Maximum allowable size disc rotor on NuVinci N171 hub?

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kiltedcelt   100 W

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Maximum allowable size disc rotor on NuVinci N171 hub?

Post by kiltedcelt » May 04 2021 3:10pm

So I'm ditching the derailleur drivetrain on my tandem tadpole trike in favor of a NuVinci N171 hub paired with my BBSHD motor. I downloaded the original spec sheet/manual for the N171 install and nowhere in it does it specify maximum size of disc rotor. Currently, with the regular derailleur rear hub I have a 203mm rotor (which is what most folks upgrade 2-wheel tandems to, front and rear), and *it brakes,* but even with the 203mm rotor it's about what you'd expect from a cable that's nearly 10 feet long. I thought I'd read something about disc brake forces having some deleterious effect on NuVinci hubs - causing some effect on the shell that caused fluid leakage? Maybe that fluid leakage thing was later N3x version hubs? It certainly looks like the attachment point for the disc brake is different and more robust looking actually on the N171 hub versus the later N3x versions. Anyway, does anyone know if there's a limitation on size of rotor? Oh, and for the record, the brakes are TRP Spyke mechanical 2-piston disc brakes all around.

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MadRhino   100 GW

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Re: Maximum allowable size disc rotor on NuVinci N171 hub?

Post by MadRhino » May 04 2021 6:41pm

You don’t need braking power on the rear, so you can use a smaller rotor. But, braking modulation precision is most important on the rear because it is easy to lock the rear wheel. Thus, your best choice would be a smaller rotor and hydro caliper, in order to prevent applying brutal braking kicks to your Nuvinci hub, and to have the precision to control progressive braking without locking the wheel.

On the front, where is 90% of the braking efficiency of a bike, you want the best powerful brake: big caliper and larger, 225mm rotor if you have a robust fork.

That is how you would achieve the shortest braking distance, but I admit it is not that easy to master on a tadpole.
Make it fool-proof, and I will make a better fool.

kiltedcelt   100 W

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Re: Maximum allowable size disc rotor on NuVinci N171 hub?

Post by kiltedcelt » May 04 2021 8:12pm

Thanks for the input. I have smaller rotors I can swap in for the rear, although originally I'd intended for this trike to have hydraulic brakes front and rear. I had decent experience with Magura on a cargo bike I built, but I found even though they were MUCH easier to bleed than Shimano, they had a kind of spongy feel compared to Shimanos I've used. A trials bike seller in the UK makes a split Magura caliper design that uses a rim brake hydro lever running into a Y-fitting and into a pair of 2-piston calipers. I find that the tolerance on the Maguras and the pad to rotor distance to be WAY to fiddly and tight-tolerance for me to want to mess around with on this trike so I swapped them out for the TRP mechanical discs. I had intended to use a 4 piston Magura hydro on the rear. Anyway, it sounds like smaller rotor on the rear - 180 probably if I've got a spare floating around.

john61ct   100 GW

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Re: Maximum allowable size disc rotor on NuVinci N171 hub?

Post by john61ct » May 04 2021 10:29pm

How about regen braking on the rear?

Put the panic-stopping up front, use rear for drag braking down big hills and to help prevent flipping over handlebars

kiltedcelt   100 W

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Re: Maximum allowable size disc rotor on NuVinci N171 hub?

Post by kiltedcelt » May 05 2021 1:36am

Regen would be nice, but it's going to have that N171 hub in the rear wheel. Also, no fears of flipping over on this trike - total length is 11 feet long! The back end is light, but not light enough to flip up off the ground, even in a panic stop. Since the cable run to the rear is so long I can only see it being truly useful if someone is riding in the stoker position and there's a lot more weight back there. Otherwise, even with 15 pounds of battery and 8 pounds of NuVinci N171, the back end is still "light" compared to the front.

john61ct   100 GW

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Re: Maximum allowable size disc rotor on NuVinci N171 hub?

Post by john61ct » May 05 2021 2:07am

Yes, I really want to explore the idea of doing regen with the N171.

The IGH goes backwards, with "some resistance".

Would long term regen "drag braking", say downhill from Donner Pass, do damage?

Think tandem / cargo 500+ lb load, kids' life at stake, so keeping it slow, trying to not burn up the pads,

a few 1000W braking resistor heatsinks leaving heat wave trails behind, for when the pack gets too full. . .

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