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Old 06-24-2019, 10:29 PM
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Default Coil over spring rate vs mounting angle

Hi,

I am trying to minimize the space a (single) shock takes up over a rear swing arm suspension and have questions about changing the spring angle and how that affects the load the spring will carry.

I assume the spring rate is 100% when the spring is vertical (90 degrees).

Just guessing on the rest of this:

... if the spring is mounted on an angle where the top is 75% of the full vertical height, would that make the spring rate be ~75% ?

... if the spring top is mounted at 50% of the full vertical height, would that make the spring rate be ~50% ?

Is there a rule of thumb for estimating the spring capacity when mounted at a particular angle (like 30 degrees, etc)?

Regards,
Gary

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Old 06-25-2019, 12:23 AM
Denny Denny is offline
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Your all confused there son. What spring rate is is how many lbs to compress the spring one inch. I have no clue on how to figure out what you want.


Denny
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Old 06-25-2019, 10:58 AM
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I did some poking around on the web and think I found what I am looking for. It is called the "wheel rate". Just trying to understand how the mounting geometry changes the effective spring rate on a suspended kart or other vehicle.

https://www.onallcylinders.com/2015/...your-drag-car/

There is more to it than I expected because I will have to consider the leverage introduced by the mount points relative to the weight being suspended.

Or I could just cut and weld and cut and weld again....

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Old 06-25-2019, 11:04 AM
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Spring rate will not be effected as much as the pressure effectively placed on the suspension due to the angle. And I'm sure it won't be linear, meaning x angle will not increase/decrease suspension effectiveness x amount as well. It will look more like a curve. I think I would be looking at already engineered suspension karts and mimic as close possible.
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Old 06-27-2019, 09:34 PM
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Here is a simple drawing showing a hypothetical swing arm rear end.

The top drawing has the spring rate equal to the wheel rate... so one inch of wheel travel equals one inch of spring travel.

The bottom drawing uses a monoshock lever on the swingarm pivot so the wheel travel can be greater than the spring travel.

I am trying to make this for my Buildoff yard kart and figured I would ask for help in case you have seen pictures of a true monoshock rear on a mini buggy.

I want to have the engine mount to the buggy frame and the swing arm will have a near vertical monoshock behind the driver seat.


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Old 06-28-2019, 08:47 AM
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You are right, and there is a formula, it's called Angle Correction Factor.

It's the CoSine of the angle divided by the spring rate.

The basic rule is the more angle, the less the effective spring rate,
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