adj speedo for new gears

**02_slp_ss** · 08-30-2010, 03:41 PM

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

**35th-ANV-SS** · 08-30-2010, 04:25 PM

I don't think there is any other way to correct it other than through a tune.

**67CamaroRSSS** · 08-30-2010, 04:36 PM

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.

**TLS_Addict** · 08-31-2010, 06:56 PM

Originally Posted by 67CamaroRSSS

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.

Oh so you when you go from a 2.41 rear set to a 4.10 the speedo doesnt read 45mph off? lol

I am looking to get a new PCM too OP, I want to change gears but my PCM is locked.

**00z28bubba** · 09-01-2010, 04:27 PM

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.

**TLS_Addict** · 09-01-2010, 07:58 PM

Originally Posted by 00z28bubba

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.

55mph in drive in an automatic with a 25.6 tall tire and 25.6 inch tall tire reads 1971 rpms with the 2.73 rear. With the everything being the same other than the gears (using 4.11) you need to run 2967 rpms. If you have 2.73 gears and are running 2967 rpms you will be doing 83 mph. That is a very far cry from the 5mph difference you are claiming. Dont try to argue it either because its simple math.

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.

**TLS_Addict** · 09-01-2010, 08:01 PM

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.

**00z28bubba** · 09-01-2010, 10:17 PM

Originally Posted by TLS_Addict

55mph in drive in an automatic with a 25.6 tall tire and 25.6 inch tall tire reads 1971 rpms with the 2.73 rear. With the everything being the same other than the gears (using 4.11) you need to run 2967 rpms. If you have 2.73 gears and are running 2967 rpms you will be doing 83 mph. That is a very far cry from the 5mph difference you are claiming. Dont try to argue it either because its simple math.

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.

whoa dude chill. i have no clue what he had prior to swap. it was a blown rear possibly due to failed gear swap knowing the guy. even if it was a stock gearing no ws6 came with 2.73s. he had an m6 so it had 3.42s to begin with assuming it was a stock rear to begin with, which again knowing him there is a possibility it wasnt. as far as the 3.73 to 4.11 i wouldnt put it past the guy. but there is no way in hell it was anything less than 3.42s.

**TLS_Addict** · 09-02-2010, 12:18 PM

Originally Posted by 00z28bubba

whoa dude chill. i have no clue what he had prior to swap. it was a blown rear possibly due to failed gear swap knowing the guy. even if it was a stock gearing no ws6 came with 2.73s. he had an m6 so it had 3.42s to begin with assuming it was a stock rear to begin with, which again knowing him there is a possibility it wasnt. as far as the 3.73 to 4.11 i wouldnt put it past the guy. but there is no way in hell it was anything less than 3.42s.

Sorry man, didnt mean to come off that way. I had a discussion with a guy the other day who tried to tell me his 3.91 geared Coronet R/T would run 155 mph. You cant argue with some people though because even if you show them with math they wont admit they are full of sh!t.

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.

**Tampa Tuning** · 09-06-2010, 05:38 PM

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

**TLS_Addict** · 09-07-2010, 04:22 AM

Originally Posted by TampaTuning

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

Why is that?

**Tampa Tuning** · 09-07-2010, 05:59 PM

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.

**TLS_Addict** · 09-07-2010, 07:12 PM

Originally Posted by TampaTuning

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.

So why does an F-body need reprogramming with an auto but a Corvette does not? Confused on this one....lol Just seems strange that GM would make it a must on one car and not another using the same basic engine and transmission.

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.