On Off Road Buggies - Why use a rear trailing arm rather than using double A Control arms ?

[TMcRally]

I'm just wondering why the top buggies use trailing arms on the rear inplace of double A arms.

Thanks
Dave

 

[patprimmer]

Length of arms to allow greater travel with less angle change.

As the trailing arms are normally set so they slope back and down at a reasonably steep angle to horizontal the wheel moves back as it moves up, thereby allowing a little more time for the amount of travel and reducing the shock load from the bump.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[TMcRally]

They must be a terrible thing with 5 or 6 degrees body roll ?

Thanks
Dave

 

[patprimmer]

You mean compared to the tyre running along or sliding into a 2' high embankment or running in a previous tyre track 8" deep or a culvert or creek bed full of rocks that are considerably bigger than bricks or one wheel running over a rock that is 2' high.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[DanEE]

"trailing arms are normally set so they slope back and down at a reasonably steep angle to horizontal the wheel moves back as it moves up, thereby allowing a little more time for the amount of travel and reducing the shock load from the bump."

And makes for graceful landings on the down slope after being airborne for a 100 feet or so, after topping the crest of a hill.

Love the design approach of the unlimited Tecate SCORE 1000 trophy trucks; awesome long travel suspensions with 30+ inches of travel.

 

[TMcRally]

Hi Pat

Before I posted I went back through the searches and I have seen a few of your posts on the off road vehicles and I understand what your saying about reliability over geometry I just struggle with it a bit.

I assume because the front is so much lighter it can get away with the A arms. If I was to build a smaller lighter buggy (around 1000kgs on the start line with crew and 200hp) to run on the same tracks as the bigger buggies - would I be better off with trailing arms or A arms ?

Regards
Dave

 

[gt6racer2]

Dave, Whilst the above points on wheel regression are valid, I believe a key design consideration is the drive force reaction. The A arms have to react this force to the body as a torque over the relatively narrow span of the A arms, whereas the trailing suspension sees mostly a compressive force in the trailing link.
Andrew

 

[TMcRally]

Ok, working with semi-trailing arms now. Listening to Pat's comments on travel I've become a bit greedy and trying for 600mm travel. Is there a reason why I can’t angle the front of the arm to chassis mounting towards the ground inboard ie. not parallel to the ground by about 8.5 degrees while angled 12.5 degrees towards the rear.

This looks like about 12.5 degrees of camber change at the cost of 23mm scrub.

I have forgotten the exact numbers but 12mm scrub was around 8.5degrees of camber change which may be easier to live with.

How much scrub is acceptable? 23mm? Will it cause the buggy to dart around if it bounces across ruts on one wheel.

 

[GregLocock]

In the 60s, before PAS, scrub radii of 100 mm were common if not de rigeur. 23 mm of scrub is a little high these days, but not unheard of.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[patprimmer]

Dave

When you are in the dirt and mud, precision is not so important as when on bitumen.

When you hit bumps that are a foot high or launch of a creek bed or a large mound and come down to land hard, travel and strength far outweigh a bit of sideways movement of the wheel relative to the chassis. Geometry as it affects the contact patch is about your third priority behind travel and strength.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules