front mech hits largest chainring

ibbz":dk4pg0gq said:

The mech is on the highest position

Bought XTR UN90 68x107 Bb and looking to get a top pull front XT M739 mech to clamp on instead
Can't be arsed with all this e type malaky and headache

Click to expand...

E-type mechs work perfectly, but of course you do also need an E-type bottom bracket to go with an E-type mech - if you fit a standard bb, the 2mm thickness of the mounting plate will effectively make the spindle even longer on that side and this could be contributing to the problem (despite what fmj erroneously suggests above).

I have a FD-M739E on my Orange E4, with a UN-72E bb and it has always worked perfectly. It does have a 42t big ring to work with though.

Ring size it not the problem, it's designed for 42/44T top

Also 47.5/50 chain line

Same as the 738/739 normal mechs.

ibbz":14as123y said:

if you fit a standard bb, the 2mm thickness of the mounting plate will effectively make the spindle even longer on that side and this could be contributing to the problem (despite what fmj erroneously suggests above).

Click to expand...

Sorry, but your math doesn't work. Because of the arcs of the parallelogram levers in a derailleur the cage moves out more initially than up, reversing (up more than out) once it's past the 45 deg. point of the radius. The closer you move the chainring towards the centreline of the frame, the less upward travel in the cage you have, and the more likely it is to contact a larger ring. I'm at work now, and I don't think my boss would be too happy with me spending a couple or 3 hours mocking up a 3D model of a front derailleur in MC-X6, so I printed up a diagram off the net and hacked it up with scissors in 5 minutes to try and show you why.

Question for you guys
I've bought the M900 UN90 68x107 bottom bracket.
For the raceface turbine.
Would I be able to attach XT M739 front E-type mech to it? I think my previous bottom bracket was too long which made my mech unable to reach out and up and over it

I understand the raceface need 107mm BB.
Would attaching an e type bracket to the BB be a problem?

FMJ":uktp4s42 said:

ibbz":uktp4s42 said:

if you fit a standard bb, the 2mm thickness of the mounting plate will effectively make the spindle even longer on that side and this could be contributing to the problem (despite what fmj erroneously suggests above).

Click to expand...

Sorry, but your math doesn't work. Because of the arcs of the parallelogram levers in a derailleur the cage moves out more initially than up, reversing (up more than out) once it's past the 45 deg. point of the radius. The closer you move the chainring towards the centreline of the frame, the less upward travel in the cage you have, and the more likely it is to contact a larger ring. I'm at work now, and I don't think my boss would be too happy with me spending a couple or 3 hours mocking up a 3D model of a front derailleur in MC-X6, so I printed up a diagram off the net and hacked it up with scissors in 5 minutes to try and show you why.

Click to expand...

Interesting, very much so and clears a lot up regards the mechanics
Though makes everything more confusing on a practical level
Does this make e type mechs a pain in the backside to install? Is a dedicated Bb required? And dedicated cranks and rings ?
So basically id be better off with a clamped front mech to be on the safe side ?

ibbz":fcac1046 said:

Interesting, very much so and clears a lot up regards the mechanics
Though makes everything more confusing on a practical level
Does this make e type mechs a pain in the backside to install? Is a dedicated Bb required? And dedicated cranks and rings ?
So basically id be better off with a clamped front mech to be on the safe side ?

Click to expand...

Ok, I run an E-type front mech XT739 on my 1996 Orange C16R, It has an e-type specific BB fitted and i have run with both STX-RC Cranksets, and XT739 Cranksets both of differing size chainrings. Only adjustment was to rotate the plate to increase clearance of the mech over chainring. Setting it up is a doddle as you can only fit it one way and its been running perfect. you willneed to be careful if fitting a conventional band on mech as it may foul on the top mount bracket where the E-Type bolts onto, some people remove them but unless done properly can look messy, you may find you can get a high mount clamp to sit over the mounting point. But personally and only my opinion i would get an E-type BB and use the set up the bike was designed for. Its up to you at the end of the day

http://www.behindthebikeshed.co.uk/1401 ... _type.aspx

Or put a wanted out add if you dont want to buy new?

Just a few options for you

Jussa

The un90 is not designed for that style mech, they had not come out.

If you tried to use it you would shift the crank 2.5mm (I think that how thick the e-plates are) and the crank on the left the same distance into the frame. That is if you can thread the none drive side into the shell enough.

Thanks again my friends
I think Ill go for a conventional clamp on mech as I've bought the BB now.
Too much headache to try and source a decent e type Bb.
I doubt very much there's a Phil Royce or UN90/91 of that type, so clamp mech it is