LocostUSA.com

Try this Excel sheet. It is based on the Staniforth calcs. It will make more sense when I get my suspension stuff done and it assumes that your chassis is plenty strong. Sorry but a book chassis is not strong enough.

http://www.ncs-stl.com/Files/ChassisCalcsPublic.xls

AW

I have 500lb in front for an effective rate of around 230lbs with the MK wide a-arms. In rear with live axle I have 175 or 200.

I've not driven the car yet and took the recomendations from a UK Track car. With the bike engine I may need to lighted the front a bit. I have some 350 and 400lbs so should find something that works.

I expect to run a 3/4 hollow swaybar in front. I'm not yet convinced I'll need one in rear.

Here is a dumb question. Let's say I have a shock with a spring rate of 500 lbs. Does this mean that the first inch of compression requires 500 lbs of force? If so, then how much additional force do I need to compress the shock another inch (to 2") how about 3 inches?

Is it 500 lbs to 1", 1000 lbs to 2" and 1500 lbs to 3"?

Or is there another formula, or a nonlinear equation here?

Help!

Yes, 500lbs per inch so 3" compression = 3 x 500lbs = 1500lbs.

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

That is correct. It will be linear, with linear rate springs.

Now look what happens if you pre-load your springs, say 1". For the first 500lbs load, nothing happens, because it's still trying to overcome pre-load. Nasty.

G

_________________
The Lethal Locost
The Lethal Locost 2 - Even More Lethalerer

That's right, and a very good point!

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

Hopefully your preload is less than your corner weight though, so depending what you are trying to figure out you may be able to ignore it.

Since it was brought up, theres a good discussion on preload in the DSR forum.

http://p081.ezboard.com/Preload/fdsrfor ... =109.topic



Andrew

hay guys

how do motorbike shocks go as far as being used for suspension.

my buils is a k6 gsxr1000 motor, but i managed to get two bikes, one of which has a good motor, and the other to get the electrics and etc out of.

but i have ended up with two shocks, which have preload, high speed and low speed compression adjustment, and rebound adjustment.

also have two neat mounting point on each one.

I'm usin Yamaha R-6 Shocks for the front. Spring rate is 495# according
to Yamaha. They have 2.6 inches of travel, wheel rate is about 225-250 lbs.
my car uses a Volvo B230 so it's a little heavy. Rears are QA-1's with
a 175# spring on a solid rear axle so wheel rate is about 175. I'll see how it
all turns out when all is said and done. I get 4" of travel front and rear.
Rear has less sprung weight.

_________________
Volvo 240/P1800 Based Locost
2004 Aprilia Mille Factory
1988 Volvo 240 5 Speed ( For Sale)
2002 Toyota Tacoma
1999 BMW M3

Long time lurker here and I realize that it has been some time since anyone posted in this thread, but I see no mention of suspension natural frequency. Natural frequency boils down all the spring rate, installation rate, wheel rate and vehicle weight into one number that can be related to ride and compared from one car to another. Natural frequency is the rate that the suspension will oscillate at after going over a bump without any damping. Shocks do change the natural frequency, but finding damping ratios for shocks isn't so easy so most comparisons are made ignoring the shocks.

The calculation is: NF = 3.13*sqrt((wheel rate)/(sprung corner weight))

This will both give a result of Hz (cycles per second)

Higher frequency will give a "rougher" ride but also respond to steering inputs more quickly. Higher frequency will also cause the suspension to "skip" over bumps more and can actually cause worse handling on real roads.

As a rule of thumb, comfort-tuned (soft) family sedans are around 1Hz, performance/autocross cars are in the 1.5-2.5Hz area and race cars above that. Somewhere around 5Hz and you are getting just insanely stiff and probably won't want to take the car off a smooth track.

Hope this helps!

It was mentioned in post #2, though not as thoroughly as you outlined here. Thanks for adding the formula!

G

_________________
The Lethal Locost
The Lethal Locost 2 - Even More Lethalerer

The natural frequency is just a number. Most every builder who starts with what that equation recommends ends up putting in stiffer springs. It's okay as a vague starting point but that's about it.

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

Blueyes, glad you de-lurked. I think it's fine to plug in the numbers, but notice that the result has a large enough range to allow for a factor of 2 maybe, so it will just produce a starting guide range so to speak.

These cars tend towards performance and lower amounts of ground clearance for various reasons. So I think the practical guide will be observing wether your bottoming out your suspension. On the street that give a very rough ride and shocks the suspension and frame etc. On the track that leads to unpredictable and dangerous handling issues.

It's important to have some type of progressive bump rubber and also think of a way to check for bottoming. I tried putting tie wraps on the shock plungers but don't remember if that worked well. With all the electronics available these days, I wonder if anything to collect suspension data, at a reasonable cost is available.

Maybe we should have an electronics / data acquisition topic area. There's seems to be enough technical people here to use that info...

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I think the biggest problem (as with many things like this) is the builder simply not knowing what they want. Some people consider cars with a NF around 1.5Hz to be too harsh and bumpy. Others find 2.0Hz just fine on a daily driver. Of course, that's why springs can be changed. The best use of natural frequency is as a way to quantify how much you have stiffened the suspension and to compare one car to another. If you ride in someones car and they have a 2.5Hz suspension and you like it, you can achieve similar results even though you may have a different car weight and spring mounting locations.

horizenjob: I would prefer to have a car with a stiff enough suspension and enough travel to avoid hitting the bumpstops on all but the worst potholes, but some sort of progressive bumpstop is definitely a requirement!