Fix Off Speedo w/ SCT?
03-25-2008, 12:14 PM
#1
2nd Gear Member
Thread Starter
Join Date: Oct 2003
Location: Cranberry Township, PA
Posts: 254
Fix Off Speedo w/ SCT?
Has anyone tried to fix the error with the speedometer with the SCT?
I have 235/55/17's and my speed is off by about 3mph at 65. The circumference for the tires are 742, per the Miata site. I tried adjusting it thru the SCT, it only goes in increments of 5, i.e., 735, 740, 745... I set it to 740 and my speedo was then off by about 5mph. I set it back to stock.
I really don't want to keep experimenting so I am hoping someone has already come up with the magic number.
I have 235/55/17's and my speed is off by about 3mph at 65. The circumference for the tires are 742, per the Miata site. I tried adjusting it thru the SCT, it only goes in increments of 5, i.e., 735, 740, 745... I set it to 740 and my speedo was then off by about 5mph. I set it back to stock.
I really don't want to keep experimenting so I am hoping someone has already come up with the magic number.
03-25-2008, 12:32 PM
#2
6th Gear Member
RE: Fix Off Speedo w/ SCT?
How are you determining how much you're off by? GPS? If so, then I'd simply zero-in on which setting gets you closest to your GPS reading. I've seen where 2 different websites had different revolutions per mile for the same tire.
03-25-2008, 02:23 PM
#4
5th Gear Member
Join Date: Sep 2006
Posts: 3,401
RE: Fix Off Speedo w/ SCT?
Well you know that speedos are never right, certainly across their whole range.
I will be corrected but the law states they must be accurate to +/- 6% or so, but that could vary between states/countries.
Don't forget that as the tire wears your speedo calibration means less and less.
3mph error at 65mph isn't that bad.
I will be corrected but the law states they must be accurate to +/- 6% or so, but that could vary between states/countries.
Don't forget that as the tire wears your speedo calibration means less and less.
3mph error at 65mph isn't that bad.
03-25-2008, 02:30 PM
#5
RE: Fix Off Speedo w/ SCT?
Go to the manufacturer website, and look for the rev/mile figure they have, it would be more accurate than using a tire size calculator.
Assuming they're Pirelli's, it would be 767.5 rev/mile.
Assuming they're Pirelli's, it would be 767.5 rev/mile.
03-25-2008, 03:39 PM
#7
2nd Gear Member
Thread Starter
Join Date: Oct 2003
Location: Cranberry Township, PA
Posts: 254
RE: Fix Off Speedo w/ SCT?
Checked Tire Rack, couldn't find the info. I'll check later tonight. I'll also check Pirelli's site.
Yes, they are the stock Pirelli's. Wow, 767.5 is a lot different than the 742 I got from the Miata site.
Since the SCT goes in increments of 5, I wonder if I should do 765 or 770? It's never easy...
Hasn't anyone tried this????
Yes, they are the stock Pirelli's. Wow, 767.5 is a lot different than the 742 I got from the Miata site.
Since the SCT goes in increments of 5, I wonder if I should do 765 or 770? It's never easy...
Hasn't anyone tried this????
03-25-2008, 04:15 PM
#9
Retired Mod
Join Date: Jan 2007
Location: Long Island, NY
Posts: 7,658
RE: Fix Off Speedo w/ SCT?
Forget trying to get it right!! IMO the stock speedo is not very accurate. I have a Aeroforce scan guage and it has a digital display for MPH and it conistantly is 3-5 mph lower than the needle on the speedo. IMO the needle is probably not calibrated properly!
03-25-2008, 04:27 PM
#10
5th Gear Member
Join Date: Feb 2005
Location: Anaheim, California
Posts: 4,205
RE: Fix Off Speedo w/ SCT?
And this site says 765.5 for your size, so I think I would try with 765. I just reset mine last night for both tire size, and rear end gear ratio. Much better, but I think I liked my speed prior to the adjustment.....[8D][8D]
http://www.1010tires.com/TireSizeCal...?action=submit
http://www.1010tires.com/TireSizeCal...?action=submit
