A balancing act

[Scorpma82]

Why is we always talk of balancing wheel/tyres, tailshafts/driveshafts, crankshafts, rods etc etc etc.......but never a brake rotor??????

It spins at the same rate as an axle, driveshaft.....maybe even faster than a crankshaft (after a certain speed) but no-one has ever mentioned or needed to balance a brake rotor???

Could this be an advantage if it were to work????? would it make a difference???

[jvflash]

I found this on the DBA brakes website which might answer the question from a performance brake rotor point of view.
"At DBA, we spent two years getting all aspects right before launching the product to the public. This research and development included perfecting the symmetrical hole pattern which ensures that the discs have correct balance"

[Scorpma82]

thats a fair answer their falsh and i appreciate it....but (in theory) wouldn't any (or every) wheel manufacturer go through the same process???.....surely they'd have to????


It's just odd that that this particular component doesnt get a mention about balancing...despite where it is on the car an its duties..... (at least i thought)

[jvflash]

On car wheel balancing would take the disk rotor balance into the equation.

When I was a mechanic (not technician as they are called today) I had trouble with a Rolls Royce hub caps throwing the wheel balance out. Wheels were balanced fine, but the car still shook. The hub caps were about 1kg each! Ended up having to do on car balance with the hub caps on. That fixed it.

[A112H]

I am pretty sure it is the tyres that through the wheel out of balance.
Two things lead me to this thought;
1. Tyres have a red spot to line them up with the valve
2. If it was the wheel out of balance then you wouldn't have to move the weights after fitting new tyres.

[Superscan811]

I am pretty sure it is the tyres that through the wheel out of balance.
Two things lead me to this thought;
1. Tyres have a red spot to line them up with the valve
2. If it was the wheel out of balance then you wouldn't have to move the weights after fitting new tyres.

Another thing is the tyre valves.

Also, if you hit a curb too hard it may deform the wheel enough to send it out of balance.

BUT back to the original statement about rotor speeds,

It spins at the same rate as an axle, driveshaft.....maybe even faster than a crankshaft (after a certain speed) but no-one has ever mentioned or needed to balance a brake rotor???

Axles and wheels yes, but you are forgetting about the diff ratio.


Cheers.

[Scorpma82]

im not forgetting about the diff ratio........coz irrespective what ratio u run......both the axles and wheels spin at road speed

[Superscan811]

im not forgetting about the diff ratio........coz irrespective what ratio u run......both the axles and wheels spin at road speed

True, but if your diff ratio is 3:1, the axles and tyres spin 3 times slower than the engine/gearbox/tailshaft (if you are in 4th gear of course).

The next factor is the speed difference between the tyre and rotor. They may be traveling at the same rotational speed but their LINEAR speed is very different.

Halve the diameter halve the velocity(on the outside edge of course).

IF you take the outside edge of a 225/50/16 tyre (approx 24" diameter) and compared its speed to a 12" brake rotor traveling at the same ROTATIONAL speed, the outside edge of the rotor is running at 1/2 the LINEAR speed of the tyre.

The inertia of an object is mass x velocity², ie: double its speed (if everything else stays the same) and you now have 4x the inertia .. the opposite is also true, if the speed is reduced to 1/2, the inertia is reduced to 1/4.

The other factor is not just the diameter rotor/tyre/rim, but the weight distribution.

With a tyre and rim, the majority of the weight is further away from the axle. With the brake rotor, it's a bit more evenly distributed.

So to sum things up, it's not a bad idea to balance the brake rotors but I would personally doubt you would see any gains from it.

Cheers.