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03:21:47 - 12/29/2024
Dakota Performance
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DarkDak
Dodge Dakota
JOIN HERE
4/02/2002
16:16:52
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 Subject: Tire/Speedo/Gear Ratio Question
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I'm looking at the ratio's for the 2002 Dak's and wanted to know if anyone had the answer for this. The rear gears are available in; 3.21, 3.55, 3.91, 4.10. IF you order/get a different tire size than the standard, say go from 215/75R15 to 255/65R65, that will change the outer diameter of the tires, 27.7 to 29.1, effecting the speedometer. Do they change the rear gearing or the calibration of the speedometer when they change the tires at the factory?
The reason I'm asking is that I noticed that the speedometer would change by a few MPH if you change tire size's later on. (Used a spreadsheet)
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Halo3
GenIII
4/02/2002
18:04:34
| RE: Tire/Speedo/Gear Ratio Question
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There are actually two answers to this. The factory and/or dealer can change the actual gearing to compensate for larger tires. When going to larger tires a gear swap may be required in order to get the overall gear ratio back to a point where the engine is operating in the strong part of it powerband. In your case, I don't think the change warrants the expense of changing gears (especially if you have a four-wheel drive...which requires two sets of gears to be changed).
The second part of that answer is yes, the dealer and/or factory will "calibrate the speedo". For us, the CAB (Controller Anti-lock Brakes) can be flashed to recognize the new revolutions per mile of your new tread. Unfortunately, most Dodge dealers will only flash your CAB for dealer/factory-offered tire sizes.
In my case, I swapped out the stock 235/75/15's for a set of 31x10.50's. Fortunately, this was a tire size that was indeed offered from Dodge for the 2000's, and I was able to get my CAB flashed to correct my speedo & my ABS behavior.
Along these lines, there's actually a very well-written article regarding changing gears in the May 2002 issue of Off-Road magazine.
Hope that helps....
Semper Fi,
Halo3
'00 Lt. Driftwood 4x4 SLT DQC w/5.9L
http://home.attbi.com/~quadcab
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DarkDak
Dodge Dakota
JOIN HERE
4/02/2002
18:37:10
|  RE: Tire/Speedo/Gear Ratio Question
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Message:
Thanks, not going to get the 4X4 because I just don't go off road enough, but the info that the correct speedo should be flashed at the factory if different than the base tires are chosen, is very welcome. Now to figure which rear end gears to choose. Decisions, decisions.
Semper Paratus
Soon to get a
'02 Graphite 4x2 Sport CC w/3.9 5-speed and then beginning that avalanche of speedtweaks mods
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