Front brake - which side?

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stude11

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Jul 15, 2008
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I'm rebuilding my Mk III and sent my discs to be reground at Old Britts.
They mentioned that by swapping the lower legs, I could switch the disc from the right to left, placing the caliper in front of, rather than behind the leg.
Any thoughts on this? It would seem to me that that configuration would maybe reduce fork compression under hard braking, but would that be a good idea? I can't see any other advantage, and maybe the difference wouldn't be noticeable anyway. Appreciate the input.
 
stude11 said:
They mentioned that by swapping the lower legs, I could switch the disc from the right to left, placing the caliper in front of, rather than behind the leg.
Click to expand...

As yours is a MkIII, then it should have the brake on the left hand side, and not on the right as all previous disc models did (except maybe some late MkIIAs?)
 
There has been a lot of discussion on why Norton moved the brake from the right to the left. My own personal belief is aesthetics. When the Mk3 came out with the rear disc, it made it look asymmetric with two large discs on the same side.

When I put my disc rear wheel on the Interstate, I kept the front disc on the right. I find no functional difference in right or left.
 
Ron,

I may have asked this of you before, forgive me if so. Why do all (I think) current single front disc brake motorcycles mount the single disc on the left? It seems it would be cheaper for the manufacture to keep the disc on the same side as the master cylinder.

The fact that Norton changed sides from right to left, at some expense when they were on their uppers, leads me to believe there is some reason other than aesthetics. I'm only speculating here.
 
stude11 said:
I'm rebuilding my Mk III and sent my discs to be reground at Old Britts.
They mentioned that by swapping the lower legs, I could switch the disc from the right to left, placing the caliper in front of, rather than behind the leg.
Click to expand...


Actually, I'm rather surprised anyone at Old Britts would suggest that, as they really ought to know that a MkIII Commando would normally have the front disc on the left hand side?
 
Norton may have thought that the bike would brake better if they were on different sides, Or why else would they change it for the MKIII? I would thought it was better on the right side, chuck.
 
L.a.b. (and others...) you're right. After checking some older pictures on me when I first got the Commando, the disc does belong on the left with the caliper in front. I guess it's been so long since I tore 'er down, I mistakenly thought it belong\ on the right. Thanks for the smack on the forehead...
 
I recall reading somewhere that for some unknown reason the factory found that putting the disc on the left cured some kind of a weave, hence the change. I also think that the front hubs for the later fitment are different with the bearing retaining collar being either left or right hand thread depending on the direction of rotation.
 
Front disc

I think the mk3 disc can go on any side as it has the bearing held in place by a circlip-which would not be affected by wheel rotation.However pre- mk3 models with the disc on the right cannot safely be swapped over in case the bearing retainer unscrewed itself.
 
Why do all (I think) current single front disc brake motorcycles mount the single disc on the left? It seems it would be cheaper for the manufacture to keep the disc on the same side as the master cylinder.

The fact that Norton changed sides from right to left, at some expense when they were on their uppers, leads me to believe there is some reason other than aesthetics. I'm only speculating here.
Click to expand...

I think the expense Norton went to was quite minimal. They simply turned the fork in the triples. The drains are even now at the front! They did add the circlip to the wheel hub to prevent the retainer from unscrewing, but this was offset by eliminating a fender stay.

Perhaps they mounted the brake on the right while the rest of Europe, Japan, and the US mounts it on the left for the same reason they drive on the left side of the road while the Europe, Japan, and the US drive on the right or for the same reason they used a positive ground system while the rest of the world used negative??

All I know is using my science and engineering training, I cannot see any theory that would provide an advantage for either side over the other.
 
I was hoping someone had an answer to this, cause I have often wondered.
I have a few theories.
1. I have heard of the speed wobble issue. Don't know if it's valid or not.
2. At the time there was talk about putting the calipers in front of the tubes for better cooling, less fade. Since Honda was the leader and they put it there, they may have followed suit.
3. The Mark III had the rear disc on the right. Maybe they put the caliper on the left for off setting braking forces?
I believe modern single discs are on the left because of this.
Most drives are the left with the rear disc on the right.
Modern day discs are also behind the legs for better balance. I believe this wins out over cooling.
However look at old racing pix and you will see the calipers in front of the tubes. This is for better cooling. times have changed.
 
This was sorted out 30 years ago by Yoshimura among others.

The caliper goes in the back (unless there is a mount problem).

It places a fairly substantial lump right under the fork's center of rotation, which is the stem.
This greatly reduces the amount of effort requires to turn, and also reduces the wobble amplitude if a shake develops - less weigh to control.
If mounted ahead, the weight's mean radius of gyration goes from almost zero to 6" or so, a huge change.
 
I've heard several explanations why single front discs tend to be on the left side of a motorcycle, but there isn't a basic engineering reason why left is better - as panic said, location of the caliper in relation to the axle is more important.

I think the left side location is more of an aesthetic thing - since a bike on its side stand is leaned over on the left, the right side of the front wheel is a very prominent feature, and a disc would cover much of that.

Conversely, since disc brakes were brand new for bikes in the early '70s, and placing a chromed disc with a high-tech caliper on the right side showed it off, rather than hiding it.

Personally, I think the front disc of an 850 Commando is better looking than the disc on a CB750 (maybe why they hid it on the left?)
 
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