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MR. WONKA
08-23-2008, 02:29 AM
I was going to change my tire height from my predator,however I think the measurements where in metric. Here are the numbers off of my tires 275/40 R20 106W. What is what? Is the 275 the height, and the 106 the width? Info I need info.
TMag
08-23-2008, 04:33 AM
275/40/20

275 is width

40 is sidewall size

20 is height(rim)

Basically thats it.
TheBeastMaster
08-23-2008, 04:41 AM
40 means the sidewall height is 40% of the tire width. So 40% of 275mm means the tire sidewall height is 110 mm. Tires of the same size may vary from one manufacturer to another. Don't input tire size to the Predator by the tire info. Input the overall height of the tire so the Predator can adjust based on that. However, going from 255/45 to 275/40 will only cause a 0.85mph difference in speedometer reading, so it's not critical to adjust in the Predator.
ewrecker2003
08-23-2008, 05:49 AM
Just use the tire size input insteed of the inches works much easier ;)
cadzilla74
08-23-2008, 09:16 AM
If the tire size you have is a choice on the menu use it ... otherwise, measure the tire with a tape measure from the ground up to the top of the tire and that is the size in inches to enter ...
stitchmonkey
08-23-2008, 09:21 PM
here's a tire size calculator
http://www.miata.net/garage/tirecalc.html

28.7" high


If you use the metric settings in the diablo, the first to enter is number is 275, the second is 40, and third is rim height 20.
05_BLKMAG_20
08-24-2008, 12:40 PM
Have any one else have this issue. I have entered it with the hieght and the tire size of 255 45 20 and I think the speedo is about 5 miles too fast.
Has anyone had the same issues.

Thanks
stitchmonkey
08-24-2008, 10:20 PM
Have any one else have this issue. I have entered it with the height and the tire size of 255 45 20 and I think the speedo is about 5 miles too fast.
Has anyone had the same issues.

Thanks

Do you have a way of checking? If you entered it in right should be dead on. We have these Radar speed signs all over Orange Co. Ca. at school zones and mine appears to be right on the nose if the signs are right?

Here in California the state allows for a 3% discrepancy.