OldiesONfoldies

Hi fellow foldies,

I'm thinking of building my ultimate touring foldie and looking at the Bike Friday Expedition. I wonder if its possible to set up a Nexus 8 hub with a triple chain ring configuration? Or at least a dual chain ring set up.

I've been told that it may damage the hub with such a set up. Any words of wisdom? Vik, I need you here....

Al

meb

A triple is doable.

The only damage would be if you had too low a small ring and overpowered the internal gear hub. Rohloff has such a limit they specify, I'm sure Nexus-8 some limit as well.

Expect to lose about 1 watt from the rear derailleur, but if you are touring in the mountains, having the extra range on ratios may be a solution.

If you are going to go with deraileurs anyway, also consider the SRAM dual drive.

datako

If you are going to that much trouble and expense, why not just make the leap to a Rohloff.

You will have a much less complicated drivetrain.

Rob_E

The price difference between a Rohloff and any other IGH and front derrailleur combo is still pretty high. I agree that it would make the drivetrain less complicated, and, if the OP was willing/able to spend the money, it would be a good a choice, but if they are understandably reluctant to put that much money into one wheel, I think the FD is a good way to go.

But then I would think that. It's what I ride. It's not a Bike Friday (or even a folder), so I can't speak to those details, but my full-size bike runs a Nuvinci in the back and a compact double in the front. I thought about a triple, but went double because I realized that the middle ring would be entirely overlapped by the low and high ring, so by going double I could have the same range and have less chainline deflection in high and low gear. There might be an arguement for a triple if you're worried about the steps between gears and a decent shifting pattern. My gear hub has no steps to worry about, and it's pretty trivial to downshift the hub after upshifting the FD, if that's what I need to do, but I usually only upshift when I've hit the upper range of the hub and want to move to my highest possible gear, so I've been very happy with the compact double and see no value in the triple on my set up, but, of course, your set up and riding habits may dictate otherwise.

But as far as damaging the hub, someone familiar with that model might want to chime in, but I think meb hit the nail on the head as far as what to watch out for: Some hubs specify a maximum amount of torque they can handle. It's usually in the form of the tooth ratio between front and rear rings, so you just want to make sure that none of your chainraing-cog combinations will have you over-torquing the hub.

Also remember that you'll need a chain tensioner. It will have to be spring loaded. It will have to work within the chainline of your hub. And it will need to pull X teeth worth of chain, where X is the difference between your smallest and largest chainraing. The tensioner was a real problem for my set up and only the Melvin fit the bill (although some folks have hand-made them from rear derrailleurs). I think the Nexus has a better (closer) chainline than my hub, so you will probably have more options for a tensioner.

vik 

Hola Amigo,

You can put a triple with a Nexus 8 no problem. The issue is the ratio between your granny and the cog on the Nexus 8 hub. Shimano requires that to be 2:1 - so a 42T chainring with a 21T cog.

Now that's the warranty requirement.



I've been using a 21T cog on my Alfine [same as Nexus 8 for all intents and purposes] with a 32T chainring on my Surly Pugsley. I just finished a fully loaded tour on the CDN Great Divide MTB Route with that bike. So dirt riding with 4 panniers, camping gear, stove, food, water, etc.. I had no issues with my Alfine even though it was abused quite well!...

So if you are willing to take a bit of a risk just go for it and I suspect you won't have a problem.

Now if that was my Bike Friday Expedition I'd probably run a double with a Nexus 8 as you'd get a huge gear range with just two chainrings up front. It would shift better and there would be no need to subject the Neuxs 8 to the huge torque from a tiny granny.



I've setup my Bike Friday NWT with a Nexus 8 running a 23T cog and a 46T single chainring. This seems like a great gear range for loaded touring although I need to get out into the mtns on this bike to validate my choice. Running just an Alfine and single ring on my Pugsley has shown me that 8 speeds can be enough for climbing with a loaded bike - even on dirt.

Dahon.Steve

The OP does not need any lower than a 18' inch gear. A 23T cog with a 46T chainring (like Vic's bike) gives you a 21' inch gear. That is so low, you would have trouble keeping the bike up. I can just imagine if you used a tripple chain ring of 24T, the bike's low would drop to 11' inches! LOL! You would be faster pushing the bike up the hill!

As Vik pointed out, the eight speed is enough even for loaded touring. A double ring setup is fine so long as the low does not drop below 18' inch tops. That is easy to do on a folding bike even with one ring.

A front derailluer should not be looked down on. From personal experience, a friction based front derailluer can last for years with very little maintenance and replacement costs are low. Heck, the front derailluer on my Schwinn World Sport from 1980 still works like new! LOL! This setup is still cheaper then the costly German Speedhub with very good results.

tcs

As Sheldon Brown once pointed out, despite the fact some manufacturers provide this specification, it is totally nonsensical. Obviously an elite pro racer could over-torque an IGH at a far, far higher tooth ratio than your 87 pound, 13 y.o. daughter. Over-torquing drivetrain components is real (and rare) but a chainwheel to cog ratio is an artificial construct.

Did you know? department: Shimano says their latest models of the Nexus 8 (SG-8R36) and Alfine (SG-S501) feature an internal torque limiter which makes it harder to damage the hub with too much pressure from the pedals.

Best,
tcs

jur

And added to this ^ is the fact that the torque on the hub is reduced again by the ratio of a small wheel to a big one - that's a factor of 3:4. So with even the lowest of low gears there isn't the slightest chance of trashing a hub on a small-wheeler due to over-torquing.

(Except if your name is jur and you are riding away from the field on your R20 with a dodgy SA8 hub on the local peak. )

bhkyte

Love the white Bike Friday! Fantastic looking bike fully loaded.
I would go for STI, even with V brakes though. I have considered a Nexus with a front drailer before. I have found it cheaper to use dual drive, plus I dislike front mechs, and chain tensioners, but this looks a great set up with less comlplication than the DD.
Hmmm..........

rhm

I agree with Sheldon, tcs, and jur that you could do it, and that you probably won't overtorque the hub.

That said, there's no need for three chain rings; no matter what you do, the middle ring will be redundant. Even with a double, you will have redundant gears; play with Sheldon Brown's Gear Calculator and you'll see. If you did something totally extreme, like 24T and 60T chain rings, you would have only 14 distinct gears; two would be duplicates.

In my opinion the gear range of the Nexus is wide enough for touring as is.

jur

+1

There is a qualifier to the 300% Nexus being sufficient. Depends on your own fitness AND that of any riding partners.

If the riding speed becomes very low for whatever reason, it is nice to have extra-low gears (say 20" or so) for just easy riding on a slope at a non-grinding cadence while your partner struggles along. Or you could get ill and only attain a very low power. For these sort of circumstances it is nice to be able to bail out.

So, just a bail-out. 3 rings? excessive. 2 - quite good.

OldiesONfoldies

Thks guys for all the very helpful and informative info. Nothing like hearing from the experts!

pibach

IMHO gear hubs may make sense on unified rear triangle frames (e.g., BF Tikit) where you do not need a tensioner. Then you can have clean chain line at acceptable weight and prevent chain offs. Otherwise better go with a dérailleur anyway (all other BFs with tuck-under fold). Combining front dérailleur with a gear hub mixes the drawbacks of both worlds and is not advisable.

bhkyte

I hear what you are saying but..........
If that chain tensioner is a drailer then perhaps it makes sense,ie dual drive or BromponX2.Also other than cespro,most drailer set ups are under geared for fasr riding.where cam i get a68 t gog?

pibach

dual drive is a pretty bad idea (heavy, needs two shifters, no clean chainline, no maintenance benefit, less efficient). Makes sense only because on some bikes it is difficult to mount front dérailleur. That's why BF usually does not feature it.

Yes, for the 16" Tikit. But for a 20" bike a 56 T front cog should be just fine.

bhkyte

A dual drive can run from one single sided dual drive spefic shifter. Is there a compactable single sided shifer for a front drailer combination? Not that I know of. It is also fully compactale with STI paddle shifters anyway. So if you want to loose both gear levers on a road bike you can.

Sram also claim that their Dual drive is a lighter set up than a two mech tripple.( I am sceptical about this claim myself, but tripples are heavier.)

Replacing a front changer with an internal hub is a lower maintence replacement option, not a higher maintence option.

Yes it is marginlyless effecient by about 2%? , but changers better than a front and gives a better better gearing up effect than using a tripple (36%). I already am using a 56T on my 16" folder, but on a 20" you get simular to a 700C road bike 53/11 gearing from it. Better to actually have the correct gearing to go this fast, than be spinning out with a 2% theoritical gain.

There are issues with dual drive. ie highter maintence over a simple internal only set up. There is less space around the rear drailer /wheel bolt area due to having both set ups installed. This may get in the way for folding.
If you can acommodate it, it is a valid alternative to an expensive quality 8 speed internal hub approach with or without a tripple or double, or a twin mech approach, espically on a 16" or 20 "folding bike.

mconlonx 

The Alfine tensioner is a double pulley design -- anyone know if it's spring loaded to take up chain slack for application with a front derailleur setup?

pibach

The DD hub weights 1067 g

bhkyte

but the Dual drive typically replaces a 39 and 47 front gog, a front drailer and a normal hub plus QR skewers. If you use a sram single sided shifter, also add a shifter. ie appromimately 60+70+150+420+200=920grams,(based on shimano 105), depending on components. The dual drive is only around 140grams extra, hardly significant.

If you use a conventional twin gear shifter than there is a 250 g approximate weight disadvantage in using the dual drive over an under geared twin mech set up. Worth the extra up gearing and facility of quicker smoother changers using the internal hub whilst stationary or under load. IMO.

tcs

It is and Shimano has advertised using it with their IGH and dual chainwheels.

tcs

bhkyte

there is a interesting upgraded Brompton on Ebay that has a nexus and a Steve Perry(?) fornt mech. 16 Speed Total gear range over all 16 gears is 408% 23 to 96 gear inches
Item number: 330345922941

Is the nexus available in a 112mm axle width?, they claim not to have forced the frame.

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Rob_E

As tcs says, it does. Check the Shimano website for exact specs. When I was planning out my system, I seem to remember it not only specifying that you could use it with a FD, but also specifying the difference in teeth that it could handle. I ended up going with the Paul Melvin chain tensioner, but I think that was largely because with my hub had chainline that the Alfine couldn't quite handle. If you're using it with an Alfine hub, I expect that you'll be in fine shape.

pibach

That's quite an interesting weight comparison. Thought it would be more difference (in fact I think difference is around 400g: 250g hub, 100g QR, 50 shifter difference). Still chain-off issue remains. And lower efficiency.

BruceMetras

Chain throwing off of the front ring is easily solved with a chain guide .. I don't suffer chain drops on any of my DualDrive bikes (TSR- Birdy- SpeedPro) .. I'm also not sold on noticeable efficiency loss in real world biking... on my TSR, I run a tight 9spd cluster, stay in the middle cogs, maintain a relatively straight chainline, mainly stay in the direct drive (#2) hub gear and simply use the 1st and 3rd hub gear for hills (up or down).. average speeds over 20+mile rides on my TSR are as good as any of my non-DualDrive bikes that are set up for the same type of road use (Airnimal Chameleon, Reach Road) ..

badmother

This is really telling us that you do not need a lot of gears if you`ve got the right gears! I think we all carry around a lot of steel (chainrings and stuff) we do not need.

I am trying out two different hubs on my folders these days, a Nexus7 and a Sachs Spectro S7. I always liked the Nexus but now it looks slike the Sachs has got a wide range so I am thinking of maybe getting one more. Doing a three days test ride in a few days.