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July 2012 Techline Reader Tech Questions

3 Off Road Tires
John Cappa | Writer
Posted July 1, 2012

Your Tech Questions Answered

Metric Tire Math
Could you tell me the math conversion for metric tires into inches?
Name withheld
Via Facebook

Let’s use a 305/75R17 metric tire as an example. First you have to convert the width (305) to inches by dividing by 25.4 (this is the number of millimeters in an inch).

305/25.4 = 12.01 inches

Then you multiply this number by the listed aspect ratio (75% or .75). This gives you the sidewall height.

12.01 x .75 = 9.01 inches

Then multiply the sidewall height by two.

2 x 9.01 = 18.02 inches

And then add the wheel diameter (17) and you will have the height of the tire.

18.02 + 17 =35.02 inches

So the 305/75R17 tire is 12.01 inches wide and 35.02 inches tall.

2 By 4
I recently paid off my truck, an ’04 Dodge Ram 2500 with a 5.7L Hemi. I love my truck but I need four-wheel-drive. Is it possible to change a 4x2 over to a 4x4 or would it be cost-prohibitive? My job was infantry in the military, not mechanics, so I would probably have to outsource the work. Considering the cost of parts and labor does this make sense?
SSG Carter Chick
D 3/141 INF Via email

Unfortunately it’s cost prohibitive to take on a conversion like this. It’s generally less expensive to sell the truck you have and purchase a 4x4 version of it.

FSJ Suspension Question
What leaf springs are you running on your current ’73 J-2000 with the 37-inch tires? I would imagine the same could be run on a ’77 Wagoneer. My Wagoneer has the 360, a TH400, and a Quadra-Trac T-case with Dana 44 axles front and rear. I’d like to just put a lunchbox locker in the rear and install the least amount of lift to clear 35- to 36-inch tires.

I don’t have a problem trimming some sheetmetal and re-working the inner fenderwells. I like the idea of staying spring-under to fight axlewrap but I’m not really into the whole lift kit idea. I was thinking of going spring-over with a set of flat springs, like 52-inch Chevy truck leaves in the front and either 56- or 63-inch Chevy truck springs in the rear with a track bar. What’s your opinion?

Can you give me a rundown of what’s been done to your J-truck? What springs did you go with for the front? Did you use a block, shackle flip, or lift springs for the rear? Your truck is spring-over in the front. Did the J-trucks come that way or did you go spring-over with the stock springs to get the lift you needed? I’m assuming you have the 360? What gears are you running with the 37s?

Are you running high-steer up front on the Dana 44?
Joe Fuerst

The main problem is that the suspension on my ’73 is altogether different than what is on your ’77 Waggy. My truck has what is known as “post-mount” suspension. All ’63-’73 J-trucks have post-mount suspension. The springs mount to posts that protrude out of the side of the frame. The front and rear suspensions are spring-over from the factory. The good news is you actually have more options than me. Your Wagoneer has lots of lift kit options that fit the ’74-’91 models. However, your rear wheelwells are less trim-friendly because of the rear doors and the general design of the inner wheelwell. Trimming the front will be sort of similar to my truck but still a little different.

My ’73 truck is suspended by Hell Creek ( 4-inch lift springs up front. In the rear I simply flipped the shackles and used the stock leaf springs. I think you will be better off going with a 4-inch lift kit front and rear along with some trimming. It may seem cheaper to do the spring-over, but the additional parts needed can add up pretty quickly. For example, you will probably need to find a way to combat axlewrap front and rear, as well as lengthen the driveshafts (among other things) with a spring-over.

My truck doesn’t have axlewrap, but it doesn’t flex as well as the setup you’re considering. My springs are quite a bit stiffer.

My ’73 J-truck runs a 360 V-8, T-18 manual tranny, and a Dana 20 T-case with a 32-spline rear output. Up front is a smallish closed-knuckle Dana 44 and out back is a swapped-in junkyard Ford 9-inch from a ’74-’86 F-150. The axles house 4.10 gears. With the non-overdrive transmission and the 6.32:1 First gear the 4.10 axle gears provide both decent on-road rpm and half-decent crawlability in the rocks.

My truck does not have high-steer. There really is no way to install it on a closed-knuckle Dana 44 unless you build something custom. I simply ordered and installed a drop pitman arm from BJs Off-Road ( I’ll eventually swap out the closed-knuckle axle for a stronger open-knuckle Wide-Trac Dana 44 from a ’74-’79 Cherokee or J-truck.

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