Tire size?

A

ahunt01

New member
Hi, I currently have 185/65R 14 tires on my car, how bad would me speedometer be thrown off if I put 185/60R 14 tires on the same rims?

Also, currently my wheel gap is gone because I lowered my car, if I put the 60R tire on, would that ugly wheel gap come back, and would my car be lower to the ground?

Should I not go down to a 60R tire, or stick with the 65?

Thanks
 
Going to 185/60 will throw off your speedo by over 3%. And yes the gap will show again since you are using a lower profile tire.



Go with a 195/60 tire to maintain speedo and size.
 
3% speedo error really isn't that much is it? 100 mph on the speedometer would only be off by +/- 3 mph. Under normal driving conditions you'd only be off by 1 mph. I guess the real problem would be the change in in your odometer reading. Wouldn't that register more miles than actually driven?
 
How would 195/60 maintain the speedo and size? I thought the 185 &195 were just tire width, and not the diameter like 65R or 60R. The diameter is what I thought would affect everything.

I've heard from some people that dropping from 65 to 60 wouldn't really be noticable in the speedo, but I did hear from just as much people that it would. I'm equally concerned about the ride height, I like the height and wheel gap now. If I had a bigger wheel gap and then in turn had to lower the car more to make up for it, I would not be able to make it over the speed bumps at my college, so that's my biggest concern.
 
The "60" in a tire measurement of 195/60 isn't diameter, it's "aspect ratio". If you take the width of the tire (195mm) times 60%, you'll end up with the sidewall height in mm. So, to figure the overall circumference of a tire, it's



circumference = (diameter of wheel + 2 * sidewall height) * pi



The diameter of the tire is the diameter of the wheel plus 2 times the sidewall height. In your case, you have a 14" wheel. Let's convert that to 355.6 mm so that all of the untis are the same. Your sidewall height is 185mm * .65, or 120.25mm. So, the overall circumference of your stock tire size (185/65) is



c = ( 355.6mm + ( 2 * 120.25mm ) ) * pi = 1872.70mm



To calculate the overall circumference for the 195/60 tire:



Sidewall height = 195mm * .60 = 117mm

c = ( 355.6mm + ( 2 * 117mm ) ) * pi = 1852.28mm



Because the sidewall is measured as a fraction of the tread width, a wider tire (195mm > 185mm) with a smaller aspect ratio (60% < 65%) can have almost the same overall circumference. In the case of the two sizes we're talking about here, it's about a 1% difference in the speedo reading.



If you change from a 65 to a 60 aspect ratio while leaving the tire width the same, you reduce the sidewall height, which increases your fender gap. It's not much of a difference in this case, though; about a 1/4" difference in the diameter of the tire.



Check out http://www.miata.net/garage/tirecalc.html for a nifty size calculator that will let you compare two tire sizes to see what the difference in diamater and speedo error will be.



Tort
 
Daaannnnggg!!!



Mad propz to Tort for that post. I was too lazy to post that same Miata.net which I used to calculate tire sizes prior to my first post.
 
Yeah, big :bigup to Tort for posting all that! :eek:



I've found the miata.net tirecalculator to be indispensible, and it's now also hosted on another site..... which I don't have bookmarked for some bizarre reason.... :nixweiss



ahunt01, I'm not sure what your motives for wanting a 185/60 tire are, but if it's because a certain tire model isn't available in the correct 185/65, then I'm with Bret and would look at 195/60, hopefully the same tire would be available in that size. Most cars (with a few dumb exceptions) should be able to fit one size wider without issue.
 
4DSC, yeah I was looking at 185/60 tires because there is a little more performance tires in that size compared to 185/65. I never knew I could use 195/60 tires, that definately should open more options for tires.



TortoiseAWD, thanks a bunch for that thread, it helped tremendously:D
 
No problem . . . glad to have helped. Just sharing some of the useless trivia that clutters up my grey matter these days . . . :D



Tort
 
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