Using shorter drag radials cause any problems??
#31
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Originally Posted by rjolly87
Originally Posted by Rogue
The VSS gets it signal from the rotation of the reluctor ring on the differential. With smaller or larger tires the rotational speed of that ring is off thereby effectiveily changing the final drive ratio.
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Originally Posted by rjolly87
what rogue is saying, is that the car will shift early <in the rpm band> because of this, which is what we are trying to understand.
Hopefully, I can just manually shift it and that'll take care of the potential problem...
Whatdya think rogue, what are my chances of being able to manually shift it and eliminate the possibility of weird crap happening??
#33
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Originally Posted by Rogue
The VSS gets it signal from the rotation of the reluctor ring on the differential. With smaller or larger tires the rotational speed of that ring is off thereby effectiveily changing the final drive ratio.
Am I incorrect in assuming the VSS only sees the rotational speed of the wheels?
The way I understand the system, the only way for tire size to change anything the PCM sees is if the VSS were in the fenderwell, with its own little wheel of known diameter spinning on the tire tread or on the ground.
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Originally Posted by jwikoff99
Does tire size affect how the reluctor ring spins with relationship to tire rotational speed?
Am I incorrect in assuming the VSS only sees the rotational speed of the wheels?
.
Am I incorrect in assuming the VSS only sees the rotational speed of the wheels?
.
#35
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okay, lets blow this out of proportions, and put little 6 inch tires on <no they wont fit, but im making a point> and set him loose on the track. he takes off, and when the vss reads 50 mph he shifts correct? it is after all at the top of the gear according to the PCM calculations. but what you are saying, is that it will shift lower, at say 3000 rpm, instead of 5800, because that is when it is doing 50mph. if that were the case, and you could magically change the shift points to be at the top of the gear, you could roll 100 mph in 1st gear<according to the vss> which doesnt make sense to me. am i correct in saying that first gear is made taller with smaller tires?
***please note, this is pretty much what i understand you saying, just with differant numbers***
***please note, this is pretty much what i understand you saying, just with differant numbers***
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The VSS calculates speed based on how many times a magnet reads a tooth in the 32 tooth reluctor wheel around the differential. The PCM Calculates speed based on how many times a hit (signal) is made on the reluctor.
When gearing is changed in the car (example 2.93 to 3.29) we used to put a reluctor spoof on, change the amount of teeth to 34. The signal hit rate would be the same time per rotation now with 34 teeth instead of 32.
Without telling the PCM anything has changed it will contintue to calculate speed based on the hit rate of the relecutor. Because the tires are smaller it will spin faster give a false reading which is why your speedometer has an inflated number (doing 75 instead of 72 for example). Because the PCM calculates shift tables based on rpm and vehicle speed an artificially inflated number will cause that calculation to be off.
In rjollys example above the VSS will see 50 mph almost instantly with 6 inch tires due to the rotation of the reluctor spinning so fast and so it will shift way way WAY early.
When gearing is changed in the car (example 2.93 to 3.29) we used to put a reluctor spoof on, change the amount of teeth to 34. The signal hit rate would be the same time per rotation now with 34 teeth instead of 32.
Without telling the PCM anything has changed it will contintue to calculate speed based on the hit rate of the relecutor. Because the tires are smaller it will spin faster give a false reading which is why your speedometer has an inflated number (doing 75 instead of 72 for example). Because the PCM calculates shift tables based on rpm and vehicle speed an artificially inflated number will cause that calculation to be off.
In rjollys example above the VSS will see 50 mph almost instantly with 6 inch tires due to the rotation of the reluctor spinning so fast and so it will shift way way WAY early.
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Originally Posted by jwikoff99
What does the PCM do if you're airborn and you floor it?