Friday, November 13, 2009

The Tread is Below Lincolns Head

So, the other day, Steve mentioned his ordeal in finding new tires for his 3/4 ton Dodge Diesel (which I will take the credit/blame for forcing him to buy).

As it happens, I also have a 3/4 ton Dodge Diesel, and I also need tires for it.

As in REALLY need tires for it.

We measured our tires, and instead of 31.6" height as they are supposed to be (265/70-17), they're down to 29.6".

As in "yeah, the tires are going to come out of this paycheck".

They were dramatically under-inflated (even though we inflate them every couple weeks at worst) and are nearly bare of tread. Technically we're at a legal tread depth... just barely at 2/32"... but I'm not happy with that.

Well, that explains the speedometer error (between 2mph and 3mph over at indicated 75. Aint GPS grand).

At any rate, I'm looking for a good compromise tire for my truck.

What I want is tires that will have good rough road, ice, and snow performance, and acceptable light duty offroad performance; without being too noisy or having poor treadlife; and without hurting my city mileage very much.

With the torque of my diesel, and my gearing, it's not really the height of the tire I'm concerned about, it's the rolling resistance. Most tires with nice aggressive offroad tread patterns, are not only noisier than highway tires, but they have far higher rolling resistance.

Unfortunately, smooth, stiff tires, aren't any damn good offroad. Of course to offset that, taller tires means lower revs and better fuel economy, once the actual acceleration portion of the days program is over.

I've got a 2006 Dodge Ram 2500 with the 5.9 Cummins, 4x4, the super heavy duty suspension and tow package, and factory skidplates, and driveline guards.

Straight from the factory with these options, it has a built in almost 6" lift over the standard 1500 2wd with the smaller wheels and tires(245/60-16 is the stock "cheap" wheel and tire package).

Frankly, it's a tall truck already, I'm 6'2", and it's a bit of a climb up, even for me. I definitely need to fit some nerf bar steps. However, the offroad performance of the tires is crap.

Basically, I'd like to have some taller tires both for better offroad performance, and for highway cruising (as I noted above, taller tires means lower revs on the highway, presuming you've got the torque for it, and I do).

Oh and cosmetically, the current wheel and tire combo looks absolutely miniature in those massive wheel wells, especially with the factory lift. I'd like to fill the wells a bit more.

So, I'm wanting to trade up a bit in size from 265/70-17 (which works out to 31.6").

I've been thinking about either a 33"x12.5-17 (obviously 33"diameter... 285/70-17 is roughly equivalent in diameter at 32.7", but about an inch narrower), or 315/70-17 (34.4"x12.4); but I'm not sure about mounting those on my stock 17x8" heavy duty (e rated) rims.

Offroaders go with sidewalls that high and tread that wide on 8" wide rims all the time; but according to tire manufacturers, 295s or 11.5" are the largest tires that will fit on 8" rims.

I learned a rule of thumb a long time ago for street tires, and that was you could go as far over your rim size, as your sidewall series rounded up to the next even size (i.e. 265, 275 etc...), and one even size above that, without causing tread pattern issues (so on 8" rims with 40 series tires, you could go to 245s or 255s)... but that's for pure street tires, not heavy duty truck tires that will be used offroad.

AT/Offroad tires are supposed to balloon out a bit, and with that height of sidewall, the wheeling guys say you can go up to 100mm over the rim with the right tire design (with 100% offroad tires you can go more, but not with street tires).

So by their measurement, 315s (12.4") would be find, but by my rule of thumb and manufacturers recommendations 285s might be a better fit.

Given that, 285/70-17 may be the best choice (they'd also be a bit cheaper), but I'd really like a bit bigger.

Oh and before anyone asks, no, I don't want to change my wheels. For one thing, getting decent E rated wheels is EXPENSIVE (around $2k for a set of 5, including spare; and when you change size, you need to change the spare).

Hell,technically speaking, if I wanted to change wheels I could fit larger tires (up to maybe 37") on the truck without fender flares or more lift (seriously, the wheel arches are HUGE, and with the lift, the 17" in there now look like rollerskate wheels); but I don't really need anything so large, and I don't feel like the significantly higher cost, or the reduced fuel economy.

There's a further connundrum, about backspacing. I've talked with several guys online, and a couple different tire places and offroad places; and no-one can seem to agree what backspacing is required for my wheels and truck, for what size tire.

Some places say that 285 is the maximum that will fit without rubbing given my wheel spacing; but some say it's 315. Others say the 315 requires a 2" spacer. Still others say no, I don't need a spacer unless I go for the 33x12.5s (almost the same size as the 315s), and then it's only a 1" spacer.

I'd love to get a straight answer, but I've had two Dodge service managers even give me contradicting answers.

One thing I'm NOT going to do is anything that compromises my load rating. No spacers, no non E rated wheels (even if I were to change my wheels right now, which I'm not), and no non E rated tires.

Which brings me to the biggest problem: finding E rated tires worth buying in larger sizes.

It seems that most E or higher rated tires, are either in much larger size (i.e. F550 dually dump truck size), or in 16"; and most of them only go up to 265 or so.

Almost all the 17" and 18" wider and taller tires top out at D rating. Oh and by the by, you usually pay about $25 per tire extra (on $200+ tires) for the E rating over the D.

In doing some basic research, I identified two options, which have acceptable on and off road traction, without excessive wear and road noise:

Firestone Destination AT: the highest rated tires in the size range at TireRack, though I'm iffy on Firestone.

Bridgestone Dueler AT Revo 2: I've had earlier versions of this tire, with good results, though Bridgestone and Firestone are the same company.

There are some great Cepek options, but none of the sizes larger than 265/70 are E rated. There are a couple of decent Kumho options, but they're a little more aggressively treaded than I'd like for onroad performance.

I've also had strong recommendations from some forum readers for:

General Grabber AT2: Great offroad tire, with good onroad performance, and severe winter weather rated (the snowflake symbol). Unfortunately, the largest size they make in 17" is 265/70... though it is E rated.

Goodyear Wrangler ProGrade SilentArmor
: This looks like a serious option. They're considerably more expensive than the other possibilities (about $50 more each), but they seem to be damn near indestructible. They're also snow rated, and E-rated; and they have the kevlar armor and extra sidewall thickness (and toughness) for the silent armor system. Oh and a 50,000 mile warranty. The only issue being, the largest size they come in 17" is 285/70-17.

At this point I'm leaning strongly towards the Firestone Destination ATs, or the Wrangler pro-grades. The Wranglers seem to be the better tire, but at a much higher price.

Any more suggestions, or personal experience? I'm especially interested if someone else with a 2006 or so Dodge Ram 2500 4x4 can tell me if they know the ACTUAL maximum tire width for our truck.

Oh and I'm putting this up on "nobody reads blogs day" so I can gather info over the weekend and Monday; because I'm going to grab the tires next week most likely.