dabac

Hi guys,
I'm rebuilding a wheel with a Nexus hub, and I'm reacting to how poorly it spins in the trueing stand. Prolly less than a second at a reasonable force. Haven't got that much experience with internal gears, but surely it should do better than this?

FBinNY 

It's a question of rotational inertia vs internal friction. With the various gears and the internal oil's viscosity providing added drag, there's no way it'll do as well as a plain hub. But this comparison is meaningless because any hub alone has little rotational inertia so you'll always be disappointed if comparing to a built wheel. And even then, it's still meaningless because all the forces are negligible compared to the vastly bigger other forces like wind resistance, which provides 90-97% of the total drag when actually riding a bike.

In summary, don't sweat it, the built wheel will spin better, and it doesn't matter anyway.

hueyhoolihan

i rode on a nexus 7 for about 2 years. coaster brake type.

three things that i didn't like about it (and many things i did).

1) cheap looking and sounding trigger shifter. it worked great but was challenged aesthetically.

2) too much pedaling friction when not in the 1:1 ratio (don't remember which one the 1:1 was, probably somewhere in the middle i suppose). and rolling friction.

3) too heavy.

like i said there are many conveniences most of which were utilized best in my city riding.

BTW, i built my wheel myself and did notice a difference when spinning it by hand. you might try different gears and see what you get.

DCB0

You'se guys seem to have misread the OP... he said he is rebuilding the wheel, so probably already has it laced to a rim.

My experience is that they have a little more drag than a non-IGH hub, but certaily should not stop spinning after 1 or 2 seconds... I would think20 or 30 seconds

fietsbob

lube may have thickened in the cooler temperatures, add some Oil.

jolly_ross

Are Nexus hubs cup and cone bearings? I imagine they are. Have you tried adjusting the cones so that they are *just* too loose (i.e. with a tiny bit of play). If the wheel spins better after this deliberate maladjustment then the cause is obvious. (don't forget to clean, relube and readjust after though). It seems easier to eliminate this possible cause first before delving into drag within IGH internals.

Tell us what it was when you work it out - I just bought a 2nd hand Nexus for my winter hack. Hasn't arrived yet tho.

MichaelW

With original grease, my Alfine hub would turn a couple of times only. After an oil dip it spins almost like a std hub. I could feel the improved efficiency a bit but its not a big deal. The main advantage of a thinner lube is that the gear changing wont freeze up in cold conditions.

dabac

Update and clarification:
Yep the hub is built into a wheel. And if I give it a spin to the point of pulling the trueing stand off the table, it'll do maybe 3-4 rotations before coming to a stop. Twirling the axle by hand is almost difficult, but it does turn reasonably "smoothly", no obvious indexing at least. It currently resides indoors, at a fully comfortable residential temperature, and that's where I've been tinkering with it. Am a bit wary about adjusting, haven't read the manual on this one. And with the coaster brake reaction arm at one side, and the gear shifting hook-up on the other, there's a lot going on around the axle.
It's off a new-ish bike, so grease congealing due to age isn't an immediate suspect.

DCB0

Perhaps the coaster brake is partially engaged for some reason.

tcs

Common misconception with IGHs. Actually, the gears are not engaged when coasting.

tcs

The Nexus 7 doesn't have a 1:1 ratio. With the Nexus 7, gears 3-4-5 are dual stage compound and are the most inefficient. Interesting what you 'felt' based on your preconceived notions.

DCB0

Correct me if I am wrong, but does not the Nexus 7 have ratcheting freewheels and/or clutches which introduce slightly more coasting drag than the roller clutches found in the Alfine and (i think) nexus 8?
Just a li'l bit though. The wheel should still spin freely for longer than 3 revolutions!

hueyhoolihan

you're right!!!

my apologies to everyone.

i guess i mistook the 1:.989 ratio for a 1:1. silly me.

dabac

Another update:
Decided to bite the bullet, and pulled the brake arm off. W/o it the wheel spun really well, but obviously the bike isn't rideable like that. Tried putting the brake arm back loosely, and as soon the brake assembly wasn't allowed to rotate together with the wheel the drag picked up again, although not as bad as before. I chickened out and decided to settle for a looser adjustment of the brake arm instead of further disassembly. Naturally the locknut for the brake arm was some sort of weird size(27mm), so I ended up grinding up an old cone wrench to be able to set the new adjustment.
I still believe there's something not entirely right in there, but I've gotten the drag down to tolerable, and I think I'll settle for that.

Retro Grouch 

I'm not the best source for IGH advice but how's it work on the bike?

Without the shifter hooked up I'm thinking you might have the internals in some combination that doesn't like to rotate.

FBinNY 

Since the brake arm seems to be the variable, is it possible that the arm doesn't naturally line up to the chainstay attachment. If the alignment is bad, attaching the arm may be putting an unbalanced load on the left side assembly, and thus causing the added drag you feel. Try using spacers, or changing the bend of the strap (if there is one) so the arm can be tightened in it's natural, aligned position, and see of that helps.

dabac

All the gears go in as expected. Apart from that, it's hard to tell. It's on a step-through bike built for solidity rather than anything else. Good quality parts all of it, but heavy, oh so heavy.

Don't think so. 1st gear on bike has the shifter hookup just as relaxed as with the wheel off.

The reason I got the bike was b/c it was ridden violently, way beyond spec. There might be some of that I'm seeing. Axle is straight though. Perhaps some dimpling in some internal bearing race?

Retro Grouch 

You sure? Every IGH that I've worked with had to have tension on the shift cable to hold it in 1st gear.

dabac

Kinda-sorta. It's the same nut(s) that hold the brake arm that holds the dust shield and the outermost cone. By backing out the brake arm, I'm also slacking off that bearing. There has to be some more bearings further in though, b/c even with the brake arm backed way out, there's no overall axle play in the hub.

If it only spun poorly when mounted in the frame, that'd be a good idea.The bike is in stock configuration, so it shouldn't be an issue. But it's easy enough to check. Now it wouldn't explain why it spins so poorly in the truing stand.

At the moment I'm thinking either sloppy initial assembly, with outer bearing overtightened. Or that something jammed momentarily when the bike was ridden out of spec, causing some internal damage, or an adjustment slipping. Or maybe someone tried riding it with the brake arm unattached, that's a pretty certain way of messing up coaster brake hubs.

dabac

Well, to be honest I don't know if it's lowest or highest gear. And turning the sprocket by hand with the wheel removed from the bike is a so-so indicator. But the gear selector part of the hub doesn't move any detectable amount when I hook the cable up.

DCB0

I did a test on my Alfine bike this weekend - at -5 deg C (possibly making the grease a little stiffer), I gave the rear wheel a spin (with the chain on, so the freewheeling mechanism actuated) and I got 12 spins with a good push. Then I unhooked the chain and let it dangle off the dropout so the cog would spin with the wheel, and I got 13 spins with a good push. Obviously this type of sophisticated scientific experiment isn't possible for everybody so I thought I would share my experience.

DCB0

Every hub is different. I think Nexus 7 and 8 and Alfine are higher (harder) gear with cable pulled out fully. Alfine 11 and old SA hubs are higher gear at less tension -they default to highest gear when cable is detached.