Using a SSR GT1 wheel, which I believe is considered pretty light weight, and Pirelli P-Zero tires, a set of 17" would weight in at 40.5 lbs per corner (P-Zero asymetricos) and 36 lbs. for 18". With P-Zero Nero tires it comes to 17" =38.1 lbs, 18" 35.6 lbs. The 18" wheels are .5 lbs heavier than 17". The lighter 18" tires make the total weight difference. As the actual total wheel and tire diameter should be equal, the lighter 18" tire should be preferable just in terms of weight distribution, not to mention reduced sidewall flex etc.

 

I still think a lightweight set of 16" wheels with non-run-flats is probably the best performing set-up for the MINI. Plus, the cost of tires for 16" wheels makes me not cry when I wear out a set on the track.

I'm going with the heavy but stylish 17"R-90's with run-flats for every day motoring, and then getting the 16" R-90's for track days. I just love BBS so much that I won't buy anything else if I can help it!

I should be able to sell my never used stock 17" S-lites that are being taken off before initial delivery for a good price to allow me to buy the 16" wheels that I really want.

Only one more week until I can post with the authority of actual MINI ownership! Yay!

_________________
~Yucca Patrol~

2003 MCS, BRG/W on the truck to my dealer!

"Good judgement comes from experience, and experience comes from bad judgement."

 

>>
>>Only one more week until I can post with the authority of actual MINI ownership! Yay!
>>

If we suddenly stop hearing from you for a while, we'll know what you're doing! VROOOOOM!

 

DK23,

You are absolutely right. The issue becomes one of cost. For a lighter weight, you can have 16" wheels and tires and not break the bank everytime you need new tires - which could be often if you drive the way I do

The other advantage of the 16s is the first gear start. The taller wheels and tires in effect give the car a taller gear ratio, making those starts a little sluggish. Shedding the weight helps, but you will still have a little better jump on the 16s if all weight is equal.

Randy
randy@webbmotorsports.com

 

What RandyBMC is getting at has to do with the Rotational Mass Moment of Inertia.

 

If you intend to use 16" wheels, and keep the speedometer accurate, you will need to preserve the original stock wheel/tire diameter, just as you would with a 15", 17" or 18" wheelset. This would eliminate any improved acceleration due to a shorter wheel/tire height. If you are willing to go to a shorter wheel/tire height, then certainly the effective gear ratio is lower, and you will accelerate quicker. You will also be continually running higher revs, and reduce your top speed.

Again using the P-Zero nero tire as an example, the 18" tire weighs less than the 16" tire, ( 16"= 22.2 lbs., 18"=18.6 lbs.) thus making the rotational mass at the outer edges greater in the 16" tires. Even if the total weight of the 16" and 18" wheel/tire sets are identical, for this example, the 18" set's weight distribution seems it will provide higher performance.

I agree that cost considerations certainly endorse using smaller wheel and tire combinations. Larger diameter, lower profile tires are more expensive, (my Porsche 18" tires are $350 each!) however, if we are discussing only higher performance issues, I think the 18" combination should be considered more than a cosmetic addition.

 

I can also confess that I am not completely familiar with the newest and lightest large diameter alloys out there. I was surprised to see that Ray Hampton's MINI's that he was testing on the track appeared to be running on 18's (at least 17's), so there might be something I don't completely understand.

But I do understand that I will get excellent performance for the price with a 16" track set-up.

I'm looking forward to the time when Ray and others like him get those cars dialed in and some of what they learn trickles down to the rest of us

 

Is there any easy way to recalibrate the speedo for smaller circumfrence wheels? Also, your fuel economy will suffer at cruising speeds with the smaller wheels...

 

DK23,

You are correct, to keep the stock speedo ratios, you would need to have the same diameter wheel/tire combo - I wouldn't do that. For the track, what do you care what the speedo says? I very much doubt the weight of a 16" and 18" P-Zero are the same if the tire width and sidewall are the same (unless there's something funky going on with Pirelli ).

That said, if you can afford it - 18" at the same weight or less than a 16" with the same diameter would be the way to go (but if you are going my route and have a straight comparison on sidewall - even if the weight is the same, you would have an advantage with 16"s because of the reduction in rotational mass). The reason is simple - taller wheel=less tire sidewall=greater contact patch. The issue for me, and I think a lot of others, is the cost of track tires for the 18" wheels vs. the 16" wheels - not to mention the cost difference in wheels.

On a side note -I am a Porsche traitor - been involved with them since I was 14 or so. I sold my primary track car to get the MINI (a 1970 914-6 with a 3.2 Motronic injected motor) but still have my 1969 911S. What do you have? From the cost of the tires, I'd guess something new - a 996 perhaps?

Randy

 

Randy,
I beleive the benefits of reduced sidewall height are significant for higher cornering performance. I've read lots of posts about fitting smaller wheels for better perfomance without stating if they intend to reduce sidewall height by reducing overall diameter or keeping a rather tall sidewall by maintaining original total diameter. As you stated, the reduced overall diameter with reduced tire sidewall and reduced weight certainly presents significant performance improvments in acceleration without giving up any handling. For a total track machine, that may indeed be the way to go. However, I think some posters are thinking a 16" setup with the same overall diameter as stock will improve handling, when actually the opposite is true.
As our (I mean my wife's of course) MCS will be a daily driver with some track time, I'd like to keep the overall diameter close to stock (actually just a bit smaller). So in the interest of reducing sidewall height, will probably go with light 18" wheels and light, high performance tires. This still allows reduced corner weights from stock and I believe greatly improved handling. You are totally correct about costs. 18" costs are through the roof creating a major downside to that setup.

What setup are you using? Are you doing a lot of track time?

Regarding your side note, yes, I have had 911 Porsches for over 25 years. Starting with a 72 "S". and currently a 993 C4S. (amazing car). Your 69 "S" is a great car, and I bet the 914-6 was a total blast to drive on the track.

 

DK23,

AKTire is making a knock off of the SSR in 16", and I think the tire size is 215/45-16, but I have to check. I'll be getting Falken Azenis tires - but if I had an unlimited budget, I'd get the Michelin Pilot Competition - great tire! The AK wheel is very light, but is only 6.5" wide. For BMWCCA, you don't have to keep the stock wheel, offset or width, so I may go with a Rota, which is also light, but has less offset and is 7" wide. The offset should provide additional tire clearance. 6.5 vs 7" with the same sidewall size would allow more sidewall flex and a smaller contact patch, so obviously the 7s would be more optimal. I plan to do the entire BMWCCA auto-cross series next year, which will be a first for me. I've done mostly road racing, with a smattering of auto-x here and there. As soon as we have insurance for track days at MINI5280, I plan to organize quite a few at Second Creek, Pueblo, La Junta, and Mountain View (or Continental Divide or whatever they call it now).

The 993 is a great car. Do you have any understeer issues at the track with that car being the C4? I had heard some guys complaining, but if you talk to Jeff Zwart, he lives by the C4. Just curious.

Randy

 

Randy,

I've not had any understeer problems that couldn't be easily corrected with a more careful line. While I don't think it is much fun to autocross, the C4S is unreal on the track. The AWD is a real asset coming out of corners under heavy throttle, and the grip is truly unbelievable. I love the car.

Good luck with your autocross season in the Mini. It should be great fun, and a terrific performer. Sounds like you have a good package worked up. I'll be anxious to hear how it goes for you.

 

For Yucca Patrol and others that were interested, Ray Hampton Racing uses a FLIK brand 17x7.5 wheel with Toyo 205/40-17 RA1 tires. For autocross the Falkens or Kumhos, depending on the class you run, are the most cost effective with very good performance. Top performance goes to the Hoosiers, but they are expensive and don't last as long.