lower control arm alignment

[dirtslinger71]

I have a blue front rocket and have been having a tight entry issue all season... I have thrown everything under the sun at the car and it doesn't react to my changes. So I decided to string out the car to mainly see how my rear is in the car. All that seems to be fine and so I checked the lower front ball joints and my rf is ahead of my lf by 7/8 of an inch. Could this be my problem? Should I square my lowers and set my caster with my uppers?

[mab475]

The RF is supposed to lead the LF. That is your caster split and helps the car turn in on entry.

[Garrettshurling]

The distance between the two lower ball joints will change depending on the caster you are running. Caster split, however, is the difference between the caster on the RF and LF expressed in degrees. Example: If you LF caster is 2 deg. and your RF caster is 4 deg, your caster split is 2 deg.

To answer your question though, thats not your problem. Do you have a setup sheet from Rocket?

[Matt49]

I use slotted uppers to adjust caster because it doesn't change the wheelbases nearly as much as using the lowers. This is due to the location of snouts on the spindle.
I personally have never understood the turn-buckle deal on the one-piece lowers. It's completely useless to me. I'm not going to put the lower in a bind to adjust caster which is the only thing you do with that deal in my opinion.

[dirt23h]

How did you determine the right front is 7/8 " in front of left side, from the rear end? The more lead in the right front the tighter, less lead looser. I square my car from the rear forward. the frame rail on the top front of the fuel cell is about the only square bar i have found on the rocket blue front. square the rear end from this bar than go forward to the lower zirks on the lower control arms to determine square or lead. Than set caster with upper adjustable a arms.

[drtrkr244]

If you are running your rr trailing arms 1/2" longer,thats standard according to their setup book, then the addl 3/8" is not out of line due to the caster split. Every dlm I have worked on has had a longer right side wheelbase.

As others have stated, I don't believe that is your problem.

[dirtslinger71]

How did you determine the right front is 7/8 " in front of left side, from the rear end? The more lead in the right front the tighter, less lead looser. I square my car from the rear forward. the frame rail on the top front of the fuel cell is about the only square bar i have found on the rocket blue front. square the rear end from this bar than go forward to the lower zirks on the lower control arms to determine square or lead. Than set caster with upper adjustable a arms.

I was measuring my points off of the motor plate and car at ride height. Like I said I think the rear is OK I just think 7/8" is excessive on the front. So square on the front is where I need to be on the lowers?...

[dirt23h]

I was measuring my points off of the motor plate and car at ride height. Like I said I think the rear is OK I just think 7/8" is excessive on the front. So square on the front is where I need to be on the lowers?...


I have used 3/8" lead in right front in the past. I now use square on the front with the wide front end and use the rear end to control rear steer , lead or trail. It is really a driver feel issue. my driver prefers the front square and do all adjustments on the rear.

[Rocket5353]

Can someone explain to me the exact procedure to squaring your front end ? And also what are the neutral bar lengths for blue front end rocket ? I keep seeing everyone saying standard now is 1/2 inch longer then the original? Sorry to dig up and old post! Haha

[7uptruckracer]

I was measuring my points off of the motor plate and car at ride height. Like I said I think the rear is OK I just think 7/8" is excessive on the front. So square on the front is where I need to be on the lowers?...
That's how the car is supposed to be in the front the RF leads LF that helps it turn it even if rear end is perfectly square to the car the RF to LF relationship helps. Your problem is elsewhere. Post your setup maybe you can find it that's a good car

[fastford]

im with you dirt23h on running the front square. as far as squaring the front end, my understanding is most manufacturers standard front end. lower control arm measurements would be considered square, as its built into the design of there chassis. I keep my lowers on the recommended settings and set caster with uppers. if anyone has a system of squaring the front that will work on any chassis, I would like to know also...

[Rocket5353]

So basically I should set my lower length from hiem to grease fitting , how do you set the forward mounting point ? I was told to set the caster with the lower mount and leave the upper square to the frame and the lead is basically built inn setting it that way but ..... Considering the source I would rather a second opinion .

[Matt49]

I have some opinions on this that many disagree with but here it is anyway.
A one piece lower control arm is essentially two sides of a rigid triangle with the third side being the imaginary line between the chassis mounting points that will remain rigid because it's length cannot be changed.
Using the "turn buckle" device to set caster puts the whole thing in a bind. Period.
I simply don't think that's good from a mechanical standpoint. So I'm a fan of setting caster using slotted uppers. People will argue this by saying that I am changing the wheelbase/lead by adjusting it this way. To which I counter by asking them to explain how they aren't doing the same thing (and even worse actually) by setting it with the lower. And here is what I mean by the "even worse": The spindle snout (where the center of the wheel will be) is WAY closer to the lower ball joint than it is the upper. The only way to change caster is to move one or the other fore or aft. So moving the lower has a much larger impact on the location of that wheel than moving the upper the same amount due to how much closer it is to the snout.
I would set the length of the traditional part of the lower to EXACTLY the length specified and then set the length of the strut part to whatever does NOT put it in a bind. If doing it THIS WAY does NOT put the lead/wheelbase where it needs to be, then the control arm is WRONG, not the way I'm adjusting it.
Then set the camber and caster entirely with the upper because it will have MINIMAL impact on the lead/wheelbase. There will be a bunch of people say that this is wrong and it may be but I don't think putting suspension components in a bind is the proper way to do anything. I think doing it with the turnbuckle "solution" is compensation for poorly designed and/or fabricated components.

[Rocket5353]

Yeah I would have to say I agree more with that then litteraly having to flex my lower to get it to mount up! Also is there supposed to be any spacers or anything on the front mounting point ? It's a 2014 with raised cross member. Same question for the left side ! I appreciate everyone for taking the time to explain these things !

[Punisher88]

My barry wright book always told me to out my rf 1/4 in front of the left front. So for 5 years I did that. Then I swapped to a different shock builder and told him the issues I was having and my settings and he said to never lead the right front. He told me to put it square or put the left front ahead by 3/16. So I lead the left front and my car has never steered into the corner as well as it does now.

[Rocket5353]

Leading the left front makes sence to me when I visualize it but this is the first I have heard of someone actually doing it! I'm going to attempt to try it square and go from there !

[7uptruckracer]

Yeah I would have to say I agree more with that then litteraly having to flex my lower to get it to mount up! Also is there supposed to be any spacers or anything on the front mounting point ? It's a 2014 with raised cross member. Same question for the left side ! I appreciate everyone for taking the time to explain these things !
That's a good car set it up geometry wise how the book tells you. That's cars are pretty good on entry so post what you have under it will Probably be more helpful then messing with the front end

[25drtrkr]

That's a good car set it up geometry wise how the book tells you. That's cars are pretty good on entry so post what you have under it will Probably be more helpful then messing with the front end

I agree with you 7up! Every Blue Rocket I have worked with turned very well, sometimes too well. I would make sure everything in the front end is set to Rocket specs. Im not saying that you cant improve their std setup but I believe there are setup problems elsewhere.

[billetbirdcage]

http://i.imgur.com/vYDExbN.png


I'm going to open a can of worms here.


Someone want to explain this theory, that leading/trailing the RF over the LF can/will make the car turn/not turn differently??

Lets for argument sake, say a change of 1/2" or even 1" take your pick. Remember a 1/2" change is a half of 1% of the actual wheel base (typical 104" wheel base).

I have drawn 2 cars both the same only difference is the pink car has front tires inline and the blue car has the RF lead .5". Caster is the same on both cars as is the caster split, only difference is either the control arm mounting points are moved on the frame to get the lead or your doing your caster with the uppers vs the lowers to get a lead on the RF.

[7uptruckracer]

If this is a crate Blue front end rocket if its who i think it is. Drop the rear a lot from rockets baseline and up the LS.

[7uptruckracer]

We have this adjustment with the lowers on the asphalt LMSC. It effects how weight is held onto and off of the RF. Dirt is no different these days the gap is closing in some aspects. They will Lead the RF or trail the LF to make it turn in on the gas better for dirt. It's "similar" for the turned stub modifieds. You can't just go changing it from the builders design or your affecting ackerman, spring angles, depending on how you do it caster gain, bumpsteer. You have to take all that into consideration. Rocket has gotten ummmm a little off and crazy with their design especially since the orange came out, they aren't as dominant. I've been working on one and it takes a lot to get it to run with the Longhorns, MBH, Club 29 cars. I saw some Jbar stuff the other week they had that absolutely blew my mind. Post your setup if your that tight for as much as you can alter your LF to RF lead or trail it probably wont make much different in what your entry.

[dirtslinger71]

I posted this over a year ago and now no longer have the rocket. I converted to a smack down this year and love it! Winning races and setting poles. But the the lower control arm adjustments probably weren't my problem at the time ... But it did make for a good discussion and I feel that the lowers should be square and adjust caster on uppers. No other type of race that I have worked on other than a dlm do u ajust caster with lowers... Jmo. Thanks for all the info also guys.

[25drtrkr]

My only concern when I see these type of posts, is what type of system was used. You have to establish the true centerline of the chassis to determine the proper alignment. Its not difficult but takes a proper method when stringing a car. When used properly, you can:
1) set caster lead or trail
2) set tie rod lengths
3) align rear tires with front (parallel)
4) align rearend side to side
5) align birdcages

I was fortunate to have an engineer pass this down many years ago. It takes very little $$ to do it, but takes a fair amount of time to do it right to obtain precise measurements.

[save the racers]

Pulling the r/f forward would change the ackerman, which could help the car turn in.Weight distubution would change a slight amount, might or might not help entry.I've offset the wheelbase in other classes to beat rules.A lot of times that is how it all starts.

[7uptruckracer]

Well if its designed into it by the builder it wouldn't if you change it after it would. Anything moving a tire away from centerlines will change the weight the tire sees