26" tire to 28" tire q's
#2
TECH Senior Member
with an A4 , yes you'd change the tire height and shift points... HP Tuners does this automatically (it rescales all your trans related tables when changing tire height or rear gear ratio)
Edit: Noticed you said using LT1 Edit... I've never used it before, but if it's similar to LS1 Edit, then yes you would first change the tire height... then go through and scale all the trans related tables by the % change
so
26" tall tire = 2(pi)r = 26*3.14159 = 81.68134
28" = 28*pi = 87.96452
% change in 1 tire revolution = ~8.15% difference
since you're effectively decreasing final gearing, you want to increase the existing shift tables... so multiply the shift tables by 108% (or multiply by 1.08) (bigger tire = more distance travelled in 1 rotation, = lower final gearing, so MPH needs to go up... RPM is RPM)
somebody wanna verify my calcs? It's late and I had a few beers tonight heh
Edit: Noticed you said using LT1 Edit... I've never used it before, but if it's similar to LS1 Edit, then yes you would first change the tire height... then go through and scale all the trans related tables by the % change
so
26" tall tire = 2(pi)r = 26*3.14159 = 81.68134
28" = 28*pi = 87.96452
% change in 1 tire revolution = ~8.15% difference
since you're effectively decreasing final gearing, you want to increase the existing shift tables... so multiply the shift tables by 108% (or multiply by 1.08) (bigger tire = more distance travelled in 1 rotation, = lower final gearing, so MPH needs to go up... RPM is RPM)
somebody wanna verify my calcs? It's late and I had a few beers tonight heh
Last edited by horist; 04-21-2006 at 11:53 PM.
#3
I found a site and figured that my mph is off bt 5.3%. I just trying to understand which way I'd move the mph & rpm.? I have been in the dark for so long about tuning I'd like to understand the basics since we depend on it so much.
Thanks for your input.
andy
Thanks for your input.
andy
#4
TECH Senior Member
the MPH would move up
increasing tire height increases tire circumference, which means in 1 revolution the tire moves the car a greater distance, as a result at any given RPM, w/a 28" tall tire you are moving a greater distance than you would with a 26" tall tire... thus MPH is greater, thus you need to raise MPH
increasing tire height increases tire circumference, which means in 1 revolution the tire moves the car a greater distance, as a result at any given RPM, w/a 28" tall tire you are moving a greater distance than you would with a 26" tall tire... thus MPH is greater, thus you need to raise MPH