TTB coil-over spring rates/lengths

[tcm glx]

Hey guys,
Helping my brother get his coilovers set up, and will probably pick up coils this weekend at Kartek for him (they have the open house, and usually have some deals there).

For a 12" coilover, what are the lenghts of coils you should be ordering, I can not remember what lenghts mine are.

thanks

[SteveG]

Your coils should have the part numbers on them.

[philofab]

Rule of thumb for dual coils is usually each coil is same length as travel. So 12" in your case.

Length and rate should be printed on the coils and possibly engraved on the ends.

The numbers are usually ID.LENGTH.RATE

Something like 300.1200.400 would be 3" ID, 12" long, 400lb.

[ChaseTruck754]

I think the coil choice varies a bit from builder to builder. I often hear people like the lower coil to be a bit longer than the stroke - so instead of 2 12" coils you'd have a 14" lower and 10" upper.

[tcm glx]

Thanks guys, I have the numbering for my lower coil, which is a 300.1600.550 so 16" with 550 lb rate, its the upper I can not find the reading on anymore.

What I was looking for is what combo in spring length should I have... so two 12", a 14 and a 10" etc etc


***Fixed for Philo!

[philofab]

Thanks guys, I have the numbering for my lower coil, which is a 300.1600.500 so 16" with 550 lb rate, its the upper I can not find the reading on anymore.

What I was looking for is what combo in spring length should I have... so two 12", a 14 and a 10" etc etc

That's a 500 lb spring.

[shockseals.com]

I recommend at least a 2" longer than stroke bottom coil. Having your coil slider slide over the bump cap which is what happens when you run a same lengtbtm coil as stroke....sucks.

You know your stroke and you know your preload and hopefully where you want them to crossover to single rate at so choose your spring lengths based solely on that. The only rule of thumb with coil springs on coilovers is....there is no rule of thumb. Its just simple math. I only recommend springs that have the travel available publicly...and the only company that offers that is eibach.

King will give you terrible "rules of thumb" when you call about coils like: "spring travel is usually half the overall length" and thats the worst advice I have ever laughed at. Sad but true.

[Deleted Account]

300.1600.550 is a 3 inch id, 16 inch long, 550 rate spring.

[philofab]

Admin edit: The following several posts were stolen from the BajaF250 thread (http://www.gofastbroncos.com/forum/view ... f=19&t=864) and transferred to this thread....

Got by Mirage today and got the shocks reshimmed. But, Bill didn't have the springs I need so we'll have to order them. Two-day shipping from the east coast on springs isn't going to be pretty!

Are you changing spring rates Tom? What were you running, and what are you planning on running?

What was changed that is causing your valving and spring rate to need to be different?

[BajaF250]

Ok, the spring rate has always been just a tad soft and the shock valving is way too soft as well. So, when we were out testing last week, I ran it on a high speed section and the truck did ok, not too technical... we then moved to a pretty heavily whooped out section to put the suspension through a little more agressive cycle and I've always known that my front springs are a little too soft and they don't match the rear. This causes the front end to dive too much and the rear to push and jump. I was actually shoveling heaps over the hood...

Next, the biggest problem I have (among many) is that my rear rebound is waaaaaay too soft... the rear end hops around because the springs are pushing the rear up and the shocks can't control the rate... I find the rear end skips down the road when I get into anything with a few bumps. The front shocks also need more compression and rebound to match. I actually think I need to go to a bypass in the rear because of the progressive nature of the leaf springs. At full compression, the springs have a tremendous force and need much more aggressive rebound damping, but in the middle, I don't need nearly the damping. So, bypass' in the rear may be ultimately the way to go. I could benefit from bypass' in the front as well, but no where near as much compared to the rear... plus, I don't have the room to add a bypass in the front without MAJOR change. So, that's not on the table.

I've always known that these deficiencies existed by didn't know how to quantify the required changes. (Again, neophite) Yes, I realize that tuning the suspension is really an iterative process and that these changes will be monumental, but not final. But, I had the advantage of a highly experienced and expert tuner last week and he's helping me understand how to quantify the required changes. The main reason I'm changine things now.

I'm currently running Hyperco 14" 500 over 14" 600 primary with crossover at about 50% which gives me an effective spring rate of 272 lbs/in. Remember, I have 14" shocks in the front and I'm using every possible inch of the stroke. They are leveraged to give me 18" of travel. So, this limits my spring selection. Given what I've built, these are know limitations and they are the parameters by which I have to work. It's all about middle ground and compromise to get the best I can given the physical boundaries I have.

I have a couple of options... I'd like to switch my top spring rate to 600 lbs/in at 12". I'll keep the bottom spring at 600 lbs/in but increase the length to 16". This will give me about a 10% increase in effective spring rate (300 lbs/in) and bring the crossover up a little. But... unfortunately, I can't seem to find a 12" 600 lb spring. Hyperco doesn't make them. Bill seems to think that they may have made a custom 12/600 and will check this morning. (And, I really don't want to go with Eibach springs! Acutally, give my layout, they won't work.)

If that combination doesn't pan out, I'll go with a 10/600 upper and an 18/600 lower. This will still have an effective spring rate of 300 lbs/in but the crossover will come in much sooner which will reduce some of compression rates I'm experiencing.

My goal is to get the new springs in by Thu to make a Friday testing run... we shall see...

[tcm glx]

Tom,
Super cool that you are working on the setup. I always find it very interesting the different spring rates folks work with, and what they consider to be too stiff, and not stiff enough. I have heard folks running 400/450, 350/450, 500/500 a myriad of combinations. Very interested in hearing how your results turn out Tom. Keep us posted, and some pics or video would be great for us to view!!

[philofab]

Every truck as well as every driver is different. Nice to know that I might be in the ballpark on Bertha. I bought what everyone considers very heavy springs for it (600 & 700 I think). I don't think a 400/500 combo will hold that beast up.

[tcm glx]

Every truck as well as every driver is different. Nice to know that I might be in the ballpark on Bertha. I bought what everyone considers very heavy springs for it (600 & 700 I think). I don't think a 400/500 combo will hold that beast up.

Im with you Philo. I am on a 550/500 combo... and I think another 50lbs would feel good. Not a big enough issue to hassle with... but 600/700 looks about right for BB

[PaulW]

Ref: Spring rates = 350/400 (187), (500/600 (272), 500/400 (222), 600/600 (300), 600/700 (323)
Issue is which rate to use at the bottom of the stack
The lower rate should ride easier until it hits the collar then the even lower rate kicks in.
With mine I have the thing sitting on the lower spring and use it for ride height and camber adjustment. I suspect the higher rate spring is the bottom one on my truck?

So what is the correct way to choose the spring stack when the springs and different rates?
I wonder if I still do not understand??
Then here is another question. Why use such high rates. Fat shocks and Hyd bumps should be able to deal with an F250 or a Bronco???

Example with the 600/600 a huge amount of rebound setting will be necessary to control such a high rate as 323

I still say I probably have it all wrong?
Response please
Brian K.?
Paul

[tcm glx]

Ref: Spring rates = 350/400 (187), (500/600 (272), 500/400 (222), 600/600 (300), 600/700 (323)
Issue is which rate to use at the bottom of the stack
The lower rate should ride easier until it hits the collar then the even lower rate kicks in.
With mine I have the thing sitting on the lower spring and use it for ride height and camber adjustment. I suspect the higher rate spring is the bottom one on my truck?

So what is the correct way to choose the spring stack when the springs and different rates?
I wonder if I still do not understand??
Then here is another question. Why use such high rates. Fat shocks and Hyd bumps should be able to deal with an F250 or a Bronco???

Example with the 600/600 a huge amount of rebound setting will be necessary to control such a high rate as 323

I still say I probably have it all wrong?
Response please
Brian K.?
Paul

More great points Paul. Now looking at this info, it starts to match up with the coil rate you would get if you kept a standard coil and shock setup.

Mods, how about breaking these comments regarding the coil spring leights, and ratings into a sticky in the tech section?

[PaulW]

Ref: Spring rates = 350/400 (187), (500/600 (272), 500/400 (222), 600/600 (300), 600/700 (323)
Issue is which rate to use at the bottom of the stack
The lower rate should ride easier until it hits the collar then the even lower rate kicks in.
With mine I have the thing sitting on the lower spring and use it for ride height and camber adjustment. I suspect the higher rate spring is the bottom one on my truck?

So what is the correct way to choose the spring stack when the springs and different rates?
I wonder if I still do not understand??
Then here is another question. Why use such high rates. Fat shocks and Hyd bumps should be able to deal with an F250 or a Bronco???

Example with the 600/600 a huge amount of rebound setting will be necessary to control such a high rate as 323

I still say I probably have it all wrong?
Response please
Brian K.?
Paul

More great points Paul. Now looking at this info, it starts to match up with the coil rate you would get if you kept a standard coil and shock setup.

More discussion requested. My comments are just off the top of my head and need evaluation. I hate to put out bad info without input.
PW

Mods, how about breaking these comments regarding the coil spring leights, and ratings into a sticky in the tech section?

[Polarcub]

Tom very interesting thanks for taking the time to share the info. One point I would like to add on the rear setup though. I am sure you already know this but the front plays a huge part in how the rear is tuned. While I think bypasses in the rear are probably in your future wait to make any changes until the front is where you want. I was very surprised with the bronco just how different the rear was as the front changed. With my initial set up 5100s in the front and 5150s in the rear all worked well once i changed the front up with the buckets and the 14" shocks the rear needed to be changed and tuned with it.
I have no input on the coils as I am still learning hahaha seems that there are so many variations that trial and error becomes the methodology.

[philofab]

The number that matters more is the wheel rate and the curve of wheel rate that increases during compression.

[BajaF250]

Ref: Spring rates = 350/400 (187), (500/600 (272), 500/400 (222), 600/600 (300), 600/700 (323)
Issue is which rate to use at the bottom of the stack
The lower rate should ride easier until it hits the collar then the even lower rate kicks in.
With mine I have the thing sitting on the lower spring and use it for ride height and camber adjustment. I suspect the higher rate spring is the bottom one on my truck?

So what is the correct way to choose the spring stack when the springs and different rates?
I wonder if I still do not understand??
Then here is another question. Why use such high rates. Fat shocks and Hyd bumps should be able to deal with an F250 or a Bronco???

Example with the 600/600 a huge amount of rebound setting will be necessary to control such a high rate as 323

I still say I probably have it all wrong?
Response please
Brian K.?
Paul

Hey Paul,
I can give you my approach and the approach that the spring guys (professional tuners) use in my experience. I hope this isn't too elementary so bear with me...

I think, to answer your question directly, as I understand it. I use the softer spring on the top of the stack and the stiffer spring on the bottom of the stack. The concept is... if you use dual springs with a crossover (a stop that limits the top springs motion) you have a dual spring rate. The spring rate calculation is k1 x k2 / k1 + k2. So, if you have a 500 lb/in over a 600 lb/in your effective spring rate will be 272 lbs/in. As the suspension goes into compression and the spring separator hits the crossover stop, you isolate the upper spring and are now solely on the lower spring. Your spring rate now goes from 272 lbs/in to 600 lbs/in. In application, as you hit the bumps harder, you now have a higher resistence force against the greater force of the wheel hitting the bumps. So, your spring progression will increase as your need for resistent force increases with more aggressive wheel/bump forces. You want a softer spring rate on the top to absorb the small bumps like washboard and on road small bumps for a "cush" and "plush" ride and the higher spring rates at the the bottom as the wheel travel brings you to bump to resist those greater forces.

You also have to take into account the rate at which your wheel travels. This is accomplished a couple of ways and folks sometime take the different approachs. First is to control wheel travel with the spring and some folks control the travel with shock valving. But, the basics are, control wheel motion with springs and control springs with shocks. Shocks are just dampers, they remove excess motion the spring imparts.

The proper way to determine your spring requirements is to get the weight of the truck at each corner... this will give you a static weight the spring must support. Then you need to determine your wheel motion ratios, how much you are leveraging the spring in relation to the centerline of the wheel travel and how much your shock is out of vertical. Then, you need to apply that wheel motion ratio to the static weight of the truck. That will result in a required static spring rate. So, I would argue that the BajaF250 is a little heavier in the front end than some Broncos... my front end weight is 3220 lbs. (In actuality, I remove the unsprung weight for a more accurate spring calc). That means your ride height static spring rate is calculated on the actual weight of the truck.

Next is the magic part. In order to determine your crossover point if using dual springs and how much ultimate spring force you need. This all depends on your intended use for the vehicle. If you want a cush ride and are not going to beat it, you can go with a much softer rate, but if you want a little extra speed in the whoops, you'll need a stiffer bottom spring to resist the more aggressive wheel travel and wheel rates you'll encounter. The trade off is with the stiffer spring, you'll have a little stiffer ride.

The next thing is to tune your shocks to you spring pack and use. Again, it it directly related to the weight of the truck, the spring rates you're using and your intended use. I'm increasing my spring rate by 10% mainly because I'm able to drive a little more aggressively now that I have a cage, plus a little extra added weight on the truck due to the material used in the cage itself. So, with a little added weight and a more spring, along with a little more aggressive driving, I need to increase both my compression and rebound valving in my shocks.

Where I have the most difficult time is to quantify the shock/valving/shim stack requirements. There aren't any formulas available that I'm aware of and it takes experience with each type setup to know how to valve. Then, you have to go out and test to see if the truck is doing what you want. If not, you iterate through by changing the shim stack until it's valved the way you want the truck to handle.

Sorry for the long winded response and I hope I addressed your question...

[BajaF250]

Tom very interesting thanks for taking the time to share the info. One point I would like to add on the rear setup though. I am sure you already know this but the front plays a huge part in how the rear is tuned. While I think bypasses in the rear are probably in your future wait to make any changes until the front is where you want. I was very surprised with the bronco just how different the rear was as the front changed. With my initial set up 5100s in the front and 5150s in the rear all worked well once i changed the front up with the buckets and the 14" shocks the rear needed to be changed and tuned with it.
I have no input on the coils as I am still learning hahaha seems that there are so many variations that trial and error becomes the methodology.

Jeremy,
You are absolutely right, the front does drive the rear, but I also have to take into account the very different type springs I have from the front to the rear. Again, the true answer to my application is to have two shocks per wheel given my specific spring setup. But, I'm not willing to completely redesign my suspension at this point to accomodate that. So, I need to deal with my particular design with the best compromise solution.