Quote:
Originally Posted by cerino2000
I think you guys are bass-ackwards on your shift point thinking. If the car shifts by MPH from the rear wheels, then a taller rear tire will make your shift point (rpm) higher. A smaller tire will see more revolutions of the tire at a given MPH. So the car will THINK it’s doing 60mph when in fact it’s only doing 58 mph.
I just put a set of the 275 35 20 Nitto 555r2’s on my car yesterday. The stock LT1 with run flats says they are 27.77 inches diameter according to the tire spec. The 555r says it is 27.56. Pretty close so I went with it. The car shifts at 6300 rpm in full auto. I didn’t pay attention to where it shifted before I put the tires on but plan on switching back in order to check. My phone GPS shows the car to be off by 1 mph. The car will show 60mph when my phone GPS shows 59mph.
Despite the measurements per the specs, here is a side by side of the stock 245 against the Nitto 275/35. I’ll tell you what the REAL measurements are in the next few days as I’m going to measure them.
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Its been shown the A10 upshifts at WOT by a mph table for each individual gear. If MPH is measured thru the output shaft of the transmission, actual MPH would be sensitive to tire diameter. If a smaller tire diameter makes a actual MPh reading faster by lets say 2mph compared to actual road speed, the trans will still shift at the same programmed MPH but the car will be going 2 mph slower. This scenario should have affect on RPM imo. If the MPH reading came from a front wheel, now the WOT shift should be at a higher RPM because the rear wheels and trans output shaft speed is 2mph faster than the front and the engine should be at a higher rpm at wot shift point. My understanding is if you want to increase the RPM WOT shift points, you have to just go into the MPH wot shift setting and up the MPH for each gear accordingly to get closer to a 6500 rpm shift point and the 2020 and 2021 A10 transmissions are not tunable yet.