riders are taking advantage of the increased comfort of wider tires. There doesn't seem to be any performance loss and on rough roads speed is often faster because the wider tires absorb the bumps and roll over them with little loss of forward speed, while in contrast narrow tires with high pressures bounce and retard speed. The only issue for most riders is whether their bike has sufficient clearance for wider rubber.

I weigh 150 and run 95 psi in the rear tire, 90 in the front when I'm using 28s. This is higher than most recommendations and I've experimented with lower pressures. However, I have ridden for over 40 years with the traditional higher pressures and find lower psi a bit squirmy in corners. Maybe it's just a question of getting accustomed to a slightly different road feel.

I respect Jan Heine's recommendations and his research seems solid. In fact, in today’s issue, I review a set of Compass Barlow Pass 700 x 38mm tires. I figured that if the trend is toward wider tires, why not go all the way! I found the increased width to be quite comfortable at inflation pressures of around 55 psi and didn't notice slower average speeds. Again, on rough roads speeds actually increased.

So my recommendation for 28mm tires is to experiment with various pressures until you find the "sweet spot" for your road surfaces and riding style. I would guess that for you, ideal inflation pressure would be 80-90 psi, but this may vary depending on your roads, riding style and the balance between comfort and performance you find ideal.

Keep a couple of things in mind. First, gauges on floor pumps are notoriously inaccurate, so if you want to be sure of inflation pressure, a good gauge is useful to get repeatable pressures. Second, beware of the usual figure of 60% of total weight on the rear tire and 40% on the front. This can vary a lot depending on the rider's body's weight distribution, position on the bike and whether the rider is on the drops or sitting up.

If your weight distribution is different, your ideal pressure may differ from the chart. Also, the suppleness of the tire's sidewalls can change the way a tire feels on the road at a certain pressure. More supple sidewalls make the ride more comfortable while rigid sidewalls mean a harsher ride at any given tire pressure.

Finally, I'm not sure that worrying too much about small variations in tire pressure is warranted for most riders (and most rides). I usually can't tell the difference when my tires are 5-10 pounds different from one ride to the other.

Coach Fred Matheny has decades of experience as a competitive racer and cycling coach. He is the author of 13 RBR eBooks and eArticles.

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