Okay my head hurts from trying to do the math and all relating to figuring out rev's/mile and comparing tire offerings and all that jazz, just need to look at getting some new rubber, getting down to about 8/32's after 70K (not bad for stockers). Now the fun, I want to keep the stock wheels but increase the circumference of the new tire size a bit, currently 235/85-16's on there with 4.10s in the diff's. I'd like to drop the rpm's a bit at highway speeds, for example at 75mph she's pushing 2500rpm, way too high by my thinkings. But still averaging 16.9mph.

Suggestions or recommendations? Keep in mind she's DRW so the width becomes an issue, and changing out the gears is really not an option I'd want to mess with (4x4 so it'd be both ends = $$$)

and shhhhh.. I know what the max speed is in WI.

 

I have heard tell you can run 255/85s on the dually. I have them on mine, 2500, adn like them so far. They dig like there is no tomorrow!

 

A taller tire will drop RPMs. For every inch taller tire will actually take from your gear ratio by .10. If you are running a 30" tire and change to a 33" tire this will drop your gear ratio to a 3:80 gear ratio.

 

If your not towing anything very big, you might be able to swap your rear with someone looking for a 4:10 and you get the 3:55. Check the for sale adds here and at TDR if your a member.

There was a post here or TDR that used an excel spread sheet that calculates all time sizes and converts the size to RPM's in differant gears for 5 speeds, 6 speeds and mush boxes. If you can't find it I may be able to send you a copy. I can't remember who posted it, but it took him a few hours to set it up.

Dave

 

I've since done a bit more research, and found an interesting page that will figure your rev's per mile and size spec's (turns those metric numbers into something useful) here

And of course found out that the 255/85-16's will work sorta, they'd be ~3/4" wider than the 235/85's. Given the dually's though that doesn't leave too much room for flattening out with any load at all. Given that every now and again I'll load her up with construction materials for projects and such, or drag the boat/camper around so the thought of the tires rubbing is one i'd rather not even consider. So the search will continue. I may end up just replacing them with the standard 235's until i can find a way around another goofup I pulled....get this I had my new garage built (to my specs none the less) in June of '01, bought my baby in July, as it is now with a 7' high door she squeaks in with only 1.5" clearance...And i've yet to add a lift kit or anything! Someone wasn't thinking gotta find a way to either add a hip roof or something to get more head room, at least 2-3 feet worth! No telling what my contractor will have to say about that short of sure.... $$$$ here's your bill.

 

We run 245's on my wifes truck. They seem to work alright on mine i keep the 235's . As far as gear changes i tow a lot with my 3:55's and have no problems

 

If you're looking to drop the rev's a 255/85/R16 will do it and will fit on your stock wheel. You should add a spacer between your wheels though. I can't remember the source for these though I believe they are readily available.

 

I ran 255-85's on my 3500 for a year. You can only get them in a load range "D" -- no "E"'s -- and usually only in a brand like Firestone. I had so much flex in the tall sidewalls that they started to fail prematurely on two of six tires. Went to 265-75's "E"'s, which have worked very well. Just pulled a 30 foot trailer 2000 miles; generator in the bed, etc., and no rub in the rear wheels. Very stable. No spacers. However, these are Michelins with stiff sidewalls, run at 70 psi +. There are some variations from brand to brand.

Problem is, the 265-75's are as tall as the stock 235's -- just wider. I don't think the 255-85's are an ideal solution, unless you're doing empty on-road miles. You can't run 265-75's on anything but an '01.5 and an '02. You can't run 255-85's on anything previous to an '00. From what I've been told, DC changed the offset twice.

 

I'm going to go out on a limb here and assume that this statement was directed towards 3500's. On the '96 1500 gasser I used to have, the door sticker showed that it should have 245/?? on it but mine had 265/75's. On my '01 2500, the door sticker says it should have 245/75's on it, but again it has 265/75's. Go figger.....