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YAPT - Low pressure question

Old 10-14-14, 07:45 AM
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DunderXIII
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YAPT - Low pressure question

YAPT = Yet another pressure thread.

This question is about low tire pressure. My question is, why are tires are always rated for too high pressure?

I'm a skinny guy, I weight between 145 - 150 lbs and I'm 5'11". I currently ride on 32mm tires; and so according to most formulas online I should ride between 55 to 65 PSI, on 32mm (!!). Personnaly, I tried 65 - 70 and its bliss. I did 80+kms with this pressure and it feels great (used to ride @ 90-110PSI).

The problem is, all 32mm tires I find are rated for 75 or above *MIN* pressure..! I have what I feel are pretty good tires (Specialized Borough Armadillo Elite) and don't really want to change them, but I feel that if I continue running them low I'll scrap them (I now run them at 75 PSI just in case)

Anyway, it seems that to get to 65 PSI I need to go 35mm..

Am I being unreasonable? Should I just harden the f*** up?
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Old 10-14-14, 07:51 AM
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I don't know why the minimum is so low on many tires. Personally, I've run tires below their minimums for similar reasons without any problems. Maybe the manufacturer is worried that the tire's bead will come off at lower pressures?
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Old 10-14-14, 08:51 AM
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Wait, There are minimums? I'm guessing the lawyers make them do that.

Tire pressure is super important to how I want and expect my bikes to perform. I run anywhere from 6-12 psi on my fat bike, to 35-50 on tubeless MTB, 45-70 on my CX bike, 70-85 on my commuter(summer), and 120 on my road bike. It depends entirely on the conditions and where I'll be riding and what I want the bike to do. I have no idea what the minimum PSI's are and I don't care. Just ride them how you like them.
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Old 10-14-14, 09:04 AM
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I've never seen a minimum PSI marked on a tire.

I ran my 32s at 80psi, and run my current 28s at 110psi. It can be a bit bouncy at times, but I was getting the occasionally pinch flat running the 28s at 80-90psi. I'm 145lbs, 5'10", with 10-20 pounds on the rear rack.
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Old 10-14-14, 09:34 AM
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I'd suppose minimums are to prevent pinch flats. I'd also guess they are conservatively high, just like the max is conservatively low.

I recently set up a trailer that my wife got me, and it came with cheap plastic rims and nylon tires. The sidewalls say INFLATE TO 35 PSI. Exactly! There's no room for error! The negative Amazon reviews of the trailer all have to do with the tires blowing off.
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Old 10-14-14, 09:37 AM
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the rim its attached to differs and is unknown by the tire manufacturer , so a range is offered .
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Old 10-14-14, 09:42 AM
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So basically, just lower the pressure until I'm satisfied; or until I get pinch flats.

Is it normal to feel really good @ 65 PSI? In terms of speed I didn't notice any change at all; I actually got my best average speed of the year on that setup.
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Old 10-14-14, 09:50 AM
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Manufacturer doesn't know how much you weigh and there isn't room on the sidewall to print a whole table.

I've never had a clincher bead come off due to pressure that was moderately low. It has happened when pressure is zero (blowout). I've felt tires get squirrelly like they want to roll off, but that's at severely low pressures, like 60 psi for a 23 mm road tire (under a 190 lb rider in a hard turn).
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Old 10-14-14, 11:24 AM
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I've been trying to get used to the feeling of low pressure in modern big soft MTB tires at 30+ psi. They feel really squirmy compared to a road tire at high pressure or even my older MTB tires at 40+.
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Old 10-14-14, 12:15 PM
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Originally Posted by DunderXIII View Post
So basically, just lower the pressure until I'm satisfied; or until I get pinch flats.
Yes.
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Old 10-14-14, 12:36 PM
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Originally Posted by Andy_K View Post
Yes.
+1. I run at or below the min for all of the front tires in my fleet (one could alternately say that I use wider tires than I "need" at my weight.) My suspicion is that minimum pressures aren't set by the engineers or lawyers, but by marketing/PR people who want it high enough to "feel fast."
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Old 10-14-14, 02:23 PM
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Originally Posted by Darth Lefty View Post
I'd suppose minimums are to prevent pinch flats.
Running a tire at pressure too low also cause the sidewall to flex more, which might result in premature wear.
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Old 10-14-14, 05:02 PM
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Originally Posted by spivonious View Post
I've never seen a minimum PSI marked on a tire.
Eh? What tires are you running? Most brand have a range on their sidewalls. I think the only ones I have that don't have minimums are my Vittoria Randos,which just have a max.
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Old 10-14-14, 05:20 PM
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Don't know for sure, but I suspect too low will wear the sidewalls out early. The instructions that came with my Conti 4000s tires say "maximum 120 psi, 20% lower is permitted". That's 96 psi. I run them 90-85 on my stiff aluminum bike. 95-90 on my Titanium light weight bike, and 120 on most of my steel road bikes.

The Panaracer pasella tour guards say "keep inflated to 115 psi" so I do. They are comfy on that steel road bike.

I also suspect pinch flats is a concern too.
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Old 10-14-14, 07:11 PM
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Originally Posted by 2manybikes View Post
They are comfy on that steel road bike.
Well that's the thing; I go back and forth between a steel tour bike and an aluminum bike and man, the ride is hard in comparison! That's why I want lower pressure; its not compensating but it does feel better. The aluminum bike is so much better at everything else though...! Its awesome.
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