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  #1  
Old 28th February 2010, 02:14 AM
correl correl is offline
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Default The Front suspension

I was thinking today about how the standard front arms seem dangerous..


Looking at the way the suspension is set up the lower arm takes all the wieght of the car while the upper are just becomes a track contol arm. Now on the original donor car the weight of the car comes down on the top of the knuckle, the lower part of the knuckle is not designed to take wieght. Anyone that has built these cars how you put a brace of any sort between the upper and lower arms? It would take the weight off the lower joint and distribute to the upper arm also.
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Old 28th February 2010, 09:17 AM
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I think if you did all the drawings of where force is applied, you would find a large proportion of the force goes lateraly through the top wishbone.

The front suspension nuckle will not stay upright without the upper wishbone so the force and weight must be being taken somewhere.

TT
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Old 28th February 2010, 09:23 AM
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It's also a standard basic design that has been used for decades in all sorts of cars form humdrum family compacts to formula one cars.

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Old 28th February 2010, 09:23 AM
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Thumbs down Dangerous

Dangerous ..... That's a bit of a strong word to use there

I am no design engineer but even I can see that the lower wishbone does not carry the entire weight of the front of the car !!??
Most of the weight will be tranfered to the main chassis structure Via the front shock's

The addition of braces or drop links as they are better known will only serve to assist anti roll .... Being that the Roadster does not suffer badly with body roll, not a lot of point fittng them !!??

Do you not think that VOSSA might have picked up any dangerous design defects !!!

There are thousands of 7 type cars out there .... All using the same type of wishbone design & that includes the original Lotus 7

One last point !! This type of wishbone design was used for many years on F1 cars & even with the advent of the Carbon fibre age .... Current F1 wishbones are still not a world apart ( theory wise ) to our humble wishbones .

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Old 28th February 2010, 09:43 AM
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What is the problem with the lower wishbone taking the load and having it absorbed by the shock absorber? Its exactly the way its meant to be. As pointed out, this is a tried and tested design. Bearing in mind the car isn't the same weight as a Sierra, so its hardly dealing with the same loads.

Hold on.... your post is at 2am! I'm sure your here to wind up this forum.
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Old 28th February 2010, 09:54 AM
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you would probably find that if you left off the inner lower wishbone bolts, that the car would still remain off the ground with the wheels upright

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Old 28th February 2010, 10:17 AM
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Yoiu are all not seeing what i mean. The lower arm is attached by a ballljoint yes. In Formula 1 the knuckle is designed to take the weight there. In the case of all the cars used to build this car the shock and spring is normally standard in the top of this knuckle. The just look and the size difference in the metal between the top and the bottom of the knuckle. On the kit cars the rolls the parts have to play are reversed.

Think about it the lower ball joint has the whole weight of the car and have to contend with the spring and shock stopping it from giving on bumps while the upper arm moves freely and just follows the knuckle.


Are these lower joints as a question common for replacing on mots by any chance? Bet the upper on ain't so prone to it.


Last edited by correl : 28th February 2010 at 10:31 AM. Reason: Adding image
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Old 28th February 2010, 10:33 AM
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Quote:
Originally Posted by deezee View Post
Hold on.... your post is at 2am! I'm sure your here to wind up this forum.
No just thinking about what i am building and so couldn't sleep
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Old 28th February 2010, 10:36 AM
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A more general question about the design of Lotus 7 inspired kitcars, might be better put forward to the Locost Builders.

No one has had a problem with the design yet. I'm sure borrowing parts from cars are putting them in a different chassis isn't what the manufacturer intended, but it works.
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Old 28th February 2010, 10:36 AM
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The upper arm does not just follow though, Because the wheel center is further out than the hub center line the wheel tilts inwards under load, this transferes across the wishbone into the chassis.

See my crude attatched drawing.

Production cars used double wishbones for decades before mcpherson stuts became common.

TT
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