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Going Below Recommended PSI

Old 05-11-23, 07:47 PM
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Noonievut
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Going Below Recommended PSI

Anyone routinely go below the low PSI rating on the tires?

I have Teravail Sparwood 2.2 on my Salsa Fargo and PSI range is 30-50. I run then them with tubes and never go above 30. I donít notice anything negative and have been on all sorts of terrain. Iím only 150 pounds and ride unweighted over rough stuff.
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Old 05-11-23, 08:15 PM
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My front tires are routinely pumped to less than their "minimum" pressure.
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Old 05-14-23, 04:40 PM
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I noticed with my Rene Herse tires, if I under-inflated them, I would get black cross-hatch marks on the side-walls, visible mostly on the inside of the tire. Apparently the tires are so supple they essentially have zero sidewall support, apart from air, so you actually have to keep them pumped up a bit more than you might a similar-sized semi-rigid tire.
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Old 05-14-23, 05:00 PM
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Tire pressure is a function of the volume of the tire AND the weight of the rider.

130 lb rider on 25mm tire at 85 PSI, 185 rider needs 100 PSI, and 240 lb rider needs 115 PSI
130 lb rider on 2" tire needs 35 PSI, 185 lb rider needs 55 PSI, and 240 lb rider needs 70 PSI
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Old 05-14-23, 05:01 PM
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Originally Posted by Polaris OBark
I noticed with my Rene Herse tires, if I under-inflated them, I would get black cross-hatch marks on the side-walls, visible mostly on the inside of the tire. Apparently the tires are so supple they essentially have zero sidewall support, apart from air, so you actually have to keep them pumped up a bit more than you might a similar-sized semi-rigid tire.
That might be a good reason to stay at least close to the minimum recommended pressure on the tire, or the pressure indicated from one of those on line calculators based on the 15% drop principle, whichever is higher. My 1.9" semi ridged tires say 40 - 65 psi. So lm thinking 40 for the front, 48 for the back. The tire pressure charts show way less then that with my weight.

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Old 05-14-23, 08:45 PM
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The minimum tire pressure recommendation is to ensure the tube does not migrate in relation to the tire while in service.

If I had a dollar for every valve stem that came in pointed at a 45 degrees out of the valve hole or was ripped out of the tube...Well, I don't know. I'd probably have enough dollars to buy a cheezeburger or something.

Thinking out loud: It really probably only makes a real world difference on the rear tire since the cyclical torque of driving the bike would cause the tube/tire migration. The front would still be affected, of course, because the the tube and tire travels on different radiuses from the wheel axle and there must be enough pressure to keep them pressed together. My guess, at least on the front is theory holds but the effect is a negligible degree compared to the rear that has additional cyclical scrubbing forces.
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Old 05-16-23, 10:38 PM
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Originally Posted by Noonievut
Anyone routinely go below the low PSI rating on the tires?

I have Teravail Sparwood 2.2 on my Salsa Fargo and PSI range is 30-50. I run then them with tubes and never go above 30. I donít notice anything negative and have been on all sorts of terrain. Iím only 150 pounds and ride unweighted over rough stuff.
I put Sparwood 2.1s on my Gorilla Monsoon at soon had them at 25 psi with tubes. So far so good but Ive only got about 6 hours riding on them. Im 150# too and have hit some rough singletrack.
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Old 05-17-23, 06:44 AM
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Originally Posted by dgodave
I put Sparwood 2.1s on my Gorilla Monsoon at soon had them at 25 psi with tubes. So far so good but Ive only got about 6 hours riding on them. Im 150# too and have hit some rough singletrack.
do you like pinch flats ? bent rims ?
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Old 05-17-23, 10:24 AM
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Originally Posted by t2p
do you like pinch flats ? bent rims ?
I'm not talking about the worst Moab style mtb trails. Just your normal rocks and roots on kind of techy trails. 25 psi is plenty to keep me out of trouble.
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Old 05-17-23, 02:34 PM
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I suppose it was inevitable. The race to the bottom of the psi parameter that has been going on for some time was bound to hit a soft limit when it reached the posted min psi of mainstream tires. Pinch flats are not what should concern the rider flirting with ultra low tire pressures. Depending on the tire bead strength and rim construction interaction, a front tire can actually come off the rim during hard cornering. Wouldn't that be fun? 25psi isn't likely to be dangerous in a 50mm tire but something in the 40's (mm)? mid-high 30's?. Deadly. And y'all's will get there. I have every confidence. Today's 25 (psi) is tomorrows 20. <shudder>

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Old 06-14-23, 03:27 AM
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Maybe the road will be slower
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Old 06-14-23, 11:00 PM
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2.2 is mtn bike size width and we run tire below 30psi as the norm. At 150lb your fine. I'm 170lbs running 2.3s in the rear at 27psi tubeless and slam off rocks roots all day. I've pinch flated a rear once on my hardtail when I slammed into a very pointy ledge of a rock at speed on my hardtail.
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Old 06-15-23, 11:21 AM
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Others have noted, but with tubes the main risk of going too low is pinch flatting. Beyond that, there is a potential of damaging the rims if you are bottoming out on hard surfaces/rocks/roots.
With tubeless the main risk is burping the tire - where the bead actually pulls off the rim and some air escapes. You can pinch flat a tubeless tire as well, but it's less of a risk than with tubes.

30psi on 2.2 MTB tires for a 150lb rider does not seem extreme to me. I'm 165lbs and frequently run 33mm CX tires at less than 30psi.
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Old 06-15-23, 11:37 AM
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Originally Posted by Polaris OBark
I noticed with my Rene Herse tires, if I under-inflated them, I would get black cross-hatch marks on the side-walls, visible mostly on the inside of the tire. Apparently the tires are so supple they essentially have zero sidewall support, apart from air, so you actually have to keep them pumped up a bit more than you might a similar-sized semi-rigid tire.
Cross hatching on the sidewalls of higher end/handmade tires is normal. It's a sign of wear, but nothing to be alarmed about. It's more visible on tanwall/gumwall tires.

Buying a supple tire and then running it at higher psi to avoid sidewall wear defeats the purpose. The whole point of tires like RH is that they have very soft/supple sidewalls, so run them low and let 'em flex! You probably aren't extending the life of the tire much by running them at higher pressure.
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Old 06-15-23, 01:16 PM
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Originally Posted by msu2001la
Cross hatching on the sidewalls of higher end/handmade tires is normal. It's a sign of wear, but nothing to be alarmed about. It's more visible on tanwall/gumwall tires.​​
This:


vs this:



​​​​​Buying a supple tire and then running it at higher psi to avoid sidewall wear defeats the purpose. The whole point of tires like RH is that they have very soft/supple sidewalls, so run them low and let 'em flex! You probably aren't extending the life of the tire much by running them at higher pressure.
These are relative terms. By "higher" pressure I am still in the recommended pressure range from the RH tire pressure calculator (about 44 to 48 psi for Barlow Pass, rider + bike = 210 lb). Before that, I was well below the recommended pressure (probably 25 to 30 psi).
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