How Far is Too Far
It’s a problem I have encountered many times in my consulting career. Teams just cannot be satisfied with what they have that many times is very successful. Either they miss-apply new technology or apply it to cars that do not need to have it. At any rate, the cars performance suffers as a result.
Early on in the 1990’s, teams whose cars were loose off tried to make them tighter until the cars pushed “like a dump truck” so to speak. No one understood dynamic balance meaning if they solved the tight condition first, the car would naturally exit without being loose.
Then we began to see the Big Bar and Soft Spring setups along about year 2000. This got out of hand in a hurry. Teams that experimented with those setups put softer springs on the front end, a bigger sway bar, and a stiffer right rear spring than anyone had previously run.
The soft springs were there to allow the front end to run lower and the bigger sway bar was there to reduce front roll to make the cars more level to the track. The bigger RR spring was needed to reduce roll in the rear to match the low roll in the front.
All was well and good for a time. Then the racers said, “If that works, let’s go bigger still.” The sway bars got bigger, up to two inches or more in diameter. The right rear spring rate got bigger too, up to 600 to 800 ppi spring rates. All of this was overkill.
To limit the front travel and keep the cars from hitting the track, we saw bump stops come into the picture. Now we could run even softer springs up front and the high spring rate of the bumps caused an anti-roll effect similar to large sway bars. We no longer needed the two inch sway bars and those were reduced to less than 1.5 inches in diameter.
Teams soon learned that they didn’t need the super stiff RR spring and large spring split either. The RR spring rates came down to around 250 to 300 ppi, the actual rate dependent on the panhard bar height. All was better, but not perfect.
The truth was the bump stop setups were very hard to manage and perfect. I talked to a well-seasoned crew chief recently who had tuned his bump stop setup and went from bad to good with just a 1/32” packer adjustment. That is way too much on the knife edge as far as I am concerned.
Then out came the bump springs. These provided a more consistent spring rate over the bump stops where with those, the spring rate was variable and increased tremendously in a very short amount of compression Bump stops traveling under a half inch go from less than 100 ppi to over 2,000 in that distance. Bump springs are much more consistent and tunable.
During all of this, the shock guru’s were having a field day. To make the soft spring and bump setups work, you needed high rebound shocks that would work with the high spring rate of the bumps. These were miss-named “tie-down” shocks. This was a misnomer because their original intent was not to tie down, but to control.
Here we go again, if 200 pounds of nose (rate before movement of the shock) were good, then 400 or 600 would be better. And if 600 pounds of force at 3 inches per second of shock speed were good, then 1200 pounds might be better.
The teams running bumps soon learned that there are limits to everything and found a happy medium for RR spring rates, sway bar sizes and shock rebound rates. But then the teams running Non-Bump setups thought it would be a good idea for them to run “tie-down” shocks on their “soft conventional” setups. They wanted the low front attitudes that we enjoyed on the bump cars, but didn’t have the proper equipment to run them.
That never stopped anyone from doing the wrong thing, and they did. Now the front shocks with the high rebound rates over came the ride springs and jacked down. That is to say, as the shock compresses, there isn’t nearly enough spring force to push it back up any time soon. So, the front ends go lower and lower.
If it needs to rebound, it cannot. The tire loses load and then grip. The car pushes badly and the setup balance is ruined. All because these teams try to do something the car was not designed to do.
The point is this, live within the confines of the design you are racing with. Don’t do crazy things that aren’t meant to be. In those classes where you must run more conventional setups without bumps, work with what you have. Match the springs up with shocks made with normal rebound rates.
You can run a little larger rebound rates and sway bars without ill effects, but don’t go overboard either. The fastest non-bump setups are nothing special, trust me. They are just balanced with the four spring rates and sway bar rate that work in combination with the right panhard bar height, and cross weight. When you get those working together, the four tires will work as hard as possible and you’ll be fast for a long time. It’s not magic, or is it?
If you have comments or questions about this or anything racing related, send them to my email address: chassisrd@aol.com or mail can be sent to Circle Track, Senior Tech Editor, 1733 Alton Parkway, Suite 100, Irvine, CA.
Anti_Squat
Hi Bob –
I read with interest your “Advanced Anti-Squat Techniques” article in the 2.17 issue of CT. Can this technique be used to advantage turning both left and right? I’m building a street rod and want to set it up to run parking lot autocross (Goodguys) and some road race track time.
I’m planning on using a four bar rear end setup in a Satchell Link arrangement (parallel top bars and diverging inclined bottom bars). This arrangement fits better between the X-members of my frame and I’m thinking I won’t need an extra bar to stabilize the rearend laterally. I understand this arrangement is suppose to provide considerable anti-squat with roll understeer and a low roll center.
Your article states the lower bars of the three bar system are not considered an adjustable item for AS. Would the Satchell Link minimize the rear steer characteristics you mentioned? Could changing the angle of the bottom bars be utilized to adjust the amount/location of the AS like relocating the front frame mount of the top third bar detailed in the article?
On the reverse side, during deceleration how long of a Swing Arm will be required to minimize traction loss and prevent brake hop? Can a good +/- AS balance be achieved? My front suspension will be a double A-frame layout with R&P steering. Any suggestions and guidelines you can provide will be greatly appreciated. Keep up the good work,
Jeff Beuter
Jeff,
Your design will have a low roll center and should control lateral movement. My thoughts on the lower control arms is this, the angles are critical to control rear steer. As the car rolls, those bars, in combination with the top bars, can create rear steer depending on the angles of the bars.
It might be wise for you to mock up the suspension using tack welds to mount the links. Then bump the wheels to see if there is any fore/aft movement of the wheel. If so, the proper side-view angle of the links to prevent rear steer might be detrimental to anti-squat.
That is why the three link systems work so well. You can angle the upper middle link to create the AS while running angles in the trailing links that won’t create much rear steer. Maybe you should re-think your rear suspension and use a three link. Most of the late model types of road racing cars have used that system for a long time.
Anti_Squat 2
Hi Bob,
Your article on anti-squat has me wondering, what is your opinion of reducing AS to allow more of the torque load to be absorbed by the rear springs and shocks? I’m considering replacing a torque absorbing third link with a solid link and running less AS on a pavement modified to achieve the same effect. Any thoughts?
Rich
Rich,
What you are doing is allowing the car to squat, which can be very useful. If you run more angle in the left trailing arm (front higher than the rear), the squat motion will kick the left rear wheel back on acceleration creating rear steer to the left. This tightens the rear of the car and points the driving force left of centerline.
You get a combination of rear tire angle of attack which provides more traction while using the trust of the motor to drive the rear end left when it really wants to go right. This combination is very effective for cars with smaller and/or harder tires to be able to use more throttle off the corners. I see no real advantage to zero rear squat anyhow.
Back To Racing
Hello,
My name is Dustin Bates and I’m from Southwest Florida. I have been reading your articles for as long as I can remember. I’ll try to keep this as short as possible. In 2008 we got out of late model racing due to the economy tanking and at that point in time everyone seemed to be shifting over to the Anderson Elite style big spring cars from BBSS coil over cars and we followed suit. We had just built a big spring car but never got to race it.
Fast forward to now and my dad and I want to get back into late model racing. We only plan on running the newly opened 417 Southern Speedway, Desoto, and Showtime. So since exploring the late model scene again I am seeing there’s a couple guys running Anderson Elite style big spring cars, but everyone seems to have shifted back to big bar soft spring coil cars, or what’s new to us, bump stop cars. So here’s my question, if you were in our shoes which route would you go?
We do not have a car yet, so we have the option of going in any of the ways. Initially we were planning on having Dave Pletcher build us a new big spring late model designed a lot like Dickies big spring cars. But after exploring what everyone else is running these days chassis wise we are left wondering if a big spring car can still be a competitive car with all of today’s new BBSS and bumpstop cars.
If it’s not too much to ask can you maybe give us a little insight into what would be our best option. We of course want a fast competitive car but one that stays consistent throughout the race time wise. Thanks in advance,
Dustin Bates
Dustin,
You could do very well with a big spring late model car. It is very adaptable to running soft springs and bump stops, or springs which I highly recommend. The shock being mounted separate from the spring helps you work with the bumps. Be sure to get the screw jack shock height adjustment for the upper shock mount.
The newest late models coming out of Wisconsin are mounting separate bump shafts outside the coil-over assembly just for that reason and they are easier to work with when the spring is not in the way.
With the spring and shock separate, you can work with the shock much easier than you could with a coil over. The car doesn’t care which it is, coil over or big spring. And the bump springs are far more consistent than the bump stops. Dick and I tested bump springs on his Elite late model and were very fast on some of the tracks you mentioned.
No one successful uses big sway bars anymore, especially when using bump springs. So the term, Big Bar does not apply now days. There are many spring companies offering bump springs today and there are more rates available than ever before.
Left Rear Axle Weight
Hi Bob,
I had just finished reading some information where some dirt late model teams are adding weight to the LR axle tube, some going as far as building the tube out of tungsten, when my latest issue of Circle Track arrived.
I was reading your article and looked at the page to the right and there was a well known company selling brackets to mount lead to left rear axle tubes. Seeing this I figured that it must really be being done and it sure goes against the theory that your un-sprung weight should be as light as possible. I think I can see where this could help the forward bite of the left rear tire but I would like to hear your take on this. Thanks for your great articles.
Fred Ehlert
Fred,
I, for one, have never said that un-sprung weight should be as light as possible. At the front, the un-sprung weight does not transfer because of the double A-arm system. So, making lighter spindles, etc. makes no sense. When you take that weight that used to be in the wheel assembly and move it to the frame, a percentage of it now transfers from left to right.
As for the rear end and weight transfer, yes some of the rear weight transfers in the rear end assembly, which includes the wheels and tires, from left to right in a left turn. But, the lower the Center of Gravity of the mass, the less weight transfer that occurs. Since the rear end assembly has a lower CG than the car in most cases, less load will transfer if you put it there.
So, more weight stays on the LR tire than before and I’m sure the teams who have tried this report more forward bite as a result. Next you’ll see heavier hubs, brake rotors, wheels and more on the left side of the rear ends.
All of this is much different than stacking lead bars off the extreme left rear corner of the car. All that does is create a leverage affect that sends the rear of the car towards the wall. Never do this with any race car. I’ve seen it tried and I’ve seen it fail.
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