Spring Pre-Load Cartridge on Dirt?

[TheJet-09]

I came across this "Spring Pre-Load Cartridge" which apparently is used on the RR of Asphalt cars:

https://www.lefthanderchassis.com/v2a/14_viewproduct_product.asp?idproduct=2351900

I believe Asphalt cars are basically 3-Link rear suspensions, but I wonder if there is a place for this on a 4-Bar Dirt car? Would it be possible to preload the RR spring to help tighten a car on entry, yet benefit from it not taking away LR on exit? Or would it be a waste based on the amount of lift we get (even on the RR) from our rear suspensions drive angles?

If anyone has experimented or had experience with one of these I'd appreciate any opinions/observations.

Thanks in advance!

[billetbirdcage]

Jones has one too. Basically allows you to preload a spring then put on a coil over to make (sort of) a digressive spring. Like preload a 200# spring 1" so to compress it the first 1" it takes 400# total and the rest of the travel it takes the normal additional 200# per inch rate.

All the one's I've seen take a 3" coilover spring instead of the normal 2.5" springs.

But to sort of answer your question, the most likely place your going to see these being tried is on the RR of a LM but could be used in other places.

[TheJet-09]

Thanks for the input. In trying to digest it, my concern with it used as intended (on the RR) was expecting it to somewhat "fall over" and just stay there (due to the digressive action you mentioned), but maybe the lift we get on the RR under acceleration would overcome that...which is to say "aren't they just canceling each other out then?" I was wondering about the LR too. I've jacked up my LR when slick by adding a bunch of turns, which then adds weight to the LR. Great for the LR, but the weight is coming from somewhere (the RR), which is no good for entry (hence, everything is a trade off). If we're coming off the LR spring under full hike anyway, you could have the necessary pre-load in this unit then basically adjust the LR "ride height" by changing where this unit sits on the LR shock body.

So now I've even confused myself, but as with everything "there's one way to find out." I haven't checked the other manufacturers prices yet, but the $200 for it and a few 3" springs gets you up around $400-$500 pretty quick. We'll see...

[RCJ]

Because of the motion ratio, a change to the r/r spring doesn't have a big effect on the car.The cartridge might work great, but I don't see it being very effective on our style of cars.

[Kromulous]

How is this any different than chaining or limiting the RR to keep it from climbing the bars?

Cool device.

[billetbirdcage]

How is this any different than chaining or limiting the RR to keep it from climbing the bars?

Cool device.

Nothing stop's it from rebounding just like a normal spring (it just has some possible preload at what I would call the old STD spring free hieght.

[Kromulous]

We followed some of your advice year ago or so. Faster entry and thru the middle, and you don't have to worry so much about exit, and it worked very well.

Using that logic, I started to think about adjustments in a different light, for I stance, if your maxed out on LR drive, decrease RR drive. Seems logical.

So, imho, using this device, sometimes could be a very good thing, and I bet alot of teams do already. That or just tether the RR tight, at a given lgth, and run a soft spring with preload. Kill off just a little RR drive on exit, or is this bad thinking?

[TheJet-09]

^^^ You're thinking along the same lines but I believe there's more to it. This contraption allows you to have pre-load in the spring which must be overcome to compress it (digressive so to speak). Chaining the RR at ride height would most likely be bad. On dirt we have to account for far more inconsistencies in track surface than on asphalt so we have to have some rebound/droop available to keep the tire on the ground when rough. I've determined it probably wouldn't be a noticeable help on the RR of a 4-bar car...but maybe on a swingarm? My idea for the LR went out the window. As soon as you have any lift on the LR you'd be off the spring. I don't see that as beneficial.

[billetbirdcage]

I'm gonna throw something out to make you think a little bit.

Anyone actually ever really looked at how much load there is on the RR spring at ride height? You don't need a cruncher, just measure the hieght of the spring at ride hieght and calculate it.

Think many will be surprised how little the RR spring carries for load statically (spring load not wheel load).

[Kromulous]

Once we get going this year i will do that, i am interested now.

What i noticed with alot of traveling teams, is there cars lay over on the RR hard, almost looks broke. Especially at Florence when the track is super slick.

Using estimates, i calculated 1237lbs on the RR at full travel. 3" bump travel, and 575lbs on the scales ( 2.5" travel) for 5.5 total travel. Thats not alot considering the car is 2300lbs, and centrifugal forces.

[TheJet-09]

I've never measured it @billetbirdcage, but I understand what you mean. I've added 8 turns to my LR and based on the change to the RR ride height (going up), you'd think I added turns there as well.