weight versus power

[Markh]

I am looking to get a bit more go from my Boxster S, tuning dose seem a bit limited, so was thinking of coming to the problem from a slightly differnt angle and try to lose some weight from the car. is there a calculation on the lines of ' 10kg saved is worth 2bhp?' any thoughts?

[stevieturbo]

Losing weight is worthwhile. But unless it is simply a matter of removing stuff and throwing it away, it can be an expensive route for very little gain.


What is the car actually used for ?

[annodomini2]

stevieturbo said:

Losing weight is worthwhile. But unless it is simply a matter of removing stuff and throwing it away, it can be an expensive route for very little gain.


What is the car actually used for ?

Yup, where do you want the performance improvement?

[anonymous-user]

F = MA, so pretty simple really! As power is just "longitudinal force at the drivin wheels" (F), weight = mass (M) (well here on earth it does anyway...), and Acceleration is A. So, halving M is the same as doubling F.

So the "gain" from mass lost scales directly as a proportion of the total mass. E.g. 1000kg car with 100bhp, pulls 1g accel:

knock off 100kg, and it will pull 1.1g.
add 10bhp and it will pull 1.1g.

BUT!

the effect of mass reduction is felt at all parts of the rpm range, and it's usually difficult to increase engine power equally across the rpm range, so weight reduction tends to be more effective overall (added to which your stopping and steering gets easier too....)


For a "road" car, i would not really expect to be able to feel much difference below approx 5% weight reduction. i.e. most drivers notice a passengers weight in a 1300kg car etc.

Getting say 50-100kg out of a Boxster without a) making it terrible to drive (noise/nvh etc) or b) spending a fortune will be VERY difficult.

[JontyR]

What about wheels?

Any weight to be saved there?

Unsprung weight is one of the first places to be looking at

[GavinPearson]

JontyR said:

What about wheels?

Any weight to be saved there?

Unsprung weight is one of the first places to be looking at

They would certainly help, especially if you can reduce inertia which will also help acceleration and braking - as each wheel & tyre assembly is effectively a flywheel then changing wheels & tyres to lightweight versions is analagous to putting 4 lightened flywheels on.

Edited by GavinPearson on Monday 8th November 10:52

[JontyR]

GavinPearson said:

JontyR said:

What about wheels?

Any weight to be saved there?

Unsprung weight is one of the first places to be looking at

They would certainly help, especially if you can reduce inertia which will also help acceleration and braking - as each wheel & tyre assembly is effectively a flywheel then changing wheels & tyres to lightweight versions is analagous to putting 4 lightened flywheels on.

Edited by GavinPearson on Monday 8th November 10:52

Also cornering....far easier to turn a lighter wheel than a heavier one.

There is an equivalence of 8kg of sprung mass for every 1kg of unsprung mass reduced. Now this is moot point and some will advocate this, and others will dismiss it.

Regardless of your opinion, the one thing it will enable is better traction, as your suspension will have less work to do. So it will be able to get the power down.