Tokwan

Hi Ya Folks,
I have been searching for a thread on off road riding tire pressure but couldn't find any (or I haven't searched hard enuff)..so I decided to throw in a question here.

Is there any way for one to calculate the correct/ideal/recommended tire pressure when you ride a mountain bike?

Information that you might need to help me.

Weight: 180lbs
Tire size: 27.5" X 2.10 (tube)
Full suspension Haro
Terrain for ride: Hard Pack Dirt (trail) with a bit of road (to get to the trail)

I have been riding all these while with about 51psi on both my front and rear. But I was alarmed when I aw on the internet, people riding with pressures as low as 18 rear and 16 front.

Withe the information I have given I hope someone could help me.

Any advises?

bobwysiwyg

Your 51# sounds far more reasonable to me.

Trevtassie

Yep, way too hard. I'd be running them at 30psi or so as a compromise between the road section and the trail. 25psi would be better for the trail section. They must be really sketchy off road ATM, well, you'll notice how sketchy they were in comparison after you try lower pressures. 18 and 16 are a bit low, you might run that low if you were running tubeless and climbing on rough stuff.

catgita

As soft as you can without pinch flatting. In the dirt especially, too hard only slows you down.
With tubes about 35#, maybe 40# rear.
Tubeless 25#.
If you feel your rims bottoming out or the tire trying to roll in hard corners, add a little.

Tokwan

I lowered my air pressure today and found riding is better. Is there any table or calculations on tire size, rider's weight rather than trial and errors? My Haro uses Presta, and i don't have a presta air pressure gauge at the moment...I only have for them schraeder valves....wont work with an adaptor.

FBinNY 

Thanks for that. Are you SURE it's not 50 or 52psi?.

No offense intended, sometimes I just can't resist.

-------------------------------

Anyway, instead of looking for a number, think about the effects of over or under inflating. So be like Goldilocks and experiment.

If the pressure is too high, you fine the bike bounces too hard on bumps like roots or exposed rocks. I describe this as like riding on basketballs. You'll also tend to ping stones out to the side at major league pitch speeds.

If pressure is too low, the bike won't bounce, but you might feel the rim bottoming, or get pinch flats (snakebites) when hitting sharp bumps. The tire can also feel sloppier when cornering, making the steering feel odd.

You might intentionally experiment near the extremes in both directions, so you feel the maximum effect, then go back to the middle, and see if it's feeling high, low or just right.

FWIW - I run tubulars on my road bike at pressures near 100psi. I also never let dirt roads deter me. Partly out of laziness, and partly to avoid possible damage from underinflation, I ride dire, even pretty rough dirt at full road pressure. Yes, it's harsh, but I've adapted to it, and have no control issues. I do however watch my speed on descents.

Trevtassie

Not for off road, because what works on one surface won't work on another. So yeah, trial and error and experience.

Tokwan

heheh,..I do have a Boulder Pump with Gauge...

thanks for the detailed reply...

I checked the tire and it shows on the side walls, 35 to 65 psi. Now, does that mean that the tire should be with a minimum pressure of 35 psi?

JonathanGennick 

Trial and error. Depends on weight and terrain and how hard you hit stuff, and whether running tubeless.

At your weight, I'd say that around 30 psi is a good starting point. Go from there, and go lower if you can. Try 30 psi. See what you think. Try 20 psi. See what you think of that. Adjust to your taste.

FWIW, those super-low pressures that you read about, those are going to be from people running tubeless setups. Without tubes, there is no risk of pinch flatting, and lower pressures become feasible. Though with some tires, I feel that too low leads to a squirmy feeling, especially in the corners.

Tokwan

Thanks! I see a lot of solid feedback coming from the members here. I now understand. To sum up,
it depends whether you're running with inner tubes or not. It also depends on what kind or riding you do, and the terrain you are riding.
It also mainly depends on your preference.

Trevtassie

Yeppo, but you'll pretty soon prefer not to run high pressures off road

gsa103

The sub-20psi crowd is also on 2.35in tires, so they have more volume.
Somewhere around 30-40psi is probably about right.

LesterOfPuppets

I'd probably go about 35 rear, 32 front.

At 155 lbs I like 32 rear, 30 front.

Tokwan

Thanks, appreciate all the feedbacks.

Kapusta

If there are such tables, they are worthless.

Like someone above said, best pressure for mtb is as low as you can go without pinch flatting. One caveat to this is that if you are able to go REALLY low, you may experience some "squirm" in hard turns (more often an issue the front). This advice does not apply to fat bikes and I am not so sure about "plus size" bikes, but neither of these situations applies to you.

As a ballpark conservative guess for your weight (which is close to mine) and 2.1" tires, I would start around 30f, 35r.

Go for a ride or two, if you don't pinch flat on the roughest stuff you typically hit, drop the pressure 2psi in each tire and repeat the process until you get a pinch flat, then bump the tire up 2 or 3 psi.

If you manage to go really low, you may find that the front tire feels like it is squirming (rolling over) in hard turns. In that case that will be the low pressure limit for you and that tire. However, with a 2.1" tire it is unlikely you will be able to go low enough for this to be an issue.

Does this sound like a big PITA? Well, it kind of is, but getting the optimum tire pressure is the single most important thing you can do for the performance of your bike. It makes an enormous difference.

The reason tables or other peoples recs are not useful is that the pressure at which tires pinch flat vary GREATLY with the following factors:

-Tire volume
-Tire sidewall construction
-Terrain (sharp edges are hell)
-how fast you ride on that terrain
-how "smooth" a rider are you?
-how aggressive a rider are you?
-Rider weight
-Rider weight distribution on the bike.

Buy a pressure gauge, it is one of the most important bike tools to own.

Tokwan

This is really good help. Its like a step by step instruction or manual...for an old geezer like me, I would be able to follow these instructions...Thank you Sir!
P.S: You oughta start writing a manual on something...easy to understand.

dirthurts

I ride 35 in both the front and the back. If I feel like I need more traction in the mud, I might drop them just a bit. Or, if I'm on gravel or want to go faster, I might add a little.
It's all preference as long as you're not going to any extremes. Don't be afraid to experiment and adjust on the fly to fit your mood/needs.

Tokwan

Found that where I tried, style of riding, it works best (tentatively, until I explore ,more options), front 36, rear 38 psi.
A wee bit faster, easier rolling!

Gallo

when running tubeless you can run lower pressures different tires will need different pressures a through trial and error this calculator is pretty good MTB tech

I think your pressure is a bit high I am 190 and run 28-32 rear 23-25 front depending on tire

I want as low as possible for both comfort and control

lower pressure on uneven surfaces is faster more tire on the trail less bouncing

on the trail I will add if I feel it is too soft but never release pressure

John9

I would lower your pressure for sure. Im 185 and ride a 29er hardtail with 30-32 psi depending on conditions. With the hardtail especially i like to go a little lower if I can to avoid all the bouncing (just like the post above said). Check what your tires say is the lowest recommended psi and go from there, just don't go so low that you get a pinch.

Tokwan

Okay, well I run tubed, with a full suspension. The lowest recommended pressure is 35psi. I ride on Maxxis Crossmark 35 psi -65psi Sized 2.10 X 27.5(650b)

Tokwan

I tried using the calculator, but it won't let go to 2.0 to 2.2.

Tokwan

Found this:

rumrunn6

depends, judge it by the seat of your pants

rasheed

Wow, 51 psi is quite high--good for riding on the road, but on the trail, you're better off running lower pressures. Generally, you shouldn't need more than about 30-35 psi rear, equal or a bit less up front. I'd suggest starting out with 30 psi rear, 25 psi front and see how that feels. You should find that you get better traction at those pressures. It'll also smooth out the ride a tad (i.e., it won't be as harsh). From there you can tinker a bit adding or taking away a bit to fine tune.