BH59 & BH90 Compatibility Q

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MichaelB
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BH59 & BH90 Compatibility Q

Postby MichaelB » Fri Nov 23, 2018 7:55 am

OK, know that there are differences in the hoses, the BH90 is the smaller ID and has the silver insert, whilst the BH59 has the larger ID and brass insert (with the small chamfer).

My question relates to a specific application and brake swap.

Bike is currently fitted with RS785 (post mount) & RS505 (flat mount) calipers at F & R respectively. They use the BH59 hose.

Will be fitting the new MT520 calipers which is meant to use the BH90 hose.

Aside from hose ID, it SHOULD be a straight fit ? The slight differences in the insert shouldn’t be an issue as the conical seating of the insert and caliber body will be the same. Right ?

Calling out to Duck!

Cheers

Michael

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Duck!
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Re: BH59 & BH90 Compatibility Q

Postby Duck! » Fri Nov 23, 2018 3:09 pm

Hoses are interchangeable as long as long as the calipers don't use banjo connections, which none of yours do. OD, olives and compression nuts are the same for both hoses, you just needs the specific barb inserts to suit the ID.

Shimano actually spec the BH90 hose with Dura-Ace (and also the original, now discontinued R785) brakes, while the other road models use the BH59 from factory. Shimano's reasoning is that those two are targetted as high-performance models, so the stiffer hose gives sharper preformance, while the other models are targetted at wider use, so the softer hose is used to improve the modulation, as it will deform slightly more under hard braking pressure. The M520 is intended as a fairly heavy-duty MTB brake, hence the recommendation to use the stiffer hose, plus the different cylinder volume ratio of the four-pot caliper will give more modulation anyway.
I had a thought, but it got run over as it crossed my mind.

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MichaelB
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Joined: Tue Feb 20, 2007 9:29 am
Location: Adelaide, South Australia

Re: BH59 & BH90 Compatibility Q

Postby MichaelB » Sat Nov 24, 2018 6:17 am

Ta :)

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