adj speedo for new gears
This is a discussion on adj speedo for new gears within the Computer & Tuning forums, part of the LSx Technical Help Section category; is there other was to correct ur speedo for different gears or wheels besides getting it done through a tune ...
08-30-2010, 03:41 PM #1
adj speedo for new gears
is there other was to correct ur speedo for different gears or wheels besides getting it done through a tune so when i run 410 with street tires then change to my slicks its not off, if any1 knows of anything plz let me no
08-30-2010, 04:25 PM #2
I don't think there is any other way to correct it other than through a tune.
08-30-2010, 04:36 PM #3
- Join Date
- Feb 2007
- San Diego, CA
2002 Z28 A4 NBM
- Sadly now demodded :(
Various hand held's allow you to change gear ratio as well as tire diameter.
These days the tranny has a VSS (Vehicle Speed Sensor) that the PCM reads to determine speedo reading. It's not like the old days when you changed out the gears in the tranny.
08-31-2010, 06:56 PM #4
09-01-2010, 04:27 PM #5
it all has to go through the the pcm, whether it is a hanheld or a full on tuning program. and no a gear change will not throw off your mph off by anywhere close to 45 mph. a friends ws6 had 4.11s put in with new rear and if i remember right it wasnt off by more than 5mph when driving next to me. it was 2-3 years ago though so i dont recall all details.
09-01-2010, 07:58 PM #6
The only reason he could have been 5 mph off is if he had 3.73s and went to 4.11s. Using these numbers you can back in to it. 3.73 gears with a 25.6 tall tire at 60 mph gives you the same 2967 rpms, with the 4.11s you are only going 55mph. There is your 5 mph difference. I doubt he had 3.73s and went to 4.11s.
Again, its math and you cant argue with it.
09-01-2010, 08:01 PM #7
One more quick thing.
My dads car had 2.41 gears in it and we went to 4.10s. You are right. It was not off 45mph after the gear swap.......it was off 39 mph.
09-01-2010, 10:17 PM #8
09-02-2010, 12:18 PM #9
Agreed, it would have came with the 3.42s which is most likely he swapped to the 3.73s. If he had the 3.73s with the PCM already adjusted than yes at 55 he was off only 5 mph, if not he was off more so.
I made the 45mph comment because my father had 2.41s in his Camaro and then went to 4.10s.....lol It was quite a swap my friend.
Going from 2.73s to 4.10s would be quite a jump as well. Which I am debating on 3.42s or 3.73s. I do some highway driving so not sure which way to go.
09-06-2010, 05:38 PM #10
HP tuners will automatically rescale your transmission for gears if you want it to caluate it automatically.
Enter your tire size and gears, and HPT with rescale your shift points
you dont have to do that in a corvette
09-07-2010, 04:22 AM #11
09-07-2010, 05:59 PM #12
Six speed manual need no re-programming after gear change
A4s need reprogramming mainly due to shift points -- but not to correct the speedo reading
Tire size changes (larger or smaller diameter) will affect the the speedo.
09-07-2010, 07:12 PM #13
However, my car is shifting at around 5500 rpm which with 2.73 gears is about 95 mph. If I do a gear swap I want it to shift closer to 6k rpms.
09-08-2010, 04:06 PM #14
Reason being that the speedo sensor on a C5 is on the output side of the differental and not on the output side of the trans like on an F body
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