Got a question I haven't been able to find and answer for on another forum, other than "it's not right". My thought is that no one that actually knew an answer saw my question.
Does the differential ratio have to be spot on correct in the tune, or could it be a little different, 1% in this case? Will that do anything other than skew the speedo/odo?
2009 Pontiac G8 GT
Last edited by J Wikoff; 01-30-2024 at 06:57 PM.
Is the rest of your tune within 1% on everything?
No, that amount will not make any difference to anything. Changes in ambient temperature from day to day will change the tire pressures and therefore the tire diameter more than 1%.
It's as dialed in as a canned tune with typical easy bolt-ons can be, I guess.
The 1% won't mess with shift points or traction control or something else counter intuitive in any other way than a minor annoyance? Someone acted like I would be commiting a sin but couldn't tell me why. I didn't know if the PCM would be upset if the wheel speeds were 1% off from what the trans output speed was, or something along those lines.
I know it's not perfect, but the option I was looking at were a 3.45 Camaro diff with a canned tune that presented 3.42 as the closest choice.
Thanks for the help!
2009 Pontiac G8 GT. Done some stuff to it.
On the 5th Gen Camaros it takes something like a 5% difference in tire size change on one end to start causing problems with traction control.
Compare what a GPS shows for MPH to what the scanner shows for MPH at 50. Since any gear ratio/tire size error is progressive I find 50 is a good medium checking point.
Most speedos are off by more than 1%.
EFI specialist
Advanced diagnostics, tuning, emissions
HPtuners dealer and tech support
email=[email protected]
Yep. Everyone says "My speedo is off by X amount" and I reply "at what MPH"? Huh??? LOLOriginally Posted by 2xLS1
I check them on the dyno at 25, 50, 75. I'll also check them by phone GPS if there is any question.
EFI specialist
Advanced diagnostics, tuning, emissions
HPtuners dealer and tech support
email=[email protected]
Tires are also smaller diameter than their sidewall/published size by a lot more than most people would think. The amount smaller depends on weight on that axle and air pressure. My supposedly 28.6" tires have an effective diameter (distance from ground to axle c/l times two) of 26.4", at 32PSI. Speedo is practically zero error if I use the effective diameter, not so if I input the advertised number.
I think the real problem for OP could be different wheel speeds if there is check between front wheel speed and "vehicle" speed. But that might only be based upon individual wheel speed sensors.
I don't care what the speedometer shows. I care what the scanner mph shows vs gps. That is what needs to be accurate.
Reply With Quote