Finding Your Ideal Tire Pressure

[scott43]

I pump up the tires enough that I don't get rim dents..

 

[cantunamunch]

Please elaborate on the benefits of not just simply using the maximum inflation pressure printed on the tire sidewall on my road bike.
Thanks.

On a perfectly smooth road, that is absolutely optimal.

On a non-perfect road it would be better to drop the air pressure but keep the same quantity of air you had before. If you're going to 110psi in a 25mm tire then you will have smoother ride with 70psi at 32mm - and approximately the same quantity of air between your rim and the rock.

 

[Wilhelmson]

I think the Patriots got in some hot water for something like this. It was pretty funny listening to the local sports radio idiots and national tv idiots talking about pv=nrt.

 

[Tom K.]

What I mean is if I check the pressure and it says 185, it was probably more like 190, but if I pump it up to 205, it is 205. I can be pretty sure about that.

Bingo. I confess to checking (and adjusting, based on the day's ride) my shock and fork pressure before each ride.

With, of course, a digital shock pump.

So based on that, I know about what the gage should read when I screw it onto the fork or shock. If it's significantly lower than expected, I know it's time to give that suspension unit some service.

Soapbox Rant Warning!!!!

It blows me away how many riders I know that spend tons of time and money to buy a bike, and get somewhere cool to ride, then seem to take pride in declaring that their shocks and tire pressures are probably "good enough", or actually squeeze their tires..

Rant over. Sorry.

 

[Crank]

I weigh 210 right now. If I rode at 20psi I would get pinch flats. Our local trails are fairly rocky here in CT.

 

[scott43]

Soapbox Rant Warning!!!!

It blows me away how many riders I know that spend tons of time and money to buy a bike, and get somewhere cool to ride, then seem to take pride in declaring that their shocks and tire pressures are probably "good enough", or actually squeeze their tires..

Rant over. Sorry.

Well..I know you're well-intentioned Tom..but..some people just don't care that much. They don't have the time, money or interest in buying tools, pumping stuff up, whatever. Get on it and ride. Which is kinda the downfall of expensive bikes. Some bikes all you do is pump the tires, lube the chain and you're good for 5k miles. Other bikes require fiddling..and some people just don't care. At least they're out riding. Look at the bright side!

 

[Tom K.]

Well..I know you're well-intentioned Tom..but..some people just don't care that much. They don't have the time, money or interest in buying tools, pumping stuff up, whatever. Get on it and ride. Which is kinda the downfall of expensive bikes. Some bikes all you do is pump the tires, lube the chain and you're good for 5k miles. Other bikes require fiddling..and some people just don't care. At least they're out riding. Look at the bright side!

Agree 100%.

It's the addicts like me, that spend a bunch on a fancy bike, then a bunch more to get to Moab, then are "too tired" to check their pressures and lube their chains.

For them, no mercy!

 

[Ken_R]

I weigh 210 right now. If I rode at 20psi I would get pinch flats. Our local trails are fairly rocky here in CT.

It all depends on the particular tires (and rims) you use.

 

[Erik Timmerman]

https://www.pinkbike.com/news/video-tech-talks-data-under-pressure-presented-by-park-tool.html

 

[SpikeDog]

I started out my MTB career with the first ride at 40 psi on a hardtail 29er. It about beat me to death. I dropped to 25 psi, and like it much better.

This was what I expected to see when I read the thread title, not casing tension, perv-nert, and altitude/temperature charts. The very first post's article was basically "keep trying different pressures until you find one you like."

 

[martyg]

This was what I expected to see when I read the thread title, not casing tension, perv-nert, and altitude/temperature charts. The very first post's article was basically "keep trying different pressures until you find one you like."

Ummmm.... No it wsn't. It outlined a testing protocol for determining your ideal tire pressure.

Sorry if you don't get into perv-nert details. Attention to those details are what will enable you to succeed in any domain from entrepreneurship to finance to skiing to cycling.

 

[SpikeDog]

The testing protocol boiled down to "Keep trying different pressures until you find one that works for you". I know what I read, MartyG. As a chemical engineer, I fully understand PV=nRT, mechanics of materials, etc. Don't guild the lily on the gearjunkie article.

 

[martyg]

The testing protocol boiled down to "Keep trying different pressures until you find one that works for you". I know what I read, MartyG. As a chemical engineer, I fully understand PV=nRT, mechanics of materials, etc. Don't guild the lily on the gearjunkie article.

No... actually the testing protocol boiled down the below. However you are probably more familiar with the article than I am.

"How do we make this information actionable? With a roll-out test. At the most basic level, you will need a stopwatch, a digital pressure gauge, and some tape, cones, or a stick in the ground to mark the start/finish of your course.

Look for a gradual downhill run over several hundred meters of terrain that’s consistent with the terrain you typically ride. In my case, I ride long loops that involve Forest Service roads and singletrack. My test run is a slight downhill of gravel road leading to singletrack. Its total length is about 500 meters.

First, inflate your tires to a few psi over the manufacturer’s maximum recommended tire pressure. Mark your course. Ride your bike a bit to get the tires warmed up before your first run. Then bleed the tire pressure down to the manufacturer’s maximum recommended tire pressure with your gauge’s bleed feature. Take a run, record your time, and record the tire pressure you started with.

Second, repeat while lowering psi. From this point forward, your goal will be to take identical runs. Focus on laying your tracks down on top of your last run so that your line is the same, and maintain an identical body position. Wind will have an influence on results, so a light-wind day is ideal.

As per Vorm Walde, Specialized bleeds down in 0.2 bar (approximately 3 psi) increments for 2.1- and 2.3-inch tires.

Record your times for each run while gradually lowering tire pressure. Note that in your first few runs, especially if you are lighter weight, you will likely not see any time differences. Keep doing what you’re doing — you’ll hit a tipping point where your tires don’t bounce you and your bike, instead becoming more compliant and forming to the ground.

At that point, your times will drop. Continue making runs until a pattern has formed and your lowest time has been established. Congrats, you’ve found your sweet spot!"

 

[scott43]

Uhh..I don't really have a dog in the fight here..but I'm not sure the protocol they're proposing can be called scientific...

 

[martyg]

Uhh..I don't really have a dog in the fight here..but I'm not sure the protocol they're proposing can be called scientific...

In skiing and in cycling it is the best that we have - make a set of predictions based on historical data to narrow down your possible options, have athletes run a section of a course, record data by time, video, or other, and repeat until the most efficient combination of ski / wax / suspension tuning / tire selection / tire pressure is attained for a given set of conditions.

My range of variation, from 40 psi, to my ideal, is a 28% drop in time over a given distance (about 1.5 kilometer). That is a profound increase in efficiency.

 

[SpikeDog]

You, sir, win the internet today.

 

[cantunamunch]

@martyg do you have a quadlock on the bike? would you be willing to do another run of rollouts while running a NVH app on your phone?

 

[scott43]

And maybe apply some scientific rigour at the same time!

 

[cantunamunch]

And maybe apply some scientific rigour at the same time!

I guarantee that the most noticeable, most trackable factor in the NVH readout will be lug noise. I am quite interested in how it scales with tire pressure.

 

[martyg]

@martyg do you have a quadlock on the bike? would you be willing to do another run of rollouts while running a NVH app on your phone?

That would be cool. Are you thinking that it would measure some aspect of vertical travel on a higher psi tire? It would be interesting if that respective app gave a graph of each run. I could where a section that might be a bit sandy would have a totally different read that one with fist sized rocks.

Negative on both. My cell phone is working intermittently. In semi-retirement I ski, ride my bikes, hike, play with my dog, take on some industry projects... I actually think that I am going to be cell phoneless soon.