Noticeable differences in drag between Nexus 7, Nexus 8 and Alfine 8?

[mzjo]

I am quite happy using my slightly borked A8 hub around town, stamping on the pedals makes it complain and jump but that is no problem because it is avoidable. However a friend has asked me to join in a bit of soft off-road and this bike will be the one to do it (it is a mtb frame and it has shorter cranks than an mtb so it is first choice in spite of offers of bike loans).

So, since I don't particularly want to convert back to derailleurs (which would probably be 1X8) the time has come to replace the hub with something less borked. The choice comes down to another A8, which is being complicated or expensive to source (Di2 models are cheap but I can't find the gearchange motors and batteries quoted and the switch is very expensive for what it is, A8 classic is relatively expensive, new internals for my hub, if they fit, cost as much as a new hub), a Nexus 8 (which could use all my existing finishing kit) or, cheapest to buy but needing a new cassette and shifter, a Nexus 7.

Obviously in order ascending of drag one would expect A8, N8, N7. The question is how much is this really noticeable? Between an A8 at 200€ and an N7at 120€ would the drag be sufficiently significant to justify the extra cost? The models I am looking at are the current ones (I think), A8 S7000, N8 C6010, N7 7R46. What are users finding in real use rather than in theory? FWIW I don't notice much difference between 4th (the most draggy) and 5th (the least draggy) on my A8.

[igauk]

"a Nexus 8 (which could use all my existing finishing kit)" - I think you've answered your own question there as I'd be surprised that in use, especially off-raoding, you'd notice any difference is drag.

[Jakob W]

IIRC current N8s are simply rebranded versions of the older A8, so you may find that you can buy an N8 and swap over the internals? I'm sure one of the resident IGH experts will be able to tell you if this is the case...

[Brucey]

due to a mistake in shimano's techdocs I thought for a while that current N8 hubs interchanged with current A8 hubs. They don't, sadly. The main differences are;

1)  in the LH end of the axle; disc brake models have a difference in the length of the larger diameter threaded section that accepts the cone (and in some models the locknut too), and

2) the shift protocol; current A8 hubs use a 'high normal' shift pattern and the cassette joint is sprung to rotate ACW by itself (like A11) rather than all older Alfine/Nexus hubs that are sprung to rotate CW by themselves, with a low normal shift pattern.

That said, the new N8 for disc brakes is remarkably similar to the older A8 hub and can use the same shifter, cassette joint etc.

Also a new 'premium' N8 (with roller bearings on the planets, like A8) can be had (in a wheel) with shifter, cassette joint, cable etc for about £125 on e-bay last time I looked. Even if the wheel itself is a bit crap it seems rude not to, if you ask me....

cheers

[Brucey]

regarding IGH dragginess; the biggest single factor is the quality of the lubrication. Very many Shimano IGHs have insufficient grease inside them. If water gets in the ring bearing claps out pretty quickly and if the lubrication on the planet gear bushes fails the hub is hard work to use and will wear out PDQ.

N7 has plain bushings on the planet pinions and uses two gear trains in series in gears 3,4,5, i.e. all the most used gears. It uses one gear train in gears 1,2,6,7. There is no direct drive gear (even though there is a near-unity gear ratio...) It is a great hub for utility purposes but it isn't as efficient as some others.

N8 basic versions have plain bushings on the planet pinions and use two gear trains in series in gears 2, 3, 4, and one gear train in gears 1, 6, 7, 8. Gear 5 is direct drive, and is the most efficient ratio. Gear 4 is the least efficient ratio. Gear 4 is essentially redundant in these hubs, IMHO. It is less efficient than gear 5 by almost the same amount as the ratio difference, so if you use gear 5 instead of gear 4 the load on the pedals  is almost identical but you will go about 20% faster in gear 5....

N8 'premium' and A8 hubs are almost identical to N8 basic ones but the efficiency is greatly improved by the use of roller bearings in the planet pinions.

cheers

[Bolt]

Is your A8 definitely "slightly borked" or could it be the cable/shifter that needs attention, or the hub needing a relube?

I've found that the occasional slip under torque in the lower gears is not unusual on both new and old hubs, but a well routed and adjusted cable can hugely reduce the frequency of this happening.

[mzjo]

Is your A8 definitely "slightly borked" or could it be the cable/shifter that needs attention, or the hub needing a relube?

I've found that the occasional slip under torque in the lower gears is not unusual on both new and old hubs, but a well routed and adjusted cable can hugely reduce the frequency of this happening.

Lubrication did definitely improve it  but it slips in 7 and 8 fairly regularly (like at any time when not going downhill with a tailwind!). Starting off in 5 gets a very nasty feeling of not going anywhere coupled to various complaining noises but otherwise 5 is quite usable. I have not yet stamped on 1-4 hard enough to get a protest (arthritis limits power output too much) but I am sure that off-road would rapidly test things. Around town using basically 3-6 is ok (enough to make me like it and appreciate its virtues) but it is definitely borked somewhere. They are sufficiently rare in this part of the world to make looking for spare bits a pointless and fruitless task (like asking the Shimano dealer about it gets you flung out of the shop).

[Brucey]

There's only a few places in which slippage can occur.  The hub layout gives clues too.

Gears 1-4 are replicated by gears 5-8 but in 1-4 there is a reduction gear operation that increases the load on the sun locking. If there is an inherent  fault in the sun locking it normally causes slippage in gears 1-4 even if it doesn't in gears 5-8, making your described fault unusual.

In gears 5-8 there is also a sliding clutch engaged.  This most commonly slips in gear 5 (indeed it is pretty much the only thing that is likely to slip in gear 5 only), and the reason it slips is usually 'bad adjustment' of some kind, e.g.;

1) bad adjustment of the usual sort (i.e. marks don't line up in the CJ)
2) bad adjustment in which the CJ marks are not correct (for your hub)
3) bad adjustment in which the sliding clutch isn't synchronised with the sun locking pawls (usually a hub build fault in factory).

If the slippage in gear 5 goes on for long enough the sliding clutch can wear so that it slips in any or all of the gears 5-8.

If the sun locking isn't working properly in 5-8 but it is in gears 1-4 this is very commonly some kind of cable fault.

A fault that can appear to be a hub internal fault is when the driver/sprocket fitting is worn, so that the sprocket slips round when under load.

You shouldn't put up with/carry on riding on a hub that is slipping; no good will come of it.

cheers

[mzjo]

There's only a few places in which slippage can occur.  The hub layout gives clues too.

Gears 1-4 are replicated by gears 5-8 but in 1-4 there is a reduction gear operation that increases the load on the sun locking. If there is an inherent  fault in the sun locking it normally causes slippage in gears 1-4 even if it doesn't in gears 5-8, making your described fault unusual.

In gears 5-8 there is also a sliding clutch engaged.  This most commonly slips in gear 5 (indeed it is pretty much the only thing that is likely to slip in gear 5 only), and the reason it slips is usually 'bad adjustment' of some kind, e.g.;

1) bad adjustment of the usual sort (i.e. marks don't line up in the CJ)
2) bad adjustment in which the CJ marks are not correct (for your hub)
3) bad adjustment in which the sliding clutch isn't synchronised with the sun locking pawls (usually a hub build fault in factory).

If the slippage in gear 5 goes on for long enough the sliding clutch can wear so that it slips in any or all of the gears 5-8.

If the sun locking isn't working properly in 5-8 but it is in gears 1-4 this is very commonly some kind of cable fault.

A fault that can appear to be a hub internal fault is when the driver/sprocket fitting is worn, so that the sprocket slips round when under load.

cheers

Thinking about this a bit
1) Is it possible for the CJ to be worn and for that to throw the adjustment when the cable is under most tension? Affecting only the top gears? The skipping that occurs occasionally in 7 and 8, more rarely in 6, is not the same fault I think as what has happened the couple of times I have tried to start off under load in 5.
2) Could my cable line be a source of problems? The gear line goes down the seat stay and I have had to play a bit to get what seems to be a smooth line (in line with the seat stay didn't work out, couldn't get the line close enough to straight)? How else to do it, covered all the way to come along the chainstay? That wouldn't please me!
3) I have spiral cable outer. Could this give compression problems at the max tension end of the operation? (I have never got on with the straight reinforced stuff, never found out how to cut it satisfactorily. Spiral does fine for me but then I don't have many bikes with indexing and that is only 7/8s)

You shouldn't put up with/carry on riding on a hub that is slipping; no good will come of it.

cheers

That's very fine said - but in a part of the world where (unless advice from on here provides the solution) it isn't going to be fixed by anyone else what are the options? Bin it straight away or carry on using it while its normal duty keeps it out of its trouble zone and it isn't mission critical until it goes bang (which might very well take a few or more years). But this is all a bit off post since the answer for the original question is current premium N8.The reliability question only becomes important if it is caused by a part of the installation which I would replicate with the new hub!
 The other thing to remember is that this hub was secondhand with no reliable history and quite possibly a lot of abuse (on a tandem apparently and in fairly dirty conditions) so faults could well exist due to wear (particularly of roller clutches).

[Brucey]

yes I am suggesting that you should have a go at fixing it rather than ride it whilst it is slipping.... and the cable is a good place to start; I think that cable run is pretty iffy-looking....

I think that

a) yes using compressionless (SIS) cable housing will improve the shift accuracy

b) fitting different NTWs would allow the cable run to be improved significantly.

On the latter point the CJ can be positioned at almost any angle, provided the correct NTWs are used.  I think you could have a much straighter housing run onto a CJ that is almost aligned with the seat stay. You always have an option to use full housing down the seat stay which will allow an even smoother run onto the CJ, too.

IIRC you can re-angle the CJ very easily if you already use the green and blue NTWs; simply swap the left for the right, i.e. fit the green NTW on the right and the blue one on the left.

Gotta be worth a go, that, using SIS housing.

hth

cheers

[Brucey]

also; re roller clutches and potential for slippage;  there are three roller clutches in this hub, lets call them A, B, C, (from right to left in the hub) and call the sliding clutch 'S'. Clutch A is used to drive the 2s reduction stage in gears 1,2,3,4. When clutch A isn't used, S take the drive instead, so it is A or S. Clutch B is used to drive the hubshell (all gears except 1,5). Clutch C drives the hubshell in gears 1,5, so it is clutch B or clutch C.  There are three locking pawls which give the increase ratios in the 4s gear stage, lets call those 2,3,4 respectively.

So gear by gear

Gear 1 uses A, C only
Gear 2 uses A, B, 2 only
Gear 3 uses A, B, 3 only
Gear 4 uses A, B, 4 only
Gear 5 uses S, C  only
Gear 6 uses S, B, 2 only
Gear 7 uses S, B, 3 only
Gear 8 uses S, B, 4 only

So as indicated previously slippage in (say) gear 7 and gear 8 only don't clearly indicate a single clutch or pawl fault of any kind; this points the finger at the cabling.  BTW I would advocate running full housing (from the top tube or even all the way) on this type of machine because there are fewer places for the water to get in. An unsealed seat stay cable run with an open top next to the CJ is a recipe for trouble IME.

cheers

[mzjo]

yes I am suggesting that you should have a go at fixing it rather than ride it whilst it is slipping.... and the cable is a good place to start; I think that cable run is pretty iffy-looking....

IIRC you can re-angle the CJ very easily if you already use the green and blue NTWs; simply swap the left for the right, i.e. fit the green NTW on the right and the blue one on the left.

Gotta be worth a go, that, using SIS housing.

hth

cheers

Swopping the NTW from side to side, been there, done that already. It puts the CJ nicely in contact with the chain. IIRC there really wasn't any available position that improved the line and didn't put the CJ in close proximity to the chain. That's why the cable run is as it is! It might be possible to use a different set of NTW to slightly improve the line on what it is at present but I haven't a clue which ones and my brain freezes when trying to work it out logically.
I was thinking of running the cable totally covered down the down tube and along the chain stays, aided by suitable quantities of cable tie and the chainstay protector for the last bit. Not very pretty but beggars and all that..... Might try the line from the seat cluster first but I don't think there's anything to be gained due to CJ interference with chain.

Rain getting into vertical openended cables is not a problem; this bike doesn't see enough rain!! Might become a problem off-roading though.

Will try to sort it but I won't bin it if I don't succeed. Am still of the opinion that it can run until it's properly bust!! I will have had my 30€ worth by then 

[Brucey]

if there is a CJ-chain clash, you could try using a different sprocket dish/chainline, and/or bending the CJ arm a little. It is usually possible to sort it out so it isn't a problem.

cheers

[mzjo]

Current sprocket is a 15t so flat. Offroad may well use a dished sprocket (SA). The only Shimano sprocket I have is an Alfine one with a platic guide on it so will only go one way! There isn't any provision as on a SA hub with spacers to change the chainline; perhaps there should be but there isn't!

Will try changing things along the lines you suggest and report back (with photos where necessary).

Thanks for the advice Jo

[Bolt]

Just to endorse Brucey's advice re cabling.  My A8 bike was a self build which used a cable routed very similar to the OPs, I used to experience the occasional mis-shift, maybe once every 20-30 shifts which I simply accepted as a characteristic of the secondhand hub.  Sometime later I acquired a secondhand purpose built A8 Kona which runs a fully enclosed cable under the downtube and bottom bracket and along the chainstay with a straight entry into the CJ, what a revelation it was, perfect shifts every time.

I then bought a new A8 cable and shifter and installed it on my self build using the same routing as the Kona, the improvement was immediate and shifting performance has remained perfect ever since.

[mzjo]

That is undoubtedly what I will do. Now where am I going to source the cable? Not in this part of the world for sure 

[Bolt]

This is what I buy, it's a twist shift but works well with an Alfine and it does come with cable ferrules and cable clamp bolt... and it's cheap!
https://www.rosebikes.com/article/shimano-nexus-sl-8s31-twist-shifter/aid:101125

[mzjo]

Well Bolt's post was the solution. Measure up with a length of old cable outer, trip to the LBS where Jeremy and his dad sorted me out, length of the right outer, new inner and a couple of plastic ferrules. Fit same (which is now a bit more awkward than the old installation with less free movement 'cos I can't unhook the cable from the frame). That was saturday. This morning test run going to fetch the bread. Stamped on ti as hard as I could, the knee was crying "mercy" before the hub. 

Many thanks to everyone who has helped with comments and especially Brucey for convincing me to keep trying to fix it and Bolt for giving me the eventual solution 

[Brucey]

apologies if this is obvious but it is **vital** that the cable ferrule that is fitted into the CJ is a metal one, not a plastic one; plastic ones are not reliable here because the ferrule stopper parts in the CJ are very small, and will usually pull through a plastic ferrule after a while.

cheers

[Bolt]

So glad the new cabling worked   You should still be able unhook the cable from the the cj easily by grabbing it where it runs along the chain stay and pulling the end of the cable out of the housing on the cj, leaving you enough slack on the inner to unclip the clamp bolt easily.  If you've zip tied the cable to the chain stay this would indeed make things tricky, I'd leave the last cable tie/clip as close to the bottom bracket as possible or use a velcro strap which is easily removed.

[mzjo]

re cable ferrule; it's plastic, I will remember this and see how long it lasts. The old cabling also had a plastic ferrule which didn't cut up and I can't be bothered to replace it just now - time to get on with life!

Re detaching the cable;  Yes mine is cable-tied to the chainstay up near the bb. It then passes inside the chainstay protection up to the CJ (which also enters inside the protection). I have mine running over the bb rather than under; it pleases me more like that but does complicate things. The real hassle I think is caused by the frame ends which have a chunky design and stop me getting my fingers on the cable clamp like I would prefer. With the cable passing inside the protection I possibly don't need the cable tie at the bb. I don't normally get many punctures but off-road could be very different;