The Brompton front hub

[rogerzilla]

It's a cute little thing, but I had my doubts about its quality.  Rather tight and rough, so I opened it up and found lots of grease and uncaged bearings.  Threw them away, wiped it clean and replaced with grade 25 balls and Park grease.  When adjusted properly it's pretty smooth.  So far so good.

This was from a surplus wheel I dismantled in order to use the spokes elsewhere.  So I got some new spokes and built a new front wheel.

When I've got the spokes tight, but before putting it in the truing stand, I generally give a new wheel a bit of a spin in my hands to see how far off it is.  Something is badly wrong here, because it's bucking like a bronco. 

Turns out the stupid thing has been drilled eccentrically, which is almost impossible to detect before it's built up into a wheel.  This doesn't mean the *rim* can't be made true with respect to the axle, which I've done, but the centre of gravity changes as the hub shell rotates, meaning there's the kind of pulsation you'd get by attaching a big weight to one spoke.  Hmmm.  Maybe it will be better with a tyre on it, when the effect of the hub shell will be reduced in overall terms.

I see the retail price of a replacement front hub is about ten quid.  I bet it cost £1 to make 

[LittleWheelsandBig]

Yes, the B front hub is a bit cheesy and benefits from care and attention.  Every one I've seen has eccentric spoke spoke drilling.

It is possible that a large part of the pulsing you are feeling is the difference between the hefty rim pinning and the large hole for the Schraeder valve, rather than the eccentric spoke drilling.  The small wheel diameter seems to exaggerate these effects when you spin it in your hands, I'm not entirely sure why.

[rogerzilla]

It's certainly less evident with a tyre fitted, although it's still worse than any other wheel I've tried.

[LittleWheelsandBig]

I've felt much the same thing on a Moulton front wheel built around a Campag Record front hub.

[rogerzilla]

Probably just that the tyre (assuming it's not equally wobbly) has less inertia with a smaller wheel - but then the rim should have less effect too.  Anyway, I can see the flanges going up and down.  Oo-er.

[LittleWheelsandBig]

With the reduced perimeter weight of the small rim, small weight differences like the schrader valve hole and the steel pins in the rim join probably have a greater effect.

[Sigurd Mudtracker]

Presumably adding the tyre (and tube) means that the valve counterbalances the pinning?  Maybe we needed precision weighted valve caps!

[rogerzilla]

Nah - the valve is way lighter than the pin (as it is for most wheels - with sufficiently free-running bearings the valve normally stops at the top when the bike is hung up).

Maybe a TireFly would help.

[LittleWheelsandBig]

I'm sure that some rim company used to make rim counterweights that went under the valvenut, Ambrosio perhaps?  Can't find details, perhaps it was the result of a fevered brain.  Of course, they were 622 while the Brompton is 349   

[chagzuki]

Anyone here know the weight of the standard front hub?

The axle on mine appears bent, I'm not sure if an 8mm axle is up to the job of supporting front-loaded luggage.

[Biggsy]

I can't find the weight of the standard front hub.

I'm wondering if the Xtra Light version (74 grams) might be stronger, with it's over-sized aluminium axle?  Mine's been fine anyway, with an S-Bag carrying as much weight as anyone would want.

[chagzuki]

I wonder if the 74 grams includes the 'axle fastener' / non-q/r skewer?

[Biggsy]

I wonder if the 74 grams includes the 'axle fastener' / non-q/r skewer?

It's a good question - that I don't know the answer to without disassembling my wheel!

This also gets me thinking about changing the skewer (that I suppose is steel) for a titanium one, despite believing that steel is the best and safest material for this job.

For what it's worth, the Campagnolo Chorus front hub, also with oversized aluminium axle, weighs 120 grams without the skewer.  The Brompton differs in that it has cartridge rather than cup-and-cone bearings, as well as being shorter altogether - though I would expect the overall weight to be not very different from the Campag's.

[chagzuki]

I notice also that Brompton have recalled the radially laced extra-light front wheel and now have it double cross laced.

[rogerzilla]

You'd think someone would have told them.  Radially-laced front wheels can be fine (I've ridden them without trouble) but to make the risk of flange cracking as low as on a tangential wheel, you have to lose the small weight advantage by making the hub flange thicker and heavier.  There's also no aerodynamic advantage although they look cool and, in the rare event that they're laced "heads in", are marginally stiffer laterally.

Paradoxically, radial lacing is better with the lowest possible spoke count, because there's more metal between each hole in the flange.  A 36-hole radial is asking for trouble.

[Biggsy]

I could argue that radially-laced wheels are more aerodynamic because the spokes are shorter - but that would be picking at small nits indeed.

74 grams for the Xtra Light hub is nice and light anyway, even if that doesn't include the skewer.

[TimO]

Does anyone make a suitable hub, aside from Brompton, and the Son Dynamo hub (which obviously makes for a substantially more expensive wheel) ?

[chagzuki]

A standard front hub you mean, i.e. not dynamo?

[TimO]

As far as I know, only the SON Brompton hub is a dynamo hub which is narrow enough.

Possibly others may make conventional hubs which will fit, but I'm not sure.

Edit: Actually, there's a modified Shimano dynamo hub, so that's at least three options, although that's still not exactly a cheap solution, even if cheaper than the SON.

[Biggsy]

I can't find anything else with a quick search for "73mm front hub" on Google, Google Shopping and eBay.

I'm happy enough with Brompton's own Xtra Light one.  I like light things.

[TimO]

It was mostly just curiosity, given Rogers original post (admittedly now several years old).

My Yak Bob also has a narrow wheel (which would probably need a similar sort of hub), so in terms of replacements it's not an entirely useless fact.

Amusingly, Googling for other options, this thread is halfway down the second page!

[chagzuki]

Dahon hubs are 74mm, however they used larger diameter axles, either 10mm or some imperial equivalent, and they're 20h. Older Dahons used to use 28h front hubs and 9mm axles.

[chagzuki]

It would be handy if there were 20h 349 rims available, then there'd be more options to switch parts. I have a Dahon equivalent to the brompton extra light hub, a sealed bearing type which is just as light, but I can't find a matching 349 rim.

[Biggsy]

It was mostly just curiosity, given Rogers original post (admittedly now several years old).

My Yak Bob also has a narrow wheel (which would probably need a similar sort of hub), so in terms of replacements it's not an entirely useless fact.

It'll be worth checking the old Bob's OLD - cos there's more than one narrow hub standard, including 88mm.  Would be nice if it is 73mm, then you can use a nice Brompton hub (if the axle diameter is ok).

[LittleWheelsandBig]

The original reason for Brompton's radial front wheels was to use the same length spokes as for the rear wheels. Then they changed to 13G spokes on the rear, losing part of the advantage.