Time attack beetle

[Humble]

2012 autox #2

I was racing in the afternoon, in the very last group this time. That worked to my advantage since I didn't get my new tires in time for the autox and the heat would help me. The weather was perfect in the mid 60's F (17-18C) and I loved cruising out with the windows down. The course was a weird one and didn't work well for 2nd gear, but had a lot of short sprints. I have so much power in 1st gear it's too easy to over-drive the car but it rotates so well with the smallest lift of the throttle. I managed a 1st place finish by .5 sec with a passenger, which makes me wonder how faster i could have gone without him.


http://www.youtube.com/watch?v=a8A3rBTq7zk

[DORIGTT]

Hey Humble,

First I'd like to thank you for all your hard work that you've shared with us. Now you can just pay for my car to be finished and I'll really respect you!

Seriously though, I've got a few dozen questions for you.

How are your tire temps with the 17's and 18's in a car that 'light'?

What does it weigh, and what is your weight distribution?

Are you able to get the temps stable across the tread / face of the tire?

I noticed you mentioned them not getting up to temp, is this because of the outside / surface temp being too low?

What compound are you currently running front and rear. I'm planning to use the Lotus Elise tire size/spec for my Ghia with 16x7 - 195/50/16 front, 17x8 - 225/45/17 rear.

Thanks

[Humble]

The reason I went with 17s or 18s was to get additional width and better tire choices. You can get 245's in 16" sizes but it's a disappearing tire size. The 17" Fikse wheels are very light for their size but are not cheap. I think 17's are the sweet spot for weight vs. tire choice, and personally I wouldn't go with 18's again.

Weight:
My bug weighs 2050lbs (930kg) with a full tank and a fat driver (the Stig's fat American cousin is 235lbs/106kg) after being stripped and caged. I've got a 45F/55R weight bias, and a 50.5% cross weight with driver. The bug is actually setup pretty damn well and is fairly well balanced.

Tire Temps:
I've struggled with tire temps for a few reasons but first the setup:
Front: -2.5* camber, 0 toe, and as much caster as possible
Rear: -1.5* camber, 0 toe

I expect to have higher inside temps due to the camber and I based my settings on the PCA 70's porsche RS cars. Those cars tip the scales around 2200lbs(998kg) and run 17x10-11" fronts and 17x13" rear full race slicks. I'm running 245/40-17 front and 275/35-17 rear which I think is about as wide as I can go and get good tire temps. That being said I've had a hard time getting the right compound under the car. The 18s I was using had a medium-hard compound which were just too hard really, even in very hot weather. The older race tires on my 17's were a medium compound and good for warm/hot (75F/24C+) weather but wouldn't warm up fast enough for autox duties. I plan on getting a soft compound next which should work for autox and hillclimb sprints, as well as a set of soft-medium compound for track days. I've got a set of Hankook Z214 c71 soft compound tires on order and they should be mounted before the next autox. I haven't decided on a track tire yet and I'm still shopping around.

For tire temps to get into the right range you have to bring the right tire, and I just haven't done that. If you bring too hard a tire out it will feel greasy and just slide around. Street tires can be faster than the wrong race tire.

For the ghia, if you haven't bought your rims yet I'd rethink your sizes. It would be better in the long run to get the same diameter all around either 16's or 17's rather than split sizes. Also do a lot of shopping to see what compounds are available, but I wouldn't run anything harder than a medium compound. The Lotus comes with medium compound yokohama A048's which wear like butter and grip like ducttape (60 tread wear rating), but, those tires don't work below 70F/21C. If it's cold, those tires are icy, I've driven an Exige S 240 track model in the cold and I had more than a few pucker moments. I would suggest a staggered size like 205 front/225 rear but again the same caveat of available compounds, so do some research. Lastly, if it's not an all out track toy, consider the same size all around, easy to find tires, easy to rotate tires (which goes a long way in extending the life of a set of tires), and you can get the same compounds. I go through 4-5 sets of tires a year so if you have a question of particular brands or tires feel free to ask.

Kind of a long answer but I hope I covered it all for you