Could someone explain what this means and which parts on your car are classed as "unsprung". I was searching ClioSport and found a topic explaining to me that for every Kg of weight you save in your wheels, it adds 1 bhp to your car (not literally, but power to weight wise). Is this the case, and does this mean that if I were to get some super light alloys on the Fabia saving me a total of 20kg in weight I would get an equivalent 20 bhp increase, because if so it seems a much more cost effective way to increase power without straining engine components/the clutch etc.

Sprung and Unsprung Weight

"Sprung" weight is a term used to describe the parts of an automobile that are supported by the front and rear springs. They suspend the vehicle's frame, body, engine, and the power train above the wheels. These are quite heavy assemblies. The "unsprung" weight includes wheels and tires, brake assemblies, the rear axle assembly, and other structural members not supported by the springs.

Thank you Jeeves

LOL @ Ross Thanks, is it true about the gains?

Just a rhetorical question really....

Do suspension components count as "sprung" or "unsprung" weight?

From my reply in this thread

The majority of the car's weight is supported by the car's springs and this is known as sprung weight. The weight of all the components not supported by the springs (including the springs themselves) is known as "unsprung weight". The unsprung weight therefore typically includes: wheels, tyres, brakes, springs and half the weight of the shock absorber and the suspension links. Note that those parts that connect the vehicle body to the suspension (or form part of it) only count as half weight because one end is part of the sprung weight of tnhe car, while the other end is unsprung.

Increasing the ratio of unsprung to sprung weight, especially when it is achieved by reucing the unsprung weight, will improve not only the general handling of the car but also traction (grip) in acceleration and braking, particularly on bumpy road surfaces. The reason being that weight creates inertia and the less inertia the unsprung components have, the more easily will the springs keep the tyres in contact with the road.

To answer your question. 5kg saved = 1 bhp gained. I thought unsprung weight came in at x2 (ie 2.5kg saved = 1 bhp), although I stand ready to be corrected.

Oh and sorry for rambling on.

Excellent reply! thank you!

Onto the next question then, without adversely affecting the practicality of my beast what the best way to save some weight?

Onto the next question then, without adversely affecting the practicality of my beast what the best way to save some weight?

Replace the spare wheel with a can of tyre foam and remove all the unnecessary pieces of trim (unoccupied seats, sound-proofing, etc.).

All done at your own risk though...

Rob.

Replace the spare wheel with a can of tyre foam and remove all the unnecessary pieces of trim (unoccupied seats' date=' sound-proofing, etc.).

All done at your own risk though... [/quote']

And always run around with only 5 litres of fuel in the tank

Chris

When you remove the spare wheel it does seem to make a noticable difference. I couldnt believe it on my Mondeo, it felt like I had another 10 bhp, one problem though, since the spare wheel is sitting on the springs is sprung weight, not unsprung.

When you remove the spare wheel it does seem to make a noticable difference. I couldnt believe it on my Mondeo, it felt like I had another 10 bhp, one problem though, since the spare wheel is sitting on the springs is sprung weight, not unsprung.

There's more sprung than unsprung weight though - getting lighter wheels/brakes, etc. will cost a lot of money and you won't be able to save all that much off the weight...

Rob.

does this mean that if I were to get some super light alloys on the Fabia saving me a total of 20kg in weight I would get an equivalent 20 bhp increase, because if so it seems a much more cost effective way to increase power without straining engine components/the clutch etc.

I remember from my cycling days that the first thing that me and my mates would upgrade were the wheels - even on a road bike where they're not 'sprung'. Scientifically speaking, a rotating mass has more inertia than one that's moving in a straight line (think flywheel, where you WANT the inertia). Therefore, 1kg saved from rotating parts (wheels, brake discs / drums) will have more of an effect on performance than 1kg saved from anywhere else on the car.

I'll give it a go tomorrow and see what it's like. I think the spare wheel is the only thing keeping the car straight under heavy braking though as it's piveting

But the gains are twice as much

Cutting sprung weight:

1. Driver - if you are generously proportioned you could lose 10kg +2bhp

2. Ditch the sub, another 10kg +2bhp

3. Ditch spare wheel, another 15kg +3bhp

Very easy, no hassle and you've "gained" 7bhp for no cost

Remove carpets, + >5bhp, remove rear seat and thats another 5bhp, replace glass with plastic gains another 2bhp, remove door trims and any unwanted dash components (eg glovebox) gain another 2-5 depending on how drastic you wanna be.

As Rob says, unsprung is harder and a lot more expensive - 4 Speedline magnesium wheels,

Would be quite interested to see what a Fabia vRS would be like with some weight reduction "a la Red Baron"... :rubchin:

Can't be that hard to get 300kg off it...

Rob.

Increasing the ratio of unsprung to sprung weight, especially when it is achieved by reucing the unsprung weight, will improve not only the general handling of the car but also traction (grip) in acceleration and braking, particularly on bumpy road surfaces. The reason being that weight creates inertia and the less inertia the unsprung components have, the more easily will the springs keep the tyres in contact with the road.

As TaviaRS mentioned, less weight = less inertia. The primary advantage of this is that the suspension will react quicker to bumps, especially higher frequency bumps. The net result is that the car rides better (I prefer the term 'more efficiently'). There are also by-products of this such as quicker turn-in giving a greater feel of agility.

The net result is that the car rides better (I prefer the term 'more efficiently').

Unfortunately that isn't always the case, the ride can actually become harsher and more choppy, I think it is due to the springs and dampers being tuned to a certain weight. Yes the dampers will react more quickly but they can only act within the parameters of the spring weights.