Cycling UK Forum

Specifically, does any one know what the specified 49mm reach on Shimano Tiagra dual pivot calipers means? Is it the maximum? Is it where the rim should end up when the frame is built? How much adjustment is available via the slot? So many questions not answered on the Shimano website......
On a historical note, why 49mm? Why not a nice round 50mm or further back why not 2"/50.8mm?

Two types of caliper - short reach for close tolerance frames and long reach for frames typically with mudguard clearance. Short reach is 49mm. Usually measured from the mounting bolt..

[Deleted for clarity]

If a single reach (drop) measurement on a caliper brake is given it normally means the maximum possible, measured centre to centre from the pivot bolt to the centre of the brake shoes, when the brake is set to clamp a rim of the intended width.

It has been like that for decades; often the number was built into the brake model designation, e.g. a Weinmann Model 750 brake would have a reach of 75mm. Road racing bikes often had (by more recent standards) quite generous clearances, until Campagnolo launched a so-called 'Piccolo' brake (~49mm drop) in the in the early 1970s. Since then for decades 'piccolo' = 'short reach' and 'standard reach' was ~58mm drop, but more recently some manufacturers have begun referring to short reach as 'standard' and anything longer as 'deep drop'. It is all a bit of a mess and it is (of course) subject to constant revision.


dual pivot calipers shown, but reach measurements apply to most shimano brake models launched ~1984-2008

So you would expect '49mm' to be meant to refer to the maximum reach of a caliper so advertised. However in relation to BR-4700 Tiagra, this figure (which is mentioned by the normally accurate SJS for example) is wrong. Shimano 'short reach' ('standard'...?) road brakes used to be 49mm (from the early 1980s more or less) but currently Tiagra (and upwards) they are all 51mm drop:

https://productinfo.shimano.com/#/spec/ROAD/Brake%20(Caliper%20Brake)

cheers

As ever, better than Google, Brucey. Thanks.