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post #1 of 11 (permalink) Old 10-31-2008, 01:26 AM Thread Starter
 
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Shock Placement

I have noticed that the original or "factory" set-up for the front suspension of the Revolt, the shocks are placed more towards the outside of the A arms.... And in a picture in one of the modifications of Rickdude's revolt, you can see he placed his shocks closer to the center of the frame..... Does anyone know the differences, and what types off effects does it have? and which set-up is better? (Sorry to put your picture on the spot Rickdude, maybe you can help us out with your input also)................. Thanks
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post #2 of 11 (permalink) Old 03-06-2009, 08:17 PM
 
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Re: Shock Placement

First of all the stock set up starts at a certain angle and as the travel increases the shock becomes less and less effective and adds angle to the shock which is non progressive which means that you get less shock stroke. The goal is to be at 90 degrees at end of stroke which is full bottom and allows the shock to work at 100%. The stock set up never allows the shock to work 100% and it only gets worse as you move through the travel until it bottoms out. The pivot points of the two arms are not of equal distance therefor it makes the action impeaded which causes alot of caber, caster change as well as major bump steer. Theses pivots are off by more than 2 inches which is why we went ahead and rebuilt the front end.

The result of getting the pivot points equal and getting the shocks set up right is a car that handles and turns like a sports car, has 25" of travel and camber caster changes and bump steer is held at a minimum.

As for the rear suspension, we could not get the stock CV/Drive to work well when we built the new trailing arm set up so, we are changing them to 930's so they will travel over 22" and never break.

This build may never end.

Bye the way. The nitrous on the car ROCKS!!!

Pics to come soon, Thanks
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post #3 of 11 (permalink) Old 03-07-2009, 07:49 PM
 
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Re: Shock Placement

Hhhmmmmm.........Rickdude. What do you mean by "alot" when you talk about camber, caster, and bump steer?

I wasn't sure I agreed with your stock comments, so I went and did my own checks. Here is a link to a video I put together showing the camber change of the suspension as it cycles from fully extended to fully compressed (and this is without shocks attached, so it is probably a larger range than reality. I placed a laser level on the top of the tire and cycled the suspension up (remember.........no shocks attached to the rig). The pictures are successive up distances of the suspension. The distance from the wheel hub to the wall is about 10 feet.


I used an angle finder along the line on the wall and measured a 4 degree camber change through the full compression. Is that a lot? My experience is that it is not a lot of camber change. Would you agree or disagree?

As for bumpsteer, I put a pair of channel locks on the steering column and had someone cycle the tire/suspension up and down. The channel locks did not move (no steering change) nor did the tires toe in or out throughout the cycle. Which means.......no bumpsteer. Looking closer at the steering link and lower A-arm you will see that their mounting points are in locations that make their lengths and arcs the same. Which is why the bumpsteer doesn't change much (if at all) thoughout the range.

So..........I'm not sure I know what you are basing your statements on. Do you have further information (measurements through the range) that prove this?

I'm certainly not trying to be an ass. I am just trying to understand why what I am measuring/seeing is differing from what you are stating.

Last edited by four_by_nut; 03-07-2009 at 07:55 PM.
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post #4 of 11 (permalink) Old 03-07-2009, 07:59 PM
 
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Re: Shock Placement

I guess I could give my opinion on the subject since that is what the thread was about. I am, by no means, a suspension expert. So I am not going to give opinions. I would only suggest that you poke your nose under a million dollar trophy truck or class 1 buggy and see what they do in the front. I think you will find that the shocks mount further out, closer to the wheel, than you might think. And you have got to believe those guys know what their doing with many years and millions of dollars of money invested.
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post #5 of 11 (permalink) Old 03-08-2009, 04:33 PM
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Re: Shock Placement

I don't think I've felt any bump-steer and I've bottomed the front suspension many times.

As far as shock placement goes, here's my thoughts.

Lets break this down into simple machines.

If you look at a double A-arm suspension, the lower A-arm is a lever. There is a fixed pivot point at one end, the frame. It has a second load point at, or near the center, the shock. This is the fulcrum. The last load is the spindle end. Its load is dynamic, pushing up and down with the movement of the tire.
The shock is pushing up on the frame, it in turn is pulling the frame up. At the same time pushing down on the spindle. With enough force, it will lift the frame, or suspend it.

Lets assume, for this discussion, that the shock is sitting vertical.

So what happens when you move the the fulcrum (shock), in towards the frame. The spindle end has more of a mechanical advantage, due to its longer lever arm. It will take more force from the shock, to over come this, to suspend the frame.

If you move the fulcrum (shock), out towards the spindle, the frame has the bigger advantage. It will take less force to suspend the frame.

Clear as mud Right?

But, because we need to angle the shock, to meet the frame, the direction of the force, gets closer to parallel, with the lever, or A-arm. The steeper the angle, the more force will be needed to suspend the frame.
Rickdude says this, "as the travel increases the shock becomes less and less effective and adds angle to the shock which is non progressive which means that you get less shock stroke."
He's right. This force can be calculated, using force vectoring equations.
To make the shock more effective, the shock would need to move closer to a verticale position.

Looking at his photos, thats what he's done. But instead of moving the top mount out, he moved the bottom one in.
Now, because the spindle end of the lever, has more leverage, he needed a much bigger shock to deliver the force needed.

I attached some "High Tech" drawings to help explain this.



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Attached Images
File Type: jpg Shock 1.jpg (25.5 KB, 24 views)
File Type: jpg shock 3.jpg (39.4 KB, 27 views)

Last edited by Bear Foot; 03-08-2009 at 04:58 PM.
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post #6 of 11 (permalink) Old 03-09-2009, 04:11 PM
 
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Re: Shock Placement

Thanks Bear Foot,

That was a very well thought out reply. Physics can be a bitch sometimes. To reply to a couple points that were made in the previous posts. First of all it is very subjective weather 4 degrees is alot but when it comes to suspension, 0 is allways the goal though sometimes not practical. My car ended up with 1-2 degrees difference through the travel. Second, the issue of bumpsteer has nothing to do with feedback to the steering wheel. It is the amount of toe in and toe out change when cycling through the travel. On my stock car this was very extreem and causes the car to push and pull every time the suspension travels.

One of the other points that I made was the most problematic and is the main cause of the issues with the front end of the Revolt. It is that the pivots on the spindles are nowhere close to being parralell and this causes problems throughout the travel.

That being said, I don't know when you guys got your cars but, I got mine in October of 2007. We took it back to the shop and cut it in half and extended it 11" so that I could fit in it and we took it out for a spin. It would not steer, it lifted a tire off of the ground every time that I tried to turn and was a huge handfull to try to keep going straight on any kind of woops (bumpsteer issue). After we anylized it we felt that it was better to rebuild the front end instead of trying to fix something so deep in a design flaw.

Perhaps I should have spent more time trying to bandaid the problems and dealt with them instead of dumping 10k plus and over a year of fab work to try and make this car something it was not intended to be. It seems that everyone else on this site has a great time with the car and you only hear the occasional steering complaint about the car.

It is also very possible that Redline has been learning and fixing the problems (at least the minor ones) and your cars came from the factory better built or set up. I can tell you that my car had much more suspension variant that you guys are stating for your car. My rear end was built crooked so I had a permenent toe out situation on the rear wheels. When I tried to align it the axle popped out. I notice that the Riot has many upgrades from the Revolt especialy the rear end set uo that is now a trailing arm as opposed to a 3 link.

Man I love to rant on and on but, I like nothing more than a spirited debate. The last point that I will mention is that it is true that the placment of Class 1 and Trophy truck front shocks is further outboard than in. This is mainly because they do not want to stick the shocks out of the hood and ugly up the 1 million dollar masterpiece. Because of this, they use massive 3" plus bodied mega shock to compensate for the leverage that they are loosing.

O.K., I am done for now. I look forward to meeting some of you guys sometime. I plan on spending some time at Sand Hollow and Coral Pink over the spring and early summer. Durring the season I go mainly to Dumont and Amargosa. And again, is anybody going to the Moab ralley. Let me know, I am going to start another post in the right spot to see if there is interest. I have never been but, I am all for tearing up some SxS.

Thanks, Guys

Last edited by Rickdude; 03-09-2009 at 04:15 PM.
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post #7 of 11 (permalink) Old 03-09-2009, 05:27 PM
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Re: Shock Placement

Guys,
This kind of discussion is priceless. Look at the amount of info there is in just this string!
Incredible !!!

Thanks.



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post #8 of 11 (permalink) Old 03-09-2009, 09:39 PM
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Re: Shock Placement

I have to agree with Bear Foot this has been a great string of information. Now Rickdude, if you come up this way to Sand Hollow or the Coral Pinks you will have to send me a PM. Maybe we can meet up.
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post #9 of 11 (permalink) Old 03-10-2009, 10:13 PM
 
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Re: Shock Placement

Rickdude,

I gain more and more respect for you every time I read a post from you!!! Seriously. Good response.

I agree that steering is very difficult in my Revolt. I don't notice issues on whoops so much as the oversteer issue. The Riot handles MUCH more predicably. And it has the same front knuckles as the Revolt. I think it has a lot to do with the rear suspension design that helps to improve that.

Eventually, we will figure out a better way to steer these things without having to spend the $10k like you did.

Good stuff!
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post #10 of 11 (permalink) Old 03-11-2009, 07:45 AM
 
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Re: Shock Placement

I should have added some clarification on my bumpsteer test. By saying the steering didn't move through the range of suspension travel, I also should have said that the toe did not change through the range of suspension travel. Which tells me that the tierod is tracking the same radius as the lower A-arm and keeping it in alignment.

Granted........my steering box has gotten a little sloppy after 4 races and possibly could be taking up the slight change through the travel, but it would still be very small. And again, I haven't noticed an issue with bumpsteer/tracking through whoops during races.

I HAVE noticed the backend wanting to buck badly through the whoops which makes the backend bounce around. I am working to fix this with different valving, oil, and nitrogen charge (or just put on some coilovers and be done with it). But can't say that I have noticed an bumpsteer being an issue.
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