Pure joy.

Ok looks interesting thanks for posting.

How does it compare to the S/A S2C. I have two (one in my TSR2) and an old duomatic currently fitted to my Raliegh Moulton MK3. The one in my TSR2 took about 500 miles to settle down.



Its since been upgraded with the modified snubber.

The idea of autoshifting sounds cool. Will it autoshift going up a hill whilst pedaling ?

Regards

Jerry

First impressions are that I like the SRAM A2 considerably more than the S2C.. it's much quieter .. it's lighter, spins more freely, less draggy... for me, it's made the bike a lot more enjoyable to ride.. I do a lot of stop and go, hills, errands and such, having the hub autoshift to low gear when the bike slows below shift point just makes me smile... You can get it to upshift going up hill whilst pedaling if your wheel speed is up.... and, if you are in high gear going up hill and your wheel speed drops below shift point, it won't autoshift to low gear as long as you have pressure on the pedals .. release the pedal pressure slightly, and it will then shift to low gear.. I wrote much more about my experience with the autoshift hub HERE

Thanks Bruce. I may try one out.

I will wait a while until they are more readily available over here in Europe. I purchase my original S2C from America when they first came out and paid a premium for import and postage.

Regards

Jerry

Horrible and uncool bike . Post it to me immediately.

Bruce,
Can you give me the hub flange diameter at the spoke holes? I'm interested in replacing my Sturmey S2 with a SRAM automatic w/o brake. I'm hoping I can reuse the spokes but i'm having no luck finding out the dimensions.

It's almost random which gear I'll be in after backpedalling the S2. Or which gear I'll be in if i hit a bump while coasting. Too bad because the thing feels solid as a bank vault. But I bought it to have a bike I didn't have to think about while riding and it's definitely not working out that way. And my son won't ride with me when I'm on that bike because the clicking in high gear drives him nuts.

Thank you, I didnt use the proper term when I Googled the hub. I have one on the way.

I used a spoke hole measurement of 69mm eyeballing center to center .. on 120mm spacing I used 32mm R and 31mm L (flange to locknut).. also, a sharp enough bump will shift it to high (even if below centrifugal shift point).. you can choose to pedal on in high, or ease pressure at the pedals and it will drop back to low.. the A2 does rhythmically tick in high gear, but I kind of like it and it's less intrusive than the S2C was on the same bike... but your son still may not ride with you

Got mine at universal cycles and they have $2.99 shipping. https://www.universalcycles.com/shopp...&category=2713

Beautiful bike Bruce!

Does anyone know if its possible to squeeze this new auto hub onto a Mu Uno? I know the spec says its a little wider. Looking to order a rim built with it right away if it fits.

The new A2 is 120mm (with included spacers to go to 130mm) .. so it will fit the Uno nicely.. however.. and this is a big ~however~ .. this hub is being distributed in the US aftermarket in one configuration only, and that is for 27"+ wheeled comfort bikes.. what that means to anyone contemplating just dropping it in a 20" or smaller wheel (like I did with my TSR-2) is that the shift point will be very low (like in the 5 to 7mph range).. any other obtainable shift points from the hub will require disassembly and modification of the shifting mechanism via springs or flyweights.. I chose the spring route and actually wound my own.. this may or may not be what a typical buyer might expect or a modder might want to deal with... just random info for those in the market.. as of right now, there are no internal parts availability for this hub through SRAM in the US.. I'm sure if the hub ever gets popular, serviceability might improve...

Thanks for the super quick reply Bruce.

120mm, perfect was afraid I would have to stretch the frame to accommodate. Never taken a hub apart, but am an auto mech so not afraid to experiment. Sounds like the heavier spring route is the safest bet, as you can change them out if desired effect isn't reached. But wonder how easy it would be to grind a little off the flyweights, knowing there is no going back if you take off too much.


Any recommendations on where to get this wheel/hub ordered/laced up locally in SF bay area? Or should I just go the online route through someone like universal cycles? I like to support small local businesses whenever possible.

I'd be leery of grinding the flyweights without a few extras on hand.. I used to do essentially the same thing back in the day with centrifugal clutch shoes on nitro powered R/C !/8 scale race cars to tune them to track conditions.. heavy shoes, early bite at lower rpm... lightened shoes later bite.. too light and clutch shoes would melt as they came in too late at say 15000rpm...

I have a few of the new hubs here.. what I would recommend (assuming you're in SF) is to come by and ride one that I've set up (I have a Mu Uno with a Sachs Automatic - and of course the TSR-2 with the SRAM A2) .. see if it comes in too late or early for your riding style... then make a plan.. I'm in the process of building another up for a fellow forum member at an earlier shift point.. I'll be doing some road testing before I ship it out, so I might have two to compare within a few days.

I see you aren't just generous sharing your vast knowledge, but also time to let a stranger test ride your bike. That's a mighty kind offer Bruce.

Didn't realize the flyweights actuate shift clutches, but makes perfect sense. Looks like springs are definitely the smarter way to go. Thanks again for sharing.

Just had acl knee surgery this tuesday, so wont be able to ride for a few weeks. I bought the Mu Uno to get in better shape before the operation, and to help with the knee rehab after. Love how it fits/rides. Two speeds in the 50's and 70's I think would make it the perfect stow away bike. Forgot how much fun riding can be. Cant wait till the knee is good to go again. In the meantime, I want to get the two speed rim going so its ready when I'm ready.

Sorry, my analogy probably wasn't clear.. the flyweights act directly on the shift drum.. no clutches.. I used to lighten clutch shoes on my R/C race cars (the shoes looked like the curved flyweights, only made from a teflon type material that worked inside of a spinning bell, much the same concept if you were going to try and lighten the flyweights).. I know the spring mods work

Hope you rehab that knee quickly..

Sorry to derail this thread, but how would the A2 work with a schlumpf speed drive? Could one realistically get 4 gear performance, or would it practically become a 3 speed. I can't get the Moulton 50 out of my head. I know the schlumpf + torpedo drive was awkward in that setup, but I love the concept. I'm no bike mechanic, but I keep dreaming about the current options (Sram A2', SA S2C, sachs duomatic) + (Schlumpf speed drive 1.65 or high speed drive 2.5).

In a discussion I can't seem to locate via search, alas, I believe Jur pointed out a significant problem with Schlumpf + 2-speed hub setups: The two most useful gears tend to be in the middle of the range and shifting between them calls for shifting at both the hub and the crank (Schlumpf). That is, getting from Schlumpf-low/hub-high to Schlumpf-high/hub-low (and the reverse) is both cumbersome and the most commonly useful shift.

The automatic-shifting A2 throws a bigger wrench in the works because the only upshift you can make from Schlumpf-low/hub-high is Schlumpf-high/hub-high (a second to fourth shift). You can use Schlumpf-high/hub-low (third) only at speeds below those consistent with Schlumpf-low/hub-high (second). So, yes: Schlumpf-plus-A2 becomes effectively a three-speed consisting of first, second, and fourth gear - with a third gear that only works at the same speeds first gear does.

OK here's what I think at the moment about this:

Combine a SRAM Automatic with a Schlumpf Speed Drive. Choose gearing of roughly 43, 59, 71 and 96", or a bit lower.

Then you get 4 gears as follows: Pulling away with Schlumpf in overdrive, you have 59". On reaching auto shifting speed, it shifts to 96". You now shift the Schlumpf down to direct drive, giving 71". On downhills, you still have 96" available. And on steeper hills, you have 43".

[edit] Bugger, scratch that. For a moment I forgot that the gears do not overlap. This scheme would work if there was neat overlap.

Does the SRAM A2 shift based on the rotational speed of the wheel or of the sprocket?

It has centrifugal weights (2) and shifts by hub rpm, it will shift even if the cog isn't spinning (like cresting a hill and coasting down faster than shift point) ..

I've got a spare Schlumpf Speed Drive on the shelf and an A2 wheel built up in my TSR-2 .. and was thinking of just that mod.. but the only way that makes any sense to me is to set the gearing low enough to still be enjoyable (like in Jur's 43/59 g/i scenario ), but then there is the huge jump to 99 g/i in overdrive (59x1.65 of the Schlumpf SpeedDrive).. I'd probably experiment with something like a 38/52 .. have the hub shift early so I'm not over spinning .. ride mostly at 52 g/i and when I feel strong or going down hill shift the Schlumpf into overdrive (86 g/i this time - 52x1.65) .. this would be workable, but I think unattractive for me personally as I typically ride high gear in the low to mid 70's with my 2 speeds.. mid 70's gets me over 22mph with a reasonable cadence.. so I'll probably target the Schlumpf for something else..

Bruce, thank you thank you thank you.

If it weren't for you I wouldn't know about this wonderful SRAM A2 Automatic!

Got my SRAM A2 laced wheel today, bolted it on the Mu Uno with a 18t sprocket. Not supposed to ride anything but exercise bikes since I just had ACL surgery couple weeks ago. But knee feeling good so figured I could ride the little Mu Duo up and down the street without falling over just to feel how it shifts. Shifts smooth as butter, I love it. A little early as you warned. But think it will be perfect for me while I'm rehabbing my knee. Once the knee is strong sure I will want to make it shift later.

Bike is so nice with two gears. The only thing that could make it better, is if it were on a suspended bike like your Moulton TSR-2. Now the difficult part is going to be not touching it for a few weeks as the doc is advising me to only ride exercise bikes till November.

Thanks again Bruce!

[IMG] Uploaded with ImageShack.us[/IMG]

Hey Frank! that's terrific... I've been riding my A2 8 to 10 miles/day over the last month due to some health giver duties... the A2 has been great .. don't push too hard with the rehab ... the Uno is a perfect platform for the hub .. so perfect that Tern has one in the lineup .. I'm sure you saved at least the price of your Uno over waiting for a production model.

I'm sure Tern making a Duo that had something to do with your Mu Duo project a while back.

As for me, had little choice, Tern Duo wouldn't fit in the space I keep the Mu Duo. Only 11" tall under the sofa bed of my sprinter motorhome van. Not many bikes that can fold that thin. Its a shame that the new Terns have a wider fold than the older Dahons.

I have room under other side of RV sofabed and need another thin folding bike, so I can have riding company while out and about. Judging from the price list I saw of the coming Tern bikes even if it fit, I likely wouldn't get one. I rather spend a little more and get the suspension and uniqueness of your Moulton TSR-2. Only thing that puts me off is I cringe of the thought of that pretty frame getting all scratched up bouncing around two halves of the TSR in that tiny 11" tall space. Its such a pretty bike, I even like the orange color.

Hey Bruce, I'm curious now that you have both hubs. How does the new SRAM auto compare to your older two speed autos. Can you tell if they improved on the older design at all?

Dahon did contact me after I did that project to feature the bike in one of their newsletters .. I still ride the Duo a lot ..


The inside handlebar fold of the Uno is what keeps it thin.. the Helios was also thin and would fit in the same shallow Alfa trunk of mine that the Uno fits in.

One thing with the TSR-2, it's powder coated, so a very durable finish.. the other thing is there are accessory soft travel bags that fit the front and rear halves if you were really trying hard to avoid abrasions..

The biggest difference is the coaster brake.. the new model uses a roller setup much like the S2C .. but for some reason, easier to modulate.. the older Sachs units will stop, but more effort is required.. much like automobile brakes before power assist came on the scene.. the shifting is about the same and uses some of the same internals.. the biggest 'improvement' I see with the A2 is the longer axles and OLN dimensions 120mm and 130mm as opposed to the Sachs 110mm .. I've got a non-coaster 130mm hub coming in to help satisfy another wild hair..

As soon as I'm cleared by my knee doc to ride again, like to come by test ride and measure the TSR 2. I'd like to have something different for a second bike to keep in the RV. Some suspension would be nice, and like the cleanliness of a belt drive. Looking forward to getting Gates centerdrive for the Mu when it becomes available.

Other possibility I'm toying with is building a Ritchey breakaway frame with the SRAM A2 coaster and a flat handlebar. That would also make a lightweight easy and quick to separate stow away bike that could possibly fit, but need to take some good measurements.