Quote:
Originally Posted by JJZ4MR
Now that my research tells me for the best grip in a ultra high performance summer tire, the Bridgestone RE-71R seems to get the most high ratings from the forum. For an extra $ 400 I now think is is worth the extra cost. On my stock " light alloys " which come to find out, are not all that light. ( Plus they need refinished, as they have the coating wearing off them in a few spots, dealership says for $110 per wheel, a company comes in and doest the work, same day, amy thoughts on this ? ) As I now have versed myself in offsets, staggered setups, spacers, backspacing etc. I've learned some, but now have more questions.
1) For spirited weekend driving, with perhaps a visit to the 1/8 runway in town, perhaps some fast Auto X and maybe looking into HPDE, what should I really look for when tire shopping/comparing.
2) Is it true that the wider I go, the more rubber on the road, so more grip in the curves
3) The 200AA rating means they will wear out quickly and wouldn't I want a AAA rating ?
4) If when using the Tire Size Calc. my decision to go 225/45-255/40 to 235/40-265-35 when comparing them on the calc.. (A) my front Diameter Variance is -2.29
my Rear DV is -2.80
(B) so actual speed is 2.25 % TOO FAST-Fr
2.88 % " " -Rear
(C) Rev per Mile Fr- 800.85 to 818.85
Rear- 799.03 to 822.03
Maybe I wrong, but doesn't this mean I have to have 18 MORE revolutions - Fr
23 MORE revolutions- Rear
So this tire change would slow me down in a straight line ? I don't want that.
(5) Staggered VS Squared ? Since the front and rears are different ET 42-F/ET 30-R,
what is the best tire size setup in the 18 inch OEM wheels ?
(6)Lastly You State On your Post -Original Z4 18" wheel sets don't seem to have the proper offset to fit correctly.
So what is the solution to your stated problem and to my fragmented thoughts.
Anyone that has any knowledge of all of this, PLEASE HELP ME GET NEW SHOES FOR MY BABY SO I CAN DRIVE HER LIKE SHE IS MEANT TO BE DRIVEN.= getting the best tire for the best price, type, manufacturer, size.
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Here's some answers to the above questions:
WRT Bridgestone RE71 tires, it is the best performing 200 treadwear tire available currently. The only other 200 treadwear rated tire that comes close is the BFG Rival 2, and they've typically been more expensive. The RE71s have a pretty stiff sidewall and are not the smoothest riding tire, but they're not as bad as the RFTs. They are a very noisy tire. When brand new they put out a chorus of roar, mud tire rumble, and a soprano like whine. The whine goes away after a couple hundred miles, but the bass and tenor hang in there. If you do autocross and you're not running the RE71s you'll be at a distinct disadvantage because almost everyone else there will be. Why is the 200 tread wear rating important? In 2014 the SCCA revamped their auto cross classes and changed classes that were designated as "stock" classes to "street" classes. As part of that change they mandated that cars running in Street class had to run tires rated 200 tread wear or greater. Previously when it was "Stock" class they allowed R-comp tires. Virtually every other autocross group uses some version of SCCA classing so paying attention to the 200 rating is important.
2) Generally wider is better, but you need to pay attention to the tire manufacturers rim width specifications, particularly with the RE71s. Once you increase the width to where the RE71s are in a pinch fit (on a rim narrower than spec) the stiff sidewall causes a lot of radius on the shoulders of the tires and you don't gain much contact patch width for the extra tire width.
3) The numbers are the tread wear rating or life estimate rating on the tires. The letters are the traction rating (first 2 letters) and temperature rating (last letter). Pretty much any known brand passenger car tire will meet the AA traction rating now, so it's really become obsoleted. If you look at the Tire Rack site I believe only the Fuzion brand is the only passenger car tire that isn't AA traction rated. That's left the softness of the rubber formulation used as the real measure of traction and the softer the formulation (lower tread wear number), generally the stickier the tire is. There's even been some bastardization of that because while the tread wear test regimen is specified by the federal government, the projection of tire life based on the wear from the test is left to the manufacturers own formulas, so a Bridgestone 200 tread wear tire isn't the same as a Michelin 200 tread wear tire which isn't the same as a Continental 200 TW, etc.
4) Roughly for every profile increment change of 5 you need to change the tire width by 20 to keep the same approximate diameter. On your fronts I believe you have 8" wide rims and you can fit a 245/40 which is within the spec for RE71s. On the rear I believe the Z4M has 9" wide rims and you can fit a 275/35 and be within manufacturers tire specs for the RE71. Any more pinch than that with the RE71 and you start to see the shoulder radius issue and you don't gain anything with the wider tires. On tires with a softer side wall like the Hankook RS3 you can go a size or two wider than with the RE71, but the RE71 in the smaller width still has more grip.
4 B&C) When you go to a smaller diameter tire your speedometer indicated speed is faster than you're actual speed. It doesn't slow the car down physically, you're just not going as fast as you think from looking at the speedo. You do gain a slight gearing advantage from the smaller diameter tire so you get a slight gain in acceleration. The negative of smaller diameter is loss of contact patch. Contact patch is a function of both the width and diameter of a tire.
5) You'll find a divided camp here. People that have bought aftermarket wheels that have allowed them to run the same size wide tires in the front and the rear will swear its the way to go and with that set up it likely is and you have the advantage of being able to due a traditional rotation of your tires. With the stock wheel sizes you wind up with a narrower tire in the rear trying to match the fronts and you get an associated loss of rear traction. My opinion is that if you're keeping your OEM wheels go with the staggered tire sizes. You can have the tires side swapped to extend their life. It adds the cost of a demount, remount and balance, but it extends tire life sufficiently that its worth it.
Hope this all helps!