Trashed rear tire

[TMC Customs]

Slow time of year for the track section of this forum so I figured there may be some people on here able to help me think through my tire wear issue (I read the sticky).

I completely destroyed my rear tire during customer appreciation day at Mid-Ohio. It was about 55 degrees and windy and I had tire warmers which were having trouble keeping hot in the wind (they are very old).  The tires are Michelin Power RS and I have had good performance out of them in the past.  I normally run them around 28 psi but I had them at 24 for the cold temps.  I didn’t get the chance to get any lower on the pressure because the tires were ruined before I could go out again. 

The pictures look to me like the worst cold tear I have ever seen but looking around at other riders who were not using warmers, they were not having this problem so I thought it could be suspension related.

I attached a picture of my sag numbers.  I was thinking either my suspension was too soft and not letting the tire get up temp (only felt warm to the touch when I got off the bike) or my rebound was too stiff (16 clicks out on stock TTX shock).  The other option would be to just get a better set of tire warmers but it just doesn’t feel like that was the issue.

Both the front and the rear suspension was refreshed last year.  The bike is a ’14 D675R

[MSerfozo]

I'm not a track guy but I AM a Michelin guy.  I worked at Michelin for 6 years  in the '80s & '90s but we only made car tires in the US.

I'm on my 2nd set of Power RSs and they've been great for me.  I know that Michelin recommends MUCH higher pressures for that tire for street use.  I run 38 psi.  

I have run Michelin Power tires of all flavors exclusively for 15 years.  I have found that when I run pressure too low, the tire seems to squirm more and wears quickly - in my case the middle "flat spots" from my highway commute.  Higher pressure seems to hold the carcass in a "rounder" shape and prevent the squirming and flat spotting.

Almost all of your damage is at FAR less than full lean so it looks like the tearing happened from acceleration coming out of turns.  

I would recommend higher pressure but that might not give you the track response you want.

[Tonik]

15 hours ago, TMC Customs said:

I normally run them around 28 psi but I had them at 24 for the cold temps

Why lower in the cold, I would think you would go higher in the cold so they will get up to pressure as they heat up. Or are you running them lower so they will get hotter and grip better against the cold pavement? Honest question, I don't know...trying to learn.

[Uncle Punk]

My guess is hot tear. I think your pressures are too low for a street tire. You don't need warmers for those tires. Those tires should let you run an easy 1:42 at Mid-Ohio without warmers and more pressure than you are using.

 

 

 

 

Edited December 28, 2020 by Uncle Punk

[TMC Customs]

10 minutes ago, Uncle Punk said:

My guess is hot tear. I think your pressures are too low for a street tire. You don't need warmers for those tires. Those tires should let you run an easy 1:42 at Mid-Ohio without warmers and more pressure than you are using

 

 

 

In the Dave Moss video you posted, my tire looks almost exactly like what is at 2:30 which he says is a geometry cold tear.  One thing I do when I get off the bike after every session, is I put my hand on the tire to see how warm it is.  If I can comfortably leave my hand on their, it is not up to temp.  With this tire wear, I would put my hand on the tire and it barely felt warm.  i think with hot tear, your tire carcass needs to be somewhere near 200 degrees.

[TMC Customs]

1 hour ago, Tonik said:

Why lower in the cold, I would think you would go higher in the cold so they will get up to pressure as they heat up. Or are you running them lower so they will get hotter and grip better against the cold pavement? Honest question, I don't know...trying to learn.

In theory, when you lower the pressure, you increase the surface area of the tire on the ground and increase the heat generated into the carcass. It may also allow the carcass to flex more which generates heat. I suspected I had cold tear which is when the carcass is not hot enough so I lowered the pressure. 
 

The left side of my tire gives a better idea of what may be cold tear, geometry issue, too hard rebound setting, or all of the above. The right side of the tire is destroyed beyond telling what happened so I am mostly focused on the left side. Check out the Tire Wear Guide under “Track is Crack” it has a lot of good information to start.

[motocat12]

 

[TwiztedRabbit]

the lower tire pressure does increase patch but only really increases  outside carcass temps  it doesnt  allow the heat to generate to the  core or throughout the tire ..  your pressure was too low and yes.. that was cold tearing  because there may have been heat but not the right heat so it cold tears... this is directly from  race tire techs from michelin  you should have maintained pressure if not raised it a psi or too.. 

thats why tires feel like they are sliding on hot days when they have too much pressure.. they are actually getting too hot.. they lower the psi to "cool" the tire

[durk]

1 hour ago, TwiztedRabbit said:

thats why tires feel like they are sliding on hot days when they have too much pressure.. they are actually getting too hot.. they lower the psi to "cool" the tire

Thanks for the schooling 

[TMC Customs]

@motocat12

Yes, this is exactly it.  STG suggested staying above 21psi on the rear tire, which I did but what I am reading on the reddit you posted and several other locations is that this tire just cannot handle a high track pace which seems to be confirmed by Michelin.  The tire is basically tearing itself apart at the connection point between the two compounds and looking exactly like a geometry tear.  I found a few instances of this in some of Dave Mosses videos and he basically said the tire was not matched to the riders pace.

[TMC Customs]

@TwiztedRabbit

I agree with you that this is a type of cold tear and I know you are a very experienced racer/track rider but your explanation on tire pressure vs temperature doesn’t sound right or I am misinterpreting what you are saying.  The only ways for a tire to independently get heat is by either absorption, flex, or friction.

The larger your contact patch, the more absorption you will get from a hot track but the more you will lose from a cold track.  This would be far offset by the flex in the carcass generating heat and this is the single biggest thing to generate an even heat throughout the carcass of the tire because it comes from the inside of the tire rather than the outside in.  The more tire pressure you have, the less contact patch you have and the less you will absorb. The less pressure you have, the more your tire will flex which will generate heat.  To some extent, the less pressure you have, the more contact patch you will have but there is a limit and when you hit it, your contact patch will get smaller because the carcass will bend between contact points in a concave shape drastically decreasing your contact.  So what I am saying so far is, less pressure=more heat throughout the tire.

The last way to get heat is friction.  So long as you are not sliding, the reactive force of friction on the contact patch and the heat generated would be independent of tire pressure meaning you will generate the same amount of heat energy.  The smaller the contact patch, the smaller area you have to absorb the same amount of heat (for example; If you add the same amount of energy to a soda can as you do a garbage can, one will feel noticeably cooler).  Adding a significant amount of heat to a small area will heat it faster than it can be absorbed by the rest of the tire and will cause the contact patch to start to peel away (cold tear).

Where I think your information may have come from is a very hot track.  If the track is very hot, your tire may be absorbing heat faster than it can dissipate to stay at its ideal operating temperature.  That would be a tricky situation to balance.