Rear wheel hub frame spacing

Johnymak

Active Member
Location
Ballymoney
Looking to extend (cold set )
S steal frames rear drop spacing for bigger wheel hub any body know of a tool that does this or anybody no how to make an improvised one
 

rogerzilla

Legendary Member
Fit old BB cups to the frame. Clamp in a vice by the BB. Pull both sides evenly and cautiously, checking width and alignment (string wrapped around the head tube and both dropouts should be an equal distance from the seat tube on both sides). You can feel when the frame is yielding and not just flexing. If going up more than 5mm, you should probably realign the dropouts afterwards but this is much harder and riskier.
 

Oldfentiger

Veteran
Location
Pendle, Lancs
He does indeed https://www.sheldonbrown.com/frame-spacing.html

Another method is to use threaded bar. Just search for something like "threaded bar cold set frame" and you'll get a zillion hits. I did research this once, but never got around to actually doing it. I still have to wrestle the back wheel into the frame of the bike in question.
I used the threaded bar method to cold set a frame from 115mm to 120mm.
Just for reference - I had to screw the dropouts out to 160mm* in order to achieve the desired 120mm dimension when finished.

* This is why it's important to clamp over the brake bridge and chainstay bridge before winding the dropouts outwards.
 
OP
Johnymak

Johnymak

Active Member
Location
Ballymoney
a friend told me to set it 1mm at a time and let it rest a day then keep adding to the desired measurement is there a specific time frame per measurement
 

Oldfentiger

Veteran
Location
Pendle, Lancs
I believe that Young’s Modulus of Elasticity is in play here.
You have to go beyond the point where the steel’s memory is defeated, then deformation becomes permanent.
Summat like that anyway.

The time thing is irrelevant. Go beyond Young’s Modulus and deformation is instantaneous.
 

andrew_s

Guru
Location
Gloucester
Some frames have a dent in the RH chainstay, to give chainring clearance. If there is one, the RH chain stay will be weaker than the LH chainstay, so the threaded rod method will very likely bend the stays by different amounts, leaving an out of track frame.
If you do have a dent, I'd suggest the Sheldon method.

Youngs modulus is stiffness - how hard you've got to push to deflect the frame by a certain amount.
To cold set a frame, you've got to go past the elastic limit, after which it won't spring back to where it was before.
 

SkipdiverJohn

Veteran
Location
London
Very important. When doing this make sure you turn each nut the same amount of times as the other. Otherwise you may over spread it on one side.;)
Unless you can secure the threaded rod in a fixed position relative to the whole frame (such as clamping it through a piece of timber jammed between the front of the chainstays), it isn't going to matter a monkey's which one of the nuts you turn as the deformation will occur in whichever stays have the least strength!. It would be sensible to run a piece of string all the way round the head tube and back so the left/right spread can be carefully monitored as you open up the dropouts. If you get the spread on one stay not both then it will be necessary to stiffen the weaker stay by clamping a steel bar or piece of wood to it in order to force the stronger stay to deform. The name of the game when "persuading" anything to change shape or size is do it slow and steady, and keep measuring progress. Clumsy and non-practical types should leave it well alone!
 

rogerzilla

Legendary Member
It doesn't take much force for a traditional road frame and you can generally pull them by hand. MTB frames need some sort of leverage as the rear triangles are stiffer and smaller.
 
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