Fun With Caster

[arctictraveller]

[QUOTE=mgmetalworks I know that my van drove like absolute crap with 1.5deg caster (how it came from Quadvan). My van with my new suspension drove like a dream with 3.5deg caster... now I have an even more updated setup, modified radius arms and ~5deg of caster at ride height. Not a huge amount of difference in how it drives but now I know that my caster values won't go too low.[/QUOTE]

Per your recomendations, I added shim's to end up at nearly 5deg's caster, and it made a noticeable difference in driveability. The steering got a bit heavier, but it was well worth the trade off. Thanks............

[mgmetalworks]

Originally Posted by Glider

^^^Thank you, MG, that's really helpful. Somebody said something to me once about increasing caster--that if it goes too high, it can cause wheel chatter. What are your thought and observations on this question?

I've not been on the too-much-caster side of the spectrum before to know what it feels like when driving. I own two straight axle rigs that have had too little caster though (between 0.5 and 1.5deg) and I can tell you that they were sketchy at highways speeds under even perfect road conditions.

Back in my street rodding/muscle car days, I don't remember a single car that was set up with more than 6deg of caster. Anecdotally I don't think I have even heard a number higher than 8deg.

I guess I've just stayed away from experimenting with more caster than I use now because some of my car/truck building mentors (Ramsey included) have all narrowed in on the same numbers.

[Flux]

According to John at Agile, the TTB is set to 5-6 degrees of Caster. Camber is +1 and toe is 1/8 on that setup. I have only noticed it getting a little squirrelly up at the 80mph range. Some of this is definitely due to the added pop top weight adding some roll. At 70-75 mph the van is absolutely stable. I think that's pretty darn good for a lifted vehicle with a lot of travel.

[Jsweezy]

Flux - I dont think it should be getting squirrelly at 80. Have you talked to them about this?

It would be nice if someone came up with a conversion kit that came right out of the box with 3.5* of caster.

[Flux]

I'll rephrase that a bit. At 80 and maneuvering, you gotta be on point. Straight highway no issue. The suspension is still settling in as well.

[mgmetalworks]

Originally Posted by Jsweezy

It would be nice if someone came up with a conversion kit that came right out of the box with 3.5* of caster.

I know, right?

[MadScience]

Yeah, that may be part of the reason that I'm sticking with the prerunner rake on my van. I like how it handles now, and I like the view up front.

Originally Posted by mgmetalworks

I know, right?

Hah.

For those not in the know, MGM has a kit that does just that.

I have a bit of experience with different casters on a lifted coil spring setup. When I got my van it actually had negative caster. Which honestly works OK. You end up with a dead spot in the center which may be familiar if you've ever backed up a vehicle with positive (typical) caster. There was no death wobble, the van self centered after turns, and was a little off in ruts, but was generally usable by regular drivers.

Then the bushings on my rear spring shackles went (a regular, high mileage e-series wear item), followed shortly by me blowing out my ill sized shocks (my own personal fault). This left me with a van that was downright scary to drive.

I ended up fixing the caster first, because it was what an alignment check brought out. I used the bd-diesel kit (second hand from MGM ), and it made the van which was still a real handful much easier to manage. Mind you, this is with a van where the rear axle is still randomly steering, which is a little bit like a couple of horses randomly kicking your vehicle off course at random moments.

The real culprit was of course the rear spring shackles (thank you Agile for having me check them!!!), with that fixed things were pretty good, working shocks being the last thing to check off.

However, this showed me that I was much more capable of catching and re-balancing a van that was thrown off kilter with more caster than with less.

Randomly, my daily driver has over seven degrees of caster, which is spec. If anything it centers more slowly than the van. However it has nearly no weight at all in the front.

I may hunt down some shims to dial in more just as a learning exercise, but I suspect that:

- either these vans aren't really susceptible to death wobble

or

- far enough away from 0 is generally stable, at least with a heavy front end

- there's a point of enough positive and you're good. More is OK, but doesn't
improve further.

Again, these are things I suspect, and would like to prove or disprove, so I'd love to hear about any real experiences that any of you may have had that are relevant, or even just adjacent.

[Jsweezy]

To add onto what Madscience said I found there wasn't a big difference in driving between 3.5* and 5* of caster except the steering was stiffer. The one plus to having more is that if you do end up loading the rear down with a trailer or whatever it won't make as big of a difference.

[Glider]

Thanks, guys. This has been a really useful read for me. Has anyone experienced wheel chatter or wheel hop with higher degrees of caster?

[carringb]

I've never even heard of wheel chatter or hop with more caster.

What too much caster can do is increase loading on the steering components, because as caster increase, it also starts to have a jacking effect.... Basically it tilts the wheel enough it causes lifting.

Tire Rack summarizes it well: "What's the downside to positive caster? If the vehicle doesn't have power steering, a noticeable increase in steering effort will be felt as positive caster is increased. Other than that, the effects of positive caster are pretty much "positive," especially increasing the lean of the tire when the vehicle is cornering while returning it to a more upright position when driving straight ahead."

Now if you had stupid-wide, low-profile tires like Dodge slaps under their over-weight boat-cars, too much caster can reduce the contact patch as the wheel tilts, which can cause understeer.