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Author Topic:   which theory is the real deal??
dirtracr
Dirt Maniac

Total posts: 199
posted February 22, 2005 11:13 AM  
corner exit handling -(on slick)

1) that it is best to run a stiffer right front spring with soft rebound to transfer weight quicker to left rear for better drive........
**or**2) to run a softer right front with say a 3-5(afco) shock on right front to keep the car rolled over on the right front and get the car up on the bars quicker...

i've heard it both ways and tried it both ways.........what do u think?

duece
Dirt Full Roller

Total posts: 28
posted February 22, 2005 05:07 PM  
softer RF

mod4
Dirt Freak

Total posts: 223
posted February 22, 2005 07:05 PM  
After watching some "Speedweeks" races, I think that some fast mods are running some spring rates in the front that are half of what "we used to run".
My guess is that we are generating more rear sidebite/forward bite then ever, and we've finally overtaken what the stock clip front suspension can keep up with unless we get wacky.
Every super soft front car I saw that was fast as heck had two things in common :
they had bad troubles when the tracks got rough, too much movement. They also to go fast had to be driven smoothly through the corners rather then pitched, even when wet, but those that could do this were again, faster then the cars that to my eyes appeared sprung significantly stiffer.

I also am sure that shocks are important, but I saw far more teams changing things other then shocks most of the time. And I could take the shocks off my car and not get the sidebite-hike that the bad boys showed, haha.

Just would like to hear others opinions on this ....

sdracer12
Dirt Maniac

Total posts: 180
posted February 22, 2005 10:36 PM  
I like your #2 setup better on a dry slick, it keeps the car over on the right front a little longer with the stiffer rebound shock. When you are running a shock like a 6 comp. / 2 rebound on the left rear, I think you also need the softer RF spring and the 3 comp. / 5 rebound shock on the RF. My car liked this combo, with a 3 rate shock on the RR.


dirtracr
Dirt Maniac

Total posts: 199
posted February 24, 2005 06:38 PM  
i've done the softer rf deal but i always ended up going back to the stiffer rf..never could get the traction with it..what's a good range of lr bite when doing that setup?? ours is a dw8..

jammin
Dirt Administrator

Total posts: 6243
posted February 24, 2005 07:12 PM  
What I saw during Speedweeks was people using sidebite to keep middle of the corner speeds high, and I've never seen mods roll this much in years past - lots of rightside clipped frame rails touching the track at times .... it may be "wrong" on paper (and for some situations) but I live in FL and only get to see the "true fast guys" once a season ... altho lately more Florida guys are buying more modern cars.

jammin
Dirt Administrator

Total posts: 6243
posted February 24, 2005 07:59 PM  
Rolling the car over more will not give you more sidebite. If the car has sidebite, or sticks good, the car will roll more because of it. However, it doesn't work the other way. Just by making the car roll over more, will not necessarily give you more sidebite.

Sidebite is affected by several things i.e.: tire grip, springs, shocks, center of gravity height, track width, etc. bodyroll is just a byproduct of these.

sdracer12
Dirt Maniac

Total posts: 180
posted February 25, 2005 08:05 AM  

Jammin, when you said "the soft rf spring soaks cross weight upon lift" I agree with you. I run an 800# LF spring, with a 750# or 700# RF spring depending on the track. With this spring combo, car gets into the corner a little tighter, which I needed, but I have to run more LR bite to help the car drive off the corner, usually around 100# - 125# of LR. With a normal 700#LF and 750 or 800# RF, I was running down around 60# of bite.

Would you say a 700# RF spring is pretty soft, or just average? I'm curious if you're talking "soft RF spring" are you more in the 600# range?

Iowamod20, I can't see your point. I think rolling the car over definitely generates sidebite, or at least feels that way. How can you create more body roll with springs, shocks, cg height, tire grip, etc. and not have more sidebite?

[This message has been edited by sdracer12 (edited February 25, 2005).]

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted February 25, 2005 08:38 AM  
I agree with Iowamod20, on the sidebite vs. roll issue. You can put a really soft spring in the RR and the car will roll over and drag the ground but you'll prob actually lose sidebite. The spring has to be strong enough to plant the tire on the track not just float up and down. We expereienced this last year, went from a 200# RR getting 2-2.5" travel to a 225# got 3" travel and more sidebite. The RR stuck better allowing the car to roll more becasue of the incresed grip.

As for the soft RF spring I think you have to have everything set to go with it. You just cant swap your front springs and expect it to work. With more and more 4 link cars I think you will and prob are seeing more of this.

Most late models I know of run softer on the Rf and usually quite a bit softer. I think there are a few reasons for this:
1) The 4 linked LR will create so much bite they use the softer Rf to loosen the car from the middle and off the corner.
2) As the car enters the corner and dives on the RF it allows the LR to rise a little which will pull rear steer into the car helping turn it aroudn the corner, at the same time W. the spring behind on the BC it will start to index and add crosseight to the car.
3) On Late models there is a big aero advantage to keeping the RF buried on the track to keep air flowing around the car instead of under it. Aero is becomeing a big deal for dirt late models. Thats why you see many of them keeping the LF down now. Any air that gets under the car is creating pressure under the body that can lift the car off the track.

Some of that will apply to mods some wont. One of the previous posters mentioned the soft cars had to be driven smoothly instead of pitched. There is a reason for that, If you are pitching the car in your are breaking traction. Drive the car in smooth and through smooth so that the tires never break traction, that will keep you hooked up better throughout the turn and will save your tires. Pitching the car sideways means you have to wait for the tires to hook back up before exiting, driving the car in smooth letting it roll around the corner with rear steer, roll steer etc, will allow you to keep your corner speed up and let you get back into the gas sooner without breaking the car loose to turn it.


dirtbuster
Dirt Forum Champ
Total posts: 2007
posted February 25, 2005 08:44 AM  
sdracer12,

If you are talking chevelle stubs then those springs are not soft. I went to a chassis seminar with Shyrock and John Logue and they were both softer than that, all the way down to 550 at times. I think 600-700 is pretty typical from what I gathered.

wfoondirt
Dirt Forum Champ
Total posts: 505
posted February 25, 2005 10:03 AM  
quote:
Originally posted by dirtbuster:

1) The 4 linked LR will create so much bite they use the softer Rf to loosen the car from the middle and off the corner.

I see this alot, guys will work and work to get bite off the corner then have to counter that with crutches like roll steer etc to loosen them back up. This usually results in a net gain of zero or even a net loss in lap times.

quote:
Originally posted by dirtbuster:

2) As the car enters the corner and dives on the RF it allows the LR to rise a little which will pull rear steer into the car helping turn it aroudn the corner, at the same time W. the spring behind on the BC it will start to index and add crosseight to the car.

You are correct on the roll steer part. The soft rf is used to gain roll steer so the car will turn. The soft rf also loosens the car through the corner by reducing front roll resistance. The part about the lr indexing adding wedge was the original idea behind the lr behind concept but it really doesn't work that way. The lr behind just helps the car get up on the bars initially. Due to the amount of antisquat involved the is essentially no weight supported by the spring because the chassis raises more than the b/c indexes. Thus the increase in crossweight comes from the antisquat geometry not from the spring.

quote:
They also to go fast had to be driven smoothly through the corners rather then pitched

You say this like it is a bad thing. Problem is you have it backwards. They were fast because they were smooth through the corners and the car was setup right and allowed them to be smooth.

[This message has been edited by wfoondirt (edited February 25, 2005).]

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted February 25, 2005 10:43 AM  
wfoondirt,

On the LR indexing what I was meaning is that as the car just started to roll it will increase bite due to the indexing for a short time. I agree once you get on the bars the spring has no effect. Now there are cars that never unload the LR spring and have a ton of indexing but thats another story. But I simply meant that for a short time when the spring is carrying weight it will index and increase LR. Now how much all depends on bar angles and locations. But the other thing is with a spring behind LR you have to get the back of the car to move around in order to get bite off. Its not like a clmaped deal where when you gas on it it laods up, (at least when there is traction) With a spring behind the LR of the car has to move to provide traction, whether through bars or indexing either
one.

I wouldn't say roll steer is a crutch. Used right it is a valuable tool, just like static rear steer. But like many other things it can be overdone.

[This message has been edited by dirtbuster (edited February 25, 2005).]

Iowamod20
Dirt Full Roller

Total posts: 73
posted February 25, 2005 11:31 AM  
sdracer12:

The point I was trying to make was that if you race your car and it rolls over "x" degrees and has a certain amount of "side" grip. Now, assuming no other changes, change the tires to a compound that has twice as much grip and go race the same car. This car will roll over more than "x" degrees and have more sidebite. What created the increased sidebite? Like a said, the car rolled over more because it had more sidebite, not the other way around.

dirtracr
Dirt Maniac

Total posts: 199
posted February 25, 2005 12:14 PM  
great replies guys, keep'em comin..thanks

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted February 25, 2005 12:35 PM  
Something I forgot to mention is that I rear suspension type will make a difference in the decision on front springs as well. I assumed in the original post you were talking 4 link because you mentioned 'staying on the bars' but I could see where a swingarm car, long 2 link car, leaf etc, might not work the same or as well as a 4 link with a softer RF.

The 4link and especially spring behind 4 link takes a little different thinking, sometimes even seems backwards. Just something to keep in mind.

Xtreme12x
Dirt Forum Champ
Total posts: 874
posted February 25, 2005 01:11 PM  
Good Debate!!

Back in 2002 in our Harris 2 link car, we ended up with a 550 RF spring and a 650 LF if I remember correctly. We had the "Normal" spring setup in the rear with long links, staggered springs and a long panhard bar. We won a few races like this and the car was the fastest like this. We had about 6 races wrapped up and in the bag until mechanical failures, tire's blowing, breaking gears happened. For some reason everything started coming apart after we got this setup on the car. A lot also depends on the stub your using, the same front springs in the regular metric would be too soft, or a wide metric would be just about right.

mod4
Dirt Freak

Total posts: 223
posted February 25, 2005 03:14 PM  
This is (maybe) a little off topic .... but I always hear that metrics "must" run stiffer front spring rates. I'm sure it has to do with width, anti-dive, etc .... could somebody who knows explain it?

And what happens if you go "too soft" ? Is it just contact with the lower A and frame ?

sdracer12
Dirt Maniac

Total posts: 180
posted February 25, 2005 06:43 PM  
Dirtbuster, you explained that perfectly, thank you. I do run the 4bar/4bar setup with left rear spring behind, and thats why I also think you need the softer RF spring than the LF, with this setup. The stiffer LF spring tightens the car on entry, the RF dives a little more creating more roll steer, and then the LR spring behind has plenty of bite to get me off the corner well. You definitely have to be smooth and drive the car in deep and straight. If your entry is good, and the car has good sidebite and turns well through the center of the corner, exit seems to take care of itself.

My car is a wide metric, (metric impala), so I know I need to be a little stiffer on the front springs than the chevelle clip.

Iowamod20, now I understand what you were saying, thanks. I had the cause and effect backward in my head. I also have seen several cars which roll over a ton, but still seem to be lacking in sidebite in the middle of the corner. Thats usually when I can get back on the gas and drive under them, lol.

Mod4, I have heard this too, but I haven't driven a small metric clip mod. Anybody else?


jammin
Dirt Administrator

Total posts: 6243
posted February 25, 2005 09:09 PM  
With a given amount of weight transfer a softer spring will compress more which produces more body roll, but not necessariyl weigh transfer. If you say the RR accepts an additional 500# of force during cornering then a 250# spring would compress an additional 2", a 125# 4", etc. The fact that they compress more is due to the way they are made, i.e. wire diameter, and # of active coils which determines the spring rate, not that there is more weight being transferred to them.

There is a difference between body roll and weight transfer. You can have a relatively flat roll angle and yet still get good weight transfer and vice versa. Springs themselves do not create weight transfer they only control what the car/body does during such transfer.



Iowamod20
Dirt Full Roller

Total posts: 73
posted March 02, 2005 09:04 AM  
dirtbuster is correct.

The equation for weight transfer in cornering is:
(W x RCGH x G)/TW

W = Total Weight (Actually should be Weight of Sprung Mass)
RCGH = roll axis to CG (Moment Arm)
G = lateral Acceleration in g's
TW = Track Width

Spring rates do not affect total load transfer, however, they do affect front vs. rear load transfer.

Ego Racing
Dirt Forum Champ
Total posts: 724
posted March 02, 2005 10:24 AM  
quote:
Originally posted by dirtbuster:
With a given amount of weight transfer a softer spring will compress more which produces more body roll, but not necessariyl weigh transfer. If you say the RR accepts an additional 500# of force during cornering then a 250# spring would compress an additional 2", a 125# 4", etc. The fact that they compress more is due to the way they are made, i.e. wire diameter, and # of active coils which determines the spring rate, not that there is more weight being transferred to them.

There is a difference between body roll and weight transfer. You can have a relatively flat roll angle and yet still get good weight transfer and vice versa. Springs themselves do not create weight transfer they only control what the car/body does during such transfer.


This is true if the center of gravity in the chassis is in the exact same plane as the roll center. With a Dirt track car as a car rolls it is rolling over the roll center and relocating the center of gravity. SO if the car rolls an aditional inch 2 inches is would actually be more than 2 inches due to the increased weight being put onto the spring by the center of gravity transfer.
Try jacking the car up on the scales and then change springs and jack it up to the exact spring weights and see what the change is. A stiffer spring reacts quicker than a softer one, so it will load quicker.
When you include the force of weight transfer and speed increased weight or increased traction will increase side bite up to the traction coeficient of the tire.

mod4
Dirt Freak

Total posts: 223
posted March 02, 2005 10:32 AM  
Not trying to be a smart alec, but it seems most of the laws and rules we can spell out are for pavement - you drive on pavement, you operate IN dirt, at least on tracks that aren't dry slick.... just an opinion.

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted March 02, 2005 11:23 AM  
Ego,
Are you saying if the center of gravity and the roll center are in the same horizontal plane? IF that is the case there would be little to no transfer at all beacuse the center of gravity would react W/ the roll center horizontally and it would be a completely sideways force, or sliding of the tires. More weight transfer depends on the height of the center of gravity above the roll center. The closer the 2 are the less transfer you will have.

Also the roll center moves as the car moves and rolls. You cannot simply say the center of gravity is moving and the roll center is stationary. True the center of gravity may move a few inches but whos to say the roll center isnt moving along with it and so the overal effect is cancelled out. This would be different depending on the car, setup, suspension etc. I think the action of the rearend moving left during roll has more effect on loading due to the center of gravity moving relative to the wheeltrack, than the center of gravity moving due to body roll.
But thats just my opinion.....

jammin
Dirt Administrator

Total posts: 6243
posted March 02, 2005 11:54 AM  
In that case the right side tires would have more load on them. But the difference I see is the fact that the left side is being thrown up in the air, not that the car is rolling, but that something , a bump in this case, is throwing the car in the air. And as the left side goes up the center of gravity is also going up which will indeed transfer more weight to the right side. After all thats what we do to get more sidebite or transfer is raise ballast in the car to raise the center of gravity.

Now the difference between this and the car rolling due to softer right side spring is that the left side is going up, with the softer springs the right side compresses and the left side stays pretty much the same. Any lift on the left is offset by dip in the right which means the center of gravity really isnt changing that much.

I do know that i was a beleiver in getting the car to roll more with soft springs for sidebite at one time. We started stiffeneing the RR spring only to try and hold the RR up better and loosen the car off the corner but fully expected to loose shock travel and possibly sidebite but to our surprise the car stuck better We went from a 175# RR getting almost 4" shock travel and little sidebite to a 250# still getting close to 3" travel but the difference in sidebite was unbeleivable. All of this was with no other changes to ballast, panhard bar or antyhing. That is when i came to the conclusion that you have to seperate body roll and transfer. Like I said previous you can get a lot of body roll and make the car feel like its really getting over, but if you dont actually transfer weight and get it to the ground it isnt doing any good.

Different drivers may develop a different feel for the car. By manipulating spring rate some may feel like the car rolls over a ton and that gives the sensation of better side bite because the car rolled more, but maybe didnt necessarily transfer more weight. My driver used to really like it when the car just layed over on the RR and drug the fender because he 'felt' like he was getting in hard and really sticking it. But it was just the opposite, he was slower that way than the way I describe. Dont get me wrong you need some travel there but dont I dont think you should rely on more travel or roll for sidebite.


[This message has been edited by dirtbuster (edited March 02, 2005).]

mod4
Dirt Freak

Total posts: 223
posted March 02, 2005 05:22 PM  
After thinking about it, I wonder if we aren't bumping driving styles against math here. I mean, I think different drivers make cars do different things with different setups. Boy, thats rocket science right there ..... laughing at myself.
Certain drivers might make a car generate more sidebite with less roll. They drive in smoothly, the sideforces building up to the maximum lateral forces. If the car doesn't roll and you have a driver that drives like this, you can be bad fast.
Certain drivers might want the car to about turn over. You "toss or back the car in" (which still works at certain tracks, thank goodness, I am bothered that dirt track racing is getting too much like pavement, but thats another post). The driver that likes to throw the car in wants the car to lean over because it "slides" into the corner ... rolls, rolls, and bites in. Seat of the pants, soft springs take longer to take a set and then hit all at once. Which is the feeling to me at least, sidebite wise. With stiffer springs and less roll, you toss the car and skate right up the track, once you start sliding it takes longer to stop. Again, my opinion.

jammin
Dirt Administrator

Total posts: 6243
posted March 02, 2005 05:34 PM  
How many of you guys have noticed that when the track dries out and gets slicker,the car becomes tighter ? The old theory use to be to add more wedge in the dry to keep the car straight off the corners. With the lack of side bite the car never wants to roll over on the right rear like it does when the track is heavy.This causes the static wedge to stay in the car.I have found that placing weight higher in the rear or droping the panhard works way better than softer right rear spring for side bite.

justin
Dirt Freak

Total posts: 263
posted March 02, 2005 07:42 PM  
quote:
Originally posted by dirtbuster:

1) The 4 linked LR will create so much bite they use the softer Rf to loosen the car from the middle and off the corner.

Correct me if I'm wrong here (because there is a good chance that I could be). I agree that a softer RF will loosen the car on entry and in the middle (how much depends on the banking of the track) but won't it tighten your exit? When the car pitches rearward on exit and unloads the front, the smaller RF spring will give up a smaller percentage of the total front weight as the front extends which increases the dynamic cross and will make the car tighter on exit.

Justin

[This message has been edited by justin (edited March 02, 2005).]

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted March 03, 2005 08:07 AM  
jammin,

I see your point, and i agree that more speed or weight will increase centrifugal force in the corner.
I thought about this some last night and I think maybe where our discussion differs has more to do with the tire contact patch. In your sprint car scenario the rut catches the RR and instantlty sticks it. Otherwise the tire is free to slide across the track a little. As soon as the tire sticks it will increase the amount or force rolled to the RR because it becomes somewhat of a fixed pivot point. The point I am trying to make in my examples is that you have to get the RR to stick before you really get any transfer or sidebite. Make it stick and obviously you will transfer more weight, and get more body roll. What we found was that a soft spring to allow lots of body roll didnt stick the tire well enough to create the weight transfer we needed. A stiffer spring, which possibly leads to less body roll will put more of the weight to the groudn which in turn creates more transfer. Like I said I used to beleive that if you layed the car over on the RR you'd get all kinds of sidebite, but with too soft of a spring all that weight gets soaked up in the spring and doesnt make it to the contact patch.

Does that make sense....

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted March 03, 2005 08:23 AM  
wissota3x
thats my point. Unless the track changes drastically I wouldnt mess with springs that much.
If you have a car that works good why change the spring setup when the only difference is the track drying out and slicking off thorugh the night. Its not like the spring suddenly got stiffer and thats why the car isnt rolling and sticking, so why change the spring. Why not adjust the car so that it still uses the spring as befroe. If the car worked good with grip in the track then as it dries out by raising the weight or lowering the panhard you are simply making the car act like there is still grip in the track. You are compensating for the lower corner speeds and thus lower centrifugal force by increasing the leverage between the center of gravity and roll center which will let the car roll, transfer, or whatever you want to call it just like before but at the slower track speeds and with less grip in the track. If you had softened the spring then the car may roll over but might not necessarily trnasfer weight as before and then the softer RR will tighten the car off even more.

[This message has been edited by dirtbuster (edited March 03, 2005).]

wissota3x
Dirt Forum Racer

Total posts: 86
posted March 03, 2005 10:41 AM  
Dirtbuster,
Very good point,I will also add that if a car is adjusted to induce roll steer ,if the car can't roll over from lack of traction or speed then it can compound a tight condition.
As a conclusion the new technology that we have in these bar cars typically requires aggresive,balls out driving off the right rear to be fast.Otherwise in traffic or slow restarts they can be pushy.

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