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Speedometer Recalibration Question For Larger Tires

multimopes

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I am considering larger tires, something akin to 33 x 12.50 R17 on a 99 Dodge Ram 1500. Stock size is 265-75 R16. Not that much taller. Can these trucks speedo's be reprogrammed or does the gear need to be changed?
 
I just use a speedometer app and note the differences at common speeds. I'm too lazy to swap gears in the transmission in the 99 is the same, need to swap gears. Someone can correct me if I'm wrong.
 
Thanks Locu, I did read somewhere recently that it can be done by a dealer without the gear swap but I don't remember where I read it. I am too lazy myself and it's more of a curiosity than anything else. I do recall on cars, that the Fords and Chevies use 2 gear drives for the speedo and you need to know how many teeth both gears were to select the right new gear. I looked up Mopar info and found nothing and even called venders who also seemed clueless. I think I found it in the FSM and it turned out most all Mopars had 13 teeth on the tail shaft and it was a known number. But because we were less in demand no one cared! I had to radically change the gear in my Satellite-RR clone.
 
If it's a mechanical speedo the gears need changed, if electrical not. Easy check would be to see if you have wires coming from the tailshaft or not 'cause I don't know when they changed all that.
 
Thank you all. I also remember some one mentioning that there wasn't much difference. I don't mind a few mph but more than 5 I would like to know due to Radar traps, etc....
I also know that tire diameter and total width and tread width are all BS. The way I measure tires differs greatly from what is published. I take an unmounted tire and put a carpenters square on top and mark on the wall the measurement. That's the true size. They may say that mounted and inflated it will make a big difference but that's also a crock! For example, I bought Mickey Thompson N-50/15 tires for my RR clone and they were advertised as being 28" tall. The real measurement was 26" tall. When mounted approx. 26,5" tall. The only way they could ever reach 28" would be to be spun on the rear of a 10,000 hp dragster at max throttle! It's a good thing I used my measurement when I ordered the speedo gear because according to those speed measuring cameras the police occasionally set up it is spot on! By the way, I have not yet even decided what size tires I am going to buy, 16" or 17" as my stock rims are 16x7" and the others I recently got are 17"x9". That's why I am looking for info as to what I have to consider before I decide. I love those big meats but also know what a negative offset can do to wheel bearings, etc...I would prefer a 16" or 17" rim that's 8 to 8.5" wide with a positive offset to mimic the factory offset. That way I can still do a 33" tall or close to that without all the hassles associated with going deep dish; ie: hitting curbs, rubbing fender wells, throwing mud and dirt all over the body as well as accelerated suspension wear. The other thing I know is 2 or 3 tires of the same advertised size can vary greatly from one brand to another. It seems that since the great outsourcing to other companies and countries has led to unreliable everything, especially if China is involved! Again, I appreciate any and all feedback to help me make a more rational decision!
Thanks!
 
I use Speedometer - app. A free down load. Use it on my android phone.
Your speedo is electrical. Any Ram dealer should be able to adjust it.
 
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