Hacker News Reader

Comment by shiroiuma | Hacker News Reader

If this is a modern bike, 80psi is way too high. 50psi is sufficient and will give you a more comfortable ride as well as higher efficiency on real-world surfaces.

80+psi is for old-style road bikes with narrow 23mm tires. Modern bikes (even road bikes for racing) don't use these any more; 28mm is the minimum these days.

View on HN

Not to be pendantic (but to be pendantic) 80psi is the correct pressure for 28mm tires ridden briskly on good roads. At least according to ye olde Silca tire pressure calculator. Back in the day when folks ran 23mm tires they would typically run above 100psi (though that may not have been optimal...).

That calculator is wrong. Cycling people have been overinflating their tires for ages (as well as using too-narrow tires), with the assumption that the ground is perfectly smooth. Lower pressures yield higher efficiency (and better comfort) on rougher surfaces.

Surface quality is an input in that calculator.

… I have a modern bike (a Specialized). The tires' rated range is 75psi to 100psi. I usually pump it to around 80–85psi. The tires are 33mm.

You're overinflating your tires. A lower pressure will increase your speed and efficiency unless you're riding in a velodrome. Here's a video about this:

https://www.youtube.com/watch?v=7r8f3w89XeM

(watch out, there's a lot of extra stuff in this video about the machine they use to measure efficiency)

(Well, they should tell the manufacturers…)

The video's result for both tires they tested was peak efficiency at 5 bar. They had a really coarse sampling of a whole bar, so that works out to a pressure of 65–80 psi.

>(Well, they should tell the manufacturers…)

The manufacturer rating is likely a max allowable pressure rating.

Reply on news.ycombinator.com