Tyre pressure debate
 

Ok, I'd be interested to hear peoples thoughts on this. I have done somewhere between 15 and 20 trackdays and have always dropped my (road) tyre pressures down a few psi - Usually run something like 28-30psi front adn 30-32psi rear. Today I went to a new track and was noticing that my tyres felt good at the beginning of the session but started to slide towards the end. A few guys in the pits said they were running around 34-36 front and rear :smt017 which I thought was way to high, so I went and quizzed to the Bridgestone guy who was giving out this advice.

He said that running lower tyre pressures gives a larger footprint on the track. I agreed. However, he then said that the larger footprint doesn't generate enough heat or the heat is to dispersed across the tyre so they don't get up to their correct working temperature. This causes small level cold tearing (the 'large' river like patterns - usually in the spot where you get on the gas). He said if you run the same pressures as on the road - maybe 1-2 psi either way depending on preference. Then the tyres footprint is smaller and the heat generated is much more focused, which is how the tyres are designed to work and offer the optimum grip. He then went on to say that you know that you tyres are getting up to temp because the river like patterns are much much smaller - that is the sweet spot.

I tried this out and for the first few laps, they felt awful. I was sliding all over the place - one corner, I could feel the whole bike drifting sideways as I exited. However, after a few warming laps, they actually felt better than before?

So, what is correct??

(remember this only applies to road tyres - not race tyres)

Re: Tyre pressure debate
 

Neither and both I'd hazard. Which felt best to you over the whole session?

Without knowing which tyres, taking temperatures, knowing the manufacturers optimum temperature range, and a whole host of other factors (left/right circuit, speed of corners) it's all about what feels best to you. Think about how much they spend developing tyres and how a given brand can be hated by one rider and adored by another.

Re: Tyre pressure debate
 

I havent done 20 trackdays, but have done a few. I never adjust my front tyre. Just leave it at road pressures, currently 32 / 33. I do drop my rear down to about 30 / 31 though.

This was from advice from Dunlop rep at CSS Rockingham. I also picked the brain of a well respected team owner in BSB 600 Supersport.

So far it has been good advice[-o<

Re: Tyre pressure debate
 

I've done less than 10 track days and all of them at Knockhill and I've not once adjusted my tyre pressures. I never thought I was 'racery' enough to notice a difference. I may look into this next time.

Re: Tyre pressure debate
 

I have a track evening at Snetterton tonight - usually just drop the pressures by 2-3 - I have found this ok at the 6-7 trackdays I have done. For the Zed that means 34 front and 39 rear I think...

Re: Tyre pressure debate
 

I've done some 15 or so trackdays and I've tried at std pressures and dropping a few PSI, at standard pressures the tyres begin to feel squirmy towards the end of a session. Dropping about 3 PSI and they feel odd for the first lap then feel great.

I thought that the idea was to run at about the std recomended pressures but that the pressure will rise in the tyre as the tyre warms so will end up wth a higher pressure than it would on the road for the same cold pressure. So you drop it a few PSI to end up with the same 'hot' pressure.

One way I've heard but never tried is to set the pressures hot, ie *straight* after you get off track, that should allow you to change the pressure relative to how hot the tyre is getting. Probably best to start with to just measure it and note it down, comparing it to cold pressures so that you get an idea of what's going on before you start making changes.

Druid

Re: Tyre pressure debate
 

chap i was speaking to at the weekend reccons i should drop my tyre pressures on the road to about 36rear and 33 front.... am not convinced....

Re: Tyre pressure debate
 

Not sure what bike/tyre combo you're on Custard, but a lot of the tyre manufacturers and Suzuki recommend 33F/36R on the SV for general use.

Re: Tyre pressure debate
 

The tyre manufacturer is largely irrelevant - the question was more the theory of lower pressure = bigger footprint, more dispersed heat, means tyres aren't getting up to optimum temperature.

Bridgestone man said road tyres are designed to work at ~70c - so after a session on the track, although your tyres may look torn up, and feel warm, they actually were operating at a lower temp, which is why you get the large river patterns - because the tyre is tearing (mildly) away from the track surface. With a little more heat, there is less tearing and more grip! I'll post some pics of the big and small river patterns from my rear when I get a chance

It's interesting that someone quoted a Dunlop guy at Rockingham saying almost the same thing. I think on my next trackday, I'll probably keep my front as is and just drop the rear a little - see how that works out.

I find this really interesting. Someone else also suggested taking pressures readings the second you get off track - to see the cold/warm difference and gauge how much of an increase hot tyres gives. Mine were ,at most 2-3psi higher, but that was it.

Re: Tyre pressure debate
 

Had an evening session at Snetterton last night and dropped my pressures -3 on the rear and -4 on the front - it seemed to work for me - but then I am no expert! lol Meant to check the pressures when I got back into the pits but was so pumped up I completely forgot every time! :lol:

Re: Tyre pressure debate
 

cool! :thumbsup: having fun is the main thing.

I took some pics of what I am babbling on about this morning, but they are out of focus, so I'll try again tomorrow!

Re: Tyre pressure debate
 

Is that not a slighlty simplistic statement from the Bridgestone man? Each tyre has an optimum temp, but works over a wider range. A touring tyre will work better over a wider and cooler range, whereas a race tyre will have a smaller, hotter, range.

You need this.

Re: Tyre pressure debate
 

We are talking road tyres on the track, not race tyres. It's not about the precise temp - the "~" means around, but more the way in which the heat is generated and dispersed and the affect this has on that operating temp.

Hmm - you link has four letters replaced with ****! Not sure what is censored.....

Re: Tyre pressure debate
 

It is indeed - only two groups and (without trying to sound big headed) I was definitely one of the faster ones in the slow/intermediate group - tried hanging off the bike to see if knee would touch tarmac to no avail - pegs ground out way before I got close :( Gave up in the end as I was going plenty fast enough through the bends anyway!

Re: Tyre pressure debate
 

:smt044 Stoopid censor. it's "bright water" without the space, which the censor seems to think contains a naughty word. :confused:

Re: Tyre pressure debate
 

You should check out some pics of yourself if you can. Really helpful for checking out body position and stuff. It will probably feel like you are hanging off a lot more than you actually are. Was there a trackday photographer?

Re: Tyre pressure debate
 

There was but he was only at the Russell chicane - somewhere I wasnt trying that hard - a friend took some pics around the circuit so will check them out - he said I was only 3-6 inches away so I was close - the Zed has very poor ground clearance on the pegs though

Re: Tyre pressure debate
 

Large River Patterns

This is what you get when your pressure is too low. Bigger footprint, less heat and larger tear patterns. Rear psi was ~6 lower than the manufacturers recommendation (36 psi):

http://img141.imageshack.us/img141/8...atternsmn7.jpg

Small River Patterns

This is the sweet spot! You get the same patterns but they are much smaller indicating that the tyre is operating at it's optimum temperature. Rear psi was ~1-2 lower than manufacturers recommendation (36 psi):

http://img232.imageshack.us/img232/9...atternseu0.jpg

NOTE: This is just the info relayed from the Bridgestone technician. I'm running Michelin Pilot Power 2CTs, but he said that the principle is the same for most road tyres on the track. Also said that the front doesn't generate as much heat, so leave that pressure as is.

Re: Tyre pressure debate
 

That first picture is pretty much how my tyre looked after the trackday on Monday evening - so the pressures were too low? I checked them last night and the rear was at 39psi - normal road pressure is 42psi.

Re: Tyre pressure debate
 

No idea! This thread was supposed to be more of a discussion than a "Do this!".

Like I said I have always dropped mine, but now have found out something to the contrary, with some theory and images to support it. I think I'm going to experiment a little on my next trackday, but as a base I'll drop 2psi on my rear and keep the front as is.

Re: Tyre pressure debate
 

Almost all racers I've compared info with are running near enough the same pressures, even across different tyres and bikes.

Front is normally 30psi and rear is 29psi when cold (I confirmed mine with a BSB Pirelli tyre technician, a drinking buddy of mine). The important point is the target temperature that they reach during your race or track session. Other than outside influence such as ambient air temp and track surface temp you can influence it most by the style and speed of your riding.

It all depends on the length of the track session and your ability. The harder you ride the faster your pressures and tyre temperature will rise.

I wish I had tyres that looked that good after a race!

Re: Tyre pressure debate
 

I usually run about 30/30 on my GSXR (standard = 36/42) and get river patterns like here, though most of the time worse.

Yesterday I ran 32/38 at anglesey. I've never had grip problems with fully warm tyres so I can't really assess the effects. This is what my brand new pirelli corsa III:
http://homepage.ntlworld.com/christo.../anglesey1.jpg

The surface has been ripped away, another 2/3 trackdays and the tyre would be squared off around that wear mark. The only other difference I could visually see was that the tyre picked up less rubber on the edges for both front/rear.

Re: Tyre pressure debate
 

Larger river patterns, small river patterns ... why are small ones better than large ones? Are smaller ones really indicating less wear? Which have given the better grip/feel on track? Surely that is more important than any wear pattern?

Now this one has always got me ... do you pump them up a bit more or let them down a bit if it is colder?!!? ;)

Oh and BTW my view on the 'focused heating' is sceptical. Lets face it, that guy is a paid tyre technician, but it is contrary to the logic I am about to present (which was originally given to me by a paid tyre technician ;)).

Flex a bit of rubber (or metal, or plastic) in your hands ... it doesn't take long before it gets hot. Its this property that actually aids heating the tyre across its width, the bit that flexes the most will provide the most heat (the same centre spot).

About to watch motoGP on telly so this is a bit brief, but will discuss/elaborate more later if anyone is interested! 8)

Re: Tyre pressure debate
 

I think you were closer to the mark with the original 30/30 although you may want to try a lower rear pressure to start with....say 29psi and see how you get on.

Other than pressures the other thing you might want to think over is the suspension setup as that can also affect tyre wear. I race Anglesey regularly and have never had tyre tear like you are showing.

Re: Tyre pressure debate
 

Hanging of would give you more traction, which may save you from a future crash. Never know how close to the edge you are until you slide. Best to have all the traction you can get just in case.

Re: Tyre pressure debate
 

I've got Diablo Rossos on my bike. Pirelli's UK Product Manager told me not to change the pressures at all and the tyre man told me to go quite low even though I said I was a novice. I've tried both and I settle somewhere in between. 33/33 or maybe a tiny bit lower instead of 34/36. Last trackday I got me knee down and the tyre to the edge with no wobbly moments. Had no rip on the right side but thick wobbly lines of snot on the left (mallory park) which I assume is cold wall rip (?).

The debate goes on.....

Edit: As a side not I mentioned to someone queing to go out on an Aprilia 250 that it looked like he had oil on his rear tyre. Patches of purple and other colours. He said it was just where they'd got hot!

Re: Tyre pressure debate
 

Interesting thread. I did a track day a couple of weeks ago and was having issues with tyre grip running a Diablo Rosso on the front and a Diablo on the rear both at 29psi. I did another trackday yesterday and tried running them at 33psi front and 36psi rear and they seemed to me to perform at least as well as at the lower pressures. I didn't have any significant slides this time, but I think I probably wasn't pushing it quite as hard as last time, doing a better job of staying within the tyres' limits. I think the tyre wear looks less, unfortunately I didn't take photos of them after running them at 29psi, but here's some from yesterday after running them at 33psi and 36psi:
http://s38.photobucket.com/albums/e1.../sv650s/tyres/

Re: Tyre pressure debate
 

Is the discussion in this tread is a bit bum about face?

Discussing cold tyre pressures is largely irrelevent when it's the hot pressure that matters, which is why racers use hot pressures to adjust their tyres.

Every rider, tyre set and suspension set up being different, Surely the advise should be to set your cold pressures so that we *all* have the same hot pressures regardless of set-up/bike/ability/power/rider weight.

Tyre pressures should be measured when coming back in from a track session, or when just finishing a spirited ride.

Sending a novice out on 29psi tyres front and rear is not a good idea simply because the tyres are underinflated. If that novice never gets to a point where his tyres are "hot", he'll be running on tyres that will be squirming all over the place due to deformation from the low pressure.

Rather than saying you should set your cold pressures to XYZ, we need a figure to set them to hot, measure them hot and adjust them hot. The point at which they run is the important measurement and as we all ride differently, we should, in theory, be all starting from a different starting point to reach the *same* end point.

So if we all want to end up with a hot pressure of say 36 front, 38 rear, some will start at 29, some will start at 32 and some may start as high as 34-35.

And tyre pressures are only half the story, Maybe even less than half.
Properly adjusted suspension is more important in terms of feel and keeping the tyre on the road. Having the rear too stiff will cause the bike to push on the exit and will increase the temperature. It may cause the rear to skip under power and increase temperature and wear.

So, is it not the case that this thread should be about "which hot pressures should we all be looking for so we can all set our cold pressures to suit our own particular circumstance"?

Cheers,
Carl

Re: Tyre pressure debate
 

Its quite simple, you do what works for you. One mans meat and all that.

I have never done a track day, but i can notice a 2psi drop in either tyre on my bike and its horrible.

Re: Tyre pressure debate
 

I've never track ridden an SV, but I have a Hornet and then a Daytona 675.
Tyre pressures (for me mind-high intermediate speeds) are set to aim for around 35psi front and rear when HOT, and i mean HOT!
I normally start a track day at around 31-32 and then adjst them after the first session as soon as i come off track.
This has worked for me, I'm hard on the brakes so kepe the front very hot. I've been known to outbrake a Blade at the end of Park despite having 100bhp less for the long drag!
I've used both Bridgestone and Pirelli track focused road tyres. 012ss and supercorsa sc2's. As well road tyres, 010's on both the Hornet and 675.
So i agree with what has been said, lowering tyre pressures is what people do and it does work.
I believe lowering the pressure allows the tyre to move around more at first but this will ultimately heat the tyre up faster, increasing the pressure higher, quicker.
HTH
J

Re: Tyre pressure debate
 

I don't know one racer who sets his tyre pressures hot, and I don't know of any tyre companies who make race tyres who recommend you do.

In the past 4 years I've been in and around race paddocks and trackdays almost every other weekend - I see a lot of people checking tyre pressures and they always do them cold. The race bikes I prep and spanner are certainly only ever checked cold and the only time we change them is under extreme ambient temperature changes in the weather.

Re: Tyre pressure debate
 

I do. quite a few of em, with the warmers on. I used to do it like this when I raced too. before every race. Maybe things have changed and maybe they know what they'll get once the warmers are on? I doubt your racer friends don't know what their hot pressures are even if they don't check them hot. I've watched race teams on the TV checking the pressures with the warmers on recently though.

C

Re: Tyre pressure debate
 

Hi Lozzo,
I found the following in June 2007's Bike magazines excellent article on Grip. (page 116 for those with the mag)

Direct quote.

Q: Does lowering my Tyre pressures give me more Grip? And should I only drop them for Trackdays?

A: It does. By extending the size of the contact patch. But you can go too low. In racing it's Hot pressures you want to check. But for the road we use cold pressures as an average guide. Many things affect the actual tyre temperature: your weight; The way you're riding; Speed; Ground temperature. The hotter a tyre, the greater the pressure. But go too low on cold pressures and the bike will become unstable.

Gary Hartshorne
Racing and technical manager, Bridgestone UK."


Its a great article if you can get your hands on the issue

Cheers,
Carl

Re: Tyre pressure debate
 

That's interesting. When we raced the Triumph 675 at Silverstone we had to run control tyres which were Michelin Pilot Race. We had no experience of them prior to going out in qualifying (He'd run Metzeler Racetechs in practice) and had no idea what pressures to run. I went and had a word with the Michelin guys on site and they gave me cold pressures, so we worked with those. Over the course of the weekend Danny neve complained about tyre pressures, desite their being quite a difference in ambient temperatures for all four sessins on the bike (2 qualifying, 2 races)

The only time I was given a hot pressure to work with was when we tried some new Dunlops to use on our old RGV250 based 'thing'. We faffed about trying to get them right but never succeeded as the hot pressure was never consistent. In desperation I searched out a Dunlop tyre tech and he told me not to bother with hot pressures but to check them cold and run the front at 31psi and the rear at some ridiculously low pressure like 22psi to start as their rear carcass had extremely flexible sidewalls that generated a lot of heat. From then on Danny never complained about tyres, and the times I rode it on trackdays it handled wonderfully