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XfireZ51 · 09-18-2011

Jeff,

Actually you just reminded me that I did observe speed discrepancy on 474. I had same wheels and size tires on that car and found speed delta to be about 3-4mph at 60. So I suspect that #458 likely had 4.10's along with the required speedo gear in the ZF. That would explain the larger discrepancy. in fact, I used my standalone GPS on 474 to measure the speed differential. At the time, I thought it wasn't worth the bother in terms of correcting the speedo.
A 5-6% differential in speed would suggest a 3.73 rear to get things back to acting "as if" it's a 3.45 with the 19's.

Paul,

The objective at this point is to get things back to "stock". That speed differential would explain the lower trap speeds with 474 once I put on the 19s. At the big end, I was coming thru at a somewhat lower rpm altho the ets were the same.

09-18-2011	#7
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,662	Re: Contemplating Rear Gear change Jeff, Actually you just reminded me that I did observe speed discrepancy on 474. I had same wheels and size tires on that car and found speed delta to be about 3-4mph at 60. So I suspect that #458 likely had 4.10's along with the required speedo gear in the ZF. That would explain the larger discrepancy. in fact, I used my standalone GPS on 474 to measure the speed differential. At the time, I thought it wasn't worth the bother in terms of correcting the speedo. A 5-6% differential in speed would suggest a 3.73 rear to get things back to acting "as if" it's a 3.45 with the 19's. Paul, The objective at this point is to get things back to "stock". That speed differential would explain the lower trap speeds with 474 once I put on the 19s. At the big end, I was coming thru at a somewhat lower rpm altho the ets were the same. Last edited by XfireZ51; 09-18-2011 at 09:52 AM.