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Tire Pressure Charts show lower PSI than Tire Minimum

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Tire Pressure Charts show lower PSI than Tire Minimum

Old 08-08-20, 08:11 PM
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channelz28
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Tire Pressure Charts show lower PSI than Tire Minimum

I just got 30mm tires on my road bike and have been trying to figure out what pressure to run them at. I looked at a few charts and all of the recommended pressures are below the 70psi minimum written on the tire. The highest one I saw was Frank Berto's chart that said 60 front, 90 rear. At least on the front, that's still well below the recommendation. Do you guys ignore the tires? If I run my front at 60, I can literally push the rim to the ground if I lean hard over the bars. I don't think there's any way I could run it that low.

Anyway, the reason I'm trying to figure this out is that on my second ride with the new tires, I slid out hard around a curve. Probably going 25 or so. I slid a long way and have the nastiest road rash I've had in many years. Broke my left pedal. It was a road I know really well, ridden it 50+ times, know the exact speed I can take it at, there wasn't any loose gravel or anything, I just can't figure out what happened. Tire pressure being too high is the only thing I can think of.

I've been using 28mm Gatorskins for the last 4 months, which I thought were poor handling tires. The new ones I got are 30mm Zipp Tangente Course, which I don't know much about. I figured they couldn't be worse as far as handling goes. I always rode the Gatorskins at max PSI, 120 front and back, never knowing any better. I had the ZIPPs at about 90 when I crashed. I don't know if I have to deflate the tires, or just ride slower. Me+bike equals about 220. I have a steel frame and I charge hard on ****ty roads. Pinch flats are a major concern. I really don't care much about comfort, though these tires are noticeably softer feeling than the Gatorskins. I do care about handling.
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Old 08-08-20, 09:01 PM
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Did it roll off the rim?
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Old 08-08-20, 09:51 PM
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channelz28
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Nope, didn't roll off.
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Old 08-08-20, 10:02 PM
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https://axs-stage.sram.com/tirepressureguide

This website recommends about 70psi front and rear. I would not ride with such a drastic F/R difference.

It’s really hard to say “your pressure was too high and therefore you crashed”. Riding 28% higher pressure than recommended should not cause a crash, since this website is a bit “newschool” and recommends lower pressures than people ran in older times. Especially compared to 120psi Gatorskins. Those tires have quite hard rubber.

I’d start at 70/75 and see if you feel anything different. Don’t worry about minimum pressures too much. I don’t think you’re anywhere close to the danger zone. I’ve run 25mm tires at 38psi in a race - but my system weight was also 65lbs less than yours.

At your weight, I would also maybe consider some bigger rubber if you like to charge hard on crappy roads. Bigger rubber lets you get more grip and not pinch flat. 35mm tires are going to be in fashion quite soon.

Last edited by smashndash; 08-08-20 at 10:05 PM.
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Old 08-09-20, 06:54 AM
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Measure the inflated width of tire. Work the chart- any chart- from measured width, not what the sidewall claims.

Same for tire pressure. Most gauges are wrong. Really, you cannot depend on your gauge. It probably reads same today as it did yesterday, so once you figure out what you like you can repeat that. Only way to know for sure is to buy much more expensive gauges.

I am close to your weight and one of my front wheels does have a 30mm tire. Usually inflate to 65 or 70. It does drift down to 60 before getting pumped again. Absolutely no way could I put enough weight on that to flatten it against the rim. Not even close.

In heavy braking or in very hard cornering your weight shifts to the front end of bike. Since bikes routinely pull 0.5g in braking force you can end up with 300 pounds of load on your front tire. Climbing very steep grades all weight is on the rear wheel and you know that because the front wheel can lift off the ground. Now go down the same grade and apply brakes into a corner. Inflating tires to what works on the flat and level in a wholly static situation will give unworkable pressures.
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Old 08-09-20, 06:57 AM
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Originally Posted by 63rickert View Post
Most gauges are wrong. ... Absolutely no way could I put enough weight on that to flatten it against the rim. Not even close.
This was my first thought, too.
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Old 08-09-20, 07:26 AM
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The minimum is on there for lawyers, ignore it.
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Old 08-09-20, 12:53 PM
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channelz28
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Originally Posted by Canker View Post
The minimum is on there for lawyers, ignore it.
Haha ok, thanks. This seems to be the consensus.

Originally Posted by smashndash View Post
At your weight, I would also maybe consider some bigger rubber if you like to charge hard on crappy roads. Bigger rubber lets you get more grip and not pinch flat. 35mm tires are going to be in fashion quite soon.
30mm is as big as I can go, I still had to lightly file the brakes to get them to fit. Maybe with wider rims I could move up.

Thanks for all the suggestions. I will try 70/75 today and see how it goes.
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Old 08-09-20, 01:41 PM
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Berto's chart is for weight over each wheel of the bike with rider on it, fully dressed and bike loaded with all accessories and other gear it's normally equipped with. It's not for just the bare bike (as the manufacturer's specs would list its weight) nor your weight when you weigh yourself on your bathroom scale trying to get a low number to convince yourself you can eat more snacks.
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