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I have a 2yo Bropmton with Shimano dynamo,
I do wonder if this is a product of the small wheels, I can spin my (very very cheap) Shimano hub and whilst I can feel the resistance it doesn't cause the wheel to stop that much quicker and in use its basically not noticed. It is much heavier than the "good" ones but its all relative for a fairly heavy bloke on single speed.
I do wonder if this is a product of the small wheels
Smaller wheels have lower rolling resistance. So it would be more noticeable on smaller wheels than on say 700c, which take more effort to push round/accelerate...
Yup I agree though I was thinking more when you spin it by hand the larger wheel with the bike upside down, the wheel would have more rotation energy to exert on the hub so it would appear to stop the small wheel quicker.
Also true, the bigger wheel has more momentum and fewer rotations per distance traveled when you spin it around, thus the effect of the hub will seem less.
I'm looking on the extra effort of the hub and the 700x32 Marathon Plus tyres as a badly needed workout to which I'll be adding 40kg of child and trailer. One thing I was less than fully whelmed with was the lowest gear, which doesn't seem that low at all (bearing in mind I need to get me, bike, trailer and bairn up some decent hills). I'll count the teeth on the sprocket and investigate whether larger sprockets would work.
I have (I think) the Shimano DN-78. For the few % extra drag and few grams extra hub weight, I couldn't justify spending (at least) 3 times as much on a SON hub that would give me exactly the same amount of light.
The dynamo hub wheel (Open Pro rim, 32h) is lighter than the Shimano R500 wheel it replaced, and significantly so in the rim. I've calculated the extra resistance of the dynamo, even when lit, is probably only 3 or 4% of energy I'm using at cruising speed. With the weight of the rest of the bike pushing you along, and aerodynamic drag slowing you down, I defy anyone to notice the drag of the dynamo when not in use.
Certainly it hasn't noticably effected performance on the Innocent Tunnel challenge, and I've had more success with the dynamo wheel than with non-dynamo wheel on the single speed.
My dynamo is notchy 'to hand' but I'd been warned it would feel like that before building the wheel up. I'm not sure that the time to stop spinning in the air is representative of enormous friction when you're riding.
For instance, today I set two PBs - up Arthur's Seat and KOM on Broughton St, yet I had the dynamo and light on. I went considerably slower when I tried with the dynamo off last week, which suggests the friction is lower than my daily noise level.
I have a cheap Sturmey dynamo with drum brake, FYI. I can recommend it for anybody who wants a hassle free urban ride, unlike their hub gears.
So, last night I dismantled the wheel with the S2C, intending to re-use the rim and spokes to build around the Automatix. Unfortunately my measurement was a little off, and the spokes are a couple of mm too short!
To add insult to injury, the new S2C internal being sent by Sturmey Archer just hit my desk, so I have the choice of building up the wheel again with the S2C, then dismantling it in a few days when I get the Automatix spokes, or ordering a new rim just for the Automatix, so I'll end up with two completely different rear wheels.
Sigh.
You've come this far. A decent rim is not a huge amount these days, plus a pack of spokes.....go on, you know you want to! ;-)
That's the same hub I've got (after reading your blog) but with 90mm brake.
Spokes on eBay are cheap as chips. Got plain gauge stainless steel for pennies.
So, I finally got my SRAM automatix hub onto the bike.
Initial impressions - shift feels much more solid than the Sturmey in an indefinable way. Coaster brake doesn't feel as good as the Sturmey but perfectly useable.
Speed chosen to change gear is far, far too low. You get going and then it immediately changes up, so you've got to crank out 40rpm uphill unless you go *really* slowly.
Will see if it beds in, but not a fan of automatic shifting unless the cadence is vaguely sensible!
Speed chosen to change gear is far, far too low. You get going and then it immediately changes up, so you've got to crank out 40rpm uphill unless you go *really* slowly.
Will see if it beds in, but not a fan of automatic shifting unless the cadence is vaguely sensible!
Is that not adjustable? I thought you could change (within limits) the speed at which the gear change takes effect?
Hmmm. Maybe not.
"The shifting points can be preset by SRAM according to the guidelines of the bicycle manufacturer at certain speed limits which can be 12, 14 or 18 km/h (7.5, 8.7 or 11.2 mph). The nickle-chrome plated internal gear hub weighs 980g and comes with a coaster brake. For different sprocket sizes: 15, 16, 17, 18, 19, 20, and 21-tooth-sprockets"
http://www.sram.com/sram/urban/products/automatix
Are you running 26" wheels? This may account for the gearing feeling low as the hub may be adjusted for 28"/700c. Change the sprocket to something smaller?
On second thoughts it may just be that the way your Automatix is set does not suit your riding style. If you're a sporty fast cadence in low gear type of rider, rather than a pootley city bike cruiser type of rider, it might not be the right set up. I see on other fora that "shifting early" comes up quite a lot in discussion of the Automatix.
Yeah, if you gear it to top out at 24mph@100rpm, at 11.2mph you'll be getting about ~46rpm which seems about what I'm suffering.
hi ho.
Yeah, if you gear it to top out at 24mph@100rpm, at 11.2mph you'll be getting about ~46rpm which seems about what I'm suffering.
It seems you are fairly speedy urban rider then. Presumably the top speed would be slightly higher on 700c or 27" wheels, and maybe the gear change at a slightly higher speed too?
With the start/stop of junctions, traffic lights, speed bumps etc. it is not that frequent that I manage to sustain speeds above 11mph in normal urban riding. When I do get into the 12-18mph range, a higher gear would help. Unless I'm on a downhill, it is rare I get above 18mph in the city.
But that's me. I'm guessing you have a style of riding where a gear change at 11.2mph seems inconvenient or breaks the rhythm of your fast cadence.
What I've tended to find is that I now change my style of riding depending on which bike I'm riding, so on my hub geared small wheelers I'm a bit more pootley; on the derailleur geared 700c bikes I tend to do a higher cadence faster style of riding; the cargo bike is somewhere inbetween; the tandem is different again as I cannot do higher cadence riding because of the junior stoker: his feet might fly out of the toeclips!
The problem is obvious although I didn't fully consider it. The change is based on RPM not cadence, so you can fit any gearing you like and it makes no difference to the speed you're travelling at when the hub shifts.
Off out with the cadence meter fitted to see what exactly the shift pattern is.
Oh, you mean rear wheel RPM and not crank RPM?
I would imagine the only thing which might influence the speed at which the gear changes is wheel/tyre diameter. Bigger diameter, bigger circumference, fewer RPM to reach a given speed, hence gear shift would occur at higher speed. Vice versa for smaller diameter.
I mentioned gearing (sprocket, chainring) only because you seemed to have an issue with pedalling cadence, particularly uphill. Which might indicate lower overall gearing required?
Yep - the core issue is simply that because it changes up at such a low speed, even if you change the sprocket so it is a low 60rpm cadence at 8mph, a rapid 120rpm will then only get 16mph.
Or, another way of thinking about it is that the shift happens at a lower speed than I ride up almost any hill on my commute, so it's really just a single speed where your first half a dozen pedal strokes away from a red light are in an easier gear...
I think this guy
http://hubstripping.wordpress.com/fs-torpedo-automatic/
reckoned that you could tweak the springs a bit but I didn't see that bit on this web page. Perhaps I dreamed it.
Found it:
This is great because stretching or pushing this little spring makes it easy to optimize the shifting point for your purpose.
Yes, but I suspect that is not an operation for the faint of heart and no doubt invalidates the warranty.
This guy stripped the hub down and there's a good discussion here about tweaking the springs. I'd be too scared to knacker the hub...
Yes, but I suspect that is not an operation for the faint of heart and no doubt invalidates the warranty.
Well I usually take the view that it's not working properly anyway so what's the harm in taking it apart?
it's not working properly anyway so what's the harm in taking it apart?
Conversely, if you spent 80 quid and the thing works but you don't like how it works, do you then break it to try and improve it and lose the 80 quid? Or do you 'live and learn'?
Personally I've bought things over the years that, though they functioned well, were not 'right' for me. Customise or cut losses and sell on? Tough one.
Well… if you're just asking me… I'd take it apart and footer. I do that with bikes, cars, computers, pretty much anything really.
One of the things I don't like about the Brompton is the back hinge because I can't easily fix it myself.
I'd take it apart and footer. I do that with bikes, cars, computers, pretty much anything really.
In principle, I agree, but it depends on how feasible said footering is. Swapping out components for better/more suitable? No problem. Adding extra bits without damaging original? Again no issues. Potentially breaking something by modifying the original component? Different story...
Yeah, I'm not sure given my track record with hub gears that I'd want to take this one apart rather than just sell it on. But on the other hand, it does feel much nicer than the S2C.
The shift point is at 10.2mph, from a cadence of approximately 60rpm in the low gear to 43rpm in the high. This means that it's never possible to pedal the lower gear at a reasonable cadence.
Speeds of 10-15mph are therefore being ridden with a strong feeling of "need to change down!" with the bike feeling more reasonable on either side. Unfortunately that's an extremely common range to be in.
Well, it's keeping me fit trying to ride up Leith Walk > 15mph!
This means that it's never possible to pedal the lower gear at a reasonable cadence
Could you put on a bigger sprocket?
That's what I reckon too. Lower the gearing, if possible. What sprocket do you have on there just now? SRAM sprockets are allegedly fairly easy to swap out.
Seems the standard SRAM sprocket is a 19T ? Possible to change to a 20T or 21T. Lower gear is direct drive, 1:1. So it i your overall gearing that maybe too high. Either bigger sprocket on hub, or a smaller chainring?
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