MurderZ

Just wondered if the tire height was wrong in the computer would it affect the tune and performance at the track? Would it affect the shift points and stuff like that. I think in my computer it says 26" and my actual tire height is 27.8".

Pacer Racer

iTrader: (6)

It would depend on which tables it is shifting from, if it was shifting from the RPM tables it would still shift at the same points but if it was shifting from the speed tables it would shift early. So it was strictly depend on the values in the tables in your tune

flame

iTrader: (13)

The values that GM used were lower than actual to take into account the weight of the car being on the tire. It shouldn't be that much different though.

SMOKINV8

iTrader: (6)

Check the rollout on the tire to be accurate. Make a mark on the tire and ground, then roll the car forward or backward one tire revolution and measure from that point to your initial mark on the ground. Divide that number by Pi and that's your actual tire height.

MurderZ

Okay I'm just trying to figure out what's going on. When I go through the traps my car says I'm going through at about 6400 rpms and 110 mph. But when I get my time slip it says I'm going through at 120 mph. I checked the racing calculators on wallaceracing.com and I figured out by the rpm calculator that I would have a 26" tire not a 27.8" tire. With a 26" tire, 4.10 gear, and 1:1 transmission gear, and 120 mph it says my rpm would be 6358 rpms. With a 27.8", 4.10 gear, and 1:1 transmission gear, and 120 mph it says my rpm would be about 5946 rpms. So what do you guys think? Would a stall converter affect these results?

Pacer Racer

iTrader: (6)

What tranny and what gear are you in. if you're in the highest gear it isn't 1:1 unless its a 4 speed or some of the older automatic. Does your stall have a clutch in it? If so are you locking the clutch? A vehicle with a stall with an unlocked clutch will go through the traps at a higher RPM then a vehicle without a stall or one with a locked clutch.

MurderZ

I still have the 4L60e and I'm in Drive (3rd gear). I have the Yank SS4000 stall converter and I'm not locking the stall.

Pacer Racer

iTrader: (6)

Since the convertor isn't locked your engine rpm is going to be higher then what the calculated rpm should be due to the convertor slipage.

jmyers

iTrader: (1)

If I'm reading this right, you have a taller tire on the back and that will slow the vss signal output. This would show a slower speed in the car because the driveshaft speed has slowed down. If you were to put a shorter tire on it, that would speed up the output signal thus showing a higher speed in the car. In HPTuners in the speedo section, there is a place to input your gear ratio and tire height to correct your speedo. I just went thru this in my s10. I had the same gear in it that the Silverado had in it but my tire height was shorter. My speedo was showing about 10 mph faster. I adjusted the setting in the computer and all is good. I think it all has to do with driveshaft output speed as that is where the vss signal comes from. If I'm wrong, someone can correct me.

jmyers

iTrader: (1)

Use a tape measure next to the tire and that will give you total height in inches. Input that and it should correct. For example if you had 27 and 3/4 just input 27.75.