Vagabond52

I have a stock 2001 Ram 3500, 4sp auto with 3.55 gears, I would like to know what size tires "shorter" I would have to go with to get in the 3.73 gear range and also what would I have to do to correct the speedo.

Thanks
Ken

93w250

Look here http://www.dakota-truck.net/TIRECALC/tirecalc.html
I'm not sure if the computer could be programmed to correct the speedo or not.
I downsized tires on my 93, went from 235-85-16 to 245-75-16, it gave a ratio equal to 3:70 I think. It did make a difference in pulling ability but my speedo read a little faster than actual speed.

BearKiller

You can do the math to figure this out.

Measure the diameter of your current tires = a known factor.

Your gear ratio of 3:55 = a known factor.

Your target ratio of 3:73 = a known factor.

The needed tire diameter = the unknown factor = X

Plug these figures into an Algebraic equation and the answer will magically pop out.

Hope this helps.

hamilton71801

That's too much thinkin and makes my brain hurt.

Hillcountry

It is simple math to do and very handy at times. I can hear my Algebra teacher now saying "this will come in handy some day!" AArrrgh!

multiply 3.73 times the diameter of your current tire. Divide the answer by 3.55. The answer will be the diameter of your new tire. From there you will have to figure out the new tire dimentions, but that should be easy.

To get diameter you can wrap string around the tread and straighten and measure..if you don't like math. That's what I would do.
I hope this helps...

-Geoff

jkitterman

I am guessing you have a DRW because of the 4500 lb slide-in in your sig. You really won't find a tire size smaller than stock that makes much difference with the weight rating for your truck.

BearKiller

Diameter is the height of the tire.

The string trick will get you the circumference.

Hillcountry

Woooooow!

Now I feel really dumb! Thanks for pointing that out

Yeah...diameter is height...sigh...long day I guess. Oh well.

Well...if you ever want to measure circumference do what I said above...other than that...you probably shouldn't listen to me anyway!


Have fun
-Geoff

bluebull

tried changing tire size on my 99 for better towing. Waste of money in my opinion. Never helped at all.

Vagabond52

Thanks for the replies everyone, I think I can get where I'm going now.
Hey Hillcountry, don't feel bad it happens to me all the time...heard someone call it a Brain Fart !

Thanks
Ken

BearKiller

The shorter tire looks good on paper; but, in practice, it doesn't really pan out.

Taller tires actually act like a bigger flywheel, keeping rolling force in action to propel the load down the road.

Also, a shorter tire will drop down in depressions that have to be clumb back out of; whereas, a taller tire will "bridge" across a rut, or pot-hole, saving the effort necessary to climb back out.

Does this make sense??

Vagabond52

BearKiller,
I agree completly, I've thought about those very things you mentioned. The drive train combo that I have is just not the best for hauling a large Truck camper, the 3.73s weren't offered when I bought my truck, The drivetrain combo I'd really like would be the HO engine with standard trans, 4.10s, 4x4

With the camper loaded and all supplies, people, dog...everything, I'm about 1100 lbs over my GVWR, I'm thinking about going on the road fulltime in the RV and would now also be towing a 3000lb truck. I'm most worried about getting the rig rolling from a standing start.

Right now,with the camper loaded, unless I'm running on absolutely flat land with no wind, I have to stay in Drive and run 60 MPH to be in the Power Band. In OD I have to run 70-75 to get in the Power Band and it's got to be flat or it'll be constantly down shifting. Also if I don't keep it in the Power Band I can feel the engine bogging. I only get about 10.5 MPG at 60 MPH in Drive.

I've been in the woods with the camper on the truck, it was bone dry weather but I was rolling on heavy pine straw, when I stopped and tried to start moving again it was almost impossible to build up enough Tourque to get moving again, it was easy to tell the Tranny wasn't going to handle much of that.

So I've been kicking ideas around to see if I can make this truck work a little better for the way I use it.

I appreciate the responses and all ideas posted so far

Happy Trails
Ken

97ramctd

i wouldn't see much difference, you would have to go alot smaller to make up that much

Just my .02

Patrick Campbell

215/85/16s is shorter and will increase your revs a little.

If you go here:
http://xj.cdevco.net/auto/rpmchart/index.php

Pick your auto trans
Pick the 2nd to last tire for left, and the last tire for the right
Change rear end to 3.55

This will show you approximate rev ranges. It pans out more on the highway. 68 MPH is 1800 on the 235's, and 1900 on the 215's.

bluebull

Your best option is to swap out ring and pinion gears. On a 2wd that shouldn't cost any more than 6 tires, probably not as much. You have a dana 80 rear end and I don't think they make a 3:73 but I'am pretty sure they make a 3:90 gear set which would help alot. Going to a 4:10 gear swap would mean you have to change out the carrier also and that will add more money.

Like I stated earlier I tried swapping tire sizes on my 99 with 3:54 gears and it made no difference.

Just throwing out more ideas.