Graded dirt-road handling questions.

[TimS]

Hello.

I normally hang out on the off road forum, but as I get closer to the untimate dual sport baja bug, I am seeking your advice to fine tune my handling.

I'm running 32x11.5 M/T's in the back, and firestone winter tires 225/70r15 in the front. I've recently changed to aluminum rims and am very impressed with the difference in acceleration, ease of turning, and smoothness over my steelies. Rear toe is 1/8" or so in. Front is probably 1/4" or so in (I don't really know because things have settled in for a few years)

Pavement is great, I will get some underseer under accel, but followed by controlable oversteer after I let off the gas.

Off road is great, it soaks up bumps well and fly's good too, letting off the throttle and turning will get me sideways just enough to scrub speed.

Ralley roads (graded gravel, hard packed silt/clay) is where I'm having troubles. I find that I'm having to "jab" at the corners by giving quick exagerrated steering input to initiate the slight oversteer situation, but once I get to the slight oversteer configuration it seems to grab well and is very controllable. On a dry lake bed, for instance, I can ease into the turns, and it seems really loose until the rear end kicks out a little bit. Once the rear end kicks out a certain, predictable, amount it grabs well and can carve a turn. I hope someone can relate to what I'm saying.

There are really two ways to approach this... 1. get used to it. Continue to jab at the turns and get a feel for how it's going to respond. My fear is that there will be a time when the jabbing doesn't create oversteer but instead understeers, leaving me lttle time to react, and sending me off the road. Or 2. find a way to make it carve without the "looseness". Is there a way to get it to carve sooner? Maybe rear end alignment? More toe?

If I have to sacrifice pavement driving and tire wear to get rid of the loose zone, I might just as well get used to it and compromise, but I figured if there is an answer, you all might know it and give me some things to experiment with.

Thank you, let me know if you need more information.

-Tim

edit-->

750lb. (37%) front
1260lb. (63%) rear
______
2010lb. gross

Since those weights, I've added about 40lbs just aft of CG on the floor.

[Dale M.]

"Performance" driving on dirt is a whole different world than "cruising" on street or dirt...

Remember you are driving on "marbles" and tire grip is absolute minimal. You have to set up vehicle to make it go in direction you want, there is no such thing as steering or under steer or over steer on high speed dirt.... I even "looped" my jeep in FWD the other day and were not going that fast.... Most of my world out in sticks of CALIF is on dirt and tire contact and steering is minimal at speed.... Even my 4k lb Jeep will dance on washboard roads, and I have to reduce speeds...

Dale

[TimS]

Ah, very good perspective. Vehicle setup... Thanks. I'll put some more thought into that. I assume you mean preparing the vehicle in terms of yaw and inertia before turn execution? Maybe I'll youtube a bunch more with that in mind and see what I learn.

So far I have no complaints about the predictability of it, Maybe I just need more experience with my current setup to get the feel. I'm gettng pretty good at judging traction visually,and am able to keep control of it when my judgement is off a bit.

So, maybe the answer is put my time into more cagework and better saftey gear.

Thanks for your input.

[Ol'fogasaurus]

Remember the problem with compromise... you don't get the best of either/any world(s). Like Dale said, get some time in the saddle before you make too many changes or compromises... you might be surprised with what you have now... once you get use to it in a different environment.

Lee

[Marc]

Still running the stock rubber control arm bushings at the pivots and at the ends of the torsion housings? Those contribute to a lot of toe change. On pavement it's easier to anticipate and is even desirable sometimes, but for dirt work I'd rather stiffen things up to reduce that variable and let me concentrate on the terrain surface. Urethane bushings are still compliant enough to live with on the street (if you don't mind the added NVH) but'll help the predictability off-road.

[TimS]

Yes, urethane front and rear, Inside and out. I just replaced the rear urethane this year. Pavement is good, nice and tight. Thanks Marc. What is NVH? I will pay attention more on pavement and see if I'm sensing any flex.

I think I'm expecting more than is possible. I just got back from looking for firewood in my truck and my bug has lots more turning traction than my truck. Time to improve the driver, I guess. Maybe I can get a video of what I'm talking about.

[Marc]

http://en.wikipedia.org/wiki/Noise,_vib ... _harshness

You have those one-piece urethane control-arm bushings in the front beam? Can't say that I'm a fan, but maybe I've just had bad luck with them being too sloppy.

More front caster will cause the wheels to "lean-in" to the turns like a roadgrader, sometimes that's all it takes to sharpen steering response on loose surfaces. More negative camber helps too (at least on the outboard tire) but the downside is considerably more stress on the outer wheel bearing/spindle - I wouldn't go there.

[JWP]

I've experienced the same thing in my rail. Like others said compromise won't get you the best of anything, meaning optimum dirt setup will not be optimum asphalt nor optimum hard pack etc.
My rail has a cutting/steering brake that helps kick the back end out, followed by throttle input to get the oversteer I wanted.

I think you hit the nail on the head when you mentioned working on the driver. Get used to the car how it is. Once you improve your skill and consistency, you will then be able to make changes and know the car is the variable.

[TimS]

Wow, thanks again. More great info. The NVH should be greatly improved once I get my intercom setup. when I have earplugs in, the ride is so much smoother.

And thanks to for the caster/camber info. That is what I was looking for. Something to experiment with, and they are both just a matter of shimming and an afternoon's work. I'll go measure what I have now.

Driver training in progress. I need to find a long stretch without blind corners to really test things out. but testing is 3/4 of the fun.

[TimS]

Okay, camber -1/2" from bottom of rim to top of rim bilaterally. Caster at beam 4.5 degrees at current ride height. Front toe 1/8" in.

I know one of my problems is my lower link pins loosen over time. I need to get some with locknuts, I think.

[Slow 1200]

I'm not sure if things off road work the same, but typically once you get to negative camber you can get away with toe-out, which might help turn in, I'm just babbling here so ask people with the real world experience

[Marc]

That's correct. But negative camber magnifies the stress on the outer bearing and spindle far more than you'd think so it's not wise off-road, especially with stock spindles.

With positive camber the wheels are constantly trying to steer away from each other and setting the toe "in" preloads the steering linkage to resist it. Conversely, negative camber requires toe-out. Another factor is the "Ackerman" effect, which generates toe-out as the wheels are steered off-center. Ackerman is changed when the wheelbase is altered; to modify it the lateral location of the outer tierod ends has to be changed (which requires altering the steering arms on the spindles) so generally you need to live with what you've got.

http://www.aligncraft.com/terms/terms.h ... t%20camber
http://www.aligncraft.com/terms/terms.h ... 20Out%20On

[TimS]

Nice website!! I spent some time there and will spend more.

I took some video of high speed pavement, high speed dirt, and bumpy dirt. I could edit into something watchable, but all I learned is that I need more practice on the dirt.

All of the above has been really helpful (thank you) to help me narrow in on how the car needs to be setup for my driving. I need the car to shine where I am weak, and where I am strong , I can tollerate a little skitty-wompus-ness.

[Jadewombat]

Take your bug to a rallycross. Don't worry about your times, some of the fastest rallycross drivers are in the least likely cars (at Nationals a couple of years ago a 10 year old very stock Sentra won FWD). I took my bug out once last year and learned quite a bit. You get into a rhythm with the car and start feeling a controlled slide around the course. Bugs are very predictable when the rear end is going to kick out and when you are about to overdo it with too much gas pedal.

[TimS]

Thanks, JW! I have a feel for the slides and can slide dirt or pavement at 50mph no problem. The problem was entering into the turns and the delayed reaction plus the exaggerated (not so smooth) input needed to get to the powerslide attitude. Also, I'm kind of a puss still and am actually turning too soon and too hard and cutting the corners too deep having to go from powerslide, to straight, then back to powerslide... Doesn't look pretty at all. Partly my trouble is that the roads I was on required 55-65mph to test the limits. I'd rather experiment on something slower and tighter (35-45mph), but I still need to find something suitable that doesn't have blind corners for traffic.

Under no accel or decel on pavement with smooth entry, my front outer tire feels like it's the one slipping, and even then it doesn't break free, just slips to let you know you've reached the limit of traction. Under full acell hard slower turns on pavement, my inner rear tire breaks free and spins. (no sway bars... yet).

I accidentally deleted my gopro videos because I thought I had already tranferred them, but I'm trying to recover them now and it seems to be working, then I could show you what I mean. EDIT -> Nevermind... They are gone.