Does the overall tire diameter remain roughly constant no matter what the wheel diameter is? In other words: is a 16" wheel plus its proper tire have the same overall diameter of an 18" wheel plus its proper tire.

The reason I ask is that I would like to increase the height of the mini's chassis to pavement clearance.

 

The tires are equivalent (close) in diameter and circumference whether 15, 16, 17 , or 18 inch. For example a 175/65/15 equals a 195/50/16.....diameter of the 16 inch is .28 smaller and the circumference is .88 smaller. This being totally acceptable. A 205/45/17 is the equivalent 17 inch and 205/40/18 is the 18 inch size. Increasing the height will increase speedometer error. For example going from a 195/50/16 to a 195/60/16 to increase height changes the speed from 65 mph to 69.22 mph. Its up to you but speedo error increases. Good luck in your decision.

 

Check out this Tire Converstion Calculator...
http://www.miata.net/garage/tirecalc.html

 

Thanks guys!

 

Actually, that's backwards. A taller tire will make the speedo read slower, because you're traveling farther for each rotation of the wheel. In your example it's 6.5% larger, so 60 on the speedo (if accurate) would actually be 63.9

 

If you use the Discount Tire Direct size calculator it provides the equivalent speed in mph for tire size. In the case of the sizes given - 195/50/16 verses 195/60/16 - it says that if the 195/50 is going 65 the speed with the 195/60 will be 69.22. Give it a try. That is where I got the information from. If you reverse the numbers in the chart and you have the 195/60 at 65 mph then the 195/50 will be at 61.04 mph. Thanks.

 

You might not want to try a larger tire just to get more ground clearance. If you got 1" taller, you only gain 1/2" of ground clearance and the speedo is off. How much more clearance do you desire?

 

yetti96,

I would like to get whatever distance I can! I live out in ranching territory and lots of debris gets dropped on the roads. I'm hoping for maybe 1-inch max. of additional clearance so anything I could get on the wheel/tire combination would be helpful! I'm not looking for anything drastic.

There's one more consideration... I have 16" Mini bridgespoke wheels... but I would like to get something a little different. I noticed there are lot's more choices in wheels if one goes to the 17"....so I was trying to see if I could accomplish a little bit with wheel size.

 

Increasing wheel size generally means that the sidewall will be lower profile to maintain the same height.....if that was what you wanted. A lower profile is a more
sport/handling package with rougher ride. There's also more of a chance side wall damage and the ride is stiffer too. These are more high performance tires. But, there is always the tire will be bigger in diameter that will fit. As long as the center is 17 inches it will fit. There other considerations in the larger the tire. Such as whether it will rub on the fender flares under load and over bumps and whether it will scrub when turning in when cornering. Again the speedo will be well off, but, as long as you the error you can adjust by varying your foot pressure on the accelerator and showing less on you speedometer. Things to think about.