Does inboard suspension reduce unsprung weight?

[CHip]

Reading a review of the CSR they mentioned several advantages to having inboard suspension, one of whcih was reducing unsprung weight.

 

I'm probably being a bit thick, but surely unsprung weight is measured from the chassis side of the spring/damper unit. Therefore how can it's location affect unsprung weight?

 

Any ideas?

 

 

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Se7en spotting until my car arrives here

 

 

 

Edited, because it obviously affects my spelling

 

Edited by - CHip on 8 Jun 2005 13:04:06

[Graham Perry]

I think we have debated this in the past and no one was sure as I think you could make the case that anything inboard of the bellcrank is part of the chassis and hence sprung. However I am not an engineer and this is purely from memory so may not be accurate.

 

Edited by - Graham Perry on 8 Jun 2005 14:03:15

[Jason Plato]

Some confusion here maybe , "Sprung" weight is a term used to describe the parts of the car that are supported by the front and rear springs. They suspend the vehicle's frame, body, engine, and the power train above the wheels.

 

The "unsprung" weight includes wheels and tyres, brake assemblies, the rear axle assembly, and other structural members not supported on the springs.

 

so the inboard suspension would reduce "unsprung" weight as the weight of the spring and damper that would impact on the rebound of the wheel is moved to a position of "sprung weight"

 

I was once shown that , if you remove the wheel and spring , then support the chassis . If you grab hold of the brake disc and lift - everything that you are lifting , plus the wheel and spring is "unsprung" .On the rear this of course includes the dedion tube .

 

I imagine the whole Freestyle setup is actually heavier overall as you are adding material , but the unsprung is reduced .

 

Dave

 

Edited by - Dave Jackson on 8 Jun 2005 14:21:12

 

Edited by - Dave Jackson on 8 Jun 2005 14:23:40

[I.Mupferit]

But because the dampers are aluminium, the overall weight difference between the CC standard and Freestyle is slightly less for the Freestyle suspension. I know, cos I've weighed them both, although I can't remember what the figures are.

 

Anyhow, despite any weight or handling advantage the Freestyle suspension offers, you have to admit that it does look the dogs bollox which when all is said and done is the main thing. 😬 😬 😬

 

Brent

 

2.3 DURATEC SV

R 417.39 😬

[Jason Plato]

the std bilstien dampers are very light and made from alluminium .

 

[MikeE]

Dave,

 

I must be being completely thick as you're explaination of why the FS system has a lower unsprung wait lost me.

 

Surely if all component weights were the same as the CC equivalent then the FS system would increase slightly the unsprung weight due to the addition of the pushrod and bell-cranks?

 

 

 

R400 Duratec Build and Modification Pictures here

[I.Mupferit]

Dave,

 

The standard Bilsteins supplied with my kit were definitely not made of aluminium and were quite heavy as a result. As I said I weighed the different components and, trust me on this, standard is heavier.

 

Mike, 'tis true that everything below the rocker (bellcrank) is unsprung weight whereas everything above (dampers, springs and damper tower) is sprung weight. Therefore, as the pushrods are considerably lighter than dampers and springs, the unsprung weight is lower. At least, I think that's how it works.

 

 

Brent

 

2.3 DURATEC SV

R 417.39 😬

[MikeE]

OK I understand what you'er saying but....try thinking of it this way, what you're actually trying to do is reduce the momentum of the suspension such that when it recieves a shock to the system (i.e. hits a bump) it can react quickly and return the tyre to contacting the road, right?

 

Well in the description you give the springs are still contributing to the momentum of the system whether they are in the traditional or inboard configuration, and as I said if all weights are equal then I don't really see how it helps (unsprung weight)

 

R400 Duratec Build and Modification Pictures here

[Mike Bees]

I'm with MikeE on this... 'Unsprung' mass is mass which is moved directly by the motion of the wheel (or more accurately the motion of the surface of the tyre on the road) without being transferred by a spring. So the pushrods, bellcrank (tho' not necessarily the whole mass of the bellcrank since it converts linear motion into a rotational motion, hmm...) and the end of the damper which moves are always 'unsprung'.

 

Mike

[rgrigsby]

I think the benefits of the freestyle system are not really down to a reduction in unsprung rate but rather from a complete redesign in the way the suspension works, ie from (I'm going to get this the wrong way around now) falling to rising rate... maybe

 

Either way it does seem to work a LOT better than the standard set-up. Although that is an entirely subjective judgment without actually having ever driven a car.

 

Rob G

www.SpeedySeven.com

[MikeE]

Don't doubt what you're saying Rob but the question of the thread is does inboard suspension reduce unsprung weight? and I think the answer is that the design does not inherently reduce unsprung weight (it may well be that the FS application does by use of alloy dampers etc).

 

R400 Duratec Build and Modification Pictures here

[rgrigsby]

Good point and I think you are probably entirely correct.

 

Rob G

www.SpeedySeven.com

[I.Mupferit]

Look guys forget all this unsprung weight tosh, the bottom line is..........it looks f**king great, especially the fact that the wishbones are a kind of 'aero' configuration. It looks the dogs bollox and is brilliant for showing off at the pub.......end of story ❗ 😬 😬 😬

 

Brent

 

2.3 DURATEC SV

R 417.39 😬

[Graham Perry]

It does move the dampers and springs out of the airflow and their mass closer to the centre-line of the car, so that can't be bad either.

 

Edited by - Graham Perry on 8 Jun 2005 15:39:45

[Mike Bees]

Although it does put the dampers a long way up off the ground...

 

Whatever, I'd like to have it!

 

Mike

[I.Mupferit]

I'm disappointed none of you appreciate the 'boozer boasting' value though.

 

Brent

 

2.3 DURATEC SV

R 417.39 😬

[CHip]

Brent - Just to make you feel better, I will take some more pics of your trick suspension at the SOM tonight (the ones I took at xtrac didn't come out very well as it was getting dark).

 

Whilst I agree there are merits to incoard suspension (otherwise why would F1 teams us it?), but I don't think unsprung weight is one of them.

 

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Se7en spotting until my car arrives here

[Myles]

(otherwise why would F1 teams us it?)

 

Pah!

 

It gets in the way of advertising-space - *that*'s the real reason F1 uses inboard

 

Project Scope-Creep is live...

 

Alcester Racing 7's Equipe - 🙆🏻™

 

Alcester-Racing-Sevens.com

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[Colin Mill]

Brent - I'm sure you have it right the main value is in raising the driver's stature at the bar rather than anything else.

 

I would think that the unsprung weight has to be dominated by the wheel and disk so anything else must be marginal in its effect. Having said that the ability to adjust spring rates and rate rises over the whole suspension travel by simply changing the geometry around the bell-crank sounds great - far more scope for rapidly ruining the handling 😬

[Mr Woo]

With all this talk about unsprung weight I was wondering if anyone had tried carbon fibre wheels?

 

Tim

[susser]

Here's a thought on the unsprung weight thing;

Consider a tipper lorry running on leaf springs. It's got 20 tons of gravel (or feathers) on board and it goes over a bump. This bump is a very short bump and the lorry is travelling at say 40 mph. The back axle is a stonking great big thing wot weighs a ton. The axle bumps up and down over the bump. The lorry doesn't bump much cos it's so stonkingly heavy it can't move that quickly up and down in response to a short shove from the stonking springs. The unspung weight here is as people have implied, the one ton axle cos it's the road side of the leaf springs.

Now, the driver goes and tips out his gravel/feathers. He drives back down the same road and hits the same bump at the same speed. This time the axle follows the bump as before, at least tries to. The lorry gets a short shove from the stonking springs. But this time its so light, that the springs don't flex much and the whole lorry is pushed up and bounces off the road. Bounce, bounce bounce it goes. (And this is the really good bit.) Because the whole lorry is now unsprung, cos it hasn't got enough inertia to flex the springs.

Don't I go on 🤔

Susser

1/2 🙆🏻d lorry driver and 1/3 🙆🏻d physicist.

PS

Watch the wheels of one of them next time you're out.

It doesn't work that way with air springs cos ,,,,,,,,,I'm going for a drink.