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Discussion Starter #1
This is the front tyre off a 08 R6, Diablo supercorsa SC2, cold 28psi, hot +6 psi
Shocks are ohlins 30mm cartridges, zip tie is about half inch from the bottom of the fork.

Laptime is about 2.26 in sepang, which is not fast by any means. I did not carry the brakes into the corner, maybe on one/two turns will use a finger to put some pressure on the lever, but it's definitely not hard braking while leaning.

Rear tyre looks great, nice and smooth.

However, the front looks like this

This shows the roughest section, and note the weird discontinuity from the groove/thread area.


Rotate the tyre half a round, and it doenst seem that bad. These pics were taken at the same time, the bike didnt go out anymore after that.


Left hand side looks okay.



This happened after we increase the preload by two turns and added two clicks on the compression.
We backed off the setting afterwards and the tyre still looked the same, in fact it got worst. No other setup or riding style change.


Any ideas?
 

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Because they're Pirellis? j/k

You've got to be running like hell to even think you're getting +6 psi after a session (or you need to buy a proper tire gauge). and you said yourself your pace isn't fast by any means. You're getting some insane tearing due to tire pressure issues. Even though there's a slight change in PSI, the overall tire temperature would change drastically.

And, even IF you are, 34 in the front is way too high. And all that tearing could be from the start of the session, until you get up to normal operating temp (assuming you actually are, and not exceeding it). Showing a picture of your rear tire will also give us a better idea of the pace your running...

BTW... the weird discontinuity of the patterns is an indicate of throttle on-off/adjustments mid turn. Even if you think you aren't, you probably aren't noticing it. If you were on the throttle continuously through the whole turn, that pattern would be continuous.
 

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What was the ambient temp at the track? Was the pavement getting direct sunlight or was it cloudy? I usually get +4 PSI rise out of a Pirelli SC2 front from cold to hot off the track at race pace, but I always use warmers. You MIGHT get +6 PSI if you went from cold pressure @ 35 degrees F to hot off the track at race pace. It looks like minor cold-tearing. It sounds like you dropped your pace because of the suspension changes...I've never really seen preload cause that type of problem. An inch of remaining travel is too much. How many turns of preload are you running? Was it difficult to get the bike to turn into the corner?
 

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Discussion Starter #6
What was the ambient temp at the track? Was the pavement getting direct sunlight or was it cloudy? I usually get +4 PSI rise out of a Pirelli SC2 front from cold to hot off the track at race pace, but I always use warmers. You MIGHT get +6 PSI if you went from cold pressure @ 35 degrees F to hot off the track at race pace. It looks like minor cold-tearing. It sounds like you dropped your pace because of the suspension changes...I've never really seen preload cause that type of problem. An inch of remaining travel is too much. How many turns of preload are you running? Was it difficult to get the bike to turn into the corner?
I guess the day started with 27/28c and got to 30/31c by mid noon.
slightly cloudy day, but you'll still sweat like a wet towel in gear just standing.

Shock marker is half inch from the bottom, first picture shows it.

Yes, +5psi sometimes +6 is from COLD (as in filled up last night and checked in the morning cold) to just back in from a hot lap (without cooldown lap).

Pace actually improved, mainly on braking, but elsewhere, cornering out and the big sweepers should be about same pace. We added the preload and damping because the bike was diving in too fast and tail wagging on braking, and I'm not confident enough to "relax and just let it do its thing".

One benefit is that I now like how the bike just drops into the corner at low speed flip flops. Sepang turn 1 to 2 and 9 to 10 requires the rider to quickly flip from full lean one side to the other, and this change made it easier somehow.

The minor suspension tweak solved the braking nervousness, but later i realised the issue and adjusted back. It didnt help.
 

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I'd Flip it :popcorn:
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That would be cold tear, due to the tire NOT heating up, your pressure is WAY to high ad when you have a higher psi it will fight the heat in the tire and will tear like in the picture. Those tires should be 29-30 HOT. How did the bike feel?


Sent from my iPhone using Motorcycle.com App
 

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Discussion Starter #8
Azim, rears look like this





if there were abrupt throttle modulations, shouldnt it show up in the rear more?
Plus, doubt i can be so rhythmic to match the discontinuity to each and every groove.
 

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When in doubtThrottle out
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That would be cold tear, due to the tire NOT heating up, your pressure is WAY to high ad when you have a higher psi it will fight the heat in the tire and will tear like in the picture. Those tires should be 29-30 HOT. How did the bike feel?


Sent from my iPhone using Motorcycle.com App
:fact cold tear you need more pressure
 

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"The Dude abides .. "
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Because they're Pirellis? j/k

You've got to be running like hell to even think you're getting +6 psi after a session (or you need to buy a proper tire gauge). and you said yourself your pace isn't fast by any means. You're getting some insane tearing due to tire pressure issues. Even though there's a slight change in PSI, the overall tire temperature would change drastically.

And, even IF you are, 34 in the front is way too high. And all that tearing could be from the start of the session, until you get up to normal operating temp (assuming you actually are, and not exceeding it). Showing a picture of your rear tire will also give us a better idea of the pace your running...

BTW... the weird discontinuity of the patterns is an indicate of throttle on-off/adjustments mid turn. Even if you think you aren't, you probably aren't noticing it. If you were on the throttle continuously through the whole turn, that pattern would be continuous.
please don't take offense, but you should stop giving advice about tires.. Not meaning to be a jerk, but your way off base on this. Throttle attitude causing this problem? LOL. So let me understand, he is on and off every half rotation of the tire.. Classic. :)
Still, 1-2 psi will NOT cause that unusual wear, especially from a rider that indicates he is not going all that fast.

Anyone care to explain how the tear was only part of the rotation???
It's a dual compound tire.. hard on the top half, soft on the bottom half :) (just kidding for anyone thinking im serious)



guys, 1-2 psi either way isn't gonna solve this issue. Personally i have never seen uneven tire wear on a front, let alone a rear. Is the rim bent? was it out of balance? were tire warmers used? it almost looks like chatter, but on a serious level. How to solve chatter? Figure that out and you would be a very sought after suspension tuner. +6psi from cold is an indication the tire is too soft and/or may have had too little psi to begin with. but a bit low tire psi doesn't in and of itself cause odd tire wear..

The zip tie showing 10mm or so above the bottom of the tube is a product of oil level. Even too much spring, but with low oil, will allow you to bottom under hard braking. conversly, a rate or 2 too soft but with high oil level, could keep it from bottoming, but working in a part of the stroke too low.

cold tear is not always fixed with more OR less air.. sometimes it just is what it is and that sucks, but competition race tires are complex. And once a tire has torn like that (cold tear, hot tear, whatever you call it) it will not clean up, and you might as well just ride it or get another tire.
 

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"The Dude abides .. "
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lil google searching does some good.. I'm not convinced most of us would be better served to just set cold psi and adjust off the track, but racing, especially how to set race tires, has NEVER been an exact science.

http://diabloracer.com/phpBB3/viewtopic.php?f=4&t=21
These pressures are general pressures for both DOT's and Slicks. Pirelli works with pressures in the only truly accurate way and that is once the carcass has been heat soaked. You should think twice about any tire tech or vendor that simply tells you to set cold pressures and be on your way. This goes for all tire brands. There are way to many variables in working simply from cold pressures such as ambient temp, track temp, humidity, track surface, cloud cover, nitrogen and the list goes on. The best way is to start with a base cold pressure of around 29psi front and 26psi rear. Warm the tires as suggested in the Tire Warmer Post and then set the pressures once again coming off the warmer.
The range for the front tire is 30-34psi and the rear is 25-28psi. Pressures should be checked everytime the bike comes off the track. Record the prssures and adjust if needed to get final hot pressure. Once this is done, you can allow the tires to cool to ambient and check cold pressures to get a good base number for the you and the bike on that day at that track. Be sure to keep an eye on track temps. It's amazing what even some clouds can do!
[URL=http://s603.photobucket.com/albums/tt119/orionmot/?action=view&current=_DSC1931.jpg]Image[/url]
Tuning the tires:
This is not an exact science but here are some good hints. The range of the front is 30-35 hot. A higher pressure will give the rider a firmer feel under breaking and turn in but the level of grip tends to decrease as the pressure increases. The tire will feel more precise and offer more or even too much surface feedback. Pressures on the lower side will offer maximum grip but will feel less precise on turn in and may tend to move around more under breaking. Most riders tend to prefer 32-23 as a true hot pressure. Riders who prefer running the tire in the higher end of the pressure range should consider testing a harder compound tire at a lower pressure. Riders who tend to run the front tire in the lower pressure range should consider testing a softer compound tire at a higher pressure. People are often mistaken in thinking a harder compound tire has a stiffer sidewall or different carcass when really the main difference is that a harder compound is exactly that. It's harder and tends to move around less on the actual carcass giving the feeling of a stiffer carcass or sidewall. Keep in mind that the stiffer set up could also cause chatter.
The rear tire should be run in a range from 25-29psi. The tire may start to spin and feel greasy above 30psi.
Ideal pressures for sprint racing tend to be around 26psi Hot! The chasis may need some work if the tire feels squishy to the rider at these pressures but set up and correct it. Keep in mind that the squishy feeling of a soft pressure will go away as the tire builds heat and the pressure rises during a session or race.
Kevin Graham
Orion Motorsports Inc
U.S. Mid West & Canadian Pirelli Racing Distributor
 

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FastForward Performance
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And all the times I was chastised because I said I used off warmer pressures as a starting point...You want the tire to work at it's optimum ON TRACK, so why not use that pressure and temp as the goal. I don't know how many times I was told I was nuts for sending a bike out with a hot pressure of 18 because my target pressure was 21 on track.
When Michelin was courting us for sponsorship and we were testing, they actually got pissed at me when I told them I could care less about cold pressures. I will set a cold tire at 40# just because of the fact it will heat up faster than 30#, then adjust to an off warmer temp that you have calculated will get you close to the desired on track pressure....
 

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Discussion Starter #14
Sounds about right for my front, but not so for the rear

I usually go with 28F and 26R cold, and this has always allowed me to get +5 +5 consistently, or sometimes +6 if it's hot out there or during aggressive (but not actually faster) laps.
My mech set the rear higher for me as that somehow helps me to conserve tyres (using two R to one F). I'm not sliding or spinning significantly anyhow, so, that's more grip that I can fully utilize anyways.

Sepang is bloody hot, ever watch an F1 or motogp race here? All the interviews will have at least a question or two about heat.

Guess it's really convey here if how fast is really "fast" or "slow".
I'm on average 10+ seconds faster than the average trackday goer, 5 seconds slower from a privateer supersport who regularly races, and 10+ seconds slower than the fast regional racers (the guys in the Asia Road Racing Championship).
Motogp time is almost 2mins flat, I'm 26 seconds away on my little 600 :(



<bet we'll see on-the-fly tyre pressure monitoring/adjustment systems in a few years!>
 

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And all the times I was chastised because I said I used off warmer pressures as a starting point...You want the tire to work at it's optimum ON TRACK, so why not use that pressure and temp as the goal. I don't know how many times I was told I was nuts for sending a bike out with a hot pressure of 18 because my target pressure was 21 on track.
When Michelin was courting us for sponsorship and we were testing, they actually got pissed at me when I told them I could care less about cold pressures. I will set a cold tire at 40# just because of the fact it will heat up faster than 30#, then adjust to an off warmer temp that you have calculated will get you close to the desired on track pressure....
I agree...cold pressure doesnt mean squat. Pressure off the warmers means a bit more when it's hot out. Cold ambient/track temps will cause a much higher amount of pressure rise. When I worked for Gobert at Laguna last year we set the pressures on HOT warmers exactly where Dunlop suggested and got +8 PSI rise and he came back in about 5 PSI over optimum. The ambient temps were colder at race time than they were all weekend, the wind was blowing harder and the sun wasnt warming the track...it was a big difference and def hurt performance.
 

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"The Dude abides .. "
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And all the times I was chastised because I said I used off warmer pressures as a starting point...You want the tire to work at it's optimum ON TRACK, so why not use that pressure and temp as the goal. I don't know how many times I was told I was nuts for sending a bike out with a hot pressure of 18 because my target pressure was 21 on track.
When Michelin was courting us for sponsorship and we were testing, they actually got pissed at me when I told them I could care less about cold pressures. I will set a cold tire at 40# just because of the fact it will heat up faster than 30#, then adjust to an off warmer temp that you have calculated will get you close to the desired on track pressure....
the trouble with off warmer temps are the variables.. How long were the tires on the warmers, how HOT did the warmers get, are they high wattage or lower wattage (as that affects the rate of warm up), how windy was it (sucks heat away), how cold was it outside (same issue), etc. etc. etc.
it's way easier I personally find, and as michelin has stated for years, to use a cold temp for most riders. A psi +- is NOT gonna affect most riders. Faster riders can then look for off track temps to fine tune the cold temps. Sure, you can also throw in some warmer temps for good measure, just have a set routine of how long they ware on, what temp is used, etc. I find that way too much trouble though.
As the day gets warmer, you may need to bleed off 1-2psi. the power Cup michelins (and hte power 1 for that matter) i like to see about 34psi off track front/26-28psi off track rear.
 

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"The Dude abides .. "
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I agree...cold pressure doesnt mean squat. Pressure off the warmers means a bit more when it's hot out. Cold ambient/track temps will cause a much higher amount of pressure rise. When I worked for Gobert at Laguna last year we set the pressures on HOT warmers exactly where Dunlop suggested and got +8 PSI rise and he came back in about 5 PSI over optimum. The ambient temps were colder at race time than they were all weekend, the wind was blowing harder and the sun wasnt warming the track...it was a big difference and def hurt performance.
yes.. it does. See my prior post. Any of the Gobert brothers are not exactly the majority of riders. It is much easier and will be IN THE BALL PARK to set cold pressures and ride. Faster riders, and those that are capable, can fine tune with off track temps.
Off warmer temps can be inconsistent, but do what works for you..
 

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In short...JMO...cold and off warmer pressures are reference only, otherwise totally useless. There is ONE pressure that matters and that is the on track pressure. Cold and hot temps will vary as stated, but the goal is to do whatever it takes to maintain an optimum on track pressure where the tire works the best for the rider.
Cold and hot pressures are affected by many outside variables including ambient temp, warmer effeciency, etc. All this changes once the tires hit the track. If the tires work at a certain pressure on track, you do whatever it takes to maintain that pressure. JMO
 

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"The Dude abides .. "
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In short...JMO...cold and off warmer pressures are reference only, otherwise totally useless. There is ONE pressure that matters and that is the on track pressure. Cold and hot temps will vary as stated, but the goal is to do whatever it takes to maintain an optimum on track pressure where the tire works the best for the rider.
Cold and hot pressures are affected by many outside variables including ambient temp, warmer effeciency, etc. All this changes once the tires hit the track. If the tires work at a certain pressure on track, you do whatever it takes to maintain that pressure. JMO
totally agree. The difficulty is finding a method that will accurately get you to the desired on track temp.. You must have a starting point. If you ride the same tire all day, this is not a huge issue. You can simply adjust a couple times when you come in and head back out. Real trouble is racing, where you are using more than one set of tires throughout the day.
Both methods must work to some degree. Tire engineers for Michelin AND other brands do not agree on how to set, yet there are riders going very fast on both tires, using both cold tire psi starting points AND off warmer psi.
:)
 

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Having pretty extensive amount of laps on that tire, you hot pressures are too high not allowing the carcass to flex. The SC's turn in FAST. 31 HOT off the track is what I've found favorable. Your high pressure isn't letting the carcass flex enough causing cold tearing that is amplified by a damping issue as well from what I see man.

Additional preload can effect rebound as well. You should try to gradually engage the brakes so you don't run throught the fork travel.

Whats your weigt and front spring rate on the bike so we can deterime if you have a chance to eliminate this front dive without messing up your damping a bunch.

Are the tires and rim heat soaked completely before you gpo out? If not, that could be why you get a huge rise in pressures from cold to hot as well.5 psi in the front is a pretty high % of the overall volume in the tire.

In short...JMO...cold and off warmer pressures are reference only, otherwise totally useless. There is ONE pressure that matters and that is the on track pressure. Cold and hot temps will vary as stated, but the goal is to do whatever it takes to maintain an optimum on track pressure where the tire works the best for the rider.
Cold and hot pressures are affected by many outside variables including ambient temp, warmer effeciency, etc. All this changes once the tires hit the track. If the tires work at a certain pressure on track, you do whatever it takes to maintain that pressure. JMO
+100000000
 
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