Tyre Pressures

I don’t have a problem with the “stock” pressures as such.

The Yamaha manual says 36psi front and back. Any recommendations for the road? Oh and for the track on the 1st.

Drop front and rear to 30 psi for track day, but remember to inflate to usual pressures after leaving!

36 ok for front, I have 38-39 in rear.

Out of curiosity, why do you let the pressure down for track use please?

Doesn’t the bike feel awful if you drop that much pressure? (Obviously not, or I assume you wouldn’t do it, but surely it must feel a lot different.) I’m sure that if my tyres were 6psi below what they should be, I’d feel all sorts of wobbly, and my lines on corners would be all over the place.

And if they’re more responsive on the track with lower pressures (which I’m guessing is why you do it), then why don’t you keep that pressure on the roads.

Sorry if this is a stupid Q to all you track-day people, but, if you don’t ask, you never learn…

I run 36 front and 40 rear on my R6 (2004 bike) and drop them the 30 front and 32 rear for the track.

Best thing to do is speak to the tyre guy who will be by the event organisers garage. :slight_smile:

On track tyres get much hotter than they normally do on the road so the air expands and the pressure goes up. Boyles law.

It’s not a stupid question at all!! The tyres get extremely hot on the track, much hotter than they ever will on the road. All that heat makes the air inside the tyre expand, so if you started with a trye full of air, your tyre would end up dangerously over inflated. The 1st couple of laps feel weird but as soon as your tyres get hot - it’s all good :smiley: Somebody more experienced than me might be able to go into more detail. :slight_smile:

No need Sherri,

You got it bang on - respect due!

Out of interest, is this from your own experience, factory recommendations or recommendations by other riders? (such as this lot :wink: )

the tyres will go out of shape when over inflated causing addtional problems too…not sure boyles law really applies as it is really only applicable to a change in volume and or pressure, not to the temperature…so technically this is not an ideal situation, nor an ideal gas as is needed for boyles law as well… as the temperature rises the energy of the gas increases and because the gas is a mixture, ie air which will vary depending on when and where it is filled, and the moisture content etc etc, trying to determine the change is impossible…the gas will therfore cause more collisions and therfore increase pressure…as the pressure increases because the tyre is NOT a fixed shape or volume it will expand under the pressure…therefore causing additional change to the pressures inside…a very complex calculation indeed…boyles law just wouldnt do at all…ops I am off again…

Shewoolfs explanation was the best…

The road pressures are from the manual and I find them fine. The track day pressures are from my own experience. I checked with the trye guy at the track and a few of the instructors. I’m turning into a bit of a track day junkie :hehe:

Thanks for the explanation. Makes sense to me (but I didn’t dwell too much on the “science bit”).

sorry just that boyles law was not totally the correct LAW…as I say SheWoolf was spot on…

also depends on how and where you ride on the road, and whether summer or winter, wet or dry track, and what bike/tyre you’re running. slightly lower pressures allow the tyre to move around and will generate more heat so can help give you grip when you’re on the road and doing shorter distances/lower speed. too low a pressure and you’ll just be dragging the tyre and ruining the life of the tyre and stopping its water displacement grooves from doing their job. can apparently also make you more prone to punctures.

with no tyre warmers (i.e. you’re not a ponce like me) when you go out for each session the bike will feel like a bit of a dog for the first couple of corners, thats normal. a couple of laps in and they’ll reach decent heat and pressure and you can push on. do not cheat on the warm up laps, its really not worth it.

as soon as you get in, check your pressures. something like a michelin 2ct should be about 36psi hot front and back. if you’re not riding fast/hard enough to get the pressures up to this, add a few psi. similarly if its cold or wet, you’ll need a few more psi to start with

Doh ! Of course it’s not, temp is constant… oh vey, should have concentrated on LB not work :slight_smile:

yes but just shows how complex tyre technology has to be…

I’ll dig out an article written by a Dunlop engineer a few years ago, it relates to car tyres but most of the principles will be the same, it was the best explanation I’ve seen of what happens to a tyre that’s being pushed hard, there’s a lot going on for something we all take for granted :wink: