unsprung weight ?

[Phil]

what does this mean please.

 

 

[sjwb]

That which is NOT suppoted by the suspension. Wheels, discs, hubs - ad nauseum. One of the reasons Porsche use aluminium wheels nuts is to reduce UW.

 

Steve B

[Phil]

So I take it that the lower the weight of these components the quicker acting the suspension reterning

the wheel to the road hence better handeling, braking and grip.

Does this mean that harder springs do the same thing at the same time reducing body roll simular to fitting gas struts rather than oil.

 

 

[Julian Thompson]

Not really Phil. I'm no expert on this, but in laymans terms the suspension settings only control the way that the sprung weight is managed.

 

The unsprung weight is by definition not cushioned or acted upon by anything you can alter and so is free to pull the chassis around as it wants. This is bad, obviously because it increases inertia and makes the car less responsive.

 

Unsprung mass is especially bad when it is rotating, unsprung mass - ie wheels!! because the spinning action acts like a centrifuge and makes the weight effectively more than it really is, by a lot. Hence the lightweight wheel argument!

 

I'm sure somebody like PC or Arnie can explain this much better!

[DohNut]

Also worth pointing out that unsprung weight should be viewed with the perspective of the car that it is on. A wheel/tyre/brake combo that may be fine on a porche will not be fine on a seven because it will be a much bigger percentage of the overall weight of the car.

the unsprung weight should be a very small percentage of the overall weight.

[V7 SLR]

You should watch the Christmas Lectures on the BBC. They showed unsprung/sprung weight a few years ago using planets as models. For example, take a planet and put in orbit a large moon (Earth is a particularly good example). As the Moon revolves around the Earth the Earth also revolves around the Moon, although the circle described by the Earth is very much smaller than that described by the Moon due to the differences in mass.

 

Now take the Sun and put into orbit a pea. Although the Sun technically revolves around the pea, the circle that the Sun describes is minute compared to the MASSIVE one that the pea describes.

 

They tried to show that a pair of bodies act upon each other with equal force, but the effects exhibited by each body depends on their mass, and therefore their inertia.

 

Now consider cars. A Rolls Royce rides very smoothly despite probably having very heavy wheels, hubs and brakes (all unsprung) simply because the difference between the unsprung to sprung (body et al) weight is large.

 

In a Se7en, to achieve a similarly good ride you need to create a similarly large difference between unsprung and sprung weights, but as the sprung weight of a Se7en is so minimal you have to resort to quite esoteric materials in order to reduce your unsprung weight enough.

 

That make any sense at all?

[V7 SLR]

Forgot to say, they also showed the effects of different "gravitational" forces by changing the spring they used to hook up their planet-models. Can't remember the outcome of this...

 

You could try an experiment with a heavy mass linked to a light mass with a pen (biro) spring. Then pull/push the small mass and see what effect it has on the larger mass. Then pull/push the large mass and see what effect it has on the small mass. If you repeat the experiment with increasing strengths of springs you will eventually arrive at an optimum I guess... one where you have good control over the small mass without transmitting too much force to the large mass.

 

I think.

[ashaughnessy]

V7 SLR wrote: "Forgot to say, they also showed the effects of different "gravitational" forces by changing the spring they used to hook up their planet-models. Can't remember the outcome of this..."

 

Either ice-age conditions or catastrophic drought, I would guess :-)

[R2D2]

Suspension is supposed to allow your wheels and tyres to follow road, irregularities while the body of the vehicle travels smoothly.

 

Suspension should also keep the wheels and tyres in maximum contact with the road for the best performance.

 

For a suspension to be effective, it must allow the wheels and tyres to accelerate and decelerate rapidly up and down while not allowing them to move excessively

 

The springs prevent the wheel assembly from travelling too far, while the dampers prevent oscillation of the spring.

 

Every time you hit a bump, the wheel assembly is accelerated upwards, decelerates to a stop, then accelerates downward till it reaches equilibrium. If the wheel can't accelerate fast enough, shock is transmitted to the body, which may upset the balance of the car.

 

As an example think of small, sharp edged speed bumps versus those gigantic, but wide, monsters. The sharp edged ones are much more annoying to traverse because they require the suspension to accelerate more rapidly.

 

Imagine going over some bumps in a corner. There will be a very rapid series of accelerations and decelerations.

 

If the unsprung weight is low the wheel will accelerate upwards and downwards more quickly and this means it will follow the road more closely. As the shock absorber and spring have to control less unsprung weight it means they can stop and start the motion of the assembly more easily.

 

If the unsprung weight is high compared to the sprung rate the car will jump around on bumps and steer and grip quite badly.

 

Cornering performance and traction is directly effected by the proportion of sprung to unsprung weight of the vehicle.

 

Reducing unsprung weight allows the vehicle to respond much quickly to the road. It will keep the tyres in more consistent contact with the surface and improve traction and allows faster cornering.

 

 

[RESOLVIWOLF]

sounds like planet polarity reversal - we're due for that pretty shortly here on earth, and yes, when it does occur all life as we know it will be wiped out ("ice age" is putting it midly)

[Phil]

ICE AGE?

 

Where can I get some studded tyres cheap sounds like fun and I get to use my heater.

 

Thanks to Chris Flavell, well explained, have you thought about sending this in to LOWflying to help others? I have sent an email to the editor to see if he would inclued this sort of thing on a handy hints and technical page, I also would like members to send in photos and words on how to do things like oil changes with the intention of having a pull out page to build up your own personal manual, what do you think?

 

 

[stevefoster]

As if ali wheel nuts would help a Porsche....

[sjwb]

Well, I guess that Porsche know something that you do not!

 

Steve B