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  #1  
Old 02-19-2009, 10:57 AM
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Gus Gus is offline
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Steering problems - Solid drive axle or rear differential?

Hey there. I'm building a 2 seater based on the Velociraptor with some modifications for the extra passenger width. It's got a 503cc Rotax engine from a 1981 Everest Snomobile including both CVT clutches. This is mated to a 17-60 chain drive to a 1-1/4" solid drive axle with 29" Mudzilla tires. The turning radius is particularly bad (massive understeer). It would appear to be related to the solid drive axle forcing the buggy to track in a straight line. My first thought was to put a limited slip rear differential in there but after looking around it seems that a lot of people are using a solid rear axle without any issues.

Any thoughts on how to fix my steering problems?
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Old 02-19-2009, 11:10 AM
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Not enough information.

Solid rear axle will induce some understear until the power is raised then you get oversteer...
You are going to need to describe the front suspension, weight distribution, tires, etc... Pictures will probably save time.
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Old 02-19-2009, 11:57 AM
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There's a glitch with my account on OFN at the moment so here's an external link to the best pic I could find of my buggy. Picture

The front end is definitely light compared to the back end with no riders in the seats. The whole rig is pretty light in general at this point (no floors, no crash bars, no skid plates, air cooled 2 stroke, no e start, no gear boxes.). It currently has no suspension outside of the 5psi Mudzilla tires. This is our first frabrication project since we finished our MIG welding course so it's not terribly pretty looking. It's definitely function over form at this point while we learn what to build and how to build it.

Other details:
10% castor angle
96% steering inclination angle

Is there anything else I can describe or show pictures of to help diagnose the problem?
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Old 02-19-2009, 01:17 PM
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Quote:
Originally Posted by Gus View Post
There's a glitch with my account on OFN at the moment so here's an external link to the best pic I could find of my buggy. Picture

The front end is definitely light compared to the back end with no riders in the seats. The whole rig is pretty light in general at this point (no floors, no crash bars, no skid plates, air cooled 2 stroke, no e start, no gear boxes.). It currently has no suspension outside of the 5psi Mudzilla tires. This is our first frabrication project since we finished our MIG welding course so it's not terribly pretty looking. It's definitely function over form at this point while we learn what to build and how to build it.

Other details:
10% castor angle
96% steering inclination angle

Is there anything else I can describe or show pictures of to help diagnose the problem?
I'm going to say that you are going to be hard pressed to have anything but understeer just based on no suspension and weight distribution/location.
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Old 02-19-2009, 01:42 PM
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Thanks for your help. If you have time could you comment on what factors are making this worse for my build? The light front end? The lack of front suspension? The short wheel base? The solid drive axle?

Thanks!
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Old 02-19-2009, 02:31 PM
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It appears that the majority of your weight is in the rear and high.
When you corner you are starting out with little weight on the front, so you have limited the amount of force that can be generated to turn. then the weight is going to shift to the outside tires, and since the inside tire can not drop away and stay on the ground it becomes even less effective. then if you are throttled up you have shifted weight to the rear and reduced the forces available even more...
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Old 02-19-2009, 02:37 PM
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That makes sense. The outside front tire is definitely not getting consistent traction. I was hoping there was an easier answer I guess. Time to consider front suspension mods earlier than we had hoped. Thanks for your help on this one.
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Old 05-15-2009, 05:00 AM
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Not knowing how the rear is setup you could move the axle back behind the motor to help add a little better weight ratio to it. Looking at your placement right now if your giving it gas it's going to try and lift the front end up (only minutly) but by putting the axle behind the engine it will distribute the weight a little better twords the front. You could also add some weight up front. Kinda like a tractor... Although that might defeat your purpose.

Paul G.
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