kindog

I've searched through all the archives on the BFG 315 topic, but never really found any firm advice on this particular subject.

I'm a new '04 CTD owner, and am on a waiting list at a local Hummer dealership for some factory takeoff 315's. However, after reading some varying opinions, I'm debating between these and possibly some 305's or 285's instead. What I'd like to know is...

**How gas mileage is altered? I'd guess better highway mileage and worse city mileage due to the added torque necessary to get these things moving. Any direct experience out there?

**Towing and gearing? I'm a little concerned about the 315's with the 3.73 axle. I rarely tow, but will be pulling heavy loads at times (Bobcat + flatbed). Are the 315's too big - both for load rating and gearing?

**Lift? I don't plan on lifting the truck any time soon. I've read about some slight rubbing at full lock, but recently read another post about the front end settling down a bit after a few months and worsening the problem. Any forseeable problems down the line?

Thank you for the help. I've learned a ton from this forum - hopefully I'll be able to turn around and help out the new guys myself after living with this bad boy for a few more months!
Steve

rossn2

No, still about same mpg. At 65mph turning 1800 rpms, fuel 19.5 mpg...drop to 55 and have gotten up to 22.5 mpg. Of course, changing everything in drivetrain to good synthetics probably helped too.

Nope, Little bit on full-lock..so don't turn into a tight parking space .

No 2" leveling kit installed on truck...just a front brush guard

Just rides different becuase of the All-Terrain treads. Rotate tires every 5-6000 miles.

kindog

cool. thanks ross. so city driving isn't a problem - plenty of power? appreciate the help.

banshee

I have that combo, too, and I get right at 20mpg on most fillups. That includes a mix of city driving and highway driving. There is plenty of low end power to get a load moving, and starting in 2nd is no problem. 1st should be more than enough to get your heavy loads moving. I have the 2" level and the tires barely rubbed the lower left front control arm when they were new, but not anymore. The look w/ the 315s is more than worth it!

John

kindog

well that's about all i needed to be convinced - now it's the wait. thanks guys!

Squidward

Although I've read about how wonderful the 315's work, I remain a little skeptical. Stock 265/70R17's measure about 31.6" tall, 315/70R17's are 34.4 inches. Thats an 8.2% increase in overall tire height. So for starters, your speedometer and odometer will be off by that much without recalibration. And with an 8.2% increase in tire height (and a corresponding overall reduction of the final drive ratio), I don't see how acceleration can be impacted in any direction other than the wrong way. The Cummins powerplant is capable of many wonderful things, but it is not exempt from simple laws of physics, momentum, or rotational inertia.

I've given lots of thought to going with 315's on my truck, but I've been hesitant to do so for these reasons. Granted they look a heck of a lot better than the stock pizza cutter tires the truck came with, but i went the 315 route on my SuperDuty, and paid the price at every stop light and fuel stop.

Nevada

If it helps, you have the mathematical equivalent of a 3.43 rear end with that change. I doubt that you will have a measurable difference in mileage, your ratio is getting better and your unsprung weight is getting worse. Probably a wash. I wouldn't sweat the towing with a 6-speed. The worst that could happen is you may actually find a use for first gear.

For odometer correction (without resetting the the computer for revs per mile) for every actual 10,000 miles you travel, your odometer will show 9,197.98

For speedometer correction at an actual speed of 60 mph you will indicate 55.1 mph. At 80 mph actual you will indicate 73.5 mph.

commonrail

My experiences with 315's & H2 wheels on my 03 HO 6 speed 4X4:

No rubbing, no lift. The offset on the H2 wheels takes care of the lower control arm problem some have withg 315's on stock wheels.

Slight reduction in fuel economy around town. I've only filled up twice since installing but seems to be about 1 mpg lower. 2nd gear starts still no problem un-loaded.

Noticed biggest difference in reduction of braking efficency. Also some difference in acceleration but not as noticeable as the braking. One good thing about going the H2 route, you can always change back to stock if you need to tow heavy for a trip if you have room to keep the originals.
Kris

Fred Swanson

Going from a dually with 19.5's back to stock, and now 315's in a single wheel setup, my mileage has improved. The overall ride is better, and handling is smoother. Plus no more bouncing over bumps, either.

kindog

Thanks for the comments guys. This is what I'm looking for. I won't be doing the H2 wheels, but I've decided I'm definitely doing the tires on the stock alloys. I'll post some pictures once done.

Thanks for the help!

grizzly660fan

I have a stock suspension, six speed ctd, and within the last couple of weeks upgraded from factory 265's to bfg at 315's.

Here is some input from me if curious...

1. on stock tires I was getting 19-20 mpg's with about 50% city 50% highway driving. now with 315's, it seems to have dropped to 17 - 18 mpg's running the same routes. (using gps for mileage and doing the math at the diesel pump, not relying on trip computer as its not accurate anymore)

2. my speedo was accurate with 265's when checked by my gps, with 315's the speedo is off by approx 10% throughout my mileage range up to about 80mph.

3. I got 5 of the bfg 315's, and the 315 on the stock steel wheels and I was able to fit a 315 mounted to the spare rim and it fits in the stock location under the truck without modification.

4. I have stock suspension on the Ram 2500, I have no rubbing at all. I have just added some photos to my gallery where I was off roading and on purpose twisted up the truck to check for rubbing. result, still no rubbing, I am very happy about that.

5. shift points seem off, I need to get computer reset, I seem to shift too soon now, this will affect towing with heavy trailer.

6. coming soon, I have a 5th wheel that weighs approx 10,000 lbs. I am still worried if the sidewall is stiff enough on these 315's. I will take a trip soon and know the answer to this question and post results.

7. I love the way my truck looks with 315's! I like the additional ride height and think it was a good idea.

I hope this info helps someone out there.

PS, when admin approves my photos, check out my gallery to see clearances when off roading.

cquestad

Get the rev per mile reset and the tranny acts fine again. I had the same issue. All better now!