wesgreen

Hi,
I would like to put a smaller sprocket on my 2 1/2 - year old Vitesse D3 i-motion 3 coaster Sram hub. I love the bike and the hub. I believe it came with a 16 tooth sprocket, but I've never been able to use 1st gear in city traffic so far, and would like to try a 12 tooth sprocket. Can a fitting 12 tooth sprocket be expected to work with this hub? I'm hoping to get some use out of my 1st gear. I measured the thickness of my chainring and old sprocket at 3mm, and therefore assume I have a 1/8" chain(?)
Does anyone happen to know what the required specs are, and where to look for it? Sheldon Brown's site says that SA makes a 12. My 3 closest lbss say they don't have anything like it. I also found this:

Brompton T Sprocket 12T 2 and this: https://www.nycewheels.com/brompton-p...ket-12t-1.html

Do you think it would fit, and/or can you think of any other sources in the US?
Many thanks in advance!

fietsbob

Pop off the snap ring and Look..

If... Its the pretty Much for you to look. .. If 9 spline ( a set by Shimano Standard ) then the 12 t is OK,
SA S3X and the SA for Brompton BWR use the 9 spline divers ,

But if its 3 spline, a Sturmey Archer, ( AW3, BSR,) and Sachs , Standard .. then its 13t at the smallest ...

Sachs made the 1st 3 by 2 Brompton Hub, for that they Sachs made a 3/32 thick Cog *, 13 & 15 as a Pair.

where SA ones for the 3 speed was An 1/8" thick one.

I've been using the shift gate 15t of the pair* .. every 5th tooth was shortened so 3 are not as tall as the rest.

Sram Bought out Sachs moved the German production machines to Taiwan ..

*54:15 on my Brompton 3 speed ..



I have My LBS order stuff I tell them what they Need to get, Sothey dont have to read My Mind ahead of time

BruceMetras

The SRAM hub takes a common 3 dog sprocket.. if you have a 16t on the hub, most likely you have a 50t on the crank, giving you gear inch range of 42/58/78g/i , which is what the Dahon site publishes for that bike..

What's common with a 3 speed is to set gear 2 (the most efficient gear) for the majority of flat and level riding one does .. gear one for going uphill ... gear 3 for going down hill.

I would drop 1 tooth at the rear to a 15t.. that will give you 45/61/84 ... 61 would be a good g/i for gear 2 .. it is close to what the single speed bikes use in the Dahon range..

If you drop to a 14t . that will give you a 48/66/90 .. unless you are a fairly strong rider with few hills, riding mostly in gear 2(66 g/i) will probably feel pretty good, but the shift to gear 3 (90 g/i) might not..

If you drop to a 13t .. that will give you 52/71/97 and probably would feel over-geared on a commuter situp 3 speed bike..

The cogs are cheap enough, get a 15t and a 14t and experiment.. you might have to remove a link from the chain ..

wesgreen

Thanks for the response, guys! The mickey mouse integrated chainring it came with, according to Dahon, and my count, is only 38T, even though they listed the gearing you quoted, Bruce.
I'm certainly not a super strong rider, but I'm in NYC, which is mostly flat, except when going over the bridges to Brooklyn. I almost exclusively use 3rd gear on this bike, which is a waste. Sheldon Brown says you save on wear if you stay with even numbers (wonder why?), so based on the info you both gave me I'm going to look for a 14T.

This one should fit (?)
https://www.amazon.com/Sturmey-Archer-14t-coaster-brake-cog/dp/B003RLE95G

BruceMetras

Yikes! that's messed up .. if you do have a 38/16 .. there was an error on assembly or someone lowered the gearing radically.. I'd probably by a cheapo front crank and get the chainring in the 52/53t range .. then you have some room to work with the gearing.. a 38/14 won't even get you to Dahon's published specs with a 406/1.75 tire ( 31/51/69 g/i ) .. you would need at least a 13t to get close (40/55/74) .. so I'd double check your existing tooth count.. if it is a 38t up front, I'd grab a 13t while you're buying cogs.. or change the crank so you don't have to run such a small rear cog... better efficiency with larger diameter gears..

BruceMetras

It will if you are running single speed 1/8" chain now .. check what it says on your existing cog... if 3/32", then a 1/8" cog won't work, unless you have a single speed chain like the SRAM PC-1 chain.. that's another reason to move to a different crank, then you can use 3/32 cogs which I think go down to 15t..

BruceMetras

Looks like Sturmey Archer 3/32 cogs go down to 13T

wesgreen

I guess it was meant as a grandma bike, which works for me otherwise. But I'll definitely will have to get a real crank at some point. Hope I can use this one up first before I get rid of it. I ordered a "Sturmey-Archer 1/8" 14t coaster brake cog", from an english ebay vendor. Was unable to find it in the US.
Really appreciate your help, thanks!

tcs

The efficiency differences between the gears of a properly lubricated and broken-in three speed hub aren't anything to worry about (as mechanical devices, three speed hubs are overall the most efficient multi-speed bicycle drivetrains.) I'd shoot for something like this:



If you're really worried about drivetrain efficiency (in this case, I wouldn't), use the largest chainwheel and cog you can.

USA retailer Bike Tools Etc. shows 14T, 1/8", flat cogs in stock, Sturmey part number HSL852, their part number SU-HSL852. The 14T, 3/32" cog is in stock too, SU-HSL944.

wesgreen

https://www.unitedbicyclesupply.com Appears to be a supplier lbss can order from.

Great find, will use in the future, thanks a lot!

fietsbob

The Brompton dealerships can supply cogs , now Most Big cities have one .. In PDX I go thru Clever Cycles ..

^ +1^ United Bike supply is a seller of a Lot of S_A small & spare parts.. wholesale to Bike Shops.
I have bought thru those channels


Years ago for Brompton , Sachs made the 1st 3 by 2 hub , a 13,& (skips 3 teeth for shifting) 15t, (I have a 54t chainring)
S-A 3 spline pattern.. 3/32" thick rather than 1/8" [54:15]
Sram Bought Sachs . moved production machinery out of Germany.. to TW.

wesgreen

Update, in case others got fooled by Dahon's fake gear specs for this model like I did, and want to bring their gearing to within a normal range. No information/help/advice was available from Dahon regarding this, either by phone or by posting questions on their forum, so it took a little research.

I received the SA 14T cog from the UK ebay store. Unfortunately it won't fit on a Sram imotion-3 hub because with less than 16 teeth the dustcap gets in the way of the chain. This is probably why Sram now offers 16T as smallest cog size (they previously made a 14T, which you can still sometimes find as NOS; don't buy it for this hub). This came as news too to the person I spoke with at Sram in Chicago.
The mystery stock crank my Vitesse D3 came with has 170mm arm length, 130mm BCD, square taper, with a 38T chainring welded on to the right crank arm. That problem aside, it seemed great to me, so I'm sorry to have to replace it. I was unable to find just a used right crankarm with the right specs for cheap, so I splurged $45 on a new FSA Vero set on ebay from Taiwan (with a 46T ring, 640 grams, took ca. 3 weeks, looks perfectly straight). If I had access to a good metal drill I would have tried drilling 5 bolt holes into the 38T chain ring and mounted a larger ring on that. (For replacing the crank you will need to borrow or buy a crank puller. Good quality ones can be had for less than $10.)
If you think you can get by with a 42/16 combination, you may be able to keep the nice plastic chainguard the bike comes with. Anything larger than a 42T size in the front, and you'll have to take it off. This is done by loosening 3 screws and unscrewing the right side lockring (in clockwise direction). At this point you might as well consider replacing the bottom bracket. I didn't see any reason to replace mine. It's 68/120, square taper. If I replace it someday I will look for a 68/110, because with the new FSA crank my chain line was off to the right. I corrected that by putting the new (currently 50T, which gives 45.4/61.9/84.3 gear inches) ring on the inside, along with 5mm spacers, which came with the 52T aluminum chainring protector ($21.50 on ebay) which is now on the outside, replacing the plastic chain guard.
You will also need a longer chain. The bike came with a 1/8 single speed chain, even though a narrower chain would have fit. I had a old 8 gear chain laying around, which I shortened (you'll need a chain tool for that).
This new setup lightened my wallet by just over $100 and added about 2-300 grams weight to the bike, but it sure is fun to have three gears!

BassNotBass

I'd have to agree with both points.
When it comes to gearing choice for a three speed you're better off gearing your top gear for the flats, that way you have 2 lower speeds to choose from for climbing hills depending on their grade, IMHO a better option because you really don't need gears to get down a hill. What works for me is something close to the following ranges:

3 - 76 g.i. - flatland travel
2 - 57 g.i. - moderate hills or strong headwinds
1 - 43 g.i. - steep hills, snowy/slushy streets

My Brompton's stock gearing (50/13) was approx. 82-62-46 gear inches... 82 was a little too high for the flats unless the conditions were perfect and I was feeling fresh (and wasn't lugging around over 20 lbs of gear) and 62 was a little too low but was decent in headwinds. If I chose 2nd gear to be my main (flat) with what I feel to be the most comfortable then the gearing would end up being 100-75-56 using a crazy 56/12 chainring/cog combo... that's nuts.

BruceMetras

You're basically using what I'm running with gear inches at 44/60/81 on my TSR .. I run in 2nd gear (60) most of the time until I hit some open road, then shift to 3rd if I can keep the cadence I want, which is around 70 to 85 which can net me a little over 20mph.. anything over 20mph for me requires some tailwind or downslope but I can spin 100 comfortably which tops me out around 25mph .. running a three speed is a compromise for sure, but enjoyable..

BassNotBass

I'm lucky and have it easy... my preferred cadence for the Brommie is about the same as my preferred g.i.. I can push it for a couple of blocks above 120 rpm to race the traffic lights but I really end up sucking wind. My track bike and single speeds are strictly for recreational/training purposes with no compromises so they can be geared a little higher.

BTW, you posted that Moulton porn pic just to rub it in, didn't you?

BruceMetras

I was going to post a pic of my medicare card, to reinforce my preferred cadences, but the TSR-3 won out ..

BassNotBass

I see where you were going with that. Thanx man.

BruceMetras

Very stylish!! ... you're obviously going the extra yard ... as one musician to another, I'll make sure and stick it in my last will, just for you

jur

Hmmm you have just given him motive to take out a contract on you... Might be safer to just gift him the bike.

BassNotBass

LOL! ​(personal note: hire jur as an aquisitions advisor)

BruceMetras

Don't get too excited, there will be contingency clauses in the will..

wesgreen

Update, since this is/was a fairly popular model:
After another few years, the original Dahon/"Chin Haur" (122 mm: 364 g ) bottom bracket started creaking, and I replaced it with a "Shimano UN55 Square Taper Bottom Bracket -
68 x 110, 294 grams, for 68 mm width bottom bracket shells; 110 mm steel spindle; Square taper spindle for square taper cranks; Sealed" (ca. $22). The chain line seems straighter than before. For one - time use I used a cheap knock - off Shimano bb adapter tool. I had to redo the operation once to add even more grease, because the new bb had started creaking too. It's quiet now, and runs a little easier than the Chin Haur.
I still think it's a great bike with these alterations. Definitely a great frame design. Hats off to Dr.Hon.