Tire size...again (sorry)

johnymd

Club Member
Just about to order my new tire, I'm planning on going for 225/45 x 16 R888's. My reasoning behind this is as follows: The 3.9 diff I had with my 225/50 x 16 tires seamed a bit too revy so I changed to a 3.7. I now feel I want something in between so I thought reduceing the tire diameter would do this. does this sound about right? The problem I have is I'm not sure if the tire will look too small in the arch. Any comments?
 

zedhead260

Well-Known Forum User
Jon - you need to calculate this sort of stuff, don't just guess. Do you honestly think by fitting a slightly lower profile will account for changes in diff ratio ????

The tyre will look too small, you need 50 profile....... and fit a 3.9 FFS.:D
 

zedhead260

Well-Known Forum User
MPH = (rpm x 60 x pi x tyre dia) / overall gear ratio x 63360

note tyre diameter needs to be in inches.


I ran this calc for my Toyota and used rpm at 1k intervals and comparing to different diff ratio's (I'd already decided on tyre size based on what suited better visually).

If you are clever with Excel, you could formulate this and convert the tabulated data into a graph.
 

racer

Club Member
John why not run a 3.9 then up your tyre size too 235/50 witch increase the rolling radius slightly and up the gearing a tad.
 

johnymd

Club Member
Good point there Sean. I'll be sticking with the 3.7 and probably going for the 225/50x16's. The smaller the tire, the more caster I can run so I don't want to go bigger.
 
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