Tire Durometers

In seeking a better tire management system I've seen tire Durometers that measure relative hardness of tires. Understanding it very subjective to the tire temperature during the measurement, I believe it could be utilized. Does anyone currently use a duromter in their tire management. The club Ford spec tires are Goodyear and Hoosier R600 series tires which are demoted after 10 heat cycles by many and for sale. My desire is track tire perfomance to durometer readings in a effort to maximize tire budget and evaluate true useful condition of used tires that have been " only drive on Sundays".

I just started this year using a durometer and tread depth gauge to try to chart the useful life of my Hoosiers.

I don't think my data are very useful yet (only three weekends). But I do expect to see a trend eventually.

(Just don't be tempted to use the durometer on your trailer tires. THAT's a scary comparison! )

Don't have personal knowledge of anyone using durometer testing on tires. Heat cycles is the key. Proper break in is also important. You should scrub in a set of stickers on a test day or during a race test session, being sure to put only several "hot" laps on them. Run a set of "sticker" tires in a 20 or 30 lap race and they could be junk for the next run. Also, heat cycles have to be counted both on and off the track. They are not counted in days but by cycles. You do 3 or 6 sessions during an open test day, that's 3 or 6 heat cycles, not one day on the tires. The tires will begin to harden with each cycle. Some competitors speak in terms of tires being weeks or months old. This is not relevent. What are the heat cycles? If you leave the tires on the car on an open trailer (to a lesser degree in an enclosed trailer) exposure to the sun (ultraviolet light) will harden the tires, not to speak of the fact that they can get very hot in the sun (heat cycle) even in an enclosed trailer. On the Club Ford Hoosiers that I run, I find that 8 to a maximum of 10 heat cycles are all that I can run them before the times drop off by a second or more a lap. Anything beyond the first or second heat cycle will produce a slightly lower lap time. Properly storing your tires between events can add life to the tires. Controlling heat cycles is the key. Also, while it may be a mind game, I've found that leaving the car in the sun between sessions seems to add to the tire life as it keeps the temps high and produces less of a heat cycle. If you keep the car in the shade or in a garage at the track, tire temps will drop lower and can "shock" the tire more when you go back out on a hot day. Here again, if you're through for the day early, put it back in the trailer or the shade. Just my $0.02 worth.

Don

I use a durometer, despite my tire guy's unwavering opposition to them. But I use it to check on the relative hardness of the fronts versus the rears. My rears tend to harden up quicker and while at first it is no problem adjusting for the ever lessening rear grip, eventually it's a real losing proposition.

Also, in order to get a reasonably good final number on each tire, it is necessary to take many readings across and around the tire and obtain an average. If you just test one spot on one tire you can forget about getting an accurate representation in terms of a durometer reading.

My opinion (probably worth nothing at all, but ...).

Don mentions above several conditions that lead to tires getting harder (cycles, sun light). I believe that that hardening can be measured with a durometer. I don't think a durometer is a super-accurate or highly reliable tool, but I do think it can be useful.

I've been fortunate enough to get decent used tires from a few different sources (I've purchased three (!) new tires in the last three years :). Since I'm never around for the first uses of the tires I obtain, I really don't know which ones are better than others. I've used a durometer (as Jim mentions - taking lots of measurements all over the tire) to get an idea of how good or bad used tires are.

I could be mistaken (I'm occasionally corrected and often learn a lot here), but I think that a set of tires with lower durometer numbers is going to provide more grip than a set with higher numbers. Is there a flaw in that thinking?

The flaw is that "softer equals more grip" is true only for some conditions. For a highly abrasive track in the middle of summer, a tire that doens't overheat may give more grip.

Good point -- that Law of Diminishing Returns rears its ugly head again.

But we can still use durometer numbers to at least predict the relative behavior of a set of tires, right? Just pick a harder set on a hotter day?

Here is some additional data from an autox perspective. I have a set of Hoosier R25A's first used in Sept 2001. Essentially one heat cycle and it was "mild" due to cool temps. Next used in May 2002 after being bagged all winter. Probably 4 to 5 heat cycles over two days. Tires got as hot as they ever do for autocrossing. Then tires stayed on the car in my garage (without bagging) for two years with only a couple of cold events which barely got them warm so no more than one or maybe two more heat cycles. Finally ran an event last weekend which got them fully up to autocrossing temp (hot and sticky). Duro'd them at 80 degrees in my garage a couple of days latter. Fronts and rears were both at 55 - 60 where my recollection is that new tires are around 50 to 55 at 80 deg. I happen to have a set of totally unused identical tires from about the same time frame (2001/early 2002) that duro'd almost exactly the same as the used set. Unfortunately I don't have a good way to compare the competitive performance of the tires in their current condition. However, the front/rear balance was "normal" (the car generally gets loose when the tires go off) and the tires felt/looked as sticky as I'm used to with fresh tires.

Dick

Thank you all that have replied and shared. Don, thanks for adding to discussion that we started at NHIS last weekend. I have also believed in "get them hot and keep them hot" theory and will rotate the cool side up every 1/2 hr. This keeps the pressures more stable and the tires are closer to operating temps when the car hits the track. I feel that my car is finally balanced enough to deserve fresh tires, my current set is 2.5 yrs old with 20 race weekends (6 dbls) and 10 test days. They still are grabby to the finger nail test when cold (poormans durometer). Thanks again!

Here's a reply from a trie guy. Durometers are not even part of our normal equipment for a race for a reason. The device measures surface hardness and does not tell you anything about the rubber under the surface. You can easily develop a " crust," that is harder than the rubber underneath. Once it gets scrubbed off you might have a totally different tire than you thought. You would be much better off keeping records of your use of the tire to develop a trend analysis. Even our engineers don't use a durometer very often. When asked they will tell you that it is not an accurate tool for all the above posted reasons. Good luck, Dennis....