recently installed 315/35/20 tires, the height is like 28.7" tall compared to stock 27" . I thought the speedo will be off but i used a phone gps speedo and it read exactly the same on mine car:shrug: Any body have experiment with these please let me know , thanks. And if its off, how can i adjust it. I have an sct x3 programmer also.
just installed 315/35/20 tires. Is the speedo off or not?
- Thread starter black2007shelby
- Start date
There is no way that a tire change that drastic did not throw off the speedometer.
Did the people who mounted the tires adjust the rotations per mile?
The rotations per mile is a setting using your tuner. Just walk through user settings and you can change it easily.
Did the people who mounted the tires adjust the rotations per mile?
The rotations per mile is a setting using your tuner. Just walk through user settings and you can change it easily.
Duplicate
so i turn on mine sct tuner and click on where it said 315.35.20 tires?
steeda sent me the wheel/tire combo, i mount on the car mine self,, have no idea what u mean by adjust rotation
If your gps reading and speedo reading are right at each other, dont worry about it. I gained I believe a half inch or so in tire height going from my 295 Goodyears to the 305 Nitto 555rs.. I saw no appreciable difference between gps and speedo reading.. not enough to adjust in the tuner anyway.
The tuner adjustment is done with revolutions per mile I believe... you just have to pick the number that makes your speedo match gps.. trial and error.
The tuner adjustment is done with revolutions per mile I believe... you just have to pick the number that makes your speedo match gps.. trial and error.
The rev's per mile screen has 3 digit numbers in the 700's. Your stock RPM is 773...so I think it's set in the SCT at like 776 which is the closest. The Nitto's have an RPM of 726, so you'd want to find the number closest to that in your SCT Tuner.
Here's the formula:
revs per mile = 20850 / tire diameter
Here's the formula:
revs per mile = 20850 / tire diameter
got pics of the installed 315s?
It may not be wrong...I noticed on my Fords with cruise control set at 65 if I pass one of those RoboRadar cameras that post your speed it reads a few miles and hour slower then my speedo. Usually at 65 is clocks me at 62. Did you clock your speed before the tire swap with the same GPS by any chance?
As I recall for every inch in tire size the speedo get impacted by approx 2 mph. So with a 1.7 difference vs stock I would suspect you are off by 3.5-4 mph assuming they did not adjust at the time of install
Good info thanks guys
You can't use the unloaded diameter to make that calculation and expect accurate results. The radius under load compresses the unloaded radius by approximately 3%. Michelin's specs 726 revolutions per mile. Most manufacturers publish these specs. Check their websites. I didn't just pull 726 out my azz. Michelin Pilot SS Specs
Wasn't trying to offend you or your azz. I'm not married to anything I found on the web and hereby give permission to anyone to use whatever calculator, gps, kentucky windage, or your butt sensor to determine the accuracy of your speedometer .
pic of the car is in mine other thread, " just bought steeda wheel"
so i have a nitto nt05 315/35/20, should i click on the sct at 703 rev like "lawdude" just mentioned using his calculator or what ? Somebody with 315/35/20 tires using sct tuner please chim in , thanks
nope, after installed new tires, i use my phone gps to determine the speed
04-08-2009, 07:57 PM
Are those the 315/35,s and 275/40's ?
TIA
Yes. Are those the 315/35,s and 275/40's ?
TIA
Yes.
315/35/20 and 275/40/20
I checked on Nitto's website and the inflated overall diameter is the same at 28.62 and both have the same revs per mile at 726. I checked this to make sure there are no problems with transfer case.<<<<<<< found these on google talking about jeep cherokee srt8. SO WHICH IS CORRECT? 703 OR 726 REV PER MILE ?
Are those the 315/35,s and 275/40's ?
TIA
Yes. Are those the 315/35,s and 275/40's ?
TIA
Yes.
315/35/20 and 275/40/20
I checked on Nitto's website and the inflated overall diameter is the same at 28.62 and both have the same revs per mile at 726. I checked this to make sure there are no problems with transfer case.<<<<<<< found these on google talking about jeep cherokee srt8. SO WHICH IS CORRECT? 703 OR 726 REV PER MILE ?
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