Tire size related performance problem?

[TraceF]

I am a new Duramax owner with questions. I have a 2003 HD 2500 4x4 CC SB D/A with 1000 miles on it. I put BFG 285's on it after a little bit of plastic trimming. Towed for the first time yesterday and was very dissapointed. My boat is a 27' offshore fishing boat, needless to say pretty aerodynamic compared to some of the hoe's, tractors, and 5th's you guys are pulling. It scales at almost 10,000# with gas, water, and ice, trailer, etc. My 2002 K2500 4x4 454 would easily outrun the Max with the same load up to any, repeat any- speed. At times I had to keep the pedal to the floor to keep the rig going 60! Spent the day at the dealer. Dealer says tires are confusing the computer and costing power... they produced a GM Tech Bulletin # 01-03-10-010B (10-14-2002) which essentially says not to work on diagnosing power complaints if the oem tire size has been changed. It SPECIFICALLY says dealer and owner should not alter tire size. Any input on tire size related performance issues? Thanks

[Burner]

Feel your pain, yes. My 02' was a monster comparied to this 03' GMC. Let it break-in a little more. You really need to let the the drivetrain break in before you start pulling.----


I would give it about 3k miles and then see what happens. It could be the "wire" in the system. It may be the "new" program. It could be a bad injector, turbo or transmission. Like I said, give it about 3k before you stammer. ;)

---- I'm hating mine right now. I'm hoping it get's better.

:(

[a bear]

The Allison web sight has good information in the FAQ section about tire sizes. One thing mentioned was that P285 tires can cause confusion with the TCM. Theres also lots of other information there.
Hope this helps.

New member as of 12/18/02

[pullinpower]

I put 285's on my 01 shortly after I got it and had no problems at all.I say give it some time and it will come around.hang in there and keep your foot to the floor :D

[NWDmax]

10,000 lbs with the camper on and pulling my 18' bass boat is no problem up a 7% + grade.
I'd follow Burner's advice on this one.
BTW I've got 15,000 miles on now and have heard the break in can run up to 24k miles.
Don't know how scientific that estimate is.
Please let us know the outcome. Blake

[1822]

My 02 took about 6000 mi. to break in. Nite and day differance.

[Toddster]

I'm glad my truck is not "confused"....I run true 33 inch tires and everything seemed to get better, shift points, shift firmness, and more comfy RPM's at highway speeds. Break in may have a little to do with it but mine was a rocket from day one....Of course I Juiced it on day 3 ! These things are VERY conservative from the factory. I'm a firm believer they all need a power add on, but I will not get into the brand debate ! ;)

[NFLDMAX]

TraceF..

I also run 285's on my 2002 Dmax. The only issue I had is the occasional downshift to 4th and not wanting to go back to 5th. Give it some more time. :D

Where you fishing out of??

[NeverForget]

I think that you've got a legitimate concern. The GM publication was issued for a reason.

Being dissatisfied with the OEM Firestones and needing additional load capacity for towing my 13,000 fifth wheel, I upgraded to Michelin LT265s. MPG dropped from 19 to 16. Although the speedometer wound up being only about 3 numbers off at 70, I elected to purchase and install a device made by Superlift to electronically correct the signal from the transmission to the ECM under the hood. I think it's called "Truespeed." My milage and towing power returned to normal. So, apparently, more than just the ABS can be affected by tire size changes.

[NeverForget]

Here is the link to the product. I thought that it was a bit pricey. But, given the increase in milage, it should pay for itself.

http://www.superlift.com/speedo.htm

[ 12-21-2002: Message edited by: NeverForget ]</p>

[TraceF]

NFLDMAX- Fishing, mostly diving, out of Ponce Inlet (Daytona). Was going today but seas picked up overnight. Thanks for the advice.


NeverForget- Thanks for the info- someone else recommended a VSS. If you had good results I may try this first. I'll keep you posted.

[TraceF]

Toddster- What did you have to do to get the 33's to fit? I had to trim the front plastic just to get the 285's to fit and the left front tire still gets within an inch of the washer fluid bottle.

[Toddster]

Washer fluid bottle ? Hmmmm....I had to do a good trim up front. Lucky for us 03 GMC owners this is quite easy....Put a nice angle cut on the air dam and some plastic trimming on the inner fender well. Still "clicks" on a tight corner but it looks damn KOOL ! :cool:

[TraceF]

My washer fluid bottle is directly in front of the left front tire behind the plastic fender liner. I trimmed the front air dam about an inch forward and the liner up about 4 inches from the bottom because the tire was grabbing it when I backed up and turned. This exposed the bottom of the washer fluid bottle.

[Toddster]

OK Dude I follow ya now....I probably went about 3 inches so just missed uncovering the washer bottle by that much.

[WillowCreekStable]

Based on experience with my neighbor

[fredw]

i as well have a true 33 inch tire 255-75-16, i had power and fuel problems on my 03 as well, then i turned over 10000 km and a whole different truck, i also have the 110hp bully in from new, but now my power is great but my milliage is even better, last night we did a 400km trip at 120km/hr empty and it ran 25 miles per gallon(imperial), this truck is now getting better milliage than my 01, 02, did, i have no problems at the warrenty shop with the large tires as well, might be that the service manager liked my tires so much he bought some for his own, thanks fred