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Discussion Starter #1
Does anyone have a bare 400 OEM rear brake rotor that they can weigh on an accurate scale? I'm asking because Spear offers a lightweight rear brake rotor that leaves the entire swept area intact but still gets the total weight of the rotor down to just 400g = 0.88 lb. I'm curious what the weight saving versus the oEM rotor would be.

Jim G
 

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The OEM rotor weighs 29.1 oz. The Norton rear rotor weighed 15.8 for a savings of 13.3 oz.

It's about $200 per pound and I would pay twice that price to reduce unsprung wight.

I've been able to reduce my rear wheel weight by a little over two pounds with an aluminum sprocket, wheel spacers and titanium fasteners and sprocket studs.

(All prices and weight are in USA units)
 

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Discussion Starter #3
Thanks Holoquest! The Spear lightened brake rotor is "on sale" for $170 US right now and is marginally lighter than the Norton rotor (Pear 0.88 lb versus Norton 0.99 lb, plus the Spear one does not take away ANY actual braking surface. I don't know if the Norton one can make that claim as well.

In the rarified cost world of weight reduced motocycle parts, the best "pounds lost per dollar spent" on the Kawasaki 400 are a Lithium battery, a slip-on exhaust, the right fender eliminator, alloy rear sprocket, exhaust hanger, lighter bar ends, cowl versus passenger seat, and even the right gas cap. All of these produce more weight loss per dollar spent than the brake rotor, but for those seeking the ultimate weight reductions, the brake rotor will still make their list.

Jim G
 

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I actually appreciate the reduced braking power of the Norton rear rotor. The original rotor activated abs and locks up the rear way to easily. I noticed the Spears rotor does not include the abs tone ring, and it is riveted to the OEM and the Norton Part if that make any difference to you. It probably accounts for a part of the weight advantage also. I was guessing the Spears part seems to be quite thin and I wonder if it is prone to warping?

Just remember unsprung weight loss has many more advantages than static weight loss, plus rotating mass also takes horsepower to spin up, and braking power to slow down. So is doubly valuable. That's why I am hoping to add Oz forged aluminum wheels next season, they are 6 pounds of the most important (but expensive) weight a bike can lose.

I agree about all the low hanging fruit, my Ninja 400 is down about 30 pounds now, and I've lost 38 pounds myself since I bought mine. With the Norton performance pack gaining me over 6 horsepower the little Ninja becomes quite a little super sport!
 

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Discussion Starter #5
Yes a drop of 68 lb between rider and bike, plus 50 rwhp, makes for a much more exciting ride! I remember that when I was in college, the "superbikes" at the time - the quickest stock bikes on the road (Norton 750, Honda 750, Kawasaki H2 750, and the BSA/Triumph twins), were barely into the high 12s in the quarter. Today, according to my performance modeling software, the Kawasaki Ninja or Z 400 (a "beginner bike") that has lost even just 18 lb and has 2 more teeth on the rear sprocket can hit mid to low 12s if the rider is a pro, and that run can be done much more safely than with the old superbikes thanks to better chassis design. That is what we hotrodders call "progress". :)
 

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Discussion Starter #6
Holoquest: I now see what you mean about the ABS ring. The Norton tetx makes it sound like the rotor weight MIGHT include the weight of the ABS ring. But, it does not say whether the Norton rotor comes PRE-riveted to the buyer, or if the buyer needs to do the riveting himself, reusing the OEM ABS ring.

Since the 2 rotors are now the same price, that makes a difference, as many people (like me) are not equipped to do riveting, and taking either rotor to a shop will add cost and time/trouble.

But the Norton text says the Norton rotor stopping power is very significantly reduced, which is ok for a racer, but not for a street rider. The Spear rotor leaves the braking surface untouched. It is unclear if the Spear rotor is reduced in thickness, but for a street rider OR a track rider, that really doesn't matter, since both use the rear brake rather lightly compared to the front brake.

Since I am not looking seriously at changing the rear rotor anytime soon (because there are better cost to weight reduction raitos for so many other parts on the bike), I had not looked at how that ABS ring was mounted. I guess it makes sense that it is riveted to the brake rotor versus otherwise fastened to the wheel.

Jim G
 

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Discussion Starter #7
I emailed Spears and Gregg Spears responded. The Spears rotor is designed for race use with no provisions for the ABS ring, so cannot accept the ABS ring at all. So if you have an ABS 400, the Norton rotor is currently the only lightweight solution.

Jim G
 
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