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Online Oyabun

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Anyone interested in lightweight rear brake disc?
« on: December 05, 2018, 03:21:17 PM »
I'm thinking of getting a lightweight rear disc lasercutted.
Stock disc is roughly 870grams, I'm sure I can knock off a good 300-350 grams from the disc only, potentially up to 400 with light weight disc bolts.
The picture below is from the Yamaha R3 forums, that new disc on the left side weights only half of the original.

Anyone interested?

Offline Irishrover

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Re: Anyone interested in lightweight rear brake disc?
« Reply #1 on: December 05, 2018, 06:12:23 PM »
I think you mean the disc on the right weighs only half.
I'm done with non stock discs. The rear one I bought a while back cracked in 3 places it looked similar in design to the lighter one on the right, still don't know if it was stress related or cheap steel.

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Online Oyabun

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Re: Anyone interested in lightweight rear brake disc?
« Reply #2 on: December 05, 2018, 06:17:03 PM »
True, apparently the left is the stock, and the right one is the lightened one.

Offline ThirtyOne

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Re: Anyone interested in lightweight rear brake disc?
« Reply #3 on: December 05, 2018, 09:51:04 PM »
You thinking about a group buy?

Offline slowrider

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Re: Anyone interested in lightweight rear brake disc?
« Reply #4 on: December 05, 2018, 10:52:56 PM »

By removing so much metal will it reduce the brake efficiency to the point where it is ineffective.
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Offline Irishrover

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Re: Anyone interested in lightweight rear brake disc?
« Reply #5 on: December 05, 2018, 11:01:38 PM »
I can't see where the advantages would be.
It might be lighter, but it wont make any difference to fuel economy.
Might look nicer, but does that really make any difference at the back wheel?
It could crack like my previous one.
If Honda thought it was worth while and save a few quid on metal, then why didn't they make one stock?

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Offline CB-500-X

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Re: Anyone interested in lightweight rear brake disc?
« Reply #6 on: December 06, 2018, 12:50:52 AM »
*Originally Posted by slowrider [+]
By removing so much metal will it reduce the brake efficiency to the point where it is ineffective.
Looks like it has 1/5 the swept surface area. Not for me. Safer to have a single instead of a double cheeseburger for weight savings.
« Last Edit: December 06, 2018, 12:52:34 AM by CB-500-X »

Offline UnmzldOx

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Re: Anyone interested in lightweight rear brake disc?
« Reply #7 on: December 06, 2018, 01:03:37 AM »
It slices. It dices. It makes julienne fries. (Too harsh?) But would it really help your 0 to 60 time? Maybe, a little? Otherwise, no effect on mileage and downsides for braking, I would guess.

Online Oyabun

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Re: Anyone interested in lightweight rear brake disc?
« Reply #8 on: December 06, 2018, 05:54:48 AM »
Well, usually love to educate, but I guess I've just opened a can of worms here.

Point number one: please recheck your elementary school physics book. Friction forces are independent of the size of the friction surfaces, it is affected only by the forces pushing the objects together and the frocrion coefficient of the materials.

Point number two: a mototcycle is a dynamic environment, where the weight of different parts affect dinamics of the bike differently. Read, first of all the rider is not a fixed weight of the system, so it's weight mainly affects straight line acceleration - changing momentum (especially) on a racebike is effectively done by shifting the rider weight. I'm sure you've heard of sprung vs unsprung weight, and rotating masses - potentially about the importance of reducing masses which are unsprung and rotating. If not, and you got interested in educating yourself, go read.

Point number three; Honda has entirely different design parameters when building a mass market bike. Namely cost of manufacture, which is directly affected by ease of manufacture, overcompliance (to avoid any possible risk by any chance) and lastly the least amount of warrranty issues.

Not all modifications are for everyone. For one, I example don't care about appearance, but effectiveness. Some others are diferent. But please get futher away from stereotypes.

Online Oyabun

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Re: Anyone interested in lightweight rear brake disc?
« Reply #9 on: December 06, 2018, 06:04:43 AM »
*Originally Posted by CB-500-X [+]
Looks like it has 1/5 the swept surface area. Not for me. Safer to have a single instead of a double cheeseburger for weight savings.

In fact, the swept area is the same on both (please check swept area definition. E.g. swept area of thin wind turbine.) What you referring to is fricrion surface area, but if you remember your physiscs classes friction is not dependent on area. Strangey and completely against what would normally think, but that's the case.
Surface area affects mass, heat dissipation, heat absorption capacity, longevity, but not braking performance, as long as there's allways a surfave contaxt between the friction materials.

 


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