Today, I realized that my planned brake upgrade will not work out like I thought. My bike is a RD350A, and my plan was to use a TX650 disc hub with a custom made 298mm "TZ replica" rotor from ISR, an Economy Cycle reproduction alloy caliper, and a RD400C RH fork slider. And a caliper bracket to allow for the larger disc. It turns out that this relocation bracket will have to be much larger than I had expected, moving the caliper close to a 9'o clock position. So much for a stock appearing upgrade. I do have a set of TX650 fork lowers, but they will require a lot of machining in order to be same diameter and weight as RD lowers.
I also have complete FZR 400 or 600 fork legs, and just found out that the caliper lug spacing is the same as on RDs, 81.50mm c-c. So now I may look into FZR or R1/R6 calipers? What size discs did the FZR models have? Ideally, I would like to find the lightest fork/brake combo using the stock spoked front wheel, and avoid caliper adapter plates if possible. The stock RD disc and caliper is pretty heavy, near 4 kg.......
fzr 600 caliper, 12mm rotor spacer, r1 or r6 caliper, adapter, and 13mm master, stock RD forks. probably the lightest setup you can do in my experience.
(http://i1097.photobucket.com/albums/g348/rooskie3/monospine%20RD/rdbracket-monospine-installed_zpsh6o2zd2g.jpg)
I probably have the cad file for the bracket somewhere. :vroom:
If you want light weight go with a modern rotor. If you want to stay stock looking you can drop quite a bit of weight off a stock rd rotor. I thinned mine down to 5mm (maybe 4.5, I would have to check), drilled 100 3/8" holes through it, and did a little work to the carriers. They are considerably lighter but probably still not as light as a modern rotor off a super sport.
If you go with a repo alloy caliper you can also get an alloy piston from Eric at oily pipes to drop a little more weight on it.
pretty sure the later xs400 and 650 one piece are already that thin i think (they are almost half the thickness of a 350 one... have one on the back of my hybrid)
Quote from: m in sc on February 26, 2019, 01:34:02 PM
pretty sure the later xs400 and 650 one piece are already that thin i think (they are almost half the thickness of a 350 one... have one on the back of my hybrid)
Later XS650 discs are definitely not lightweight. My 1977 XS650D had dual one piece discs, and they are stupidly heavy. IIRC, going from stock discs and single piston calipers to a single 320mm floating ISR disc and 4 piston Brembo dropped at least 3 kilos. And an alloy fender dropped at least 0.5 kilo more.
Maybe XS750/850/1100 one piece discs are thinner and lighter?
beats me, maybe. there were different variations of the single disc for sure though, ive seen 3. the one on the back of my hybrid is def lighter than the stock rd350/400 one. However, i agree though, the 'modern' stuff is wayyyyyy better and lighter. Danny took a dirtbike one and trimmed it down for his bike. that was pretty cool.
Quote from: m in sc on February 26, 2019, 01:02:51 PM
I probably have the cad file for the bracket somewhere.
Hey Mark, I'd be interested in that if you come across it and you're willing to share. :cheers: Thanks.
i'll find it and put it in the tech library.
Quote from: m in sc on February 26, 2019, 04:25:51 PM
i'll find it and put it in the tech library.
Sweet! :righteous: Thanks!