Physics question with shock spring pre-loading...
 

I own a few 1/10 scale rc's I use primarily for backyard racing and bashing. Specifically I have an assortment of old Traxxas e-maxx, rustlers, and stampedes. When we race/bash it is typically on flat ground (grass/dirt). The biggest gripe is that my less-experienced friends who try to race with me will constantly roll the vehicles with sharp turns and braking-while-turning, etc. I would like to configure my setups so that they are as roll resistant as possible. Obviously setting suspension/COG as low as possible helps, but in terms of shock tension what should I do? I figure that pre-loading all of the shocks to make them as stiff as possible should help prevent rolling as much as possible but am I wrong? I noticed that when I accidentally roll one of my trucks on a turn (while slowing down for control) it seems like the front wheel I am turning towards is dipped way down because of inertia. This dip places the entire body on an angle towards the turn and forward which I am guessing will make it more likely to tip over. Am I correct in this assumption? I figure that a heavy pre-load of the shock springs would help prevent this tip (for inexperienced racers, myself somewhat included). Again, since we really race primarily on flat ground should I heavily pre-load the shock springs? Any other suggestions (aside from more practice haha)?

Thanks!

-Brian

You know in can get well in depth trying to find the right balance of ride height, camber, roll centers, shock oil, springs, tires, blah, blah, blah, etc.,etc.

Me, I primarily use springs for setting ride height, and that's it. There comes a point where spring rates interfere with adjustability of shock collars, so I strive to have the collars in the middle of the threads somewhere, and not at the extremes (if at all possible).

I think a lot will have to do with your turnbuckles, camber, and ride height. If you can lower your inner links a bit, use about -2° camber on the wheels, and lower ride height a bit, that should help. Again, it will be about balance and compromising. Setting up for just one part of a track, may hurt you elsewhere. What tires you are using, and what foams you are using...all will play a part in factoring in a good setup.

Hudy, and Tekno have great setup guides that you can download and study. Roll center videos...

What specific car are you trying to tune?

It would be a lot easier to start with a baseline setup for your given track condition and then make minor tuning changes from there. To get rid of "traction roll" there is a really nice chart provided by Hudy which shows you the priority of changes you should make... once you've maxed out a given option for your car, then go down to the next item in the list until you get the car working as desired.

Keep in mind that there is always a give and take.... for example tuning out traction roll tends to take away steering so you might discover that the car can't make as tight as turns as it used to, but with the benefit of not traction rolling.

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generally the preload rings and spacers have no effect on the rates or static rates, the only time they effect the static rate is if they have been adjusted excessively and there is no longer droop in the suspension.

in short, use preload to adjust ride height only


rolling over is a combination of speed, to much traction, suspension travel, roll centre, cog and the suspension not been able to absorb the forces from changing direction.

one big thing i recommend...... try limiting the suspension travel and use a slightly thicker shock oil.... say for example, if the shocks have 2 lower holes, use the outer holes, and if needed you can use nitro fuel line under the shocks piston to limit the shocks range.

once u have a workable suspension range, then play around with springs and fluids...

something to be mindful off.... to much traction is a killer. if u reduce the front so it favours understeering rather than rolling over, it might be nicer to drive

This is a really nice trick for many 2WD cars which don't have droop tabs, but most 4WD cars already include this tuning option, so be sure to only go this route as a last resort. I also favor using plastic spacers instead of cutting fuel tubing because it's difficult to cut perfectly equal lengths which is very important for consistency. In contrast, most of my car setups have me extending my droop by backing out the shock ball ends a few turns.

Traction roll is typically mitigated with ride height, which was listed as the #1 priority adjustment in the chart I linked earlier. These guys should start with a good baseline setup before blindly making any other tuning changes, they could have their cars so far out of whack they could easily create bigger problems elsewhere. It's better to start in the center of the tuning window rather than in a far corner which will drastically limit your options :(

For the traxxas vehicles you mentioned in the original post, I would recommend lowering the ride height, adding some front toe-in (helps the car understeer going into the corner), and using bald tires up front (again, adding understeer at higher speeds).

Some pretty good tips here for tuning the Traxxas Rustler:
Ultimate Rustler - Ultimate Traxxas

oh single out my post..... heheh but yeah correct me if im wrong but do any of the vehicles he has offer drop tabs? (emass, rustler, pede)

and i respectfully disagree.... nearly every traxxas vehicles ive played with has to much suspension and i recommend it as one of the first things to do not the last, and by doing it, it can reduced the ride height witch is one of the first things u reccomend lol

and.... if ya struggling cutting fuel hose to the same length, traxxas has some little blue bump stops that are perfect and protect the piston and the bottom of the housing

Thank you for all of the advice! I will play around and let you know what worked out best after a few races.

Wonder how sway bars would work in a situation like he has?