Unsprung weight

[Botus]

less is more.....

Excess lard touching the road without being suspended is terrible for ride comfort, handling and safety. Which is why carbon fibre wheels, low profile tyres, ceramic brakes and aluminium suspension components will allow a car go round corners faster and stop quicker, whilst at the same the time being safer.

If you watch a lorry go over an expansion joint on a motorway, you can frequently see air between the bottom of the tyre and the road surface. This is because the 2 tonne of "unsprung" axel, brakes and wheels have been thrown up in the air and even a road spring and damper from hell have failed to control it. its also a key reason they don't stop and carry straight on thorough your car.

I only mention this because I had a large parcel (of new front discs and calipers) turn up today. This package without 2kg of brake pads, must be in the region of 35kg !!!, all of which goes with a wheel and tyre that's easily the wrong side of 22kg a side. Aside from helping to explain why it weighs 2.2t I guess its another reason it handles more like the QE2 than a motor car

If we want to go round a corners (or stop on a bumpy road) we should be aiming for less than 15kg a corner, which makes me wonder why Mercedes felt at least 60kg was desirable on my car?

 

[Botus]

I was cycling to work (as usual) on my 26" wheel mountain bike, when I realised most cars can't keep up as I go over a series on nasty speed bumps. The have such a steep up ramp to a flat top I never go exceed 20 mph in a car over them.

This lead me to thinking about the current crop of silly sized and elastic band tyres of 22" (which is becoming popular), years back (55 or more), proper cars like RR always had huge wheels and tyres to the benefit of ride comfort. These would have handled these bumps better than any modern car. Of course the difference was back then they got away with the weight of this tyre combo, because they were half the width and thus about the same weight as today.

And the point of this post, now there's no beam axel in the way leading to silly ride heights, with funny money computers picking up and throwing back down the road wheel... unsprung weight can be negated and big wheels and decent ride comfort should be on the way back

 

[L John]

If you want a light car with light wheels and brake systems perhaps the S class was the wrong choice?
On the other hand, if you want a smooth ride and handling of the QE2...

 

[Craiglxviii]

Out of interest. Today I saw an engineering change request for brake backing plates... steel >>> aluminium. Mass difference was 0.6kg per wheel. That’s pretty significant...

 

[Botus]

Out of interest. Today I saw an engineering change request for brake backing plates... steel >>> aluminium. Mass difference was 0.6kg per wheel. That’s pretty significant...

my s class has half sized aluminium back plates

each front caliper is 6.25 kg, the pads must be the wrong side of 1kg per side and the discs needs a crane to pick them up

 

[Rappey69]

These are Mercedes, not lotus.. If you want to go round a corner like a lotus elise then get an elise !

 

[rifiki]

For normal road use it probably makes no difference. Some time ago on YouTube, show chaines on the front wheels of a series 1 BMW.

 

[Uncle Benz]

You really need to look at the relationship between sprung weight and unsprung weight. Sure, unsprung weight has a huge effect on the handling and feel of a lightweight sports car, but when you are looking at two tonnes of luxury saloon car, the proportion of unsprung to sprung weight moves the goalposts somewhat.

 

[Botus]

You really need to look at the relationship between sprung weight and unsprung weight. Sure, unsprung weight has a huge effect on the handling and feel of a lightweight sports car, but when you are looking at two tonnes of luxury saloon car, the proportion of unsprung to sprung weight moves the goalposts somewhat.

I agree from a ride comfort factor, from braking side of things, as I put in the original post... check lorries on motorways u get daylight for 5 to 10 metres at a time, so if they try to stop on a bumpy road they don't

 

[Uncle Benz]

Reminded me of this. Cracking brakes on that one!

 

[L John]

I agree from a ride comfort factor, from braking side of things, as I put in the original post... check lorries on motorways u get daylight for 5 to 10 metres at a time, so if they try to stop on a bumpy road they don't

I've seen them getting air under the tyres and bounce as they go over bumps but it's nowhere near that distance and motorways are pretty smooth.
Lorries are designed to carry a lot of weight, so when it's empty the suspension movement will be minimal.
The tyres can skip if the brakes are locked up with no load and they leave a dotted line.
I believe they all have ABS these days including artic trailers.
They stop good even on a bumpy road considering the weight they're carrying / are designed to carry.
Without using exotic materials the design is as heavy as it needs to be to do it's job and be as reliable and safe as possible.
Lorries have moved a long way in tech and safety.
If a lorry is trying to stop on a bumpy road and "they don't" as your post said, they were just driving too fast.

 

[Botus]

I've seen them getting air under the tyres and bounce as they go over bumps but it's nowhere near that distance and motorways are pretty smooth.
Lorries are designed to carry a lot of weight, so when it's empty the suspension movement will be minimal.
The tyres can skip if the brakes are locked up with no load and they leave a dotted line.
I believe they all have ABS these days including artic trailers.
They stop good even on a bumpy road considering the weight they're carrying / are designed to carry.
Without using exotic materials the design is as heavy as it needs to be to do it's job and be as reliable and safe as possible.
Lorries have moved a long way in tech and safety.
If a lorry is trying to stop on a bumpy road and "they don't" as your post said, they were just driving too fast.

1/4 of a second on the motorway at their limited 60mph is 22 foot in distance (6.7m).
And a main cause of air under the tyres is expansion joints, so depending upon the surface/condition we could be talking a significant % of flying. With so many factors allowed on lorries that are not helping road safety, I can't agree lorries stop well enough.

A big factor on not stopping and on road wear is lorries 100k mile tyre life. If I was transport minister I'd change this to 50k with softer more supple tyres, which would enhance safety and drop noise levels enormously. I would also mandate retro fitting of radar cruise on anything over 5 tonnes and set min distance about 20 times more than lorry drivers do on the M1. And as Italian motorways have, put count down markers in the central reservation so car drives actually get to know there's a junction.

Other provocative thoughts,

Research on big lorries and crashes by not stopping in time, proved if we are prepared to accept lorries current stopping distances (and associated levels of devastation), motorbikes should be allowed to travel at 300mph on motorways!

Roads are not equal, the stuff we have to drive on in south Bucks / east Berks would be better described at an off road vehicle assault course. I am literally bewildered how you can find billiard tables with no traffic at all if you venture 100 miles out. yet we pay all the tax and get nothing for it.

I expect info on joint frequency is in here somewhere

http://www.standardsforhighways.co.uk/ha/standards/mchw/vol3/section1/c_series.pdf

 

[L John]

Other provocative thoughts,

Research on big lorries and crashes by not stopping in time, proved if we are prepared to accept lorries current stopping distances (and associated levels of devastation), motorbikes should be allowed to travel at 300mph on motorways!

Lorries need around 40% more stopping distance than a car, considering the weight that's pretty amazing.
It would be ideal for all heavy transport to use railways but road travel will always be needed and safety can always be improved whether it's a car or a lorry.

I'd like to see other members views but we are a long way from agreeing as I don't see lorries bouncing and skipping anywhere near as much as you do.
The motorbike comparison is comparing apples to oranges, I prefer oranges.
[Dragons Den] I'm out.

 

[Botus]

in a none to accurate (balancing on domestic scales) experiment I just weighed the front discs

12kg each (for part worn ones)
6.5kg each "alloy" caliper
1kg each side for brake pads
7kg each lower control arm
and if you could see the size of the antiroll bar you'd be expecting the price of steel to come down when this thing gets scrapped !