Kawasaki Sportsbike Riders Club - Australia - Online Forum

Ladies & Gents,

Just a quick one regarding pressures for the track.

What do you feel if tyres are under/over inflated? looking for peoples impressions to match with my own.

Cheers
Matt

Tyres will slide around heaps, and I mean heaps with a bit of heat in them.

I ended up qualifying at winton with 57psi in the rear and it felt like was on ice skates. The rear was sliding out more than normal out of every corner and over shot the first turn at the end of the straight and went grass exploring as the rear wouldn't sit down on hard braking .

its all down to weight of the bike+ rider just keep playing with the presures until your happy

Good starting piont is 30F 30R then adjust from there, either up or down. Down is probably better cause as Blurr said she skates at high temps.

Rod has it... start at 30psi, but with relation to high temps
Under inflation makes a tyre run hot. Increased flexing of the sidewall increases the temperature of the tire & your contact patch will be larger & give a feeling of a slow reaction to turns.
Too much tyre pressure gives a stiffer springrate, and less sidewall flex resulting in lower tyre temperature, you will also have a smaller contact patch hence the sliding.
Thats why drag cars run low pressures.... more heat & larger contact patch, same for sprint cars... as low as 12 psi or less

robracer wrote:Rod has it... start at 30psi, but with relation to high temps
Under inflation makes a tyre run hot. Increased flexing of the sidewall increases the temperature of the tire & your contact patch will be larger & give a feeling of a slow reaction to turns.
Too much tyre pressure gives a stiffer springrate, and less sidewall flex resulting in lower tyre temperature, you will also have a smaller contact patch hence the sliding.
Thats why drag cars run low pressures.... more heat & larger contact patch, same for sprint cars... as low as 12 psi or less

Yeah what Rob said.... been a long day.

Blurr wrote:Tyres will slide around heaps, and I mean heaps with a bit of heat in them.

I ended up qualifying at winton with 57psi in the rear and it felt like was on ice skates. The rear was sliding out more than normal out of every corner and over shot the first turn at the end of the straight and went grass exploring as the rear wouldn't sit down on hard braking .

57PSI? Typo?

But +1 to what the others have said. 30PSI cold to start and adjust from there.

Nup no typo. Didn't deflate it after dunlop gave me the tyre. They just inflate it to set the bead then give it back to you with whatever is in it. Made qualifying interesting

Blurr wrote:Nup no typo. Didn't deflate it after dunlop gave me the tyre. They just inflate it to set the bead then give it back to you with whatever is in it. Made qualifying interesting

I've made same mistake. Only once though it teaches you to check every time since! (Just like running out of fuel on last lap)
My race bike rolls with 30Psi checked as I take the warmers off! Cold would be somewhere near 26-28 Psi? I only work with Temp from hot tyres, Being that you have warmers on and off all day. A cold temp is irrelivent.
Wets run approx 5+ Psi higher.

wow. I'm up for a new set of slicks soon. Definately will be checking the pressure on those before riding

Thanks guys, thats pretty much what I was feeling, my starting point was always 30 f/r but never paid much attention to it after that. I'm down to 28 f/r after PI so we'll see how that works at EC.

my first track day on the new bike i completely forgot to check the pressures, i ended up doing 2 sessions with 18psi (if i remember right) int he rear and 28 in the front, and yes, this is hot pressures.
The bike felt slow coming out of turns and when ever i opened it up coming out of corners it felt like the front would come up a bit and i would get a front end shake.
after it was pointed out to me that i may have the wrong pressures, i set it to 30 f/r and the bike felt like new. front end stopped lifting, quick into turns and out. i had a few moments where the rear end would step out after upping the pressures, but after i adjusted my throttle control it calmed down.

So if I've got warmers on I should give 30 front and rear hot a go? I've always started with 30 cold on the RGV, and only at the last track day did I notice them getting a bit tatty looking (looked like cold tearing but wasn't, if you know what I mean). Maybe I was just having more of a go that day and that's what they're supposed to look like?

I go with the rule that you should get a 4 psi increase from cold when you come in. adjust it up or down according to the difference and how it feels on the bike , but 4 psi is a pretty good mark. The ideal pressures will change depending on tyres, rider, ambient and track tempreture etc but 4 psi is a pretty good constant.

Blurr wrote:Nup no typo. Didn't deflate it after dunlop gave me the tyre. They just inflate it to set the bead then give it back to you with whatever is in it. Made qualifying interesting

I had that once at PI, on the ZXR ; tyre changed but foolishly assumed they'd set the pressure 'correctly' ; big rear drift through Southern Loop, ran off into the grass at MG, andwhen I got back in found 52 psi in the back ... A lesson hard learned is one you don't forget in a hurry, that's for sure !

Cheers,
Brian