Explanation needed on front disc rotation please?

[Suzuki_Don]

On the modern disc brake the disc is mounted to the wheel hub and then this inner part of the disc is attached to the out part of the disc with round type fastener that it seems allows some movement of the disc within the pad area when the brakes are applied. These discs have a direction of rotation marked on them. Yet the left and right discs look identical. Check out the diagram below if my explanation is a bit vague.

Why is the directional arrow on the discs and why cant they be mounted on the opposite side and rotate in a different direction.

The reason for this question to fill you all in is that I have found a disc that is ideal for my purposes in fitting it to the front of my GS550 but this disc comes off a single disc bike and to do a dual disc setup I would end up with one of these discs rotating the wrong way.

Is this a real issue? How would it affect braking? Would there be some movement or play in the disc that would be mounted the wrong way?

Hope someone can give me a technical explanation of this?

 

[ArttuH]

My guess is that usually that direction marking is just because of drilling pattern on the disk. If the pattern isn't symmetrical then the patterns will face different directions if you use two same hand disks. I doubt that will have any effect on braking.

 

[Suzuki_Don]

My guess is that usually that direction marking is just because of drilling pattern on the disk. If the pattern isn't symmetrical then the patterns will face different directions if you use two same hand disks. I doubt that will have any effect on braking.

Thanks ArttuH. That sounds reasonable to me too. We'll see what others offer up as well and get a consensus of opinion. I can't see any difference in mechanical construction and what you say makes sense.

 

[salty_monk]

I've wondered the same thing, I'm sure it can't really be anything to do with construction unless it's in the rivets where the spider joins the braking surface.....

 

[Agemax]

there is no mechanical difference in a left or right handed disc, just the hole pattern. when they drill a disc it is done in a way to give optimum disc cooling and minimum pad wear. you can easily run a left disc on the right with no ill effects. i do!

 

[Suzuki_Don]

Thanks Guys. That is a real relief to me. Now that I have a disc with the correct overall diameter and correct offset I should be able to start looking for them on EBAY and I can go for the twin disc setup without having to make up a collar, spacer to make things line up.
Cheers.

 

[Old Colt]

Hi Don,
One of my Honda rotors has RF stamped on it but there are no markings on the other one. The rivets appear to be symmetrical and the drillings in the rotor are not directional. So if these rotors are intended to be handed I do not see any reason for it.
I did get a chance to work on my front brakes on my 550, welded the lower tab for the caliper mounting, all is good, they are structurally finished. I am getting close to riding it with the new brakes.

 

[Suzuki_Don]

Thanks Charlie, let me know how it performs (I mean stops) when you can get it on the road. I will be really interested to find out how things work out and if you're happy with the conversion. How about another picture of your front brakes now that you have welded the bottom mounting bracket. Thanks. Don

 

[tone]

Right heres a quick expaination as i understand it .....

discs are the same apart from the drillings which are there to disapate water ! i doubt there would be any problems running a disk on the wrong side if you were to buy 2 new ones, however as they are floating discs any second hand ones will have wear to one side of the bobbins & if that disc was reversed the wear to the other side would very soon make it useless as the disc would quickly be floating too much or to put it in techinical terms.... knackered

if you have ever ridden a bike with knackered floating disc bobbings you will understand my concern over this

hope that helps

 

[tone]

Another thought after looking at the pic above, that looks like a 310mm sv650 disc & if thats what you intend using why not use bandit 6 discs same dia & available in left & right hands

or if its a 320mm disc bandit 12 or slingshot 1100 (different ofsets)

 

[Suzuki_Don]

Another thought after looking at the pic above, that looks like a 310mm sv650 disc & if thats what you intend using why not use bandit 6 discs same dia & available in left & right hands

or if its a 320mm disc bandit 12 or slingshot 1100 (different ofsets)

Thanks for your reply. The disc is actually a VT Honda which has six bolt holes where it attaches to the GS front hub. The later Suzuki discs have a five bolt set up and would need quite a bit of work to make them fit. Thanks.

 

[salty_monk]

If it's the one that I sent him it's a 310mm disc off a Honda CBR900RR 1998 Vintage.

Dan

 

[Suzuki_Don]

Dan I am planning on using a disc off a Honda Spada VT 250 which is the same design as the CBR disc but with an overall size of 295mm.

 

[salty_monk]

No idea if we got them here... sure it would work though if offset & PCd are the same.

Dan

 

[Suzuki_Don]

Hey Dan. What's PCd. I know it will be something simple, but just can't wrack my brain enough to think what it must be.

 

[Suzuki_Don]

Dan there is a pic of the VT250 Spada front end on my first post in this thread. It is a Honda Spada VT250 vee twin. Maybe you did not have them in the U.S. The discs could be a bit hard to find here as well.

 

[Guest]

Hey Dan. What's PCd. I know it will be something simple, but just can't wrack my brain enough to think what it must be.

pcd, pitch circle diameter - indicates the spacing between the holes that hold the disc on the hub, or more accurately the diameter of the imaginary circle that goes through the center of those bolts

 

[Suzuki_Don]

pcd, pitch circle diameter - indicates the spacing between the holes that hold the disc on the hub, or more accurately the diameter of the imaginary circle that goes through the center of those bolts

CHEERS. Thanks Psyguy. I knew it had to be that or the offset from disc surface to where it bolts to the hub. Just could not work out the letters.

 

[PAULYBOY]

there is no mechanical difference in a left or right handed disc, just the hole pattern. when they drill a disc it is done in a way to give optimum disc cooling and minimum pad wear. you can easily run a left disc on the right with no ill effects. i do!

Yeah, maybe so Max, but in this country if you went to catholic school and yu were left handed, you were the same as devils spawn in the nuns eyes!!!!