I've tended to run around 30ish psi f+r on both my 250 and 400 on the road and track with no problems ever since they were lowered to that when I did the California Superbike School (level one) and forgot to pump them back up afterwards.
Most people seem to be of the opinion that you lower tyre pressure on the track as the tyre gets so hot that the air inside expands more thus raising it again which probably does occur, but when I did the school the tyre guy there (I believe he was from Dunlop) said the main reason for running them lower was that you could get away with it as it would increase the size of the contact patch and there is no risk of damaging the rim as there tends not to be potholes on the track. So with that in mind in theory on the track you can just keep lowering them untill you either start to go slower or don't like how it feels.
When I checked my pressures at Llandow (1) they were down to 28psi f+r and that was fine. _________________ Please do not PM me technical questions, if you can't find it on the Forum start a thread
OK, so I run BT090 and I don't know how much this does and doesn' translate to other tyres. Oh! And I'm talking track only.
In most (relatively hot) conditions here I run 1.8 (metric). When it gets really bastard smoking hot and/or I want to conserve tyres I'll got to 1.9-2.0, but only in practise sessions. Personally I ride pretty hard these days, but my bike is tuned for reliability (56.5 RWHP, but I'm aiming to move it to 60 not too peaky) so I get through two front tyres for every rear, and have little reason to go above 1.8 (maybe 1.9) in the rear.
Rain ... a different matter: in the rain you want more pressure (counter-intuitive) maybe 2.1max (keeps the tread open to shift water), unless there is light rain and the track doesn't have a layer of water ... then if you can ride hard and keep the tyre hot a lower (1. pressure works.
The main point about tyre pressure is not contact area (increasing contact area gives you more roll on the tyre), but the key point is tyre temperature. Hysteresis is a property of your tyre. That means when you bend it through riding, you put enrgy into the tyre, then its elasticity springs back, but not as much as you bend it. The difference in energy between what you put in and get back goes into heat. So the lower the pressure, the more you deform the tyre, so the stronger the effect of hysteresis, so the more heat goes into the tyre.
You want the tyre to be the right temperature, and different compounds are chosen at different hysteresis rates. For us (mostly) we have only one compound to choose from (at the race tyre level, e.g. BT090) since we don't have the power that the bigger bikes do.
Another important factor is how long tyres last. Often what determines a tyre's life is not so much how much it gets worn, but how many heat cycles it goes through. The rubber has oils in it which are exuded and sticky at temperature. If you get it up to temprerature too many times all of these sticky oils come out of the tyre and you are left with a hard dry tyre. Again we have to worry far less about this than the bigger bikes since we rarely will be really gettin gthe tyres hot. A 600-1000 bike ridden hard enough can cycle a tyre only 3 times before rendering it useless. I usually find that the BT090 on the NSR wears down before it looses stickiness.
So if in doubt -for the track- choose 1.8. _________________ MC28 SE -sold-
MC21 with RS250 engine -for sale-
MC21 race bike -soon for sale-
I did experiment with this when racing, and with pressure set to 30psi before a race, it was up to 35 / 36 after, confirming the 'experts' advice.
If the tyre is already at running pressure at the start of a race, it gets up to 38 / 39, and gets very slidey.
For the road, I use 32 Rear 34 front as the tyres are not worked consistantly hard enough to maintain the heat and therefor pressure. _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
But Dave, the more pressure in the tyre, the cooler it will stay. The less air in it the rubber will get hotter. Or have I just completely miss-read what you typed!?
Yes, you are correct. If you run too low of a pressure, the tire will heat up alot more and the pressure will rise just a tad more. You will also get more tire "roll" around the corners. I was told the magic number for the track was about 5psi of pressure rise.
Dave, you are right on track. When I was in Japan, Harc Pro recommended around 1.8-1.9 (about 30psi). This would put your post-track temp at around 35.
On the street, it is a totally different story. You should start out with a tad higher pressure with less pressure rise. This is what the street compound tires are designed for.
In a nutshell, run around 30psi for the track and 34psi for the street. _________________ Paul Herr
'88 FZR4/GSXR/YZF Frankenbike
MY BIKE PICS
Yup. Basically, the track tyre gets hot quickly and stays hot as it's being worked constantly. A road tyre takes a while to warm up, and then cools again as you sit at traffic lights, roundabouts, junctions etc. Having the pressure rise and fall every five minutes would feel horrid, and make the tyres wear out pretty quickly. _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
Last edited by Dave Ett on Wed Aug 17, 2005 9:03 am; edited 1 time in total
Ever since i had a chap recomend 29 front 30 rear ive stuck with it, for both road and track, Although i must add, most people i speak too have this reversed. 30 front and 29 rear....can i ask why dose the tyre go Blue ? I know its heat but is this a sign that the incorect preassures are in the tyres?
It's the oils coming out as mentioned above. _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
Difference between 29 and 30 is negligible, you'd be unlikely to feel it.
Pressure guages vary in accuracy of reading by more than that, so I wouldn't worry too much about front and back.
Whether you have front or back higher/lower pressure depends on the circuit, depends on the bike (how much power you've tweaked from you NSR), depends on your riding style, and depends a great deal on suspension set up. It also depends on what you want from the tyre. _________________ MC28 SE -sold-
MC21 with RS250 engine -for sale-
MC21 race bike -soon for sale-
... and if you can be bothered to check and pump it up! _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
these pressures seem massive i use 32 front and back.
I agree with Monkey.
He is roughly using the recommended pressures supplied by Honda for 110 and 150 Cyrox OE tyres which is 2.25 bar front and rear = 32.6 psi.
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pressure works.
