Low Pressure = Slipery Tires??

[Dan Filetti]

OK, So I'm a bit stumped about a recent tire-related experience and I thought I'd pick the brains of the collective to see if there are explanations I had not considered. 

Went for a early morning ride with a buddy a week back.  It was 0600, and I was barely awake frankly, and I neglected to check tire pressure.  Outside air temp was 65F.  I do usually check my tire pressure, and the past ~20 times I had, I had to add little to no air, so when I realized I had not done this at the end of my drive way, I did not go back, we were underway and time was tight...

I took it easy, for the first 20 miles or so, just to get some heat in the tires.  Then I slowly started to ease into the power of the Gixxer.  I truly do love the feeling of opening the throttle at the apex, feeling the weight transition from the front to the back of the bike, and having the bike dig it's way out of that corner.  But I digress...  I began to ride with a bit more gusto, all well within ~safe street speeds, and inside of what I had done on the bike on previous occasions.  It was about this time that, around one easy left-hander, I opened the throttle as normal, and the back of the bike suddenly stepped out to the right, maybe a foot.  Fortunately, I kept the bike upright, but it scared the hell out of me, let me tell you...

My buddy riding behind me, slowed to examine the offending-pavement, there was nothing obvious, looked normal to him.  So a few miles (of somewhat subdued twisties) later, I pulled over at a convenient location.  I examined my rear tire and it felt a bit soft.  Running up the street to a nearby gas station, the gauge on the air line showed just over 20lbs!  Wow.  I filled the tire up, and kept riding with no additional slippage.

This tire is a PP2 with LOTS of sidewall tread left, but it is slightly squared off [still some tread left on the center] from commuting duty.  Side point, my next set will be a PR2 out back, and a PP2 up front for this reason. 

So my question is, was the step out related to the low pressure?  I would have thought lower pressure would actually allow a bigger contact patch so at least no worse traction, but I'm just not sure -thoughts anyone?

If there is very little pressure, I guess the rim could spin inside the tire, but that's not the issue here, the bike stepped out for traction reasons, for sure.

Again, it's got me scratching my head. 

Appreciate your thoughts/ wisdom.   

Thanks,

Dan     

[RichBaker]

I'd bet that it was pressure-related.....  As an aside, NEVER trust the built-in gauges at a gas station! Carry your gauge with you.....

[racerman_27410]

low tire pressure may give you a larger contact patch but too low and it will overheat the tire..... makes the rubber greasy instead of sticky.


squared off tread profile prolly didnt help much either as there would be a pronounced transition from the flat center to the round sidewall....

maybe a combination of both things


its good to have some offroad riding experience when shit like that happens!

KOokaloo!

[ribbert]

OK, So I'm a bit stumped about a recent tire-related experience and I thought I'd pick the brains of the collective to see if there are explanations I had not considered. 

Went for a early morning ride with a buddy a week back.  It was 0600, and I was barely awake frankly, and I neglected to check tire pressure.  Outside air temp was 65F.  I do usually check my tire pressure, and the past ~20 times I had, I had to add little to no air, so when I realized I had not done this at the end of my drive way, I did not go back, we were underway and time was tight...

I took it easy, for the first 20 miles or so, just to get some heat in the tires.  Then I slowly started to ease into the power of the Gixxer.  I truly do love the feeling of opening the throttle at the apex, feeling the weight transition from the front to the back of the bike, and having the bike dig it's way out of that corner.  But I digress...  I began to ride with a bit more gusto, all well within ~safe street speeds, and inside of what I had done on the bike on previous occasions.  It was about this time that, around one easy left-hander, I opened the throttle as normal, and the back of the bike suddenly stepped out to the right, maybe a foot.  Fortunately, I kept the bike upright, but it scared the hell out of me, let me tell you...

My buddy riding behind me, slowed to examine the offending-pavement, there was nothing obvious, looked normal to him.  So a few miles (of somewhat subdued twisties) later, I pulled over at a convenient location.  I examined my rear tire and it felt a bit soft.  Running up the street to a nearby gas station, the gauge on the air line showed just over 20lbs!  Wow.  I filled the tire up, and kept riding with no additional slippage.

This tire is a PP2 with LOTS of sidewall tread left, but it is slightly squared off [still some tread left on the center] from commuting duty.  Side point, my next set will be a PR2 out back, and a PP2 up front for this reason. 

So my question is, was the step out related to the low pressure?  I would have thought lower pressure would actually allow a bigger contact patch so at least no worse traction, but I'm just not sure -thoughts anyone?

If there is very little pressure, I guess the rim could spin inside the tire, but that's not the issue here, the bike stepped out for traction reasons, for sure.

Again, it's got me scratching my head. 

Appreciate your thoughts/ wisdom.   

Thanks,

Dan     

Someone may chip in with a lengthy explanation as to why, but a tyre running around half the recommended pressure is going to do that. As for the reasoning of a semi deflated tyre having a bigger contact patch, a fully deflated tyre has an even bigger one! The only positive thing under inflated tyres do is heat up faster from the friction, but with a loss of traction. In the extreme, you've probably seen someone who continues to drive on a flat car tyre until it is literally smoking - friction!
Noel

[SlowOldGuy]

Dan,
I once ruined a friends brand new rear Dunlop due to underinflation.  He was keeping his R1 in my garage and I was doing him a favor by stirring up the oil and making sure the fuel stayed fresh.  Unfortunately somewhere during the ride I picked up a nail in the rear. 

I just thought I was really riding hard.  About halfway thru the ride, I started feeling the rear step out in these cool slides.  I thought maybe the roads were getting a little hot and the R1's power was just too much.  When I got home, I finally checked the tire and the tread was toast.  I ruined a perfectly good tire with only a few hundred miles on it.  It only had about 15 psi in it.  I considered just letting it go, but felt bad so I bought him a new tire.  He sold the bike before even riding it again.

DavidR.

[andyb]

Underinflation can also lead to a lack of control over the tire's shape (obv!), in addition to making it overheat and go off.

[Dan Filetti]

Thanks folks,

Guess the step out was related to low pressure.  I've noticed that suddenly my rear tire has a slow leak.  Undoubtedly the cause for the most recent under-inflation related step-out.  I have looked closely and found no punctures, that I can see anyway, so I guess it's corrosion at the bead or some such.

Thanks again,

Dan

[racerman_27410]

i would check around the valve stem.... soapy water can help you track down the leak.... if the valve stem lets go while you're riding it can be  bad scene.

i replace my valve stems every other tire since i had one fail on me .... the tire went down REAL quick! and tire stems are cheap.


KOokaloo!

[Dan Filetti]

Thanks Frank.  I'll do just that.

Dan

[Pat Conlon]

Dan, I once ruined a friends brand new rear Dunlop due to underinflation..... 

Be careful with that tire Dan, if you got it hot enough for the tread to get greasy, you may have damaged the cords (delamination) in the sidewall.  Pat

[RichBaker]

i would check around the valve stem.... soapy water can help you track down the leak.... if the valve stem lets go while you're riding it can be  bad scene.

i replace my valve stems every other tire since i had one fail on me .... the tire went down REAL quick! and tire stems are cheap.


KOokaloo!

I ALWAYS replace the valve stem when I replace the tire..... cheap insurance.

[moparman70]

I'd bet that it was pressure-related.....  As an aside, NEVER trust the built-in gauges at a gas station! Carry your gauge with you.....

Totally agree and add one -- buy yourself a very good one not the normal looking sticks you can get.  I finally bought a dial gauge  - purchased at Cycle Gear on sale --- and it works great.  The stick type seem to change when check and double checking the same tire.  The new dial gauge reads the same on the same tire --very reproducible.  I know there are digital types as well -- they may work fine.  I just got tire of the other type because it seems they varied too much --

stevec