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Tire Pressure

Old 07-12-15, 03:27 PM
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Tire Pressure

I just got a new 29" mountain bike yesterday. I was looking at the side of the tires for the required pressure. It says 35 psi recommended, 60 psi max. Is there a benefit to putting more than the recommended psi in the tires for the trails?
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Old 07-12-15, 09:00 PM
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Originally Posted by milesofsmiles
I just got a new 29" mountain bike yesterday. I was looking at the side of the tires for the required pressure. It says 35 psi recommended, 60 psi max. Is there a benefit to putting more than the recommended psi in the tires for the trails?
Stay toward the low end of the range, imho. Your lower back will thank you.
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Old 07-13-15, 05:34 AM
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My tires say 40-60 psi. I run them at 22 psi front and 28 psi rear. Lower pressure means better traction (though at some point probably also more rolling resistance, and more flats). You'll have to find the pressure that best suits your terrain, body weight, and riding style though.

Last edited by turky lurkey; 07-13-15 at 05:43 AM.
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Old 07-13-15, 08:50 AM
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25-30 here.
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Old 07-13-15, 11:38 AM
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18-28 here. Running 29'' tubeless
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Old 07-13-15, 04:15 PM
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The safe low pressure formula that's generally a safe starting point for a hard tail with a rookie pilot who has yet learned to ride light is as follows:

In full gear rider weight divided by seven = X
Front tire PSI is X-1 psi
Rear Tire PSI Is X+2 psi..

For me using this formula I would run 25.5 psi front and 28.5 psi rear.

27.5 X 2.35 out front and a 2.25 on the back.
Tubed,
My ride weight with full camelbak is 185 pounds.
My full suspension bike is 28 pounds
Now running 25 psi rear and 24 front, so far no snake bites...

Lower tire pressure allows the tire to deform over bumps as opposed to bouncing over/off things.
Bouncing off things burns more energy Increasing rolling resistance

That's one of the reasons tubeless is even better for traction and less rolling resistance.
Tubeless allows even lower pressures with no snake bites, (Tube sidewall pinches) and this means more traction to a point!

Too low and you get tire squirm. Or tubeless the dreaded 'Burp', that's the tire/rim letting air out.
I have run 22 front and 23 rear and felt squirm out front.
Here is where wider rims come in to play,,,

and on It goes,

To find out how far down the rabbit hole the Holy Grail of the perfect bike set up Is often takes a fat wallet
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Old 07-13-15, 05:22 PM
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Thanks for the help.
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Old 07-14-15, 02:12 PM
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About 9 years ago I bought a Specialized FSR XC in my second season on an MTB. I figured if I put more pressure in the tires I'd go faster so I pumped them up to 65PSI. Yes the bike was faster, and I crashed hard, five times in one hour.
So much for that brilliant idea.
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Old 07-17-15, 07:20 PM
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35-40 in the front 40-45 in the rear. 26 inch easton UST/schwalbe RR on an hardtail trail/xc rig
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Old 07-17-15, 07:36 PM
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I mainly commute on mine, but I'm a fair beggar for not checking tyre pressure regularly. So I err on the side of caution and top them up to 60psi, with the view that if they slowly lose pressure, I've got plenty of leeway before it gets to the minimum.
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Old 07-18-15, 12:39 PM
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Before I started riding today I checked the pressure in both tires. The front was 22 psi and the rear was 30 psi. I will work from there and adjust the pressure on each to see what works. I only just had gotten started riding today, 4.5 miles on flat smooth paved ground, when the chain broke. My fault, shift while not pedaling then trying to go up hill, the chain couldn't handle the strain. So I'll have to continue tomorrow on the rougher terrain.
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Old 07-18-15, 02:09 PM
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to add further confusion:

i was running ~10psi in my 3" knards since i got my ecr a couple months ago, i thought it was ideal.

till i got 2 slow leaks from thorns and i didnt bring any patches or anything (i was on a trail down the block). as the tires started losing air i noticed my overall speed, traction and ride quality go up tenfold.

since then i run them probably about 5-7psi, i cant imagine running any higher psi now

as others have mentioned, less is more.
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Old 07-18-15, 04:16 PM
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Yeah, less is more until you hit that big root or rock or go over a drop or jump and then: pinch flat! Mid twenties at least if you're riding in the mountains, and thirty plus is safer. But I know guys who put up with the odd flat just to get the extra grip.
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Old 07-18-15, 05:43 PM
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I went back out this afternoon, couldn't sit home and wait for the storm that never came. I road on actual mountain bike trails. Now I have raised the pressure up to 35 psi in each tire to see the difference.
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Old 07-18-15, 07:28 PM
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Lower PSI will give you more traction. I lower the PSI in my tires when on a muddy trail or what not... Increasing the PSI will reduce rolling resistance, making you travel faster with less effort.
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Old 07-18-15, 08:13 PM
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Originally Posted by ParkingTheBus
Lower PSI will give you more traction. I lower the PSI in my tires when on a muddy trail or what not... Increasing the PSI will reduce rolling resistance, making you travel faster with less effort.
Maybe on the track, and on very smooth pavement, but that is generally not the case off-road.

Google "Schwalbe tire pressure study", "tire hysteresis", etc.
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Old 07-19-15, 11:31 AM
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Originally Posted by Duke of Kent
Maybe on the track, and on very smooth pavement, but that is generally not the case off-road.

Google "Schwalbe tire pressure study", "tire hysteresis", etc.
I did 80 km on my mountain bike with the max PSI. It was pretty smooth, but it was on solid gravel so it was easy.

Would you recommend decreasing the psi even on trails littered with roots, branches and wood?
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Old 07-19-15, 11:36 AM
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for best traction low pressure is better, for better rolling resistance more pressure is better, depends on what you are doing. Back riding and racing dirt motorcycles we used to run around 12psi, but dirt motorcycles had bead locks so you couldn't spin the tire on the rim and ruin the tube. Not sure why there are no bead lock options for mountain bikes.

I don't run tubeless tires so I keep the pressure up so I don't ruin a tube, but I also bought a full suspension bike so the ride and traction is pretty good even with higher tire pressure.
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Old 07-19-15, 11:43 AM
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Originally Posted by ParkingTheBus
I did 80 km on my mountain bike with the max PSI. It was pretty smooth, but it was on solid gravel so it was easy.

Would you recommend decreasing the psi even on trails littered with roots, branches and wood?
Yes. Like many of the people here, I run <30psi off road. Rocky, rooty singletrack of western VA and NC.
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Old 07-19-15, 11:45 AM
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Originally Posted by hig4s
for best traction low pressure is better, for better rolling resistance more pressure is better, depends on what you are doing. Back riding and racing dirt motorcycles we used to run around 12psi, but dirt motorcycles had bead locks so you couldn't spin the tire on the rim and ruin the tube. Not sure why there are no bead lock options for mountain bikes.

I don't run tubeless tires so I keep the pressure up so I don't ruin a tube, but I also bought a full suspension bike so the ride and traction is pretty good even with higher tire pressure.
Because you don't have a 50hp engine providing massive torque to the rear wheel. You also don't have a bike that weighs more than the rider.

You have a ~1/2hp engine, if that. I've never heard of anyone slipping a tire on a mountain bike, but even if it did happen, I don't know anyone that runs tubes, so we'd likely never know.

And, as previously stated, no, higher pressure is NOT going to result in decreased rolling resistance on a typical mountain bike trail.

https://www.schwalbetires.com/wider_faster_page
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Old 07-19-15, 12:05 PM
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Originally Posted by Duke of Kent
Because you don't have a 50hp engine providing massive torque to the rear wheel. You also don't have a bike that weighs more than the rider.

You have a ~1/2hp engine, if that. I've never heard of anyone slipping a tire on a mountain bike, but even if it did happen, I don't know anyone that runs tubes, so we'd likely never know.

And, as previously stated, no, higher pressure is NOT going to result in decreased rolling resistance on a typical mountain bike trail.

Wider is faster! | Schwalbe North America

Actually people running under 30psi on hard climbs, spinning tires and ruining the stem on a tube is not uncommon, that is why they have tubeless mountain bike tires, so you can safely run lower pressures. At least that is what the mountain bike guy at the local Specialized dealer told me.

I assume you mean you will not be able to notice the difference in rolling resistance on the typical trail, technically the rolling resistance is still reduced at higher pressures.

I mentioned the less rolling resistance because it is noticeable on pavement and I often go from the trail to riding around the local park on pavement.

Last edited by hig4s; 07-19-15 at 12:10 PM.
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Old 07-19-15, 12:19 PM
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Originally Posted by hig4s
Actually people running under 30psi on hard climbs, spinning tires and ruining the stem on a tube is not uncommon, that is why they have tubeless mountain bike tires, so you can safely run lower pressures. At least that is what the mountain bike guy at the local Specialized dealer told me.

I assume you mean you will not be able to notice the difference in rolling resistance on the typical trail, technically the rolling resistance is still reduced at higher pressures.

I mentioned the less rolling resistance because it is noticeable on pavement and I often go from the trail to riding around the local park on pavement.
Did you actually read what I wrote? I just said I don't know anyone that uses tubes. Literally. Every single person I know that rides MTBs is on tubeless tires.

And, did you actually open up the link and read the results of the study? Rolling resistance was found to be lowest at "lower" pressures; this will vary based on tread, casing size/shape/material, rim width, etc., but generally speaking, yes, lower pressures ARE faster than "high" pressures.

"The avid, German League road racer wanted to determine the best tire width and air pressure combination for fastest performance. He completed 300 test-rides with SRM cranks to establish the exact energy consumption for his thesis "Road Rolling Resistance". He tried three different tire types in three widths at 20 psi, 30 psi, 45 psi and 55 psi on road, dirt track and cross-country The results were clear.

Higher pressure was only faster on the road. Off-road rolling resistance was lower, the wider the tire and the lower the pressure. This was similarly true for dirt tracks, soft forest roads or cross-country and up to 40 Watts could be saved in extreme off-road conditions; poor acceleration caused by higher tire weight being generally compensated for. Explanation: A tire at low inflation pressure adapts better to uneven surfaces. It sinks into the ground less. Overall it suffers less ***********."
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Old 07-19-15, 02:22 PM
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To quote myself...
Now I have raised the pressure up to 35 psi in each tire to see the difference.
That was the pressure my bike pump gauge said so I checked it with my car tire gauge and it said 45 psi rear, 42 psi front. So after riding today I stopped at the store to get a gauge that I am just going to use for the bike.

I road the same paved park trails today that I road yesterday before I broke my chain with the higher pressure, definitely bouncier. Then I went to the unpaved park trails, it road really good trough the wood chips and mud, I'm liking these big 29" tires. Then I went to the park where the real mtb trails are, waaaaay too bouncy. I kept loosing traction, mainly uphill, when I hit roots and rocks. So when I got home I lowered the pressure to 30 psi in each tire.

Which brings me to the question about traction v bounce in the front and rear. Is it ok to have more bounce in the front and concentrate on the traction in the back or should it be some what equal? It kind of seems like you would want to bounce the front over obstacles (without sacrificing steering control of course) and maintain traction in the rear to keep your momentum. But this is my beginner's point of view.
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Old 07-19-15, 02:35 PM
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Originally Posted by milesofsmiles
Which brings me to the question about traction v bounce in the front and rear. Is it ok to have more bounce in the front and concentrate on the traction in the back or should it be some what equal? It kind of seems like you would want to bounce the front over obstacles (without sacrificing steering control of course) and maintain traction in the rear to keep your momentum. But this is my beginner's point of view.
Hey, it's a theory. Go for it! That's what makes the whole thing fun.
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Old 07-19-15, 03:34 PM
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Originally Posted by milesofsmiles
To quote myself...

That was the pressure my bike pump gauge said so I checked it with my car tire gauge and it said 45 psi rear, 42 psi front. So after riding today I stopped at the store to get a gauge that I am just going to use for the bike.

I road the same paved park trails today that I road yesterday before I broke my chain with the higher pressure, definitely bouncier. Then I went to the unpaved park trails, it road really good trough the wood chips and mud, I'm liking these big 29" tires. Then I went to the park where the real mtb trails are, waaaaay too bouncy. I kept loosing traction, mainly uphill, when I hit roots and rocks. So when I got home I lowered the pressure to 30 psi in each tire.

Which brings me to the question about traction v bounce in the front and rear. Is it ok to have more bounce in the front and concentrate on the traction in the back or should it be some what equal? It kind of seems like you would want to bounce the front over obstacles (without sacrificing steering control of course) and maintain traction in the rear to keep your momentum. But this is my beginner's point of view.
If you're EVER bouncing, you aren't in contact with the ground, and unless you are intentionally jumping the bike (jump, drop, whatever), that means that you are NOT in control. Loss of control = loss of speed.
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