New Tire Ratio vs Old...
Thread Starter
Safety Car
Joined: Mar 2002
Posts: 3,556
Likes: 2
New Tire Ratio vs Old...
The Factory Rear Goodyears check in at 26.7 inches tall. My new Pilot Sports check in at 26.1, a fairly significant difference :(
I know this will help my acceleration times (the shorter tire is like adding more gear) but my question will be how much will it affect it-do I technically have a "3.55 rear pinion" now...? How much will my speedo be off?
I know this will help my acceleration times (the shorter tire is like adding more gear) but my question will be how much will it affect it-do I technically have a "3.55 rear pinion" now...? How much will my speedo be off?
Race Director
Joined: Feb 1999
Posts: 14,263
Likes: 1
From: DFW, Texas...2001 Millennium Yellow Z06
Re: New Tire Ratio vs Old... (MiamiDave)
i thought the C5 has way of compensating for tire changes....some kind of speed sensor or some chit like that ?!?!??!?!?!
been wrong before :cry: :lol:
thanks
been wrong before :cry: :lol:
thanks
Thread Starter
Safety Car
Joined: Mar 2002
Posts: 3,556
Likes: 2
Re: New Tire Ratio vs Old... (Ram Air Tony)
Hmm...I thought you had to adjust the whatchmacallit-or the thingamajig...
Who knows with these C5's :banghead:
I'm only guessing my 3.42 rear will become a 3.55...
Who knows with these C5's :banghead:
I'm only guessing my 3.42 rear will become a 3.55...
Race Director
Joined: Oct 2002
Posts: 16,477
Likes: 26
From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
Re: New Tire Ratio vs Old... (MiamiDave)
Well, the tire height is a 2.3% difference. Applied to the axle ratio, that would leave you with 3.49. You'll probably not notice the difference.
As for the speedo, it will read slightly faster than you are actually going. At legal speeds, the error factor would be within 2 mph, so consider it a slight built-in safety cushion.
:cheers:
As for the speedo, it will read slightly faster than you are actually going. At legal speeds, the error factor would be within 2 mph, so consider it a slight built-in safety cushion.
:cheers:
Melting Slicks
Joined: May 2001
Posts: 2,596
Likes: 120
From: East Tennessee
Re: New Tire Ratio vs Old... (Ram Air Tony)
i thought the C5 has way of compensating for tire changes....some kind of speed sensor or some chit like that ?!?!??!?!?!
been wrong before :cry: :lol:
thanks
been wrong before :cry: :lol:
thanks
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Safety Car
Joined: Aug 2000
Posts: 4,154
Likes: 1
From: Murphy TX
Cruise-In II Veteran
Re: New Tire Ratio vs Old... (MiamiDave)
kp is correct, you must program for speedometer accuracy when changing tire sizes. (This is a textbook example of a calibration value.)
tire size change: auto reprogram, 6-speed reprogram
gear change: auto reprogram, 6-speed not needed.
Note too that WSSs work in terms of vehicle speed. I haven't yet seen a way to recal the EBTCM for altered tire sizes or looked closely at the way it interfaces with WSS and VSS sensor signals. I did do the math at one point to get a better handle on what front and rear tire diameter combinations could be expected to cause problems and wasn't alarmed enough by what I saw to pursue it any further. Technically, there is some gray area regarding what all needs to and can be reprogrammed to accurately and completely correct for this. I think the EBTCM and PCM both need to be adjusted but we can only handle it for the PCM.
tire size change: auto reprogram, 6-speed reprogram
gear change: auto reprogram, 6-speed not needed.
Note too that WSSs work in terms of vehicle speed. I haven't yet seen a way to recal the EBTCM for altered tire sizes or looked closely at the way it interfaces with WSS and VSS sensor signals. I did do the math at one point to get a better handle on what front and rear tire diameter combinations could be expected to cause problems and wasn't alarmed enough by what I saw to pursue it any further. Technically, there is some gray area regarding what all needs to and can be reprogrammed to accurately and completely correct for this. I think the EBTCM and PCM both need to be adjusted but we can only handle it for the PCM.
Safety Car
Joined: May 2000
Posts: 4,827
Likes: 351
From: Albuquerque NM
Re: New Tire Ratio vs Old... (MiamiDave)
"technically" you still have a 3.42 R&P. The change in tire diameter will change your engine rpms Vs. road speed ratio just like a change in gearing, but this is only a 2.3% change. This will be like running a 3.50:1 rear gear set, with stock height tires. The speedometer will be off because of the tire change, it wil read higher than you are really going. :cheers:
Burning Brakes
Joined: Aug 2000
Posts: 802
Likes: 0
From: Boca Raton, FL
Re: New Tire Ratio vs Old... (MiamiDave)
So which is it...? I think it must be programmed...
Race Director
Joined: Feb 1999
Posts: 14,263
Likes: 1
From: DFW, Texas...2001 Millennium Yellow Z06
Re: New Tire Ratio vs Old... (kp)
The speedo is driven off the axle so changing the gear itself will not affect the speedo but tire size will change the speedo..
thanks
R
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