Drilled vs non drilled rotors?

[rfbatman]

I find I need to replace the rear rotor on my 81 XS1100 SH.

I see that there is one for sale on ebay for a 78. It has a different look, not drilled on the 78 and 81 is drilled.

Anyone know if that makes a difference? Are they interchangeable?

Also, can these rotors be turned like the ones on cars?

Thanks!

[Ken Talbot]

I believe the slots on the late-model rotors are supposed to help wipe dirt and water off of the rotor and perhaps help cool the rotor a bit. If you don't mind the look, you can swap solid rotors for any one of the three on your bike. If you look for another slotted rotor, be sure you don't get a left side slotted rotor - stick to another right side (i.e. front right or rear) rotor.

IIRC, I don't think there have been too many people have much luck getting rotors turned. Even if you don't have very much of a warp, you end up having to turn it down past minimum thickness to get it straight again.

[rfbatman]

Thanks Ken,

I'll buy the one on ebay. It is cheap and I don't think the abscence of slots will be very noticable. Besinds I don't know when I'll be able to find a slotted one.

Rick

[Jerry]

Bike rotors are alloy, not cast iron as on auto rotors. Standard turning equipmet will not work. A machine shop may be able to surface-grind them for you, but the stock spec leaves very little margin of wear.



Solid vs drilled.

Couple differences here. Surface area vs head dissapation and theoretical vs actual performance. Many people think the drilled (or slotted) rotors look better, and Yamaha went with them beginning in '81. These late-model units are directional, having different part numbers for the left and right sides. Rear rotor caries a different part number as well.

Drilled rotors (holes and slots with dressed edges) will cool faster and break water film more easily than solid rotors, even though theoretically the brake pads should brak through with no problems. They may warp faster, having less mass to disapate heat internally. Truth is, for normal street use there is very litle difference in performance. If you have the money, there are sinstered iron rotors available for the XS/XJ, same as used on race courses. 'Course, they rust like crazy.....

There have been several threads on this topic in the past, and Gary Granger put together a cross-reference (some other Yamaha bikes used the same rotors) that will tell you what rotors fit your bike. Do a search on "rotors" and see what you get.

[newmaac]

Did you already buy the rotor?
If the auction has not already ended, I can offer you a slotted rotor. I have a few left.
I don't know what you were going to pay on e-bay, but I ned to get rid of some of this stuff. I am not looking to retire here.
Let me know of your status.

[rfbatman]

re....ebay rotors

newmaac

Thanks for the offer. It looks like I will remain the high bidder at a whopping $12.95. If it holds out I'll have to buy it.
Shipping is another $12.00.

I would have preferred a slotted rotor tho.

Any idea on what you want for the rear one? I could save shipping as I get to San Jose every month for meetings.

Thanks,

Rick

[newmaac]

Rick,
I will see if I have one that has already been pulled off of a bike.
If not, I will check the condition of those still mounted. (if it stops raining for a little while)
If I have one already pulled, I will match the price on e-bay.
Do you know when you might be this way again? (San Jose)

[rfbatman]

San Jose?

Hi Mike,

I ended up having to buy the solid one on Ebay. I would still be interested in 3 slotted rotors if you have them. I'll keep them for future use.

As far as when I'll be in SJ again, I know it won't be until February.

I'll let you know when I get the exact date.

Rick

[Pat Kelly]

I don't remember the details, but I remember an article in a bike mag long ago (late 70's early 80's) that compared rotors on bikes.

They tested solid, vented, and drilled to determine the most effecient.

Solid was best for total contact area and light weight.
Vented was heavy, good contact area, and ran cool.
Drilled was light but less contact area. Drilled looked the best.
The differences were very slight but measureable. I don't think that performancewise they make any difference to mere mortal road riders.

They determined that a drilled rotor didn't make a difference with shedding water or dirt because that was squeeged off by the brake pad anyway.

I drilled my front rotors and have a slotted rotor on the rear .

Someday I'll buy the drilled full floating rotors from Merriams at $200 each ........ someday.