Tire Size & Link Suspension Design (Help me plan my K5)

[Mudbone]

First some background info: I have a 91 K5 that I purchased with 6 inch spring lift and 35 inch tires. Everything else stock. Leaf springs are typical old school lift style that are overly stiff. I am planning my build for this truck and want to use a linked suspension front and rear. This will be my first linked suspension. I live in mid-NC so it will see use on everything from pure sand and mud down east to the muddy rock trails you get in NC, TN, and KY. I want to keep it street legal and will drive it to wheel it. I want to keep it "full size" and not get into dovetailing but am planning on extensive trimming to the wheel wells to accommodate larger tires. My current thinking is to go with tires in the 38 inch range. I think I can do the wheeling I want to do without going to a tire in the 40 to 44 inch range. This will keep the truck lower to the ground, it will be easier to use on a daily basis, etc. So I have a few questions.

1. Realistically, what is largest tire you can trim out for and still get under the truck (with reasonable suspension travel), without lifting the truck so high that you can't really wheel it? (Afterall, you can design a suspension to run 44 inch tires with no cutting on the body at all. And the truck would be 5 feet in the air and tip over the first time you got sideways with it.)

2. How tight is the relationship between tire size and the suspension design? Suppose I have a link suspension that was set up with 38 inch tires in mind and I decide I want to go to a larger tire, say a 40 or 42. Can that be done without changing the length of the links, spring height, shock length, etc.?

 

[blazinzuk]

The web is a good source of info on link suspension. Google link calculator.

There is alot going on in a do it all link setup. You need to understand alot of different factors and how they are going to affect each other.

As far as tire height I have about 4" of lift and fit 42s with pretty good flex. Links actually make it easier because leaf springs (with shackles on the trailing end of the spring) cause the tire to move rearward on compression. Links (on the vast majority of builds) will push the tire just slightly forward under compression.

On a do it all rig you need to read a ton on links. You can really mess up a truck with a link suspension, or it can be a flexy monster that still drives nice on the road.

Tire size? As big as you can afford. The only thing links should affect as far as tire size is where the axle it. If you build the suspension right bigger tires will just require more cutting of the body.

One more thing on a truck that is going to see alot of use. I would not use Heims. I would use a rebuildable joint. Heims wear out.

 

[Mudbone]

Thanks for the reply. As far as designing the link suspension, I have looked at some of the calculators and done some reading here on CK5 and at Pirate. But their is no way in hell I am going to try to design it by myself. So many folks have already done this for a K5, why should I try to reinvent something. I plan to use as much prefabbed mounts, supports, etc as possible.

As far as tire height I have about 4" of lift and fit 42s with pretty good flex. Links actually make it easier because leaf springs (with shackles on the trailing end of the spring) cause the tire to move rearward on compression. Links (on the vast majority of builds) will push the tire just slightly forward under compression.

When you say it makes it easier, do you mean from a tire clearance standpoint? I thought that it is better to have a suspension compress to the rear instead of the front because compressing forward is against the object you are trying to drive over. Wasn't this a complaint in older Jeeps that had front mounted shackles on the front leaf springs?

Where can I see some pics of your rig? Do you have a build thread? I have looked through the "what will my truck look like on XX tires" sticky but its hard to tell all the details of a specific rig. I am interested to see how much cutting you had to do for the 42s.

Tire size? As big as you can afford. The only thing links should affect as far as tire size is where the axle it. If you build the suspension right bigger tires will just require more cutting of the body.

One issue with the afford part is its not just the cost of the tires. I have a set of CUCV axles I am going to use with this build. Since they already have 4.56s in them I should be able to use 38s without a problem. But I thought if I go 40 or higher I should consider going to 5.13s which is an additional cost.

What I wanted to make sure of is that if I go to bigger tires at some later date(with or without the gears), that I won't have to change any parts of the suspension. As long as the tire will fit the well, all I will lose will be some axle travel. IE if I have 12 inches of upward compression with the 38s and I go to 42s I will now have 10 inches of upward comprssion. correct?

 

[MNorby]

Research alot when you design your links geometry. The calculators work great but often with your packaging it can't be perfect. Use the calculator to decide which way you can fit the suspension that will work best. I like the ballistic fab joint for being greaseable and rebuildable. My rear link setup works great and the front is gonna be done next winter.

 

[Hogback Fabrication]

When you say it makes it easier, do you mean from a tire clearance standpoint? I thought that it is better to have a suspension compress to the rear instead of the front because compressing forward is against the object you are trying to drive over. Wasn't this a complaint in older Jeeps that had front mounted shackles on the front leaf springs?

The idea is to try to keep roll steer as minimal as possible, i.e. so that the axle does not move forward or back during articulation. You want your steering linkage to steer the vehicle, not the axle physically turning under the truck due to the suspension.

One issue with the afford part is its not just the cost of the tires. I have a set of CUCV axles I am going to use with this build. Since they already have 4.56s in them I should be able to use 38s without a problem. But I thought if I go 40 or higher I should consider going to 5.13s which is an additional cost.

What I wanted to make sure of is that if I go to bigger tires at some later date(with or without the gears), that I won't have to change any parts of the suspension. As long as the tire will fit the well, all I will lose will be some axle travel. IE if I have 12 inches of upward compression with the 38s and I go to 42s I will now have 10 inches of upward comprssion. correct?

Bigger tires shouldn't mean a change in suspension, and it won't mean a change in suspension travel either (the clearances between the axle and frame/oil pan etc shouldn't change). You just need to trim the fenders to clear the fenders.

As far as gearing, it would depend on your trans, motor, and how much you drive it on the street. You're probably better off looking into deeper t-case gearing rather than re-gearing the axles.

 

[Greg72]

Build the suspension with where at least one link mount has adjustability...

When you move to a different tire size you can accommodate. Don't assume that your first suspension design is going to be perfect anyway... Having adjustability will allow for fine tuning. A completely non-adjustable link suspension is a waste of money and effort.

 

[Mudbone]

Bigger tires shouldn't mean a change in suspension, and it won't mean a change in suspension travel either (the clearances between the axle and frame/oil pan etc shouldn't change). You just need to trim the fenders to clear the fenders.

Then I am going to start in the 38s and go from there. I just didn't want to back myself into a corner. Now I have to decide on wheel size......

As far as gearing, it would depend on your trans, motor, and how much you drive it on the street. You're probably better off looking into deeper t-case gearing rather than re-gearing the axles.

Thanks for that suggestion. I will be driving it to where ever I wheel it. So I plan keeping the 350 and some version of the 700r4 to get the overdrive. But since I plan to replace the t-case anyway, I can get any extra gearing done there.

 

[Mudbone]

BTW Chris, shouldn't you be recommending that I buy ORD's front coil over kit?

 

[blowedupmotor87]

I've never done one so, take all this with a grain of salt (or even a shaker's worth, LOL!):

Looking at the different setups that are around, if I were to do a coilover link setup, I would keep the lift mild (3-5"), stretch the wheelbase a little (front axle forward about 1.5", rear back about 3") it'll help keep your tires outta the firewall, will shorten your front and rear overhangs a little, give you a good amount of travel, keep your center of gravity low, and makes for a nice balanced look (IMO). Cut the fenders accordingly! (I'd love to set mine up at 3" lift, wheelbase stretch and 40's!!!)

For 38's, a swap to CUCV axles will give you a just about perfect gear ratio (the stock half ton axles would be a pointless waste to incorporate into a fully custom suspension that has 38"+ tire size intentions). This part I speak of from personal experience, I have a CUCV axles under my Jimmy running 37's and my speedo is pretty much spot-on. I believe my stock axles were 3.42 gears with 29" tires (all long gone now), jumped up to 4.56 with 37's (the math says a gear ratio of 4.36... would be perfect but, dang close!). The CUCV axles are a Dana 60 front and a 14BFF rear, and already have a Detroit locker in the rear diff.