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Author Topic:   tight in question
Desert Mod
Dirt Full Roller

Total posts: 60
posted June 06, 2005 01:36 PM  
I'm a little confused here: I've got a three-link, swing arm LR with 150# coilover on the arm in front of the axle and a straight link RR with a 125# on top of the read end. Spring bar with progressive spring (20 degrees). Long parnard bar, which I've raised above the center line of the rear end (14" height). About 3-4" rasied on left chassis. (I'm ready to try a J bar but am concerned that I'll have too much angle in it, given the mounting points I'm working with.) I've tried 120# LR bite, down to about 85# this past weekend. 58% rear (but have run 60%).

The car has been tight in, which pushes me up out of the groove into the loose stuff too often on entry. I was thinking about increasing my 1" of rear stagger but am reluctant to do so on our medium-banked dry slick track.

Any suggestions? Still too much bite?

[This message has been edited by Desert Mod (edited June 06, 2005).]

wfoondirt
Dirt Forum Champ
Total posts: 505
posted June 06, 2005 03:09 PM  
Unless this isn't an imce/ump mod or you have some funky geometry those rear springs are too soft.

Desert Mod
Dirt Full Roller

Total posts: 60
posted June 06, 2005 03:14 PM  
Thanks for the response, wfo. This is an IMCA-type Mod. Wouldn't the softer springs make it looser going in? What would you suggest for heavier springs: up 25#? Up 50#? What amount of bite would you suggest for this setup?

KeimRacing
Dirt Roller

Total posts: 22
posted June 06, 2005 03:17 PM  
I hope I can help you out.
From what you have written you have a very tight racecar and it has no side bite.
This is a very bad situation.

What I would do is:

Rear springs-
LR-400 on swing arm, your lr spring is way to light for a swing arm.
RR-175 on rear end


Put the J-Bar on. Preferrably a 19" or close to it. You will need a pinion plate. Make sure the rear end is in the car side to side per the manufactures base line. If you do not know for sure, the right rear is usually inside the RF 1-2". This usually is a good starting point.
Take shocks and spring off and run through travel to make sure you have enough driveshaft clearance all around, also check your trailing arms to make sure no binds are present in the heims and make corrections by moving the birdcages if you have to.

J-Bar Height
Mount on LS frame- 8" from bottom of frame to center.

Pinion plate- 1/2" below center of pinion.

Square your Rear end in the car. Then lengthen your RR lower link a half inch. This should put a 1/2" of static rear steer in the car

Weight Percentages

Left Side-53-54%
Rear-58% keep it where you have it for now, till you try all this.
LR Bite-100

Mount all your lead as high as you can in the middle of the car to the right side door bar.

Stagger- I would go for more than 1". If you have a tire pyrometer use it on the rear tires or check by hand. I always try to get both rear tires even temperature all the way across. Meaning outside tire temp. to inside tire temp.

Stagger in the rear is like camber in the front end. Try to get all of the rear tire rubber in the dirt.

Hope this helps.
P.M. me if you would like.

Jason

badfastjr
Dirt Maniac

Total posts: 193
posted June 06, 2005 03:44 PM  
im kinda confused about some stuff you said jason, I thought that if you added static rear steer to the car it would actually tighten it more going in, and the same with taking lr weight away, also ive never ran a swing arm car but isnt 400lb of lr spring a lot? please help me out with this cause im kinda confused.

wfoondirt
Dirt Forum Champ
Total posts: 505
posted June 06, 2005 03:58 PM  
I aggree with Keim on most of his baseline. I don't like trailing the rr but otherwise it should be a good starting point for you.

As far as the stiffer rear springs go no it shouldn't tighten entry since your lr being on the swingarm is actually way softer than the rr. With the soft rear springs you are transfering all the weight to the rf and probably overworking it on entry which is compounding your push. The soft rear springs are also the reason you have to run you panhard bar so high.

KeimRacing
Dirt Roller

Total posts: 22
posted June 06, 2005 05:07 PM  
I myself have "never" had a car get tighter on entry because I increased roll oversteer.

Why do you think 4 link cars are designed for the RR linkages to get longer (sometimes as much as 2" if the bars get parallel to the ground or each other) as the car rolls?

It helps turn the car on entry and thru as soon as you start turning to the left on the brake and the weight starts rolling to the right rear it is getting longer even with a 3 link car with 5 degrees uphill angle in the lower trailing arm. (depending on the length of the arm too. The shorter the arm the less time that 5 degrees is going to lengthen that arm and start shortening it on compression of the right rear).

On the gas off the corner it may drive the rear of the car towards the wall if you have to much or are to loose.
I would much rather have the rear of the car coming close to the wall than the front.

Better yet, get it right and turn and drive straight up off the corner on the gas.

Ok, lets say you have a 20 1/2" swing arm and the spring mounts on the arm from the front center heims to the center of the spring at 16.25.

20 1/2" divided by 16.25=.79
So your spring is 79 % of it's original rate mounted at 16.25".

So lets say I wanted a 300 lb. spring in the LR. You would want a 400 lb. spring rate but on the swing arm its actual rate would be 316 lbs. (400 x .79=316)
This spring will increase side bite greatly from his 150.

Try to increase grip with all your changes to improve the car if all possible.
His explanation tells me he is extremely tight on entry and lacking side bite...
I am trying to help him get his car to turn and thru the middle.
100 LR bite about what he was running...and is a good starting point.

Hope that I explained it well enough.

Jason

[This message has been edited by KeimRacing (edited June 06, 2005).]

Desert Mod
Dirt Full Roller

Total posts: 60
posted June 06, 2005 09:35 PM  
Jason,

Thanks for the info. I'm a little unsure of the 400# LR but I'm getting really tired of the push so I'll give it a try. I forgot to mention the swing arm angle is about 20-22 degrees.

On the weight placement, I've currently got weight on both sides of the fuel cell, on the down bars. If I move it to the right side door bar, I not sure I can get back to 58%. If I have time before Saturday night, I'll move it around and see what it looks like, I guess.

On the stagger, I can get +2" with the tires I have in the trailer. Would you suggest that much? Seems excessive.

Thanks for your help, and your's too, wfo.

KeimRacing
Dirt Roller

Total posts: 22
posted June 06, 2005 11:08 PM  
Desert Mod,

Don't be afraid to take rear percentage out and put some high on the right side door bar.
Too much rear on the tacky will make you push and too much in the slick will make the steering not as responsive.
Don't be afraid to get rear as low as 56 percent. GRT recommends 56-58 rear.
I keep taking rear out (55.5) of my Rayburn late model which is a swing arm both sides and it keeps getting better and better.
Go to JimmyJudd.com and go to tech articles.
Scott Bloomquist has a article on weight distribution that I think will help you out a lot.

How are you measuring your swing arm angle?

If you are measuring thru center of both heims it should be around 15 degrees at ride height. (This is the proper way).

If you are measuring by just putting a angle finder on the bar then it should be around 25 degrees or so at ride height.

RR trailing arm start it at 5 degrees up to frame at ride height.

Rear Tire Stagger-start 1 1/2"
Front Tire stagger-start at 3/4"

Jason

Desert Mod
Dirt Full Roller

Total posts: 60
posted June 07, 2005 08:26 AM  
I've been measuring the swing arm on the bar and it's in the middle hole on a five hole bracket. I may raise it up a hole to get to the 25 percent. On the weight, I was 56.5 percent without any weight bolted in, so I might be okay with it on the side bars.

Changing all of this at one time goes against what I've learned in many years of racing (only change one thing at a time and record what it does) but I'm getting fed up with struggling every week, so here we go ...

Thanks, Jason.

KeimRacing
Dirt Roller

Total posts: 22
posted June 07, 2005 03:33 PM  
Desert mod,

I was the same way. I didn't want to change too much at one time.
You need a car that at least makes you feel like you can be competitive. Fighting the car to make it turn in the corner, waiting on the gas is no fun at all! Very frustrating!

When you are far off on your set up changing a lot can get you going in the right direction, and able to hang with cars you couldn't before.

When you get the car better than it was, then you can start making small changes and notice the improvement. When you are far off on set up, it takes big amounts of changes to turn your racing program around.

*That is only a 1.5 percent weight off the rear. Mounting it up high on the right side will definately help side bite and transfer it quicker to the rear tires.

Get 25 degrees in the left rear swing arm and this too will increase forward bite.
Along with your other changes we have talked about, this will increase grip. I assume you are just putting an angle finder on the top of the swing arm?

Drive in hot laps and heat race without changing anything. Allow yourself time to adjust to the different way the car is handling.

If it is loose on entry stiffen LF spring 50 lbs., or lower j-bar a hole on pinion.
You could also soften RF spring 50lbs if your shock travel indicator still has some room left before it bottoms out. Pick one of these changes if loose on entry.


Jason

Desert Mod
Dirt Full Roller

Total posts: 60
posted June 07, 2005 07:54 PM  
Jason,

I picked up a 400# spring today and the guy looked at me like I was crazy. I've been running 16 inch rear springs but could only find a 13, so I'll put it in tonight.

I do use an angle finder on the swing arm.

If this gets too loose on entry I can always lower the stagger to even it out. Or isn't that such a good idea? I hate changing springs at the track, being a one-man show and all. The lower panard bar would be easier, too. I'm going to use one with the biskets because that's just what I have laying around.

Thanks for all your help.

KeimRacing
Dirt Roller

Total posts: 22
posted June 07, 2005 09:49 PM  
You are headed in the right direction...

If you don't want to change springs at the track if it is loose on entry,you can...

1. Lower J-bar on pinion a hole.
2. Raise J-bar on Frame raising 1" and lengthen to get rear end back to where it was.
3.Take LR bite out. It takes about 30 lbs. of bite for you to feel a difference. Make sure you know how many turns it takes on or off the LR to achieve + or - 30 and 50 lbs.
This is good to know so you aren't guessing.
4. Shorten RR trailing arm a 1/4".

I would not take stagger out. Stagger generally only effects the Middle of the corner. More, makes you faster through the center. To much will make you loose on the gas in center.

If it is still tight on entry...
1. Add Left Rear. Turns down.
2. Raise LR swing arm up another hole.
3. Raise RR trailing arm up a hole.
4. More RR air pressure.

All this is without changing springs. Make sure you are keeping good records of your shock travel indicators. Push them up before you go out on the track and measure them when you get back to the pits.

Travel Indicators
RF-3" of travel
RR-2 1/2"-3"-sometimes more is good too.
LR-maybe a 1 1/2" of bump, just holds the car up.
LF-1 1/2-2"
This will give you a good indication if you need to soften or stiffen a spring during the week.

Hope this helps,

Jason

P.S.
Sorry for the edits, but when you are up late sometimes you don't type your thoughts clearly. I wanted to elaborate some more.
Good luck, Saturday!

[This message has been edited by KeimRacing (edited June 08, 2005).]

Desert Mod
Dirt Full Roller

Total posts: 60
posted June 08, 2005 11:25 PM  
Okay, Jason. I've got the setup in the car. I had to shorten (and Rube-up) the J bar to 17" to get it to fit. If I like the setup, I'll go get a new one. I hope that doesn't change anything.

I still need to get it on the scales (and hang some new body panels) but I only have a few hours available on Saturday afternoon, so I don't know if I'll make it in time for hot laps, if at all.

If I can get the percentages correct, I'll try it without any weight bolted in.

I'll keep you posted on how the car works.

Thanks again for your input.

donslink1
Dirt Freak

Total posts: 318
posted June 09, 2005 04:48 PM  
No one said anything about front springs when the front springs get the car in the corner!!
what are you running for front springs.
I have never seen anyone run a 400# spring on the left side swing arm before, 200-250#

and if you are running IMCA your 17" J-bar is not legal!

KeimRacing
Dirt Roller

Total posts: 22
posted June 09, 2005 05:02 PM  
You read the article...take that lead weight off the rear...17" J-bar will work fine if it is legal.
400 is pretty common on swing arm, especially on LR.

Again, You are headed it the right direction.
We may have to discuss some more to get you tuned in more after this weekend.

Get out there and try it.
Let me know how you do and how it worked.

Jason

KeimRacing
Dirt Roller

Total posts: 22
posted June 09, 2005 10:13 PM  
When I first read this post, I could see the obvious with the set up problems with Desert Mod's modified in the rear end set up.
I think Desert Mod knew there were problems in the rear end set up, and that is what he decided to focus his attention on, and ask for some help.

The springs and panhard mounting heights were definately red alerts.

Lets get the rear end set up lined out for him first, Then work on the front end and shocks if need be.

Trust me, a 400 on the LR is actually closer to a 300 on the swing arm. Go to TeamGRT.com and look at the swing arm set up for a modified. He says a 300 in the left rear. That is pretty much the the rate that 400 lb. spring is going to be on the swing arm.
A swing arm these days are at 400 and above. That is what complete Rayburn late models are leaving his shop with these days.

A 200 "tagged" spring on the swing arm would be close to a 160 lb. actual rate on the arm.
A 250 "tagged spring would be close to 200 lb. actual rate.
I have tried a 225 on the left rear of my car and the car didn't have a planted feel to it. I couldn't be smooth with it and it didn't stick real well. I put on a 350 on the left rear (that was the biggest spring I had at the time of that practice)and went out and immediately the car gripped the track better and I could be smoother and use the gas more. It would drive in the corner deeper and stick somewhat(I had other things that needed worked on too), and plant the left rear off the corner. All at the same time adding to the side bite.
This didn't make me a front running car but at least I was headed in the right direction with increasing the LR spring rate at the time. I am at 400 now and thinking about more this Friday and Saturday. We'll see this weekend if I go up in spring some more.
NOTE:
On high banked tracks that are really fast I have seen upwards of 550 rear springs on the swing arms.

Desert Mod,
I hope you get out there this weekend...I am anxious to hear how the changes worked.

Jason

Desert Mod
Dirt Full Roller

Total posts: 60
posted June 09, 2005 10:57 PM  
Jason,

I'm not in IMCA so the J bar should be legal. I just finished in the shop and where I'm stopping is 110# LR, 57.2% rear and 53.4% left side. I'll be able to go up on the rear percentage later but need time to build a better mounting system, given how things are layed out on the car.

The swing arm is 25 degrees on the bar and the springs are as you suggested. I should note that the coil over on the swing arm is mounted in the back of the two holes. I don't know if that matters.

So, I should make it, unless the Friday night and Saturday morning camp activities with my young daughter wear me out too much. The real test will be the Sunday morning camp. Hope it's an early night. :-}

Can't wait to see how this works. I'll let you know Sunday or Monday.

Yee Haw!!!

KeimRacing
Dirt Roller

Total posts: 22
posted June 10, 2005 02:37 PM  
Sounds good.

Yes, you do have the spring mounted in the right hole on the swing arm closest to the rear axle. If you were to mount it in the front hole, the spring would be a little softer yet.

I am staying home tonight. Both the tracks I could have ran, are rain outs. So I have a option of 3 tracks tomorrow. But the forecast doesn't look good for them either.
Keep your fingers crossed.

Good luck.

Jason

Desert Mod
Dirt Full Roller

Total posts: 60
posted June 12, 2005 06:38 PM  
Well, it was fast for 3/4 of a lap in the feature, before I got caught up in some other guy's problem on a dusty mess of a track. I didn't get any earlier laps for a variety of reasons. I'll keep this setup in the car for the next time, which may be on another track, probably with a higher banking.

Did you find a drier track to run on?

[This message has been edited by Desert Mod (edited June 12, 2005).]

KeimRacing
Dirt Roller

Total posts: 22
posted June 12, 2005 10:36 PM  
Sorry to hear about the mishap early. At least you did get to race, though it be a short period of time.
It should work on a higher banked track too.

Let me know how the set up does when you race again.


The rains kept me and a lot of other racers from racing all this weekend, here in the midwest.
Shoot, it is still raining here!

Jason

Desert Mod
Dirt Full Roller

Total posts: 60
posted June 13, 2005 01:31 PM  
Sorry to hear about the rain. Wish you could ship a little our way.

I probably won't run for a couple of weeks but will stay in touch.

Desert Mod
Dirt Full Roller

Total posts: 60
posted June 27, 2005 08:36 PM  
Jason,

Back in the saddle, so to speak. I ran this past weekend and the car was a whole bunch better, especially in the wet. Our track is consistantly junk as it dries and if you get out of the groove, it just takes off toward the fence. However, if I resist the urge to pass on the outside going in, it's less of a problem. This past weekend, I was running a strong fourth before I got punted and lost a bunch of positions. It also didn't help that there was a bind in the steering (I think I've found a slightly bent frame horn.)

The car is still loose in the middle and at exit. Shock travel is as you suggested, give or take. I didn't change anything on the car for the main in order to see how it did and it was better on entry but could use a little tighening on exit. Throwing my dry-track setups at it (wheel offsets, lower J-bar, etc) could help this, I think.

There are a few kickers in all this: the track is going to replace the clay after our next race and I'm starting to build a new four-link car. So basicly I'm looking to get this thing around the old clay one last time before I sell it.

Any suggestions on the exit?

Did you guys finally dry out enough to race?

KeimRacing
Dirt Roller

Total posts: 22
posted June 28, 2005 12:27 AM  
Hey Desert Mod,

Good to hear that your car is turning now!

Loose in middle and off corrections ideas:

Try using a wheel on the RR with more offset, tuck it in. This will add side bite and forward bite by placing more weight on the RR.
Stiffen the LR spring 50 lbs. (450)
Lower J-bar on pinion plate.
Raise lead weight higher on frame.

Make sure that on LR shock (9")that you only have about 3 1/2"-4" of the shock shaft showing. I have seen cars roll over on the right and top out the LR shock where it is actually pulling the LR tire off the ground making the car loose and not have good forward bite.

Rain has stopped here. Now it is really hot!
We have 3 races on the car in 2 weeks.
We keep improving the car and looks like we will have a shot at winning in the coming weeks.

Good luck to you,

Jason


Desert Mod
Dirt Full Roller

Total posts: 60
posted June 28, 2005 08:43 AM  
Jason,

I've been following the other threads on here about J-bar height and angle. Should I lower the bar just on the pinon or the frame also?

KeimRacing
Dirt Roller

Total posts: 22
posted June 28, 2005 03:10 PM  
From your description of the track as being dry slick, I would want to add more side bite to make the car stick where I drive it in the corners.

I would lower it on the pinion plate only and try it.

The more downhill angle the J-bar has on a left side frame mount to the pinion, the more side bite and tighter the car is.

A less amount of angle and height on the frame, the looser the car and less side bite.


Hope this helps,

Jason

Desert Mod
Dirt Full Roller

Total posts: 60
posted June 28, 2005 03:29 PM  
Thanks, Jason, I'll give it a try. Our track is not just dry slick, but gets a layer of loose stuff between the top of the groove and the wall that I've never seen the likes of before. Impossible to drive on.

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