Cycling UK Forum

I successfully used Syklist's method to cold set my Bob Jackson mixte frame to take a modern 8 speed hub.
The mixte is 1953 vintage.
I was surprised at the amount of over spreading needed to get the frame to stick at the new setting of 130mm instead of reverting to 126mm.
Whilst a little scary, it felt under control. I did not want to use the more brutal levering with a piece of wood.

I did not want to use the more brutal levering with a piece of wood.

The advantage of the piece of wood method is that it moves only one side of the rear triangle at a time, ensuring that each side can be moved by the same amount. Spreading both forkends at the same time risks one moving more than the other, resulting in misalignment. It's best to use the string around the headtube, or similar method, to check - whichever setting method you use.

Whatever method is used, the alignment must be checked.
Surely some people will say "yeah, it's fine like that", but then we're speaking different languages I don't think anyone like to ride a bike that feels "not exactly right" instead of having one "just right"

I used a set of hub bearing pressing tool similar to this

The method was this [youtube]https://www.youtube.com/watch?v=QwxEPRk3LFg[/youtube]

Checked the result with Sheldon Brown method.

I wouldn't try the Sheldon Brown cold setting method though, that looks too risky.

Thanks folks you have given me a lot to think about, and read up on, I will try and post before & after photos when I decide which way to go. Thank again

Gattonero wrote:Whatever method is used, the alignment must be checked.

...first before you start spreading your forks.

Edit: it worked fine on our Bromptons without any checking alignment at all. We haven't noticed any ill effects. Maybe because the forks are so short.

resus1uk wrote:I successfully used Syklist's method to cold set my Bob Jackson mixte frame to take a modern 8 speed hub.
The mixte is 1953 vintage.
I was surprised at the amount of over spreading needed to get the frame to stick at the new setting of 130mm instead of reverting to 126mm.

I went to 138mm under tension on one Brompton and 140mm on the other to get a desired width of 122mm.

There is a difference between getting something thats "rideable" and something thats exactly right.
If you take a touring bike thats exactly right, and install a back wheel where the dishing is 4mm out, it rides OK. It will even go in a straight line no hands, but you have to have the saddle under one cheek. I suspect a bike with race geometry would be worse.
I don't know if its even possible to ride a Brompton no hands, but it is possible to check the alignment of your frame to a good standard of accuracy with a piece of string, and its possible to pull out the rear stays to a good standard of accuracy if you pull them out one at a time, as I posted before.
If you jack the dropouts apart, the less stiff stay will bend more than the stiffer stay. Generally that means the right stay which is dented to clear both tyre and chainwheel will bend more than the left stay, which is only dented to clear the tyre. You can use this to your advantage and build a less dished wheel, but you can't then use a dishing stick in a conventional manner, because the wheel will need to be asymmetric to fit the asymmetric frame.
Unless you intend to build one wheel for a particular frame, and that frame alone, its probably easier to keep everything symmetric.

syklist wrote:

resus1uk wrote:I successfully used Syklist's method to cold set my Bob Jackson mixte frame to take a modern 8 speed hub. The mixte is 1953 vintage.
I was surprised at the amount of over spreading needed to get the frame to stick at the new setting of 130mm instead of reverting to 126mm.

I went to 138mm under tension on one Brompton and 140mm on the other to get a desired width of 122mm.

That's what I meant about

Bicycler wrote:Watching a beloved frame being cold set is not for the faint hearted!

531colin wrote:There is a difference between getting something thats "rideable" and something thats exactly right.
<snipped by syklist>
Unless you intend to build one wheel for a particular frame, and that frame alone, its probably easier to keep everything symmetric.

I thought about building a jig that held the one end of the fork in a clamp and clamping the spreader to the same jig so that each side could be wound out independently. But I didn't do that in the end. We we dished the wheels identically according to my calculations (centred over the new 122 mm OLD) and they fitted in the rear forks with very similar clearances (tyre to right and left hand fork) as the original SRAM hub wheels. There was actually a bigger difference at the hub ends of the forks, on Mrs Syklist's Brompton the rear fork required some extra fettling to give clearance for the spokes coming out of the hub on the non-drive side. Looking at the forks before I started it seemed that Brompton had quite wide production tolerances for the rear forks in the period the bikes were made (2003-2007). The bikes folded up with the rear wheel in the same position as before relative to the main frame. Neither of us noticed any worsening in the road manners of either bike after the operation. I guess we got lucky. Or there is something unusual about Brompton rear forks that makes this method work.