Originally Posted by
CEBEP
Could you advise which other popular brand would do XDR hubs? I searched 135mm XDR HUB and had no prices in local google shopping. Every bicycle shop I came across had Shimano products all over them.
Yeah, it seems very limited. For the combination of 135 mm quick release, disk brake, and XD, I find only 2 hubs in a big online shop like Bike24:
https://www.bike24.com/cycling/parts...rchTerm=&sort=
For XDR, I find none at all.
You could ask a local shop if they would be willing to import a hub for you, of course. If that doesn't work out, it seems the only cassette options are keeping the Sunrace (until it breaks) or going with Shimano HG like you're planning.
Originally Posted by
CEBEP
Regarding flipped disk, I’ll definitely try before I buy as my mechanic who will rebuild the wheel and install all parts is the one I’m buying parts from. He will definitely check the alignment first. If alignment is fine is there any other issues to use it flipped? The reason why I’m thinking about RT86 in the front is the front brakes get the most load while breaking and better cooling properties of the rotor can’t hurt.
If alignment is fine in the correct rotation direction, there should be no other issues.
Better cooling doesn't hurt (apart from the higher cost), but there is no practical benefit either, unless you do
a lot of braking. I mean, riding up and down high mountains. I am heavy and I ride only with plain one piece steel brake disks, no special cooling features. I have had disk brake fading only once, on a 406 (20") wheeled bike with 160 mm disks. That was when coming down from 1250 meters altitude to 240 meters (1 km vertical distance) over a 14 km distance. Of this, 800 meters of vertical distance was on the last 8 km of this road. That's a 10% average downhill slope over 8 km, with many tight turns so I couldn't go very fast and get much help from air resistance to slow me down. This was when coming down into Rjukan, Norway, from the south.
https://norgeskart.no/#!?project=nor...03.57719052507
Then consider brake disk diameter divided by wheel diameter. The larger the disk, and the smaller the wheel, the higher the ratio is, and the better your brake power. Some approximate examples, assuming roughly 50 mm height tires:
622 (29er) wheel with 200 mm disk: 0.277 ratio
584 (27er) wheel with 220 mm disk: 0.322 ratio
559 (26") wheel with 180 mm disk: 0.273 ratio
406 (20") wheel with 160 mm disk: 0.316 ratio
Birdy 355 (18") wheel with 160 mm disk: 0.352 ratio - the clear winner!
So looking at this ratio alone,
the Birdy is better equipped for braking than pretty much any other bike you will find in a store, even some downhill specific bikes. Of course those downhill bikes use specially powerful brake calipers, large pads, and special disks, to compensate for their extreme use. The Birdy doesn't need this.
You will not have any kind of brake heating problem with the Birdy, not unless you do downhill runs that are
both steep and very long, like my example from Rjukan. With for example 200 meter hills there is nothing to worry about, in my experience. Anyway, there is nothing wrong with buying expensive high performance disks. There is just no practical need for vast majority of Birdy riders.