Dynamos - Hub or Bottle?

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Re: Dynamos - Hub or Bottle?

Postby Greystoke » 24 Jan 2019, 6:42am

I ran bottle dynamos for years, a good one really has less drag than you'd imagine it does, I think the noise makes you think it's worse than it actually is.
My shimano hub dynamo gives more power for less speed than the bottle dynamos. I run 2 3w halogen lamps off mine and the hub dynamo powers both at a lower speed than the bottles ever did.
£30 is a steal for a complete dynamo wheel, you can't buy the parts for that...buy it before they realize how cheap it is.

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Re: Dynamos - Hub or Bottle?

Postby Ontherivet77 » 24 Jan 2019, 8:50am

Steve O'C wrote:
A couple of follow up questions.
Is the Decathlon hub wheel good enough for a Ridgback Panorama

The Decathlon wheel has a Shimano hub. I have had mine for 3 months and have done about 600 miles in all weathers. It has not given me any problem in that time. I paired it with this light;


Which is both brighter and has a better beam pattern that the cheap Lifeline light it replaced. I tend to ride with the light on day and night and I do not notice the extra resistance. I am however slow and overweight so YMMV.

For more money you could probably get a wheel with a hub that is lighter and more efficient with thinner spokes and a rim that is stiffer. When I first started using it I thought I could just detect some vibration from the hub on a short stretch of my commute that is on particularly smooth tarmac. It seems to have run in now and I no longer notice that. This is my first dynamo hub and I rather like the whole experience of battery free lighting. When the rim wears out I will probably buy a better hub and build it in to a lighter wheel. For the price I paid however I am not complaining.

I do not know if it is good enough for a Ridgeback Panorama but it is good enough for me.

Thanks for this.
Is the B&M light you are using compatible with Cantilever brakes?

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Re: Dynamos - Hub or Bottle?

Postby Brucey » 24 Jan 2019, 9:19am

Q. is the decathlon wheel good enough for a ridgeback voyager?

A. yes, provided you don't plan to use it for loaded touring.

The wheel (as a wheel) suffers from several shortcomings vs 'perfection';

a) it has a single wall rim. So not as strong as a double-wall rim. But in practice this is OK for a front wheel on a bike with (say) a rear-only commuting load. [years ago we had nothing but single-walled rims on touring bikes; front wheels caused hardly any problems.]
b) it doesn't have stainless steel spokes. So they won't be all shiny. But if you are commuting in the winter this probably won't matter to you unless you are a bike-cleaning fanatic.
c) it is a machine-built wheel; like any other machine built wheel it will almost certainly benefit from being stress-relieved. It might be OK without, but don't hold your breath.
d) the hub will benefit from having its bearings adjusted. Most shimano generator hub bearings are set too tightly from the factory.
e) the hub bearings will benefit from more, better grease. This will benefit both smooth running and longevity in the face of high mile/ bad weather use.
f) the hub is slightly heavier than a more expensive hub generator.
g) it is slightly draggier than a more expensive hub generator.

On the latter point there is maybe 0.5 to 1W difference when the lights are on and a similar amount when the lights are off vs a more expensive hub generator. There is typically ~ 5 to 7W of drag when a generator is outputting ~3W. To put this into perspective if you are doing about 15mph on fairly heavy duty tyres (puncture resistant, such as you might use for commuting), chances are that you are putting about 20-25W into each tyre. Most folk don't notice if hub generator lights are on or off. I think that (with the aforesaid type of tyre) the extra drag with the lights on is about the same as letting ~5psi out of the front tyre, so you could try that and see if you can feel that as a difference or not.

My experience is that with the basic shimano hub generators they work well (the electrical output doesn't vary wildly between different hub generators BTW) and are reliable provided they are greased and adjusted properly. If you just use them as is, they might be OK, they might not; lots of people take the view that at £30 they are prepared to replace the wheel if it gives trouble (and I think that the wheel is a 'spare part' in Decathlon's eyes explains why it doesn't come with the connector BTW; most other wheel vendors supply the connector with such a wheel). Anyway if having dipped your toe (rather inexpensively) into hub generator waters thusly you decide it isn't for you, you can flog the wheel etc and it won't have cost you much. On the other hand if you want a more 'perfect' wheel you could get a different one or rebuild that one with better parts. For example I'd be tempted just to rebuild it using stainless steel spokes.

It is the same deal with lights more or less. For less than £15 you can buy an LED headlight that is about as good as anything you could buy ~15 years ago, and is more than adequate for urban use. The best lights are a lot more money than that but the benefit per £ is less. So you could spend £50 all in for a basic hub generator wheel and lightset and this might be fine for commuting but if you want to roll the boat out you could spend ten times that on a system that is better but it won't be ten times better.

FWIW even when hub generators weighed about 1kg and stuggled to make 2W (which made very little light with tungsten bulbs BITD) using a hub generator was still preferable to anything else if you wanted trouble-free lighting. With modern kit it is pretty much a no-brainer.


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Re: Dynamos - Hub or Bottle?

Postby pwa » 24 Jan 2019, 9:30am

I'm sure there is a lot to be said for going down the Decathlon route, keeping things as cheap as possible, but it is probably worth looking at what you can get from Spa Cycles by paying a bit more.

https://www.spacycles.co.uk/m2b0s209p38 ... ter-Bundle

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Re: Dynamos - Hub or Bottle?

Postby NUKe » 24 Jan 2019, 10:02am

You seem to be looking at the 2 extremes, the axa bottle is one of the better ones, I used one for commuting for a couple of years.
The hub dynamo is by far the better option
Shimano do some arrange of options which go from low end value models to the higher end 3N80 which is still considerably cheaper than the SON.
Take a look at the German retailers whilst you still can, such as Rose or Bike 24. Because dynamos are more widespread in Germany they are lot cheaper
Rose UK site here (they are shipped from Germany)

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Re: Dynamos - Hub or Bottle?

Postby iandusud » 24 Jan 2019, 11:58am

For a commuter bike I would definitely go down the Decathlon route. I would also echo Brucey's comment about the cost of front lights. I recently fitted a SA hub dynamo on my cargo bike and with it a Union Hilux Steady 35 lux headlight. These retail around the £15 mark. I don't doubt that some of the more expensive lights available are better made, brighter etc but this light is very good. I regularly ride down a totally unlit cycle path that follows an old railway line, so it is pitch black. This light throws a great beam that lights up the path very well. It also has built in standlight.

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Re: Dynamos - Hub or Bottle?

Postby PH » 24 Jan 2019, 12:02pm

Ontherivet77 wrote:Is the B&M light you are using compatible with Cantilever brakes?

If you're lucky a fork crown light will be a simple fit and forget, if you're a bit less lucky it might require a little modification to either the fitting or the brake cable, if you're really unlucky it'll be a right PITA but I've yet to come across one that wasn't possible. A spacer is sometimes required to put the light a little further forward, those with wire brackets can often be bent to avoid conflict, then the brake yoke may need raising which may or may not effect brake performance depending on type. If you do a google image search you'll find plenty of examples, some of them leading back to this forum. Peter White Cycles is also a good source for info on all things dynamo
If you find the supplied bracket isn't going to work, SJS cycles have a good range of alternatives
When it comes to buying the light, the German stores are worth looking at, the likes of Bike 24, Rose, Bike-Discount, they usually have a better range and keener prices than found in the UK.
Last edited by PH on 24 Jan 2019, 12:03pm, edited 1 time in total.

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Re: Dynamos - Hub or Bottle?

Postby pwa » 24 Jan 2019, 12:03pm

Do very bright LED dynamo lights produce more drag than lower output equivalents?

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Re: Dynamos - Hub or Bottle?

Postby gazza_d » 24 Jan 2019, 12:33pm

Dynohubs are easily better than bottles.

Another good source for well built decent wheels with dynohubs is Taylor Wheels. I have 2 20" wheels which were about £40 each - Shimano DN31 3w hubs, stainless spokes, and basic but perfectly functional rims. Both wheels have done about 8000 trouble-free miles though all weathers and a mix of terrains.

As others have said, in practice you don't notice the drag from a hub and as such I never bother to turn my lights off. When I ran an Axa HR, I often would turn it off when climbing and rely on the then rubbish LEDs

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Re: Dynamos - Hub or Bottle?

Postby Brucey » 24 Jan 2019, 12:38pm

pwa wrote:Do very bright LED dynamo lights produce more drag than lower output equivalents?

depends how they work; in general I suspect the answer is 'no' except perhaps at low speeds.

Most front light shunt excess current (which is nearly always somewhat finite) rather than cope with high voltages (which occur if you try and limit the current through the generator). This means the generator is usually producing as much current as if it were driving a higher powered light and current is what mainly creates drag. (You can demonstrate this very easily by turning the wheel with the generator shorted; it is like an electric brake.)

But some higher powered lights (with clever internal circuitry) may work differently at speed (eg drawing less current at higher voltage) and may create less drag per W of power extracted.


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Re: Dynamos - Hub or Bottle?

Postby gaz » 24 Jan 2019, 12:59pm

In contrast to gazza_d, I can notice the lights on drag from my DH-3N31. I can't tell if the lights are on/off from the drag alone, only by looking. If they are on and I switch them off whilst riding on a smooth road I can feel the difference.

FWIW anecdotely I cannot feel any difference in drag between that dyno-hub with lights off and the ordinary hub it replaced. I accept the reality that the dyno-hub has more drag.

I've been running it since the winter of 2016/17 and wouldn't be without a dyno-hub for my commute. I may invest in a better model next time.

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Re: Dynamos - Hub or Bottle?

Postby SimonCelsa » 24 Jan 2019, 5:14pm

I fitted the decathlon dynohub wheel a couple of months ago to my middle daughter's paper round bike to replace a bottle Dyno which I had fitted previously. I just asked her if she had noticed any difference between the two, to which she replied "I thought I was still using the bottle one"…........!!

There you have it, scientifically proven, there is no difference!

I can only add that the bottle dynamo was quite a bit noisier which hence gave the perception of higher drag. Both of them perform well with no problems to date.

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Taylor Wheels and SJSC options both good

Postby zenitb » 24 Jan 2019, 5:43pm

The Taylor Wheels £45 dynamo wheel I bought has lasted 10,000 miles/4 years of muddy all-season canal commuting with no re-trueing. It has 36 spokes and has a proper Ryde Zac box section rim so is a step up in quality from the Decathlon single wall rim. I am about to cycle home from work with it as it happens :-)

Here is the modern equivalent at Taylor Wheels
https://www.taylor-wheels.com/taylor-wh ... 0-3n-black
but they have lots of other pre-built options.

I would also point out that the Shimano Nexus dynohub wheel that SJSC handbuilt for me back in c1997 is still working reliably. This one was more expensive - £100 back then -but the wheel build is rugged and it has even survived a couple of years student usage by my son..a real quality wheel build.

So you pay your money and take your choice for dynamo wheels..all good options though.

Regarding the original question...I ditched bottle/bottom bracket dynamos in 1997. I am amazed they are still sold. Shimano made them obsolete long ago. :-)

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Re: Dynamos - Hub or Bottle?

Postby mercalia » 24 Jan 2019, 7:56pm

if you are a commuter & intend to ride a lot in the dark then a hub dynamo the way to go. I have a bottle dyno ( B&M - now discontinued so any stock is left overs) that I dont use much. But I do when I cant be botherd to get the battery lights out. The advantages a) you can use any wheel you want b) no drag when not used c) maybe run better at low speeds without flicker. c) wheel hub mainenance maybe more straightforward with normal hubs than with hub dynos? d) lighter than a hub. Rather than a dyno of any kind I am inclined to use battery lights with removable AA batteries,. Lidl used to sell cheap battery lights that worked well and lasted well on the lowest setting. I also have a lithium powered light that you charge thru an usb port that also will run from an external power pack to give silly longevity

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Re: Dynamos - Hub or Bottle?

Postby Ontherivet77 » 25 Jan 2019, 8:57am

Looks like I need to get down to Decathlon.
Thanks for all the in depth replies.