I stand corrected. The old US tire size system used A- N load ranges which do not correspond to tire diameter. The metric tires are indeed a specific size. Based on info at tire rack, it appears that:

225/75-16 is 29.3
235/75-16 is 29.8
245/75-16 is 30.5

The difference in diameter amounts to 683 revolutions per mile vs 735 is .93 so the number I get is 7%. The increased tread width will increase rolling resistance so I think in this case you might just break even. The tread wear would seem to indicate that you aren't fully loading the current tire and going to 245 will exacerbate that contact patch (tire wear) issue. I think you will have to run them at lower pressure to correct it and obviously that won't help gas milage.

The profile or aspect ratio ( 235/75 )is actually a ratio of sidewall height to section width. The section height's measurement can be calculated by multiplying the section width by the aspect ratio. So at a given size an aspect ratio of 60 is always going to be shorter (smaller diameter) than the 75.

I installed Michelin LTX MS/2 P235/75-15 (XL load rating) on mine. They aren't cheap but they are worth it. Excellent tires in the rain and after 10k miles the tread still looks like new.

A set of ring and pinion gears is $255 - $550 online and another $200 for the kit. The cheaper gears are ok but are a lot louder and they don't recommend them for vans. You could probably get this done professionally for $900 or just find a differential and swap it out for half that. If you don't need the torque from your 4.11's, a set of 3.5 gears will certainly increase your gas milage and you can still tow. My 2000 5.2L swb van, overdrive, 3.5 gears, Chrysler Corporate rear end gets at least 18mpg highway with 1,000 lb payload. That is at 70 - 75mph with the A/C on.

 

Man.. I am sorry, thats awful!

I have a super-sensitive alarm, multiple video cameras and alert neighbors but none of that would have prevented this. It is sad that some jerk with nothing better to do can inflict $1,000 worth of damage in less than 60 seconds. I am fortunate at the moment to have a garage that my van will fit into but I realize many people simply don't have that option.

 

Stev, you mentioned in a post
Next, drain our the rear OEM oil and replace with Redline synthetic 75W90 per the Chrysler TSB. This helps with wear life and MPG.

I stopped today at NAPA and asked how much oil to buy for my diff case... the reply was 2.2 QTS of 75W90 EXCEPT if I have the DANA M60 and in that case use straight 90 weight...

At that point I stopped getting the 75W90 because I know my hood sticker refers to the Dana 4.10 M60/24 rear end.

So my question is... well do I leave the 90 weght in there? Do I drain and reinstall new after 155,000 miles? I have never heard of replacing rear end oil... but then again there is lots I don't know.

Any thing you can add to this NAPA info?

thanks again for the help

 

At the DTR forums, the 75W90 SYNTHETIC is the preferred diff oil to use in the Dana M60.

Ford puts 75W90QL SYNTHETIC in the Dana M60 on the front 4x4 axle as OEM. And Ford uses the same in the Econoline vans in the rear.

Per the Chrysler TSB-03-08-00, NOTE: THIS BULLETIN APPLIES TO ALL VEHICLES EQUIPPED WITH AN 8.25, 9.25, OR C205F CORPORATE AXLE.

 

Well I did it... I went to local Goodyear dealer and bought top of the line Wrangler Silent Armor LT245X75-16 tires to put on the B2500 extended van. The fronts just clear the sway bar. I went with these tires but it was a toss up with the Michelin LTX M/S bqsed on reviews I read on tirerack.com . In the end I decided to use the local tire store as the manager there talked nice to me and gave me a good deal, plus $80 + $80 (using their credit card) so $160 rebate brought the cost per tire down below what Sams and equal to what Tirerack offered. He also offered to make sure that the larger size would work and gave me a 30 day TEST RIDE to make sure. Otherwise he would swap out to the stock LT225 size if the 245 size would not fit.

I looked at many of the things that Stev posted to increase mileage, and changed rear diff fluid to 75W90, greased front wheel bearings, changed front brake hoses. I found the rear brakes were put together incorrectly and would not adjust, but with the help of a master mechanic friend who pointed out the error of how the cable was attached, I got everything working in the rear brakes now and got them adjusted properly. I now have great brake pedal and she stops on a dime.

NOw I need a place to go to see what kind of MPG I will get. If there is no improvement, I won't be totally disappointed, as I like having good quality new tires under me, and knowing that all of the brakes and mechanicals are as good as I can get them.

I will report in a couple of weeks when I take a 500 mile round trip to central TN and back to Cincinnati in that van. Thanks to everyone that gave great input to this decision.

 

I think you'll be pleased with the Goodyears especially in the unfortunate instant you have to slam on those good working brakes and turn at the same time to avoid something. I made up a saying back in the seventies after a hydroplaning crash on cheap tires in the rain when I was only going 55. No matter how much money your vehicle cost, there's only one thing between your butt and the road, your tires, never ever go cheap on tires.

 

It will be a hard pressed issue for good MPG with the wider tires. Been there, done that. Had a better MPG and tire improvements going to a higher load range.

Report back your findings.

 

You mean 245/75/16 isn't the OEM size? I've had E-Rated 245/75's on my van since I bought it. Love them to death, and get great fuel economy, and even wear with a great ride at 55 psi.

 

The sticker on my door panel specifies LT225x75-16 tires at 50# and 65# pressure. I have the '01 B2500 extended work van (no windows or rear seating), 8-lug wheels with the step bumper and B3500 frame underneath. I like the larger tires that I just got so far (LT245) and hope to get good road grip from them, plus long mileage. By upping the size I hope to get an effective higher ratio rear end (stock is 4.10). I calculate the larger diameter tires give me an effective 3.93 ratio, hopefully giving me a bit more MPG on the highway. At current gas prices +1MPG boost would be a benefit. I currently have them pumped to 50/65# but may change that to 55# as you mention, as I do not carry any great loads in the rear.

 

Need to check my door panel now to see what mine says.