Cycling UK Forum

ukdodger wrote:

[XAP]Bob wrote:Rear wheel...

Front. They're easier to turn on and off.

It is common practice to mount bottle dynamos on the front wheel but some folk are dead set against it for one reason in particular; if the dynamo comes adrift on its mountings, you can go over the bars. I think that the manufacturers must agree with this view, because the most common bottle dynamo mountings you see are

a) front wheel, braze-on bracket, or

b) rear wheel, clamp-on bracket.

IIRC you don't find dynamo manufacturers selling clamp-on brackets (similar to rear fitment ones) meant for front fitment. Too risky perhaps...?

cheers

Brucey wrote:

ukdodger wrote:

[XAP]Bob wrote:Rear wheel...

Front. They're easier to turn on and off.

It is common practice to mount bottle dynamos on the front wheel but some folk are dead set against it for one reason in particular; if the dynamo comes adrift on its mountings, you can go over the bars. I think that the manufacturers must agree with this view, because the most common bottle dynamo mountings you see are

a) front wheel, braze-on bracket, or

b) rear wheel, clamp-on bracket.

IIRC you don't find dynamo manufacturers selling clamp-on brackets (similar to rear fitment ones) meant for front fitment. Too risky perhaps...?

cheers

I'd never use a bracket to mount a dynamo. It might not bring you off if it went into the rear wheel (and that's debatable) but the tapering of the seat stay lends itself to a loosening of the bracket. Also they make a mess of the paint job. If I were the OP I'd stick to batts until he could get a bracket brazed on. Perhaps before an intended respray. If he's not fussed about colour matching he could have one brazed on the front fork blade and have the forks resprayed alone.

Another vote for the bracket recommended by Fatboy and Wooliferkins. Much more rigid than a standard bottle-dynamo bracket.

I've got one bike with a Nordlicht bottle dynamo, and another with a very cheap Shimano hub dynamo. The Nordlicht is good (better than the AXA HR I had before, IMHO) but eats rubber pulleys about once every six months. It can slip a bit in the wet. The cheapie Shimano hub (£20 from eBay... built the wheel myself) whilst it does have a bit of drag on or off works brilliantly and from what I've read elsewhere compared very favourably to more expensive hubs.

I'd strongly encourage you to think of a hub dynamo. It's a lot less hassle and you really don't need to go to a SON for utility use.

Brucey wrote:IIRC you don't find dynamo manufacturers selling clamp-on brackets (similar to rear fitment ones) meant for front fitment. Too risky perhaps...?

That was my thought.

I don't like things that could rotate into a front wheel.

hercule wrote:The Nordlicht ... slip a bit in the wet.

I use my Nordlicht 2000 with the alternative metal drive wheel, instead of the standard one. I've found it reliable except in snow. I did have a problem the other week, when I moved my wheel back to maintain chain tension, and the dynamo made a horrible noise, and slipped, until I realigned it - it's important that the axis of a bottle dynamo passes through the wheel axle.

hercule wrote: .....The cheapie Shimano hub (£20 from eBay... built the wheel myself) whilst it does have a bit of drag on or off works brilliantly and from what I've read elsewhere compared very favourably to more expensive hubs.

I'd strongly encourage you to think of a hub dynamo. It's a lot less hassle and you really don't need to go to a SON for utility use.

http://www.bikequarterly.com/VBQgenerator.pdf

gives good drag measurements of generators including the DH-3N30 which has a generator that interchanges with the (cheaper, slightly lighter) DH-3N20 model.

I disagree with BQ's statement that the NX32 and 3N30 have cones that will only last 3000km; the NX32 does have inferior seals and the 3N30 has (like many inexpensive shimano hubs) bearings that become super-smooth with use. They just need correct lubrication and adjustment. Plenty of people have since put tens of thousands of miles on 3N30s with no problems.

Regarding drag; basically the NX32 models etc have a generator that doesn't have any laminations in the soft iron. This makes it very lossy even when the lights are off. I think present SA generators are made in the same way, with no laminations. [Why? Even the old SA dynohubs from 60 years ago had some laminations, rather than none.]

The more recently designed shimano generators, the DH-3N30 (and presumably the DH-3N20 too) all have highly laminated soft iron stators and this makes them pretty efficient (lights on) and pretty drag free (lights off). Lights off, the best Schmidt generators might slow you by 0.1kph. A DH-3N30 might slow you by almost 0.2kph, lights off. Lights on, at normal speeds either will slow you by around 1kph. For utility riding, I can live with that.

In fact I might live with the '-1kph all the time' drag of the NX32 et al., come to that.

cheers

Brucey wrote:It is common practice to mount bottle dynamos on the front wheel but some folk are dead set against it for one reason in particular; if the dynamo comes adrift on its mountings, you can go over the bars.

How? The dynamo mounts in front of the fork so it would have to stay in the spokes for almost a complete revolution before it traps in guard stays or fork. Not very likely IMO. And at least in front you stand a chance of seeing it start to come loose, unlike if it is on the rear.

Now I'm reminded, it's the DH-3N20 that I have. I was struck how few times the front wheel spun when I'd fitted it (and a very definite difference lights on vs lights off), but on the road it makes no major difference (discernible to me, at any rate).

The B&M dynamo is a good buy. You get a choice of caps depending on weather which are easily changeable. Dynamos slip a lot in the wet and dont move at all in snow. The B&M has a wire brush type cap for the worst conditions. Also all dynamos work best with two wires each for both front and back bulbs. Using the frame as an earth always ends up blowing bulbs and/or intermittent lighting.

mjr wrote:

Brucey wrote:It is common practice to mount bottle dynamos on the front wheel but some folk are dead set against it for one reason in particular; if the dynamo comes adrift on its mountings, you can go over the bars.

How? The dynamo mounts in front of the fork so it would have to stay in the spokes for almost a complete revolution before it traps in guard stays or fork. Not very likely IMO. And at least in front you stand a chance of seeing it start to come loose, unlike if it is on the rear.

Normally a bolt comes loose and the dynamo either slides down the fork (NB clamping stuff like this to fork blades is a pretty dumb idea to start with BTW; this is just the icing on a whole big cake of dumbness), or just swivels on its mounting (BO on not). They very rarely just fall off cleanly! One that slides down the fork will definitely jam the wheel. A front mounted dynamo ( a left-handed one on the left fork blade or a right handed one on the right blade) that swivels can get snarled up in the spokes easily enough, but a rear mounted one will just jam almost instantly.

You will also have noted that dynamos are spring loaded and swivel about either a horizontal axis or a vertical axis. The kind with a vertical axis are probably a bit safer because they usually have a smaller stroke overall. However some models with a horizontal swivel have a large stroke and these can force themselves into the spokes pretty well.

If you are going to mount a dynamo on the fork, I'd suggest to use a front mounted one on a secure bracket of some kind (braze-on or maybe one of those that mounts to a canti boss, if you have strong cantibosses). Mount it using nyloc nuts and washers that will make for a secure mounting.

If you look at how dynamos are mounted on good quality dutch-style bikes, this is a fairly good guide. There are any number of other ways of doing it that are not as good as this.

cheers

ukdodger wrote:The B&M dynamo is a good buy. ....

only if u dont buy it in the UK but in say Germany from Rose @ £24. I think UK sellers must still l think its pre 2000? when hubs where still specialist and they could charge high prices for bottle dynamos?

Brucey wrote:
Normally a bolt comes loose and the dynamo either slides down the fork (NB clamping stuff like this to fork blades is a pretty dumb idea to start with BTW; this is just the icing on a whole big cake of dumbness), or just swivels on its mounting (BO on not). They very rarely just fall off cleanly! One that slides down the fork will definitely jam the wheel. A front mounted dynamo ( a left-handed one on the left fork blade or a right handed one on the right blade) that swivels can get snarled up in the spokes easily enough, but a rear mounted one will just jam almost instantly.

You will also have noted that dynamos are spring loaded and swivel about either a horizontal axis or a vertical axis. The kind with a vertical axis are probably a bit safer because they usually have a smaller stroke overall. However some models with a horizontal swivel have a large stroke and these can force themselves into the spokes pretty well.

If you are going to mount a dynamo on the fork, I'd suggest to use a front mounted one on a secure bracket of some kind (braze-on or maybe one of those that mounts to a canti boss, if you have strong cantibosses). Mount it using nyloc nuts and washers that will make for a secure mounting.

If you look at how dynamos are mounted on good quality dutch-style bikes, this is a fairly good guide. There are any number of other ways of doing it that are not as good as this.

cheers

Ive never had any such trouble, but then I make sure the bolts are veeeeeeeerrrrrrrry tight. Its a shame the dynoshoe is not available any more as it was the best of the cantiboss systems that also secured to the forks with ties. Even in kid days with bolt on rear brackets I never had any trouble either. I think the risks are over stated. Possible dont mean likely. Has any one here ever had such incidents? , I would like to know

I spent a fair amount of time wrestling with various dynamos as a youth; these experiences eventually drove me to construct a wheel with (an even then, vintage) hub dynamo. Possibly my recollections are coloured, but I had several bottle dynamos start to rotate around the seat stay under their own steam, which is but a small step away from sliding, and a chum did have one come adrift wholesale (although I have no idea how tight the bolts were in that case).

The conclusion I came to back then (rightly or wrongly) was that the strength of the brackets I was using was marginal, and no matter how tight the bolts were, the thing might never be held securely. It seemed to me that in many cases the earthing screw needed to be driven into the frame hard and this was what was actually stopping the thing from moving. I may have even removed the earthing screw to test this hypothesis.

I still wince when I see a quality frame with a standard 50p dynamo bracket nailed onto it. I know exactly what will be underneath; a ruined frame.

cheers

Brucey wrote:
I still wince when I see a quality frame with a standard 50p dynamo bracket nailed onto it. I know exactly what will be underneath; a ruined frame.

cheers

I agree with that. I wouldnt use one of those kid bolt on brackets any more. But then my kid bike was nothing special & once bolted on who cared if the paint was scratched under neath. what you dont see you dont worry about. I had lights!