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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
Via www.facebook.com/fourwheelermag

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 (www.hellcreeksuspensions.com) 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 (www.bjsoffroad.com). 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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