Home Forums Gear Hunting Trucks and Four-Wheel Drives NEW TIRE QUESTION

HI FELLAS I HOPE SOMEONE CAN HELP ME. I HAVE A 2003 FORD SUPER DUTY WITH THE 7.3 DIESEL IF IT MAKES A DIFFERENCE.I HAVE 265/75/16 FIRESTONES ON IT NOW. I WANT TO CHANGE THEM TO BFG AT TA 285/75/16. MY QUESTION IS WILL I HAVE TO GET THE COMPUTER REPROGRAMED FOR THIS TIRE SIZE. ALSO IS IT SAFE FOR THE TRANNY, I HAVE HEARD FROM SOME PEOPLE THAT IT MAY SCREW IT UP. ANY HELP WOULD BE GREAT. THANK YOU RED.

I doubt that it would require any computer reset, and I don't think it would adversely affect your transmission, because it's just not that big a difference in overall height. According to a website that has a tire size comparison program, your new tires would have an overall diameter only 1.18 inches greater than your old ones, and if your speedometer reads 65 with the new tires, you'd really be going 67.42 MPH. Doesn't sound like too big a difference. It will make your rear axle ratio a little "taller" but you've probably got plenty of torque already with your diesel.

Usually one tire size isn't an issue. I have BFG AT KOs in 295/75R16 on my '02 Dmax. The stock tire size was 245 75/R16. I did have the ABS flashed for 265s when I put them on a while ago, but it was only an ABS flash. I have since went to 285s and now 295s.

The 295s are almost 3" larger than the 245s. The truck runs great and stops great, but then again I do have a 125 HP/350 ft lb torque power module as well as a lift kit................The speedo is about 5 mph off at 60 mph. My power module has a display that shows corrected mph--eventually I'll get an sftermarket programmer that will let me change the actual speedo reading.

BTW, the BFG AT KOs are excellent all-around tires. They are good in the mud, but not as good as mud terrains. They are quite on the highway, but are a tiny bit noisier than pure hwy tires. There sidewall is very stout--I had to soften my shocks one click each after going to the BFGs.

AZBob and Blaine:
Good info as usual, but Please remember we up here are a Metric nation, so you must convert all info into Metric before you reply. ie. MPH to KPH
<img src="/ubbthreads/images/graemlins/grin.gif" alt="" />

Just multiply MPH by 1.6 to get KPH, or divide KPH by .621 to get MPH. I can't help you with ft lbs vs Newton metres, or litres vs gallon vs Imperial gallons.......... <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

One of my buds exchanged the 265/75(?)x16 load range E tires that came on his then-new Chevy 2500 4x4, for the 285 load range D version of the BFG A/Ts. Rode a bit better with the larger, lighter-duty tires and IIRC, he figured it threw the speedo off by a tad less than 5 mph, since that's what the employee told him that followed him down the interstate in one of their new company trucks, right after he exchanged the OEM tires.

When he got his first speeding ticket with that new 2500LT, told him me might wanta fire that guy. Think he got "microwaved" doing about 85 in a 65 area, so don't think the tires made any difference. <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />

Lighter duty may not be the best description. The factory's "E" rated 245/75R16 is rated at 3050 lbs, while the "D" rated BFG 295/75R16's are rated at over 3400 lbs.

Dunno, wasn't my truck but he was happy with them. What's the 265 E-rated gum good for, pretty sure that's what it came with? He had two 2500 shortbed 4x4 xcabs, did the same tire deal with both of them when he bought them new. '99 and '01.



Former diesel mechanic turned management guru in that business, pretty good on the research end of things, so figure he had a reason. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />

The GM Dmax's come with 245s. As far as anyone can guess, GM does that to keep the truck lowish so it will fit under any fifth wheel. Also, the stock engine with 3.73 gears does very well with the 245s. Of course, many of us add more power, lift the truck, and go to a larger tire.............



As far as I know, the "E" rating means 10 plys while the "D" rating means 6 or 8. Regardless, the size and construction of the tire has as much to do with it's load capacity as the number of plys. It is hard to find a more durable tire than the 3400 lb rated BFG AT KO in 295/75R16.

Why not check your speed with a GPS?

Fairly sure his '99 and '01 trucks came with E-rated 265s on them...know he replaced them with D-rated 285s. Weren't diesels, 2500 extended cab w/LT trim package, short bed 4x4 with the 6.0L Vortec gasser. Darn nice trucks and much better looking than them awful Silverados they sell now with all that plastic garbage on them. Damn near as ugly as the Awfulanche.

Here's what is troubling for me: His trucks averaged all but 17mpg on the trip to my cabin (180 miles), while my S-10 ZR2 gets 20mpg on the same trip. That's a 300/345HP V8 vs a 190HP 4.3L V6. 'Course them trucks listed for about $7K more than mine did. He called his rigs Real Trucks, said the S-10 stuff was intended for wimmin and small boys. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />

Don't need a GPS. I mostly hunt in the same 2 square mile area of mountainous "big woods", woodlots and hilly farm country that I've hunted in for over 40 years. Couldn't get lost around there if someone sealed me up in a fuel drum and rolled me into a briar-infested swamp or a deep holler. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

I am not sure about the gassers, but the 2500 HD DMax diesels came with 245s, starting in '01 when the engine was introduced. I have heard there might now be an option for 265s on the new DMaxes. All of which is too little--these trucks need 33" tires (295s) and enough wheel well clearance to run them without a lift.

The 6.0 is a very underrated motor, and getting 17 mpg in a 7000 lb truck over the same route where a V-6 s-10 gets 20 is impressive. My Dmax, which is lifted 4" and runs 285s and a 125 HP chip gets around 13.5 in town and 20 on the freeway when empty.

Back when my bud got his first 6.0L 2500 in '99, another friend had bought a new Ford F250 4x4 the same year, also an x-cab shortbed, with whatever their biggest gas V8 was at the time.

Ford-boy's hunting camp is about 45 miles SE of mine in the same county, so we share the same roads for most of the trip to northcentral PA. While the then-new '99 Chebbie was averaging all but 17mpg on the trip, the guy's new Ford maxed out at 14mpg and in my opinion, didn't even come close to the performance of the 6.0L V8. Factor in that those extra 45 miles are all on hilly, winding, two lane rural roads and it's even more revealing. Ford-boy's cabin is a mere 5 miles from the four lane we use to get up there, close to the NY border, making his primarily true highway mileage. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />

The '99 was rated at 300HP, IIRC and had some serious stomp to 'er. I think the '01 version of the motor was rated at 345HP. Could've bought that truck when it was still fairly new yet, when my ol' bud kicked the bucket. Probably shoulda, just sits in the widder's driveway, doubt they've put 10,000 miles on it since he passed. <img src="/ubbthreads/images/graemlins/frown.gif" alt="" />

I have the 03 GMC 2500HD w/Duramax. I just put the first replacement set of new shoes on it. I went from the stock 245s to 285s. No lift needed and all seems fine. I checked with my GMC dealers service dept first and they said no problem. They also said the difference in the speedometor would be very little but they would check it and reset it if necessary at next service. I like the bigger tire and it seems to ride a bit better. If anything is wrong with doing it I sure can't tell. 163bc

You are probably okay with the stock wheels and 285s in terms of front tire rubbing, as long as your t-bars are cranked, which they probably did when installing the tires.

Because the min recommended tire size for 285s is 7" and the stock GM wheels are 6.5" wide, I went with an 8" rim, which is about ideal for the 285. I didn't like the idea of running a too narrow rim on a heavy duty work truck. However, an 8" wide rim with 285s has lots of rubbing issues--especially when turning sharply while braking. To try and fix this, I cranked my T-bars 2" with higher lift t-bar keys, tied back the parking brake cable, reformed the inner wheel well liners, and even was running an aftermarket bumper.

I still had rubbing. When the steering wheel was turned about 3/4 travel, I had about 5/8" clearance between my tire and the rear portion of the wheel well. There was no way I could have run chains on the front.

So I finally quit messing around and installed the Rancho 4" lift. It has solved all the tire clearance problems, even though now I am running 295s. However, installing a lift kit on an IFS truck is not for the faint of heart......

One note on your speedo recalibration. Unless something has recently changed at GM, all they can do is reflash your computer with an ABS correction for the larger tires. In '02 I went from 245s to 265s and thought the reflash they gave me was for the speedo, but I noticed I still had the same rpm at the same indicated MPH. I later learned GM did not have a flash for speedo, only for the ABS. I know this was still the case last year.

Perhaps something has changed in the last few months, but I recommend you press the service dept to find out if they really can correct your speedo. With 285s, you're speedo will read about 8% slow, meaning if you indicate 60 mph you are really going about 65.

I know that there are a couple of aftermarket programmers that will correct your speedo reading: the Predator and Hypertech; and Superlift has a wire in module. I run the "Juice" with the "Attitude" monitor from Edge products, and it displays a corrected speedo reading on the monitor.

The only potential downside to the 285s on a stock truck is towing power. I have a 125 HP power box in my truck, and the 295s are no issue. However, guys with power modules say that if they go over 33" tires the truck doesn't pull so well when towing. These power modules all reccomend around a 45-60 HP setting for towing, and even with that increase, 33" tires is about all the truck likes with the stock gear. This makes me thing a stock truck with 285s would also not pull so well. However, most of us with chips are used to running around with 90 - 145 extra HP when empty, so maybe it's more a matter of just stepping the power down and adding weight...................

I towed my Kabota 5030 tractor w/ front bucket and a heavy duty bush hog today first time with the new 285s on my GMC w/ duramax. It is a full load and tough for any truck. Towing was on highway, gravel roads and tough mountain logging roads. Everything worked fine. I can't tell ANY difference at all between 245 and 285s. I set the cruise on 65mph and was right with everyone else on the interstate. 163bc

Blaine, what do I need tool wise to do the t-bars?? And how??

Not sure I understand what you mean as a downside to 285s on a stock truck and towing?? Would a chip really make a difference in towing?? And if so good or bad with the 285s. Thanks, 163bc

163,

Sorry it's taken so long--almost every moment not at work I've been using to get my house ready to sell.

The downside to 285s and towing is power--you have in essence put 3.47 gears in your truck. For light towing it won't matter but you will really notice it with heavy trailers. You need around a 4.01 gear to get the final drive ratio back to stock.

Also, the TCC locks up the convertor at 53 mph. This is based on tranny output shaft speed and there is no way to correct it. So when you put on 285s you are not getting the convertor to lock up until 57 mph, which can affect both power and economy.

The power modules make a huge difference. With a 4" lift kit, my truck gets 13 mpg in town and 20 mpg on the freeway with 295s and stock gearing. It will also spin the tires through the first three gears and will go zero to sixty in less than 6 seconds. Now, all that is on the 90-125 HP level. When towing, you want it on the 60-75 HP level, and guys that tow with it set as such report a huge difference in towing as well. The best chip is the "Juice" by Edge products: http://www.edgeproducts.com/

Realize the power modules for these new turbo diesels are not at all like the Hypertech style chips for gas rigs. The gas chips might add 25-30 HP. The diesel power boxes add up to an honest 220 HP increase as measured at the rear wheels--power off the engine is about 60 HP higher with a Dmax/Allison.

The 220 HP boxes are race versions. The Juice with the Attitude monitor is what I have, and it is as hot as you want to go with a stock tranny. The Juice Attitude will add 125 HP and 300ish ft lbs safely--as long as you don't continually do full throttle runs on the 125 HP setting. When I get my tranny upgraded I will also get the 145 HP Juice/Attitude set-up.

OK you got me seriously thinking on this chip. Any downsides too it?? I'm totally stock except the 285 tires w/Duramax and Allison tranny. How hard is it to install?? I really just want to get some improvement in towing and overall performance. Thanks, 163bcm

The main downside is warranty. The way to get around that is to get the 90 or 125 HP Juice without the Attitude monitor. You can always add the monitor later, and the monitor makes the 90 HP chip 125 and the 125 HP chip 145.

If you have just the chip, it only takes about 5 minutes to remove and install. Many dealerships have a "don't ask, don't tell" policy toward such items.

It is smart to run an EGT gauge if you plan to push it hard with the chip, but if you keep it at the 60 HP level you shouldn't have any problems. Also, the chip will cause smoke if you get ahead of the turbo--IE, too much throttle too soon. It is not a lot of black smoke, but you do see it.

An advantage to the Attiotude monitor is that you can set the chip so it won't smoke--they call it low fuel boost and it just delays the rate at which the fuel enrichement is added. However WOT power is the same regardless of the low fuel boost setting. Also, the Attitude monitor has an EGT probe and can display EGT. However, the Attitude takes about an hour to remove, and you will have to plug the hole where the EGT proble goes. BTW, this is what I have, and when I wanted the dealer to look at a potential warranty issue I took the whole thing off and nothing was said about the plugged hole in my exhaust manifold.

Another disadvantage to the chip is if you hot rod your truck too much with the chip set above 90 HP you can hurt the tranny. Occassional full throttle runs are okay. If you really want to hot rod, the you need a $3K tranny upgrade.

The biggest downside to the chip is you may find yourself "not taking it anymore" form kids in rice burners. On the street with the 90 HP setting and the truck in 4WD, you will beat most hot sports cars stoplight to stoplight because you will get traction and they will not. Of course, we shouldn't be racing on the street anyway.........................

Fuel mileage will increase if you drive like an adult. However, if you hot rod you will get worse mileage than stock. Check out this website for more info. Rick Bin also posts there ocassionally: http://dieselplace.com/forum/default.asp

Alos, here is where I but my stuff from: http://www.kennedydiesel.com/

Blaine

Blaine, Thanks for sharing your knowledge. I'll let you know how it goes with the chip. 163bc