Left rear in front

[Bcollins82]

Not really. The dynamic wheel rate is as important, or moreso than the wheel rate at ride height.

Agreed. But the dynamic wheel rate with the spring behind is softer than the spring being used on that corner, if you don't account for the weight being transferred through the bars, only the spring. Softer rate=less spring rate unloading per inch of down travel, correct? So you would have to be extremely soft if you were in front to try and mimic the loading of the spring behind. I'm still not sure you could go soft enough in front to keep the load in the spring at dynamic height since the spring would unload so much faster in front. I'm sure you would have to use shock valving and bar angle as a crutch to help keep the car up and going.

[MasterSbilt_Racer]

Agreed. But the dynamic wheel rate with the spring behind is softer than the spring being used on that corner, if you don't account for the weight being transferred through the bars, only the spring. Softer rate=less spring rate unloading per inch of down travel, correct? So you would have to be extremely soft if you were in front to try and mimic the loading of the spring behind. I'm still not sure you could go soft enough in front to keep the load in the spring at dynamic height since the spring would unload so much faster in front. I'm sure you would have to use shock valving and bar angle as a crutch to help keep the car up and going.

Correct. But the front mount typically has increasing spring rate in rebound and the rear is decreasing.

[TheJet-09]

Maybe I'm misunderstanding something, but how can the spring in front gain rate (technically ride rate) during rebound if the upper and lower shock mounts are headed in different directions?

[Bcollins82]

Yep, MasterSbilt_Racer that is true. The curves would be complete opposites. You could increase lower angle, and decrease upper angle to help it some, while trying to keep thrust angles similar. You won't make it act completely the same with it in front, but from what I've experienced the amount of LR drop makes a much bigger difference than LR rate. I don't think anyone is going to switch it to the front and win a Lucas race, but this rule won't leave the cars flat and sliding either. IMO.. And Jet09. It's not that it gains rate as in loading the wheel, the motion of the front mount is faster than axle speed, making the spring act stiffer by loading faster in compression and unloading faster in rebound.

[TheJet-09]

Great suggestions by everyone and memories of things we used to run! What I don't understand is the intent of the rule. If it's engine related then address that. Make them run a 7000 RPM chip, or a 2-barrel. Don't Crate Cars run the spring behind? If it's to assist "older" cars I don't think they have an issue. LaSalle used to run a Limited class that was very competitive and not everyone had a brand name chassis. Even with the rule, where there's a will there's a way.

[LM14]

We were down to 125# spring on LR in front before spring behind caught on big. The soft spring and a short straight bar will make the car hike just like a spring behind car. You have to be careful with the short bar and make sure there are no binds anywhere.

SPark

[Dirtmod13]

With the short bar, does the chassis weight ( when rolled over)Push down on the left rear and drive that tire into the track tightening the car vs. using the jbar?Is anyone using the short bar now?

[Matt49]

Pretty much...The down side is that if you miss the setup you will have your hands full with a VERY erratic race car. There is a lot of sudden and sometimes unexpected movement with a short bar.

[hpmaster]

With the short bar, does the chassis weight ( when rolled over)Push down on the left rear and drive that tire into the track tightening the car vs. using the jbar?Is anyone using the short bar now?

The set up I put up earlier in this thread is one we used in the 1990's. The long J bar I listed as part of the set up gave you a slower reacting car. With a short bar and that set up I bet you would be heading in a very bad direction faster than the driver could react to it.

[Dirt2727]

But you need to remember we didnt have todays shocks back when we all were on the straight bar.

[MasterSbilt_Racer]

But you need to remember we didnt have todays shocks back when we all were on the straight bar.

You put a short straight bar on today's cars and you win the barrel roll contest. It was never a particularly good idea.

[lovinlatemodels]

A lot of great idea's on here but way to much thought going in to this. Probably the best car I ever had was my 99 Swartz which was built to a square tube chassis by our rules back then. Simple set up with a simple shock and spring package with a Z link RR and 4 Link LR. LF 550 Shock 5 valve, RF 350 shock 5 valve, RR 250 Shock 4 valve on the bird cage. LR Clamped 125 Shock 3 valve. % simple 53.5 L 54.0 R and we ran 10 lbs of bite. That car had great side bite and forward bite. The lift bar was simple also 33" with a 350 spring 3 valve shock and no preload and the J bar was simple 19" long with 6" split. This new class would be great for a financial stand point get rid of the high dollar shock package keep it simple put it back in the drivers hands not the check book.

[Dirtmod13]

Exactly. We were ready to buy a new modified chassis for the usra Bmod class we run up here in Minnesota Iowa and Wisconsin. Roller cost was $16,500Plus shocks, tranny , seat, motor etc. so easily over $20 k to get a new car out. We decided against that idea and bought an 09 rocket from a local shop for 9k with seat, trans, fiber driveshaft, everything but motor. Seems like a no brainer. When the track owner ran one at the last race of the season, he went out with the usra Amods. Started half a lap behind as to stay out of the way. Within two laps he was up to the Amods. Also he said the tires had 20 or more runs on them at 5-10 laps per run and still looked like new. American racer -56 compound. Must be hard tire.

[bullittwrench]

I'll try to describe a LR set-up I saw on a car at Brownstown around 2000 or so (I don't remember who it was, but if Matt49 was around back then he might). The LR birdcage was two independent pieces, with the outer half having two links mounted to it (normal configuration, running forward) and the inner half having the spring/shock mounted to it, in front. From that inner half was a link mounted to the bottom that ran forward/angled upward to the chassis. When the LR lifts in the corner (and under acceleration), the mounting point (chassis end) of that link also raises, which in turn rotates the bottom of that half of the birdcage up, thereby keeping a load on the spring (or at least diminishing the loss of the spring load when compared to that of the old style birdcage with the spring in front). If it sounds like that would work, I could try drawing a picture to make it clearer. Thoughts?

I had a 99 Bullitt with this deal on it. Ray called the bar that hooked to the inner cage with the shock/spring a bite bar. It worked pretty well but was very picky on bite bar angle.

[GRT62]

Straight bar with today's right side shocks=bent up roof and roll cage