Problems with Dunlop D212 gp racer slick rear

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bmwbadboy

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Hi

I'm running a new rear Dunlop D212 GP racer slick medium compound at Silverstone today. It's not a warm day, outside temperature is +17-19.
I'm running 21psi after warmers as Dunlop tire warmer guide suggests.

After 2 sessions on track the tire looks like this.

Rear rebound and compression are 0.

Any ideas what is causing this?
63409d4bfb39984877d5cf4f455a38cf.jpg
9374258fabcb22c2a85c3738eb8fa99f.jpg


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I had problem with Dunlop before yes, that was due to incorrect pressure, I ran it 4psi too much.

This time, nothing changed, correct pressure and it got destroyed...
appologies if not you but someone just been on with dunlop problems,,

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I'm in fast, doing around 1:02 at Silverstone National circuit.

Need to double check the gauge...
well im thinking suspension even more as 2 in a row ? the gp isnt even a full on kr slick and is a little more forgiving to a not perfect set up its mullered that one, if you dont mind the ask what sort of pace you on fast , middle, lower ?

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1. It's Hot Tear, too little pressure, add 2psi on the warmers, whatever the gauge says.
2. The Endurance rear would probably be better in the UK's cooler conditions.
3. Change only one thing at a time.

I thought you paid a yearly subscription? Did you reverse the once per year payment to revert to standard?
 
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Checked
is your gauge accurate
Checked the gauge, it's correct.

Just finished the another session. Tire after warmer: 20psi. Tire after track (same minute): 21psi


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I tried one session with +2-3psi, it didn't change the wear pattern.

I'm looking to get a harder compound.

Something didn't work in payment, PayPal rejected after 2days. Let redo it.
1. It's Hot Tear, too little pressure, add 2psi on the warmers, whatever the gauge says.
2. The Endurance rear would probably be better in the UK's cooler conditions.
3. Change only one thing at a time.

I thought you paid a yearly subscription? Did you reverse the once per year payment to revert to standard?

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I'm 84kg no gear, I guess with gear 88-89-90.

Again, if I trust 2 suspension guys: A&S racing at donington and 100% at Caswell, sag and rear rebound are set correctly.

What do you weigh kitted up?

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I assume the track is clockwise all right handers?

You may need to add 3psi, reduce rebound (-1) and increase compression (+1) to get the weight off the rear then. But you'll also have to look for signs it's switched to cold tear... can you flip those tyres? I can't remember.

But ultimately I think it's the wrong tyre for the conditions.
 
Correct. All right handers, except one but it's a short left that goes into a long/fast right hander.
I assume the track is clockwise all right handers?

You may need to add 3psi, reduce rebound (-1) and increase compression (+1) to get the weight off the rear then. But you'll also have to look for signs it's switched to cold tear... can you flip those tyres? I can't remember.

But ultimately I think it's the wrong tyre for the conditions.

So what I've done, I reverted back to 20psi after warmers as the manual says. Did 2 more sessions, here how it looks now.

A bit better, no?
218063fe397a9ec56077415a9a03cdc5.jpg
9da99ee268fb610fa9a464de49dfc8a0.jpg


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Yep I was going to say go lower, you did a bloody good job cleaning that up really. Looks f**ked now anyway, i'd not do out on that any more!!!
 
What happened to the track temps?
If the carcass was cold but the top was being overworked it could cause what you saw.
There appear to be centrifugal flow lines which is hot tear, but maybe it was cold carcass with too little TC tearing up the surface.

Endurance carcass holds temp more consistently for colder days. Medium probably needs 30+ degree track temps (that 'fact' needs checking).



- Alex
 
i didnt know you could get the correct sag with DDC

Sag is entirely dependent on the spring rate and preload.
The only things to be aware of when altering preload with DDC is to ensure the ignition is switched on prior to taking measurements and that following any preload adjustment the DDC is re-calibrated
 
yeh when I had mine the max I could get was 8mm if i remember,

I?m a bit of a heffer lol, so don?t have issues getting sufficient sag with the OEM springs.

Have you switched to a cartridge kit and shock, or have you sold your RR?
 
I assume the track is clockwise all right handers?

You may need to add 3psi, reduce rebound (-1) and increase compression (+1) to get the weight off the rear then. But you'll also have to look for signs it's switched to cold tear... can you flip those tyres? I can't remember.

But ultimately I think it's the wrong tyre for the conditions.

What happened to the track temps?
If the carcass was cold but the top was being overworked it could cause what you saw.
There appear to be centrifugal flow lines which is hot tear, but maybe it was cold carcass with too little TC tearing up the surface.

Endurance carcass holds temp more consistently for colder days. Medium probably needs 30+ degree track temps (that 'fact' needs checking).

Let me reply on all items,

Silverstone National is a clockwise track with all right handers (except one, that is very short). There are 2 right-handers where you exit flat out with TC kicking consistently (I run -5 in slick mode).

Unfortunately I didnt have pyrometer with me, so can't say anything about the track temp. Ambient temp went up from ~13-14C in 1st session to about 19C towards the end. The track was a bit wet in morning (no rain, but it was misty and humid), and it dried up towards lunch time.

I did try to run 2-3psi higher after 80C warmers during 3rd session, but that didnt make any noticeable effects on the rear's wear. Towards the close, I ran 2 sessions at Dunlop's recommended pressures for D212 - 20psi after warmers, and the wear got better.

So all in all, I suspect you're right, this tyre is not right one for today's conditions, especially in the morning. Although, I didnt play with rear's rebound/compression settings as you wrote above, didnt have time unfortunately.
 
I have read it again and maybe my armchair opinion is wrong.

My initial view was hot tear because of the shape of the tearing the way it pitched to the centre. But hot tear just isn't as deep as cold, its more of a disturbed surface than a destroyed one.

If you can get a nail or flat screw driver under the rubber and lift them then thats more likely cold too.

So although its not easy from the mobile screen I think there are more factors going cold tear.

What to do.
1. never run LESS than the recommended minimum pressure.
2. If you are at the minimum and still cold tearing, you can try weighting the rear to get more heat into it. Slow the rebound (+1) and speed up compression (-1). Slowing the rebound keeps the rear compressed in the corner and keeps the weight on it. Speeding the compression lets it get to that point in the stroke faster.

FWIW, I run +2 rebound and +0 compression and am closer to 90kg without kit. OEM spring. Dave Moss confirmed that was the right move (extra rebound) after I trashed a Power RS on a cold Snetterton.




- Alex
 
I have read it again and maybe my armchair opinion is wrong.

My initial view was hot tear because of the shape of the tearing the way it pitched to the centre. But hot tear just isn't as deep as cold, its more of a disturbed surface than a destroyed one.

If you can get a nail or flat screw driver under the rubber and lift them then thats more likely cold too.

So although its not easy from the mobile screen I think there are more factors going cold tear.

What to do.
1. never run LESS than the recommended minimum pressure.
2. If you are at the minimum and still cold tearing, you can try weighting the rear to get more heat into it. Slow the rebound (+1) and speed up compression (-1). Slowing the rebound keeps the rear compressed in the corner and keeps the weight on it. Speeding the compression lets it get to that point in the stroke faster.

FWIW, I run +2 rebound and +0 compression and am closer to 90kg without kit. OEM spring. Dave Moss confirmed that was the right move (extra rebound) after I trashed a Power RS on a cold Snetterton.

Thanks, Alex! I will try playing with rebound next week at Donington.

Re: cold tear

another guy who was in my group ran Superbike SC1 yesterday. He started the day from 24psi after 80C warmers and had been doing fine until after afternoon when the track warmed up to decent temperature. In last 3 sessions of the day, his rear developed a definite cold tear - a thumb-sized strip of tear on right side (same as I had last week at Donny). At the same time, mine rear seemed to clear up...

I tend to think it's just a wrong compound for morning cold track conditions. Possibly I could have compensated this by your suggested suspension settings.
 
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well that doesnt make sense because the warmer it gets the better softer pirellis work the only softer one is a zero, so sc1 should work better as it gets hotter i think all this hot / cold tear is a possibility but again to me its suspension, you cant tell rebound by pressing up and down, yes its a starting point but tyre wear is a good indicator , suppose you could leave the shagged tyre on for your next session go plus 5 reb then minus5 reb see what difference it makes, or move to kr slicks, or vo2
I guess what I was trying to say about Pirellis is, the guy had them overinflated and it worked just fine in morning when it was coldish, but as soon as the track temp went up, his tire got a cold tear...

I got an interesting view/advise from another forum, is to try to run higher pressure in morning when its cold and drop it down as track heats up to manufacture's recommended.

Basically the bottom problem, I was too slow in morning and couldn't generate enough heat in the tire whilst running recommended pressure.



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