Cycling UK Forum

I have bikes with ST 4700s and ST 5700s. The cables on both last about 18 months before fraying if I leave them that long. I change them at yearly intervals now (I set a reminder in my phone calendar) because it's really not worth the hassle of teasing strands of cable out of the brifter nor the risk of wrecking the brifter for the sake of a £3-4 stainless cable.
The underlying problem is the too tight radii for the cable to navigate in the spooler/ratchet mechanism and in the contortions the cable does to route under the bar tape.

Cyclothesist wrote: ↑17 Aug 2024, 9:46am....The underlying problem is the too tight radii for the cable...

if the requirement were for infinite fatigue life with that cable, the sheaves (pulleys) would be about a foot in diameter; as it is, it is only a matter of time before they fail, regardless of the type of shifter. The exact fatigue life is probably weakly sensitive to the tension in the cable, which can be made lower in the shifter by using a 'helper' spring. A typical fatigue life for such a cable inside a shifter is ~150,000 shifts. Most trouble is sidestepped by precautionary replacement at ~120,000 shifts.

roubaixtuesday wrote: ↑15 Aug 2024, 7:52pm

jessand wrote: ↑15 Aug 2024, 6:28pm Thanks PeterH.

Is this problem unique to Tiagra 4700 or does it happen on all Shimano under tape shifters .e.g. 105 7000?

It's the same with all under tape brifters, the cable needs replacing fairly frequently. It's a quick job once you've done it a couple of times.

Can't comment as the only ones I have experience of maintaining are the Tiagra 4703 type. I have noticed that the cable goes through a tight bend inside the shifter, and this is where it breaks. I think this is the weak point more than the cable going under the tape. I would not surprised if it affects many if not all products of this type as at least Shimano ones probably have a common design pattern.