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  #16 (permalink)  
Old 08-04-2009, 06:52 AM
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Quote:
Originally Posted by Augusto
should the tie rod be parallel (horizontal wise) to the lower A arm?

should the tie rod be parallel (vertical wise) to the lower A arm or perpendicular to the centerline of the chassis?
Of greater importance is the location of the inner pivot when viewed from the rear (or front). It should be roughly on a line between the inner suspension pivots and roughly 2/3 of the way toward the lower pivot. Yeah, that's a lot of "roughlys," but you asked for a starting point.

I have SolidWorks, also, but I'm certain a later version of AutoCad also allows you to "operate" the assembly so that you can see what's happening during suspension travel.

The steering geometry is really not as critical as you might think. Think about it: How often are you making steering changes when the suspension is in full rebound or full jounce? If your CAD software tells you nothing weird is happening during the wheel travel normally encountered, it's time to get out the welder.
http://www.racetec.cc/shope

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  #17 (permalink)  
Old 08-04-2009, 08:29 AM
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Autocad is not the best for this task but since I don't have solidworks I use this, it's better than plain paper, the bigger problem is that autocad can only have one pivot point at a time and I have to move one arm first then the other and takes some time to do so but it works fine.

2/3 down, that's a good reference, I have seen it but have not realized trully about the relative location, thanks.

as I said before my main concern is bump steer, I don't want the car to turn by itself upon landing after a jump without my comand.

Augusto.
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Old 08-04-2009, 09:06 AM
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We found that the bump steer was controlled by the vertical height of the tie rod on the spindle arm and a Bill said the placement of the inner pivot. There are lots of bump steer kits for the circle track guys and this is what they use. It's a set of shims and spacers that fit between the tie rod outer end and the spindle arm. The big problem is that you wind up with a 3/8 rod end on a long 3/8 gr 8 bolt that can get bent. Ours survived a high speed encounter with a tree however. Broke the inner clevis and not the rod end or bolt.

If you have problems with Auto cad i'd suggest making some yard stick sample and bread board them on a 1/2 inch chip board. Use model air plane instant glue it's cheaper and better to glue things together. Even if you spend a day or two messing around with this method it will save you in the end.

Billyshoppe is right. Flog it for a while then do it. You don't have to be exact for dirt stuff. It slips and slides anyway.

My son is a fanatic over 1/16's and 1/32's 1/2 deg etc. he and I have had all day battles over this suspension thing. I challenged him to give it a test. I sent him in the house and said I'd make some changes and he could go out and drive the kart and tell me the difference. He tried it out and said it was all messed up. I never touched a wrench to it. haha I had to go thru all the measurements just to prove it.

BTW my son's buggy is very similar to the single seat Rage. It has a 954 Honda and is geared for about 115 flat out. It has a live rear axel so it pushes in the turns but you just steer with the throttle and it works great.
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Old 08-04-2009, 03:39 PM
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  #20 (permalink)  
Old 08-04-2009, 06:19 PM
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Quote:
Originally Posted by bentwings
BTW my son's buggy is very similar to the single seat Rage. It has a 954 Honda and is geared for about 115 flat out. It has a live rear axel so it pushes in the turns but you just steer with the throttle and it works great.
my off road karts also use live axles and push a lot in the turns, I used a simple trick we use in asphalt kart racing to cure understeer (they also use big 40mm live axles) , give a lot of caster and increase scrub radius, this unloads the inner rear wheel on the turns and makes it turn like if it was a 3 wheeler, works great, in asphalt we develop close to 1.5 G's turning.
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  #21 (permalink)  
Old 08-04-2009, 06:25 PM
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Quote:
Originally Posted by staleg
staleg,

for off road racing a different setup is used, the upper arms lean down outwards, so the instant center falls outside on the same side of the car, it works well also because the roll center also is located above ground level, some sedans have a setup like yours but the roll center sometimes is under ground level and this is not good for performance driving.

Augusto.
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  #22 (permalink)  
Old 08-05-2009, 05:09 AM
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Quote:
Originally Posted by Augusto
...it works well also because the roll center also is located above ground level....
Augusto.
This is true only if the instant center is located below ground level.
http://www.racetec.cc/shope
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  #23 (permalink)  
Old 08-05-2009, 09:16 AM
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Indeed, the instant center is below ground and quite far away from the pivot points because the arms are only a little off paralell, takes a lot of screen to draw the schematic.

been quite bussy latelly but as soon as I build a model of the suspension I'll post a pic here for you guys to comment (or laugh..lol..)

Augusto.
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