Tire diameter and computer
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Senior Member
Joined: Jan 2000
Posts: 135
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From: Miami, FL USA
Tire diameter and computer
Hello all..
I guess this question is for the chip and computer gurus.. How much will an over or under sized tire effect the computer and performance of the truck ? With the 20" replica wheels comming out, I have been looking for tires.. It looks like the 295-40-20 is a good bet.. but it is about 3% to tall.. ( compared to stock )
28.45 inches tall for stock..
29.29 inches tall for the 20"
I know this 3% will effect the spedo.. but will it effect the computer as far as performance ? Shifting ?
I am sure the computer can deal with a certain degree of variance.. but 3% ?
Much thanks..
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Got Boost ?
1999 SVT Lightning
I guess this question is for the chip and computer gurus.. How much will an over or under sized tire effect the computer and performance of the truck ? With the 20" replica wheels comming out, I have been looking for tires.. It looks like the 295-40-20 is a good bet.. but it is about 3% to tall.. ( compared to stock )
28.45 inches tall for stock..
29.29 inches tall for the 20"
I know this 3% will effect the spedo.. but will it effect the computer as far as performance ? Shifting ?
I am sure the computer can deal with a certain degree of variance.. but 3% ?
Much thanks..
------------------
Got Boost ?
1999 SVT Lightning
Former Sponsor
Joined: Mar 1998
Posts: 13,385
Likes: 4
From: Virginia
Hi Big,
The ECU normally looks at mph for determining it's shift points, as long as the speedometer is correct. The ECU gets it's basic speed info from the VSS (vehicle speed sensor), but it also looks at numerous other data streams (rpm, output shaft speed, etc.)to confirm VSS data, and if there is a large enough conflict there between the VSS and the other data streams the ECU uses to verify & confirm the VSS, then the ECU can default over to using rpms for shift points instead of mph.
So you can probably get by without a really noticeable "deficit" in your shift points with your proposed size change, just "hipshotting" this with a guess from what we've seen from our other Lightning and regular F-150 customers, but if it were me, I'd prefer to have it corrected if possible. This is strictly up to you, of course.
The way to correct for that is to do a speedometer recalibration, which we can do for these Lightnings in the Superchip, and that will restore speedometer accuracy as well as odometer accuracy and shift points as well.
If you have need for such services, just get it touch with us, our contact info is just below.
You can always go ahead and do this change, and if you feel that you can live with the results, do nothing about it, just enjoy your vehicle as usual. If you find that you can't live with the results, then we can take care of that for you, if you like.
Good luck!
------------------
Mike Troyer
Performance Products, Inc.
National Distributor of Superchips
(540) 862-9515
Email: mtroyer@compuserve.com
Performance Products F150Online Superchip ordering system: F150Online Superchip Ordering System
First National F-150 Online Rally Event Organizer
[This message has been edited by Superchips_Distributor (edited 05-14-2001).]
The ECU normally looks at mph for determining it's shift points, as long as the speedometer is correct. The ECU gets it's basic speed info from the VSS (vehicle speed sensor), but it also looks at numerous other data streams (rpm, output shaft speed, etc.)to confirm VSS data, and if there is a large enough conflict there between the VSS and the other data streams the ECU uses to verify & confirm the VSS, then the ECU can default over to using rpms for shift points instead of mph.
So you can probably get by without a really noticeable "deficit" in your shift points with your proposed size change, just "hipshotting" this with a guess from what we've seen from our other Lightning and regular F-150 customers, but if it were me, I'd prefer to have it corrected if possible. This is strictly up to you, of course.
The way to correct for that is to do a speedometer recalibration, which we can do for these Lightnings in the Superchip, and that will restore speedometer accuracy as well as odometer accuracy and shift points as well.
If you have need for such services, just get it touch with us, our contact info is just below.
You can always go ahead and do this change, and if you feel that you can live with the results, do nothing about it, just enjoy your vehicle as usual. If you find that you can't live with the results, then we can take care of that for you, if you like.
Good luck!
------------------
Mike Troyer
Performance Products, Inc.
National Distributor of Superchips
(540) 862-9515
Email: mtroyer@compuserve.com
Performance Products F150Online Superchip ordering system: F150Online Superchip Ordering System
First National F-150 Online Rally Event Organizer
[This message has been edited by Superchips_Distributor (edited 05-14-2001).]