Crank preload bolt

[Guitars and Bikes]

I bought a 4700 10 speed tiagra 165mm compact crankset to fit onto my 105 caad8. I removed the 5700 170mm compact from the bike and the preload bolt that came with it is shorter than the one that came with the 4700. I think the 4700 preload is chunkier as well because it won't fully tighten up. The bottom bracket is a hollowtech ii unit. Why would the preload bolts for 4700 and 5700 be so different and is it safe to use the shorter bolt ?

 

[si_c]

If by preload bolt you mean the plastic bolt that goes in the centre of the cranks then you can use any which threads in. The crank is retained by the two pinch bolts and the locking tab, once the preload is set the plastic bolt acts only as a weather/dust cap.

 

[super_davo]

There is a difference in length in the HT2 preload bolt between generations. But they really aren't doing anything requiring strength hence they can make them from plastic.
If anything the thing you don't want to do is run the long version on a crank set designed for the short as you may lock it out on the threads before it has taken the play out of the system (but even then, may be OK depending on spacing).