Rear FD 3.54 Problem!!! (P1574)
#18
01-25-2011, 11:47 AM
Changing the overall diameter of your rear tires is similar (though not quite as dramatic) as changing your FD ratio.
A smaller diameter tire shifts the true "final" ratio in the same direction as when you swapped from a 3.33 to a 3.54
So really, you're even more than a 3.54 so to speak.
A smaller diameter tire shifts the true "final" ratio in the same direction as when you swapped from a 3.33 to a 3.54
So really, you're even more than a 3.54 so to speak.
#19
01-25-2011, 12:01 PM
Ok i understand, that explains sometimes on the highway i can set my cruise
control and sometime I can't. I would like someone that has my yr and the 3.54 and different tires to chime in. Not to say your not helping me or giving me a better understanding. Have your heard of this issue or anything to resolve this issue.
Also is the TCM which i think is the tranny cpu connected with that because my car gave a tcm code but later disappeared ????
control and sometime I can't. I would like someone that has my yr and the 3.54 and different tires to chime in. Not to say your not helping me or giving me a better understanding. Have your heard of this issue or anything to resolve this issue.
Also is the TCM which i think is the tranny cpu connected with that because my car gave a tcm code but later disappeared ????
255/35 rear
3.54 gears
2003.0 old *** g
no cel
#20
01-25-2011, 01:07 PM
#22
01-25-2011, 01:13 PM
#23
01-25-2011, 01:19 PM
#24
01-25-2011, 01:26 PM
#25
01-25-2011, 07:50 PM
#28
01-25-2011, 08:16 PM
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Ok, when you change from the 3.33 to the 3.54, you change your FD ratio by 6.3% from stock.
With OEM size tires (or tires that are equal diameter front and back) the computer will only see a 6.3% change.
Apparently, this isn't enough to throw a code.
However, your rear tires are 1.3% smaller diameter than stock.
That brings you to a 7.6% difference. Basically the same as having an equivalent FD ratio of 3.59. Likely still not enough to freak out anything... until you factor in front tires...
Your front tires are actually 1.4% larger than the OEM diameter, throwing the imbalance up to 9% which is apparently enough to trip the computer out.
Consider that with this difference, when you're close to 90mph the car thinks it's front tires are going 10mph slower than it's back tires.
In Chris' case, the difference in tire diameter (though greater) actually works in the opposite direction because the larger diameter tires are on the back, not front.
Again, starting with the same 6.3% discrepancy from gear swap:
Chris' back tires are 2.7% larger than stock, bringing his equiv-FD down to a 3.44 and the difference to 3.6%
Then, factor in his fronts are actually 2.9% smaller than stock diameter, so that brings the driveshaft/front tire difference down to only 0.7% from the expected ratio.
So Chris computer barely sees any difference at all from what it was stock despite the rear end swap.
With OEM size tires (or tires that are equal diameter front and back) the computer will only see a 6.3% change.
Apparently, this isn't enough to throw a code.
However, your rear tires are 1.3% smaller diameter than stock.
That brings you to a 7.6% difference. Basically the same as having an equivalent FD ratio of 3.59. Likely still not enough to freak out anything... until you factor in front tires...
Your front tires are actually 1.4% larger than the OEM diameter, throwing the imbalance up to 9% which is apparently enough to trip the computer out.
Consider that with this difference, when you're close to 90mph the car thinks it's front tires are going 10mph slower than it's back tires.
In Chris' case, the difference in tire diameter (though greater) actually works in the opposite direction because the larger diameter tires are on the back, not front.
Again, starting with the same 6.3% discrepancy from gear swap:
Chris' back tires are 2.7% larger than stock, bringing his equiv-FD down to a 3.44 and the difference to 3.6%
Then, factor in his fronts are actually 2.9% smaller than stock diameter, so that brings the driveshaft/front tire difference down to only 0.7% from the expected ratio.
So Chris computer barely sees any difference at all from what it was stock despite the rear end swap.
#30
01-25-2011, 10:51 PM
Ok, when you change from the 3.33 to the 3.54, you change your FD ratio by 6.3% from stock.
With OEM size tires (or tires that are equal diameter front and back) the computer will only see a 6.3% change.
Apparently, this isn't enough to throw a code.
However, your rear tires are 1.3% smaller diameter than stock.
That brings you to a 7.6% difference. Basically the same as having an equivalent FD ratio of 3.59. Likely still not enough to freak out anything... until you factor in front tires...
Your front tires are actually 1.4% larger than the OEM diameter, throwing the imbalance up to 9% which is apparently enough to trip the computer out.
Consider that with this difference, when you're close to 90mph the car thinks it's front tires are going 10mph slower than it's back tires.
In Chris' case, the difference in tire diameter (though greater) actually works in the opposite direction because the larger diameter tires are on the back, not front.
Again, starting with the same 6.3% discrepancy from gear swap:
Chris' back tires are 2.7% larger than stock, bringing his equiv-FD down to a 3.44 and the difference to 3.6%
Then, factor in his fronts are actually 2.9% smaller than stock diameter, so that brings the driveshaft/front tire difference down to only 0.7% from the expected ratio.
So Chris computer barely sees any difference at all from what it was stock despite the rear end swap.
With OEM size tires (or tires that are equal diameter front and back) the computer will only see a 6.3% change.
Apparently, this isn't enough to throw a code.
However, your rear tires are 1.3% smaller diameter than stock.
That brings you to a 7.6% difference. Basically the same as having an equivalent FD ratio of 3.59. Likely still not enough to freak out anything... until you factor in front tires...
Your front tires are actually 1.4% larger than the OEM diameter, throwing the imbalance up to 9% which is apparently enough to trip the computer out.
Consider that with this difference, when you're close to 90mph the car thinks it's front tires are going 10mph slower than it's back tires.
In Chris' case, the difference in tire diameter (though greater) actually works in the opposite direction because the larger diameter tires are on the back, not front.
Again, starting with the same 6.3% discrepancy from gear swap:
Chris' back tires are 2.7% larger than stock, bringing his equiv-FD down to a 3.44 and the difference to 3.6%
Then, factor in his fronts are actually 2.9% smaller than stock diameter, so that brings the driveshaft/front tire difference down to only 0.7% from the expected ratio.
So Chris computer barely sees any difference at all from what it was stock despite the rear end swap.
