Converting Shimano road bike with STi hydro brake levers to flat bar hydros?

[deliquium]

Is this possible? Unable to find any conclusive evidence elsewhere - which could just be my poor search skills

Specifically, on a new unused bike, swapping out a pair of new Tiagra ST-4720 levers, replacing drop bars with new flat bars and either Shimano BL-MT401 or BL-MT501 hydraulic brake levers? Whilst retaining the flat mount Tiagra BR-4770 calipers?

Are there compatibility issues with hydraulic brakes - as there are on cable disc road and MTB versions?

[PH]

Yes they're interchangeable. Shimano do two hoses, with slightly different internal bore, but the external diameter is the same so they use the same olive and fit the same levers and calipers, you just have to be sure you get the right barb if you're shortening them. There is a theory that the larger bore, thinner wall, hose distorts more giving a less firm feel, having run the same brakes with both, it isn't something I'd notice.
But why would you? Price of drop bar hydraulics, wouldn't you be better off selling them complete and getting flat bar stuff, current Deore is flat mount. Or better still, isn't there a bike with what you want already fitted? Changing stuff on a new bike always looks poor value to me.

[slowster]

Presumably the bike is fitted with Tiagra 10 speed rear and front derailleurs, since the levers use a different rear derailleur cable pull to Shimano's other 10 speed road groupsets. You would therefore need new shifters to go with the flat bar brake levers, specifically the Tiagra 10 speed flat bar shifters:

https://www.sjscycles.co.uk/gear-shifte ... rs-double/

https://www.sjscycles.co.uk/gear-shifte ... rs-triple/

[deliquium]

Presumably the bike is fitted with Tiagra 10 speed rear and front derailleurs, since the levers use a different rear derailleur cable pull to Shimano's other 10 speed road groupsets. You would therefore need new shifters to go with the flat bar brake levers, specifically the Tiagra 10 speed flat bar shifters

As far as I am aware, Tiagra 10 speed has the same cable pull as other 10 speed Shimano road levers. I have that covered with some recently acquired hardly used Dura Ace SL-BS79 bar end shifters which will be mounted on "thumbie" brackets, which I have in the "spares" shed (because I'm deffo not a fan of flat bar trigger shifters ) And if I decide to want a larger rear cassette than the Tiagra max 34 sprocket, I'll replace the rear derailleur and cassette with Deore and use a Shftmate - as for sure 10 speed Shimano road and MTB levers definitely do have different cable pulls.

( I admit, it's not easy nor cheap, living with myself at times - being such an awkward, contrary and determined cuss )

[slowster]

As far as I am aware, Tiagra 10 speed has the same cable pull as other 10 speed Shimano road levers.

It does not. See the Shimano compatibility chart here - https://productinfo.shimano.com/#/com?c ... acid=C-453, according to which both front and rear shifters are only compatible with the Tiagra 4700 series derailleurs*.

* The 4700 rear derailleur has the same actuation ratio as Shimano's 11 speed road rear derailleurs, but the 4700 rear shifter pulls a different amount of cable per click compared with the 11 speed shifters because the sprocket pitches of 10 speed and 11 speed cassettes are different.

[deliquium]

Yes they're interchangeable. Shimano do two hoses, with slightly different internal bore, but the external diameter is the same so they use the same olive and fit the same levers and calipers, you just have to be sure you get the right barb if you're shortening them. There is a theory that the larger bore, thinner wall, hose distorts more giving a less firm feel, having run the same brakes with both, it isn't something I'd notice.
But why would you? Price of drop bar hydraulics, wouldn't you be better off selling them complete and getting flat bar stuff, current Deore is flat mount. Or better still, isn't there a bike with what you want already fitted? Changing stuff on a new bike always looks poor value to me.

Thanks PH for the info and experience. I wasn't aware of the flat mount Deore calipers. Sadly I've not found a suitable bike off the shelf. In an ideal world, I'd only want to purchase a frameset, together with the Fazua gubbins attached. Unfortunately that's not possible. It's something I've always done and enjoyed doing since my first Longstaff frameset in 1992. With regard to the current possible project, value can be ignored and indulgence pandered to

[NickJP]

I've done this conversion for one of my wife's bikes that could only be purchased with drop bars, which she doesn't like. It came with full 11-speed Ultegra components - I kept the Ultegra calipers and front derailleur, and on the flat bars I fitted Deore XT hydro levers, a pair of SLX 11-speed shifters that I already had, an XTR 11-speed RD that I already had, and I swapped out the 11-32 cassette that had been provided on the bike with an 11-40. The XT hydro levers seem to be a perfect match for the Ultegra calipers, and (with only two chainrings) the SLX shifters work fine with the Ultegra FD.

[Redvee]

With regards MTB callipers and road levers, I'm running R7020 levers and SLX callipers so there won't be no issue with going the other way with road callipers and MTB levers. Assuming pull ratios are the same you should be able to pick up a set of suitable levers on ebay etc.

[deliquium]

Thanks ^ NickJP and Redvee - very encouraging

[Jupestar]

As highlighted above the Tiagra 4700 10s RD is not compatible with Shimano other 10s shifters due to different pull ratios. As you have the 4700 Hydraulic Shifters you almost certainly have the 4700 RD.

You may be able to use your thumbies in Friction mode (if they have it). Or I understand some Shimano 11s shifters may have the correct pull ratio. If true (I've never tested this) Obviously you would have a ghost shift.

[deliquium]

Apologies Slowster for assuming ignorance Only just saw your compatibility chart post

Thanks Jupestar for confirming my

Edit: My latest thoughts are to sell the new unused Tiagra 4700 gear/brake levers, the 4700 rear mech and the 4700 front mech anyway