I have the Enkei RS-6 18X7s and I need to replace two of the tires. I'd like to get some Michelin Pilot Sport A/S or Sumitomo HTRs, but it seems the 18" sizes only fit 8"+ widths. I've checked the usual tire places and it seems Nittos and Kumhos are the only tires that will fit 18X7 wheels. Is that all we can use? I'm tired of sliding around in the rain on my Nittos.

I can't afford the Volks until summer.

 

225/40/18
or
235/40/18
would both fit

Only difference is 235s are a little bit wider than the 225s

 

Hmm, I checked the specs for the Michelins and Sumitomos and both show 225/40/18 fits 7.5-9" and 235/40/18 fits 8-9.5". Would it be safe to use the 225/40/18 on a 7" wheel? On the Tirerack.com website, it says that you can fudge by .5", but I think that's already included in the 7.5-9" rating. Going another .5" out of spec might be a bad idea?

 

Good for you, Tanman. NYCe MaXiMa's post is a perfect example of why it's always better to check your facts than to trust the word of anyone on the Org concerning tire and rim specs, particularly when the facts are so easy to find. (For those who don't know where to look, check out the post on Page 5 of the FAQs in the 5th Gen Forum called Tire & Rim Association Contour (Rim Width) Charts.)

By the way, would you mind telling me precisely where on the Tirerack.com website it says that you can fudge the T&RA and manufacturer specifications for rim width? I've looked on their website and I can't seem to find that statement anywhere.

Thanks.

 

Crap. I was hoping I'd be able to fudge and get the Sumitomo's rated for 7.5-9" to fit on my 7". Oh well, might have to stick with Nittos.

I don't think tirerack.com actually said you can fudge it, but they sort of suggest it about some manufacturers:

From the tirerack.com website, if you bring up specs on a particular tire, then click on the column header "rim width range", it shows tire spec explanations.

Rim Width Range
Because tires have flexible sidewalls, a single tire size will fit on a variety of rim widths. A tire's rim width range identifies the narrowest to the widest rim widths that the tire is designed to fit. The width of the rim will influence the width of the tire. A tire mounted on a narrow rim would be "narrower" than if the same size tire was mounted on a wide rim. NOTE: Because the overall diameter of a steel belted radial is determined by the steel belts, there is little, if any, change to the overall diameter of the tire due to differences in rim width.

The industry rule of thumb is that for every 1/2" change in rim width, the tire's section width will correspondingly change by approximately 2/10".

For example: a tire in the P205/60R15 size is measured on a 6.0" wide wheel and this size tire has an approved rim width range from 5.5" to 7.5" wide. The tire has a section width of 8.23" (209mm) when mounted on a 6.0" wide wheel. If that tire were mounted on all of the rims within its range, the tire's approximate section width would change as follows:

Difference from
Measuring Rim Rim
Width Approximate Tire
section width
0.5" narrower 5.5" 8.03"
Measuring Rim 6.0" 8.23"
0.5" wider 6.5" 8.43"
1.0" wider 7.0" 8.63"
1.5" wider 7.5" 8.83"

Because of the different wheel widths used in the above example, there is a 8/10" projected difference in tire section width when comparing a tire mounted on the narrowest rim to the widest rim within its range. This may affect fenderwell and frame clearances when selecting optional aftermarket wheel and tire packages

Additionally, some vehicle manufacturers and tire companies have permitted rim widths that are not within the tire's original approved rim width range. For example: BMW has combined 235/40R17 sized tires on 17x7.5" rims (which are 0.5" less than the narrowest 8.0" wide rim listed for the size) on certain M3 models; and Chevrolet has combined P255/50R16 sized tires on optional 16x9.5" rims (which are 0.5" wider than the 9.0" wide rim now listed for the size) on certain Corvette models. While these applications have received the approval of the vehicle and tire manufacturers, staying within the approved rim width range helps assure that the tire's internal stresses are within its design parameters.

 

I'm going to call some local Discount Tire stores to see what their installers think. I'd really rather use the Sumitomos or Michelins instead of Nittos.