2001 dodge ram 1500 4x4 tire sizing

I currently have LT245-70-R-16 on the truck....I saw another truck the same model and year with LT285-75R-16..........will using a slightly larger tire mess up gearing or affect the transmission (automatic) or
rear diff??
Thanks'
Charlie The OC
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I have a '94 Ram 1500 4x4 with BFGoodrich 285-75R-16 Mud Terrain, which are great tires by the way. Yes, going with bigger tires will throw off your speedometer reading, so you should have it adjusted by a shop (I think it's the law, although that choice is left to you). I haven't had any issues with gearing or transmission problems, but the bigger tires give slower acceleration (if you care about that) and add weight and are less aerodynamic (assuming you will be getting tires with an aggressive tread). On the plus side, they look awesome and fill out the wheelwells better, and make the truck sit up higher.
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Thanks for the input......I really don't care about the speedo.......I don't really drive all that fast anyway, but my main concern was that they don't affect anything important....and you're right, they will fill out the wheel wells a lot better than those little 245's.....one last question; I also have the stock rims, and I've heard that some tire stores will tell you that they won't put a larger tire on a stock rim....is there any precautions with that, or is it just a tire dealer preference?? Thanks for helping me out....
Charlie The OC
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I have also heard that because they don't want to deal with messing up people's vehicles and then something going wrong and then suing them. I think that is mostly larger nationwide chains that have policies like that. You will most likely have to check with smaller, privately owned tire shops for the best chance that they'll install whatever you want.
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I'd think the '01 was supposed to have 75 series tires not 70. Check you owners manual. If that is the case, your tires are actually smaller than OEM.
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Laszlo Almasi
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Yup, just found it. OEM is 245-75/16 with optional being 265-75/16 or 275-70/17. So 285-75/16 is closer to OEM diameter I do believe. Your speedo should read slightly higher than OEM and going to the right size will bring your RPMs down slightly for the same speed.
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Laszlo Almasi
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Ok....ran the numbers....the tires you are running are 3.3% smaller than what is OEM (not optional equipment). The tires the other truck were running are 7.8% larger. A lot bigger difference than I thought it would be.
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