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Question about tires air pressure and trails...

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RebelPro

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Discussion starter · #1 ·
Hey everyone. Although I've been riding bicycle since I was a little kid, it wasn't until this past Sunday I rode a mountain bike went for a ride on an off-road trail for the first time. I must say I loved it and found it pretty challenging at times, but survived from falling (although I brought back home some bruises and scratches).

Anyway, here's my question. When I bought my bike, the guy at the store suggested if I was to hit the trails, to lower the tires air pressure to avoid slipping and falling. I didn't really asked him how much, so I did as he suggested but I think I probably went a little beyond the appropriate (based on how I'm used to see on regular bikes).

Anyway, is there a standard or reference I should follow? One, I don't want to make it easier to fall if the tires have too much air, and two I don't want to damage the tires if they don't have enough air.

While I live in Miami and we don't have mountains here, the people who have worked on the trails have done an awesome job with obstacles and I think they could be rough, at least for me that I'm new to this.

This is the bike, a 26" Specialized Hardrock
 
#2 ·
Lots of variables. Your weight, tire width, and rim width are among the most important.

Easy answer: Start with 40psi. Lower it 2 psi per week until you get a pinch flat or the rear tire feels squirmy. Raise in 2 psi increments until you no longer get pinch flats or the rear tire no longer feels squirmy :~)
 
#3 ·
No standard. jeffj pretty much nailed the "easy" answer.

On my skinny mtb (26x2.2-2.4), I tend to use about 22-23psi, tubeless, with tubeless ready tires that have stiff sidewalls.

On my fatbike (26x4.0), I will run 2-9psi depending on conditions (2 psi, for example, in deep snow with higher pressure the faster I'm riding and the firmer the trails).

On my commuter (700x38), I run about 60-65psi for pavement, and maybe go as low as 35-40 if I'm riding rough gravel, or postholed ice on the rail trail.
 
#5 ·
There is the talc or baby powder trick as well if you'll be running tubes. You can let the air out and and throw some baby powder in there. Seal it back up, give it a good spin to distribute and inflate. This will allow you to run lower air pressure while reducing your chances at getting pinch flats.
 
#6 ·
^^ never heard of that trick.

Every ride I run a different tire pressure. Depending on the trail, trail conditions, tires, what I have in my pack, etc. I'm running Hans Dampfs this year on my chameleon. 26" tubeless.


Sent from my iPhone using Tapatalk
 
#9 ·
The trick is to find what suits you, too low and you lose control / get pinch punctures / tyres come off the rims, too high again you can get less grip / more punctures / shaken around a lot. I run mine at about 40psi purely as it suits my riding.
 
#10 ·
Tire pressure is a lot of trial and error and varies with rim width, the tire sidewall (esp. tpi), tire width, tire volume, trial, rider weight and personal feel. You can also run lower pressure in the front than the back. Generally, the wider the rim, stiffer the sidewall, wider the tire, the lower the pressure can run. Tubeless allow lower pressures than with tubes. A lot depends too on how the particular tire plays with the rim. With tubes for 26" I'd start with 30 psi. Your Hardrock probably has 2.0 tires with a low tpi sidewall. That makes it sensitive to too low a pressure where it's prone to pinch flats and rolls. Start at 30 psi and ride. Air down the front a few psi and ride again. Repeat the process until you're happy with your set up generally. Your front tire is your control tire. You can run lower pressure in the front because more of your weight is on the back. The lower pressure allows more traction and control. Run about 5 psi less in the front. You can then start messing with it based on the trail conditions, but with tubes on a 26 x 2.0 tire a few psi more or less is not making a noticeable difference. Remember also that this all goes out the window if your tire pressure gauge is analog with +/- 5 psi margin since you'll be giving a good guess as to the pressure rather than spot-on pressure. Also use the squeeze test - if it feels too squishy it probably is. Make sure to ride with a mini-pump and spare tube, whatever pressures you're running. Have fun with the new bike.
 
#13 ·
Shayne said:
Tires and tubes do get melted together...FACT
Click to expand...
Very true but mine always get changed long before that happens. I agree that using a little talc is technically optimal but in practical terms I've found it seems to make little difference. It definitely wouldn't allow me to run lower pressure or prevent pinches, talk can't stop a rim strike.
 
#15 ·
J.B. Weld said:
And so far my experience with tubeless has shown me that the ideal air pressure is pretty much exactly the same whether using tubes or running tubeless, a rim strike is a rim strike.
Click to expand...
I've found the tire casing plays a bigger role with pressure than whether there's a tube or not. I'll agree, though, that with the same tire, I run the same pressure no matter if there's a tube. It feels a bit more supple when the casing flexes with a tubeless setup, but to avoid rim strikes, the same pressure does the job.
 
#18 ·
Shayne said:
Tires and tubes do get melted together...FACT
Tubes do move inside tires...FACT
Mr Brandt must not actually ride any of the wheels he knows how to build :rolleyes:
Click to expand...
Melting is a bit strong, don't you think? Sure, they stick a little if they've been in there a while but it's not like they fuse and can't be pulled apart. And as for the movement issue, if the surfaces are tacky that should help to minimize/eliminate that until you get to the point where the pressure is so low that you're likely to pinch flat anyway. So really, no benefit. I'd take Mr Brandt's and Sheldon Brown's advice over yours any day at this point.
 
#20 ·
andytiedye said:
Wouldn't the weight of the rider be a significant factor?
Click to expand...
That's a good question.

Back when I was riding 26" tires, it made much more of a difference to me than it does now with 29" tires.

With 26" tires, I had to run anywhere from 43psi (with 2.5" tires) to 52psi with 2.0" tires (with me being at least 250+lbs) to keep from pinch flatting.

Now, with 29" tires and running tubeless, I prefer tire pressures around 27-30psi no matter what the tire, and I have tried quite a few. I can get by with pressures down slightly below 25psi, but things get too 'squirmy' for me down there.
 
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RebelPro
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