Trials tire PSI question

i think i may be wrong but when i checked the psi on my luna tire it says i have it at 22psi :astonished: which doesnt make sense because i weigh 235lbs and ive never bottomed it out and ive done drops up to 2 feet on it. is this possible or is my guage just way off?


were you using a bike tire gauge? I have found automotive tire gauges really unreliable for measuring bike tire pressures.


yeah i used the guage at the bike shop where i work.

I’m at 17PSI on a low-pressure guage that should be pretty accurate. I weigh 165 and don’t come close to bottoming out.

well theres a big difference between 165 ans 235 and not much of a diff between 17 and 22. plus ive seen people who are like 170 running pressures of like 30-40psi…thats why i was wondering.

You may just land too well. I have my tire at 20 PSI and I weigh 126 pounds. I,ve taken six foot drops without bottoming out.

I never realized I was in your sig. Cool.

I weigh 170, and i keep my psi at 30, one time i tried 20 but it was too close to bottoming out, but 30psi is perfect for me =p

That’s a lot of pressure for a trials tire. I run mine right where I can give it a hard landing from about 2 feet and be just short of bottoming out.

i run at 35 mostly, on a dirty old creepy crawler, can still bottom out if i do something stupid. was running at 25 and that was just too soft… but nice and bouncy :wink:
i weight around 80Kg most of the time and my riding style is somewhat agressive. im sure that when i finally get a luna of something other than CC that i will drop that down to 25-30psi due to the sidewall thinggy and less folding ability :wink:

so you guys think that 22psi isnt that bad and that i just have good landings?

my landings tend to be pretty smooth so 17 is plenty for me. I would think that a smooth landing helps a whole lot.

ok then i feel beter now!

There is a big difference between the difference of the numbers which is unimportant. The ratios of the numbers are quite close. The contact patch area of the tire should be very close to the same in both cases.

I weigh in at 195 and keep my trials tire pressure so I just don’t bottom it as I precompress for a big hop. This is about 18 psig for me. I am bottoming my tire on four foot drops. I don’t care. Trials unicycles are for beating up. I have been riding mine with a broken spoke the last three times out.

Your idealized contact patch area is just that, an area. The pressure of your tire is given in units of force per unit area. Your weight is given in units of force. The quotient of the two yields a number with units of area. If you weigh 235 pounds and your tire pressure is 22 psig then about 10 square inches of your tire would ideally being making contact with the pavement. Tires are not ideal and are not perfectly elastic.

Psig stands for pounds per square inch gauge which is the pressure above the local atmospheric pressure. Psia stands for pounds per square inch absolute which is the pressure compared to vacuum, zero, free space. Psi is commonly used to indicate psig.

Jump, drop, scrape your trials uni and have a ball. Experiment with different pressures. I will eventually pinch flat my trials tire. You will too if you take my advice. Gerblefranklin is an accomplished trials rider who will disagree with my assessment entirely. He differs from me. He’s talented, I’m not.

well seeing as how you seem to be a quite respected member of the forum ill go out and buy a few new tubes and test out some diff pressures tommrow and reprt back.

i generally run between 20-25 psi in my luna. any lower and i fold like crazy and bottom out anything higher than 3 feet. too much higher and i have a significantly lower side hop. i weigh 190 or so.