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Author Topic:   LR spring rate
dirtbuster
Dirt Forum Champ
Total posts: 2007
posted January 05, 2005 10:48 AM  
Was looking thru some mastersbilt setups (just for fun) and i noticed that with their LR clamp setup the ran 175 LR and 250RR. But with the LR behind they ran the other way 250LR and 200RR. So I got to thinking that maybe there was something to this and it may apply to our 4 link mod that has the LR clamped up in front. Has anybody tried running a light LR with a heavy RR sping in a mod and how did it work?

WPP
Dirt Freak

Total posts: 451
posted January 05, 2005 11:07 AM  
dirtbuster i think alot of the soft lr clamped has to do with tires a late model has more foward bite than a mod and even with the mod i have seen that i needed a softer lr myself car was tight off the corner on hoosiers with a 225 lr 4-bar clamped z-link on rr was 200 i should have switched the rear springs 200lr 225rr or even went less on the lr this was with hoosiers

wfoondirt
Dirt Forum Champ
Total posts: 505
posted January 05, 2005 11:28 AM  
With the setups used today and all the dynamic changes (anti-squat, roll steer, etc) spring theory is not as straight forward (especially on 4-bars) as a chassis designed without these dynamics. You have to think about alot more things that a spring change effects. That being said I think alot of people get in the trap of working with bar angles and ignoring the springs since they really don't understand the effects. Personally I rarely change bars and work more with springs/shocks and diagonal percentage.

quote:
Originally posted by dirtbuster:
their LR clamp setup the ran 175 LR and 250RR.

You have to realize that the rr spring is on the birdcage on the mastersbilts, thus the motion ratio is much different than having it on the housing. Also as WPP aluded to l/m are inherantly tight on the gas which is the opposite of most mods. Another reason alot of 4-bar l/m guys are going to a stiffer rr is to tighten entry (less roll=less roll steer).

Now there is a trend (especially in asphalt racing) of the rr being the stiffest spring in the car, but it takes pretty major changes in setup and is really beyond the scope of a short explination on a forum. Mark Ortiz did an article on this recently in his newsletter that explains it all really well. I haven't done alot of testing so I can't directly comment on this approach.

[This message has been edited by wfoondirt (edited January 05, 2005).]

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted January 05, 2005 12:53 PM  
I figured the tires would have somethng to do with it. But why does the spring behind seem to require a lot stiffer spring on the LR. Seems like the spring would be similar maybe 25# different not 75#.
Ill have to go back and look at front springs too. It seems like the RF was stiffer with the soft LR compared to the spring behind setup. Maybe they do that to free it up getting in a little bit but I would think that would tighten it up middle and off when on the bars. Wheras the srpign behind runs the stiff LR with a soft RF which keeps it free in but when on the bars the softer RF will keep it from being tight off.

One thing i noticed on our car is that when it is on the bars the spring seperates. and is loose. Thats with a 250# spring. I thought maybe going to a 175 would require more preload to get the same ride height and thus keep the spring tight even when on the bars so that the srping was loaded some all throught travel? Make since?

FYI: Our RR is on the front of the BC too. Even though its z linked the spring is still on the BC so it acts similar to a 4 bar spring in front but doesnt index as much.

[This message has been edited by dirtbuster (edited January 05, 2005).]

wfoondirt
Dirt Forum Champ
Total posts: 505
posted January 05, 2005 01:12 PM  
The theory behind the whole lr behind theory is to use the lr spring to get the car on the bars to create roll steer to loosen the car through the corner but still maintain the bite off the corner. The lr clamp typically will create more bite but not get up on the bars as much. The reason alot of guys switched to the lr behind on l/m is to get through the corner not off the corner. The reason more mods run the lr clamped is they need the drive off the corner and don't need as much roll steer (same reason alot of mods have a z-link rr) to get through the corner. Also the thinking behind the soft rf on 4-bar l/m is to let the car roll onto the rf to create more roll steer in the rear. Its sad to say but alot of l/m guys throw conventional spring theory out the window and use the springs to tune roll steer more than anything, so you have to becareful relating l/m setups to a mod.

Short version. The reason for the stiffer lr on the lr behind setup is to get off the corner.

donslink1
Dirt Freak

Total posts: 318
posted January 05, 2005 03:05 PM  
We run a Pierce and our lr is clamped in the front, We went up in rate for more forward bite and it didnt work and Bob told me that with a stiffer lr spring it will work against the pullbar and not let the rear suspension work like it is suppose to

WPP
Dirt Freak

Total posts: 451
posted January 05, 2005 04:20 PM  
How much preload do you run on your pullbar

donslink1
Dirt Freak

Total posts: 318
posted January 05, 2005 04:22 PM  
1/4"

FlyNLoIMCA17
Dirt Forum Champ
Total posts: 753
posted January 06, 2005 02:30 AM  
quote:
Originally posted by dirtbuster:
One thing i noticed on our car is that when it is on the bars the spring seperates. and is loose. Thats with a 250# spring. I thought maybe going to a 175 would require more preload to get the same ride height and thus keep the spring tight even when on the bars so that the srping was loaded some all throught travel? Make since?

The LR will seperate under acceleration if the spring is on the birdcage. Check out the 4 bar suspension videos on this forum. It will show you alot.


Dman
Dirt Freak

Total posts: 270
posted January 06, 2005 09:28 AM  
The spring on a clamp bracket in front is softer so the car doesn't get too tight coming off because the rotation of the rear end is loading the spring and coil springs are progressive in rate.Too stiff in this spring makes the car ungodly tight on the throttle as the cross or left rear % skyrockets.The spring behind is stiffer because it is on the birdcage and not clamped to the rear end housing and "indexes" away and unloads the spring as it gets up on the bars quickly (very quickly as the stiffer spring helps to launch the LR up on the bars).Most of the time you will need to soften the right front spring rate so the car isn't too tight and drives to the wall coming off on the throttle. You should get the newest version of the Joe Garrison/Steve Smith GRT book and do some homework before relying totally on this website for answers. 4 bar suspensions can be very confusing unless you really do some studying to understand how they work.I have seen so many guys dial themselves out with the 4 bar because they are so adjustable and there are so many variables.You must always realize that a suspension change on one corner of the car will affect other corners of the car as well.Not all advice is good advice.Some people love to see others struggle.

rrrrick
Dirt Maniac

Total posts: 192
posted January 06, 2005 10:28 AM  
quote:
Originally posted by Dman:
[B]Not all advice is good advice.B]

That is probably the truest thing ever typed here


G17RACING
Dirt Full Roller

Total posts: 45
posted January 06, 2005 01:07 PM  
Dman, I thought when the lr birdcage idexes it loads the lr spring. As the car lifts the bars increase angle and the top bar pulls the top of the birdcage forward or counterclockwise if you are looking at the lr. see the pics http://www.g17racing.com/1724.html
http://www.suspensionsimulator.com/images/4linkdemo.GIF

FlyNLoIMCA17
Dirt Forum Champ
Total posts: 753
posted January 06, 2005 06:10 PM  
G17,
The suspension simulator photo is a good example. When the car gets on the bars the birdcage does index towards the spring. But notice the distance that the birdcage moves downward during this travel. If you look at the 2 rods running upward in the simulator you can see exactly how much it moves. Now imaging the spring attached to the BC and to the frame, the distance that the BC moves down will unload the spring.

The only way that I could see that the spring would not unload once the car gets on the bars is if you have like a 25" tall spring and preloaded it until it was only about 5 or 6" tall at ride height. Of course thats impossible.

Once the car gets on the bars the LR spring (when mounted to the back of the birdcage) is just along for the ride, unloaded, until the car drops to go into the next corner.

I have lost the LR spring in a race and finished it. The main thing you'll notice is the car is looser going in the turn, there is a slight loss of forward bite but not as much as you would think.

Hope that helps!

4-bar
Dirt Roller

Total posts: 16
posted January 06, 2005 08:37 PM  
Gary Clark won a feature last year at Volusia after the left rear spring came out on the 2nd lap.. Things to make you go hmmmmm

G17RACING
Dirt Full Roller

Total posts: 45
posted January 07, 2005 06:14 AM  
I'm with ya! Thanks!

WPP
Dirt Freak

Total posts: 451
posted January 07, 2005 07:06 AM  
Were was Gary Clark running his spring clamped infront or behind floated

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted January 07, 2005 07:55 AM  
It was clamped in front. He runs lots of RR bite so there isnt much preload on the LR spring and when it gets on the bars there isnt much holding it in there. Honestly i dont know how he ever keeps it in there.

WPP
Dirt Freak

Total posts: 451
posted January 07, 2005 08:42 AM  
I have talk to Gary and he told me ran right rear bite and a stiffer spring on the right front but with my car will not turn with rr bite it is just to tight in.He must be adding alot of static rear steer 1in or more to get it to work and also gary is a pretty big man wonder what his left side %%%% is . I have tried the clamped 4-bar deal how they said to do it and it would not work for me i think you do need a softer rf spring with this and a softer lr also just to get you threw the corner. With the clamp deal in front does it load or uload if you are running with out the lr spring it has to be done on the rf hmmm

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted January 07, 2005 08:51 AM  
He runs like and 850 in the RF and a 750 in the LF. And it beleive he does run about 3/4 trail in the RR which would free it up a bunch but to me i think it would hurt coming off a little. I think he told me once he runs 52% or less left. I want to say closer to 51.5% but dont hold me to that. We tried running our dw9 the way they sent it home but it didnt work that great for us either. We actually stiffened the rear springs a bunch because we were geting 3.5" shock travel on the RR. Then we softened the front springs all the way to 600/650, which i think was too soft. WE went back up a little and it seems to work pretty good. I think I might try running a soft LR but bump the RF up another 50# or so and see what it does. That way it will stay free getting in and keep the LR spring loaded up more on acceleration due to preload, instead of having it seperate the drop so hard at the end of the straight away.

Kromulous
Dirt Forum Champ
Total posts: 796
posted January 07, 2005 10:55 AM  
Its winter, i'm bored. Read this thread and got interested. I dont like the fact that the spring seperates, we run LR behind 4-bar and i am worried it will come out, has before.

Anyway, we run a 13" 200 lb LR spring. Now i notice on AFCO's webpage they offer a 18" 100 and 125lb springs.

I wonder if at a 9 to 10" compressed length if the 2 springs would equal out in pounds?

I'm not to savy on figuring spring rates, so i dont kow. Anyone ever try to calculate this?

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted January 07, 2005 12:07 PM  
kroumous thats kind of what im thinking as well. This is an example.. i know its not exact but just for demonstration. I fgiure if you have roughly 700# on a corner of the car and you have a 250#/in spring that spring should compress 700/250=2.8" under that weight. Now put a 175 there and you have 700/175=4" so you have the spring loaded for another 1.2" of travel as the LR moves down. They will hold the same wieght one will jsut compress more. I figure the longer you can keep the sprign under pressure the easier the transition will be from sprig to bars and back again, maybe keep it from dropiing so hard off the gas.

i can see where you might possibly need to run more LR bite and/or stiffrer RF/softer lf spring to keep it free in and tighten it off.

Kromulous
Dirt Forum Champ
Total posts: 796
posted January 10, 2005 08:21 AM  
Another idea is a travel spring like the run on the LF on a Late model with a spacer in between the 2.

Might have to search for a spring to do it, but shouldnt be to hard.

rrrrick
Dirt Maniac

Total posts: 192
posted January 10, 2005 12:13 PM  
I tried a 125# spring on the L/R this year, figuring the compression would let me stay on the springs longer. However, the big problem was getting off the gas the car bottomed out on the track.


dirtbuster
Dirt Forum Champ
Total posts: 2007
posted January 10, 2005 01:25 PM  
rrick

I dont know if i would go to that extreme but its nice to know somebody is trying it. Do you think a 175-200 would have made a difference?

On entry did it feel like it dropped as hard before bottoming out?

We tried running a 8-3 and 6-3 shock on the LR last year and it seemed to help keep it from dropping so hard, maybe a little stiffer spring than a 125 and a stiffer compression shock would work pretty well.

rrrrick
Dirt Maniac

Total posts: 192
posted January 10, 2005 02:52 PM  
It dropped hard when I got off the gas. I also ran a lot of R/R weight in the car ( about 47% cross). I tried a 200 l/r one night and finshed second, although the spring had popped out about halfway through the race. In Vegas I switched to a 300 L/R spring and the car drove pretty nice into the turns

STICK01
Dirt Maniac

Total posts: 164
posted January 17, 2005 07:31 AM  
we were at 150 RR bite on a cushioned up race track and were 1/2 tracking the field...until brake fade (lube on RR brake rotor) caused the car to drift real bad in the center of the corner and jumped the cushion, ended up 4th...

That was without any static rear steer at all, and 700LF 650RF 175LR 200RR in the car.

WPP
Dirt Freak

Total posts: 451
posted January 17, 2005 12:26 PM  
rrick did you have your lr shock clamped behind if the shock was floated the car will drop 2 inches it works clamped in the rear on the shock will make a bigg differce

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