zordon Posted September 18, 2011 Share Posted September 18, 2011 I currently have 15x7 rims on my '76 280Z equiped with 215/60 R15. I bought new 15x8 and 15x9 rims, but haven't gotten tires yet. I was wondering if anyone knows what sizes would fit these new rims. I know the widths are different, but would the tires I have right now on my 15x7s fit the 15x8s and 15x9s? Quote Link to comment Share on other sites More sharing options...
Miles Posted September 18, 2011 Share Posted September 18, 2011 Shouldn't you have asked that question before you bought the new wheels? Try a tire store they can answer any question about tire and wheel combinations. Quote Link to comment Share on other sites More sharing options...
getoffmyinternet Posted September 18, 2011 Share Posted September 18, 2011 Look up any given width tire and it will show a recommended rim width. The aspect is irrelevant. Quote Link to comment Share on other sites More sharing options...
Driven5 Posted September 18, 2011 Share Posted September 18, 2011 (edited) Whether your current tires will fit on 8 and 9 inch wide wheels, or not, depends entirely on what size tires are on your current 15x7's...In addition to whether you prefer your tires to look stretched, square, or bulging that is. The class of tire for the driving you plan to do will also play a factor in size availability for 15 inch rims in general, which are rather limited these days. The best place to look, and the same info you'll be able to get from most tire shop monkeys, is on the Tire Rack web site as it consolidates all of the manufacturer specs into one easy to use location. For the 215/60-15 I generally see a 6-7.5 width recommendation. Personally, I certainly wouldn't put it on the 9's and probably not on the 8's either. But then again I'm not a fan of the stretched look. I don't know exactly how far you can stretch tires, but I'm pretty sure .5 beyond the manufacturer recommendation shouldn't be a huge deal either in regards to the 8's. And contrary to what some people claim, aspect ratio can actually play a role in how wide of a wheel is recommended for a given tire size, not just tire width. The higher the aspect ratio, the narrower the recommendation can be for any given tire width, and conversely the lower ratios can increase the recommended wheel width for a given tire width. This is of course more prevalent/noticeable in the lower aspect ratio ranges than the higher ones. Edited September 18, 2011 by Driven5 Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted September 18, 2011 Share Posted September 18, 2011 My understanding is that 215 is only ~10mm too narrow for optimal fitment on a x8 rim, which makes it ~35mm too narrow for optimal on a x9 rim. This is based on most actual rims being approximately 1" wider than their stated width. Thus a x8 is actually a x9 at the seal point for the bead. 9 x 25.4 to get it to mm is 228mm, so a 225 width tyre would be optimal (hence ~10mm too narrow), and you can elaborate from there. I imagine the tyres will fit just fine. Dave Quote Link to comment Share on other sites More sharing options...
Driven5 Posted September 18, 2011 Share Posted September 18, 2011 (edited) Wheels are not ~1" wider at the sealing surface than advertised. The advertised wheel width is measured across the inner edge of the wheel lip, which is the sealing surface. People who don't know any better tend to try measuring across the outer edge of the wheel lip, which is what gives the impression that the wheel is ~1" wider than it really is because each lip is ~.5" on aluminum wheels. In other words, tire manufacturer recommendations are based on the advertised (distance between sealing surfaces) rim width, and there is absolutely no fuzzy math necessary. Also the "optimal" width for any give tire is not simply wheel width x 25.4, nor is tire width / 25.4 going to provide you with the "optimal" wheel width. As stated above, the recommended wheel width for a 215/60-15 is 6-7.5 inches, where as 7.5 x 25.4 = 190.5 and 215 / 25.4 = 8.5...Neither of which coincides in any way with the manufacturer specifications. Edited September 18, 2011 by Driven5 Quote Link to comment Share on other sites More sharing options...
beermanpete Posted September 18, 2011 Share Posted September 18, 2011 The recommended wheel size for a tire is specified by the tire manufacturer. Typically they provide a range of wheel width and a single size that was the size used to measure the tire for creating the nominal size rating. You should go to a variety of tire brand web sites and look at the tire specs for the type of tires you are interested in. My rule of thumb is: The wheel width should be close to the tread width. Note: Tread width is NOT the nominal tire size as specified by the tire manufacturer. It is the actual width of the tread surface that touches the road. The nominal tire size is cross-section width, which is widest part of the whole tire at the bulge in the sidewall when the tire is inflated. Quote Link to comment Share on other sites More sharing options...
BLOZ UP Posted September 18, 2011 Share Posted September 18, 2011 (edited) http://www.miata.net...e/tirecalc.html http://www.1010tires...ecalculator.asp http://www.rimsntires.com/specs.jsp There's also one somewhere to give you recommended sizes, but I can't find it. Edited September 18, 2011 by BLOZ UP Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted September 18, 2011 Share Posted September 18, 2011 Wheels are not ~1" wider at the sealing surface than advertised. The advertised wheel width is measured across the inner edge of the wheel lip, which is the sealing surface. People who don't know any better tend to try measuring across the outer edge of the wheel lip, which is what gives the impression that the wheel is ~1" wider than it really is because each lip is ~.5" on aluminum wheels. In other words, tire manufacturer recommendations are based on the advertised (distance between sealing surfaces) rim width, and there is absolutely no fuzzy math necessary. My bad on stating the bead width. Also the "optimal" width for any give tire is not simply wheel width x 25.4, nor is tire width / 25.4 going to provide you with the "optimal" wheel width. As stated above, the recommended wheel width for a 215/60-15 is 6-7.5 inches, where as 7.5 x 25.4 = 190.5 and 215 / 25.4 = 8.5...Neither of which coincides in any way with the manufacturer specifications. Fair enough. Hard to argue against following manufacturer recommendations, and I agree with the spirit of your point that all tyres are subtlely different. However, my ``fuzzy'' maths would be something along the lines of 7.5 + 1 = 8.5 * 25.4 = (as you so correctly point out) 215. So following the very, very rough rule of thumb I understand, I'd recommend the 7.5" rim for a 215 tyre. The reason for this rule of thumb, again, just as I understand them are: * The section width of the tyre is measured sidewall to sidewall * For decent handling (optimal is clearly too strong a word), it is sometimes best to minimize tyre bulge, and keeping the sidewall flush with the lip is a reasonable way to do this. This tends to put a little less tyre on given rim than might be typical for tyre manufacturers and OEMs, whom I guess have to weigh other things like protection from curb rash, against handling. With the sidewall flush with the lip if you bump a gutter it tends to be all rim. Again, might be completely wrong with all of this, but it makes enough sense to me to be worth a mention. Dave Quote Link to comment Share on other sites More sharing options...
Driven5 Posted September 19, 2011 Share Posted September 19, 2011 Ok, I can see how your applying that rule of thumb better now, and in that context yes it will generally at least get you into the right ballpark when you don't have internet access. Quote Link to comment Share on other sites More sharing options...
johnc Posted September 19, 2011 Share Posted September 19, 2011 The recommended wheel widths listed in all tire advertising in the US is per a DOT rule. The widths are a recommended safe range within normal operation on a street driven car. Per Jeff Speer at Hoosier and Rudy at Kumho, the ideal performance rim width is .5" wider then the actual measured tread width (between the tips of the wear indicating triangles). And the actual tread width has little do do with advertised tread or section width. I used to run Hoosier R6 race tires listed at 275. The actual tread width was 297. Quote Link to comment Share on other sites More sharing options...
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