[jdearhart]

I saw a picture the other day that got me to thinking about front end geometry and why we set the upper a-arms like we do. It seems as though the way to do it is to set the left front in the top hole and the right front in the bottom hole. But, why? The picture I saw had the right front in the bottom hole and then about .060 or .070 of washers on top off the steering block, apparently trying to get more angle on the upper.

Can someone help me to understand why this seems to be the setup of choice? I have a background with full scale cars and this way of setting the front end is almost the exact opposite of what we were doing on the real cars. It just doesn't make sense to me. :freak:

 

[Mr.fastman]

I'm sure others can articulate this better than myself, but the right front settings that you described is to increase camber gain, which at least for me seems to make the steer more aggressively. It seems there are a number of things that are opposite full scale cars.


Doug p

 

[BRhodes]

From my experience with a full sized short track asphalt late model we always ran a long upper A-Arm on the LF and a shorter RF upper arm. In essence this has the same effect as the way we run RC front ends. It moves the front roll center closer to the rf. I am by no means an engineer so I am sure there will be allot better explanations but my two cents nonetheless.

 

[jdearhart]

From my experience with a full sized short track asphalt late model we always ran a long upper A-Arm on the LF and a shorter RF upper arm. In essence this has the same effect as the way we run RC front ends. It moves the front roll center closer to the rf. I am by no means an engineer so I am sure there will be allot better explanations but my two cents nonetheless.

We did the same thing with the uppers, but it's not neccesarily the length of the upper that determines the where the roll center is at. It's more of the angle that determines the static placement. When we started trying the big bar / soft spring setup, we moved the roll center closer to centerline or even to the left of centerline.

But the main thing that doesn't make sense to me is why we try to run so much angle on the right front, and next to none on the left front. I assumed it was for camber gain in the right front and to try to prevent negative camber gain in the left front. But why the extremes? The right front has an extremely short instant center and the left front has an extremely long instant center, and I just don't understand what is trying to be accomplished.

 

[BRhodes]

We did the same thing with the uppers, but it's not neccesarily the length of the upper that determines the where the roll center is at. It's more of the angle that determines the static placement. When we started trying the big bar / soft spring setup, we moved the roll center closer to centerline or even to the left of centerline.

But the main thing that doesn't make sense to me is why we try to run so much angle on the right front, and next to none on the left front. I assumed it was for camber gain in the right front and to try to prevent negative camber gain in the left front. But why the extremes? The right front has an extremely short instant center and the left front has an extremely long instant center, and I just don't understand what is trying to be accomplished.

On the full size car the two mounting points (chassis and top of spindle) for the a-arms are static which the shorter arm caused it to be more of an angle. Also keep in mind that the lower arms on a full size car a much longer than the uppers which creates allot more camber gain without needing as much angle. If we could place a shorter top arm on the rf then we would not need as much angle. Good thread though because I have often tried translating full size setup info to R/C and vice versa. We even went as far as trying "reactive caster" on the full size car similar to the old Trinity cars back in the mid 90's.

 

[Dan]

I agree, that there are a lot of things that do not transfer
well, from real, to r/c.

Another factor to consider, with regard to the "importance"
of the left front upper, is the fact that these cars do not have front brakes.

The left front experiences very little compression, during cornering.
Especially if you run with the hammer pulled all the time.
The right front, moves a lot, as the car wants to roll
around that point.
There isn't going to be very much camber change,
due to spring compression, on the left front.
As for rebound, it's only going to extend the amount of
droop you preset the corner at.
A lot of guys run, eg. .040"
That's not a lot of extension.

In a real car situation, as you enter a corner, you are on the brakes,
and the whole front of the car drops. Especially with the gorilla bars
used today. The LF stays down, more so with trailbraking, until
the car starts to change direction. Then it extends considerably.
So it has a lot of travel.
Compared to the r/c counterpart..

So in conclusion, my theory is, the angle of the left front upper
is not as important, for instance, as just setting the camber to
allow for good tire wear.
The angular change, from suspension movement,
is extremely minimal.

Next time you are at the mall, get your car up to 30,
throw it in neutral, and crank the wheel to the left.
It will explain all of this in a lot more detail.

 

[jdearhart]

Next time you are at the mall, get your car up to 30,
throw it in neutral, and crank the wheel to the left.
It will explain all of this in a lot more detail.

LOL! That would be interesting!

I figured that the steep angle of the right front was because these cars don't travel very much, and we are trying to get as much camber gain as possible. And as you said with the left front, just the opposite.

Thanks for the thoughts!

 

[3wideroberts]

What I have learned, is the more Camber gain on the LF (Lowering the Upper A-Arm on the Left side) Reduses bump steer, and allows the car to be more stable on the straight away, but if you run Camber gain on the left side you want to run more Positive camber on that tire because as the left front compresses, it is actually losing camber(Not Really Gaining camber :freak: ) So my rule of thumb is to run both lower A-arms down for more stability on flat tracks, and on banked tracks you want to run the Left A-Arm up. That is my understanding of this situation thanks for the great reading material, and please correct me if im wrong :thumbsup:




3wide

 

[Todd Putnam]

Dan:
I agree with a lot of your post, except the statement that just because the LF doesn't compress much, it doesn't matter as much-

It still dictates where the front roll center will be, which greatly affects how the car will react when cornering-

If you run your LF arm raised, (at the inner point) and your RF in the stock AE location, the front roll center will jump to the right and lower-both which will tighten the car. :thumbsup:

 

[Ralf]

There is also one big difference between "our" cars and the real ones, the lower A-arm on ours is solid unlike our upper arms. Ralf

 

[DK47]

If you run your LF arm raised, (at the inner point) and your RF in the stock AE location, the front roll center will jump to the right and lower-both which will tighten the car.
Thank you for this info Todd,i been beating my head for 6 weeks trying to get the tight out,now i think i can!!!!!

 

[Josh Keller]

.....

 

[Todd Putnam]

Josh,
KSG makes a "toe corrector" (atleast I think that's what they named it) and it is an aluminum ear that bolts on to the LF steering block. It relocates the ball stud to a lower position, (more parallel to the upper arm) which will reduce bump steer.
Another way is to run a RF steering block on the LF. You flip it upside down, then have the ball stud facing the ground. This will also make the LF tie rod more parallel to the ground. I'm sure Eric or Steve Slavas have some high resolution pics of this system on their website, as this is how they run their front ends...
Hope this helps...:thumbsup:

 

[Danny B]

Dan:
I agree with a lot of your post, except the statement that just because the LF doesn't compress much, it doesn't matter as much-

It still dictates where the front roll center will be, which greatly affects how the car will react when cornering-

If you run your LF arm raised, (at the inner point) and your RF in the stock AE location, the front roll center will jump to the right and lower-both which will tighten the car. :thumbsup:

And the truth shall set you free!!!

We could discuss dozens of combinations and results and what is best and when. There are so many factors as to why one car reacts to a front end change and one car doesn't but I know we messed with the front end three times as much this winter than the back of the car and had much better results than the past couple years.

 

[Dan]

Dan:
I agree with a lot of your post, except the statement that just because the LF doesn't compress much, it doesn't matter as much-

It still dictates where the front roll center will be, which greatly affects how the car will react when cornering-

If you run your LF arm raised, (at the inner point) and your RF in the stock AE location, the front roll center will jump to the right and lower-both which will tighten the car. :thumbsup:

Good point about the roll center, Todd... :thumbsup:
I was only trying to explain the camber change deal to the original question,
and didn't mean to imply that the angle was not important 'at all'...

 

[3wideroberts]

Last weekend i tryed to move the RF A arm up and the left down... this in attempts to bring the roll center to the left, but making the car very uneffiecient, LOL

 

[Larry B]

If I lower the LF a-arm to the center location will I need to file the stearing block to keep the a-arm and stearing rod at the same angle? From what I have read here it seems as though having the a-arm on the LF level stops camber gain and lowering the LF mounting moves the roll center more to the center.

One other question. I have seen spacers used on the LF caster block to lenghten the a-arm. What effect does this have?

 

[MIKE VALENTINE]

reduces camber gain and moves the rollcenter.

 

[Larry B]

Mike, is that what the spaces do and what direction does the roll center move to?

 

[MIKE VALENTINE]

Making the upper A-arm longer will reduce camber gain. Assuming you haven't changed any other spacers or ride height the rollcenter will move to the right more and up some. IMO