drop spring rate

[Ishmael]

Why do the hotchkis drop srings have a 600 lb spring rate and qa1 coil overs only have 450 lb for the same application? May seem like a dumb question but I'm not that bright.

[dhutton]

Edit: just realized you were talking about front springs....

[ArtosDracon]

IMHO, it's because with 3" of drop you're just about out of bump travel and it's better to have a stiff spring than to be riding on the bump stops way too often.

[Bryce]

I think QA1s are just too soft of a spring.

If both springs have the same mounting point on the LCA then the motion ratios are both the same. The only other difference would be angle of the installed spring. The steeper the angle the less effective the spring will become.

[Henesian]

Alright, bro, here's the skinny. It's all about the inside/overall diameter, wire diameter, and number of coils of the coil spring. The larger the wire diameter, and the lower the number of coils, the higher the spring rate. Look at the Herb Adams book, Chassis and Engineering, or find the equation online for calculating coil spring rates for GM cars. I don't know it off the top of my head, and I would look it up for you, except I'm surfing the internet at school. And I bet you're capable enough to do a google search. Anyway, back to my point. Stock T/A springs from 78(for example) have a spring rate of around 400 lb/in, and have a wire diameter of I think 0.672. The overall diameter of F-Body coil springs are 5.5", so, if you double the wire diameter, and take 5.5-(0.672x2), you get the inside diameter of the spring. Stock T/A springs also have a free height of 16", which means that there's alot more coils than the Hotchkis springs, which means that the spring rate is much lower. From seeing a picture of the Hotchkis springs in the "77 T/A ride Height" thread, you can see that they're about .75" wire diameter and 14.5" free height. Which equates to alot stiffer than the stock T/A springs because there's less coils.

If you didn't understand that. Lowering coil springs have higher spring rates, because to get the spring to properly lower the car, they have to make the spring shorter, which equates in less active coils, which equates in more spring rate.

For a real life example, my springs are 13.23" free height, 0.75" wire diameter, and the overall diameter equates to 5.65". They have 5.7 active coils, and a spring rate of 660 lb/in, and lowered the car easily 2.5-3". It made the front end so low that the bottom of the subframe was 3" off the ground in a 76 T/A.

For Coilover shocks, I don't know what the deal is. But, 450 is not even close to being enough spring rate. You can probably have them put in 700 lb/in springs, which would be correct. If you want to know how much YOU should have in an F-body race car. The Knox Hill Mountain Climb champion guy who drives an 80 T/A, has 800 lb/in springs.

I hope that answers your question in more words than you wanted.

[strtlegal]

That was all spot on but we need to keep in mind the end user. 700 lb springs will ride rough on the street, remember it takes 700 lb of force to move that spring one inch. So on the street unless his car weights a crap load on the front the car would hardly move the suspension. maybe to inches at most. Then when he comes out of lets say a wash or a big dip the front end up will come up so fast because that spring is trying to get back to its desired ride height that it could potentially cause the front end to walk a little.

A shock with more rebound and less compression would work good since the spring is doing most of the work on the compression side.

Obviously when your building a car for more specific application like a road course, higher spring rates will help control the car when the car is seeing alot of compression and alot of lateral movement.

Oh and dont forget springs that are mutli rate...haha Thats another story

Ishamel when you say application do you mean that half coil over setup? You can order any spring you want but keep in mind with that setup alot of force is going onto that shock eye. I dont like it, I run a Qa1 up front but its setup like a true Coil over and Im running 450 springs on the street and 550 for a little more agressive track tune.

[Henesian]

Well, strtlegal. I'm talking about a 3600 pound car with a 51/49 or 55/45 or something close to that weight distribution, which most of us have. You're just an oddball with a 2800-3200 pound Nova. With the big springs that I have, the ride isn't that worse at all. If anything, it's better, because the car is actually turnable now.

For a 2800 pound car, 700lb is too much. 700lb/in is about 13 or 14k in ricer terms. Ricers that have 50/50 weight distribution and weigh 2400-2800 pounds, like 240sxs',Civics, Integras, run alot less spring than we need in our big bombers. For example, 240SXs, the most you can get easily is 10k/8k, which equates to around 500lb/in infront. Civics usually go with 6/4 or 5/3, which is way less than that. So it's all in terms of vehicle weight of course.

Shocks and Springs are not independent of eachother. For really stiff springs, you need really stiff shocks. Hence the street philosophy of big sway bars and soft springs, so that you can run soft shocks for ride quality, and still get nominal handling.

I like big sway bars, big shocks, and big springs, because each one has been a performance enhancement, with nominal degradation in ride quality. If you have the ass cheeks for it, and an F-body, I would get the Hotchkis 2" lowering springs with 600lb/in. It'd be alot better than QA1s with 450 lb/in springs, as the QA1s would feel like stock. I've seen so many threads on Performanceyears.com, where guys with GTOs and other 3600-3800 pound cars get QA1 Coilovers with 450 lb/in springs, and the car feels like it doesn't have enough spring.

[Ishmael]

I want a performance improvement but i was worried about the 600 lb springs being too stiff with an aluminum engine up front. I know the two springs are different lengths and diameters but they must share the same formula to come up with that spring rate which is what I needed to know. So the qa1s really are a softer ride then?

[6'9"Witha69]

QA1 also has 550 lb/in springs for their single and double adjustable coil over setups. I saw them on the BMR website yesterday.

http://www.bmrsuspension.com/index.c...&productid=609

[Ishmael]

That might be my best choice.

[strtlegal]

Well, strtlegal. I'm talking about a 3600 pound car with a 51/49 or 55/45 or something close to that weight distribution, which most of us have. You're just an oddball with a 2800-3200 pound Nova. With the big springs that I have, the ride isn't that worse at all. If anything, it's better, because the car is actually turnable now.

For a 2800 pound car, 700lb is too much. 700lb/in is about 13 or 14k in ricer terms. Ricers that have 50/50 weight distribution and weigh 2400-2800 pounds, like 240sxs',Civics, Integras, run alot less spring than we need in our big bombers. For example, 240SXs, the most you can get easily is 10k/8k, which equates to around 500lb/in infront. Civics usually go with 6/4 or 5/3, which is way less than that. So it's all in terms of vehicle weight of course.

Shocks and Springs are not independent of eachother. For really stiff springs, you need really stiff shocks. Hence the street philosophy of big sway bars and soft springs, so that you can run soft shocks for ride quality, and still get nominal handling.

I like big sway bars, big shocks, and big springs, because each one has been a performance enhancement, with nominal degradation in ride quality. If you have the ass cheeks for it, and an F-body, I would get the Hotchkis 2" lowering springs with 600lb/in. It'd be alot better than QA1s with 450 lb/in springs, as the QA1s would feel like stock. I've seen so many threads on Performanceyears.com, where guys with GTOs and other 3600-3800 pound cars get QA1 Coilovers with 450 lb/in springs, and the car feels like it doesn't have enough spring.

I was reffering to the OP I thought he had a 68 Firebird. Which would be relavent to mine. I was just reffering in general how he was going to use it. If he wanted to push the twisty's then yes more spring rate, but for a street driven car 450 would be okay. It may feel spongy but a good shock tune can cure that.

[Ishmael]

You guys should stop being so helpfull - now I don't know what to do. My major concern was that qa1 told me to go with the 350lb spring with my block and hotchkis said the 3" 600lb drop spring to get 2" because of my block. I think 700lb is too stiff for what I want to do with it. I want to tour, not autox so I don't want it to be too stiff but at the same time I would like to handle like a 4th or 5th gen camaro which the tvs system has been proven to be when its sorted like Carl's car. Supposedly it isn't a bear to live with either. Two hours ago I thought the 550lb qa1s would be a nice balance. Knowing what I want to do with it, is there a right spring?

[70camaro406]

Scott, this is a great tech article I found about coil springs...

http://www.afcoracing.com/tech_pages/spring.shtml

I've been debating whether to use traditional coil springs or coilovers myself. What I found is that you can't compare a 600 lb traditional coil spring to a 600 lb coilover. From what I've read, they are rated differently. So what you've been told from the manufacturers is probably spot on, 600 coil is pretty equal to a 450 lb coilover. Plus, since you have an all aluminum engine (LS?) you don't want to go too stiff. Like others have said, and what I've heard from the pros, you should use a softer spring, but go heavy on the sway bar and use good shocks. I would also call multiple spring companies and compare all the results. That's what I did when I bought my last cam, and it turned out they all recommended similar sizes. The same might just be true for the springs.

[Ishmael]

I started to read that. My head doesn't work like that. I quit math before the end of grade 11. But thanks for the link. If the two springs aren't rated in the same fashion and the 450# coil over is roughly the same as the 600# coil and the qa1 guys were thinking about the aluminum block when they suggested the 350# spring and hotchkis was suggesting the the 3" drop spring to get me 2" of drop then . . . I have no idea which way to go. Since I'm going with a stiffer sway bar and the qa1 shocks are good to start with perhaps I should stay on the side of caution. I have no clue. Is there anyone running a light engine and one of these two springs that wants to let me know how they behave or what they think?

[Bryce]

I dont have time to search for it right now. But i have a post in one of the suspension threads with simple step by step plan with formulas.

Search my name and spring rates. It was late late year when I wrote it.

[Bryce]

When I choose spring rates I do (two) calculations.

First what is the weight of the car at that axle. Divide that number by 2. this gives you F (force or weight)

Since F=kx next is to determine the amount fo droop you want or the shock has. This amount of droop gives you the minimum preload on the spring at ride height. If you have 3" of droop you dont want the spring to become unloaded. take F/x=K. K is your MAXIMUM spring rate.

Now this is where personal preference comes in. I design around a 1G bump. How much travel do you have in your shocks from ride to full compression, this is your x for the next equation. Take F times 1G, or whatever number you want to design around. F/x=K this is you MINIMUM spring rate. Now you have a range.

The only way to adjust this is to adjust your shock length and your shock length at ride height.

[Henesian]

What AFCO said on their site is that a racer replaced a 720lb/in coilover spring, with a 750lb CLOSED END Afco Racing Coil spring, and it was actually less stiff, because when both springs compressed, the coilover gained a little bit more rate. It was a difference of 780 lb/in to 750 lb/in.

So, therefore. a 450 lb coilover spring DOES NOT EQUAL a 600lb/in Coil Spring. MAYYBBE!!! And that's even stretching it. MAYYYYYYYYYYYYYYYYYYYYYBBBBBBBBBBBBEEEEEEEEEEEEEEE EE! When you compress both on a spring compressor, the QA1 550lb/in will be equal to the 600 lb/in Hotchkis. If I were you, I'd get the Hotchkis TVS that comes with the Hotchkis Control Arms and the Hotchkis lowering COIL SPRINGS.

[Ishmael]

I though about it but I think I'll have to do it in phases as I'm putting in an ls and that's going to cost me.

[Tweaked Zed]

Tried all this myself. I do not autox, just drive the car (69 camaro) everywhere. Including thru the Rockies on some nice roads, and some not-so-nice roads. The 550# springs were HORRIBLE on the rough roads. Beautiful on new pavement! But that's it. I went back to 350# and the ride is MUCH nicer. With my swaybars on the car I don't notice a handling difference either (on the public roads). Like I say tho, my car is a driver and it depends totally where you are driving your car. I went with what I read on here for the 550s, and hated them. But we don't have the nice smooth roads of the southern states it seems. LOL. And this is just my .02.

[Ishmael]

Your .02 are worth a lot actually. I was hoping to hear from somebody who would be driving a similar car in a similar fashion with similar equipment. thanks for the input.