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Discussion Starter · #1 ·
Here's the sketches of the oem rotor and my modification.




I'm planning on getting the program and fixture ready by early next week. Round 1 of CVMA races are the next weekend, so I'll have to do the machining when I get back the week of the 21-27, then I'll send them back to you.

Let me know who all wants to send their rotor for modification and let me know if that time frame works for you. I recommend wrapping it in cardboard and ship via USPS flat rate envelope or flat rate padded envelope, which costs about $6 and only takes 2 days and I'll return them the same way for minimal down time. I'm only asking $20+$6 for return shipping for this first batch.
 

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Here's the sketches of the oem rotor and my modification.




I'm planning on getting the program and fixture ready by early next week. Round 1 of CVMA races are the next weekend, so I'll have to do the machining when I get back the week of the 21-27, then I'll send them back to you.

Let me know who all wants to send their rotor for modification and let me know if that time frame works for you. I recommend wrapping it in cardboard and ship via USPS flat rate envelope or flat rate padded envelope, which costs about $6 and only takes 2 days and I'll return them the same way for minimal down time. I'm only asking $20+$6 for return shipping for this first batch.
Nice design.

Just wondering, with that much metal removed is there a greater, or lesser, possibility of warping with the higher temps from track usage?
 

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Under track/race use, the rear doesn't get used enough to really get hot, so probably not an issue there. Not intended for street use I'm guessing - more of a weight saving mod for us diet-conscious types. Jesse - please post up how your prototype performs when you get a chance to test it out.
 

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Discussion Starter · #4 ·
Under track/race use, the rear doesn't get used enough to really get hot, so probably not an issue there. Not intended for street use I'm guessing - more of a weight saving mod for us diet-conscious types. Jesse - please post up how your prototype performs when you get a chance to test it out.
I'll drive it down the street and see if I can stop the bike with it hehe. Other than that, my rear brake rotor generally gets rusty because I literally never use it on track :)

I did a solidworks analysis of the design and it should cut the weight of the rotor by more than half, from 1 lb 13 oz to about 14 oz. Combined with the 2.5 lb drop in weight by changing to a 415 chain kit, that's 3.5 lbs off the unsprung, rotating mass. That's definitely noticeable on the track.
 

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I will check our rule book and see if its doable.
Havnt touched the rear brake on a motorcycle since 1994 road or track. (disabled right foot)
but this may change when I find a way of doing a thumb brake.
 

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Discussion Starter · #6 ·
Nice design.

Just wondering, with that much metal removed is there a greater, or lesser, possibility of warping with the higher temps from track usage?
This is a good question, I'm not completely sure, You are removing a lot of material, so there's a lot less friction and heat being generated, plus you are creating more surface area and air flow to cool less area, so it may actually run cooler. However, if you are actually trying to stop the wheel, you will have to press the lever harder, which may concentrate the friction on the smaller area heating it up more than if there was more surface area.

I can't say for sure, might be a wash, just will take you longer to stop and will require more lever pressure.
 

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Looks like a whole lot of edges to catch a pad. I would re-shape the slots to be narrower and longer and run 'concentrically' so they overlap. Think Nike swish without my drawing it out.

Personally I think it's a silly thing to do. If for some reason you need a rear brake and you effectively don't have one, you're in a bit of a pickle. Hopefully there's Air Fence in the way.

It's inscrutable that race org will stipulate a f'ing airbox snorkel but let competitors do this to safety equipment.
 

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Discussion Starter · #8 ·
Looks like a whole lot of edges to catch a pad. I would re-shape the slots to be narrower and longer and run 'concentrically' so they overlap. Think Nike swish without my drawing it out.

Personally I think it's a silly thing to do. If for some reason you need a rear brake and you effectively don't have one, you're in a bit of a pickle. Hopefully there's Air Fence in the way.

It's inscrutable that race org will stipulate a f'ing airbox snorkel but let competitors do this to safety equipment.
Is something bothering you? You seem to be so negative in the tone of your posts.
 

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This is a good question, I'm not completely sure, You are removing a lot of material, so there's a lot less friction and heat being generated, plus you are creating more surface area and air flow to cool less area, so it may actually run cooler. However, if you are actually trying to stop the wheel, you will have to press the lever harder, which may concentrate the friction on the smaller area heating it up more than if there was more surface area.

I can't say for sure, might be a wash, just will take you longer to stop and will require more lever pressure.

Why do you want to stop the wheel? its a racebike.
Seen the size of a MotGP bike rear disc? its smaller than an R3.


Not hard to chamfer the edges, very few racers I know even touch the rear brake except to settle the bike in bumpy left handers.
Ive never touched the rear brake in racing at all so my pedal is adjusted out of the wsy so I never touch the stupid thing and ive got abs.
 

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professional racers have the luxury of riding on tracks with oodles of run-off, have the best mechanics, and air-fence or equivalent in abundance. Amateur racers generally don't have any of that. Maybe it hasn't happened to you but sometimes front pads get knocked back so when you go to brake for T1 you find out you've got nothing. No, the rear brake alone won't save you but it's handy to have it do some useful work while you feverishly pump the front.

I'm not sure why pointing out a design risk like a pad catching and locking the wheel, or questioning the value of compromising a piece of safety equipment in a nonsensical pursuit of a few ounces is seen as negative.

I've raced, done sprints and endurance. No, I don't use my rear brake much. The big weight savings matter, the piddly stuff doesn't. Indeed I've had my ass handed to me by riders on the same model but show-room stock with every last OEM part still on it (well, minus the ones Tech won't let thru). It's the rider, always the rider. Nobody shaved tenths off their lap times by skeletonizing rotors.

You'll make up 10x more time just taking some corners a few MPH faster or getting on the throttle sooner or changing a line, or tucking in better, or running a liter less fuel, etc. ****, you can probably make up more time by figuring out the optimum chain tension and how much of what weight oil to lube it with.

Nobody with any sense sits under their awning thinking "I could have won that race if only I had saved 8oz by milling my rear rotor."

But let's talk machining. How do you know that by making these very large cuts you didn't uncork the built up stresses and the rotor doesn't warp all to **** as soon as you unbolt it from the table let alone after it gets subjected to a couple of heat cycles? I have a mill too. But I'm not about to offer a service without some honest to god testing before putting some naive, trusting soul's life on the line.
 

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Discussion Starter · #11 ·
professional racers have the luxury of riding on tracks with oodles of run-off, have the best mechanics, and air-fence or equivalent in abundance. Amateur racers generally don't have any of that. Maybe it hasn't happened to you but sometimes front pads get knocked back so when you go to brake for T1 you find out you've got nothing. No, the rear brake alone won't save you but it's handy to have it do some useful work while you feverishly pump the front.

I'm not sure why pointing out a design risk like a pad catching and locking the wheel, or questioning the value of compromising a piece of safety equipment in a nonsensical pursuit of a few ounces is seen as negative.

I've raced, done sprints and endurance. No, I don't use my rear brake much. The big weight savings matter, the piddly stuff doesn't. Indeed I've had my ass handed to me by riders on the same model but show-room stock with every last OEM part still on it (well, minus the ones Tech won't let thru). It's the rider, always the rider. Nobody shaved tenths off their lap times by skeletonizing rotors.

You'll make up 10x more time just taking some corners a few MPH faster or getting on the throttle sooner or changing a line, or tucking in better, or running a liter less fuel, etc. ****, you can probably make up more time by figuring out the optimum chain tension and how much of what weight oil to lube it with.

Nobody with any sense sits under their awning thinking "I could have won that race if only I had saved 8oz by milling my rear rotor."

But let's talk machining. How do you know that by making these very large cuts you didn't uncork the built up stresses and the rotor doesn't warp all to **** as soon as you unbolt it from the table let alone after it gets subjected to a couple of heat cycles? I have a mill too. But I'm not about to offer a service without some honest to god testing before putting some naive, trusting soul's life on the line.
not even gonna bother.
 

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Jess, I agree with pattonme on the size/ shape of your slots. Maybe you should consider narrower or different shaped slots. That said, I'm still in for your first production run. Keep me posted so I can get my disc to you in time.
 

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Might try something like below. It is a GSX-R rotor. You can see all the edges have been chamfered too.



Won't do much to slow you down. Of course, when I went off at Blackhawk last year, my full rear rotor didn't do much to slow me down.
That one's kind of Zen Mandala Yin-Yang like. Stare at it a while before a race to center yourself and cleanse your chakras! Then simply become one with the R3 and find your bliss on the ride!

Did I miss anything in that? ;)
 

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Discussion Starter · #15 ·
I will chamfer all edges of course, didn't feel the need to say that before, but I guess I have to say it. The design isn't new, I didn't create it, it's been done sucessfully on plenty of superbikes, that's where I got it. it will work fine.
 

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Discussion Starter · #17 ·
If the whole point of this is to save weight, why not just remove the stock muffler like this one: https://www.youtube.com/watch?v=XJyXltgB8NQ
Certainly that would save more weight than the rotor modification.
mikiee, read my post here about rotating unsprung mass:
http://www.yamahar3racing.com/2015/...-race-bike-and-the-different-types-of-weight/

Here's the pictures of the finished rotor. As you can see, the oem rotor weighs 1 lb 12.9 oz, the modified rotor weighs 12.1 oz. This drops more than a pound of rotating mass with a decent diameter.




If you want yours done, send me an email to [email protected]
Cheers,
Jesse
 

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mikiee, read my post here about rotating unsprung mass:
http://www.yamahar3racing.com/2015/...-race-bike-and-the-different-types-of-weight/

Here's the pictures of the finished rotor. As you can see, the oem rotor weighs 1 lb 12.9 oz, the modified rotor weighs 12.1 oz. This drops more than a pound of rotating mass with a decent diameter.




If you want yours done, send me an email to [email protected]
Cheers,
Jesse
Thanks for the link. Very interesting read! Good luck with your modification.
 

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Ok, this looks better then the rendering you had in the first post. Now both inside and outside edges are always in contact with the pad and you took material out of the center also. :)

I always have problems with a heavy foot on the rear brake and locking up so this should reduce some of the bite in the rear brakes I assume. Taking my rotor off next week!
 
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