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PSI beginner question

Old 05-28-15, 07:42 AM
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bennybenny
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PSI beginner question

Hello,

As riding the trails before work is typically not possible, I'm trying to log on some good base miles on a concrete trail really close to my work.

My question: do I pump up the tires PSI to 'normal' or full levels for such riding? And if I hit a trail lower the PSI?

I just noticed that today on the concrete trail that my tires were a tad low on air.

Thanks for any advice.

Benny
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Old 05-28-15, 08:58 AM
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Originally Posted by bennybenny View Post
My question: do I pump up the tires PSI to 'normal' or full levels for such riding? And if I hit a trail lower the PSI?
You could do that, sure. I generally just leave my pressures the same.

What you might do is look for a compromise tread. I run some sort of Bontrager-brand micro-knobby tire on a bike that I tend to ride on pavement more than on trail. The smaller knobs roll reasonably on pavement, and I get some, not a lot, but some, value from them on dirt.

Now that I think on it, I'm not sure that I'd notice the benefits of added pressure without first getting rid of the big knobs.
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Old 05-28-15, 09:20 AM
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You can just leave the pressure the same. I have smaller knobs tires on my old bike which is what I been using on paved so it rolls better.
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Old 05-28-15, 12:33 PM
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how much do you weigh, and what size are your tires? we can suggest a reasonable range of air pressures for trail riding.
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Old 05-28-15, 12:53 PM
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If you want to go fast, you can pump up the pressure to the max on concrete, just don't forget to lower the pressure when you hit single track. You can also ride at max pressure on a smooth gravel trails like some rails to trails, I do. Lower tire pressure is good for shock absorption so if you hit some real bumpy trails, you want to be at the lower end of the allowed range. When I was a new rider, I tried riding a technical, single track trail at 70 PSI to increase my speed. I'm not sure if I increased my speed, but I did increase the number of times I was thrown from the bike after hitting an obstacle. As I recall I crashed five times in 45 minutes. I don't recommend it.
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Old 05-28-15, 05:05 PM
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Optimum tire pressure is a function of tire size, rider weight and terrain. For technical trails, you generally want lower pressure. For smooth trails, add ~5-10 psi (for standard MTB tires) over your standard trail pressure. Adding more than that just gives a harsh ride without changing the rolling resistance.

High pressure for low rolling resistance is a myth, it only works for track riders on perfect surfaces. For the rest of us, a modest pressure will have good comfort and good rolling resistance. The road racing community is moving to 25mm tires at 70psi, as a good optimum for rolling resistance. If you're on 2+" tires, chances are your optimum pressure is closer to 30-35 psi for road riding.

Micro-knobby tires are also a good compromise. They wear better and do well on most hard surfaces.
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Old 05-29-15, 12:50 PM
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Originally Posted by gsa103 View Post
Optimum tire pressure is a function of tire size, rider weight and terrain. For technical trails, you generally want lower pressure. For smooth trails, add ~5-10 psi (for standard MTB tires) over your standard trail pressure. Adding more than that just gives a harsh ride without changing the rolling resistance.

High pressure for low rolling resistance is a myth, it only works for track riders on perfect surfaces. For the rest of us, a modest pressure will have good comfort and good rolling resistance. The road racing community is moving to 25mm tires at 70psi, as a good optimum for rolling resistance. If you're on 2+" tires, chances are your optimum pressure is closer to 30-35 psi for road riding.

Micro-knobby tires are also a good compromise. They wear better and do well on most hard surfaces.
Completely agree. File tread with micro-knobs is great as well.
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Old 05-29-15, 01:34 PM
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Unless you are riding a LOOONG way on the concrete you probably won't notice much difference either way.
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Old 05-29-15, 01:45 PM
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Originally Posted by bennybenny View Post
Hello, do I pump up the tires PSI to 'normal' or full levels for such riding? And if I hit a trail lower the PSI?
yup
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Old 05-30-15, 01:13 PM
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I was always constantly experimenting with tire pressure, probably too much (a little bit OCD I used to run higher pressure for concrete or smooth fire roads/gravel, etc., and then I'd go as low as I possibly could for single track (which is all rocky and roots where I live). I eventually settled on tire pressure that seemed to be a good compromise for everything and just got on with it (though admittedly I rarely ride on anything paved--might be different if so). But I just put a bigger tire up front and now I'm back to mucking around with it, toying with the pressure looking for the sweet spot!

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Old 05-30-15, 05:42 PM
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Off road a good base line for mountain bike size tires, riding with tubes in, 29 x 2.25 or 27.5 x 2.25 or 2.35 tires

Take Rider IN GEAR weight, Hydration pack and all. divide that by 7 then add 2 PSI for the rear tire and take 1 psi out of the front tire...

I like and need my tire tread, the above pressures on concrete will wear my rubber out pretty fast.

Get a second bike...
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Old 06-01-15, 01:41 PM
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Originally Posted by osco53 View Post
Off road a good base line for mountain bike size tires, riding with tubes in, 29 x 2.25 or 27.5 x 2.25 or 2.35 tires

Take Rider IN GEAR weight, Hydration pack and all. divide that by 7 then add 2 PSI for the rear tire and take 1 psi out of the front tire...

I like and need my tire tread, the above pressures on concrete will wear my rubber out pretty fast.

Get a second bike...
Handy formula! That puts me right about where I ended up through constant fiddling and trial-and-error! I just went from a 2.25 to a 2.4 on the front, so I need to play around with that one a little bit--still feeling it out.
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