Replacing front derailleur

[Dave the Smeghead]

Need some advice please

I need to replace the front derailleur on my Tern Joe D21 commuter.

I have just swapped out the crankset and increased the big ring from 48 to 52 (better cruising speeds). The bike is a 24 speed (8 rear sprokets, 3 front chainrings) and the cable layout is above the mech mount but has a cam that routes the cable around to pull from underneath although this is part of the derailleur.
Generally for the rides I do on the commuter I leave it on the large chainring and only use the rear gears so it is currently fine but I do want the full range available if I choose.

So in order to do this I need to change out the faulty front derailleur but with the range available I need some advice in which one will be most appropriate.

Fellow CC'ers please help and I welcome your advice

 

[fossyant]

Can you take a pic of the current mech.

 

[Citius]

I have just swapped out the crankset and increased the big ring from 48 to 52 (better cruising speeds).

48/12 at 90rpm gives you 28mph - is that not fast enough?

 

[Dave the Smeghead]

On or off the bike?

 

[Tim Hall]

I can't see from your post what is wrong with the existing front mech. You've gone to a larger front ring but then say the mech is faulty. If all you've done is increase the big ring I think all you'll have to do is move the mech up a bit.

 

[Dave the Smeghead]

48/12 at 90rpm gives you 28mph - is that not fast enough?

It probably would be if my legs could do that!

Seriously for the commute it is about acceleration in traffic and sustaining a reasonable speed when possible - something around 15 - 18 mph

 

[Citius]

It probably would be if my legs could do that!

Seriously for the commute it is about acceleration in traffic and sustaining a reasonable speed when possible - something around 15 - 18 mph

I'm just making that point (in fact, you just made it for me) that swapping a 48 for a 52 is unlikely to make you 'faster' in any way...I can cruise at 15-18mph on a 42 ring. The size of the ring ain't the issue...

 

[Dave the Smeghead]

I can't see from your post what is wrong with the existing front mech. You've gone to a larger front ring but then say the mech is faulty. If all you've done is increase the big ring I think all you'll have to do is move the mech up a bit.

Sorry if I didn't make that clear. The mech is faulty.

 

[Dave the Smeghead]

I'm just making that point that swapping a 48 for a 52 is unlikely to make you 'faster' in any way...I can cruise at 15-18mph on a 42 ring. The size of the ring ain't the issue...

As can I on my Giant - however this is on my folding commuter with 26 inch wheels. Not designed for speed.

 

[Citius]

The principle is the same, regardless of wheel size.

 

[fossyant]

The OP wants an answer about his mech, not a debate on cadence/chain ring size.

 

[fossyant]

You most likely need a top swing or conventional mech - ideally if we can see the existing mech and the cable mechanism. What current mech is on it ?

 

[Citius]

The OP wants an answer about his mech, not a debate on cadence/chain ring size.

The OP also mentioned chain rings (we didn't force him to)...

 

[Tim Hall]

Sorry if I didn't make that clear. The mech is faulty.

Was the fault there before you put the bigger ring on? If not you might be better adjusting the one you have. What fault is it anyway?

 

[Ajax Bay]

If the FD IS faulty (as opposed to needing to be shifted a few mm higher up the seat tube because you've now got 52-38-28) then 14 teeth is quite a step up middle to large and most FDs are not designed for it. Describe the fault you find with the current FD.

for the commute it is about acceleration in traffic and sustaining a reasonable speed when possible - something around 15 - 18 mph

I roughly agree with @Citius that you maybe have gone the wrong way here. The cassette is a 14-28 so 14:48 and 26" wheels doesn't give you quite the speed he suggests. But the better way to sort this is to put the 48 back on and get a 12-25 cassette. Since you rarely use the other rings that would give you the ratios you (feel you) need. 48t to 52t gets you 8% higher gear. 52t or 48t, a smallest sprocket of 12 (cf 14) gets you 14% higher gear, and a 13 (cf 14) gives you 7%. And the FD (or its replacement can continue to operate as designed. This would be cheaper and easier.

This from the Evans site (amended - you have a 3x8):
Front Derailleur:Microshift
Shifters:Microshift 3 × 8 spd
Chainrings: 48/38/28T