Shock Talk, lets have it!

[IronFreak]

So I have been throwing some ideas around in my head. I know when it comes to figuring out shocks and springs many things come into play like rates, sprung and un-sprung rates and so on. I have played with some calculators when I was building my jeep to figure out spring rates, but I am having a hard time finding anything to calculate compression and rebound for road racing.

So here is my question:

Whether it be a book you've read, your own experiences or calculators you've used would you share them with me? This is an area I really want to learn more about to continually understand the dynamics of why my car does what it does. (Update) - I just picked up the book "Competition car suspension - a practical handbook" after it was suggested by one of our site sponsors.

And please don't tell me to go buy adjustable shocks (I already have them). That's not why I am asking the question, This is to gain knowledge, and understand how and why a shock does what when different variables are involved.

Thanks r3v!

[IronFreak]

No one?? Seriously, I know there are guys on here that can give some sort of feedback....

[Komzorz]

bump because I'm also interested in this. I've read stuff over the years but don't have a solid source.

[IronFreak]

I picked up the book "competition car suspension, a practical handbook" after it was suggested to me by one of our site sponsors.

[bmwguy325is]

I just paid some one. Of course I didnt just go buy konis or bilstiens either.....

[IronFreak]

I just paid some one. Of course I didnt just go buy konis or bilstiens either.....

Explain......

[Eric]

That's not why I am asking the question,

I hope you realize that you did not ask a single question in your post.

[bmwguy325is]

Explain......

Ok. I called up this shop. Ill drop their name. Performance Shock. I siad Id like to upgrade my suspension. I then told them Id like an autocross/track set up that would give me repeatable results when making adjustments.
I gave them the sway bars Id be running and they figured out all the rest.
Oh and to get all the wheel rates and stuff perfect they borrowed an E30 to mock up my setup.

[acolella76]

That's weird that they did that, because both sway bar thickness and 'wheel rates and stuff' are fairly negligent when valving shocks...

I've never built a set based off of any of those variables, and I doubt Ohlins does. Extended length, travel, compressed length and bump/rebound stiffness are what matters.

[IronFreak]

I hope you realize that you did not ask a single question in your post.

Good call, thank you for pointing that out. I fixed the first post up a litle bit. I know that you run AST 5100 I believe on that sick little 4-door. With all your track experience, what made you decide on those versus other brands?

That's weird that they did that, because both sway bar thickness and 'wheel rates and stuff' are fairly negligent when valving shocks...

I've never built a set based off of any of those variables, and I doubt Ohlins does. Extended length, travel, compressed length and bump/rebound stiffness are what matters.

The more I read about shock rates it sounds like it comes down to a trial and error system. There are so many variable involved from car to car that one setup won't be a direct fit with the same performance on a different car unless they were exactly the same. I believe that you run BC coils on your ride, how have those been working out for you?

[Berkut]

IMHO, there are two ways to go at this:

Number one:

You get a shitload of data from the shock manufacturer, spring, car and track and crush a lot of numbers. Then you'll get a value of what you want. If you want to go this route I definately recommend Race Car Vehicle Dynamics, and the exercise book as well.

http://www.bentleypublishers.com/automotive-reference/engineering-and-motorsports/race-car-vehicle-dynamics-textbk.html

This requires some previous knowledge, especially maths and algebra. If you've had/have a Mechanical Engineering degree and paid attention to whatever class they discussed Vibrations in machines, etc. makes things much easier.

A much less cumbersome and technical book is the one you picked up but it doesn't go that deep into the topics.

Mind, the books won't give you any magic formula or tell you exactly what happens when you do things, that's the bit where practice and experience go a long way.

Now, is it easy to get the information you want from the manufacturers? Absolutely not, and it will be hard unless you're doing some development for them, or that's been my experience.
You can buy and measure them and go from there, but some dynamic variables are still not easy to measure and could be provided by the people who designed them.


Number two:

Go to someone you know understands what they're doing, I've seen "reputable" shops doing absolutely disastrous things and see what brands they know and if they can help you set it up, which may happen if you buy from them instead of the cheapest internet deal around. If they know the shocks, they'll be an invaluable source of information, from a starting point for your car to how much to adjust and how the shocks behave.
You'll learn through practice and if you give them feedback and they're good folks, they'll help you out all the time.

You can do both of these together, and it would be the best, but you can also go around checking for online reviews and base your opinion on that instead.


I actually got some knowledge and researched stuff a little so I had an idea of what was good, bad, how technicalities changed, etc. But then I actually got to a couple of good race guys and asked around who was the best suspension guy for BMW, talked to him, and decided to go with a brand that might have been slightly worse than what I could've gotten for the price but all that came with the advantage of being able to tune it and learn from there. I know sort of know how to get the shocks right, at least the way I like them, sometimes against what the manufacturer says.

Then you try this, try that, improve here, get less grip there, etc. and your experience and practical knowledge goes up. Next time you can probably go with a brand that doesn't have that good a technical support for you but manage it better.

I know if I started off with no help or just the theoretical stuff, I wouldn't be very happy for a long time until I got everything properly done, and in the end, just the useless testing needed to get to a base point would've cost me much more.


Regarding manufacturing of shocks, if you want something really good it's bound to be adjustable, and at least double as no manufacturer would do a shock for your specific use and car.
Of course you can get a non adjustable kit including springs for something that resembles your car and use, but it's going to be very dependent on who developed the kit.
When they initially design a shock they have a set of parameters that should be a good compromise for some springs that might be the most commonly used. Then it's the hard bit about getting it just right.

Some are still better and worse, some have more internal damping and need slightly less spring stiffness, etc. But I'd rather have a cheaper unit that's been correctly set up than a more expensive one that's out there with the set up. Up to a certain point :)

Sorry about the length, just carried myself away there for a while. Hope it's not too confusing.

[IronFreak]

^^^Thank you very much. And I understand that this isn't something that I am going to learn over night, but the information you provided will help me move in the correct direction. The more I dive into shocks the more confused I get haha. calculating spring rates are one thing, but shock theory is a whole different animal.

[Berkut]

Don't take me for a pro or anything like it. It's just something that I'm interested in, and hope I haven't said anything wrong or misguiding.

By the way, I forgot, I run KW Competition 2 way adjustables with rear coilovers and custom spring rates. In spite of the very poor service times on builds/rebuilds, the costumer service is good, even if sometimes they get things wrong so in general I'm happy with them.

Anyway, what are your plans?

[IronFreak]

I have been throwing around the idea of true rear coilovers. I'll go with all the parts I have now, but I want to continue researching it. I know some companies make them especially if you up to a 5-lug setup. There are some great shock manufactures out there that offer threaded body shocks. True coilovers are common on 2002 setups as their rear subframe is designed a little differently. With the mods I am doing to the chassis the shock towers would be able to support the force of true coils, its the E30 rear shock mounts I'm worried about. Seems like they'd need a little reinforcing to hold the cars weight at that point.

[Berkut]

It's something you hear about but never actually seen one with the deformed tower. Still, cage it, double skin it, or even rebuild with thick metal out back and give some more room the wheels.
No way you can use the standard mounts on there. Several options if you go true coilover, either inverted shocks (more room) with something like this:

Or just a good solid aluminium top mount, doesn't need to be as fancy as this but:


Something to bear in mind, standard e30 with true coilovers, not that much room for tires in the back. so think big flares.

Regarding threaded shocks, it's the same for 4 or 5 lug applications, the trailing arm is the same/similar.
But you should be able to find one easily that's threaded, on budget, it's another story. :)