rhm

For what it's worth: I have a Primo Comet 16 x 1.35 tire on the 305 mm rear wheel of my Downtube Mini. The diameter of the whole wheel, tire and all, is a little tricky to measure, but looks to be 370 mm.

senseamp

How does "morbidly obese" fit with "hung it in her attic for 30+ years"? Damn Doctors don't understand a thing about human bodies! If I new as little about my business as they do about theirs, I'd have been fired years ago.

Sammyboy

Hmmm. Oddly, the more innappropriate this seems, the more I want to build at least the gold one as a hot-rod. If we're getting down to 305 rims, then even an AW with a freewheel down to 14 teeth still only gets you 76 gear inches max, so the derailleur/AW combination is off the menu. Shame really, as the idea of the Dura Ace RD on their was rather appealing. It looks like the best approach is probably a Sturmey Archer 8 speed, because of the way it all goes up from 1-1, but they're a tad spendy. I'd need to find one on the cheap somehow.

On the plus side, the 305 tyres and rims are cheap as chips, so it all looks doable. What kind of shifters are there for the SA-8? Is there anything that works on drop bars? I'll definitely remove the mudguards from the speedster one, but that would allow me to use them on the other, which I'd be building up with more like period kit.

rhm

There is only one shifter available for the SA-8, and it does not fit on drop bars or moustache bars.

Consider a used nexus 4-speed hub if you can find one; like the SA-8 it starts from a 1-1 and goes up from there. Also, even though it doesn't start from 1-1, the gearing of the Nexus 7 and 8 hubs isn't too bad; you can put a fairly small sprocket on them, and with a 52-T in front, your gear range will be acceptable. The SA-8 only takes larger sprockets.

Sammyboy

Let's see. These are the sort of ranges you'd get with a 52 tooth front and a 14t rear:

Nexus 7 - 31.6-77.2
Nexus 8 - 26.3 - 80.7
Nexus 4 - 50-92
SA AW - 37.5 - 66.6
SA FW - 33.3 - 63.3
SA 8 Speed - 50-152.5

The Nexus 4 would do the job, but I'd quite like more than 4 ratios. If it's anything like my Nexus 7, I can't see how I could do Sheldon's multi speed freewheel bodge. The 7 and 8 don't really get high enough. I'm also extremely pleased to find that the SA 8 is relatively inexpensive, compared to a Nexus 8 at least. I'd run it with an 18 tooth sprocket, which would give me 38.9 - 118.6. It's tempting.

Sammyboy

Hmmm. As cheap as an SA8 looks at £155 (how can that seem cheap to me, when I got my brand new Nexus 7 for £33?) a new Nexus 4 with fitting kit can be had for £69.99. Is there no way at all that I could bodge a cassette onto that? Also, does anyone know what the OLD is on the SA-8. The Nexus is 130, which is bound to mean some spreading.

Diode100

The last of the Moulton Majors, built by Rayleigh, had the SA four spped hub, and 14in wheels, why not see if you can source a rear wheel on its own ? That would be about the cheapest gearing upgrade I'd have thought.

Sammyboy

Actually, the 4 speed, whilst it gives slightly more range, and obviously closer shifts, gets a slightly lower top ratio. On a 14" wheel bike, top gear is the challenge.

LWaB

You can't fit an 18t to that hub, it has a different size of spline. 25t, 23t or (rare) 19t cogs only.

Sammyboy

It's as though the world was against this happening. 19t would do, 23t would be less good.

stevegor

Sammyboy,

SA 8 speed has a grip shifter, which I have on the Wasp. I'm using narrow 70's steel drops which I cut, installed the shifter, then mig welded the bars back together. It's working fine, but Sheldon's reply in an email about fatigue failure makes me worry....a little. Not sure if the shifter will fit on more modern drop bars as they are of a wider diameter.
There are other ways to have drops with the SA shifter, namely, if you are using a long 22.2 quill stem the shifter will fit on it, even if you have to use a shim....a strange place, but it works.
Sheldon's red R20 has it mounted at the end of the bull horn bars...a matter of personal taste.
Another way is using a hubbub which attaches to the stem near the headset, but it looks like an alien growth hanging out in space.
To me the best solution is using MTB flat bars and a set of drops bar ends from Origin 8, that way you have the shifter where you can easily reach it AND the advantage of the drops.

Sammyboy

Actually, I have a plan to manufacture a stand-off to mount twist grips on drop bars - I can prototype on this, potentially. I need to do some investigation though, because I suspect that a Minoura computer/light mounting bar will do the job, providing that A) it's not too large a diameter, and B) it's sufficiently robust to deal with the torque.

Sheldon Brown

Alas, not possible.

The Nexus hubs require a 16 or larger sprocket. That's the smallest size that is dished, and the Nexus requires a dished sprocket to clear the shift cable linkage.

The Sturmey-Archer 8-speed uses a MUCH larger driver than the other models in your list. The smallest that exists for that model is 19 teeth.

Sheldon "Epicyclic" Brown

awetmore

The SRAM S7 doesn't require dished cogs. 53/14 gives you an 88" top gear with 305mm wheels. From Sheldon's calculator:
88.7
75.4
63.2
51.0
41.3
34.6
29.0

Sheldon Brown

The Moulton Mk III (the version built by Raleigh) has a triangulated rear end, which is way stronger than the classic Moulton rear fork, but it uses a rubber ball as a spring, instead of the rubber shear block used on most of the classics.

There's a neat trick for improving the performance of the Mk III: wrap a worm-drive hose clamp around the equator of the suspension ball. This will allow you to fine-tune the rear suspension (tends to be a bit too soft & mushy without this.)

Sheldon "Performance Tuned" Brown

Mooo

I have to ask...
Have you considered holding off a bit and seeing if Sturmey comes through with the "new" ASC?
That'd be your hot rod hub, wunnit?

Sammyboy

I don't think it would. I'll level with you here, I'd like this to be a nice fast city bike, but I also have this vision of myself hanging with groups of roadies riding my 309 wheeled bike, and that's not going to happen without a decent top end, and much as I enjoy fixed gear riding, it doesn't make me go faster. Of course, there are other barriers to me frightening the carbon and lycra crew, mostly my own ability, but it'd be nice if it were possible.

Sammyboy

Ok. A 23 on an SA 8 gives me 30.4 to 92.8, and a 16 on a Nexus 4 gives me 43.7 to 80.5. For comparison, a road bike in 52 x 13 on 700 c's gets 105.1. It takes a lot of cadence to make up for 15 gear inches, and still more for 25! However, if I retain the existing cranks, or spring for cotterless where there are 60 tooth rings available, I'm better off. That would make the Nexus 4 50.5 to 92.9, and the SA8 35.1 to 107.1, which is a lot more like it. Hmmmm.

tcs

Are you sure? I mean, absolutely sure?

Best,
TCS

tcs

There are two axle lengths/hub shells/OLDs for the SA-8. The narrower one has a nominal 116mm OLD.

HTH,
TCS

PS - If the urge to fit a Nexus 8 or SRAM P7 is uncontrolable, you should know that spreading old Moulton rear forks is rather more involved than cold setting a normal bike's rear triangle. Check in with Moulton Preservation.

Sammyboy

With a 19 tooth sprocket, it's the perfect hub for the job, assuming I can do something clever to mount the shifter. Now to the infinitely harder job of finding a cheap used one. I might be able to get hold of some more cheap Nexus 7's, which I might be able to trade if I could find someone with an SA8.....

rhm

Four suggestions:
1. I frankly don't believe you need such high gears. The SA range you describe above would probably be enough most of the time; and though the Nexus-4 range doesn't have the top end, you'll really miss the bottom end. I'd try to get it down to 35 or so.
2. Compare the shifters and how well they'll fit different handlebar options. I had little trouble mounting the SA-8 perpendicular to the handlebar, but once that was done, I had a very hard time shifting it. It's a stiff shifter anyway, and I did not have it at a place where it was easy to shift.
3. Include, in your consideration of the shifter options, the Nexus Auto-D system, if you can find it. Some parts are available now:
https://cgi.ebay.com/Shimano-Nexus-4-...QQcmdZViewItem
Even if you can't find it now, you may find the whole auto-D system later (knowing your luck, I guess you will). You could mount the auto-D shifter anywhere, like somewhere you don't need to reach it, because it would do the shifting for you (just when you least expect it, no doubt).
4. consider what brakes will fit on those hubs. The Nexus-4 came in both a coaster and roller brake version. I have the latter. I have heard people complain about them, but I found it an excellent brake. I'm thinking on your Moulton mod, you will have a hard time mounting good brakes, so this is important. If you got a coaster brake and an Auto-D system, you could have a very clean looking bike.

Sammyboy

Thanks for this, and indeed all the very helpful stuff you've posted in response to my threads. I'll take these one at a time:

1) Maybe I don't need such high gears, but what I've got in mind is a small wheeler that's as near as possible the equal of a road bike on the long country road routes I ride, as well as being super-nippy in town, and there are large sections of my regular ride where I'm cranking along in 52 x 13 on my road bike. I know it's kind of a stupid aim, but it's just a fun thing to do with such a little bike. I don't think I'd miss the bottom end too much, I'm a strong climber, but I could be wrong.

2) I want to construct a shifter mount for revo-shifters; because this is such a common problem, I suspect it would sell well. My idea is a strong drop handlebar sized clamp with a tube coming out from it about 6-8 inches forward, and then a 90 degree bend. This would be in 25.4mm tube, and would act, effectively, as a stand-off for the shifter, meaning it was mounted in it's natural orientation, just in front of the flat of the bar (which is probably where you'd want it if you could bar mount it). Then it should be simple enough just to reach forward to shift.

3) The idea of auto-shifting does not appeal to me one little bit.

4) Looking at the Moulton, it appears that the dual pivot caliper brakes I'm using for the R20 would work even with the current wheels. Move up to 305's, and I would've though there would be plenty of calipers that would fit. I haven't looked closely though - is there something unusual about the brake mounts, or is it just a matter of reach? All that said, I'm not opposed to drum brakes, although they do add weight to a bike which could concievably end up very light indeed......

Sheldon Brown

Actually, I had forgotten that they started offering a 19 some time after I got my S-A 8-speed.

Sheldun "Infalabble?" Brwon

MnHPVA Guy

You can't blame the doctors in her case. She was well aware of the benefits of exercise. She was very active in running our bike club and a large X-C ski club. Her husband is now in his sixties, bikes, skis, runs marathons and has about as much body fat as Lance had during the last week of a TdF. She never let on that she'd ever owned a bike, until she could no longer work and needed money.

Good ones and bad ones. Mine have been great. Cardiologist is a runner and my new GP does triathlons. My old GP commuted on a Raleigh 3 speed in the winter.