Dynamo hub and wheel build

HeebyGeeby

Regular
I want to add a dynamo to the front wheel of my Ribble CGR bike.
Currently the wheels I have are Mavic AllRoad, 24 spoke.

Rather than rebuilding my wheel, I am considering buying a new Mavic rim (£25) with 32 spoke holes to match up with a 32 spoke Shimano DH-UR705 dynamo hub (£100) and having my local shop build a new wheel with those.
I'll also need to convert my front brake disc to centrelock.

Is there anything wrong with mixing 32 spokes at the front with 24 at the back?
 

rogerzilla

Legendary Member
Yes. It is an offence to God and to man if you have fewer spokes at the back than at the front (the other way around is fine).

Seriously, there is no problem but it will look a bit odd.
 
OP
HeebyGeeby

HeebyGeeby

Regular
Seriously, there is no problem but it will look a bit odd.
Unfortunately the better option is a Shutter Precision dynamo with 24 spoke holes and 6 hole disc but it's twice the price of the Shimano and only seems to be in stock in the US. £100 more is a lot to pay to avoid the scorn of OCD cyclists.

Or just buy a centre lock disc to go with new wheel.
The adapter is only £10 or so but yes, it's worth considering.
 

si_c

Guru
Location
Wirral
Unfortunately the better option is a Shutter Precision dynamo with 24 spoke holes and 6 hole disc but it's twice the price of the Shimano and only seems to be in stock in the US. £100 more is a lot to pay to avoid the scorn of OCD cyclists.


The adapter is only £10 or so but yes, it's worth considering.
Go to Spa Cycles - PD-8X hub is £123 https://www.spacycles.co.uk/m2b0s133p3776/SP-DYNAMO-PD-8X-Thru-Axle-6-Bolt that's assuming you want a thru-axle version - the QR version is cheaper again.

Combine that with excellent service from Spa and you're good to go.

Edit: just to say that 24 spokes is too few IMO for a front disc wheel - you can always get a second rear wheel with 32 spokes too :laugh:
 
OP
HeebyGeeby

HeebyGeeby

Regular
If it helps I went through this process fairly recently
Thanks, great thread... once you get through the pedantry of whether it's technically a dynamo... :rolleyes:

Found that item on Amazon.
Unfortunately the skewer dynamos are far more plentiful than 12mm thru-axle. SON make exactly what I need but it's £250 or so.
 

CXRAndy

Guru
Location
Lincs
Why pay so much for a Shimano dynamo hub?

I bought a Shimano Hub Dynamo DH-3D37 32 Hole 6V / 3W Disc Black for £50 from europe

Holland bike shop;)

Centre lock adaptors are a few quid

Use Halo Skewers for a little added security
 
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OP
HeebyGeeby

HeebyGeeby

Regular
Why pay so much for a Shimano dynamo hub?

I bought a Shimano Hub Dynamo DH-3D37 32 Hole 6V / 3W Disc Black for £50 from europe

Holland bike shop;)

Centre lock adaptors are a few quid

Use Halo Skewers for a little added security
But my bike uses 12mm thru-axles. I agree, loads of options if I had skewers, but the 12mm axle and 24 spokes narrows the field to two possibles, I think.
Also, I'm an idiot, my discs ARE centre lock, I mistook the rivets for bolts...
 

rogerzilla

Legendary Member
24 spokes in a hub-braked wheel, as si_c, says, is a bit low. Disc front wheels are often dished, too, which means the RH spokes will see very high tensions under braking. They won't actually snap the first time you use the brakes but they'll see a lot of tension variation in use. This wheel needs to be very well built, using top quality spokes and with the spoke line corrected so there is no possibility of flexing at the elbow or where the spoke enters the nipple.
 

bladderhead

Well-Known Member
I had 24 spokes front and back, and a Schmidt dynamo in the front, and disk brakes. The front spokes kept breaking, and then the dynamo packed up. I realised it was the braking. I got a 36 hole dynamo and rim. This was 10 years ago. No broken spokes since then, and the dynamo still works. People with a dynamo and disk brakes have a special dispensation allowing them to have 36 in front and 24 at the back.
 

Nebulous

Veteran
Location
Aberdeen
I've recently bought new wheels with a son dynamo.

This thread has just reminded me though, that I have a Shimano lx disc dynamo in a box. I've just checked, it has a centerlock and is for 36 spokes. I had intended building it myself, but couldn't work out what I needed to build it, so forgot about it.
 

Ajax Bay

Guru
Location
East Devon
Disc front wheels are often dished, too, which means the RH spokes will see very high tensions under braking. They won't actually snap the first time you use the brakes but they'll see a lot of tension variation in use. This wheel needs to be very well built, using top quality spokes and with the spoke line corrected so there is no possibility of flexing at the elbow or where the spoke enters the nipple.
"Disc front wheels are often dished, too, which means the RH spokes will see very high tensions under braking."
If the disc front wheels are dished, won't the LH spokes be at a higher tension than the RH spokes? Why will the RH spokes see "very high" (presumably you mean much higher than when the brake is not being applied) "tensions under braking". If the tensions in the static wheel are (say) 1000N on the RHS and 1200N on the (dished) LHS, how much higher are these "tensions under braking"?
"They won't actually snap the first time you use the brakes" - No, really? What do you mean by "actually snap" btw?
"but they'll see a lot of tension variation in use." - how much is "a lot"? Is it significant compared to the variation which happens every time the wheel rolls round and the lower spokes drop to maybe 75% of static tension? And will this spoke tension variation caused by braking have any material effect on the number of tension/less tension cycles which would cause spoke failure by (metal) fatigue?
"This wheel needs to be very well built" - ideally all cycle wheels need to be well built, surely.
". . . with the spoke line corrected so there is no possibility of flexing at the elbow or where the spoke enters the nipple" - Please could you explain how one chooses components (hub, rim and spokes) which allow the "spoke line [to be] corrected" or how one does this in (wheel building) practice?
I think @bladderhead has pointed out that 32 is sensibly better than 24 when it comes to spoke number in a disc braked front wheel. But the quality of build is probably more important.
 
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