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thewheelerZ

RS4 (and other tires) heat cycles

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14 hours ago, Team Infiniti said:

Sebring September and December will be the tell as we are going to be both buying another set of Hankook and recycling what is left over from this race.

 

Will be very interested to see your thoughts on the recycled tires. 

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3 hours ago, thewheelerZ said:

 

Will be very interested to see your thoughts on the recycled tires. 

I also plan on running my used tires in a session at my next test day, to see how the grip is as compared to a fresh set.

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As a followup, I don't really have any good data about the RS4s.

The first driver went out and was hitting good consistent lap times before doing something stupid and bending up the right front corner suspension.

He reported the tires were getting a little greasy as the ambient temperatures went up.

An hour later the clutch grenaded and we retired. 😞

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I went out first on our sticker RS4's at Indy and when I finally learned how to use the gas pedal got it into the 2:05's.  The next closest time was a 2:06.  When I got back in the car for the last stint, the track felt slicker for sure but I attributed that to track temps.  I got into the 2:08's before the axle snapped and ended our weekend, but I don't think I would of extracted much more.

 

We've run a 2 sets of RS4's for about 6 races and god knows how many HPDE's/Autox for a full year   The tires never got unusable but you could def tell they had lost a good bit of overall grip.  Yes I agree that the RS4 will get hard and lose grip way before they wear out or cord.  That being said I've found they don't fall off like RE71's (IE: Cord) and the time they take to lose enough grip that I would call them unusable is huge.

Edited by Jab31169
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On 7/26/2019 at 4:24 PM, skierman64 said:

How much did the track temp change?

Track warmed up, not sure how much.  But it was cooler on day two in the morning and we still had the same issue.

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9 hours ago, Jab31169 said:

We've run a 2 sets of RS4's for about 6 races and god knows how many HPDE's/Autox for a full year   The tires never got unusable but you could def tell they had lost a good bit of overall grip.  Yes I agree that the RS4 will get hard and lose grip way before they wear out or cord.  That being said I've found they don't fall off like RE71's (IE: Cord) and the time they take to lose enough grip that I would call them unusable is huge

We've run RS4s to the cord on the E30 in the summer with no significant loss of performance.  So, I'm not sure if it's the tire, or something else.  We overheated the diff on day 1, so I thought maybe that was it...But we had the same issue the next day with a new diff.

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10 minutes ago, zack_280 said:

We overheated the diff on day 1,

e30? Tell me more about what happened.

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47 minutes ago, Team Infiniti said:

e30? Tell me more about what happened.

E46.  I'm not sure what happened, but the lash was at the minimum tolerance (0.025")...And I built it in my garage and I probably am not qualified to do such work.  I'm guessing it was too tight on lash and when things started getting hot, it got worse.  But I guess it could have been something else.  I checked bearing pre-load for the pinion and carrier and everything was good.  I also checked the wipe pattern and it looked good.  The only thing that was questionable was the lash.  With the shims I had, it was either a bit loose or right at the edge of the tolerance. 

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Sounds like you did your research but it does take practice to feel like you are doing it right.

What fluid?

Did the problem resolve itself?

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And when you say overheated, what were the symptoms? Did it catch fire? Did it start slipping too easily? Did you get a temp reading on it? How hot is too hot?

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2 hours ago, enginerd said:

And when you say overheated, what were the symptoms? Smelled diff fluid, came in.  Did it catch fire? No. Did it start slipping too easily? Might have been slipping, but the slick tires made me think it was breaking loose, not diff slipping. Did you get a temp reading on it? IR gun showed 460 degrees F.  How hot is too hot?  Dunno, 300F seems too hot to me.

I was running Redline Shockproof gear oil.  The poly bushing did not appreciate the temps either.  Looked like candle wax running down the diff.

 

20190713_175016.thumb.jpg.737f972f59761a572cded7efa6cf871d.jpg

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2 hours ago, Team Infiniti said:

Did the problem resolve itself?

Sort of.  Replaced the diff.  No further diff issues, but the tires were still slippery.

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1 hour ago, zack_280 said:

I was running Redline Shockproof gear oil.  The poly bushing did not appreciate the temps either.  Looked like candle wax running down the diff.

 

 

Yea, you could smell the pungent odor of diff fluid for miles that day.  

 

giphy.gif

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15 hours ago, zack_280 said:

I was running Redline Shockproof gear oil.  The poly bushing did not appreciate the temps either.  Looked like candle wax running down the diff.

 

20190713_175016.thumb.jpg.737f972f59761a572cded7efa6cf871d.jpg

HOLY HECK! 460 degrees is ridiculously hot!

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I've driven some different vehicles on different tires. Kart tires put everything else to shame. When you come off the track and are in line for the scales, you'll hear and feel the tires un-stick from the asphalt if its been sitting for a little bit. Those tires are best on lap 2 or 3 of the very first heat cycle and are on a steady decline in performance with every heat cycle and day that they sit on the shelf not in a bag. After about 3 or 4 heat cycles, you might see up to a second of time lost per lap on a 40 to 50 second lap.

In cars, Hoosiers are pretty good. The biggest problem with those are the tread depth in that they will cord if you aren't careful. There is some drop off from new to old but not as much as others like kart tires.

200 tw tires feel like a paddle in the water. If you take a turn faster, more noise is made and the tire is heated up more. In most any tire that you'll drive, there is a sweet spot between going slowly and sliding. This spot is effected by the track temp and tire temp which is why you have to be careful not to overheat the tires sometimes. Based on my experience and other drivers I've talked to, this sweet spot is harder to find in the 200 tw tires than other race tires.

As for degradation, 200 tw tires are not bad. To be able to go 24hr on a single set is pretty good and I also think that heat cycling has little to do with a speed drop throughout the day. These tires are just round rocks compared to others. The speed drop is most likely that the air temp increased so you make less power. I remember a day when I drive at NJMP on the Lightning course that my top speed was found in the first or second session even though my apex speed of the last corner was higher in the later sessions.

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22 hours ago, zack_280 said:

E46.  I'm not sure what happened, but the lash was at the minimum tolerance (0.025")...And I built it in my garage and I probably am not qualified to do such work.  I'm guessing it was too tight on lash and when things started getting hot, it got worse.  But I guess it could have been something else.  I checked bearing pre-load for the pinion and carrier and everything was good.  I also checked the wipe pattern and it looked good.  The only thing that was questionable was the lash.  With the shims I had, it was either a bit loose or right at the edge of the tolerance. 

Most diffs I do spec 0.008-0.0012" for lash but those are for domestic V8s. Did you mean 0.0025" lash? I just checked and some specs say 0.0024" - 0.0055".

 

Biggest issue is usually the bearing preload, that builds heat if too tight.

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Adding my 2 cents since we were pitted with the Tirerack guys and asked for their professional opinions a couple times during the race.  We go back many years with a couple of the members and they were gracious enough to offer their input, being tire experts and all.  Also to note: this was our first time on the RS4.

 

All of our drivers reported the Hankooks felt slippery, moreso than we felt with Falkens and more than we expected.  Also notable was the feel of the tire; very difficult to tell when you were overdriving and almost impossible to detect brake lock,; easy to make them go greasy slick with a couple laps of aggressive cornering/sliding too.

 

Asked our neighbors, at least one agreed that the feel on the Hankook is suboptimal compared to other offerings (Falken and RE71R were mentioned) and that one can easily overdrive the tire and not realize it.  He did mention the tire is recoverable in that they will come back to you during a stint if you let them cool off.  I found our best time of the weekend by a lot on Sunday morning first stint with the same set we finished Saturday with.  Also did so on a lap I figured was way off pace as I was attempting to cool the tires back down after remembering the discussion from Saturday when things got greasy.  I know the adage slow down to go fast and have lived it many times, but this time seemed to be way more than that this time.

 

Wonder if the margin for overdriving is just so razor thin that you can heat cycle the tire out just over the course of a day's racing? Would be surprising but if it does indeed overheat and stop working and then come back to you over the course of a stint, might each instance cycle them sooner?  If one cannot feel when the tire is unhappy, could drivers trash the compound without knowing and without any visible sign on the tire itself? 

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5 hours ago, mender said:

Biggest issue is usually the bearing preload, that builds heat if too tight.

That's what I figured.  The pinion bearing was about 20 in-lbs.  It was hard to measure the carrier, but it was ~18-20 in-lbs.  IIRC both were on the low end of factory recommendations.  When it was all together, it was pretty firm to spin by hand, but not too hard. It felt similar to the diff I had a shop put together for me.

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7 hours ago, The Aero Man said:

The speed drop is most likely that the air temp increased so you make less power.

That would make sense, but we had 3 days on track. 

 

Day 1 (test day) - Hot, no drop in mechanical grip all day long. 

Day 2 - Also hot.  Noticeable drop in grip 3 or so hours into the race (felt like oil on track in a few of the slower turns), but diff was dying.  

Day 3 - Still hot.  New diff, still felt like there was oil on the track in some turns. 

Conclusion: Either the tires were dying or some suspension component was out of whack.  No abnormal tire wear noticed.  We did have a partially split front right control arm sleeve (see sleeve insert in pic below), but I don't think that would have had a major impact on alignment. Still have about 50% tread left.

Image result for bmw fca delrin bushing

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