# D-Max question concerning suspension



## 4x4_Hunter (Jan 2, 2002)

Was thinking that maybe someone on this sight has already done this and can help me out with the concerns. I want to put new tires on my Duramax CrewCab and I am gonna put on 285/75/R16's and all the tire places highly recommend the BFG KO's. Was wondering what all of you think about this tire as a good off-road and on-road tire???

Also, I would like to raise the front of my truck about an inch and was told I could do that by simply tightening the torsion bars up. I would think this would add considerable stress and tension on the whole front suspension and possibly the shocks would not work in their intended range. Has anyone done this to there 2500HD and if so, what was the outcome??? Thanks for the help with this. 

I would love to see some pics of trucks that have stock suspension with bigger tires and maybe just some minor tightening of the torsion bars or 1 inch lift in the front end. The rear is fine the way it is.


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## Dasher (Jan 12, 2004)

I have a set on my 1500HD (265's BFG KO's) and like the performance to date. They do tend to "pack up" with snow in the winter yet perform well in the snow (just not like the mudders) sand, mud and other terrain. Overall a very good tire. The vehicle came with the 245's and I went to the 265's to give me 1" more clearance plus the KO's add an extra little lip next to the rim so that when you air down the tires to 15 psi "for sand and mud" sticks and other debris will have a harder time of penatrating the rim. Going up two sizes did not change my shift points in the transmission as it was in the 5% calibration range for the transmission (4l80e). I am not sure if the change in tire size for your vehicle will make a change to the shift points going up 4 sizes from the 245's to 285's may change the shift points. Usually 2 sizes is no big deal yet 4 sizes may mean a difference in shift points and possiblity of setting codes in your vehicle. I do not have any information on the torsion bars yet tightening the bars can have a bearing on the overall vehicle dynamics for the front end suspension and steering (can give you a feeling of no control/harsh control in certain driving conditions). Also, get a set of good mudflaps as you will tend to throw up more debris from the road. Your MPH will be off as well due to larger tires.


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## SalmonBum (Feb 28, 2001)

I have a Duramax 2500HD and I left mine stock, All the way around. I hear from most guys going upto 285's that the fuel mileage goes down quite a bit. Plus, if you do go with the 285's, you need to lift the front of it up. That can be done by messing with the torsion bars. Whenever you mess with that kinda stuff, you change the way the components work. I hear that just a slight ajustment is twice as hard on the parts. If your leasing it, who cares. But when I BOUGHT a $50,000, I would rather have my truck last longer than have it sit an inch higher.

As for the BF's, They are great tires that seem to have a good tread-life. I had them on a truck of mine in the past. If you do alot of towing, you may want to check out others. Whenever you have a tread pattern that is somewhat of a criss-cross, you may feel the truck swaying form side to side when towing.

If your going to take your truck and play in the mud, then get a good lift and tires and put a bunch of money in the bank to fix the stuff that breaks. It will happen every time you go out. I have learned from Experience. Taking new expensive trucks out playing will cost you lots of cheeze. If your tuck is a hi-way truck, leave it the way it is and it will last you a hell of a lot longer with less repair bills.


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## gilly (Apr 3, 2002)

My brother-in-law went up to the 285's and tightened his front torsions for the extra lift. He loves the tires and my other brother-in-law buys nothing but BFG's AT. So far I haven't heard him complain about handling or excessive wear yet he is only 6 months in. Man they really fill up the wells and look awesome.


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## djkillaz (Mar 7, 2004)

first thing is. I'd get leveling kit. also, never crank your torsion bars all the way. it does give ya lift. but its not good for them.leave 1-3 turns back seated. also, if ya go w/a body lift at all . dont get poly urethane for the new trucks. get the welded ones . like summit racing sells. w/ the polyurethane blocks your truck will slide a little.also, the cab floor supports arent as sturdy as the 1970's and 1980's models. they will give away after a period of time.


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## plugger (Aug 8, 2001)

I cranked my old truck up when I put the plow on and ended up leaving it up, 100000 miles , no problems.


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## Warlock (Aug 10, 2004)

4x4 - some info from a couple of Duramax online sites regarding what you're planning. When you put anything but the stock 245's on the truck, it will change the shifting pattern/timing of the Allison. I put 265's on my 2003 D/A without too much of a difference in the shifting pattern. 

However - be aware that if you do have a problem with the shifting pattern and take it to your dealer complaining, GM has instructed the dealers NOT to look at the truck until the original size tires are back on the truck! Appears to be something specific with the D/A combo as GM can recalibrate the computers to take care of this problem on the gas trucks - but either will not or cannot do the same with the D/A. If you've got a friendly dealer that may not be an issue, but could be a royal pain if not. Of course, this only applies if you've got the Allison transmission. And only applies if your truck is still under warranty - guess they'll take your money if you want to give it to them.

When you get to the 285's you will need to raise the truck or you will rub on the lower portion of the front fender. Most people seem to do okay with just cranking up the torsion bars - but that will change the ride of the truck.

Seems that with the power of the DMax that towing is not affected too much regardless of tire size.

One other thing - be careful on how wide you go with your 285's - the stock wheel is narrow, only 6.5 across - not a major problem, just have to watch your air pressure so you're not running only on the crown of the tire. Or buy new, wider wheels to run the wider tires.

Upside with larger tires is you get more traction, more ground clearance and better looks. Downside is potential problem with shifting pattern, loss of mileage and storing the 245's if you want to play it safe. (I've still got my original Firestone 245's just in case.) 

I've put on over 20,000 miles since switching to the 265's and have had no major issues and will put 265's on it when it needs new tires. I like the looks of the larger 285 tires, but guess I don't want the increased risk of hassles or problems. Like SalmonBum said $50,000 is a lot of money to put into a truck to mess up just for an extra inch of ground clearance (and with the weight and size of these things, they'll never be the greatest off-road vehicles). 

Guess it boils down to how long you plan on keeping the truck: short time - do what you believe fits your needs and don't fret it; long time - do what's best to keep the truck in excellent shape to save you money, repair costs and time and to get the most from the money already spent.


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## djkillaz (Mar 7, 2004)

super lift offers a computerized plug in module for vehicles w/ tires larger than stock. thatsets shift points and speedo to manufacturers specs.


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