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FST ORNG
10-21-2006, 10:54 AM
Getting some 18+11's made for the rear of my 04 and was wondering whats the biggest size tire anybody has used and not had ANY problems with !

ausie
10-21-2006, 12:22 PM
Once you go larger than 10 inches, your choices may become limited on what brand or type of tire will fit. You may have to use the same tire that is used on the viper or what is typical on the exotic european sports cars that have wide width wheels. Some tires that fit a 10 inch will also fit an 11 inch. Look at the fitment guide of the tire you want to have. In most cases, a 295/35 - 18 will fit 10" up to 11.5" width. You may want to search for a 305 to 315 width to increase the side wall buldge to prevent damage to the wheel from road damage. I think BFG has sizes in that width in the KDW2 tread pattern. Some drag radials may also fit the 11 x 18 wheel in the 315 inch width.

ausie
10-21-2006, 12:25 PM
Also, as long as the wheels you are having made keeps the same inner offset of the original OEM wheel you should not have any issues with fitment with the exception of the fender lip when the car is lowered.

FST ORNG
10-21-2006, 03:23 PM
Thanks ! The KDW2 is what I was planning on but was trying to squeeze a 335 on the back .....I think on the safe I will go with the 315 ! What you running on those BBS's?

blk04cobra1
10-22-2006, 09:17 AM
Right now im running a 295/35/18 on my 18x11's, they are the BFG KDW 2's...had some 335's on there, but they just looked too big for our car's IMO...do have some 315 drag radials that will be going on soon though :thumbsup:

ausie
10-22-2006, 11:50 AM
right now I have 285/35-18x10 on the rear and 245/40 18x8.5 up front. I wanted to keep the speedo as close to that with the stock tire sizes. The 285/35 and the 245/40 are comparable in size and the ABS does not go whacky on me. For me to go wider on the rear say 295/35, the front would have to increase to 265/40 just to maintain the diameter of the tire the same.

the 285's create a 0.8% speed error, the 295 would cause a 1.8% speed error and 315 would cause a 4% speed error which may cause the ABS to act up everytime you come to a stop.

A 315/30-18 is amost the same diameter as the 275/40-17 (0.9% error) but the 30 series are harder to find and far more expensive.

It all depends on what use the wider tire will serve. if for track duty, and having a slightly taller tire in the rear you could always disable the ABS system or get a set of skinnies up front that would maintain the same diameter.

Play around with the miata tire size calculator (link posted below) this should help you decide what size would be best for the street.

http://www.miata.net/garage/tirecalcold.html

ausie
10-22-2006, 12:15 PM
just went to the BFG web site, the KDW (2) tires in the 315 width are a 30 series tire (315/30-18) and the same applies for the 335 width. 295 is the widest they offer in the 35 series. With an 11 x18 wheel, I would opt for the 315/30ZR18 since the 11 inch wheel width lands in the middle of the wheels size (10.5 to 11.5). 295/35 range is from 10.0 to 11.5 which is the largest tire I could use on the 18x10 without over stressing the tire bead. It is the sidewall that is supporting the weight of the vehicle. Over stretched side wall will increase load on the bead and if the tire is too wide for the wheel, they probably could not mount it (most likely the tire shop will not). The same applies if it the tire is too narrow for the wheel.

Brand of tire I have on the BBS is Toyo Proxes T1R but was going to change to the BFG KDW (2) which are equivalent in performance and many who have them like them. I still have the Toyo's and with 24 passes down the track they still look almost new. So far the best tire I ever drove on in the rain. I also have a set of 17x9 10th anniv. wheels with bridgestone wide ovals but they do not come in larger sizes for 18 inch wheels. I think I have too many wheel sets for my car. The third set is the 17x8 2001 SVT wheels with snow tires. (great for cold weather and ice, not really meant for driving in the snow, but I do get that desire to take it out when the streets are clean).

FST ORNG
10-22-2006, 01:38 PM
Wow ...thanks for the info !:eek:

FactoryFreak197
10-22-2006, 08:05 PM
From my experience 315's run a little wider with the bfg, I ran 315/3517 on a 10.5 wheel out back and it rubbed, even with a small spacer, when I went to a nitto 315, they fit perfect with no rubbing. If you run a 335 you migbt need to grind down on the irs bolt keep from rubbing and def. run a spacer out back, 3/8 hubcentric by M/m is what im using now and works great.

ausie
10-23-2006, 07:56 AM
If the wheels you are having made are single cast wheels, the inner offset should match that of the OEM wheel so that tires will not cause any issues. Most of the issues with the 10.5 inch widths do not have the same inside offset that is suitable for the IRS cobra's (depends on the wheel). When I compared the 10x18 inch BBS wheels to the 17x9 inch 10th anniversary wheels I have plenty of room for much wider tires that would overhang out from the wheel lip.
The nice thing about the BBS (single cast wheel) is that it maintains the same inside offset of the 17x8 5 spoke 1999/2001 cobra wheels.

From what I was told by the tire shop I take my cobra too is that Nittos run on the narrow side. What tires end up on the too wide side would be tires intended for SUV/Truck use in the low profile series. Keep in mind that BFG makes the KDW tires for SUV's and trucks so some sizes may be too wide and probably have a much lower speed rating. When getting tires in wide widths read the specs carfully and get the ones with the highest speed rating possible. Based on the chart from BFG, the 315/30zr18 and the 335/30zr18 both carry a Y speed rating which is capable to 186mph as long as you increase the tire pressure to the specified increase listed below the tire size chart. Tires specified as XL (extra load) are designed for SUV use.

http://www.bfgoodrichtires.com/specs/g-force-t-a-kdw/22.html

I would highly recommend before you buy the tires, find a good reputable shop that has the special equipment to mount them (typically reverse mount type equipment which does not place the mounting arm on the outside lip of the wheel) and talk to them about the tire sizes. They may offer some good advice in which direction you should follow (not your typical sears or simple tire center, look for places that cater to mercedies, porscha, BMW etc...) the mounting and balance may be a little higher in cost but the custom wheels will not be damaged from the mounting equipment. Also it would help to check fitment of the wheel before tires are mounted on them to verify the amount of clearance you have, this would indicate how wide of a tire you can use before you need to install wheel spacers. It would be best not to use wheel spacers since they allow for sheering of the lugs under high loads if the wheel becomes loose.

FST ORNG
10-23-2006, 09:11 AM
Thanks again for the info , I am going to go with the 315/30/15 BFG KWD2 and the local company that I am buying the wheels from do use the reverse mounting for there high $$$$ wheels ! Thanks again !