One of my buddies has a 240 and was telling about these helper springs he was putting on to give him more droop with stiff springs. So, I wanted to check it out and see how to properly build a setup like this. In my googling I came across this page:

http://forums.rennlist.com/rennforum...coilovers.html

Now I realize that this is a porsche board but I would imagine the concept would be the same with any car.

So, here's my question, are any of you guys with super stiff springs running tender springs to help maintain full droop as well as better bump compliance? If you are, please post up the details of your setup.

 

why not run a longer spring of the already given rate?

 

That would raise your ride height, and wouldn't give you the bump compliance of the tender springs.

 

*edit*

 

yes. and in a way i see tender spring kind of as a degressive setup.

 

Lolz.

EDIT:

How so? You get your high spring rate to limit body movement during cornering, and you also get a couple inches of spring to be used on bumps and the like.

 

Yeah, doesn't change anything, does it

 

Nope, a 350 lb/in spring is still going to take 350lbs of force to compress one inch no matter how long it is.

 

yes sorry i meant progressive but in my head was thinking in different terms. but yes that is my point say you have a 650lb spring with a 200lb tender spring. say on that bump the 225 will compress before the 650lb.

 

Yeah, with a 650lb & 200lb spring, the effective spring rate will be 152.9lb until the tender springs blocks. Once the tender spring has blocked the effective spring rate will be 650.

 

well damn. you can see my mind was other places on the last post too. i referenced 200 then 225. lol.

 

I ran this setup (although OP helper springs have ~0 rate and TENDER springs do have a rate) a while ago.

Posted about it too, there are many posts about this on here.

A couple of points.

1) IT IS NOT DUAL RATE. You are just creating a "progressive spring".

2.) No matter what any one says you can't figure the curve out with math. For whatever reason it doesn't work. I tested the tender and the main spring, they both came out to within ~5lbs of what they were labled as, and a formula doesn't get you the curve.

3.) you aren't going to get "a couple of inches of soft spring for the bumps", at least not on a honda. You are lucky to have a couple inchs of travel before the UCA hits the body.

I didn't like the way the car felt, it was too unpredictable for me (on the race track).

 

Yeah, I find myself using the terms interchangeably even though they aren't.

When I said dual rate I was simply referring to the fact that one would use two springs of different rates.

I find it hard to believe that the curve cannot be calculated using math. I'm curious about what spring rates you were using and how you proved that the theoretical numbers didn't match up with the real-world. I'm not trying to bash you here but there are a lot of people who seem to think that simple mathematics can explain exactly what would happen when you stack two springs. If you are correct then there must be something that's not accounted for when performing these calculations.

I would have to say that this would heavily depend on the ride height. Also, 3 or four inch spring might only compress an inch before it blocks anyways(depends on the spring).

What spring rates where you using? Could you elaborate more?

Sorry for all the questions, I'm trying to sponge up all the info on I can on this setup, as I'm thinking about getting a set of GC w/ tenders to replace the Pro-kit on my Konis.

EDIT: I just realized this post might come across as condescending, and I'd like to say that it's not my intention at all.

 

the reason the math doesn't work out is because springs are not exactly linear, and further, they are not always the rate at which they say they are. You need to get to springs tested over the full range of travel.

Some guy named Solo-x ran tender springs with good results.

 

slammed and solo-x seems like the only two rr/ax members who have personally tried dual rate setup... i guess i'll be next.

 

Kozy is the only person I can think of on HT that could calculate the curve of a normal and tender spring combined; if it's even possible.

 

seems like a direct measurement is the only way to be sure though, right?

 

Um, it's just 2 springs in series. You don't get a truly progressive curve, you get a linear curve of the 2 linear springs in series until the tender coil binds, then transition to a linear curve of the unbound spring.

Static corner weight, spring length at coil bind, and the motion ratio would need to be known to be able to determine when bind will occur.

Before bind, where k1 is the tender spring rate, and k2 is the main spring rate)
k = (1/k1 + 1/k2)^-1
after bind, it is simply k2

Finding tender springs in the exact length and rate required would be the true challenge for most of us. It is much easier to just use long bumpstops (or a stack of them to fine tune), which provide a smoother transition and tend to have a progressive rate themselves.

Also, I should add that beanbag is correct in that springs do not usually carry their claimed rate all the way to coil bind, which does reduce formula above to the "pure theory" realm. Reality is that most will slightly increase in rate immediately prior to bind, which will smooth the transition a bit but also change the point the total rate changes. But, I don't think it will matter enough to warrant throwing out the theory, just something to be aware of when trying ti fine tune such a setup.

 

Probably because the car had a pitch dependent spring rate. If you're braking, and that collapses the tender springs (which is likely), then you already have the stiffer spring rate of the main spring only at "turn in" up front, while the rear will still be on the combined softer rate of main + tender. Then, as the car rolls and you transition off trailbraking, the rear will compress enough to block the tender and suddenly you have a higher rear rate.

This is somewhat the opposite of what we want, since the stiffer rear rates we tend to run are to help turn in behavior.

The opposite is true if you stop braking and go on throttle before turn in, where the rear squat could block the rear tenders.

*And I just noticed, after posting, that I'm replying to old posts in this thread...