Wikkid911

Hi All,

May sound like a bit of a daft question this but only if you already know the answer.
I have heard the term unsprung weight a few times. What does it mean, can you affect what it is, how is it measured. Have we all got it? I know Christer will probably have some BUT will his be better than mine?
Cheers,

Dave
'90 C2

Andy Roe

Dave,

Un-sprung weight is everything that is not supported by the suspension. ie. the wheels etc. By buying some light weight wheels, you'd be reducing the un-sprung weight of the car.

Andy

DaveK

We've all got it. Not sure what the technical description will be, but it's basically the stuff between the springs (suspension) and the road. So - your wheels, brakes etc.

You can affect it - most obviously by changing your wheels for heavier / lighter ones. Reducing unsprung weight is a good thing.

warmfuzzies

Reducing unsprung weight or mass is most defintely a good thing, providing you compensate with the settings of the suspension.
Just reducing the mass alone might give results to suspension movement that weren't originally calculated into the design spec.
Mass and velocity are the key issues here. Controlling them is the art.

kevin

Wikkid911

Cheers Andy, Dave.
I saw a programme a few weeks back covering an auto show in America. They were showing wheels they had developed that were 28" in diameter. They were saying that the rolling mass of the wheel was so great that once the wheel was in motion it would be difficult to stop. It was here that I heard the term unsprung weight so I guess the diameter of the wheels not just the weight must have some bearing on it?

Dave
'90 C2

DaveK

Only that the bigger they are, the more they are likely to weigh.

Christer

Your question doesn't make sense.

I can't really add anything to the replies already posted, other than agree that a larger diameter wheel will have more centrifugal force. I don't think this counts as unsprung weight though.

I would guess no one has less unsprung weight than Mr. Boggiano at the moment, though his handling might be slightly tricky.

Wikkid911

Christer,
I knew you would have some!!! I'll let you know on Mr Boggianos when I meet him later this month.

Cheers
Dave
'90 C2

Christer

Knew I would have some what???

johnfm

Unsprung weight - as the terms suggests - is any mass that is not supported by the suspension system, ie the suspension systems themselves, and the wheels, tyres, brakes etc. SO, the mass of the car, people in it, the engine - anything that bounces up & down on the springs is SPRUNG WRIGHT.

Why is it important?

In real terms, when the wheels go over ripples & bumps, you want the tyre to move up & down so it can follow these bumps & stay on the road - if the tyre is not on the road surface you have VERY little grip! If the mass of the unsprung suspension system is very high, it will need very high spring rates to keep it on the road to overcome the linear inertia of the system. There are also probably some very good steering geometry reasons, not to mention energy losses, the size & strength of components and others.

A clever car designer can probbaly tell you the most important reasons in laymans terms.


The rotational problems of the mass of the wheels is another problem.

Wikkid911

Sorry Christer,

It was my attempt at humour/ a joke. Not funny really. What I meant was you usually have an answer/ opinion on most things so I thought I would bring you to the forefront of the discussion. Dont worry, I wont attempt any more jokes with you, after all this is a serious technical forum.
Cheers,
Dave
'90 C2

John Boggiano

Must be the heat - it's getting more like the 993 board all the time!

Except that we apologise afterwards!

Wikkid911

OK, Sorry Christer.

John Boggiano

LOL - Dave, - meant you already HAD apologised!

Let's just take it as read that everyone is sorry if they've offended someone.

Unless they meant to, of course!

And I'm sorry to have pulled this off topic.

DaveK

I've slipped into an alternate universe. People are apologising to Christer for offending him!