Contemplating Rear Gear change - Page 2 - ZR-1 Net Registry Forums

WVZR-1 · 09-18-2011

You didn't actually mention MPH in your initial post, only a % and that you were confident that the gear was a 3.45. The 3.45 gear, 12-15% error didn't work with any of the 19" tires that I was aware people were using. That suggested an error someplace. Now we're assuming the error is the drive/driven combination?

The 3.73 certainly would likely accomplish the performance balance you're looking to accomplish and while I was doing it I'd certainly check the drive gear in the transmission. If it's been changed to the 13 tooth to accomplish speedometer correction for 4.10's then I'd go back to the stock 15 tooth which makes correction with the 3.73 quite easy.

You would require a lesser tooth count than the 45 tooth if you wished to change and that's pretty straight forward. If it's a 13 tooth and you required a tooth count of less than 40 that usually suggests a different VSS that's indexed differently. You could also accomplish it with the DRA suggested.

I've always assumed a mechanical correction is the preferred.

Ccmano · 09-18-2011

Quote:

Originally Posted by WVZR-1

I've always assumed a mechanical correction is the preferred.

Just curious, why would this be the case? It's an electronic speedo to begin with?

H

WVZR-1 · 09-18-2011

Quote:

Originally Posted by Ccmano

Just curious, why would this be the case? It's an electronic speedo to begine with?

H

The VSS in some/most (not just Corvette) is used to electronically control emission devices, ECM, cruise control, ABS, converter lock-up etc. DRA's are used to correct only the speedometer/odometer aspect.

Ccmano · 09-18-2011

Quote:

Originally Posted by WVZR-1

The VSS in some/most (not just Corvette) is used to electronically control emission devices, ECM, cruise control, ABS, converter lock-up etc. DRA's are used to correct only the speedometer/odometer aspect.

Very true... from my perspective all the more reason to have a corrected signal go to the system. It's probably worse to drive around uncorrected. I'm not sure why it would make a difference if that is done mechanically or electrically. Maybe the more electronically minded on this forum can shed some light on this.

I have to say, I've been running this setup going on two years now and have not had a single issue. Everything works just fine. I'm very ahppy with it.

H

XfireZ51 · 09-18-2011

Hans,

I think swapping the speedo gear to one for 3.45s would be the least expensive alternative. Now if I did that and left the current 3.45 rear gears where they are, I'd be back to the situation I had with 474. That's why I am thinking 3.73s which, given the taller tire, would actually bring the VSS back to what it thinks it has, 3.45s. There are some parameters in the cal that use mph, like where idle should take over, but nothing terribly critical. Most of the main parameters utilize RPM since the motor really doesn't care what "speed" is but rather what rpm vs load is.

09-18-2011	#11
WVZR-1 Join Date: Oct 2004 Posts: 1,890	Re: Contemplating Rear Gear change You didn't actually mention MPH in your initial post, only a % and that you were confident that the gear was a 3.45. The 3.45 gear, 12-15% error didn't work with any of the 19" tires that I was aware people were using. That suggested an error someplace. Now we're assuming the error is the drive/driven combination? The 3.73 certainly would likely accomplish the performance balance you're looking to accomplish and while I was doing it I'd certainly check the drive gear in the transmission. If it's been changed to the 13 tooth to accomplish speedometer correction for 4.10's then I'd go back to the stock 15 tooth which makes correction with the 3.73 quite easy. You would require a lesser tooth count than the 45 tooth if you wished to change and that's pretty straight forward. If it's a 13 tooth and you required a tooth count of less than 40 that usually suggests a different VSS that's indexed differently. You could also accomplish it with the DRA suggested. I've always assumed a mechanical correction is the preferred. Last edited by WVZR-1; 09-18-2011 at 12:44 PM.

09-18-2011	#15
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,708	Re: Contemplating Rear Gear change Hans, I think swapping the speedo gear to one for 3.45s would be the least expensive alternative. Now if I did that and left the current 3.45 rear gears where they are, I'd be back to the situation I had with 474. That's why I am thinking 3.73s which, given the taller tire, would actually bring the VSS back to what it thinks it has, 3.45s. There are some parameters in the cal that use mph, like where idle should take over, but nothing terribly critical. Most of the main parameters utilize RPM since the motor really doesn't care what "speed" is but rather what rpm vs load is.