Fat and Belted 9:ZERO:7: but Alfine or SS?

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  • Fat and Belted 9:ZERO:7: but Alfine or SS?
  • druidh
    Member

    From the 11-speed Alfine Techdoc:
    http://techdocs.shimano.com/media/techdocs/content/cycle/SI/Alfine/SI_37R0A/SI-37R0A-002-ENG_v1_m56577569830728103.pdf

    It is recommended that the gear ratio of the front chain ring be set to approx. 1.9
    Example: F34T – R18T, F39T – R20T, F45T – R23T

    It doesn’t say what the consequences of running a lower ratio is. However, there must surely be a reason and it’s odds on that running a lower ratio would harm your chances of any warranty repairs.

    The only similar recommendation for the 8 speed is that the rear sprocket should be between 16T and 23T.

    I had a 11-speed Alfine fitted to my 9:ZERO:& on first build (using a Philcentric BB) and staying within Shimanos recommended ratios. I found that it didn’t really go low enough to make the most of the massive traction available from the tyres.

    However – I definitely prefer a wide range of gears on all my bikes. A stronger, “toque-ier” rider might not have had such a problem.

    FWIW, if I didn’t already have my 9:ZERO:7, I’d have one of those frames in an instant.

    Premier Icon ir_bandito
    Subscriber

    Alfine AND belt?

    Can you get a suitable primary ratio within the belt choices available?

    druidh
    Member

    There’s a 24T rear for Alfine/Nexus hubs. A 46T or 50T front would keep you close to or within Shimanos guidelines.
    http://www.carbondrivesystems.com/downloads/CarbonDriveProductListRev_Web.pdf

    So, I’m being very tempted by the 9:ZERO:7 Sliding Rear Dropout frame, but what to do with the drivetrain?

    Very interested in fitting a Gates belt-drive because on my regular bike the chain lasts only hundreds of km, despite cleaning and lubing every ride: lots of sand…

    Choices are:
    – Run it SS and have some different cogs lying around to play with ratios (within belt length limits as per the Gates calculator thingummy, of course).
    – Stick an Alfine on it.

    I’ve been doing some reading on Alfines and there seems to be a perception that there is a higher failure rate in MTB applications because of the lower primary ratio – in my mind a lower gear is one where you get relatively less wheel revolution per pedal stroke, i.e. more torque. However Mr 9:ZERO:7 is recommending a “lower gear ratio” for the same reason – is this a mix up of terminology between UK and USA?

    Anybody got any advice on gear ratios off-road, fat-tyred and Alfined?

    On the WBO/STW scale I’m a middleweight mincer (75kg, have been known to average 20km/hr for 4-5hrs on generally flat trails, prefer to walk down steep hills). Plan is to use this bike for day-rides on sandy cattle trails, salt pans and the like.

    Premier Icon ir_bandito
    Subscriber

    i run 46:24 with a 113T belt (shortest available) on my Kona a with 17″ chainstays.
    So you should be fine with a longer belt with the Zero7’s 18.4″ CS length.

    Thanks, chaps.

    In a fit of procrastination last week I spent some time flicking between the Gates’ calculator linked above, Sheldon Brown’s Gear Calculator and MTBR.

    With a 39F:24R you get a primary ratio of 1.6 and overall range 0.53/0.64/0.75/0.85/1.00/1.22/1.42/1.62. The 1.6 primary is probably acceptable for the type of use it’s going to see and MTBR people (well, one of them) reports going down to ~1.5 without issues. Aesthetically better to run with smaller cogs, so will be back on the Gates’ charts tonight!

    [Edit: I see you were both typing at the same time as me, thanks again for the input]

    Premier Icon Andy R
    Subscriber

    As far as the Shimano recommended minimum ratio goes – surely if you’re climbing somewhere steep at, say, 4mph aren’t you better doing this with a low gear and higher cadence as for a given ground speed surely the torque is then less for the same power output.

    So, is it better to gear an Alfine at 34:16 and have to use brute force to conquer a given climb or to gear it at 32:23 (as I do)and be able to use a higher cadence instead of having to be out of the saddle and riding it more like a singlespeed – ie just hammering it up?

    As far as invalidating any warranty goes (not that I worry about such things)how would anyone know what primary ratio you were using when the hub died if you didn’t tell them? I’m sure some brutally strong sprinter could rip one apart whatever ratio they were using.

    Anyway – I’m now experimenting with an 8 speed Alfine and a primary ratio of 28:22. So far so good but then I’m old and feeble…

    *edit* I reckon a primary ratio of 1:1.5 is certainly a reliable ratio from my experience but then I’m not brutally strong nor especially heavy at about 70kgs.

    Premier Icon letmetalktomark
    Subscriber

    On a side I run 29 : 18 with my 8 speed Alfine and 29er.

    is this a bad thing?

    loum
    Member

    However, there must surely be a reason and it’s odds on that running a lower ratio would harm your chances of any warranty repairs.

    Does anyone know of any warranty repairs that have been turned down due to “low ratios”?
    I’m asking because IMO, this could be being misinterpreted, and could be purely a recommendation to allow the user to set up their bike gearing to give predicted gearing expected to be useful to them – a start point to work around similar to what a derailleur set up would give.

    I’d hope and expect limiting ratios to be explicitly stated as such if they were intended as such, and intending to refuse warranty work. Direction/instruction rather than recommendation. That’s how I’m interpreting it anyway, currently running 32-20.
    For comparison, the only off-the-shelf Mountain bike I know that’s supplied with the alfine11 is the Genesis iO iD, which comes with 32-18. On-one used to do some too, but can’t see any at the mo’.

    druidh
    Member

    letmetalktomark wrote:

    On a side I run 29 : 18 with my 8 speed Alfine and 29er.
    is this a bad thing?

    There are no recommended ratios in the 8-speed documentation.

    Well, too late for Christmas, but here we go:

    drofluf
    Member

    Have fun on it!

    What did you decide gear wise?

    Late to the party but I’ve just switched my Pugsley from singlespeed to an Alfine and I don’t regret the change, lower ratios gives me better traction when seated. Before I had to stand up when it got steeper which meant my back wheel lost grip and I was walking up stuff I should have been able to ride up.

    …you need to be back home Mike, we’ve got some snow here 😉

    Premier Icon bruneep
    Subscriber

    Pop over to UK fat bikes and post the build up there as well.

    The joys of the day job keep me far away from the bike, only managed a couple of short rides with wife and kids in the last 2 months so not much to report, except that the village kids love it: had a gang of them running after us for 5km last time out.

    Thankfully Easter provided a long weekend at home so I managed to get out for my first proper ride on it: a 20km loop with some nice streambed singletrack (mix of hard ground and soft sand patches).

    (Hoping the images work for everybody: Picasa has merged into Google+, but I think I’ve got the sharing set up right now.)

    On the spec: it’s exactly as per Fatbikes’ Tusken build kit:
    – Medium frame in anodized black (matt finish but doesn’t match the glossy forks
    – Nuvinci continuously variable hub gear
    – Gates belt-drive (42:28 (1.5 primary ratio) with a 128T belt to suit 456mm BB-Rear Axle, pretty much central in the sliding adjustment with 7/10mm fore/aft adjustment left)
    – Dillinger tyres (website now changed to Knards, tubed with ~150ml Stan’s sealant in each)

    My thoughts so far:

    Frame: for my build (178cm) and riding (dry, dusty, sandy) I think the large frame might have been a better bet as the dropped top-tube for better standover in winter gear is kind of redundant.

    Gearing: feels a bit short on the faster bits (spins out at 20-25km/hr), but might order a 46:24 (suits the belt and frame) for a primary ratio of 1.92. Will have to see how it fares in more challenging Kalahari sand. I also rotated the cable-hub interface to point up the seat-stay.

    Tyres: running at quite high pressure (haven’t measured it, but maybe 5mm of give under the thumb). Had one wash-out in a fast corner on soft sand but otherwise no problems…

    …except for thorns. Got home and de-thorned the front and the Stan’s just flowed out for quite some time, much pumping and spinning later it seems to have stabilised. I’ve left the thorns in the rear tyre, will see how it holds up. Thinking of ordering up a few extra tubes and trying a ghetto tubeless rig. Anybody tried it? Have also read of people using motorbike tubes (heavier, but might offer that fraction of extra protection.

    Weighs in at 14kg according to the bathroom scales, tail heavy due to the hub gear.

    Thanks for the linky bruneep: will be over there in the hopefully not too distant future.

    Pushbikerider: I believe you still have the white stuff… was 20C at 9am here.

    Oh, and it’s FUN: more relaxed than my 100mm hard-tail Cube but still a blast.

    dancingjames
    Member

    Am just in the process of building up a 9zero7 with an Alfine hub. Hub gears are new to me so not entirely clear as to what would be an appropriate ratio to run.

    If honest the bike is mainly going to be used in the UK on trails, with the occasional use on snow and beaches. I tend to spin more than push pedals, my 29er has 38/26 chainrings and 11/36 but I rarely use the bottom end of that gearing, though I would imagine I would be more likely to with a fat bike.

    Any suggestions for chainring and sprocket size?

    Premier Icon scotroutes
    Subscriber

    Play around with the gear ratio calculator on Sheldon Browns site

    http://sheldonbrown.com/gears/

    The 26″ fat tyre has around the same diameter as a 29er wheel – and you’ll therefore be after something to replicate the 36T cassette.

    I built up my 9ZERO7 with an 11-speed Alfine and found almost immediately that I really wanted a lower gear ratio than the Shimano recommended. The fat tyres generate so much traction and you’ll end up riding on soft sand and snow where the lower gears make a lot of sense.

    Remember that you can also use Nexus sprockets – they’ll give you more options.

    Last winter I ran the bike with the standard 22/34T Raceface Altas rings up front and an Alfine 20T sprocket on the rear with an Alfine tensioner taking up the slack. Loved it in that configuration and will re-fit it next winter.

    dancingjames
    Member

    my frame is the sliding drop version so was not planning on using a front mech too.

    do the alfine’s fail if they are used outside of shimano’s suggested range?

    Premier Icon scotroutes
    Subscriber

    Mine is going fine 🙂 I don’t know how strong a recommendation it is, but it’s listed in the Alfine set-up guide. FWIW, there are pre-built bikes for sale that fall outwith the recommendation.

    2×11 gives a range equivalent to a standard 3×9 geared setup. I do find I can spin out when running 2×9 but hey – what’s the hurry!

    dancingjames
    Member

    i am thinking of getting the raceface turbine cranks, which chainring would people suggest to work with the alfine. is there a 104 bcd single speed ring that will work best with the alfine sprocket

    http://www.silverfish-uk.com/ProductDetail/0/12822/Turbine-Fat-Cranks-Arms-BB-100mm

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