Reducing the rotational unsprung mass - wheel weight reduction benefits

[Hurdy]

I've been searching the web and there are several features etc on the benefits of reducing wheel weight, namely better performance and better handling.

Calculations vary wildly from 1kg saving on the wheel = 1.5kg from the body of the car all the way to 1kg saving on the wheel = 10kg saving on the body of the car.

I found a more accurate spreadsheet that calculated savings by different formulas that basically meant for my 5kg saving per wheel (20kg total) it was the equivalent of saving 84kg from the body of the car. This calculation took into account diameter of the wheel, mass (at both the outer limit+tyre), width etc and seems to comply with some other calculations that equate 1kg saving at the wheel is the equivalent of saving 4-4.5kg on the body of the car for acceleration purposes.

Other additional benefits are that reducing the wheel weight will put less stress on the suspension parts and as a result a better ride and less "crashyness". Also the wheels have a "gyroscopic effect" on the car's handling and so the lower the weight and the smaller the average diameter of the rotating mass, the easier it is to turn the wheels and as an effect the handling appears crisper.

Has anyone got any more sources of information that could be helpful?

[gazon69]

Good thing i got my superleggeras then john 

[Hurdy]

Good thing i got my superleggeras then john 

Yup, my new alloys should be here tomorrow

Yours probably save around 5kg a corner over stock too

[scopes]

I was always made aware 1 kg on the outside = 5-8kg on the inside... You seem to be on the right track...

[Hurdy]

Well, when I had a passenger in the car at the pod my fastest time was 12.787. The fastest time without was 12.615, so if the calculations are correct I should be looking at around 0.15-0.17 off the 1/4 mile time with just lighter wheels

[gazbutS3]

so the same/similar must apply to weight savings on brakes too, although its not all rotating mass

[rich83]

so the same/similar must apply to weight savings on brakes too, although its not all rotating mass

True... the weight of an R32 disc is the same as a wheel and tyre..... (... well... nearly  )

[gazbutS3]

so the same/similar must apply to weight savings on brakes too, although its not all rotating mass

True... the weight of an R32 disc is the same as a wheel and tyre..... (... well... nearly  )

can't be much in it

[Hurdy]

so the same/similar must apply to weight savings on brakes too, although its not all rotating mass

A solid rotating disc will have a greater effect than the weight it saves, but due to the bulk of it's mass being nearer the centre of rotation it doesn't have as much overall effect as alloys which have the bulk of their weight at the rim. It is still all on the unsprung mass though and will make for better handling too.

My god! I must have learned something to remember that

[DaveB@Vagbremtechnic]

Indeed

Peripheral weighting is a trick of gyroscope engineers, before laser ring gyros and Solid state accelerometers ....avionics engineers used to peripherally weight the small gyroscopes inside aircraft instruments to make them more gyroscopic for less weight...the technical term when a gyro is spinning is rigidity...

Precession is the phenomenomenon of any force acting on a rigid gyro at 90 degrees to the force applied, Caliper position is designed in to help,or hinder the ability of a wheel and tyre to turn in when braking.

Remember when you span a cycle wheel on your finger tip and it didn't fall off, remember trying to push it from the top say 12 oclock and it just spinning left and right.

Thing is looking at things in a complicated manner...simply remember unsprung weight is the scourge of performance and handling.

[rich83]

Indeed

Peripheral weighting is a trick of gyroscope engineers, before laser ring gyros and Solid state accelerometers ....avionics engineers used to peripherally weight the small gyroscopes inside aircraft instruments to make them more gyroscopic for less weight...the technical term when a gyro is spinning is rigidity...

Precession is the phenomenomenon of any force acting on a rigid gyro at 90 degrees to the force applied, Caliper position is designed in to help,or hinder the ability of a wheel and tyre to turn in when braking.

Remember when you span a cycle wheel on your finger tip and it didn't fall off, remember trying to push it from the top say 12 oclock and it just spinning left and right.

Thing is looking at things in a complicated manner...simply remember unsprung weight is the scourge of performance and handling.

I fully understand precession but how is caliper position relevant... front or back of the disc, what implications does it have?

[gazbutS3]

Indeed

Peripheral weighting is a trick of gyroscope engineers, before laser ring gyros and Solid state accelerometers ....avionics engineers used to peripherally weight the small gyroscopes inside aircraft instruments to make them more gyroscopic for less weight...the technical term when a gyro is spinning is rigidity...

Precession is the phenomenomenon of any force acting on a rigid gyro at 90 degrees to the force applied, Caliper position is designed in to help,or hinder the ability of a wheel and tyre to turn in when braking.

Remember when you span a cycle wheel on your finger tip and it didn't fall off, remember trying to push it from the top say 12 oclock and it just spinning left and right.

Thing is looking at things in a complicated manner...simply remember unsprung weight is the scourge of performance and handling.

ah your bringing back my college days, the 3 finger rule, or was that something else 

[rich83]

LOL....left hand rule.... feels like someone else is working it out! 

[DaveB@Vagbremtechnic]

Indeed

Peripheral weighting is a trick of gyroscope engineers, before laser ring gyros and Solid state accelerometers ....avionics engineers used to peripherally weight the small gyroscopes inside aircraft instruments to make them more gyroscopic for less weight...the technical term when a gyro is spinning is rigidity...

Precession is the phenomenomenon of any force acting on a rigid gyro at 90 degrees to the force applied, Caliper position is designed in to help,or hinder the ability of a wheel and tyre to turn in when braking.

Remember when you span a cycle wheel on your finger tip and it didn't fall off, remember trying to push it from the top say 12 oclock and it just spinning left and right.

Thing is looking at things in a complicated manner...simply remember unsprung weight is the scourge of performance and handling.

I fully understand precession but how is caliper position relevant... front or back of the disc, what implications does it have?

If you look at some Porsches Rich they have the Caliper at 10.30 o clock instead of 3 o'clock or 9, it's a handling tuning thing. It's more prevalent on bikes where caliper position is pretty much always on the vertical or near the forks

[gazbutS3]

LOL....left hand rule.... feels like someone else is working it out! 

thats the rascal, the 3 finger rule was in the student union lol