Moment of Inertia, Turn In, Unsprung Weight, blah, blah...

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Robert Striemer - 29 Oct 2005 00:39 GMT

Does anyone have experience with low mass wheels such carbon fibre? Can
reducing the inertial mass of wheels and associated rotating components such
as brake rotors produce a noticeable (as opposed to theoretical) improvement
in handling? Who makes GP wheels? What do GP wheels weigh? Are carbon fibre
wheels the standard in GP?

Radial brakes are common to new sport bikes. Has anyone made a reasonably
controlled test of radial brakes? Do they really reduce stopping distance?
Better calliper performance, could allow for reduced rotor diameter and
reduced moment of inertia right? Are rotors getting smaller as radial brakes
are introduced (or getting bigger with greater HP and speed)?

Basically, I'd like to know if taking a few pounds of weight off the wheels
can make a noticeable difference in handling and ride.

Thanks for your observations and enlightened opinions ; )

Striemer

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wheelieking - 29 Oct 2005 01:26 GMT

No enlightened opinions here, but, if the entire bike only weighed one
pound, and if the weight of the rider seems to disappear at some point in
every turn then it would seem logical that lighter is better.

Signature

Phil

> Does anyone have experience with low mass wheels such carbon fibre? Can
> reducing the inertial mass of wheels and associated rotating components
[quoted text clipped - 14 lines]
>
> Striemer

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~kurt - 29 Oct 2005 01:56 GMT

> Does anyone have experience with low mass wheels such carbon fibre? Can
> reducing the inertial mass of wheels and associated rotating components such
> as brake rotors produce a noticeable (as opposed to theoretical) improvement
> in handling? Who makes GP wheels? What do GP wheels weigh? Are carbon fibre
> wheels the standard in GP?

I guess it depends on what type of wheels you have to start with. I'm
looking into some new wheels just to hold track tires on the RC51. Since
they are a bit on the heavy side, I have heard some people say aftermarket
wheels are the single best mod you can make in terms of handling. I guess
I'll eventually find out. As it is, it takes a bit of effort to snap the
RC51 back and forth in tight switchbacks. Apparently a great deal of that
effort is reduced with lighter wheels.

- Kurt

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R. Pierce Butler - 29 Oct 2005 03:22 GMT

>> Does anyone have experience with low mass wheels such carbon fibre? Can
>> reducing the inertial mass of wheels and associated rotating components
[quoted text clipped - 11 lines]
>
> - Kurt

It will be interesting to hear your report on the new wheels. I always
assumed that it was the gyroscopic acton that made the bars hard to turn at
speed. I think decreasing mass would also help reduce the amount of effort
required as well. Are the new wheels smaller, larger, or the same size?

pierce

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~kurt - 30 Oct 2005 03:22 GMT

> It will be interesting to hear your report on the new wheels. I always
> assumed that it was the gyroscopic acton that made the bars hard to turn at
> speed. I think decreasing mass would also help reduce the amount of effort
> required as well. Are the new wheels smaller, larger, or the same size?

They will be the same size. My primary goal is to just have an extra set
of wheels. One for street tires, and one for track tires. So, if I run
across stock wheels for cheap, I would probably go for that. Time will tell -
right now I'm having to spend a good bit of money on my house.

- Kurt

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Andy Burnett - 29 Oct 2005 03:43 GMT

> Does anyone have experience with low mass wheels such carbon fibre?
> Can reducing the inertial mass of wheels and associated rotating
> components such as brake rotors produce a noticeable (as opposed to
> theoretical) improvement in handling? Who makes GP wheels? What do GP
> wheels weigh? Are carbon fibre wheels the standard in GP?

I had magnesium wheels on my TZ and also ran it with the stock wheels. I
have also ridden other bikes with and without magnesium wheels. They do
make a difference. I couldn't tell you myself if I noticed a difference in
braking and accelerating, but the bikes were easier to turn and you could
run a little less damping in the suspension.

> Radial brakes are common to new sport bikes. Has anyone made a
> reasonably controlled test of radial brakes? Do they really reduce
> stopping distance? Better calliper performance, could allow for
> reduced rotor diameter and reduced moment of inertia right? Are rotors
> getting smaller as radial brakes are introduced (or getting bigger
> with greater HP and speed)?

I've tried radial brakes that I wasn't that impressed by and radial brakes
that I was impressed by. So far, my experience doesn't say they're vastly
better, as other components may have varied as well. Pretty hard to have a
controlled test, as some of the other components will necessarily be
different, such as the caliper itself. In some cases, manufacturers have
reduced rotor diameter on radial brakes, but I don't think the weight
savings you can get from that amount to nearly as much as the weight
savings of a lighter wheel. To me, weight savings isn't the advantage in
radial brakes; controlling how the pad meets the rotor is.

ab

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G C - 30 Oct 2005 01:12 GMT

Carbon wheels make a difference in the flickability and stability. (more
and less)
Dymag makes CF wheels.

> Radial brakes are common to new sport bikes. Has anyone made a reasonably
> controlled test of radial brakes? Do they really reduce stopping distance?
> Better calliper performance, could allow for reduced rotor diameter and
> reduced moment of inertia right? Are rotors getting smaller as radial brakes
> are introduced (or getting bigger with greater HP and speed)?

More rigid mount, less unsprung weight in some configurations, Better
feel with less chatter. Radial MC is for feel. (Now put on steel lines)
CF Rotors are not allowed in CSC racing, so I'm not spending on 'em.
Rotors are not getting smaller, swept area is the key and a large rotor
allows for better cooling.

> Basically, I'd like to know if taking a few pounds of weight off the wheels
> can make a noticeable difference in handling and ride.

Yes, Unsprung weight is BAD. However, on the street I doubt it is worth it.

> Thanks for your observations and enlightened opinions ; )

Just remember, opinions are like my kids, nobody else wants 'em.

> Striemer

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Gopher Greg
'77 CB750K Stock '78 CB750K AHRMA (Brembo and 320MM rotors)
'00 ZG1000 Stock '96 Ducati 900SS Former track bike
'01 GSXR750 Current race bike (Brembo)
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Motorcycle Forum / General / Sportbikes / October 2005

Moment of Inertia, Turn In, Unsprung Weight, blah, blah...