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Front Derailleur mount offset

Can bikecad help me determine the distanse from the center of (frame-plan) the seattube to the braze-on/frontderailleur bolt mounting?

Or is there a simple trick to calculate this?  In my case I use a shimano ultegra with a 43.5mm chainline and I need to know how far from the center of the frame-plan I have to intall the front derailleur braze-on bolt hole.  A qualified guess is 25.0mm but it would be nice to know how to do this calculation incase the chainline changes.(diffrent crankset)


greetings from Slovenia




Front derailleur mount offset

As far as I'm aware, this is not a dimension that people are playing with a whole lot to suit a particular derailleur or a particular chainline. I think derailleur manufacturers still accept that their components need to fit most bikes and therefore ensure that their front derailleurs have a suffficient range of motion to cover the intended chainlines. The diagram below is taken from SRAM's 2010 technical manual which does not appear to have been replaced by anything more current.

Thank you , this gives me a

Thank you , this gives me a little peace in mind . One thing I have noted is when having short chainstays and big tires 35cx700 , the derallearur cable arm comes unpleasent close to the rotating tire when in outer chainring. But by moving the deraillearur bolt attachment more out from the center of the frame can give a few mm more clearince. This is why I feel it is worth expirementing a little with this mount point.

greetings Chris




This is a dimension I've been

This is a dimension I've been playing with a whole lot, particulary MTB disc rear on Road/Gravel frames. An MTB axle has solved spider/BB clearance and chainline problems. SRAM make a wide spaced clamp for their road doubles with MTB spindles, an Easton 129mm road axle can be replaced with a RaceFace 134mm MTB axle. GRX adds 2.5mm to road but looks to be less than MTB. I have 3D printed road and mountain derailleur adapters to adjust for the wider chainline. It would be nice to see this dimension in BikeCAD, the chainline adjustment available on some derailleurs can be quite limited. 

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