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-   -   Ladder bar adjustments (http://www.hotrodders.com/forum/ladder-bar-adjustments-63475.html)

JSracing 05-29-2005 02:54 PM

Ladder bar adjustments
 
has anyone here adjusted their ladder bars with reference to the four corner weights of the car? if so did you preload the right rear any? How much preload is acceptable and why do alot of racers run preload even if the car weights are equal across the back?

What I am looking for here is why not just run it equal from one side to the other?

Deuce 05-30-2005 05:57 AM

:)


When I raced on the dirt ( Late Model Sportsman ) .....we would weigh all 4 corners and adjust.

Your question has not gotten any responses in almost two days.........I guess because most drag racers ( at least around here ) ....run 4 link suspension.

I suggest just trying your combination and seeing what works BEST for you.....

DEUCE....


:D

theHIGHLANDER 05-30-2005 07:36 AM

Pre-load is sometimes something that is mis used. However there is reason to use it on certain applications.

Standing at the back of the car, veiwing the rear axle, on launch the rear axle wants to lift the right wheel into the wheel well from the forces of torque. A high powered big block combination that makes say 650lbft of TQ probably rolls out around 4500lbft by the time it hits the tires due to the multiplication of the gears in the trans and axle. So in the case of an overpowered combination a small amount of pre-load can help manage this action. Pre-load is sometimes a bandaid fix for something out of whack. Excess pre-load can cause a dangerous situation at the finishline when the brakes are applied because the forces are opposite.

To answer your question specifically would require more input, but in most cases ladder bar cars need little if any pre-load. The farther apart the bars are the less needed. Same applies to HP, as more power maybe a lil pre-load to manage launch. We used to set our pre-load needs with the drivers side adjuster...make it longer and only turn the adjuster 1 flat on the nut at a time and test from there. Just cranking away by guessing or even using corner weights never really got it done. On my last combo I used 2 flats from neutral and launched straight as a string every pass, any track. That was a 477 BBC w/14.25:1 pistons, .714 roller, Dart/Merlins, and a Turbo 400 w/5500 stall and a brake...this was in a 72 Camaro with 10.5x29.5 tires and a 4.88 gear. At 3545# the car had a best 60' of 1.40 and a best run of 10.30 @132mph.


I hope this was helpful.

JSracing 05-30-2005 01:01 PM

which side of the rear... left or right weighed the most when you added your preload? and why did you do it thagt way?

Also what other info would you need? I have all the stats on my car.

theHIGHLANDER 05-30-2005 03:59 PM

Well like I said I didn't use corner weights. If I had then the right rear weighed the most when done. I never weighed that car by corner just front and rear. Why did I do what I did? I was at the track shakin down the new set-up and susp. The car left a little to the right indicating that on launch it had too much weight on the left rear tire. Does that make sense? If you read back about how the rear axle behaves on launch it will. So why adjust the left bar adjuster? By making the lower link on the left longer (about 1/16th in my case) it added just enough compensation to the right side tire to allow it to leave dead straight every pass.

Ladder bars are very violent and simple suspension components. They can take a major hit and still plant tires real hard as needed. I guess I need to mention that this was used with coilovers and a diagonal link. As heavy as the car was it only needed 110# coils in the rear due to placement and spring pre-load. There's a lil science and theory to that as well but maybe another subject.

As far as input, is your car behaving in a certain manner? Is the ride hgt where you want it? Coilovers are assumed. What spring? Did you weigh the car as you would be at the line ready for launch (I.E. you sitting in the drivers seat and fueled to a similar wt)? Lots of TQ? Auto trans? What convertor stall? Using a trans brake?

I've been under way more than my share of drag cars both in the shop and in the gravel in the pits. I'll be happy to help out any way I can.

JSracing 05-30-2005 06:15 PM

Quote:

Originally Posted by theHIGHLANDER
Well like I said I didn't use corner weights. If I had then the right rear weighed the most when done. I never weighed that car by corner just front and rear. Why did I do what I did? I was at the track shakin down the new set-up and susp. The car left a little to the right indicating that on launch it had too much weight on the left rear tire. Does that make sense? If you read back about how the rear axle behaves on launch it will. So why adjust the left bar adjuster? By making the lower link on the left longer (about 1/16th in my case) it added just enough compensation to the right side tire to allow it to leave dead straight every pass.

Ladder bars are very violent and simple suspension components. They can take a major hit and still plant tires real hard as needed. I guess I need to mention that this was used with coilovers and a diagonal link. As heavy as the car was it only needed 110# coils in the rear due to placement and spring pre-load. There's a lil science and theory to that as well but maybe another subject.

As far as input, is your car behaving in a certain manner? Is the ride hgt where you want it? Coilovers are assumed. What spring? Did you weigh the car as you would be at the line ready for launch (I.E. you sitting in the drivers seat and fueled to a similar wt)? Lots of TQ? Auto trans? What convertor stall? Using a trans brake?

I've been under way more than my share of drag cars both in the shop and in the gravel in the pits. I'll be happy to help out any way I can.

I agree with everything you did. If you don't have acess to scales you have to do what you can. I was just double checking my method. I agree too much weight on one wheel will make it drive opposite. Thanks for verifying my thinking on this... I was right.

My car was pulling the back end to the right during a burn out. Launches are violent. Zero Traction. I had to peddle the car for the first 100 ft. 60 ft times vary from 1.30--1.55 1/8th mile is anywhere from 5.60- 6.05
Ride height is good, coilovers yes double adjustable. 110 lb springs.
Transbrake yes, stall @ 4500 rpm shift at 6500 rpm; Auto trans 2 speed powerglide. 3 degree pinion angle ( old slicks, 14X 32 goodyears, lots of check hole left but I think they are shot anyway ) new ones ordered.

Race ready weight..fuel and me...

LF 805 RF 735 F 1538
LR 700 RR 602 R 1301

After movin right rear bar 5 1/2 flats ( havent tried this setting yet )
LF 863 RF 677 F 1540
LR 645 RR 657 R 1302 total 2843


What do you think? Oh I just stuck some wheelie bars on it too, but I weighed it with them on it.
Just wanting to get some input from someone eles who knows this stuff. I'm not a rookie by any means but it always helps to have a second "eye" on a problem.
Thanks a bunch, You've already helped. I just got these scales, before that I always had to do it like you did yours.

JSracing 06-01-2005 07:01 PM

bump to the top

theHIGHLANDER 06-05-2005 05:56 PM

That LF wt has me scratchin my head...slicks are moot right now. A real hot burnout or VHT would be a "fix" til you sort it out. You moved the right bar...made it shorter by looks of things. I assume the wheelbase is right on the money.

Still, LF makes it look like a handful at the other end (on paper at least). Once you get the new boots on it any mis-adjustment will show up big. Sounds like a fun car. Pinion angle looks good to me.

I'm throwin in wrinkle here...Your bars, are they up, down, or level at ride ht standing still? Heres the reasoning...Look at the bar as a lever arm and picture the arc of the rear axle as it travels say 10deg up, then 10deg down from dead level (a pencil on a flat surface helps the visual here). So if the bars are level, on launch the wheelbase wants to "shorten", and this is exagerated if the bars are in the up position before launch.

If the bars are down from level at ride ht ready to launch, On launch the wheelbase wants to "lengthen" and thereby softening the hit just enough to do the work of planting the tires. How much does it lengthen? On my car, bars down 1 hole from level, raising the car (bars) to level from the ladderbar Xmember, my wheelbase extended just under 1/2".

So what? So then the car is, in a sense, moving forward before it rolls forward, while the bars are doing their job planting the tires. Vehicle reaction time improves. Launch seems less suitable for hollywood action flicks but remains consistant. Since the tire cant go "down" on launch the body comes "up" changing the level of the forward mount on the ladder bar.

Bars up=hard hit, violent launch, bar tries to shorten W.B.

Bars down=softer hit, less violence, bar wants to lengthen W.B.


Try the pencil thing. The point is your mounting bolt. The eraser the axle center. At level length "x". Up or down length "y". Launch at "y" with point down, you end up at "x". Launch at "y" point up you bind or go "shorter". Something to schmooze on in your head. Hope it helps.

JSracing 06-05-2005 06:25 PM

They are straight, anotherwords level with the ground. On the bottom hole, can't go any further down, just three up.

What makes you think it'll be a handful on the other end? the left front weights?

BillyShope 06-06-2005 03:19 AM

The driveshaft torque, on any car that doesn't have an independent rear suspension, tends to unload the right rear (and, of course, load the left rear) during acceleration. For best tire performance, you want those rear tires equally loaded and static preload is one way to do it.

Suppose, just to have some numbers to work with, your car weighs 3000, the rear track is 62 inches, the axle ratio is 4.11, and the effective rear tire radius is 13.5 inches. Now, suppose you're launching at 1.5 g's. The difference in rear tire loading, due to driveshaft torque alone, would be:

(3000)(1.5)(13.5)/(4.11)(62) or 238 pounds.

In other words, the load on the left rear would be 238 pounds more than that on the right rear. But, fortunately, it isn't as bad as all that, for a portion of the reaction torque, acting through the engine and transmission mounts, shows up at the rear to cancel some of the driveshaft torque. This reaction torque is distributed, front-to-rear, in proportion to the relative roll stiffness. Suppose 60% of the total roll stiffness is at the front suspension. That means:

(0.60)(238) or 143 pounds

of imbalance remains to be "fixed" with static preload. You can tighten the coilovers at the left front and/or the right rear until the right rear weighs 143 pounds more than the left rear. Then, as the car launches, the loadings will be equal.

But, some of these numbers are pretty shaky, specifically the acceleration and roll stiffness percentages, so this just gives you a rough idea of the magnitude of static preload that is necessary.

And, if you do use static preload, it's important that the ladder bar adjustments be the same, side-to-side. In other words, you either do it with ladder bar adjustments or you do it with preload, but not with both at once. Which, then? Well, even with the shaky estimates used in the calculation, I'd go with the static preload.

Don't worry about the inequalities during braking. When your 250 pound mother-in-law sits directly behind you, so she can yell in your ear as you drive, the inequalities are equal or greater. So long as you don't lock up the wheels, braking torques remain equal.

Finally, there are ways to dynamically cancel driveshaft torque, so the static loads can be equal, but I don't want to go into these other ways here.

theHIGHLANDER 06-06-2005 07:45 PM

JS, yes the difference of 186lbs lft to rt on the front when sitting static. Billy has a point somewhat about the braking torques, just that at high speeds and instantanious braking it looks (like I said...on paper) as though it could pull left a bit on the initial hit of the brakes.


While I don't totally agree with Billy about his numbers, the point about reaction of the driveline remains the same. Actual TQ is multiplied through the convertor, 1st gear, rear axle ratio, then divided by 2 and multiplied by the tire radius in excess of 12inches. Putting it simply your 600lbft of TQ turns into around 4500-5000lbft at the ground. That's a lot of "work".


I do these power calculations on my snowmobiles. I disagree with track dynos that say a 160 HP combination has only 80HP on the snow. Converting HP back to TQ says different. You can't launch 750lbs of sled and rider skis up from zero to 100mph in 500ft on 80HP. Logic tells us what were doing here on both examples.

Though it's a little dated, I suggest a copy of a book by Dave Morgan titled "Doorslammers". The information is very valuable in helping sort out chassis combinations. The book is like $30. I haven't looked at mine in years, and my scanner is malfunctioned at the moment or I'd scan some sample info and pics.

Did we get off topic a bit? I still stand by my way of initiating pre-load. The bars are the levers doing the work. The shocks and springs do support and damping. IMO shocks and springs should always strive to be equal.


Last note...if the car was level at the rockers would the bars be up or down? How do they relate to the car's "level" profile?

JSracing 06-06-2005 09:42 PM

the rockers are level with the ground, the bars are maybe 2 degrees down from the rockers. Also I have a copy of Dave's book. Good book definately.

BillyShope 06-07-2005 02:42 AM

Quote:

Originally Posted by theHIGHLANDER
While I don't totally agree with Billy about his numbers....

How much do we differ at 1.5 g's acceleration?

Quote:

Originally Posted by theHIGHLANDER
You can't launch 750lbs of sled and rider skis up from zero to 100mph in 500ft on 80HP.

Yeah, I agree. Even assuming constant acceleration, that would take a minimum of 134 horses.

Quote:

Originally Posted by theHIGHLANDER
I still stand by my way of initiating pre-load. The bars are the levers doing the work. The shocks and springs do support and damping. IMO shocks and springs should always strive to be equal.

Like I said, you can do it one way or the other. (Actually, I suppose you could do a bit of both, but that's really complicating the issue.) I just prefer the springs because they're less "touchy" than the ladder bar adjustments. And, don't forget the roundy-round boys preload with the springs all the time. No reason it can't be done in a straight line.

johnsongrass1 06-07-2005 08:33 AM

Drag cars don't use the engine and it's applied torques to slow down. So the forces aren't the opposite reaction of acceleration.

theHIGHLANDER 06-08-2005 03:01 PM

"And, don't forget the roundy-round boys preload with the springs all the time. No reason it can't be done in a straight line."


I'll try not to rant here...roundy-round cars are night and day different. They ask for a completely different dynamic action than drag cars because it's a straight line. We want launch control and firm handling down the track. Pre-loading springs for control causes ill handling at speeds and braking. The ONLY exception being shocks as they're dampers. They can be made to dampen the same in one direction and different in the other if they're double adjustables. Pre-load by virtue of the bar adds work force when needed (launch) and control when needed (down track and braking) without unwanted forces after launch.

JS...Look into the deal Dave says about lighter springs and "stored energy". Consider everything we've been discussing, and if possible have someone knowledgable watch your car launch and take notes. Remember, longer on the drivers side (lower ladder bar adjuster) adds static wt on the pass side. The opposite is also true. Don't cloud the issue with "instant centers". The instant center is the forward mount. The bars are the levers. The levers plant the tires and when right will not allow the car to sag at all on launch. in fact the top of the tire should be nearly visable on launch depending on how low the car sits. It also sounds like they're in the right position to get the lengthening force I was talking about earlier.

Billy...I don't disagree on G forces, maybe you're even a little low. And I came up with roughly 140HP in my sled example based on observed times/speeds. So we're there.

JS...lookin forward to hearin how the car's doin. You never said what it was, did you?


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