A good read for Brake-whores/technophiles.

[poll250 0]

Long, and at times pretty technical read; but well worth it if you're if you've got some time at work:

 

http://forums.vwvortex.com/showthread.php?1811355-Another-proof-why-BIGGER-brakes-are-NOT-always-best!

[boost monkey 0]

increasing the unsprung mass means your car will be slower unless you have lighter wheels and have adjusted suspension to compensate :D

[Timbo 0]

It's not really the increased unsprung mass that is the issue here, it's the increased rotational inertia required to turn the wheels. More unsprung mass will affect your suspension performance though. I'm splitting hairs to a certain extent as it's the same mass that affects acceleration and suspension, but it's an important distinction to make. For example, bigger calipers will increase the unsprung mass but will do nothing to the rotational mass. An effect would be made on the overall power to weight ratio of the vehicle and thus the acceleration, but only slightly. On the other hand, bigger discs will increase the unspring mass AND the rotational mass. It's the latter that increases the turning moment of the wheels and makes them harder to accelerate.

[boost monkey 0]

Yeah you're splitting hairs dude :D

 

bigger calipers (assuming the same metal, and not lighter) will also affect unsprung mass but not rotational as, well, they don't rotate.

 

You seem to be assuming I'm talking about straight-line acceleration, but actually I'm talking about lap time performance. Any added weight to the car will make it slower, especially if the high speed bump, low speed bump and rebound haven't been adjusted to compensate for this. Of course, this is only possible if the car has such suspension equipped.

 

As you said unsprung mass affects suspension performance, which affects overall vehicle performance resulting in slower times.

[Timbo 0]

Right but a change in unsprung mass only (e.g. bigger calipers) will have almost zero effect on the dyno, which is what they're talking about. Rotational mass is the important factor here.

[boost monkey 0]

Fair enough, I was referring to the track performance which they mention later in the OP.

[Kevin Bacon 5]

It's not really the increased unsprung mass that is the issue here, it's the increased rotational inertia required to turn the wheels. More unsprung mass will affect your suspension performance though. I'm splitting hairs to a certain extent as it's the same mass that affects acceleration and suspension, but it's an important distinction to make. For example, bigger calipers will increase the unsprung mass but will do nothing to the rotational mass. An effect would be made on the overall power to weight ratio of the vehicle and thus the acceleration, but only slightly. On the other hand, bigger discs will increase the unspring mass AND the rotational mass. It's the latter that increases the turning moment of the wheels and makes them harder to accelerate.

 

Spot on.

 

Modern cars get round these issues by tackling the car as a whole. For example they can make the gearing shorter, increase / decrease track (with suspension components, not wheel spacers), alter the torque delivery, alter the spring / damper rates, alter the roll centre, steering ratios etc etc. All of which when applied together can make a very big and heavy wheeled / braked car actually feel surprisingly lively.

 

As modifiers of existing cars, all we can easily change is wheels and brakes and big discs and wheels as said can really mess up a Corrado's handling / turn-in.

[Jim Bowen 1]

i want my calipers on the back of front discs and front of back discs like modern cars