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Discussion Starter · #1 ·
I'm getting ready to sign up for a track day at Laguna Seca in June and wondered what the implications are for me/my car, on leaving my 20" RAC RG41's on for the track day (or do I need to put my stock set up back on). It's a pain to get them swithed but will if there is a good reason.
Any thoughts?
 

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I'm getting ready to sign up for a track day at Laguna Seca in June and wondered what the implications are for me/my car, on leaving my 20" RAC RG41's on for the track day (or do I need to put my stock set up back on). It's a pain to get them swithed but will if there is a good reason.
Any thoughts?
19's are def. better as the rim/tires are lighter. But if it's only 1 event, you should be ok. Are the RAC's a 3 piece wheel? How heavy are they? Generally 1 piece wheels that are light are the preferred choice. I have a heavily modded M3 for the track and I run 18's for many reasons. Weight and availability of R compound track tires beinging the main reasons. Again, if this is a one time deal you should be fine. If you plan on going often, not so good.
 

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why not.....check the wheel bolts and inflation pressures first..be safe
 

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Discussion Starter · #4 · (Edited)
UFH, absolutely and thanks.

The RG41's are actually lighter than the stock 19's and one piece, that should be good. The tires are lower profile so enogh pressure would be key! We'll see how the Sumitomo's grip. At least it will be dry so they should be OK.
 

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Set the pressure for your tires HOT what the door says COLD. That is a good starting point.

So 36/36 HOT.

Remember to fill them back up when you leave.
 

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Go for it...

Take a tyre pressure gauge and check pressures, especially after the first run.

Don't forget to post some pics afterwards...
 

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Barry, I don't think it will be a problem, and Michael S' response is from lack of knowledge. The RACs are lighter overall, about 5lbs total per wheel, than stock, and also stronger. The wider track is a small advantage as well, but that will also put a little more stress on the rest of the suspension compared to stock. I personally run my stock wheels/tires on the track...the car is already way beyond my skills as a driver, and since I took off my stock wheels/tires at about 6,000 miles, why not burn up the rest of the rubber on the track and not risk my nice RACs and the expensive rubber on them on the track.

I'm doing the Las Vegas CCA track event here in just a couple weeks, and I'm either going to run stock tires both days, or stock one day and the RACs with my 275/305 rubber the second day. Either way, until you're really good, running the RACs won't be a significant difference. If you still have your stock wheels around, with only a little wear on the tires and you have nothing else to do with them than keep them, why not run the stock wheels on the track and burn up rubber you don't care about anymore?

I don't know what tires/wheels Cosmos is running, but watch out for running 36psi HOT. With the stock tires last year, I had to run the front at 40psi. With my RACs, I run the fronts with 275/30 tires at 38psi COLD as my regular pressure, and with 305/25 I ran the rears at only 34psi but with 305/30 I need to keep them up at 36psi. Those are not track pressures either, which usually need to be upped by about 2psi at least on the front to keep from rolling over the tire too much on turns.
 

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Discussion Starter · #8 ·
James thanks, I actually want to burn up the rubber I have on my rims to get the ones you have! The main concern I have is "rolling"over the rim. The front rims seem so close to the ground as it sticks out beyond the sidewall of the tire by a bit. I think I'm going to error on the high side of the pressure to start. I'd love to hear of the comaprison between your 2 setups if you can do it. My stock tires are nowhere near where they can be installed and hard to get to the track.
Barry, I don't think it will be a problem, and Michael S' response is from lack of knowledge. The RACs are lighter overall, about 5lbs total per wheel, than stock, and also stronger. The wider track is a small advantage as well, but that will also put a little more stress on the rest of the suspension compared to stock. I personally run my stock wheels/tires on the track...the car is already way beyond my skills as a driver, and since I took off my stock wheels/tires at about 6,000 miles, why not burn up the rest of the rubber on the track and not risk my nice RACs and the expensive rubber on them on the track.

I'm doing the Las Vegas CCA track event here in just a couple weeks, and I'm either going to run stock tires both days, or stock one day and the RACs with my 275/305 rubber the second day. Either way, until you're really good, running the RACs won't be a significant difference. If you still have your stock wheels around, with only a little wear on the tires and you have nothing else to do with them than keep them, why not run the stock wheels on the track and burn up rubber you don't care about anymore?

I don't know what tires/wheels Cosmos is running, but watch out for running 36psi HOT. With the stock tires last year, I had to run the front at 40psi. With my RACs, I run the fronts with 275/30 tires at 38psi COLD as my regular pressure, and with 305/25 I ran the rears at only 34psi but with 305/30 I need to keep them up at 36psi. Those are not track pressures either, which usually need to be upped by about 2psi at least on the front to keep from rolling over the tire too much on turns.
 

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Barry, I don't think it will be a problem, and Michael S' response is from lack of knowledge. The RACs are lighter overall, about 5lbs total per wheel, than stock, and also stronger. The wider track is a small advantage as well, but that will also put a little more stress on the rest of the suspension compared to stock. I personally run my stock wheels/tires on the track...the car is already way beyond my skills as a driver, and since I took off my stock wheels/tires at about 6,000 miles, why not burn up the rest of the rubber on the track and not risk my nice RACs and the expensive rubber on them on the track.

I'm doing the Las Vegas CCA track event here in just a couple weeks, and I'm either going to run stock tires both days, or stock one day and the RACs with my 275/305 rubber the second day. Either way, until you're really good, running the RACs won't be a significant difference. If you still have your stock wheels around, with only a little wear on the tires and you have nothing else to do with them than keep them, why not run the stock wheels on the track and burn up rubber you don't care about anymore?

I don't know what tires/wheels Cosmos is running, but watch out for running 36psi HOT. With the stock tires last year, I had to run the front at 40psi. With my RACs, I run the fronts with 275/30 tires at 38psi COLD as my regular pressure, and with 305/25 I ran the rears at only 34psi but with 305/30 I need to keep them up at 36psi. Those are not track pressures either, which usually need to be upped by about 2psi at least on the front to keep from rolling over the tire too much on turns.
You are correct, I am not familiar with the RAC wheels and that is why I asked about the weight. Now that I know about the weight, I would have a little different answer. However, if it was me and I had stock wheels in the garage, I would not use the 20's just because of the wear and significant cost to replace 20 inch tires. Even with running higher pressures the tire can wear on the outside (rolling over as you call it) due to lack of neg. camber.

James - what club (s) do you drive with in LV? I have been driving with a few of the clubs in the south east (NASA, Chin, PBOC) and was curious what clubs are good in your area. Thanks..... Michael
 

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Michael, the local BMW CCA chapter in Las Vegas is holding our annual (possibly last) track event here at LV Motor Speedway. I want to get into NASA or SCCA more, but not with the M5. In a year or two I expect to have a semi-dedicated track car, probably an E36 M3, and then I'll get involved in more club events if possible. I don't think there is a lot of racing though in the west, just enough to make some trips out to Laguna Seca, Buttonwillow, Phoenix, and maybe a few others to participate in events.

Barry, seems like Michael and I are in agreement, but based on what you said...burn 'em up!

I have the Toyo T1Rs, and before that had the ContiSportContact 2 in front and CSC 3 in the rear. The Toyo setup is 275/30 and 305/30, and the CSC setup was 275/30 and 305/25. The Toyo setup keeps the rear rolling diameter closer to stock (just 0.3" over instead of 0.9" under), but I have more rubbing. The Toyo's have a more "boxy" design, which means I might be getting the fenders rolled just a little more (where the rear bumber comes up to the wheel well isn't rolled, and the front fender to the wheel well might need about 1/2" more rolled to keep from rubbing). I have to tell you, if I could do it all again a little differently I might stick with 255/35 and 285/30. Why? Save a few hundred dollars on tires, and you'll have fewer problems too. Both times I've had the tires installed I've had radial pull on one of the front tires and had to get one swapped. Even then, the front tires are simply so wide that you get more tramlining, and the crown of the road (roll-off for water dispersion) also affects you even more. I really don't think there are significant gains in the setup, but since I'm putting the stock tires back on in a few days, I'll let you know what I think again from experience. I do remember one major difference...I could spin and spin and spin the stock wheels/tires all day long just into 3rd gear, but with the 305/25 rears as soon as I hit the 1-2 shift I had solid traction every time. At least in straight-line running, there was a difference.
 

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Discussion Starter · #11 ·
James, thanks for the tips. I did see your car (not you) in Vegas and I do like the way the wider tires "look" but may need to re-think my plan.
This board is great!
 

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36 HOT is the starting point and as far as the tire "rolling" it depends upon modifications, driving style and other things.
 
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If you want to go out and enjoy yourself and burn some rubber, the weight of the wheel is immaterial. But I would only add that a lighter 20" wheel is not necessarily going to perform better an a heavier 19" wheel as most of the weight in the wheel is in the barrel and the further the weight is from the centre of the wheel the worse it will perform, but you are not talking about huge differences anyway.

The only really good reason to use a smaller wheel is the choice in tyres, but as you want to burn the rubber on the 20's, just use them.

I can't comment on running 20" wheels but when I was at Silverstone, my cold pressures were 28psi front 31psi rear which was around 35psi when hot and looking at the wear I could have probably gone down a little from there. I am running 19" wheels with 2 degrees of negative camber so my tyres will roll over less than stock.

As you said, start on the high side and just look at your tyre wear, that will tell you if you need to go down or up.

I hope you have a blast and would love to see some pics...:thumbsup:
 

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Discussion Starter · #14 ·
well it's a long way away (june) but I will post pics
 

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For track use, use 19" tires/wheels and be aware that available rubber is not up the the vehicle's weight. If you push the car over 6/10ths, understeer will eat up the outer edges of the front tires during a weekend. I tried from 29 to 38 PSI, ~4200 lbs is too much for the 255/40s on a tight track.

During the event check the bolt torque as well as pressure. Don't use the parking brake between segments.

Michelin is supposed to sell three new 19" Pilot Sports this year, hopefully one will be the Sport Cup variety in sizes we need.
 

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The only really good reason to use a smaller wheel is the choice in tyres, but as you want to burn the rubber on the 20's, just use them.
Actually, another good reason to stay with 19" is to keep sufficient sidewall height. Without sufficient sidewall, the breakaway characteristics of the vehicle at the limit of adhesion become far worse.
 

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Barry:

FWIW - I ran with the GGC BMWCCA at Infineon (2 days) March 8 & 9 (while most everyone was in LV for MFest) & had a blast. I ran the stock wheels with Conti Sport Contact 2's at 38 psi cold; there was some understeer and the tire edges did show some definite wear, but overall the tires performed pretty well. I'm already signed up for the club event at Laguna Seca in June, so if this is the event you're talking about, I'll see you there! :thumbsup:
 

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Actually, another good reason to stay with 19" is to keep sufficient sidewall height. Without sufficient sidewall, the breakaway characteristics of the vehicle at the limit of adhesion become far worse.
Bingo.

You loose control of the contact patch- the sidewall cannot flex enough to maintain road contact.
 

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I ran the stock wheels with Conti Sport Contact 2's at 38 psi cold; there was some understeer and the tire edges did show some definite wear, but overall the tires performed pretty well.
38 psi cold??? Holy cow! Did you measure the pressures right after a session? With Contis and the PS2s my tire temps normally rose 8 psi after each session (Pilot Sport Cups rose about 6 psi), leading me to run 30-31 cold because you do not want to get to or over 40 psi. (With the Cups I started at 26-27 cold due to the nature of those tires.) Obviously, the amount of the increase is related directly to how hard the car is run and the nature of the track, but 38 cold sounds high to me. In any case, Barry, pick a starting pressure then take a measurement immediately after coming off the track, and let air out to get down to the high 30s hot. Keep monitoring and experimenting during the day, just keep in mind that tire pressure is one of the biggest determining factors in how well the car handles, so it is worth the attention.
 

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38 psi cold??? Holy cow! Did you measure the pressures right after a session? With Contis and the PS2s my tire temps normally rose 8 psi after each session (Pilot Sport Cups rose about 6 psi), leading me to run 30-31 cold because you do not want to get to or over 40 psi. (With the Cups I started at 26-27 cold due to the nature of those tires.) Obviously, the amount of the increase is related directly to how hard the car is run and the nature of the track, but 38 cold sounds high to me. In any case, Barry, pick a starting pressure then take a measurement immediately after coming off the track, and let air out to get down to the high 30s hot. Keep monitoring and experimenting during the day, just keep in mind that tire pressure is one of the biggest determining factors in how well the car handles, so it is worth the attention.
Sorry, I meant to say 38 psi warm (i.e. not immediately off the track). ouich
 
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