Sportbike Forums on WristTwisters banner

Brake Rotors

5K views 29 replies 10 participants last post by  nathanktm 
#1 ·
My rotors are all beyond the point where they should have been replaced. It's a struggle to remove calipers because of how ridged they are. I don't understand the differences between cheap and expensive rotors.

My question; What exactly is the science behind good and bad brake rotors?

I struggle to see what the difference is between a good and bad rotor. All the research I can find is about automotive brake rotors.
Essentially, drilled rotors really are more aesthetic than anything else, but do provide extra venting. Slotted helps expel brake dust and gas and possibly to bite into the pads.

For motorcycle rotors, I see that galfer's wave rotors "Keeps the brake system cooler by allowing air to pass over every point of a brake pad surface." Mr. galfer says they have better bite while keeping rotors cooler. Yet, you very rarely see them as stock on any performance oriented motorcycle, nor in any race setting. They do look really cool though.

Basically, I want some snazzy looking brakes, but I also don't wanna break the bank or lose any braking performance, and gaining performance would be nice. What blows me away is that even cheaper brake rotors are AT LEAST 200 bucks a POP, OEM is like 300 each from what I'm seeing.

Maybe LDH would know these answers as he actually probably sees what rotors work and what don't all the time, but I for sure have no clue what the difference would be between 200 dollar chinese ebay rotors, 400 dollar EBC replacement rotors, and 600 dollar galfer or OEM rotors.
 
See less See more
1
#2 ·
I was shocked at the price a few months back when I was going to replace mine. I went metal to metal one day and stopped riding, got replacement pads (NON OEM) and they made awful noise. I replace them with OEM ones and took the rotors off the rim. I sat the rotor on a sheet of plywood and ran a drill based "paint remover" wheel on them. It looks like an ultra stiff brillo pad. I worked the heck out of the rotors and they came out pretty nice.

I measured them several times and I'm still well within spec.

This was discussed at length about March of this year, IIRC, LDH said the wavy rotors were crap. Most said that OEM brakes were actually very good, that's why I reworked mine.

I rebuilt the whole front end about a month or two ago... New tire, fork seals, oil, brake pads, brake fluid upgrade to DOT 4 and drained. Pretty much everything but the wheel bearings. If you take the rotors off, you can get to the back side with the surface pad.

It looks like this, but has a rubber backing pad. I spent quite a bit of time getting all the marks off the disks. 4 sides total, takes a good while. Then seating the new pads took a bit as they felt funny at first.

https://www.lowes.com/pd/3M-Paint-a...rXsOndDBXGM7-D3MlycaAiNAEALw_wcB&gclsrc=aw.ds

IDK about the groves/holes and cooling, I just trust so many people saying that OEM brakes on the 919 are great. I think I'd spend the money on a fork gold valve upgrade or a rear shock or PC III or something like that.
 
#3 ·
Measure your rotor thickness and runout if you have the capability. I'd guess that they're well within spec still unless you have hundreds of thousands of miles or have misused/mistreated them in some way. The smartest thing would be to rehab and use your stock rotors, beyond that, you're just throwing money at something. It sounds like you're looking for looks as much as anything, and for street braking on a 919 you'll likely never have problems with the wave rotors and you'll get the cooler look you're going for.
 
#4 ·
There is a very good reason why motorcycle discs are drilled: originally the rotors were solid, and worked pretty well ... unless it's raining. In that case the water spins off the center of the rotor carrier(s) and onto the rotor(s), and when the brakes are applied the pads hydroplane for several revolutions, then as the rider tries to get some reduction in speed by squeezing harder on the lever the water is pushed out of the way and the brake locks up, usually resulting in a crash. No fun. The holes in more modern rotors are usually made to overlap slightly to make sure the pads are scanned completely to vent gases and water into them which then escapes as soon as the holes leave the contact surface of the pads. In this way there is a maximum amount of metal for the pads to grip.

Looking at the Galfer rotors it looks like there is about 30% less metal for the pads to bear against, resulting in less braking force for the same amount of pull at the lever (air is a lousy braking surface). This requires more pull which builds up heat in the rotors, eventually causing warpage and a significant decrease in braking power. In the real world they may look cool, but that's the only positive that can be applied to them.

As was said before you can take down the ridge with the careful use of a relatively fine grit sanding wheel on an angle grinder without cutting into the actual braking surface, that is as long as they are not to the minimum thickness.

Rob
 
#7 ·
If you have problems with your rotors, then you need to talk to these guys: https://truedisk.net/

Unquestionably, THE best source to solve your problems. Have used them extensively. You will not find better. A call or e-mail is free.

Best, MyCB919.
I never realized anyone would turn motorcycle rotors. I searched for it and everyone said "buy new ones" without considering the price.

How much does this guy charge? Used to be about $20/each to get something turned.
 
#12 ·
I picked up an aftermarket rotor for my KLR rear for $69.
It was purely garbage in quality and material. I ended up using it as a target.
Bought one off a stacked KLR and got a free caliper to boot.
 
#16 ·
Bought a set of chinese ones for 160 bucks. Haven't come across any negative reviews other than people just saying to not get them because they are cheap. Got the insurance option on ebay so if they turn out to be trash I suppose I'll just get my money back and try something else. A set of OEM would have been 640 dollars so I'd be happy if these perform at least as well as the OEM did and last 1/4 as long.
 
#20 ·
Tournament rotors turned up. They seem OK. I've used Tourmax spare parts before. OK for budget Japanese stuff. I've never used their rotors.
I won't be using theses either. At least not soon I hope. They are going in my spares box.
Slightly different pattern to the OEM. 7 rotor buttons, OEM has 5. The min thickness is 4mm not OEM 3.5mm. So thats a big difference. Also made out of stainless. At least they shouldn't rust in storage.
 

Attachments

#23 ·
I would not do that as the WD40 will migrate subsurface into the microscopic voids.
While nothing like a cast material in this respect, seeing as the rotors are from wrought form, it's still a legit issue.
I would wipe down with a clean towel using a high flash non residue cleaner like acetone, or even rubbing alcohol.
Then wrap in wax paper, waxed one side that is, such as a freezer paper, wax side out, then fully tape, then bag in good plastic, with some dessicant bags inside.
Leave in a place with stable temperature and humidity, preferably warm and dry.
Think military grade specs for long term weapons storage, except no application of preservative upon the rotors.
There are some funky preservatives available that would be suitable for putting on rotors, but I don't know anything about them other than have reading such things do exist from somewhere, for some to be able to access, for some price assumed not to be of our realm.
 
#27 ·
It's not the most common thing, but I've found it in packaging where something with an uncoated iron or steel surface is expected to be in the box long enough for rust to be a potential problem. Ford ships OE truck rotors wrapped in rust preventative paper in boxes. My PowerStop brake upgrade kit for my truck came with the rotors similarly wrapped.



Could I get a link to the eBay ad?
 
#30 ·
I got a set of brake pads (2 pairs) for $5.90 shipped. Since my rotors are hooped anyways, figure I'll give em a try and see if they last me until it's warm out again. I've heard stories of the friction material just falling off. Can't wait to try em out.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top