Driver72 Posted September 24, 2004 Share Posted September 24, 2004 As title states. Wondering what putting 225/45/17's on 17x7's and also 17x7.5 rims will do to my overal diameter (and therefore gearing/speedo changes) Thanks Link to comment Share on other sites More sharing options...
SC GT Posted September 24, 2004 Share Posted September 24, 2004 [url]http://www.miata.net/garage/tirecalc.html[/url] There's the tire size calculator. The diameter of the tire is going to remain the same. Link to comment Share on other sites More sharing options...
Driver72 Posted September 24, 2004 Author Share Posted September 24, 2004 Mooch aahs grassy asss! Link to comment Share on other sites More sharing options...
Driver72 Posted September 24, 2004 Author Share Posted September 24, 2004 Well, going to the 225's from 215, will increase diameter by just a bit. This of course, raises final drive ration a bit too, but not much. But, how can I figure what will happen when switching to a 17 x 7.5 wheel from the stock 17 x 7 wheel. I'm guessing it will "flatten" out the tire a bit and lower the overall diameter a bit, most likely matching the stock tire/wheel set up. Anybody know? Link to comment Share on other sites More sharing options...
SC GT Posted September 24, 2004 Share Posted September 24, 2004 225/45/17s on 7.5 inch rims will not flatten out the diameter of the tire so that it will be the same as a 215/45/17. Since 7.5 wide rims are the optimal width for 225s, their diameter is probably measured on 7.5" rims, so the manufacturer's reported diameter of the tire is likely what you would get if mounted on 7.5 rims. If anything, the diameter of 225s on 7.0 inch rims theoretically should be slightly (albeit imperceptibly) higher than the reported diameter for those tires, as the narrower rim would slightly increase the height of the sidewall. Link to comment Share on other sites More sharing options...
Driver72 Posted September 24, 2004 Author Share Posted September 24, 2004 The numbers found on the tires are not measured with the tires mounted on any wheel. A 225/45/17 tire mounted on a 7 inch wide wheel will be taller than on mounted on a 7.5 inch wheel. The 225 refers to the width of the tread the 45 basically means the sidewall is 45% of the width of the tread (the 225 part). The 17 refers to the diameter of the inside of the tire. I'm almost certain this is done with no load on the tire and not mounted on a wheel. Therefore, the wider the wheel you put that tire on the flatter it will be stretched out. And the skinnier you put the wheel on the more it will be pushed up. Obviously there are limits (ie: you cant put a 225/45 tire on a 5.5 inch wide wheel). Link to comment Share on other sites More sharing options...
SC GT Posted September 24, 2004 Share Posted September 24, 2004 Au contraire. The tire size calculator may use straight calculations, but if you want to determine real world diameters, go to either the Tire Rack or the website of the tire manufacturer to figure out the actual tire diameters. You will find that the diameter for 225/45/17s ranges from around 24.8" to 25.0". And the manufacturers list the width of the rim they used to measure the specs (width, sidewall height, diameter). The calculators good for giving you an idea if something fits, but if you want as close to exact measurements as possible, check the manufacturer's specs. Although you might be right about load. Link to comment Share on other sites More sharing options...
Xenonk Posted September 25, 2004 Share Posted September 25, 2004 The best one I have seen is the Dodge/Mopar tire calculator. Well, anyways,you can always do a Google search on it and it will pop on up online. Keefe Keefe Link to comment Share on other sites More sharing options...
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