tires/wheels for racing

[squid]

My Mini Cooper has arrived.
It has the stock 15 inch wheels with all season
tires, which I will keep for winter driving.

I plan on getting one more set of rims, and now
I'm toying between getting a light set of rims
for autocross[*] use only (with Hoosier/Kumho autox tires),
or a strong set of rims for use all summer long
(with high performance summer tires).

Is this the right way to frame the question ?
Are some rims really that much stronger and less likely
to be bent driving over real world bumps and potholes ?

Also, I note that TireRack doesn't yet have much to offer
in 175-65-15, the Cooper's stock size, or in 195-55-16,
the Mini's Cooper sport or S's stock tire size.

For 205-45-17, the optional size on the Cooper S,
tire rack has 5 models of tire (though three are Yokos).

* I'm in the US and compete in a sport called autocross
which is a solo timed event around cones on an
airfield or big empty parking lot. (I think
in the UK 'autocross' means some sort of dirt track
which in the USA would be known as 'rallycross'.
Autocross looks like this photo I stole from some
forum here which I now can't find again to credit.


Enthusiast drivers usually have a set of sticky
R-coumpound tires and wheels for such competitions,
in addition to their street tires.

squid@panix.com
2002 Mini Cooper

[Garfield]

The photo is one I took of Chris Kellett from Helix MINIsports the same day I raced this car.

Do a search, there have been several discussions about autocrossing the MINI. I've actually run this Swedish car and on March 23rd in D.C. I ran a US Cooper on some 16" Cooper S wheels (the lightest of the MINI wheels at 17lbs.).

Yes, a forged aluminum wheel is much stronger than a cast aluminum wheel. Most stock wheels are cast. Now, for autocrossing, a cast wheel will generally be fine, but they usually weigh more.
You get what you pay for. If you want a lightweight wheel, stick with the smallest you can run. But, also consider the tire sizes available for the wheel diameter. Especially in the Cooper, you'll want to run the lowest rolling diameter possible without sacrificing width.

As for the MINI Cooper, you're allowed to run a 15x5.5 or 16x6.5 in H Stock (or in G Stock where it will end up in 2003 after it eats the competition alive in H Stock). Even though you bought the car with 15's, the 16's are legal because they're a stand alone option.

Don't worry about what Tire Rack offers in tires. If you don't mind a little speedo error, there are plenty of selections, and some that aren't far off the stock diameter. I would at least run a 195 or 205 on the Cooper. For autocrossing, the 205/50R15 is perfect at .9" smaller in diameter. For the road, a 205/55 is only .1" smaller in diameter so speedo error would be unnoticeable, and they come in several variations of performance tire.

Check out a couple of other pics of that race day on my personal gallery on this site.

Brian

[abscars]

I picked up my MINI on March 23, wandered all over Kansas to get past the 1200 mile break-in period, and ran a Wichita Region SCCA Solo II autocross on Sunday, April 7. I ran in the first heat. It was a cold, rainy 47 degrees F. I ran the stock, Czech made,Continental Contacts, with 40psi all around. The results were great. I was first of 4 cars, in class, also finished 17th of all 39 cars in the event, even though weather improved and all my direct competition had a nearly dry course! I have ordered Kuhmo Ecsta V700's in the 205-50-15 size, to run on the stock 7 hole wheels. $481.02, delievered to central Kansas.

I would like to buy another set of stock wheels, with or without tires, either 15 or 16 inch, any of the original equipment styles.

Abner, Regional Executive, Salina Region SCCA,
President, British Automobile Club of Central Kansas
Liquid Yellow MINI Cooper, Black top, Premium group, Heated seats, Fog Lights, $997 Dealer Pack
1965 Triumph TR4

[SSCRacer]

Is anybody out there planning to race a MINI Cooper in SCCA Showrom stock racing? Hoosier is talking about making an "R" compound tire if the interest is there. The SCCA rules make the maximum allowable tire size an unusual 195/55R15. The car should be a major competitor in the SSC class.

[chris@helix]

Gerry Walsh @ OTTO's BMW is planning on running a car this year in SSC. You can contact him at OTTO's 610 399-6800. If your in the Wash DC area this weekend (4/13-4/15) we will be testing some new products on our MINI @ a three day BMW event @ Summit Point Raceway. Gerry Walsh will be there with us.

All the best

Chris
helix MINIsport
helix13.com

[squid]

As I read SCCA *stock* rules, any publicly available
tire which is DOT approved is legal, if it fits
on stock rims, and fits inside stock bodywork.

So, this means replacing a 175/65/15 with a
205/50/15 would be legal for H-stock.

If I'm wrong, tell me so, and tell me why.

Countdown:
Days to first autox: 13

[Garfield]

You're absolutely correct.

[abscars]

Those are the rules for Solo II. The only danger with wider than stock tires is that they may rub somewhere, but since 205/45/17's fit, it shouldn't be a problem. Also, a 5.5 inch rim is on the narrow side for a 205 tire, but it is in the acceptable range according to Tirerack. I should have my tires by next week and be able to report back then.

No one currently makes a competition tire narrower than 205 in 15 inch diameter, to my knowledge. Yoko used to make 195 /60/15's in the old A008R, and I know where a set is, but they are so old, they seem harder than the stock tires!

[Garfield]

First of all, don't always go by "recommended" tire sizes. Go by what other autocrossers have run if you like.
On my 15x6 Miata wheels, I raced with 225/45R15 Hoosiers, VERY WIDE, but arguably the best tire to run. I can assure you that a 205 will easily fit the 5.5. I've even seen people run a 225 on a 5.5.
I've already been running the 205 on a Cooper, it fits with PLENTY of room.
As soon as I can, I'll be running the 215/40R16 from Hoosier.

[SSCRacer]

I'm in South Carolina, but Summit is my old home track. Let me know what kind of times the MINI turns at the Point. I'll contact Otto's and see about tires.

Thanks!

[abscars]

My 205-50-15 racing Kuhmo's have arrived. They are 2.25 inches wider than the stock tires and about 2 inches less diameter, which should make for better acceleration. First outing will be a local SCCA Solo II on the 20th.

I'm still shopping for another set of stock wheels and tires - 16"

[squid]

Thanks for your advice. I didn't see the
215/40/16 listed on
http://www.tirerack.com/tires/Sizes....=A3S03%2CR3S03

www.hoosiertire.com is has some info
if you know where to look.

Is this size announced, or actually available ?

squid@panix.com
edit fixed URL

[Garfield]

Yeah, of course, I didn't want to say anything because nobody seemed to be paying attention, BUT, I figured I'd tell you all about the 215.
So you know, it would even be the better tire to run on the Cooper, as long as you bought some lightweight 16's. If you're not going to spend money on lighter wheels, stick with the 15's and 205's. The 7-hole is only 12lbs.

[BrantV]

Quote:

Originally posted by abscars
My 205-50-15 racing Kuhmo's have arrived. They are 2.25 inches wider than the stock tires and about 2 inches less diameter, which should make for better acceleration. First outing will be a local SCCA Solo II on the 20th.

Not to burst your bubble, but your math is a little off. The actual numbers are about half what you calculated.

Given a 15" rim or 381mm diameter. 190.5mm radius.
But if you just want to see the height and width change, you can ignore the rim radius.

175/65R15
width = 175mm
sw height = 175 * 0.65 = 113.75mm

205/50R15
width = 205mm, delta = 30mm or 1.18".
sw height = 205 * 0.5 = 102.5mm, delta = 11.25mm height.

Your car will ride 11.25mm or 0.443" lower, which is indeed good because it lowers the center of gravity.

[abscars]

Math is fun, but tires don't necessarly follow the formula, my numbers are from a tape measure applied to the subject tires. My width measurement is at the tread surface, shoulder to shoulder, not necessarily very close to the nominal size the manufacturer inscribes on the sidewall.
My diameter is at the inflated diameter of the tire, not the actual laden rolling radius with the car on the ground, so it is really approximate and not necessarily relevant. Anyway you cut it, the Ecsta's are significantly wider, and of smaller effective diameter thereby improving the effective gear ratios and, as you pointed out, lowering the c.o.g.


Thanks for the input,