PDA

View Full Version : "Fun" with tyres (tires). Should I recap it?



The Bigfella
12-06-2009, 08:23 PM
I do an annual "tour" with some mates that have similar or identical cars. This involves a day at a racetrack and a whole heap of back roads in interesting parts of the country. This year we were back to Winton Raceway and also some back country roads in Australia's Alps.

I had a pair of old "R" Spec tyres that I wanted to use.... very old, 1998 manufacture in fact - and yes, I know that old rubber is dangerous. I'd been beaten by a quarter of a second at Winton our last time there by a car using R spec tyres, whilst I was on pretty crappy street tyres.

I didn't use these old tyres on the road, but fitted them to the front of my old 1990 BMW M5 for the track session. They made a huge difference compared to normal road tyres... a lot more grip. I had reasonably good road tyres on the rear... 255 x 40 ZR17 Dunlop SP Sport Maxx - a bit over $450 each here. They held up pretty well until towards the end of each session.

The fronts were good.... until towards the end of my 4th track session. My front left threw its tread at 170 kph (about 106 mph) when I hit the brakes at the end of the short straight. Wow..... very interesting few seconds.... but fortunately the corner at the end of the straight is a left hander and that wheel is unweighted. If the right tyre had blown it would have been a different matter.

Here's the tyre....

http://i240.photobucket.com/albums/ff112/igatenby/iansecond/tyre1.jpg

http://i240.photobucket.com/albums/ff112/igatenby/iansecond/tyre2.jpg

I was totally through the first layer of steel belts and into the second layer in parts. The tyre must be close on 3" larger in diameter where it blew the tread, compared to where it didn't.

It blew at point X in the photo below.

http://i240.photobucket.com/albums/ff112/igatenby/iansecond/esses.jpg

Point Z is there to mark what happened at the start of the day. The last car to come in from the session before our first one hit the ripple strip there.... he bounced hard, his right rear wheel broke off and he rolled - the first flip being 10' or more up, down hard on his roof (lots of flying glass at that stage) a couple more flips until he ended up back on his remaining wheels. His wheel came straight at me (I was first in line to go out onto the track) but was stopped by the concrete wall.

Paul Pless
12-06-2009, 08:25 PM
255 x 40 ZR17skinny little things:p;)

The Bigfella
12-06-2009, 08:37 PM
Hey Paul.... there was a brand new Nissan GTR there.... and I nearly had "a moment" with it. I'd have loved to have had it for a few laps...

I could keep up with him through the back section of the course, which is all about corners and cornering.... but every time he got to a straight bit, he pulled a lot of distance on me. I reckon I could have pulled 10 seconds out of his lap time... and its a short course (I was doing 1:50.5's). He blew past me on the straight but I braked 30 metres after him.... and he stuffed up his braking and over-braked big time. I was within a micro-second of "going bush" to avoid him. I ended up going through the esses at least 30kph slower than normal.

I really, really want a drive of one.... I hope that whoever he was, he gets enjoyment out of it and gets to know how to wring it out properly.

btw - my new Brembo 4-spots are fabulous.

Ross M
12-07-2009, 10:30 PM
Good to read the brake upgrade was worthwhile.

Care to hazard an estimate of the time period between noticing something odd and clear awareness of failure?

Ross

Garret
12-07-2009, 10:37 PM
Care to hazard an estimate of the time period between noticing something odd and clear awareness of failure?

Ross

I know it wasn't addressed to me, but....

Isn't that directly related to speed? faster = quicker
Then to experience: less = quicker
Then to cost: more = quicker
Then to parts availability: less = quicker
Then to beer: quicker = more.

Just a hypothesis mind you....

The Bigfella
12-07-2009, 11:13 PM
I noticed the steering wheel off centre the lap before it blew and should have called it quits then I guess, but I had the bit between my teeth and was trying to set a fast time. The off-centre wheel would have been due to the bulge.

I should point out that I fully expected these tyres to fail... but not to this extent. I had 6 of these tyres originally, and had 4 on for last year's track day. I noticed a problem as I came in from my second session last year, with the car pulling to one side... and found a bulged tyre. I didn't do any more runs that day and had the two fronts replaced immediately. One of the rears failed later - and I threw the other rear away as well.

This tyre was one of the remaining two - and had never been fitted to a car. I should point out that heat is a real enemy to tyres and it was a hot day - and after I blew the tyre, I had some difficulty changing the fronts. The wheel bolts were too hot to handle. Maybe it wouldn't have blown without the heat soak - who knows? Either way... I had a great day's fun.... and no children were harmed.

Bob (oh, THAT Bob)
12-08-2009, 01:12 AM
WWWWEEEERRRRRR*shift*WEEEEEEERRRR*shift*WEEEEEEEEE EERRRRR*brake*>CHUNK<WHAPWHAPWHAPWHAPWHAPWHAPWHAPWHAPWHAPWHAPWHAPWHAPWH APWHAPWHAPWHAPWHAPWHAPWHAPWHAPWHAPWHAPWHAPWHAP. whap. whap.