Left rear stack

[doyle hargraves]

I had a chassis builder tell me that if you are racing under a droop rule that there is no need for a stack on the left rear. He says stacks are for deck height rules. I have a 125lb spring with about 125lbs extended load (spring preloaded 1 inch). And my car seems to set really high on the left rear. Is there a downside to this?

[MasterSbilt_Racer]

I had a chassis builder tell me that if you are racing under a droop rule that there is no need for a stack on the left rear. He says stacks are for deck height rules. I have a 125lb spring with about 125lbs extended load (spring preloaded 1 inch). And my car seems to set really high on the left rear. Is there a downside to this?

There's a lot of truth to that, but I wouldn't say it's completely true. There's nothing wrong with your car sitting high if it's not illegal.

[billetbirdcage]

While I see why they may say that, I disagree. Sure you might be able to get the loads you want extended with a single spring, but with that your limited with what you can do with all the other numbers at anything but full extension. With the droop rule, sure your not overly worried about being to high load at your ride number and have LR sit high since there is not LR deck height being used at ride hieght but you couldn't change your other load numbers without effecting both ride and full extended and can't change those numbers between the two.

[doyle hargraves]

Billet could you explain a little bit about about left rear load numbers? All I ever really hear about is extended load numbers. What does ride load affect on the lr?

[doyle hargraves]

I guess I should say what does it affect while racing? Obviously it’s going to affect deck heights in the pits

[billetbirdcage]

Lets go with these pin to pin for ride to full extended height. 18.0" for ride hieght and 22.0" for full extended load. Lets also say that anything under 600# makes the LR set low at ride height and can/will make car lazy on starts because it is sitting to low and slow to get up on take off.

With a single spring (or a stack but with no stop nut), once you define either the ride or the extended load all the loads at any other point is set and can't be changed.

Example: Using a 125# spring and we want say 150# of extended load at the 22.0". So loads would look like this:

18.0 650#
19.0 525#
20.0 400#
21.0 275#
22.0 150#

I can NOT change the 22.0" number without effecting the 18.0" number or any of the other numbers or vice versa.

Lets say I want a really high 22.0" number like 350# and not running a deck hieght rule so can just increase the ride load and not hurt anything by changing the 18 thru 20 numbers. So i can just put rounds in the coilover and get this:

18.0 850#
19.0 725#
20.0 600#
21.0 475#
22.0 350#

Again lets say for whatever reason the high 18 thru 20 numbers cause a problem on starts or on off gas entry. so to lower those numbers and keep the 350# 18" number, I can reduce the spring rate to say 75# and looks like this:

18.0 650#
19.0 575#
20.0 500#
21.0 425#
22.0 350#

This is close to the original numbers but with the high 350# extended load.
SO WHY WOULD I WANT A STACK?

Lets say the car at full hike is overly rigid and would still like some more load at 20" to 21.5" to help hold car up (off the gas) but if I add more the car becomes super rigid with more then 350# at full extension when against the chain. So I'm gonna stack a couple springs to make something in the 60# range on overall rate. Lets say I go with a 100/175 spring combo but install a stop nut under the separator plate between the 2 springs which allows me to make a digressive stack. The stack works just like a singe 63.6# spring until it extends enough for the separator plate to hit the stop nut and completely deactivates the upper spring removing any load it has thus reducing the load from that point on.

Example: 100/175 (I'm gonna use 60# rate per inch instead of the 63.6# just to make numbers more even). I'm staying with the 650# 18.0" number and working from there

##This is with out a stop nut installed for NOW

18.0 650#
19.0 590#
20.0 530#
21.0 470#
22.0 410#

OK, I have increased the 20 thru 21.5 numbers (as I could have if someone offered a 60# single spring) but my 22" number is too high thus making car even more rigid on the chain. This is where a digressive stack allows me to fix that by adding a stop nut under separator plate that hits the nut at say 21.0".

It now will look something like this:

18.0 650#
19.0 590#
20.0 530#
21.0 470# HITS STOP NUT AND REMOVES ALL LOAD FROM TOP 100# spring
22.0 300#

I can end up with the same 350# or even less depending on how its adjusted and the length of each spring used and can actually cut it way down close to zero under the right set of springs. So I have all the extra load at 20 thru 21" to help hold car up but not so much load when against the chain and not make car so rigid and more compliant when on the chain.

Hope that makes sense

[billetbirdcage]

Billet could you explain a little bit about about left rear load numbers? All I ever really hear about is extended load numbers. What does ride load affect on the lr?

Again all numbers can be important or about meaningless at given pin to pins. Again lets use the 22.0 thru 18.0 numbers as examples.

Obviously the 18" number is ride height and car is generally never there on the race track except maybe on starts. So the higher that number is the higher the car actually sits (won't sit in the pits or track at 18" but higher then 18"), this increases the bar angles and j bar rake as well as raising the center of gravity. All of this may/can help the car get up quicker and take off on starts to a degree. Also if the car is sitting higher its close to full hike and takes less time to get there as well as less steer change from the rear end since it doesn't travel as much from ride to full hike and could be more consistent for a driver if they have to or let the car sit down at some point.

The other numbers matter if the car is getting to those numbers after your actually racing. Now if the car is against the chain (22.0") and never gets lower then that, then the 21" thru 18" car not overly important and have no effect since the car is never there. However the car upon getting out of the gas could/may reach those numbers and at that particular point those numbers will effect the car. Obviously the 21" thru 22" are important because the car will osculate against the chain cushion and when hitting bumps so the 21" can be just as important as the actual full extended number at 22".

Hope that helps

[cjsracing]

I like the LR stack because I can keep my ride height load at 650 lbs all the time while adjusting the droop load.

[doyle hargraves]

Thanks billet! That makes a lot of sense. One more question, are people playing with the left rear extended loads much?my chassis builder basically told me to set it to 125lbs and do your adjustments on the right rear. Mainly loads on the coil over

[billetbirdcage]

While hard to know what all guys do, I would say once you find what you like on load most likely don't change it a ton but could see using different loads for different types of tracks. Like big fast momentum vs stop and go tracks, I will say I think the 125# is way on the low side on average.