invisiblehand

Looks like Bike Friday modified their rear triangle design. Should be available soon.

fietsbob

Ah, its on the rear bit rather than the Main one as it has Been .. My Pocket Llama has its Braze on On the main frame..
Though I dont use any Derailleurs , just a chain Tensioner.

IGH... I coped with a chain-minder on the seat Tube. the crank has a disc chainguard, on the outside.
+ I Have their clamp on the BB thing that keeps it on as the slack is made with the fold motion..

It now has a chain that wont come off, I Made My own Piece for the 1 Cog on the IGH to keep it from coming off, backpedalling to lube the Chain.

Foldable Two

Received that BF e-mail, too. Interesting solution, but will stick with our current Fridays. Chains fall off occassionally when folding/un-folding, but not that big of a deal.

Lou

CHenry

They need a separable driveside rear triangle if they want to put belts on the NWT. It's do-able different ways (S&S-type sliding collar, separable bolt-on horizontal rear dropouts that when unbolted leave the seatstay and chainstay separated.) SOMA has a stock frameset (Wolverine) that uses that solution. The Silk appears to be their solution already to the belt-drive demands--no triangle, just a central strut--and seems sturdy enough for touring.

fietsbob

But, NWT/PocketLlama, also has Had the problem of the Fold Hinge is behind the BB *, whereas Silk & Tikit the BB is part of the Rear end section.
so belt stays in a tensioned Loop.

* I had to use a chain tensioner because of that, on my R'off IGH pocket Llama.

Derailed

If the new NWT frame design becomes able to accommodate belt drive, will the Silk frame remain necessary in the line up?

(In the next year or so I'd like to get a Bike Friday for touring, and I'm torn between the Silk and the NWT. Rationally I suspect the NWT is the best bet for me, but I can't shake my attraction to the Silk 11.)

fietsbob

Big IF Assumption, going there,
If the sales Drops Off on the Silk it is a Business . and they mau shelve the Jigs for those Parts
Its Not like they build up an inventory and wait for Customers .

the rear assembly & Frame has to be Redesigned to be including the BB,
instead of having the BB in the frame and a Hinge for the fold Behind the BB.

Belts take a Lot of Tensioning to work, as it Is.. thats a DNF with a Hinge point in Between BB and rear Hub.
so we shall watch..

NWT with a Chain Drive and Chain-tensioner would be fine.. Its works on my P Llama. ..

here is a Tikit, note the BB is in the rear section . https://www.bikeforums.net/attachment...p;d=1419194789

smallwheeler

this makes me think again about the interesting fact that certain technologies are adopted while others fall by the wayside for no immediately apparent reason.

about 6 months ago, i bought two bridgestone picnicas from a retired engineer living in woodside, queens. he informed me that he and his wife purchased these bikes new in 1984 and had probably put 10,000 miles on them in the 30 years they'd owned them. i sold one of the bikes to a friend and kept the other to play around with.

when i decided to fit the rims with big apples i anticipated it was going to be a pain to remove and refit the rear wheel due to the beltdrive mechanism. it was actually extremely easy because the belt isn't designed to be under constant tension; i just pulled the wheel back in the drop-outs finger-tight, gave the wheel a spin and eye-balled it to make sure it was basically square in the drops- and i was on the road in few minutes. 30 years on, the kevlar belt is just as supple and strong as i imagine it must have been the day it was installed.

the picnica was fitted with the bridgeston beltrex system which, thanks to bootiebike.com, the function of this brilliant design is well-explained in this clipping from an 1987 issue of popular mechanics:




a few weeks ago, i did a leisurely 30 mile round-trip ride on the picnica through parts of brooklyn and queens. it was a blast.

fietsbob

Note: the banjo bolt to pull the axle Back.. the eccentric is in between the 2 crank parts Too that is where the belt is pulled sufficiently Tight

I dont think the Gates Belts are the same as that one. , and that is the current trendy favorite.

smallwheeler

never mind.

BruceMetras

Not really .. you can run them very loose and they work great .. see HERE for an extreme example.. Mark has used this setup since 2002 with many, many miles through the years (note the very substantial snubber at the rear)

The currently sold Moulton TSR-2 run 8mm pitch belts as do Stridas without the need to run high tensions because they use a snubber at the rear cog to prevent belt slipping/jumping/ratcheting .. 8mm pitch belts was the European norm until the Gates 11mm belt .. I run a snubber that I cobbed up for my personal TSR-5 and very little belt tension .. as Smallwheeler mentioned with his Bridgestone, rear wheel pulled barely hand tight so as not to put drag on the bearings ..

fietsbob

Whatever ~! Maybe the snubber lets that happen , I just wont Pony up the bucks to buy one .. Chain drive Pocket Llama Rohloff pricy enough..

got some data -- numbers vs Gates published ones?

BruceMetras

There's no "maybe" .. works fine as I indicated ..


I rely on what's known in the industry as 'hands on experience' .. sometimes trumps 'I read it on the internet' ..

smallwheeler

that's a very cool solution, bruce.

invisiblehand

Quote:

8mm pitch belts was the European norm until the Gates 11mm belt

That's interesting. Are cogs with smaller diameters available for the alternative to Gates?

Just visually looking at a few Gates rear cogs it appears that they could physically get smaller. I guessed (perhaps the wild-assed kind ... I have very little experience with belts) that for the given pitch, going smaller would mean that too few teeth would be engaged. Of course, it occurred to me that it could be the case that the desire for anything smaller than 19t only applies to folks with very small rear wheels ... less than 20" ... such that there simply was no demand for it.

After a few years with the STRIDA, I've come to appreciate the belt drive. I'm on the fence for ponying up the bucks for an IGH bike with wide enough gearing for me with a belt drive, but it was out of the question a few years ago.

mconlonx

We have two of these in the shop right now for service. Interesting bikes, but nowhere near as small a fold (they merely collapse and form a folded package not much smaller than a Strida, i.e. large...) as their size might indicate.

And I'm still not a fan of current belt drives, think they are overrated and that traditional chain drive is just fine, if not better.

smallwheeler

the point i was making about the 30+ year old beltrex design is that it has some very smart features that have been discarded in today's contemporary designs - slack belt with an internal gear housed in the crank case to increase belt tension only when needed under increased load (no doubt this is a contributing factor to the extraordinarily long life of belt), steel rear cog with flanged side-walls that capture the extremely durable kevlar belt. i think bridgestone also used the same design on some of their mamichari bikes as well, but for some reason, the design was not widely adopted or developed further.



regarding the picnica itself, i don't disagree with your assessment much. the folded package is almost as big as a strida. and at 12.5kg, it's pretty heavy. that being said, it does fold in literally one second and is very strongly built and a pretty stiff ride compared to an early brompton or the creaky and even heavier dahon bikes from 1984. the picnica is an interesting and unique design that has it's merits.

Derailed

Unless you're doubting the text attributed to Bike Friday in the OP, or you're referring to something else all together, it's not clear to me why you say that belt drive for the new NWT frame is a big assumption.

Here's the line from the OP:

BruceMetras

Any 8mm pitch cog will be smaller in diameter compared with the 11mm pitch by design .. more belt, bigger teeth need more room to wrap .. the image of my TSR-5 shows an 8mm pitch 25t cog at the rear..



I'm running a belt on both my TSR-5 and 2 speed automatic Mu Uno .. I'm pleased with both .. the good thing to keep in mind, if I were ever displeased, it's a simple matter to revert to chain drive pretty painlessly..

fietsbob

topic hamster wheels have gone from Moving a Front Derailleur Mount into a new location on the Frame to a belt drive which has no derailleur at all

any one ready to order a new Bike Friday with the new front derailleur mount ?

1-800-777-0258

not exactly front and center on their website.

Derailed

invisiblehand: would you mind specifying the source of the text you quoted in your original message? Perhaps it was silly of me, but I assumed that it was sent to you by Bike Friday, and thus the claim that the NWT and Pocket would now be compatible with belt drive was being made by them.

But, it seems others, specifically fietsbob, have knowledge that the frame-design change is only related to the location of the front derailleur mount as shown in the picture you provided.

invisiblehand

It's from Bike Friday.

The traditional design shortened the distance between the rear axle and chainring when folding. So if you wanted to run a fixed gear bike, you'd have to use a chain tensioner otherwise the chain would fall off. The new design is more like the tikit where that distance is kept constant during folding.

mconlonx

Absolutely, ahead of it's time -- belt drive, flanged cogs, kevlar/carbon belt... Although I'd take issues with the flanged rear cog tech and admit that the Gates CenterTrack is a better solution in most cases.

Not shown in the pic you posted or descriptions -- what is the belt tensioning system? Hinge revised to maintain tension, OK, great, but what is the new system used to establish tension, either regarding belt drive or ss/fg chain setup?

invisiblehand

There appears to be an adjustable dropout.

mconlonx

Ah, cool. Thanks for posting this...