Community Forums

fvstringpicker · 01-24-2013, 09:14 PM

2007 Duramax crew cab currently with 285/75/16E. I would like to downsize to a 265/75/16E because they would purportedly cause the trck to set lower and get better MPG. What tires should I get?. At least tell me what you get good service from,

Skip426 · 01-25-2013, 10:49 AM

You may run into , problems with the Allison trans, shift programing with a smaller tire, and require reprograming of the trans and speedo.
A smaller tire = more RPM at highway speed, although you may get some advantage in acceleration and holding speed on a hill, similar to a rear end gear change, better fuel mileage.. I don't think so

RustyJC · 01-25-2013, 11:12 AM

What tire size came standard on your truck? Check the sticker in the driver's door jamb. Aside from the diameter considerations, you'll lose tire load carrying capacity by moving to a smaller size.

LT285/75R-16E = 3750 lbs @ 80 psig (SRW application) 634 revs/mile

LT265/75R-16E = 3415 lbs @ 80 psig (SRW application) 657 revs/mile

This may affect your rear axle GAWR, depending on the size of your original equipment tires. If you're towing a heavy 5th wheel and are marginal on GAWR, you'd better check to ensure that you won't be exceeding the tires' load ratings if you downsize.

Rusty

fvstringpicker · 01-25-2013, 12:21 PM

The standard tire is 245/75/16E. We I got the truck, it had the 285s but the speedometer is off by about 4-5 mph. (showing 60 but traveling 65) Owners seem to go the 285s because they look better.

450Donn · 01-25-2013, 12:31 PM

i would not any bigger than the 265's for the simple fact as you go bigger you loose pulling power.

Franka548 · 01-25-2013, 04:13 PM

fvstringpicker,
I run B F Goodrich Commercial T/A all season on my dually, my last dually had over 50,000 miles on them and they were a little under half tread when I sold the truck. When I needed tires on my current truck, put the same tire on, I did go to L R E instead of D. Have about 20,000 miles on this set, and they still have about 3/4 tread, and most of the miles is towing my 16,000# 5er. You should be able to have your speedometer reflashed to show the correct speed for the tire size.
Frank

Ray,IN · 01-25-2013, 06:22 PM

I do as Frank, use B.F. Goodrich T/A commercial LR E tires. My reasoning_ I figure if those tires meet the requirements of UPS for their delivery trucks they are good enough for my truck. I suggest you return to the stock OEM tire size at this opportune time.They will cost less, have very near the same carrying capacity, slightly improve fuel mileage (narrower tires have less wind and rolling resistance), lower the ground-to-bedside clearance, and might help getting your truck/5er to both sit level when hooked up.

Capt Steve · 01-30-2013, 03:35 PM

Take a look at the Michelin LTX M/S 2's. They come with a nice street tread that rides smooth and quiet. The mileage warranty is 70,000. I replaced the original P's on my F-150 SCab with these LT's and the improvement in performance is astounding. Pulling the 5,000# TT was always good but with these tires it got way better. Got a set out the door for $879 and that included 4 free oil changes and that's worth at least another $160 to me. I stayed with the same size, 265/70 17's.

F239141 · 01-30-2013, 04:56 PM

You may be susprised that the MPGs will be their best with the 245's

Alot of that will have to to with the rear end gear ratio, if its a fairly high like 3.45-3.73 I would deffently go to the 245's 3.93 and up in number (of cousre thats a lower gear) the 265's will be fine.

The 285's affectively numaricaly lowered your ratio by .26 from the factory setup the 265's will lower the affective ratio by .14

Too tall of of tire and too high of a gear ratio will cause worse milage that a tall tire with a low ratio because you may not be at your peak power point what is 1800-2400 RPM for the duramax

Either way a good LRE tire will get you going

Jpetrey · 01-30-2013, 07:21 PM

Quote:

Originally Posted by Capt Steve

Take a look at the Michelin LTX M/S 2's. They come with a nice street tread that rides smooth and quiet. The mileage warranty is 70,000. I replaced the original P's on my F-150 SCab with these LT's and the improvement in performance is astounding. Pulling the 5,000# TT was always good but with these tires it got way better. Got a set out the door for $879 and that included 4 free oil changes and that's worth at least another $160 to me. I stayed with the same size, 265/70 17's.

Where did you by the tires that included oil changes?

Capt Steve · 01-31-2013, 06:58 AM

Quote:

Originally Posted by Jpetrey

Where did you by the tires that included oil changes?

Fletcher Tires, they are all over Arizona but not in other states as far as I know. I haven't paid for an oil change in years. I have used Fletcher for all of my tires, brakes, shocks and fluid changes for 7 years now and they always have the best price on tires even without the free oil changes. They drive Discount Tire nuts.

Jpetrey · 01-31-2013, 08:11 AM

Quote:

Originally Posted by Capt Steve

Fletcher Tires, they are all over Arizona but not in other states as far as I know. I haven't paid for an oil change in years. I have used Fletcher for all of my tires, brakes, shocks and fluid changes for 7 years now and they always have the best price on tires even without the free oil changes. They drive Discount Tire nuts.

Thanks for letting me know. Alas, I am in North Texas and Discount Tire so far has the best prices around.

JohnBoyToo · 01-31-2013, 08:24 AM

Fletcher Tires - sounds like a Franchise deal for us here in TexUS

AND FYI - Discount will match internet pricing in a lot of cases ....

Re tires size - I'm with Rusty here - go back to stock size, but consider upping your tire carrying capacity as a safety measure for those long hot summer pulls !

SmokeyWren · 02-02-2013, 04:47 AM

2007 GM 2500 came with LT245/75R16E tires on 16x6.5" rims.

The percentage change to speedo error and effective axle ratio is the same as the percentage difference in tire revs/mile. BFGoodrich AllTerrain T/A tires in size LT245/75R16E have 682 revs/mile. Same tire in size LT285/75R16E has 630 revs/mile.
Tire specs: BFGoodrich*All-Terrain T/A KO

682 minus 630 = 52, divided by 682 = 7.6%. So the speedo (and tripmeter used to compute MPG) should be slow by 7.6% until you have the speedo calibrated for the taller tires. And your axle ratio will be 7.6% longer legs than stock.

So at 70 MPH indicated, you'll actually be cruising at 75.3 MPH. That's enough to get Officer Bob's attention. Your tripmeter will be 7.6% slow, so 400.0 miles on a tank of diesel will be an actual 430.4 miles. So your MPG wasn't as bad as you thought.

Your 3.73 axle will "feel like" a 3.44 = not a huge difference unless you're towing weight close to your GCWR.

I don't know about Government Motors, but on a Ford the dealer can calibrate the speedo to match the tires you have on the truck. I wore out one set of LT285/75R16E tires on my SuperDuty, and my speedo was calibrated to 99.7% accuracy with those tires. (99.7 miles per the tripmeter when the interstate highway mile markers showed 100.0 miles.) I didn't appreciate the reduction of towing power with those tires, so I went back to stock-size tires and had the speedo re-calibrated so the tripmeter had near 100% accuracy again.

For folks with half-ton pickups that came with P-metric (instead of LT) tires, if you move up to LT tires in the future, DO NOT inflate LT tires to more than about 45 PSI unless you also buy new wheels designed for higher PSI. Your stock wheels are probably designed for 44 PSI max PSI available on P-series tires, and 65 to 80 PSI common with LT tires can result in disastrous wheel failure. The max PSI a wheel is designed for is stamped on the inside of the rim, so you have to remove a tire from the rim to see the max PSI for that wheel.