Ackermann ?

[mignum]

2002 GRT wide front I checked the ackermann in my front end and the RF is out steering the LF BY 5/8" how do I correct this or should i worry with it? I was reading about this in Bob Bolles book and checked it out on my car.

[MasterSbilt_Racer]

Sounds like your spindles are mismatched. You need to buy the correct ones. The steering arm should be shorter on the lf spindle.

[mignum]

I measured them and they are both the same 5.5 inches the old one I bent on the RF had a 5.0 in. arm on it, not sure whats going on here.

[HEAVY DUTY]

Slide the rack back if you have slotted mounts. The more angle forward from the rack to the steering arms, the more ackerman you will have.You definitely dont want it toeing in as you turn.

[mignum]

I talked to joe at GRT and he said that i need a 19 3/4 rack and I have a 19 he said the steering arms should be 5.25 on both sides with the 96 spindles.my steering arms are 5.5 inches.,

[95rayburn]

Would it be the same on a rayburn where the lf would have a shorter steering arm than the RF?

[MasterSbilt_Racer]

Would it be the same on a rayburn where the lf would have a shorter steering arm than the RF?

They should be the same or shorter lf for any car I know of. He was off so far I figured that was his problem. Spindles for the same car, but from different suppliers often have different steering arm lengths.

[mignum]

I think thats one problem the spindles I have are not from GRT and the steering arm lengths are not what joe said they should be, I bought this car and the guy told me he wanted the rack off of it and he would put the one off his other car on it. He said it had a very fast ratio that he wanted, so I agreed to it. I think by doing this I have ended up with the wrong length rack. I need a 19 3/4.

[mignum]

Should my inner tie rod ends be inline with my inner pivot points, with the wheels pointed straight ahead?

[let-r-eat]

Yes. You should be able to draw a straight line through your lower control arm pivot, inner tie rod pivot and upper control arm pivot.

[mignum]

Yes. You should be able to draw a straight line through your lower control arm pivot, inner tie rod pivot and upper control arm pivot.

I understand that about the inner control arm pivot and inner tie rod pivot but I dont understand how the upper control arm pivots could be in the same line, the way I am seeing this is paralell to the frame rail, to me the upper control arm pivots are outside these points, right? Help me to understand what your seeing here.

[F22 RAPTOR]

I understand that about the inner control arm pivot and inner tie rod pivot but I dont understand how the upper control arm pivots could be in the same line, the way I am seeing this is paralell to the frame rail, to me the upper control arm pivots are outside these points, right? Help me to understand what your seeing here.

I was wondering about that too. Its the lower/inner pivots you should be concerned with, the top control arm pivot has no bearing on it. I think he mistyped.

[mignum]

I did not mess with it alot but it looked like to me if I line up the inner pivot points that the rack end on the left side is sticking out so far that it doesnt leave much room to turn left. But I will start on it in the morning and see how far I can get, thanks to everyone for your much needed input.

[mignum]

I worked on the car today and I measured and my rack is 19 1/4 and the inner pivots are 19. checked all my measurements multiple times and I still come up with 5/8 toe in, I dont know what to do too fix the reverse ackermann problem, can I just shorten my left steering arm?

[HEAVY DUTY]

I worked on the car today and I measured and my rack is 19 1/4 and the inner pivots are 19. checked all my measurements multiple times and I still come up with 5/8 toe in, I dont know what to do too fix the reverse ackermann problem, can I just shorten my left steering arm?

I wouldnt just shorten the steering arm. I would get the right spindles and rack for it so everything will be right. If the rest of the spindle ( height, drop, inclination) isnt right, the whole front end will be screwed up. I am a chassis builder and see people buy used stuff to save money and it ends up costing them more to make it right in the end, and they make the chassis builder look bad when the car doesnt work right when all the parts are wrong.There is a lot to the design of a front end and it all has to work together.It costs alot to buy new parts, but it costs way more to drag a car that dont turn to the racetrack week in and week out and never win any money. I dont want to sound like a jerk, but I am trying to save you a lot of hassle.

[MasterSbilt_Racer]

I agree with Heavy Duty. If you buy a used car, you should usually plan on putting a new front end on it. The parts may not be right or may at least be bent up or in need of an upgrade.

[pcope98]

i had one of those 02 GRt wide cars it indeed had to have a 19 3/4 rack it used the 96 style black tall spindles looking thru my notes from back then, if i remeber correctly it was very very similar to a black front rocket used longer rf lower i do belave it was 19 on the rf and 17 5/8 on the left we always ran 10 inch uppers, but to make a long story short i was glad it was gone after about 10 races , we could never get it to work out, they fellow who bought it decided to have it restubbed back to the standard front clip and won over 40 races with it afterwards.

[mignum]

[QUOTE=MasterSbilt_Racer;1651314]I agree with Heavy Duty. If you buy a used car, you should usually plan on putting a new front end on it. The parts may not be right or may at least be bent up or in need of an upgrade.[/QUOTE
Every part except the left front spindle on this front end is new, that spindle has the GRT sticker still on it so I assumed that the steering arm length was right at 5 1/2 but I'm not sure now. I talked with someone on here that has an original wide front from the builder and my measurements check out with his all except the steering arm lengths his are 5 1/4 and thats what everyones saying best I can tell. This really screws me up because of the left front spindle steering arm length on my car being 5 1/2 with that GRT sticker on it, so are you all thinking that I should get new spindles straight from GRT? Thanks again

[HEAVY DUTY]

[QUOTE=MasterSbilt_Racer;1651314]I agree with Heavy Duty. If you buy a used car, you should usually plan on putting a new front end on it. The parts may not be right or may at least be bent up or in need of an upgrade.[/QUOTE
Every part except the left front spindle on this front end is new, that spindle has the GRT sticker still on it so I assumed that the steering arm length was right at 5 1/2 but I'm not sure now. I talked with someone on here that has an original wide front from the builder and my measurements check out with his all except the steering arm lengths his are 5 1/4 and thats what everyones saying best I can tell. This really screws me up because of the left front spindle steering arm length on my car being 5 1/2 with that GRT sticker on it, so are you all thinking that I should get new spindles straight from GRT? Thanks again

You need to call GRT with the chassis number so that they can get you the right stuff for that chassis. All chassis builders continually change and test new stuff. Just because it has a GRT sticker doesnt mean it is right for your chassis.The best way to explain it would be a spindle for a 2002 chevy monte carlo wont fit a 88 monte carlo. Things have to change as we figure new things out. Otherwise we would all be running a 79 model rayburn and still be competitive.

[rcmaster]

make sure you check ackerman and bump together,and the best way is mark your tires around the center, set your toe, roll your car to what travel on RF you want, re measure your toe front and back, then steer your tires at different amounts and re check, make sure to measure as low as possible to the contact patch front and back, this will tell you exactly what is happening with your front end.

[mignum]

Do I need to set caster with the upper control arm or the lower? I am thinking that this could have an affect on my bump steer and ackermann, after more investigation I am quiet sure that I need a 19 3/4 steering rack, per Joe's recommendation.

[DLM06]

make sure you check ackerman and bump together,and the best way is mark your tires around the center, set your toe, roll your car to what travel on RF you want, re measure your toe front and back, then steer your tires at different amounts and re check, make sure to measure as low as possible to the contact patch front and back, this will tell you exactly what is happening with your front end.

I tried this and finally gave up on our '11 Rocket. The bump went all over the place when we steered from straight ahead and every expert I called including Rocket told me to just set the bump straight ahead and forget everything else. What kind of bump readings do you get when you turn the wheels from straight ahead? Do they change significantly left vs right? What do you do if the bump is fine straight ahead but changes when turned?

[MasterSbilt_Racer]

Do I need to set caster with the upper control arm or the lower? I am thinking that this could have an affect on my bump steer and ackermann, after more investigation I am quiet sure that I need a 19 3/4 steering rack, per Joe's recommendation.

Chassis manufacturer recommendations vary, but it will affect the ackerman. I think few cars have it right when straight ahead, turned left, and turned right.

[hucktyson]

Chassis manufacturer recommendations vary, but it will affect the ackerman. I think few cars have it right when straight ahead, turned left, and turned right.

With the geometry required to have correct bump steer at all 2 locations it would be impossible ..

[mignum]

So I need to be concerned with the wheels turned like I'm headed off into the corner instead of straight mostly right?

[hucktyson]

So I need to be concerned with the wheels turned like I'm headed off into the corner instead of straight mostly right?

When the car is handling their not turned very far anyway ..

[let-r-eat]

Draw a straight line through your lower control arm inner pivot and your upper control arm inner pivot. Your rack inner tie rod position should fall along that line. If your rack and pinion is too short the inner tie rod pivots will fall inside that line and the rack would likely need LOWERED in the car to make it work. That is why you shim a rack and pinon up and down, side to side to correct bump. What you are trying to accomplish is get that inner tie rod pivot in line with the lower inner and the upper control arm inner pivot.Think about this. Looking from straight ahead at the steering the pivots need to lie on the same plane. To illustrate this you would take a string and put on your lower control arm inner pivot and stretch it to your upper control arm inner pivot. Stand back and look at the inner pivot of your rack.............inside that line or outside that line with the wheels pointing forward. If your pivot is outside that line you need to shorten or inside you need to lengthen.Ask yourself this:What determines the length of rack I need? Is it the distance between the lower control arm pivots? Yes if the rack is level with the lower control arm pivot points. No, if the rack is higher. The rack must then lengthen.Here is something else that might help.How do you post pictures here:http://i890.photobucket.com/albums/ac102/let-r-eat/frontendpicture_zps06737ef5.jpg

[7uptruckracer]

Thanks Let-Er-Eat Ive always wondered what determined the rack width and I'm about to use this on a car. Really great info!

[mignum]

Yep, thanks that helps clear things up for me.

[let-r-eat]

Glad that helps you. Sometimes its easier to get a piece of graph paper and map out all the front end points. A design software is much easier, of course. You can use one square on the graph paper for one inch and get the basic suspension mapped out in front view and side view. Things like anti dive and caster etc can all be figured using mathematics. There wasn't all this computer stuff back in the day, we just used pens and papers.

[mignum]

Took the tie rod ends loose and put the inner pivots on the string line and it looks pretty close with the tie rod ends out of the way. With the tie rod ends on the rack it appears that it may be a little inside the string line which would indicate that a longer rack would be needed. But... its pretty close... Joe said that front takes a 19 3/4 rack, if I go that route it appears that it might be a little long.... but that may help me with my ackermann and bump steer problem, I am sure Joe knows a lot that I dont, they may have found that after more testing that the 19 3/4 worked better... heck I dont know!

[let-r-eat]

This is very important because that is what determines the ability to control bump steer. We can talk about the relationship between the LCA lengths and tie rod lengths, steering arm position another time.

[let-r-eat]

Took the tie rod ends loose and put the inner pivots on the string line and it looks pretty close with the tie rod ends out of the way. With the tie rod ends on the rack it appears that it may be a little inside the string line which would indicate that a longer rack would be needed. But... its pretty close... Joe said that front takes a 19 3/4 rack, if I go that route it appears that it might be a little long.... but that may help me with my ackermann and bump steer problem, I am sure Joe knows a lot that I dont, they may have found that after more testing that the 19 3/4 worked better... heck I dont know!A 1/4 of an inch on each side may not seem like much but will make a ton of difference when looking at bump. There's a ton of difference between 19 1/4 and 19 3/4. That's a 1/4 of an inch per side and depending on suspension travel could amount to 4 or 5 times that in bump.