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Discussion Starter #1 (Edited)
Hey gurus, I need some advice please.

Running a Pirelli SC2 slick. **Edit: its a 200/60 on my '11 zx-10R. Ohlins rear shock, Kyle link.
heat cycle 1: from fresh mount 15 laps in 3 sessions, 28 psi hot, 2:02 to 1:59's at Thunderhill wear looks good
heat cycle 2: 7 laps at 60 psi (had the tire mounted to a new wheel and forgot to set the pressure: rookie mistake) surface was melting off, then 14 laps at 28 psi hot, 1:59-1:57 lap times, wear looks good
heat cycle 3: 10-12 laps, 28 psi hot, unknown lap times but probably 1:59 to 1:57, notice the tear and assume its a cold tear
- drop to 27 psi hot, run 6/8 laps, still see the tear
- drop to 26 psi hot, run 6/8 laps, not getting any better, I took all the attached pics at this point. Turn 6 is the fast acceleration left hander, and I felt the rear spin and grip in repeated sequence


- work on smoother throttle application to not punish the tire out of the corner, but at this point the wear dots are gone and the damage is done. Thunderhill is super hard on the left side. The uneven wear grooves make me think it's a geometry/suspension induced tear? Is it a hot tear because I can't get a fingernail under the peal?


SO, did I just use up the tire and that's what happens when you run this pace with them? Do I need to switch to the SC1? Is there something about my suspension that needs to change?

Thanks :thumbsup::helmet:
 

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There are soooo many variables that need to be answered to troubleshoot your problem. But lets see if we can narrow it down.

You mentioned in the beginning you were running sub 2 min laps and didnt have a problem. The first thing that comes to mind is what was the ambient/track temp when the tires didnt tear vs when they did? If there was a drastic change temp throughout the day this could be your issue and pressure wasn't set for the conditions. Also when you came off the track how did warm/cold did the tires feel?
 

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Discussion Starter #3
I figured it was a bit of a crapshoot, but can't hurt to ask right?
ambient temp on Sun was 90-95, not sure on the track temp. I was running 1:57-1:59 and didn't see any unusual wear. Other than the melting when I raced on it for 6 laps inflated to 60 psi.
Yesterday ambient temp was 90F, and I would guess the track temp was the same.

Both days the tires felt hot coming off the track, but not burn you hot, I'd guess somewhere between 160-180F. 140F I can hold my hand on all day, tires were hotter than that. I know that;s not super useful data and I should get a tire probe for the future.
 

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Discussion Starter #5
Sunday 90-95 was the peak ambient temp. The morning started out cooler, maybe around 75? and got hotter as the day went on. It was partly overcast.
Yesterday the peak ambient temp was 90. It seemed to get hotter earlier in the day compared to Sunday and it was sunny all day.

I'm going off memory here, and I generally don't pay attention to the weather too much. Sounds like I need to start doing a better job of that.
 

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Sunday 90-95 was the peak ambient temp. The morning started out cooler, maybe around 75? and got hotter as the day went on. It was partly overcast.
Yesterday the peak ambient temp was 90. It seemed to get hotter earlier in the day compared to Sunday and it was sunny all day.

I'm going off memory here, and I generally don't pay attention to the weather too much. Sounds like I need to start doing a better job of that.
Yup, sounds like that's probably your issue. At 75 your pressures were probably good, but as it got warmer those pressures weren't correct. We've seen swings in temps so much here in the midwest that in the morning 1 compound is need and then you have to switch to another in the afternoon.
 

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I dunno that's an odd wear pattern. Almost pressure related looking or maybe a rebound too slow by the rhythmic pattern. What did you run the pressure at?
 

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Well, 60+ laps is a lot of laps on a liter bike.

The wavy look to the tear pattern makes me think it's a suspension issue (rebound too slow? spring too soft?) but with 60+ laps on that tire grip will be falling off so it's not working properly.
 

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So you're saying I should switch to the SC1? Thanks for talking things through with me. I appreciate it.
No not at all. Im just saying you'd be surprised how much can change in a single day and they are just things to be cognizant about. I would start with pressures and go from there. It sounds like you're going in the right direction, you just may not have gone far enough.

While others have mentioned suspension/geometry, there are clues that would lead me to believe to start with pressures. You mentioned in your first two sessions you didnt have any problems. Then later you saw the tearing. Your times are about the same from session 2 to 3 and one saw tearing, the other didnt. Suspension will not change like that without adjuster changes. So the only thing that changes would be ambient temp as the day continues (which you have kind of confirmed).

So whats with the weird pattern? You actually mentioned the answer. Turn 6. The the wide part of the shark tooth shape is the initial loss of grip and shreds the tire. Then as grip comes back the rip narrows til you have control again.

I just looked at the track map (never been to TH) and it mostly being a left handed track Im leaning more and more towards pressure.
 

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https://www.youtube.com/watch?v=VURa84Tmzjk Race video from Sunday, before I started getting the bad tire wear
Looks good! But if I may I'd like to make a few suggestions.

First, you're leaving too much room on the insides of the turns. If you watch, most of the riders passing you are on the inside, this is no bueno. You want your knee down running in the grass. This does two things, first it forces them to go outside and run an unnatural line when trying to pass. And second you can use this to push guys wide if needed when fighting for position.

Second in certain corners you're getting too swoopy. Obviously you want to use the whole track, but sometimes you dont need to. Here's a perfect example; jump to 8:15, there are two guys ahead of you. The guy in front goes waaayyyy out to right and then cuts in, the guy behind takes a tighter line. Notice when they exit the turn the one in front didnt make any gain on the guy behind. By being too swoopy he added more ground to cover. They do the same thing at 10:00 except the rider behind uses the swoop to his advantage and passes him.

And last turn 9 going down the hill. When you go through turn 9 you complete the turn pulling almost all the way to the left side of the track then have to pull back to the right going down the straight. If you drift out a little bit at the exit of 9 to the right and hug the kink it automatically sets you up for 10 and you shorten the distance between the two turns. Obviously with crest there it may be hard, not sure, but ultimately you want to straighten out that kink as best as possible. One thing we do is walk the track and look back through a turn and see how to straighten it out. So go out past the kink and look through the kink to the exit to turn 9. You might be surprised how straight you can take it.
 

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Discussion Starter #15
Yes, my inside apexing needs some work. This is exactly what I did on Thursday is go to a trackday an focus on hitting my apexes. I also, worked on my exits. Turn 1, at 8:15, and T14 at 10:00 are both huge exit corners, so the fast guys, use the whole track to set up for a better drive out of those corners, and especially at T1, if a guy goes up the inside there's a 90% chance they'll get passed back on the exit.

I was/am struggling with getting the bike to turn without over-slowing in some places. My plan was to drop the forks 2mm to give me some quicker steering.

T9 has been a tough one for me because it's blind, and I've tucked the front there before. On Thursday I worked on keeping my eyes up and using a reference point for the exit so I can accelerate sooner, carry a wider radius, and use the inside toward the kink as you described. I was dropping down to 3rd during the races, but I found on Thursday that if I stay in 4th I get a better drive because it doesn't want to pick up the front wheel as bad. Plus, tightening my core as I transition the bike helped me keep the front end only come up 1ft instead of 3.
 

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Yes, my inside apexing needs some work. This is exactly what I did on Thursday is go to a trackday an focus on hitting my apexes. I also, worked on my exits. Turn 1, at 8:15, and T14 at 10:00 are both huge exit corners, so the fast guys, use the whole track to set up for a better drive out of those corners, and especially at T1, if a guy goes up the inside there's a 90% chance they'll get passed back on the exit.

I was/am struggling with getting the bike to turn without over-slowing in some places. My plan was to drop the forks 2mm to give me some quicker steering.

T9 has been a tough one for me because it's blind, and I've tucked the front there before. On Thursday I worked on keeping my eyes up and using a reference point for the exit so I can accelerate sooner, carry a wider radius, and use the inside toward the kink as you described. I was dropping down to 3rd during the races, but I found on Thursday that if I stay in 4th I get a better drive because it doesn't want to pick up the front wheel as bad. Plus, tightening my core as I transition the bike helped me keep the front end only come up 1ft instead of 3.

I noticed you wheeling over the crest so I could see how turn 9 is a bitch. As for the turn in before you drop the forks lemme ask you a couple questions.

When you have problems with turn in, is it on the throttle or on the brakes? Also where in the turn (entry, apex, exit) are you having problems with turn in? And you mentioned Ohlins shock, whats on the front? And what springs are you running front and rear?
 

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Discussion Starter #17
Im struggling getting the bike to turn mid corner to the apex. In most corners I carry the brakes until I have the direction.

Front is stock forks, stock springs. Rear was sprung for my weight (215) with gear, its marked L1213 if that means anything?
 

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Im struggling getting the bike to turn mid corner to the apex. In most corners I carry the brakes until I have the direction.

Front is stock forks, stock springs. Rear was sprung for my weight (215) with gear, its marked L1213 if that means anything?
Pull out 2 turns of preload (counter clockwise). You have too much trail in the front which is pulling you wide on entry. What you have found is by riding the brakes it compresses the forks taking away trail dynamically. Pulling out the 2 turns will allow the forks to sit lower in the stroke and effectively doing the same thing as you riding the brakes. BUT it will allow you to carry more corner speed since you dont have to use brakes to modulate the front end.

If you find that you are bottoming after pulling the two turns out THEN drop the forks and put the two turns back.

As for the rear spring there should be a 5 digit code, then a - and a 3 digit code. The 3 digit code after the - is the spring rate in NM. So it will probably say 100 or 105
 
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