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How sensitive are the tires to PSI changes?

H

HyperstradaHopeful

Joined Jan 2014
215 Posts | 0+
California
Hey guys, quick question: I just did a 200 mile ride today and knew I needed to top off my tires a bit beforehand (I have the Garmin TPMS, but for some reason only the front sensor is working, but it showed the rear as 3 PSI low so I can only assume the front was low as well).

So I stopped at a gas station and tried to fill the front to 32 and rear to 34. Their tire gauge sucked though. I need to buy one. I did the best I could but when I filled the rear to what looked like 34, the Garmin TPMS said it was 35.8. So I aired it down to 34. But since I don't have a working front sensor, I have no idea what it was air before or after. I'm confident I got it to somewhere between 32 and 35.

So how sensitive are the tires to PSI changes? If the front was 35, is it going to behave significantly different than at 32?

I know for cars, a 3 PSI difference is small and can be noticed, but just barely. Since motorcycles have 2 less wheels I'm guessing the difference is more profound?

Going to get a gauge and make sure they are set exact from now on, but just curious how important it is that they are exact. Also, is it more important that the front is exact than the rear, or vise versa?

Thanks!
 
Some body might chime in with the science of it, but I've always been sensitive to bike tire pressure as there's only 2 wheels in contact with the ground. When you see a stretched out Gixxer with a 3" wide flat spot down the spine of his rear, it's probably because he didn't stay on top of his pressure well enough.

I can tell on the highway when the rear's low. It wallows and tracks the grooves a little more than usual.
 
HyperstradaHopeful said:
Hey guys, quick question: I just did a 200 mile ride today and knew I needed to top off my tires a bit beforehand (I have the Garmin TPMS, but for some reason only the front sensor is working, but it showed the rear as 3 PSI low so I can only assume the front was low as well).

So I stopped at a gas station and tried to fill the front to 32 and rear to 34. Their tire gauge sucked though. I need to buy one. I did the best I could but when I filled the rear to what looked like 34, the Garmin TPMS said it was 35.8. So I aired it down to 34. But since I don't have a working front sensor, I have no idea what it was air before or after. I'm confident I got it to somewhere between 32 and 35.
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You really should proofread what you type. And you have been riding for how long and have never checked your tire pressures with your own gauge? :eek:

You should check them every time before you ride, while they are cold. "Stick" gauges are cheap and fairly accurate; a small air compressor and suitable fittings are also cheap at Harbor Freight. I run 32 - 33 psi front and 36 rear on our modern bikes with radial tires. Low pressures let the carcass flex more, which can cause overheating and failure. A flat tire is a minor hassle on a car, possibly life-threatening on a bike.
 
And TPMS aren't that accurate. They're great for alerting you to a really low tire, but every car I've owned with them the owner's manual had a warning about inaccuracies.

and +1 on air compressors. You'll wonder how you ever got along with out one once you delve into it's many, many uses.
 
gatdammit said:
And TPMS aren't that accurate. They're great for alerting you to a really low tire, but every car I've owned with them the owner's manual had a warning about inaccuracies.

and +1 on air compressors. You'll wonder how you ever got along with out one once you delve into it's many, many uses.
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Modern ones (within the last two years or so) are very accurate. I would agree about previously -- my 2008 Jeep wasn't nearly as accurate as my 2014 model car. The one in my car is bang-on dead balls accurate to my local shop's $1,000 digital filler.

And I'd say the Garmin TPMS is pretty darn accurate since it's giving me the PSI in tenths!! If it says the PSI is 31.8, I'd say there's a very good chance that's what it is.
 
zippy49 said:
You really should proofread what you type. And you have been riding for how long and have never checked your tire pressures with your own gauge? :eek:

You should check them every time before you ride, while they are cold. "Stick" gauges are cheap and fairly accurate; a small air compressor and suitable fittings are also cheap at Harbor Freight. I run 32 - 33 psi front and 36 rear on our modern bikes with radial tires. Low pressures let the carcass flex more, which can cause overheating and failure. A flat tire is a minor hassle on a car, possibly life-threatening on a bike.
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I've rode about 400 miles in total so far. They were checked and filled by a shop about 200 miles ago. I have hardly been careless about it. There's a lot of people in the world you need to talk to and warn about making sure they monitor their tire pressures. I'm not one of them. :)
 
For our European / "Metrical system" guys: Pirelli says 2,4 Bar for the front tire and 2,5 Bar for the rear tire with the Scorpion Trail
 
My experience with the OEM Pirellis is limited, but I can say that Pirellis are generally pretty soft carcassed and are sensitive to pressure changes, whereas Dunlop's sidewalls are far more stiff.

When I test rode the 1200 Multi, I could easily tell that the tires were under-inflated and had to return to the dealer after 20 miles to have them checked. The bike was pushing on corner entry and the Skyhook suspension was doing some very strange things. The only setting which felt decent was Enduro.

When I pulled back in, I asked the salesman to check pressures. Sure enough, they were at 29psi front and 32 rear. Once the tires were inflated to 35 front, 32 rear, the bike handled better, and the active suspension stopped feeling terrible.
 
Usually on a sport bike the visable flat spot is due to the profile of the tire. If he was riding mostly straight roads then the center will wear more than the sides. Most of the performance tires have a triangle shape to them so if one doesn't spend a lot of time in corners the center gets flat. I live in S. Arizona and have to ride 100 miles to hit a curve, my nice expensive Pilot R3s get a flat spot..and I am anal about tire pressure.
 
NiceweatherManni said:
For our European / "Metrical system" guys: Pirelli says 2,4 Bar for the front tire and 2,5 Bar for the rear tire with the Scorpion Trail
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I have an old Engineering handbook that calls it the "French system" of units...and when I was at school we learned both side-by-side. PITA.

Relying on fancy electronic gear for basic info is not as reliable as a plain old direct physical measurement. When I check my tire pressure, I also inspect their condition. I've had a dealer service department cut the sidewall during installation without telling me. One reason I do my own changes now.
 
zippy49 said:
I have an old Engineering handbook that calls it the "French system" of units...and when I was at school we learned both side-by-side. PITA.
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I saw a video explaining how the French created and maintained possession of the original Kilogram reference weight that the entire system is calibrated on. Some scientists in Europe are creating a new one that is considered the "roundest object in the world". More interesting than I make it sound.