Off-Course Excursions - FINDINGS

[RaceProEngineer]

As a final contribution, we have some results from a recent informal polling of track drivers’ off-course adventures.

The impetus for this study came from a very disturbing “trend” which we noticed at the track this summer, and which was too imposing to simply ignore. More about that later.

We were primarily interested in 911 episodes, level of track prep, driver experience, tire choice, track condition, circumstances of mishap, and extent of damage. We had 29 drivers respond. The exact number of incidents is impossible to pin-point, but a fair guess is between 65 and 90. Of these, GREAT NEWS: only 6 resulted in extensive damage, and not a single one was caused by anoher car!

EDITORIAL COMMENT: Porsche drivers are obviously very refined at car control, even while spinning!!

A full 70% of the cars involved (including two 944es) had extensive track preparation, and most were older, and normally aspirated.

Tire choices included Dunlop (5%); Goodyear (2%); Hoosier (2%); Kumho (35%); Michelin (25%); Pirelli (5%); Toyo (5%); and Yokohamma (20%).

Only a couple novice drivers responded, and the rest were divided with twice as many intermediate as advanced. Predictable, the advanced drivers reported more “offs”.

Track conditions were predominantly warm and dry, with 5 offs reported in rain, and 2 due to oil on the track.

We were surprised to discover only 3 mechanical failures resulting in spins, and 2 from oil. All the remaining were attributed to general “driver error”. And this is an area which we would like to explore.

EDITORIAL COMMENT: From several years of track experience, various cars, all sorts of conditions, we believe that incidents are caused by (1) mechanical failure, (2) treacherous track conditions (3) another race car(s) transgressions, (4) driver error, or some combination of these. There is also a 5th cause, much more difficult to define, usually afflicting advanced drivers, which we call “inconsistant behavior” (for lack of a better phrase). Granted, a broken spindle, oil on the racing line, another car spinning in front of us are all “inconsistant” in the sense they are surprising, but the phenomonon we are considering is far more clandestine and insidious, hidden WITHIN the car and its equipment.

Several of our respondents used the words “sudden”, “unexpected”, “violent”, “out of nowhere”, “for no apparent reason”. These were not novices describing the tail-happy nature of our 911es, but experienced guys with lots of track saavy, depicting unexplained loss of grip! It was obvious most of these drivers agonized over these events, analysing and re-analysing; often digging for any explanation; evaluating how to handle it next time. Some of these same gentelmen simply chalked their incidents up to “driver error”, but a close look at the data is somewhat more revealing: ALL BUT ONE respondant describing our “sudden lack of grip” phenomonon had ALL these traits in common:
- Light weight 911
- Extensive track preperation
- Experienced to Advanced driver
- Dry track, good visability
- Kumho (various compounds) OR Michelin Pilot Sport Cups

Statistical fairness: Unfortunately, we have no data telling us what percentage of ALL Porsche tracked cars are lightweight or heavily prepared. Likewise, we do not know what percentage use Kumhos or Michelin Pilot Sport Cups, or what percentage of the time these tires might be used. It would have been a better base of data if we had 200 respondants. Likewise, we would have liked a higher percentage of actual racers to draw from.

Nevertheless, in our little study, Kumho (a couple of compounds) and Michelin Pilot Sport Cups were in use in 60% of the total incidents reported, yet every single account alluding to sudden lack of grip also mentioned these model tires, in varying sizes, as part of the equipment.

We solicited extra input from sources we thought might contribute a broad spectrum of information, and add a touch of scientific rigor. These were all Pelican, and included Chris S., Jack O., Wil F., and Bill V. Thank you for their time, and considered opinions.

CONCLUSIONS:
While we were certain we saw a very disturbing “trend”, our goal was to determine if it was just happening locally, or more universal. We attempted to ask the questions in such a way as to make responses unbiased. We also wanted to be careful about naming or blaming any equipment, especially without concrete stats.

Collecting data is of nebulous value without puting it to use. Our sincere hope was (and is) to provide a few cautions to drivers of certain 911es, with heavy track preparation, using certain equipment. Chris has suggested that we “spell it out” for everyone to see. While that is certainly very tempting, we think it best to present the facts we have found, and let the board draw their own conclusions.

[304065]

Thanks for taking the time to compile the study, Ed. My own experience with Kumhos and Yokohamas supports your findings.

[Chuck Moreland]

Ed, very interesting. We do need to be carefull drawing conclusions, statistics can lie like a used car salesman. We could slice the stats to paint any picture desired.

As a suggestion, it would be very useful to correlate the incidents with the popularity of the tire. ie. Kumhos are overepresented in your findings, but they are also the most popular DOTR in my informal observation. One would expect them to be involved in more incidents.

Show it is at "incidents per unit sold". I realize you may not have access to that information, but it really is critical to meaningful conclusions.

It may also be useful to breakdown the Kuhmo results by model: ecsta v700 and victoracer.

The sample size is also very small with the less popular tires, making conclusions involving them very difficult.

The one point that does stand out to me is the Hoosiers. These are popular tires that are clearly underepresented in your results at only 2% invlovement.

I am also surprised at the Michelin at 25%. Again my informal observation is that this is not a popular tire that seems overepresented in the incidents.

Again, good info. I personally would love to see it correlated.

[dtfastbear]

These findings are pretty timely for me. I was instructing in an extensively prepared early 911 with MPSC tires a couple weeks ago at Sears Point. The tires felt very strange to me (even in the passenger seat) and I told the driver that I thought the tires were either severly under-inflated or just plain heat-cycled out. He dialed it back to about 60% aggresssion - I was in the process of telling him we should just go in to the pits. We were going through turn 10 (a very dangerous, medium-high speed turn) and the back end just "suddenly, out of nowhere" stepped out. We ended up about 2 feet from the tire wall.

He made no sudden inputs to either the steering or pedals.

The tires ended up being fine pressure-wise, but they had been through waaaay too many heat cycles.

I wonder if we can ask those who responded with Kumho or MPSC tires to say how many events were on the tires. I know that when I used to use Kumho victoracers, my wife and I could get exactly 6.5 track days with both of us driving before the rear tires would very suddenly become about as slippery as cat snot. The fronts would give up about a session later...

Dean

[Chuck Moreland]

As a thought, perhaps a poll asking "what tire do you use at the track" would get at least a ballpark percentage popularity of a given tire. This would not be cars involved in OTEs, but all tracked cars. That info could then be correlated.

[armandodiaz]

I didn't contibute to the poll, but in my last DE my front tires (Kumho 712) would not grip out of turn 6 @ Moroso Speedway in Florida. I finally had to track out into the grass in order to straighten out. My car: 85 Carrera no modifications but had a serious deit (all extras taken out).
I had 12 30min sessions up to then. The rears I have Goodyear F1, no fishtailing at all. My next set of tires will be the BF gForce.

my 2c

[Zeke]

Originally posted by Chuck Moreland
Ed, very interesting. We do need to be carefull drawing conclusions, statistics can lie like a used car salesman. We could slice the stats to paint any picture desired.

As a suggestion, it would be very useful to correlate the incidents with the popularity of the tire. ie. Kumhos are overepresented in your findings, but they are also the most popular DOTR in my informal observation. One would expect them to be involved in more incidents.

Show it is at "incidents per unit sold". I realize you may not have access to that information, but it really is critical to meaningful conclusions.

It may also be useful to breakdown the Kuhmo results by model: ecsta v700 and victoracer.

The sample size is also very small with the less popular tires, making conclusions involving them very difficult.

The one point that does stand out to me is the Hoosiers. These are popular tires that are clearly underepresented in your results at only 2% invlovement.

I am also surprised at the Michelin at 25%. Again my informal observation is that this is not a popular tire that seems overepresented in the incidents.

Again, good info. I personally would love to see it correlated.

All good points, Chuck. Just what I would expect from you, a very professional and educated analysis of what appears to be some statistics brought together for a "conclusion."

My comments are obviously going to be suspect due to what I've said in another thread which, more or less, puts me at odds with Ed. However, this survey needs a lot more work to be meaningful to me.

In light of all this, what does anyone think of Toyo RA1's?

[ted]

Originally posted by Zeke
what does anyone think of Toyo RA1's?

I went through two sets this year, just ordered another.
Muy bueno, great DE or practice tire and the prices seemed to have dropped a little too.
http://www.frisbyracetire.com/toyo_proxes_ra1__spec.htm

[Zeke]

I'm sold. Ordering today.

[dtfastbear]

Toyo RA1's are awesome. Not the same ultimate grip as some other tires (Hoosiers, obviously. I believe even Kumhos have a little more grip) However, there are three things about them that make them my tire of choice:

1) They are VERY predictable to drive and have stable characteristics through the entire temperature range. If they are too cold, they just aren't quite as sticky. If you get them too hot, the get a little greasy. nothing weird like the MSPC.

2) They wear like iron. They can be run on the track with full tread, so if you are more worried about tire life than that last tenth of a second, don't bother to shave them. They won't chunk. One caveat - you need to run them a couple hundred miles on the road before taking them on the track so they'll release all the remains of the chemicals that lurk in there from manufacture. If that isn't an option, get a super thin enduro shave...

3) They absolutely, positively WON'T heat cycle out. The last lap before you cord the tire will be the fastest lap that tire gives you. With a two driver car, this is probably the biggest selling point.

Have fun.

Dean

[Plavan]

Raceproengineer- Great work on putting this together.
This is good info to read and digest, its not good info to base a tire decision on. The info is not perfect as Chuck has pointed out.
I deal with statistical medical studies (p= value .05) every day. I look at this study design and see data of a very small sample size with unrealized tire popularity. Again, nice data to look at being a "clinical" guy. However, this data has too many variables for making an informed decision on tires based on this study design.
I understand you have to analyze what data you get. In all fairness, the study would have to be on a much bigger scale to derive real world findings.
Then again, there is no such thing as a "perfect" study.

I'm not knocking your motivation or drive. I think it is great info. Just be careful of "your" conclusions

[ChrisBennet]

Originally posted by armandodiaz
I didn't contibute to the poll, but in my last DE my front tires (Kumho 712) would not grip out of turn 6 @ Moroso Speedway in Florida. I finally had to track out into the grass in order to straighten out. My car: 85 Carrera no modifications but had a serious deit (all extras taken out).
I had 12 30min sessions up to then. The rears I have Goodyear F1, no fishtailing at all. My next set of tires will be the BF gForce.
my 2c

I thought the BF Goodrich GForce has been out of producation for a few years. Are they getting back in the game?
-Chirs

[cstreit]

Chad,

I definitely know, and so does Ed, that there is not a real strong statistical case here. I spoke with him at length about this when he started it, particularly because of my rather strong feelings about a particular tire that I feel is mis-marketed resulting in potentially hazardous consequences used outside the parameters where it is effective.

However Ed has shown true professional restraint as to no massage statistics to support a subjective conclusion.

I know what I know and have made it clear on this public forum in the past. For those interested, search this forum for the tire brands that I have posted about.

Kudo's to Ed for compiling this information.

Chris

[armandodiaz]

Originally posted by ChrisBennet
I thought the BF Goodrich GForce has been out of producation for a few years. Are they getting back in the game?
-Chirs

You might be referring to the Comp T/A
From Tire Rack:

http://www.tirerack.com/tires/Sizes.jsp?make=BFGoodrich&model=g-Force+T%2FA+KD+SSS%2Cg-Force+T%2FA+KD&partnum=25YR5GFTAKDL&partnum=25YR5GFTAKDR&vehicleSearch=false&index=0&fromCompare1=yes&orgTireModel=g-Force%20T/A%20KD

If memory serves me right from another thread, I believe Jack Olsen is loyal to these.

[ChrisBennet]

Originally posted by armandodiaz
You might be referring to the Comp T/A
From Tire Rack:

http://www.tirerack.com/tires/Sizes.jsp?make=BFGoodrich&model=g-Force+T%2FA+KD+SSS%2Cg-Force+T%2FA+KD&partnum=25YR5GFTAKDL&partnum=25YR5GFTAKDR&vehicleSearch=false&index=0&fromCompare1=yes&orgTireModel=g-Force%20T/A%20KD

If memory serves me right from another thread, I believe Jack Olsen is loyal to these.

That link doesn't work but I looked again and I think I know where I got confused. BG discontinued their G-Force track tire but they still make a G-Force street tire. Since we were talking about track tires I didn't think of the street version.
-Chris

[armandodiaz]

From my understanding, the GForce is the closet (grip) there is for a street tire to the R compond. Anytime I mention going to an R compond people start lecturing me why it's better to stick with the streets. Personally I like the idea of not having to shave or heat cycle them. Maybe as I start acquiring more rims shaving and heat cycling won't be much of a hassle.

[cstreit]

FWIW I don't shave the Kumhos V700's. THough I wonder if unshaved last any longer than shaved...

[addictionMS]

also for the DE guys, unshaved Toyo RA1s will last forever, I have gotten an entire summer of many many weekends out of a set. I did not have a job, so as you can guess if there was a track day, I was there. And we have four tracks within reach of my home, so I was a busy boy

Jim

[armandodiaz]

Quote from the Tire Rack (in their description):

Important Notice: Kumho ECSTA V700 tires must be shaved to 3/32" - 4/32" tread depth for any autocross or track use in the dry.

Kumho advises that the ECSTA V700 DOT-legal competition radial must be shaved prior to use in dry conditions. If this tire is not shaved, excessive wear may occur causing the tire to wear to the cords prematurely in a localized area.

Tire heat cycling will not prevent the excessive localized wear of full tread depth tires but will continue to enhance tire consistency and wear on shaved tires.

The ECSTA V700 should only be used at full tread depth (6/32") for wet track and wet

[chrisp]

Very interesting read. It would be nice to get some opinions from tire engineer-types.

Keep in mind most DOT-R tires are street tires on steriods. The Hoosier is probably the most like a racing tire. DOT-R tires don't heat cycle like true race tires do. It's my understanding that it's less about the # of cycles and more about time within the temp range. For this reason using # of cycles as one of the statistics may be creating inconsistent or skewed results. Again a tire engineer who is familair with these models could shed more light.

I have put over 25 DE days on a single set of Victoracers. This would equate to over 100 "heat cycles". I never experienced anything along the lines as mentioned above. But, my car doesn't have some of the other defining criteria listed above. Also worth noting, approx the first 1/3rd of their life I was at 85% of a "competitive" lap time, approx the second 1/3rd at 90% and the final 1/3rd at about 95%...with "competitive" being a PCA sprint race average lap time for my class of car (I don't race but it's similarly set-up)

This is a great study and a good start to something hopefully more comprehensive. I commend you for undertaking it.