Smaller disc?

[takehikes]

I like the look of a smaller disc on the front. Are there any straight bolt ups of disc and caliper that are noticeably smaller in size?
I’m also looking to move the disc from the right to the left.

 

[RC4MAN]

You'll not find any "direct bolt ups" for smaller caliper and disc. The bikes were designed for a particular sized disc, the caliper mounting lugs on the fork lowers are placed based on that and are not moveable.
As for switching sides, the 650 wheel is made to mount a disc on either side and some models did have dual discs so you will find some fork tube sets that have caliper mounting lugs on both lowers. I that case the swap is easy.
Early models had the caliper ahead of the lower. I think over time it was discovered that brake performance or perhaps better suspension loading under braking were improved if the caliper was behind the fork. Some guys would swap the fork tube assemblies right/left, to put the caliper on the back side but you would lose the speedo as the anti rotation lug is only on one fork lower.

 

[jetmechmarty]

@nj1639 put an XS750 front end on a Special once upon a time. The XS750 rotor is smaller than the 650 rotor and it bolts up to the 650 wheel. The XS750 sliders have caliper mount lugs both left and right. The XS750, 850, and 1100 standard can get you a left side caliper. Avoid Specials as 750 and up have completely different forks and brakes. So, I'm suggesting using the entire XS750 forks and triple trees.

 

[gggGary]

The caviot for Marty's swap is the xs750_850 neck is shorter. I've done a couple stem swaps putting the longer 650 stem in the 750 triple. It's not too hard, grind out weld. Press out stems, swap, reweld. Access to a bigger lathe makes machining out the weld a good option. IIRC first year 750s used 35mm legs so they would swap right into your 650 triples. Thinner aftermarket rotors can be found on fleabay

 

[gggGary]

PS front 750 rotors are the same part as XS650 special rear rotors

 

[arcticXS]

RD 350 A/B has 267 mm rotors, of the same 2 piece design as 73-76 TX/XS. They bolt right up to a XS hub, as they have the same PCD, center bore and offset. Later RDs (Daytona only? ) have 1 piece discs, just like later XS models.

 

[5twins]

A smaller rotor means less swept area by the pads and less braking power. That's fine if you have dual discs, not so much with a single disc.

 

[gggGary]

RD 350 A/B has 267 mm rotors, of the same 2 piece design as 73-76 TX/XS. They bolt right up to a XS hub, as they have the same PCD, center bore and offset. Later RDs (Daytona only? ) have 1 piece discs, just like later XS models.

Those early 73, 76 rotors won't fit with an xs750 fork which needs the later one piece type rotor offset

 

[jetmechmarty]

A smaller rotor means less swept area by the pads and less braking power. That's fine if you have dual discs, not so much with a single disc.

I think that makes a case for using the entire XS750 front end as it has a brake on each side. The downside to that is likely more unsprung weight regardless of the smaller rotors.

 

[5twins]

Yes, I've never felt the need to go dual disc on this bike. A sorted single disc set-up (stainless line, drilled disc, good aftermarket pads, slightly smaller MC) seems to work well enough.

 

[RC4MAN]

I think this guy is more into the "minimalist" look than what's best or practical.
Also while a decent fabricator can make most anything work it appears that he's looking for something that is easier or more readily bolt on.

 

[takehikes]

I think this guy is more into the "minimalist" look than what's best or practical.
Also while a decent fabricator can make most anything work it appears that he's looking for something that is easier or more readily bolt on.

Exactly.
I do have resources to have made or modified what I want but always easier to see if Yamaha already did the heavy lifting.