Wheels - What's 1 KG Weight Savings Equivalent To?

[kenntona]

I read this off a reputable wheels homesite:


The performance gain achieved by reducing the wheel mass (un-sprung mass) can be quantified using a factor of six. This means that to achieve the same performance gain by reducing the body mass, it is necessary to remove six times the wheel weight saving.

Example: A saving of 1 kg Per Wheel x 4 Wheels = Removing 24 kg from the bodyframe.


Is this true? Can anyone comment?

 

[Justin Ang]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

The car feels more responsive and the milage becomes better. Not sure on the 6 times weight saving tho.

 

[axl]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

6 is too much.. IIRC the weight savings from unsprung weight (vs sprung weight) is a factor of 2.

 

[Breyton]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

Saw a simple calculation some techie did using kinetic energy considerations - he pretty much used ideal conditions (no drivetrain losses, cg/weight of wheels in ideal location, etc) and the result was something like 1kg saving at each wheel (ie 4kg total for 4 wheels) gives an effect of about 6.5kg savings on the car.

 

[iScoupe]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

kenntona is 6 times of the 4 pieces of rims.

 

[JuzzforCars]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

Maths makes me MAD!

 

[Crazy_]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

kenntona is 6 times of the 4 pieces of rims.

You sure only that ratio????

 

[Ahbengdriver]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

So If I Shaved Off About 1.7 Kg Per Corner, I 'save' About 40kg Equivalent?

 

[Breyton]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

So If I Shaved Off About 1.7 Kg Per Corner, I 'save' About 40kg Equivalent?

If you shave 1.7kg per wheel, the effect is shaving off 1.7 x 6.5 = 11.05kg.

 

[tom_ting]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

if i hav shaved off 5kg each wheel, so 5 x 6.5 = 32.5kg ?

 

[axl]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

Might clear things up a little..

-> Sprung Vs. Unsprung Chassis Weight: Definition and Examples

Interesting:

The unsprung vs. sprung weight percentage greatly affects wheel control, but its importance is almost entirely limited to un-even surfaces, or conditions where the attitude of the vehicle changes (such as through G forces). This is most important in off-road and pavement road racing, somewhat less important in dirt track, and has almost no value in drag racing.

 

[kuvesh]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

i was thinking about this at the gym today... what is the ratio for 1kg loss in driver body fat?

 

[Shaun]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

axl don't confuse sprung and unsprung mass with rotating vs non-rotating mass... wheels are both unsprung and rotating masses and each of those properties is important in different situations

 

[kenntona]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

Might clear things up a little..

-> Sprung Vs. Unsprung Chassis Weight: Definition and Examples

Interesting:

The unsprung vs. sprung weight percentage greatly affects wheel control, but its importance is almost entirely limited to un-even surfaces, or conditions where the attitude of the vehicle changes (such as through G forces). This is most important in off-road and pavement road racing, somewhat less important in dirt track, and has almost no value in drag racing.

This paragraph is interesting......

"Unsprung vs. sprung weight have no difference in their effect on acceleration or top speed. There is no “1-10” rule (or any other ratio) where 1 lb. removed from unsprung weight “has the same same effect as” a higher amount of sprung weight. Any benefit from weight reduction towards increased MPH or reduced ET will be exactly the same as if the weight were removed from the chassis. Weight removed from an unsprung component, such as a rear wheel or axle housing, may affect traction if the wheel is not under control during launch. Lighter wheels & tires do have a very small additional benefit due to the lower amount of power required to rotate them (true of all rotating components), but this is not due to their classification as unsprung weight."

(1) If this is true, then it will quash the common perception that lighter wheels lead to vast improvement in acceleration ???

(2) How about the effect of tyres? Not on the weight portion, but surely, under this premise, the tyres will play an indirect role via traction? You save weight on wheels and install poor tyres - worse?

i was thinking about this at the gym today... what is the ratio for 1kg loss in driver body fat?

Kuvesh, don't even go there. Christmas coming.........

 

[Remus325]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

If you shave 1.7kg per wheel, the effect is shaving off 1.7 x 6.5 = 11.05kg.

u forgot to multiply by four since there are four wheels ... so ah beng is right

 

[Breyton]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

u forgot to multiply by four since there are four wheels ... so ah beng is right

No I did not. See my original post:

Saw a simple calculation some techie did using kinetic energy considerations - he pretty much used ideal conditions (no drivetrain losses, cg/weight of wheels in ideal location, etc) and the result was something like 1kg saving at each wheel (ie 4kg total for 4 wheels) gives an effect of about 6.5kg savings on the car.

Total of 4kg savings from all 4 wheels, gives an effect of 6.5kg savings. Which, in effect, is 6.5kg savings for shaving off 1kg each wheel. If you want to calculate on a 'per wheel' basis, the factor is more like 1kg at wheel = 1.6+ kg effect overall.

 

[Remus325]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

No I did not. See my original post:



Total of 4kg savings from all 4 wheels, gives an effect of 6.5kg savings. Which, in effect, is 6.5kg savings for shaving off 1kg each wheel. If you want to calculate on a 'per wheel' basis, the factor is more like 1kg at wheel = 1.6+ kg effect overall.

wow! that is a really low multiplier ... contrary to what most pple think.

 

[axl]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

(1) If this is true, then it will quash the common perception that lighter wheels lead to vast improvement in acceleration ???

(2) How about the effect of tyres? Not on the weight portion, but surely, under this premise, the tyres will play an indirect role via traction? You save weight on wheels and install poor tyres - worse?

1) I think lighter wheels will still aid acceleration, not due to the weight savings but lesser rotational mass, as pointed out by Shaun. And even then, the timing improvement in reality will not be of a large magnitude.. maybe 0.1s tops?

2) I would think any top-tier road tyre will easily more than offset its heavier weight, as compared to a hypothetical cheaper AND lighter tyre. After all, we all can see how tyre grip is one of the most important factors directly affecting track timings.

Just my 2 patacas' worth.

 

[Breyton]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

wow! that is a really low multiplier ... contrary to what most pple think.

Haha... yes, a lot lower than expected...

Anyway, for those interested in the maths, I managed to dig up the old article....

AudiWorld Forums: A study investigating the effective inertial weight of wheels. Warning: technical in nature.

There were some people who disagreed with his calculations, saying it's too simplistic. I tend to be conservative and think simple 'basic principles' physics, so I kinda agree with his energy calculations.

 

[Shaun]

Re: Wheels - What's 1 KG Weight Savings Equivalent To?

The guy's analysis is right. Max is factor of 2 (mass at pure circumference moving at road speed). min 1, both exclusive. To find out exactly where between 1 and 2 is it, measure the inertia of the entire wheel and tire assembly... huygens theorem. Hang it from 3 points equidistant on circumference, center guided by a low friction rod, apply torsion around wheel center, let assembly swing free, and measure period of the oscillation. Make a bright mark on the tire and use that as reference point. I'm not sure about road car wheels and tire types, but the racing stuff usually works out to around 1.57.

Axl from this you can work out what the true change is on hooked accel... can be more than 0.1 sec then, and esp when you start to talk about slipping the tire at launch where it is rolling at faster than road speed but necessary for power band is.

Unsprung mass effect on handling is entirely separate and much more complex to measure since it interacts with much else.