BMW M3 Forum (E90 E92)

BMW Garage BMW Meets Register Search Today's Posts Mark Forums Read


Go Back   M3Post - BMW M3 Forum > E90/E92 M3 Technical Topics > Wheels + Tires Sponsored by The Tire Rack
  TireRack

KEEP M3POST ALIVE BY DOING YOUR TIRERACK SHOPPING FROM THIS BANNER LINK!
Post Reply
 
Thread Tools Search this Thread
      09-30-2009, 07:58 AM   #23
lucid
Major General
 
lucid's Avatar
 
Drives: E30 M3; Expedition
Join Date: Apr 2007
Location: USA

Posts: 8,034
iTrader: (0)

Swamp, buddy, nobody said a worn out tire will not lose traction. Actually, everyone seems to agree on that although there are different potential explanations although one factor that is obvious is hardening. (I did say that less tread would be more responsive, but that's different). However, if you read your OP, you didn't say anything about the fronts not being worn out (the 7/32" F - 2/32" R situation you did have). The way I read your OP, all of your tires were worn out with only about 2/32" difference across them. If anyone is in such a situation (worn out tires with 2/32" wear difference), I would give them the same advice: to put the tires to rest during a track day with the note that they might have less traction overall, which requires one to drive accordingly (which both Ben and I pointed out). If one wants to be fast, obviously one should be on new/shaved tires, and has also been brought up several times.

Then there is the part about what significant difference in wear F/R does to the balance of the car--if the balance would be significantly altered. My experience with seriously worn out fronts vs OK rears on PS2s was manageable. Your experience with worn out rears vs well treaded fronts seems to have been not so manageable. Since "manageable" is a subjective term, we most likely will not agree on this, but the fact is understeer is often easier to deal with than oversteer, and this car has plenty wtq that it can easily come around you at track conditions (lateral + longitudinal loads @ high speeds) regardless of the tires you are on. If I had driven your car on the track that day, would I have shared your opinion on the altered balance? Maybe yes, maybe no. No way to tell.
lucid is offline   United_States
0
Reply With Quote
      09-30-2009, 09:22 AM   #24
attila
Lieutenant
 
attila's Avatar
 
Drives: 2011 GT3RS, 2010 MX-5, 2009 M3
Join Date: Dec 2008
Location: Omaha, NE

Posts: 526
iTrader: (0)

I have somewhat the opposite experinece than the OP with my PS2s. I keep them as wet tires for track. Not too long ago I had a wet day but the track dried up relatively quickly. I did not change to the BFG-r1s since I was about to leave in 2h so I kept the PS2 on.
It's hard to compare but I clearly had the impression that they did better than on my first two track sessions, when they were new. My PS2 are not badly worn but not new either. I did not feel any change in balance and could feel very well when the tail was about to step out. Indeed better than with the BFG-R1s. I do not use MDM now, but I did on my first few track sessions with the PS2's and even with the BFG-R1s. Maybe that explains the difference, I am not sure.
attila is offline  
0
Reply With Quote
      09-30-2009, 12:01 PM   #25
swamp2
Lieutenant General
 
swamp2's Avatar
 
Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

Posts: 10,201
iTrader: (1)

^Sounds not too relevant to my OP since I am talking about extremely worns rears with fronts worn but in good shape.
swamp2 is offline   United_States
0
Reply With Quote
      10-01-2009, 07:33 PM   #26
Dascamel
Lieutenant Colonel
 
Dascamel's Avatar
 
Drives: 2008 e92 M3, 2010 e91 328i
Join Date: Jul 2007
Location: Bakersfield, CA

Posts: 1,662
iTrader: (0)

Swamp my tires are almost the same situation as yours. Almost no tread on he rear and with the fronts being med-low.

With regular street driving, hard s-4, s-5 shifts I can break traction, but before this would almost never occur. The tires feel far worse as they got older. I spent the entire second day becoming an expert on throttle control through almost every corner. Tire pressures became a issue, tried all sorts of combinations before leaving them at stock pressures cold.(which worked best....) Anyway, nearing the wear bar doesn't seem to work best on PS2s.

Just had some Hankook V12s mounted($750 after rebate on tirerack shameless plug), feel good so far, lets see how they handle extremes.
__________________
2008 E92 M3 Jerez Black,DCT,Fox Red ext,Prem,Tech,19", ipod/usb, CF roof and trim
2010 E91 328i Space Gray,Black int, M sport, most options
2007 Montego Blue 335i (retired)
Dascamel is offline  
0
Reply With Quote
      10-02-2009, 01:30 AM   #27
swamp2
Lieutenant General
 
swamp2's Avatar
 
Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

Posts: 10,201
iTrader: (1)

Quote:
Originally Posted by Dascamel View Post
Swamp my tires are almost the same situation as yours. Almost no tread on he rear and with the fronts being med-low.
...
The tires feel far worse as they got older.
...
Anyway, nearing the wear bar doesn't seem to work best on PS2s.
Thanks. Glad to hear a nearly identical experience (not that it was a good experience...). As I mentioned I have had the same experience on previous tires only on the street. I should have trusted my experience as I really had to take it easy cornering.
swamp2 is offline   United_States
0
Reply With Quote
      10-02-2009, 11:30 AM   #28
AMPowerJ
One mod leads to another ...
 
AMPowerJ's Avatar
 
Drives: 2013 E92 M3
Join Date: Apr 2008
Location: Blythewood, SC

Posts: 2,490
iTrader: (9)

Garage List
Not much to add here but I don't think the PS2 is the best street tire in terms of dry drip anyway. In my experience they lose traction with or without tread fairly quickly once they heat up. If you refer to Car&Driver's recent tire test that someone posted around here a few weeks back the PS2 actually was very good in wet weather but not near the top in dry grip.

To the OP did you ever track your car with your PS2s when they had more tread? It might be they just don't fit your driving style.
__________________

Current: 2015 F80 M3 (SS, Full Black Interior, 6MT, LED, Adaptive, 19's) - On Order - 10/28 PCD
Previous: 2013 E92 M3, 2013 F10 M5, 2009 E90 M3, 1998 E36 M3
AMPowerJ is offline   United_States
0
Reply With Quote
      10-02-2009, 01:07 PM   #29
swamp2
Lieutenant General
 
swamp2's Avatar
 
Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

Posts: 10,201
iTrader: (1)

Quote:
Originally Posted by AMPowerJ View Post
To the OP did you ever track your car with your PS2s when they had more tread? It might be they just don't fit your driving style.
No, older Michelin Pilots on another M.
swamp2 is offline   United_States
0
Reply With Quote
      10-03-2009, 12:30 AM   #30
lucid
Major General
 
lucid's Avatar
 
Drives: E30 M3; Expedition
Join Date: Apr 2007
Location: USA

Posts: 8,034
iTrader: (0)

Here is another perspective on this topic from "Going Faster", the Skip Barber manual, which I was reading last night.

On p. 199, after a brief discussion on tread and how it relates to chunking and overheating in dry conditions, he states:

"Shaving the tire not only reduces the temperature of the tire and eliminates chunking, but it increases the CF of the tire. Showroom stock tires are typically run at depths between 5/32" and bald. In our testing we have found that CF differences from 5/32" down are inconsequential."

So, that is some reference to some actual data arrived via testing. Although the details of the test are not provided, I assume they took new showroom stock (unhardened) tires and shaved them to different tread depths and tested their coefficient of friction. No references to specific tires brands are made, but the term showroom stock clearly means street tires in our lingo.

A few paragraphs down, he also states:

"A tire's grip deteriorates with time and exposure to ultraviolet light."

Prior to that, on p. 197, in a section titled "Street vs Slick", he also states:

"For the most part, a tire's rubber compound determines its grip. Pure racing tires are generally much softer than street radials since they have an intended life, at most, of a few hundred miles. Street tires that last over 40000 miles have become common, and that longevity comes from a harder, more durable rubber compound. What you gain in longevity you lose in ultimate grip. A secondary advantage of a harder compound tire is that its traction doesn't vary as much over the course of its life as it would for a pure racing tire."

Therefore, an r-compound tire should exhibit a much more significant drop in traction with time and UV exposure than a harder street tire, and not vice versa as the "track nuts" Swamp spoke with at the track claimed. What Skip Barber says is much more consistent with my experiences with street vs r-compound tires.

In conclusion, Skip Barber seems to be saying that traction of a street tire has very little to do with tread depth as long as the depth is not more than 5/32", but more to do with the duration of use and exposure to UV. There are more nuanced issues such as slip angles, but those are not particularly relevant to this discussion.
lucid is offline   United_States
0
Reply With Quote
      10-03-2009, 06:14 AM   #31
SenorFunkyPants
Colonel
 
SenorFunkyPants's Avatar
 
Drives: E92 DCT M3
Join Date: Mar 2009
Location: UK

Posts: 2,482
iTrader: (0)

That doesn't fully match my experience.
Firstly I'm never very happy with new tyres, the way that the tall tread blocks "lean" with lateral load makes them feel imprecise with a delayed reaction response to input.
I do find (in these tyre sizes) that they improve in feel and grip peaking around 4mm (don't know what that is in old school numbers) and then gradually fall off in performance as they approach the wear bars where the grip is most definitely less than at their peak.
I've run endless sets of tyres on my M3s over the last seven years and the pattern is pretty constant.
SenorFunkyPants is offline   United Kingdom
0
Reply With Quote
      10-03-2009, 08:07 AM   #32
lucid
Major General
 
lucid's Avatar
 
Drives: E30 M3; Expedition
Join Date: Apr 2007
Location: USA

Posts: 8,034
iTrader: (0)

There will obviously be a correlation between tread depth and usage time + IV exposure. Meaning, observing a correlation between tread depth and traction does not mean that the relationship is causal. The real cause is explained above as time and IV exposore, which I assume result in the hardening of the compound, with references to test results that negate the role of tread depth (as long as it not more than 5/32"). In other words, it seems like they have done the testing to prove that tread depth (as long as it not more than 5/32") is not a significant cause in the reduction in traction.

They say that tread depth comes into play as a significant cause only if you have more than 5/32" tread on a street tire, and yes, they are saying that you will indeed have significantly less traction if you have more tread than that on a street tire you are pushing on the track. (That was the reference to "chunking" and "overheating" in my previous post).
__________________
lucid is offline   United_States
0
Reply With Quote
      10-03-2009, 11:07 AM   #33
swamp2
Lieutenant General
 
swamp2's Avatar
 
Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

Posts: 10,201
iTrader: (1)

Calling a quote from Skippy proof is a bit of a stretch. Even saying there was any scientific approach to gather this information is probably a stretch. I would tend to trust what they write about track or race tires more than street tires as the author(s) surely have way more experience with track/race tires at the track.

We now have three folks here with the exact same experience with street tires. My observation of the effect is not subtle and just like SFP above I concur traction new is poor, after a short break in period until extreme wear the traction is relatively constant, finally resulting in markedly reduced traction. I suppose the observed reduction may be related to UV or other weathering/aging effects but I think it is unlikely. My reasoning for this is because folks tend to wear their tires in drastically different amounts of time. One would tend to not see the direct correlation between wear and traction if other effects were the causal ones.
swamp2 is offline   United_States
0
Reply With Quote
      10-03-2009, 02:33 PM   #34
lucid
Major General
 
lucid's Avatar
 
Drives: E30 M3; Expedition
Join Date: Apr 2007
Location: USA

Posts: 8,034
iTrader: (0)

The authors of Going Faster most likely know more about driving on any kind of tire on a race track than you, I, or anybody else on this forum ever will. You asked for test results, I referenced their test result. Now, you're saying they don't know what they are talking about and their tests are not scientific. The test procedures are indeed not documented, but I'll buy their test results over any "opinion" expressed here any time.

Moreover, they bring up street tires because they seem to have racing experience with them!

"For the Spec Racer and Skip Barber Formula Dodge 2000 series, there are multiple reasons for preferring street tires to slicks. Safety and durability are high on the list..."

I don't think they run street tires in any of their current series though. However, their Formula 2000 racing school cars are on street tires. So, your dismissal of their expertise is perplexing.

And, if you really think the opinion of the average enthusiast serves as proof that decreased tread depth decreases traction, there are two people here who reported no "major" issues with grip on PS2s at the bars, and we've got the guy I know who turned faster laps at LRP on PS2s at the bars that were stashed away for several years than he did before when they had more tread despite not so significant loss in traction. As I said, the "significance" of the loss of traction is a subjective consideration, so opinions will not establish much either way. What we are discussing is if and how tread might be related to the loss in traction (as in the title of this thread "traction vs tread depth"), not if there will be a loss in traction (we've been over that and everyone agrees hardening will decrease traction).

Skip Barber manual says time is a factor, but it also says the effect is primarily experienced up front--that there is a noticeable drop in traction after initial use and the effect of time then somewhat stabilizes. So, they are not claiming a linear relationship there.

The UV exposure is more straight forward. Cars that experience tread wear must, by definition, experience exposure to the elements unless one wears the tread down on a dyno in an insulated garage. So, if UV exposure (and compound hardening) is the cause, the tread depth correlation can indeed be meaningless for the most part.
__________________
lucid is offline   United_States
0
Reply With Quote
      10-03-2009, 03:18 PM   #35
Gearhead999s
Major General
 
Gearhead999s's Avatar
 
Drives: E93 335is(wifes)F82 M4
Join Date: Apr 2007
Location: Toronto

Posts: 6,718
iTrader: (0)

I guess I have to chime in on this subject.My PS2's have 31000 kms on them and they are at the wearbars.In the last week with the temps falling the grip has gone away big time on the street.I used them yesterday at Mosport when it rained and the grip level was no where close to what they had at my last wet trackday in the spring.New rear PS2's are going on next week as I am very happy with the PS2's as a normal street tire.
Gearhead999s is offline  
0
Reply With Quote
      10-03-2009, 03:22 PM   #36
lucid
Major General
 
lucid's Avatar
 
Drives: E30 M3; Expedition
Join Date: Apr 2007
Location: USA

Posts: 8,034
iTrader: (0)

Why does it surprise you that their grip went away in cold weather, and that they performed poorly in the wet with very little tread left? Even if you discount the cold weather, how do you know that it was the low tread that caused the loss in grip--if that is what you mean?
__________________
lucid is offline   United_States
0
Reply With Quote
      10-03-2009, 03:31 PM   #37
Gearhead999s
Major General
 
Gearhead999s's Avatar
 
Drives: E93 335is(wifes)F82 M4
Join Date: Apr 2007
Location: Toronto

Posts: 6,718
iTrader: (0)

Quote:
Originally Posted by lucid View Post
Why does it surprise you that their grip went away in cold weather, and that they performed poorly in the wet with very little tread left? Even if you discount the cold weather, how do you know that it was the low tread that caused the loss in grip--if that is what you mean?
I think it is a combination of heat cycling hardening the compound & lack of tread depth that does not allow any tread squirm which helps to create heat in the tire.When I have run in the PS2's in the past in the wet the tires have been steaming when I came in after a session and were drying because of heat buildup in the wet.Not this time!I even tried to build heat in them
Gearhead999s is offline  
0
Reply With Quote
      10-03-2009, 03:37 PM   #38
lucid
Major General
 
lucid's Avatar
 
Drives: E30 M3; Expedition
Join Date: Apr 2007
Location: USA

Posts: 8,034
iTrader: (0)

Quote:
Originally Posted by Gearhead999s View Post
I think it is a combination of heat cycling hardening the compound & lack of tread depth that does not allow any tread squirm which helps to create heat in the tire.When I have run in the PS2's in the past in the wet the tires have been steaming when I came in after a session and were drying because of heat buildup in the wet.Not this time!I even tried to build heat in them
Sure, in the wet, lack of tread depth will definitely result in drastic loss of grip, so no surprises there. The discussion so far has focused on dry grip.

Also, the Skip Barber manual claims that if you push a street tire with more than 5/32" tread hard on a track, you will weaken the bond between the tread and the tire body. So, if you have done that earlier (and I think you have based on your previous reports?), and if what they are saying is true, your tires had most likely already lost grip before you got to the bars.

Yes, tread squirm increases tire temps, which is normally not good for a street tire as it will overheat quickly, but when you run in the cold and on a wet track, that might actually indeed help.

Nice drift!
__________________
lucid is offline   United_States
0
Reply With Quote
      10-03-2009, 04:03 PM   #39
Gearhead999s
Major General
 
Gearhead999s's Avatar
 
Drives: E93 335is(wifes)F82 M4
Join Date: Apr 2007
Location: Toronto

Posts: 6,718
iTrader: (0)

Quote:
Originally Posted by lucid View Post
Sure, in the wet, lack of tread depth will definitely result in drastic loss of grip, so no surprises there. The discussion so far has focused on dry grip.

Also, the Skip Barber manual claims that if you push a street tire with more than 5/32" tread hard on a track, you will weaken the bond between the tread and the tire body. So, if you have done that earlier (and I think you have based on your previous reports?), and if what they are saying is true, your tires had most likely already lost grip before you got to the bars.

Yes, tread squirm increases tire temps, which is normally not good for a street tire as it will overheat quickly, but when you run in the cold and on a wet track, that might actually indeed help.

Nice drift!
I have never used those tires on the track in the dry only once before in the wet where they worked awesome.It has been my experience with new tires over 4/32 tread depth that they have to be shaved as by the time they get down to 2or 3/32's where they should work at their best the grip has already started to go away because of the heat cycling.By starting at the proper tread depth for track use you end with a tire that has a longer useful track life.
The grip on the PS2's have gone away quite progresivly over their life but the colder temps really pointed it out.
Gearhead999s is offline  
0
Reply With Quote
      10-03-2009, 04:07 PM   #40
lucid
Major General
 
lucid's Avatar
 
Drives: E30 M3; Expedition
Join Date: Apr 2007
Location: USA

Posts: 8,034
iTrader: (0)

Quote:
Originally Posted by Gearhead999s View Post
I have never used those tires on the track in the dry only once before in the wet where they worked awesome.It has been my experience with new tires over 4/32 tread depth that they have to be shaved as by the time they get down to 2or 3/32's where they should work at their best the grip has already started to go away because of the heat cycling.By starting at the proper tread depth for track use you end with a tire that has a longer useful track life.
The grip on the PS2's have gone away quite progresivly over their life but the colder temps really pointed it out.
Yes, if you want ultimate grip out of them on the track, it makes sense to shave them when new, which is what the Skip Barber manual suggests.
__________________
lucid is offline   United_States
0
Reply With Quote
      10-03-2009, 09:59 PM   #41
swamp2
Lieutenant General
 
swamp2's Avatar
 
Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

Posts: 10,201
iTrader: (1)

Quote:
Originally Posted by lucid View Post
The authors of Going Faster most likely know more about driving on any kind of tire on a race track than you, I, or anybody else on this forum ever will. You asked for test results, I referenced their test result. Now, you're saying they don't know what they are talking about and their tests are not scientific. The test procedures are indeed not documented, but I'll buy their test results over any "opinion" expressed here any time.

Moreover, they bring up street tires because they seem to have racing experience with them!

"For the Spec Racer and Skip Barber Formula Dodge 2000 series, there are multiple reasons for preferring street tires to slicks. Safety and durability are high on the list..."

I don't think they run street tires in any of their current series though. However, their Formula 2000 racing school cars are on street tires. So, your dismissal of their expertise is perplexing.

And, if you really think the opinion of the average enthusiast serves as proof that decreased tread depth decreases traction, there are two people here who reported no "major" issues with grip on PS2s at the bars, and we've got the guy I know who turned faster laps at LRP on PS2s at the bars that were stashed away for several years than he did before when they had more tread despite not so significant loss in traction. As I said, the "significance" of the loss of traction is a subjective consideration, so opinions will not establish much either way. What we are discussing is if and how tread might be related to the loss in traction (as in the title of this thread "traction vs tread depth"), not if there will be a loss in traction (we've been over that and everyone agrees hardening will decrease traction).

Skip Barber manual says time is a factor, but it also says the effect is primarily experienced up front--that there is a noticeable drop in traction after initial use and the effect of time then somewhat stabilizes. So, they are not claiming a linear relationship there.

The UV exposure is more straight forward. Cars that experience tread wear must, by definition, experience exposure to the elements unless one wears the tread down on a dyno in an insulated garage. So, if UV exposure (and compound hardening) is the cause, the tread depth correlation can indeed be meaningless for the most part.
The experience nor skills of the authors is not in question. Great driver however does not always equate to great observer. Drivers and racers probably do their fair share of perpetuatation of myths. Why might that happen? Fairly obvious - without the big bucks science/engineering behind really well funded types of racing this can happen. Come on you are a scientist as well, tell me that you haven't found something in this book that you are fairly certain is not correct? It is not gospel.

Next without looking at the book it is hard to say, but to call what they did as testing or scientific (as opposed simply to limited anecdotal evidence) is almost for sure a huge exaggeration. I will not set aside my observations and the identical observation of others herein without much stronger evidence than that.

I am really quite surprised you have not experienced the same effect. More have chimed in that they have (even discounting confounding wet and cold effects).

I am not sure what you mean in the your last comment. My point was this: tread wear depth and UV exposure will always be correlated but the level of correlation can vary dramatically. If you drive the hell out of your car with lots of track days and combine that with a less UV intense area vs. then consider opposite of all of those things I suspect you could go from an decided observation of UV hardening effects vs. nearly no effect from it.

Lastly the traction I am getting from your used rear PS2s is substantially better than my entirely worn ones. They are much more resistant to slipping and spinning and first and do not give nearly as much/as easy chips under WOT shifting.

Lastly I have never been claiming that traction decreases linearly with depth or something of the like. Perhaps that makes the title of the thread ever so slightly inappropriate to describe my observations. But I think I have made this point quite clear.
swamp2 is offline   United_States
0
Reply With Quote
      10-04-2009, 04:03 AM   #42
lucid
Major General
 
lucid's Avatar
 
Drives: E30 M3; Expedition
Join Date: Apr 2007
Location: USA

Posts: 8,034
iTrader: (0)

Quote:
Originally Posted by swamp2 View Post
Next without looking at the book it is hard to say, but to call what they did as testing or scientific (as opposed simply to limited anecdotal evidence) is almost for sure a huge exaggeration. I will not set aside my observations and the identical observation of others herein without much stronger evidence than that.

I am really quite surprised you have not experienced the same effect. More have chimed in that they have (even discounting confounding wet and cold effects).
I did not call their testing scientific or unscientific, so I did not exaggerate anything. I said, "that is some reference to some actual data arrived via testing". I even noted that their testing procedure is not documented in the book. I did say I will take their testing and driving/racing observations on street tires over anyone's opinion here. No need to reiterate why.

On the other hand, what makes you qualify their testing as "limited anecdotal evidence"? How do you know that they did not take CoF measurements in a somewhat controlled environment for instance since they are making a specific reference to "CF", a somewhat technical term, as opposed to grip or traction? These guys are not simply drivers, and the book is not simply this is how I drive fast. They run top notch driver training programs and racing series, and have access to resources a driver would not have. And testing a tire is not rocket science.

I don't think we are interpreting what they are saying the same way. My interpretation is that they are not saying the grip of a street tire will be roughly the same from 5/32" to no tread as it is consumed and wears out. That would not be a very meaningful test to run as there would be too many other variables. My interpretation is that they took a tire and shaved it to 5/32", tested it, shaved it again to a shallower depth, tested it, and so on. Or, they could have taken several new tires and shaved them to different depths below 5/32" and tested them. Then you can end up with some kind of grip profile vs tread depth without worrying about other effects. That question would be relevant to ask because you need to decide what depth you want to shave your tires to for optimal grip. Since they seem to be running street tires on some of their cars, it makes sense that they want to know the answer. And, they are saying they have not noticed a significant difference in that profile.

There is nothing that anybody has said in this thread that offers any evidence to the contrary since nobody has run such a test here. Gearhead999s has added nothing that disputes such an outcome. He just said that his grip has decreased progressively over the life of the tires. Fine, but again, that's not news.

Quote:
Originally Posted by swamp2 View Post
I am not sure what you mean in the your last comment. My point was this: tread wear depth and UV exposure will always be correlated but the level of correlation can vary dramatically. If you drive the hell out of your car with lots of track days and combine that with a less UV intense area vs. then consider opposite of all of those things I suspect you could go from an decided observation of UV hardening effects vs. nearly no effect from it.
Well, one could try those different conditions, and one would most likely arrive at tires with different traction levels, which is kind of the point, so I don't understand what you mean either. The really informative, but rather unlikely conditions are, you buy a new set of tires and wear them out in a very short period of time--say a week--without any significant UV exposure and compare that to what happens if you tracked them occasionally over a year or something. Apart from UV exposure, there is also the whole business of heat cycling that I haven't gone into as opinions vary greatly on that. And if you wear them out at the track with too much tread on, there is also the issue of overheating and chunking the tires, etc. Again, that doesn't help you pinpoint the effect low tread depth does or does not have on traction, and the reason we are discussing that is the inbalance in handling you reported with your car with different tread depths F/R.
__________________
lucid is offline   United_States
0
Reply With Quote
      10-04-2009, 06:49 PM   #43
cchan
Private
 
Drives: '12 F30 328i/'11 C2S/'04 GT3
Join Date: Jun 2008
Location: SF Bay, CA

Posts: 91
iTrader: (1)

For the sake of completeness, one other variable that has not been mentioned is alignment. Now, I personally doubt that swamp's (and Dascamel's) alignment changed over time, but it is technically a non-zero possibility since alignment specs were not taken before and after. Anyway, just for the record, since some cars are sensitive to small changes in alignment.

I agree with lucid regarding the Skip Barber analysis of tread depth, that it is based upon all other variables being held equal in terms of tire age, heat cycles, etc. Taller tread blocks=more squirm=less grip. And at this point in the history of motor racing, I would say this is a common knowledge fact, just like knowing that the earth is round.

When it comes to competitive racing, do you think race teams would shave their tires if it was only an "old wives tale"? No, they do significant testing and analysis to maximize performance and minimize lap times. I'm sure there were thousands and thousands of data points of lap times and data acquisition on very consistent and skilled pro/near-pro drivers. But it's not like all of these were collected and published in some scientific journal for public consumption as "proof". If shaving tires resulted in worse performance, I'm sure they would have stopped doing that. Or perhaps all the collective advice/wisdom of thousands of racers is just one big conspiracy plot to unjustly enrich the pockets of the Tire Rack and other companies that offer shaving services!
__________________
Golden Gate BMWCCA - Car Control Clinics
'13 C4S/'12 328i/'04 GT3
Past: '09 M3 DCT/'03 M3 SMG/'95 M3... missing an E30 I suppose...
cchan is offline  
0
Reply With Quote
      10-05-2009, 02:54 AM   #44
swamp2
Lieutenant General
 
swamp2's Avatar
 
Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

Posts: 10,201
iTrader: (1)

Quote:
Originally Posted by cchan View Post
For the sake of completeness, one other variable that has not been mentioned is alignment. Now, I personally doubt that swamp's (and Dascamel's) alignment changed over time, but it is technically a non-zero possibility since alignment specs were not taken before and after. Anyway, just for the record, since some cars are sensitive to small changes in alignment.
I seriously doubt this is a factor.

Quote:
Originally Posted by cchan View Post
I agree with lucid regarding the Skip Barber analysis of tread depth, that it is based upon all other variables being held equal in terms of tire age, heat cycles, etc. Taller tread blocks=more squirm=less grip. And at this point in the history of motor racing, I would say this is a common knowledge fact, just like knowing that the earth is round.
And they have possibly two data points maximum - new-ish tire vs. shaved to a constant depth? It is not inconsistent to have a new partially shaved tire exhibit more traction than a nearly new tire and yet have an extremely worn one have way less traction. So the observations myself and others have made are not really entirely inconsistent with the observations in the book.

Quote:
Originally Posted by cchan View Post
When it comes to competitive racing, do you think race teams would shave their tires if it was only an "old wives tale"? No, they do significant testing and analysis to maximize performance and minimize lap times. I'm sure there were thousands and thousands of data points of lap times and data acquisition on very consistent and skilled pro/near-pro drivers. But it's not like all of these were collected and published in some scientific journal for public consumption as "proof". If shaving tires resulted in worse performance, I'm sure they would have stopped doing that. Or perhaps all the collective advice/wisdom of thousands of racers is just one big conspiracy plot to unjustly enrich the pockets of the Tire Rack and other companies that offer shaving services!
Again, see my point just above. I would be a fool to argue against shaving tires to increase grip for many reasons; it is a generally performed and successful endeavor, it has theory on its side and I have no doubt there is plenty of data to support the procedure. However, one point making that not entirely "apples to apples" is that I am talking about a UHP street tires and shaving is generally done on dedicated track tires.

______________________________


Let me propose a thought experiment. If you could take a new set of tires, break them in just enough to get rid of their low traction upon being brand new, then do an instrumented skid pad test on it. Have preped in a que 10-20 or so identical sets of tires but shave them say 1/64"-1/32" at a time, mount set each successively and skip pad test them. My guess is that the traction vs. amount shaved will be basically a bump, it will increase for a while, peak and then decrease. It will undoubtedly decrease at some point - say when you hit cords. The question is will is decrease substantially before that point and will it decrease to a point much lower than the nearly new set? I think they will, once near or significantly into the wear bar and at the point when the tread pattern really fundamentally changes I think you will have already lost substantial grip. This is precisely what I believe many of us have observed. Sure UV/aging/thermal cycling etc. may also be contributing through confounding effects. Nonetheless, I think you simply must find this bump shaped curve (before cording).
swamp2 is offline   United_States
0
Reply With Quote
Post Reply

Bookmarks

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -5. The time now is 07:41 AM.




m3post
Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
1Addicts.com, BIMMERPOST.com, E90Post.com, F30Post.com, M3Post.com, ZPost.com, 5Post.com, 6Post.com, 7Post.com, XBimmers.com logo and trademark are properties of BIMMERPOST