I currently run 245x75 R16 size tires and am wondering what changing to 265x75 R16 will do to the gearing?

I have 3:54 gearing now, would that go higher or lower with a larger tire size? Also what speedometer adjustment would be required, if any?

 

The 265/75R16's should be about 1 inch taller and an inch wider than the 245/75R16's. I went from 265/75R16's to 305/70R16's which more than 2 inch difference, and my speedo is off by 2 mph at 75. Your's shouldn't be off my much at all, probably less than 1 mph. Taller tires makes your gearing numerically lower, so you'd probably be at 3.44 or something like that. There is a formula, but I forgot where I saw it. In my opinion, that small a change in size is not enough to worry about speedo or gearing changes. You should be fine.

 

When my truck was new the same change was made, there was some speedo difference but not enough to correct, just put them on, you will be happy. Looks a lot better also.

 

Goto tirerack.com and find your tires. Look up the specs for rev's per mile, and do the math (division) - calculators are permitted in class today.

The bigger tire will yield higher effective gearing (lower numerically).

From 245's to 265's, I wouldn't worry about it. Make sure the new ones look good.

 

I had 265 on my truck with 3.55s and the MPH was off by about 4. It caused the tranny to shift funny.

I went to 245s and the tranny now works like it should and tows better. If your going to tow with it don't up size the tires.

 

since 265's are an optional tire size on the rams you can take your truck into your dealer and reprogram the computer for 265's then the speedometer will be correct and so will your shift points


oh if you don't do the reprogram thing your speedo will read 7.5 % low

so when the speedo says 75 you'll be doing 80

 

[quote author=dodgeram link=board=10;threadid=19100;start=0#msg179938 date=1062580202]
since 265's are an optional tire size on the rams you can take your truck into your dealer and reprogram the computer for 265's then the speedometer will be correct and so will your shift points


oh if you don't do the reprogram thing your speedo will read 7.5 % low

so when the speedo says 75 you'll be doing 80
[/quote]

That would work, but I don't think you'll find a computer on a 12V! It's actually a bit more complicated for us properly valved guys. The dealership should be able to take care of it for you.
When I bought my CTD, it was set up for larger tire size, so my speedo was of by about 7-8%. It sucked, because I didn't know it until about 36,001 miles. Go figure. But most likely I had 7-8% less miles than that!

 

With my 265s I'm off 5% mileage and odometer.

This link will give you all you want to know and you don't need a calculator.

http://www.dakota-truck.net/TIRECALC/tirecalc.html

 

I have the 245's on now & was planning to jump to 265' or 285's. I knew about the speedo issue & it wouldn't bother me too much but I din't know it would mess up my shifting. That's not good because it already isn't shifting properly w/only 40k miles on it(started at 35k) Will this cause me more of a problem w/my shifting ???

 

[quote author=Bearfoot2 link=board=10;threadid=19100;start=0#msg180478 date=1062690515]
With my 265s I'm off 5% mileage and odometer.

This link will give you all you want to know and you don't need a calculator.

http://www.dakota-truck.net/TIRECALC/tirecalc.html
[/quote]

That graph is useless unless you check with the manufacturer for the turns per mile of your tires. My goodyear tires were 30 inches diameter and the michelens that I now have are 32 inches, both tires are 235/85-16. That is near 4 mph difference.

 

i have 285,s and noticed no difference in gearing ( not sure about the mileage theng and dont care ;D ) pulls a trailer just fine and get 18 +/- mpg later,scott


p.s. properly valved trucks rule

 

here is a link to a thread I had started earlier. from the calculations, the only diffrence between a 265/75/r17 and a 235/80/r17 is the width (265 being an inch wider) They are both 31 inch tires.
http://www.dodge-diesel.org/yabbse/i...threadid=18961
sorry for the width, I can't get the url thingy to work...

edited to add the proper info...
the 265/75/r16 = 10.4x31.64
the 245/75/r16 = 9.64x30.46

 

I have 285's and mine works fine ......but I have a 5spd standard and can adjust my shift points acordingly

the auto guys on the other have been known to have problems with bigger tires as the shift points are programmed to happen at certain speeds, the bigger tires throw them off