Canti straddle wire - is it special?

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james01
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Canti straddle wire - is it special?

Postby james01 » 17 Jun 2019, 11:55am

Is there any reason why I can't use ordinary brake cable to replace a frayed straddle wire in an old MTB? The wires look and feel like the same gauge, but presumably the straddle wire suffers more powerful forces?

PH
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Re: Canti straddle wire - is it special?

Postby PH » 17 Jun 2019, 12:28pm

The ones I use are a good bit thicker and the fitting at the end chunkier. I can't remember where I bought them, but the cost was pennies. However, the Shimano link wires that replaced many yoke types, uses the brake wire so on that basis I'd assume it's fine.

Brucey
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Re: Canti straddle wire - is it special?

Postby Brucey » 17 Jun 2019, 12:48pm

there are at least three different thicknesses of cable used for straddles; ~1.5mm is most common but ~2.0 is/was used in some MTBs and a much thinner cable (about 1.2mm) was used in Mafac brakes.

The straddle only sees a force that is greater than the main cable if the included angle in the straddle is more than 120 degrees when the brake is applied, i.e. not often. IME the most common cause of straddle failure is fatigue via flexing near the pinch bolt, and thicker cables flex less easily so may fatigue more. A few brakes have pinch bolt designs that allow a small articulation; most don't. Some manufacturer's fixed length (half) straddles tend to fail by the centre 'button' cracking in half; unlike a frayed cable there is often no clear sign that failure is imminent.

FWIW when a Mafac straddle cable fails, it is usually necessary to fit a (carefully chosen and tested) gear cable these days. I usually make my own by silver-brazing a brass fitting onto a length of cable; this works Ok provided the nipple end is mounted in a freely articulating swivel.

cheers
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james01
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Joined: 6 Aug 2007, 4:48am

Re: Canti straddle wire - is it special?

Postby james01 » 17 Jun 2019, 1:16pm

Many thanks for the advice. The original cantis are obviously cheap (maker's name has long ago rubbed off) but work well. A standard MTB brake nipple sits nicely in the yoke, I'll go ahead using standard brake wire and keep a cautious eye on potential fraying points.

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gaz
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Re: Canti straddle wire - is it special?

Postby gaz » 17 Jun 2019, 7:16pm

PH wrote:The ones I use are a good bit thicker and the fitting at the end chunkier. I can't remember where I bought them, but the cost was pennies.

Possibly NOS Suntour straddle cables from SJS.

Over engineered but I like them.
Hand wash only. Do not iron.

mattsccm
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Re: Canti straddle wire - is it special?

Postby mattsccm » 17 Jun 2019, 8:17pm

I have been chopping down old cables for decades. Never given it a thought. Only replace them when the ends get too chewed up.

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Redvee
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Re: Canti straddle wire - is it special?

Postby Redvee » 18 Jun 2019, 1:30am

I've used old brake cables as straddle cables in the past, only problem I had was getting enough purchase on the cable when I needed to release the brake as it didn't have the longer barrel sticking out of the canti. I had to push the cable out and run the brake slightly loose.