PSI for bumpy dirt roads

tt3876
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PSI for bumpy dirt roads

Postby tt3876 » Fri Jul 01, 2016 12:46 pm

I have this bike Image

Which came with Schwalbe Tyrago tyres with a minimum of 35 psi and max of 65 psi. I put it at 65psi today and it was too bumpy for my liking on dirt. I would reduce it to 50psi but I ride about 15-20km of pavement to get to the dirt roads and am worried it would drag on the pavement (some decent hills on the pavement). Do you think those lower pressures are will be alright for the paved roads?

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trailgumby
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Re: PSI for bumpy dirt roads

Postby trailgumby » Sat Jul 02, 2016 11:41 pm

It will be slightly slower on pavement, but faster and more comfortable on the dirt. Unless you're on a roadie group ride and need to keep up with your mates, I wouldn't sweat it.

A more comfortable ride, less spoke breakage, and more traction on loose surfaces helping to keep the rubber side down and my wrists from suffering stress fractures wins it for me every time.

I ride my 29er about 10-15km to get to the dirt, but always have the pressures set for the dirt. It's the point of the ride anyway, the rest is just a commute to where the real ride starts.

Edit: nice bike by the way :D

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Thoglette
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Re: PSI for bumpy dirt roads

Postby Thoglette » Sun Jul 03, 2016 1:13 pm

tt3876 wrote: I would reduce it to 50psi but I ride about 15-20km of pavement to get to the dirt roads and am worried it would drag on the pavement (some decent hills on the pavement). Do you think those lower pressures are will be alright for the paved roads?


They'll be fine. They may even be fast be faster. It's a complex equation and you've got to find your comfort point for your tyres and style: go too low and you'll get squirm in corners (fun on descents :shock: ) &/or pinch flats on pot holes.

Jan Heine has tested and written extensively about tyre pressures, most recently confirming that the rollers used in most tests are flawed
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trailgumby
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Re: PSI for bumpy dirt roads

Postby trailgumby » Sun Jul 03, 2016 9:17 pm

Thoglette wrote:It's a complex equation and you've got to find your comfort point for your tyres and style: go too low and you'll get squirm in corners (fun on descents :shock: ) &/or pinch flats on pot holes.


That's where a little trial and error come in. On the 29er I kept going down until I got said squirm, and then went back one step. The ideal point will vary between tyre brands and models, so the experiment should probably be repeated if you change.

It would be interesting to see the redoubtable Mr Heine apply his rigour to the the question of wheel size too.

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singlespeedscott
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Re: PSI for bumpy dirt roads

Postby singlespeedscott » Sun Jul 03, 2016 10:49 pm

I would be tossing the knobbies and finding a smooth 32mm tyres. I have found that knobby tyres are of no use on the dirt unless its muddy. Just get your pressures right and you'll have plenty of grip for fast high speed turns and descents.

I weigh 76kg and run my 32's at 70psi rear and 45 psi front on both the bitumen and dirt.
Image

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trailgumby
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Re: PSI for bumpy dirt roads

Postby trailgumby » Sun Jul 03, 2016 11:33 pm

That's fine if the road is swept clean, but if there's any kind of loose dust on top you will at least want shoulder knobs.

There is a reason the guys on MTBs tend to win dirt sportives. The crossers climb a little faster but lose a lot more than they gain on the turns and descents. A part of that is suspension, but a lot is down to tyres as well.

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silentbutdeadly
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Re: PSI for bumpy dirt roads

Postby silentbutdeadly » Mon Jul 04, 2016 3:59 pm

Annywhere between 35 and 50 with a little more in the back than in the front suits me - the actual choice depends on bike load and road/track conditions. Though I weigh 90 something kgs. The tyres will take 65 psi but unless you're always on the road (and what is the point of that?) then it's unneccesary.

My Niner RLT runs Challenge Gravel Grinder tyres in 700x38 (they measure at 35) and it eats long distances of unsealed road no worries. Stunning tyre - file tread in the middle, lugs on the outside. Due to the amount of sand, there's no way I would run a smooth 32 mm tyre on the tracks out past my way...
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