Sandman

Anyone have 285/75/16 tires that can tell me what RPM they are running down the road at when going 65 MPH? How about 70MPH? This is with the 3.55 gearing. Also what is the best way to correct speedo?

Trying to decide if I should go back with my stock size of 265/75/16 or go bigger. I am only concerned about keeping my truck above 1700-1800 RPM's when towing my 10K 5th wheel.

Thanks.

bulabula

I consider that difference in size to be insignificant. The new tire (larger) will probably result in about a 3-4% decrease in rpm's over the orig tire for a given speed. I wouldn't worry about recalibrating the speedo for that.

I'd be more concerned that the tires are rated to do whatever you needed them to do, and to look good too.

Someone will probably chime in with a url that does the calculations for you (I don't have it). You can also go to tirerack.com and look up the tires in question and do the math based on revolutions per mile.

BIG MIKE

Sandman,
the 285/75/16 tires have a revs per mile of 614. The 265/75/16 turn 637 revs per mile. That is a difference of
- 3.6%. Hope this helps! BIG MIKE

k w

i beleive that at 65 you'll actually be going 69. your gear ratio if i did not make a mistake will be appx. 3.334

Sandman

Well I bought them today. Ride is definetely smoother with the 285's than the 10 ply 265's. Looks better too!

bulabula

Great Looking Truck! But it seems that you've got a bunch of leaks and wetspots under it .....

jefe4x4

S-man,
I have the aforementioned setup and it's almost dead on 2000 rpm at 65 mph and about 2125 (estimate) at 70. My experience was the Mich. OEM tires were too short for the speedo, making them a bit faster than actual speed. The 285's are now v-e-r-y close to actual and read speed. I notice a slight degredation in power and pickup with the larger tires. Also, the wear is bad on the BFG ATKO's. I'll be very surprized to get 20K out of them. This is with the Lance on the back and pulling a Jeep or Jeep on trailer.
There is another tread about 3.55 vs. 4.10 vs. 3.73. I like the 3.55's, expecially when going 75-80 mph. I just got back from a trip and we moved down the freeway at 80mph a lot with no winding up of the engine.
regards, as always, jefe

jefe4x4

S-man,
Your rig ilooks to be exactly the same as mine except mine's get-in-line appliance white.
regards, as always, jefe

Sandman

The shop I bought mine at talked me into them saying that they wear much better! I will be rather ticked off if 20K is all I get out of them.

My truck goes down the road at 2000 RPM showing 75 on the speedo. Every notch on the tach (125 RPM's) seems to make the truck go exactly 5 MPH faster or slower, example 80MPH is 2125 RPM's or 70 MPH is 1875 RPM's.

I haven't had the speedo corrected for the new tires, and I'm not sure it is off enough to mess with it. I took a trip to Tulsa last weekend and set the cruise on 70 and stayed even with the traffic in the slow lane, speed limit was 70.

slighfoxs3500

my 3500 does 70mph at 200rpm if that helps any. Don't know about the tires though. I went with a off brand and E ratings. A little bouncy and a little noisy but I kinda like a truck to ride like a truck.

slighfoxs3500

200 yuh right I mean 2000

bkrukow

I have that setup on my truck as well. I figure based on a few mobile radar sighns at the entrence to construction zones that my speedo is 4-5 mph slow. At 2000 rpm I am doing 70by my speedo 75 ish actuale. I was a bit disapointed on my las trip to colorado. I rented a 27 foot camper and tried to tow it in overdrive at 70mph and it would not hold speed if I hit any form of a grade or any head wind. I had to run at 75 the hole way witch is a bit faster than I realy wanted to tow the camper. If I got it up to 2000rpm it would forget the camper was back there. Had a real strong head/cross wind on the way home and had to run several hundred miles at 2500-2700 rpm out of OD. I wish the auto had a gear somewhere between 3rd and OD. The Cummins dident care though and dident even drop more than abought 1 mpg running it that hard over 2000.

Holycack

I have the exact same tires as you but with 4:10 gears. My dealer calibrated the factory computer for the increase in tire size. He said this is a very easy procedure. I was so impressed with my BFG AT KO that I just bought a second pair. On my previous BFG I got 90,000 KM out of them with about 50% towing. Hopefully you to will have no problems.

Sandman

How much did your dealer charge for that? Mine wants $65 whether he can change it or not, doesn't project alot of confidence to me!

bulabula

Sandman, find another dealer who can talk turkey.

Fact of the matter is, not all dealers are created equal. And when seeing other folks experiences with different dealers here online, we expect ALL dealers to perform to the same level. I do, but it ain't gonna happen. And what we're talking about isn't rocket science, nor is it a science experiment. If in the eyes of your dealer it IS a science experiment to recal your ECM, you shouldn't be required to fund that experiment.

Talk to the service manager; I'm sure he'll (she'll??) work with you.