Author Topic: Converting rim braked wheelset to disc  (Read 489 times)

Converting rim braked wheelset to disc
« on: July 11, 2020, 09:20:22 pm »
Mrs DF has a disc braked Trek hybrid which has a fairly poor wheelset, we are getting spoke breakages at a disturbing frequency in spite of repeated efforts by the lbs to keep them going. I have a set of Hewitt handbuilds in the garage that only saw about a years worth of use on my old rim braked bike before I transitioned to discs and so retired them.

Is it technically/economically feasible to rebuild these with disc specific hubs? Apart from the hubs, what else would need changing?

Thanks in advance

DF

Re: Converting rim braked wheelset to disc
« Reply #1 on: July 11, 2020, 10:20:29 pm »
New hubs will normally mean different spokes, especially on the left side where extra space is needed for the rotor.

I can't see it being economic vs selling the wheels and buying a disc set.

Re: Converting rim braked wheelset to disc
« Reply #2 on: July 12, 2020, 08:35:39 am »
some options to address the problem;

1) stress-relieve the ext.ant wheelset and carry on.
2) rebuild the extant wheelset with new spokes
3) rebuild rim brake wheelset

option 3) is not very appealing because you will need new hubs and as pointed out above the spokes will need to be different lengths, so really you are wrecking a set of wheels in order to gain a set of rims which may or may not be ideal for a disc-brake wheelset anyway. But on the plus side it can be carried out 'offline' and it gives you a spare set of wheels (always handy).

Option 1) ought (unless there is a fundamental problem with the spokes or how they fit) to result in a wheelset that may break a few more spokes (essentially those which are already cracked) but ultimately should give a reliable wheelset.  How many spokes might you break?  Well, a small number, up to about as many as you have already broken in the wheels.   

Option 2) is a good opportunity to learn how to build wheels.  I wouldn't suggest that the LBS does it; the logic here is that if they knew what they were doing they would have done (or suggested) 1) already.   

cheers

fd3

Re: Converting rim braked wheelset to disc
« Reply #3 on: July 12, 2020, 11:48:51 pm »
If you are buying a new hub and new spokes and then need them rebuilding you won't be making a significant saving in reusing the rims on your handbuilt wheels. 
You would probably be better off selling the handbuilt wheelset and buying a new one.

I agree with Brucey in that I would have reservations in bringing the wheelbuilding to an LBS who can't solve your broken spoke issue - though wheelbuilding from scratch is different from swapping spokes to be fair (I'm not sure how happy you would be if they had "tested" your wheel and told you that half the spokes needed replacing, while you're at it why not go for a complete wheelbuild?  maybe easier all round for them to replace a spoke and call it a day).

It's a good opportunity to learn to build wheels, but it's not the easiest start point and I'm not convinced you will save money in the short term as you will probably make costly mistakes in building/spoke selection.

Brucey what method would you recommend for spoke stress-relieving?
[/I could be wrong]

Re: Converting rim braked wheelset to disc
« Reply #4 on: July 13, 2020, 01:12:14 am »
Brucey what method would you recommend for spoke stress-relieving?

spoke squeezing (eg using  Brandt's method) is more likely to be both controlled and effective than many other methods. However there is an exception to this, and that is if the nipples are already at the limit of their articulation in the rim, in which case you can be left with residual stresses at the nipples and this can cause spoke breakages near the nipple. In this case (or if in doubt) I would recommend  a lateral squeeze instead, i.e. such that the spoke crossings are deflected parallel to the axle.  I have built many wheels this way and it is a reliable and effective method of stress-relief.

cheers

Re: Converting rim braked wheelset to disc
« Reply #5 on: July 13, 2020, 11:42:50 am »
A device to help with lateral deflection - second image shows it in use

https://www.centrimaster.de/en/product/prepress-device/

fd3

Re: Converting rim braked wheelset to disc
« Reply #6 on: July 13, 2020, 03:03:52 pm »
I've had two or three methods of stressing explained to me, all claiming that the other one is wrong!  I've generally used a combination of these, but then I'm light, ride fat tyres at low pressure and have undished wheels.
[/I could be wrong]

Re: Converting rim braked wheelset to disc
« Reply #7 on: July 13, 2020, 04:29:23 pm »
If you are stress relieving by squeezing the spokes, you might find a pair of gloves quite useful. It can ge a bit uncomfortable until you’re used to doing it.
Loving life with a beautiful Bianchi.

Re: Converting rim braked wheelset to disc
« Reply #8 on: July 13, 2020, 04:36:32 pm »
A device to help with lateral deflection - second image shows it in use

https://www.centrimaster.de/en/product/prepress-device/

interesting, but I note that it will only work if you have a really strong wheelbuilding jig.

The loads applied by leaning on the rim are usually thought to be not as high as those achieved via spoke squeezing, so the stress-relief may not be as effective in some cases.  Most wheelbuilders who use rim side loading do so by laying the wheel on the floor and then pushing down on the rim on opposite sides (balanced load) so that every part of the rim (both sides) gets pushed down at some point and every spoke sees an overload.   One good thing about this method is that if the wheel survives the side loads thus seen, it probably won't fold up in service either.

cheers

Re: Converting rim braked wheelset to disc
« Reply #9 on: July 13, 2020, 04:57:35 pm »
I have a large ring spanner that I  twist into the crossings - seems to work OK but no good for radial spokes..

Re: Converting rim braked wheelset to disc
« Reply #10 on: July 13, 2020, 06:01:16 pm »
A device to help with lateral deflection - second image shows it in use

https://www.centrimaster.de/en/product/prepress-device/

interesting, but I note that it will only work if you have a really strong wheelbuilding jig.

The loads applied by leaning on the rim are usually thought to be not as high as those achieved via spoke squeezing, so the stress-relief may not be as effective in some cases.  Most wheelbuilders who use rim side loading do so by laying the wheel on the floor and then pushing down on the rim on opposite sides (balanced load) so that every part of the rim (both sides) gets pushed down at some point and every spoke sees an overload.   One good thing about this method is that if the wheel survives the side loads thus seen, it probably won't fold up in service either.

cheers

I squeeze spokes and have not felt the need to spend e90 on a long lever, though I suspect my stand is strong enough. There is a video somewhere of that tool in use and they apply a lot of deflection to the rim whilst turning the wheel through a full revolution.