Friday, March 19, 2010

Yokohama A048 & cold weather

Recently I've been dealing with a relatively technical issue surrounding my street tires, and their temperature requirements. Last spring when I deemed the factory original Yokohama AD07 tires to be nigh unto bald, and definitely unsafe in wet weather, I decided to replace them. A number of factors played into my decision. I definitely wanted to have a high performance tire, anything else seems a travesty on a lotus. I also was still thinking that I might still do some track days at NHIS and wanted something that would perform well there. I also wanted something that had at least minimal tread since I definitely planned to take it out on the road, not just racing.

In the end I decided to go with the "other stock tire." My vehicle has the lotus factory sport springs and dampers, installed after delivery, so the wheels and tires were not from the sport pack. The sport pack comes with a higher performance Yokohama A048 tire, which is basically a race compound tire setup with enough tread and durability to survive on the street. They definitely were not the cheapest option, but clearly would support me in a high performance driving situation. Basically, the decision was to run A048's on the street/track days, finish out the Kumho V710's and then buy Hoosier A6 tires for Autocross.

Through the summer I had no complaints. I never did go back to NHMS for a track day, but none the less had no regrets. The A048's give good grip on the road and their wide block tread gives the car an exotic look. One of the things I discovered upon purchase was that there was a sticker on the tire that warned "do not operate or store below 14 degrees F." That was a bit of a shock, but I have no plans to let the car out where it could get salt coated, or suffer an ice-induced skid. The latter was the fate of my Father's 1969 Lotus Elan. The elan traveled with the family for over 30 years in an state where it was always "going to be repaired" but never quite got there. I never saw it move except when pushed. I've promised myself that I won't repeat that mistake. I might make another, but driving my Lotus in ice and snow I will do my best to avoid.

The this past fall the Lotus was involved in a minor accident. Nothing serious, not even the hint of a possibility of anything other than cosmetic damage, but repair required removal and repainting. The removal uncovered additional cracking in the fiberglass, and eventually what I had anticipated to be a patch fill and paint turned out to be an entire clam replacement (covered in full by insurance thankfully. Hooray for Safety Insurance and my agents at Eastern Insurance!). None of this particularly bothered me since I had taken the car for repair with the intent of putting it directly in storage for the winter thereafter.

The problem however arises from the storage requirements for the tires. I had expected to have the car back in time to switch to the old stock tires, which I retained on the stock rims to be my "storage tires." The auto-body shop claimed they kept the car indoors all winter, and I believe them, but I saw the building when I went to check on it, and it appears to be unheated. I gave them my "storage tires" but I didn't think of it until after there were several single digit lows in our area this winter, so now I don't know how cold my tires got. To make matters worse when I looked over the tires, they seemed to have small horizontal marks on the flat rolling surface of the tread that might be cracks that I had heard referenced (but not described in any way) on the internet.

Since replacing the tires is a thosand dollar prospect, I spent hours trolling the Lotustalk forums, and the internet in general and found very little information on how to know IF your tires were suffering the effects of being over-chilled. I finally did what I should have from the start, and called the manufacturer. They referred me to Track Side Performance, I left a message, and one of their folks called me back. Here's what I learned:

If the tires have gotten too cold and cracking does occur it will be cracking in the side-wall/shoulder. Usually the tread face will not show a problem. The cracking will generally show up in the first few miles of driving the car, so the issue may not be visible until the tires are driven. He listed several things that are clearly cause for concern:
  • Any cracking that appears to expose lower layers of the tire
  • Any cracking over a half inch long
  • Any cracking in the inner side-wall or near the bead
  • Any cracking that runs along the circumference of the tire. This type of cracking changes the way the tire flexes, will get worse with time and can lead to failure.
If cracks are small and only running vertically the tires may still be OK. You can contact them and sent them pictures if there is doubt, and it is definitely not in any way guaranteed whatever you happen to deem as a small crack is at all safe. However, one thing he did point out is that marks on the flat tread surface that I was seeing are unlikely to be related to this problem, and some shops use dollies to move cars around and those sometimes create small marks running across the tread. Please Please Please remember this information is not to be considered authoritative, but based on a single phone conversation, and if you have any doubts get a professional involved. The fact that the crack is less than 1/2 inch and in the shoulder of the tire does not mean it's safe, it means that it might or might not be unsafe. In other words, if you have big or badly placed cracks don't waste your time investigating further, junk the tires. If they are small, and in the shoulder it might be worth further investigation.

We also discussed the changes to the tire rubber when it gets cold, and he said that getting the tire really cold had a similar effect as getting it really hot (heat cycling), both tend to harden the rubber, and permanently reduce grip. That's nicely consistent with the description of cracking that shows up after a little driving has flexed the cold-hardened rubber, so his descriptions seem to be internally consistent and I feel like I probably have found trustworthy advice at last.

So what's the verdict? Well, the marks I saw examining the tires in my basement probably aren't the problem so THAT is good. But I need to put on the A048's take them for a (SHORT!) drive and see if the cracking appears. I'll do that tomorrow...

2 comments:

Jill & Rupert Richardson said...

Great post. I've just dashed out and fitted my Yokos and warmed them up (carefully!), then checked them. No apparent problems, although they will have gone down to -10C over the past winter... (but stacked fitted to wheels, not on the car). I fear they may have hardened, though. Is there any way I can test hardness?

Gus said...

I'm glad you liked the article. I would be very careful with those tires. I recommend that you continue to keep a very close eye on them, and talk to the folks at yokohama racing if you have any doubts. I don't think it matters if they were on the car or not. The damage occurs from the temp, not the continuous pressure (although that can cause flatspots which is different problem).