Speedometer correction?
Melting Slicks
Joined: Dec 2006
Posts: 2,694
Likes: 106
I don't know where the speedometer picks up the signal, but if it's in the tranny, gear ratios obviously affect accuracy. If in differential, it would not.
Tire circumference changes for sure affect speedometer accuracy, but if less than 5%, you should be fine. But more importantly, just changing rear circumference could affect Active Handling (AH), and cause error codes. I don't know the tolerance.
Post EXACTLY what you want to do with both tranny and tires so an expert can help you. Good luck.
Tire circumference changes for sure affect speedometer accuracy, but if less than 5%, you should be fine. But more importantly, just changing rear circumference could affect Active Handling (AH), and cause error codes. I don't know the tolerance.
Post EXACTLY what you want to do with both tranny and tires so an expert can help you. Good luck.
Le Mans Master
Joined: May 2011
Posts: 5,022
Likes: 18
From: Tampa FL (formerly Justinjor)
Tech Contributor
St. Jude Donor '11-'12-'13-'14
In my experience, my speedo reads 5mph low when I put on my drag radials that are about 1.5" shorter. Also, I've read that you're not SUPPOSED to need to adjust the speed if you change the ring/pinion but my speedo was way off until I corrected for the 3.90 gearing.
Drifting
Joined: Nov 2005
Posts: 1,745
Likes: 35
From: Turlock CA
Le Mans Master
Joined: May 2011
Posts: 5,022
Likes: 18
From: Tampa FL (formerly Justinjor)
Tech Contributor
St. Jude Donor '11-'12-'13-'14
Ya, I make the applicable changes, except that if you look at a stock 2008 LS3 manual transmission tune, those tables are untouched by the factory. I left them alone and just adjusted the tire size by the applicable correction factor.
Tech Contributor
Joined: Jul 2002
Posts: 14,950
Likes: 264
From: St. Louis, MO
St. Jude Donor '08
Scratch that, reverse it.
Swapping gear ratio doesn't matter as the VSS reads off a reluctor ring bolted behind the ring gear. The ring gear has nothing to do with the VSS.
However, tire size absolutely changes the speedometer reading. You can correct it very easily with HP Tuners. Smaller tires make it read faster, taller tires make it read slower.
Check out my 'expanded' rear end view and you can see the reluctor ring, the VSS sensor bolts on top (when you have the other side of the diff connected).
Swapping gear ratio doesn't matter as the VSS reads off a reluctor ring bolted behind the ring gear. The ring gear has nothing to do with the VSS.
However, tire size absolutely changes the speedometer reading. You can correct it very easily with HP Tuners. Smaller tires make it read faster, taller tires make it read slower.
Check out my 'expanded' rear end view and you can see the reluctor ring, the VSS sensor bolts on top (when you have the other side of the diff connected).
Tech Contributor
Joined: Jul 2002
Posts: 14,950
Likes: 264
From: St. Louis, MO
St. Jude Donor '08
Your 08 had a odd vss pulses per mile, unlike any other tune as I recall. Didn't you just have to put in a "regular" tune's vss pulse factor?
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Le Mans Master
Joined: May 2011
Posts: 5,022
Likes: 18
From: Tampa FL (formerly Justinjor)
Tech Contributor
St. Jude Donor '11-'12-'13-'14
No, I tried a bunch of different things. The 2008 has a very strange default setting in the OEM tune. I tried to have it mirror the 2009, 10, etc, but it would never read correctly. I ended up putting it back to normal and just changed the tire height by my % error, 5 or 6% I believe.