Reducing Rotational Mass - real world gains - Corsa Sport - for Vauxhall and Opel Corsa B, Corsa C and Corsa D

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Member

Registered: 5th Jul 00
Location: Aberdeen City
User status: Offline

3rd Jan 13 at 10:38

Hear this a lot, and understand the theory.... but whats the general rule of thumb for weight saved on parts that moke the car move... wheels/shafts etc

Double?

I.e a 10kg saving on a tail shaft would be like losing 20kg deadweight

[Edited on 03-01-2013 by AK]

ShEp

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Registered: 9th Aug 05
Location: Dingwall, Highland
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3rd Jan 13 at 10:50

Steve will be researching this on google as I type,

He will arrive shortly, all knowledgeable.

I'll give my answer as "fuck know's" lol.

Member

Registered: 5th Jul 00
Location: Aberdeen City
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3rd Jan 13 at 10:58

i've googled for a bit and it's all pretty much down to folks opinions... nothing concrete or remotly clear cut that doesnt involve heaps of calcs.

Going by what I've read though it would seem it does have a saving, but pretty minimal on shafts when comapred to wheels/tyres for example.

Perhaps 1.2x dead weight.

daine

Premium Member

Registered: 28th Feb 07
Location: rossington
User status: Offline

3rd Jan 13 at 11:03

Did you never mend a puncture in your push bike AK!?!?!? hole the wheel with the center spindle!
move each side up and down, you can do it very easy.
Now spin the wheel and try it..... so much harder, cos the mas is moving.
the weight you refer too, is the un-sprung weight on a car!, this is every part below the spring.

Member

Registered: 5th Jul 00
Location: Aberdeen City
User status: Offline

3rd Jan 13 at 11:10

you're refering to a gyroscopic effect (i'e using a gyro to stabilise)... i said I understood the theory, its more of a realword 'figure' i'm after.

[Edited on 03-01-2013 by AK]

Member

Registered: 5th Jul 00
Location: Aberdeen City
User status: Offline

3rd Jan 13 at 11:14

I'm looking at light(er) weight propshafts for the GTR...

Budget option is about 5kg saving
Medium - maybe 8kg
Gucci - about 10kg

I.e If I save 5kg off a propshaft that spins at something like 4000rpm, what would I have to lose in DEADweight (i.e seats, doors) to have the same gains

Member

Registered: 5th Jul 00
Location: Aberdeen City
User status: Offline

3rd Jan 13 at 11:16

in short, acording to google (without getting a nosebleed and headache with the maths) the answer would appear to be 'cabbage'

Losing 5kg off a prop may have the same effect as losing 6kg from the shell.

Kyle T

Premium Member

Registered: 11th Sep 04
Location: Selby, North Yorkshire
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3rd Jan 13 at 11:18

This topic came up alot on the Civic forums I frequented when I had my FN2.

I heard 1.5 banded around but I never remember seeing any solid numbers on it. I'll do a search tonight to see if I can find any of the old posts.

Lotus Elise 111R

Impreza WRX STi

Member

Registered: 5th Jul 00
Location: Aberdeen City
User status: Offline

3rd Jan 13 at 11:20

yup, 1.5x seems to be punted around for wheels/tyres but less for things like drive/prop shafts

Robin

Premium Member

Registered: 7th Jan 04
Location: Northants Drives: Clio 182 Cup
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3rd Jan 13 at 11:45

I'd imagine diameter has a lot to do with it, hence the wheel figure being quite substantial

Ben J

Member

Registered: 31st Jan 05
Location: Cheshire
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3rd Jan 13 at 11:48

Steve is building meccano driveshafts as we speak.

chris_uk

Premium Member

Registered: 8th Jul 03
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3rd Jan 13 at 11:52

Gm said it cost them 10bhp to turn the balancer shafts in my engine, flywheel aswell, from 9kg to 4.5kg changed how the engine felt.

When you remove mass from these areas you change the way the engine responds, you change its characteristics. When i did the flywheel it revved much quicker but at the same time when letting off now there is quite a lot of engine braking, on a track its better to be smooth so i have to left foot brake a lot to stop the engine slowing me down and spinning the car. But i think the gains of a quicker acceleration outway the cons.

I think with my car being as light as it is exagerated the feelings, in a heavy car i wouldnt of thought there would be much of a change.

Member

Registered: 5th Jul 00
Location: Aberdeen City
User status: Offline

3rd Jan 13 at 12:01

quote:
Originally posted by Robin
I'd imagine diameter has a lot to do with it, hence the wheel figure being quite substantial

very much so

Balling

Premium Member

Registered: 7th Apr 04
Location: Denmark
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3rd Jan 13 at 12:04

quote:
Originally posted by Robin
I'd imagine diameter has a lot to do with it, hence the wheel figure being quite substantial

I was just thinking this.

My guess would be that diameter and weight distribution would have to make a world of difference, hence it would be impossible to give an even remotely accurate "general" figure.

Two 17" wheels both weighing the same could have different rotational mass on account of the weight being closer to either the center or the outer edge of the rim.

Just guessing, though...

Robin

Premium Member

Registered: 7th Jan 04
Location: Northants Drives: Clio 182 Cup
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3rd Jan 13 at 12:09

With that in mind then, I wouldn't say it was even worth considering, unless you have a 17 inch diameter prop.

Member

Registered: 5th Jul 00
Location: Aberdeen City
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3rd Jan 13 at 12:24

but you still lose the 5kg deadweight... that is also rotating.... so it is a saving.

We're needing some repairs on our prop - the central bearing/bush is a bit worn. This is where the 2 piece prob is supported to the floor pan.

Some pics

The prop will be about 3" O.D.

this is the OE R32 GTR prop / tail shaft. 16kg or so...

Id expect a 1 piece to save about 5k on that... rotational mass so much more gains

pic of a steel 1 piece R32 tail / propshaft

An Alu one - £800 or so

CF one - £gucci

daine

Premium Member

Registered: 28th Feb 07
Location: rossington
User status: Offline

3rd Jan 13 at 12:35

How much quicker would it make the car per lap from the steel one to the Gucci one and would
this justify the massive price difference at the level of racing you do

If the steel one loses you 5kgs and you need a prop!
then go for the steel one, see if you can feel the difference it make and take it from there.

Member

Registered: 5th Jul 00
Location: Aberdeen City
User status: Offline

3rd Jan 13 at 12:50

the only one i'd go for is the cheap one... fuck spending thousands on carbon fibre

level of racing..... ? If it was BTCC or an F1 car I wouldnt be having this discussion

Daimo B

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Registered: 20th Mar 00
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3rd Jan 13 at 12:53

Won't the weight also allow the engine to spin up easier?

Can't help with the weight, but I know that less weigh can only equal faster acceleration and later braking and quicker directional change. As said below the spring line its going to be much less of an effect than above it. Cornering etc won't be as much effected by the loss, but acceleration, less weight on the engine, and less weight to spin the propshaft, should all be improved?

SportBoy

Member

Registered: 5th Oct 01
Location: Retford, Nottinghamshire
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3rd Jan 13 at 12:57

Makes cars quicker in gran turismo......

Member

Registered: 5th Jul 00
Location: Aberdeen City
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3rd Jan 13 at 13:07

yup, less weight, less work, less momentum, less joints to loose power through, but more backlash etc (not weight related but moveing to 1 peice)

IvIarkgraham

Premium Member

Registered: 27th Mar 04
Location: Ellesmere Port, Cheshire
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4th Jan 13 at 02:13

stop being a minge bag and just buy the carbon one

CORSAguy93

Member

Registered: 7th Jun 12
Location: Wirral/ Chester Corsa b 1.6 8v, Vectra b 1.8
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4th Jan 13 at 13:05

quote:
Originally posted by SportBoy
Makes cars quicker in gran turismo......

This

Member

Registered: 5th Jul 00
Location: Aberdeen City
User status: Offline

4th Jan 13 at 13:54

yes, very good

Just going for a custom made steel prop. Will be 1 piece so loses the middle knuckle, should be around 3 - 3.5" OD - roughly same as it currently is.

I'd love the carbon one, but i'm not really a carbon whore

and I dont have a bottomless pit of cash

Toby

Premium Member

Registered: 29th Nov 05
User status: Offline

4th Jan 13 at 22:35

I was under the impression that wheels carried a bigger ratio than 1.5x fast ford did a test which I'm sure they worked out at nearer 4x based upon 17inch wheels

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