Question: what is the ideal setting for the castor on our trucks? or specifically, a 2003 F-250 4x4 Supercab short bed? I know negative is the way to go (top pulled back)... Say the truck is 3" taller up front over stock and 1" taller in the rear...

Dilemma: I'm converting my leaf sprung truck to a set of radius arms / trac bar and coilovers. Goal is to get either 10" or 12" of travel up front (metal to metal, depending on what size of coilover I can fit). Also trying to fit 37's, but we'll see about that... also at first I was planning on making the radius arms adjustable but I just wanted to set it once and forget about it...

thanks for the info in advance!

Joey

 

bump... anyone???

Joey

 

The factory specs call for I think 3.5 +/- 2 degrees. If you were using the truck mainly on road for towing/hauling etc I wouldn't be afraid to use the most negative value of this range for better tracking. I would assume, however, the reason you are lifting and converting the front end is for offroading. I believe more negative caster is going to put larger strain on the steering system (pump, box, drag links, tie roads, etc) but I would guess with 37" and converting to a coil 10-12" lift you have come up with something to handle the extra load.
In the end I'm not sure what the ideal caster would be in your situation but at least I'm good for a bump.

 

yeah, I do the occasional towing and I drive mostly on-road but do take out the truck maybe 10 weekends a year out to desert and just off-road... not the best platform for that by far but building up the truck to be a good chase truck for my friend when he starts racing...

FYI, I'm NOT gonna have 10-12" of lift... goal is to someday run 37" tires, so I'm designing everything with that in mind, but probably won't happen for another year or so... goal is 3"-4" of lift over stock with 37" tire down the road and 11" of travel bumped/strapped... I guess its a california thing ... thanks for the bump! anyone else?

Joey

 

bump?

Joe

 

The nore positive camber the better as far as driveability goes. I like to see it around 4-4.5 degrees. Higher caster gives you more stability in the steering. Negative camber makes for a wandering ill-handling vehicle. Imagine riding a bike with the fork pointed backwards. Not much fun.

 

ahhh, so I got it mixed up but we were saying the same thing... and I agree with positive caster, just looking for a concrete number... +4-4.5* is a good start... thanks

Joey

 

Opps I did too. I was thinking negative when I should have been thinking positive!

 

No no no...you want positive caster. Positive caster tends to straighten the wheel when the vehicle is traveling forward, and thus is used to enhance straight-line stability.

Negative caster makes the vehicle wander and nervous.

Please read Caster, Camber, Toe

You want as much positive caster as the alignment shop can dial in but still stay within factory specs.

 

I just sold a set of Fabtech radius arms, they use a cam bolt to make castor adjustments. For doing a conversion like this though, I would just go with a 4-link setup that has the adjustability.

 

ahhhh! thanks for the link... I thought it was the other way around... works out better for me that way, as the truck cycles to bump, it'll go towards the negative but during normal street driving it'll pretty much always stays positive... and what are those factory specs? better yet what number has given everyone the best luck?

you know, I thought about the 4-link with the panhard bar but two things make me wanna do radius arms:

1) You need to set up the truck very tall to get any decent travel numbers, mainly because the frame side bracket hangs very low to accomadate both links

2) Drastic pinion angle changes with the four-link because of the smallish (30") links. Keeps the castor in check better than radius arms, though, but I prefer to save my diff/driveshaft

A buddy of mine did the four-link on his truck. He built it all himself. He doesn't regret the four link because it works good but he loves the route that I'm going because of the simplicity behind it... also, he had to set up his truck with a 6" lift over stock, which he originally wanted to keep lower. Another downer to doing the four link, once again comes from the added height and the added travel: how much the front axle moves side to side... granted, he still hadn't bought a drop bracket for the trac bar...

keep the replies coming!

Joey

 

ahhh read on it some more... so if I think of it as a clock looking at the wheel from the drivers side, positive is going clockwise and negative caster is counter-clockwise... and I may be able to make a 4-link work... don't need that massive of a frame-side bracket to keep geometry as I thought... this is helping me with cycling, check it out...

racing aspirations » Suspension Geometry Calculator

for a-arms, but the principle is exactly the same (with camber change being caster)... bump? someone give me a good degree to set the truck at...

Joey

 

I'd go the factory set 3.5 degrees as a minimum, and don't be shy of going as much as 5 degrees. Really, anything in that range will work fine. In my project I've aimed for 5, but I am running a hydro assist ram so steering loads won't be an issue at all.
I'd say jhooch is right on the money with 4 - 4.5 degrees.

 

thanks for the reply, DJ... I think I'll go with +4.5* of caster and see how that works out... hopefully I'll start putting it all together pretty soon... just gotta get all my measurements in order and start making some brackets and such... and btw, you have a cool build! I remember reading it some while back...

Joey

 

sooooo, bringing this thread back from the dead...

still designing the parallel 4-link w/ panhard bar for my truck in solidworks but still have a couple of questions...

1) What is the pinion angle set at from the factory?
2) what dimensions does the axle have? wms-to-wms measurement, how far is the carrier from the driver side perch?

Going to put some more time into the modeling right now... I'll probably post up some pics of solidworks in the next coming weeks, so you all can see what I'm working on... thanks in advance!

Joey