Correct Front Derailleur !

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hondated
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Correct Front Derailleur !

Post by hondated »

Just been out in the garage trying to trim my triple front mech but struggling to get it right.
I think I know why but thought I would ask the question and seek advice on how to cure the problem.
I have built up an Audux frame with a 9 speed Deore triple chainset with external Bottom Bracket and the rear mech is a Deore long caged.

Now the part that I think is the problem is the triple 105 road mech. I have read that Shimano road and mountain bike parts are not compatible but although obviously not perfect it is functioning.


Trying to solve this problem I even tried fitting a Deore MBK front mech but it still wouldn't trim correctly.

Could my problem be chain line or is there another front mech I should try. Welcome all advice.
gxaustin
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Re: Correct Front Derailleur !

Post by gxaustin »

Is it the small ring that is the problem or the outer big ring? Have you measured the chain line? Do you have spacers on the BB?
Brucey
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Re: Correct Front Derailleur !

Post by Brucey »

what shifters are you using?

cheers
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SimonCelsa
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Re: Correct Front Derailleur !

Post by SimonCelsa »

You don't really want to fit a MTB triple crank set on an Audax frame (assuming it is 130mm OLN??). You would be better off with a road triple say SORA or 105 for example. The spacers on the MTB triple will probably put your chainline askew.
SJS had some good deals on Deore triples recently......I bought one & tried a similar build configuration to what you are doing - no Bueno, runs a lot better with a road triple!!
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hondated
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Re: Correct Front Derailleur !

Post by hondated »

gxaustin wrote:Is it the small ring that is the problem or the outer big ring? Have you measured the chain line? Do you have spacers on the BB?

Its the small ring which will of cause then affect the other two rings. I have measured it in as much as I have lined up the chain on the middle rear sprocket and the middle chain ring. I have used 3 spacers two on the drive side and 1 on the other side . Thanks for responding.
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hondated
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Re: Correct Front Derailleur !

Post by hondated »

Brucey wrote:what shifters are you using?

cheers

I am using some Deore quick fire levers on Butterfly Bars. Thank you.
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hondated
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Re: Correct Front Derailleur !

Post by hondated »

SimonCelsa wrote:You don't really want to fit a MTB triple crank set on an Audax frame (assuming it is 130mm OLN??). You would be better off with a road triple say SORA or 105 for example. The spacers on the MTB triple will probably put your chainline askew.
SJS had some good deals on Deore triples recently......I bought one & tried a similar build configuration to what you are doing - no Bueno, runs a lot better with a road triple!!

Thanks I think given your advice I will delve into my box of abandon parts to see if I can garner a triple road set up and if I cant I will check SJS out as you advise.
Brucey
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Re: Correct Front Derailleur !

Post by Brucey »

hondated wrote:
Brucey wrote:what shifters are you using?

cheers

I am using some Deore quick fire levers on Butterfly Bars. Thank you.


OK the deore shifters won't work with the 105 FD.

The Deore FD, shifters and crankset should work together, provided it is a matched set (eg all 9s, no 10s parts). You don't say what the problem is exactly, so what do you mean when you say that it 'won't trim'? [The deore shifters don't have trim clicks.]

Simon's suggestion about chainlines and 130mm OLN hubs etc is quite justified. The normal arrangement on an MTB is that the middle chainring runs at ~50mm CL (ChainLine) (i.e. the middle chainring is 50mm from the centreline of the bike). Chainrings are spaced at about 8mm from one another, BTW. A 9s cassette in a 135mm hub is centred at ~45mm CL so it is already centred further to the left than an MTB chainset. The same cassette in a 130mm OLN frame is a further 2.5mm leftwards of that, at about 42.5mm CL. The largest sprocket is ~17.5mm to the left of the middle one, i.e. at about 25mm CL. [On a 135mmOLN frame the biggest sprocket is at ~27.5mm CL]

This means that a road triple chainset (which is about 45mm CL on the middle ring, and happens to be almost perfectly centred over a 9s cassette in a 135mm OLN frame) has the small chainring at about 37mm CL, and an MTB triple has the inside chainring at ~42mm CL. This means when you are running in bottom gear the offset of the small chainring and the largest sprocket (i.e. when in bottom gear) is


Road triple chainset/135mm OLN frame = 9.5mm offset (NB the chainset is perfectly centred over the cassette with this combination only)
Road triple chainset/130mm OLN frame = 12mm offset
MTB triple chainset/135mm OLN frame = 14.5mm offset
MTB triple chainset/130mm OLN frame = 17mm offset

The offset angle is also made worse by short chainstays vs long chainstays. This is worth about 10% on the offset value, comparing short (racing, audax) chainstays vs the longer stays on a touring bike or an MTB. More offset means more problems when setting the FD up, by and large.

Anyway you have the worst possible offset in bottom gear with your setup (the big ring is more or less centred over sprocket #9, not between 5 and 6 like it should be), although it might be worse than that given that you have more BB spacers on the right than the left. Normally the FD setting on the small chainring is dictated by the limit screw in the mech but in your setup it is anyone's guess really; it certainly won't work with a 105 FD attached to those shifters and on that chainset (what made you think this might be OK?) and even with matched parts up front the short chainstays and small OLN value could mean that you are straying into forbidden territory.

With a bike like that I would have specified 135mm OLN from the start (the only reason not to is that roadies like 130mm OLN wheels, but if you are not buying roadie wheels then you don't need to worry about this) or reset the frame to 135mm (or compromise 132.5mm OLN) and I would use a triple chainset with a 'road' chainline. I'd use flat bar shifters/mechs meant for a 'road' chainline too, (or thumbshifters/similar which have non-indeed front shifting), not MTB parts .

One reason the triple chainsets offered by Spa cycles are so popular with tourists/audaxers is that they have a 'road' chainline (when fitted onto an appropriate BB) and yet accept MTB sized chainrings, so you are not stuck with 'road gearing' (high) or a rubbish chainline. It is very difficult to achieve this result using combinations of other parts.

Note that if you use a 'road double' chainset on a 135mm OLN frame, you do have a pretty rubbish chainline in top gear. In my book this is OK, because most tourists/audaxers only use this gear when going downhill anyway. Similarly if you can set a triple up with a chainline of ~43mm (which is about the practical limit with any parts) this is OK too, for similar reasons. Both give you a better chainline in the lower gears, which you will perhaps use more often, for longer, and under higher load than the other gears.

Note that all the bottom gear offsets are a bit worse with a 10s cassette (on a 9s freehub, about 1mm further to the left) and quite a bit worse with an 11s cassette (about 2mm leftwards vs a 9s cassette), even at the same OLN value.

cheers
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hondated
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Re: Correct Front Derailleur !

Post by hondated »

Brucey wrote:OK the deore shifters won't work with the 105 FD. <SNIP>

Well Brucey you prove yet again how little I know and that said thanks so much for taking the time to explain it to me so fully. I am definitely a Fitter rather than a mechanic in that if its replacing the same for the same its not a problem but any deeper than that perhaps I should leave it alone. All the responses I have had have been helpful and I am grateful for them all but I must admit when Simon mentioned Audux OLN130mm ( whats OLN ) it made me remember that a Touring frame is 135mm so that could be the problem.

To give you a better idea of why I am where I am I will explain. I bought an Audux Revolution frame from Edinburgh Cycles and I have built it up or perhaps cobbled up may be more appropriate and got it running on 9 speed triple with drop bars. Fed up with the drop bars I recently fitted the Butterfly bars with the Deore quick Fire levers and the 105 front mech but it was irritating me with the chain rubbing on it.

So given all the information I have received having Goggled the bike I am wondering whether I should fit a 50/34 Chain Set on it but that would also mean replacing the levers so do you or any of our colleagues know whether you can buy double levers that fit on straight bars. Alternatively trying to save money again would it be possible to use the triple levers I am currently using.

Yet another question does anyone know what BB length I will need if I do fit a double chain set.

As I mentioned in my previous post I have delved into my box of parts and this morning tried a couple of BB's I have one even being a Campag one
and a Suntour MBK CS but of cause all to no avail.

Just as well I have a few other bikes I can use that are fitted with compatible parts whilst with all of the help on here I try to get this bike running properly. Thanks again Brucey and everyone its like having a LBS in my living room.
Brucey
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Re: Correct Front Derailleur !

Post by Brucey »

50/34 road chainset is a relatively large, and (by comparison with an MTB chainset) flexy one. You will only find this specced on manufacturer's bikes in combination with either

a) non indexed front shifting (that can be trimmed anyhow you like) or
b) with indexed front shifting, using a mech that is suitable for a road chainline/road chainset and shifters that are compatible with the mech and that have trim clicks.

If you are running 9s at the back (with 9s chain) I would recommend that you use a 9s FD, or perhaps an 8s one. A 10s FD will just cause problems, for most setups/riders.

One of my (many ) criticisms of modern bike design is that whilst a typical 50/34 chainset (in combination with a suitable cassette) has enough low gears for most (unladen) riders (in 'unchallenging' terrain anyway) and high enough gears for fast descents, it leaves most riders running cross-chained most of the rest of the time. I think that 50-34 might be a poor choice from that standpoint, and you might be better off with (say) a 46T big ring.

I would strongly suggest that you buy a spa triple (or a spa double if you think a ~34T is small enough) or similar with perhaps a big ring in the 40-46T range and a thumbshifter to work the FD, eg https://www.sjscycles.co.uk/gear-shifters/sunrace-m90-friction-thumbshifter-left-hand/ If you choose carefully you may be able to use the 105 FD you have (what model is it?).

BTW the thumbshifter above has a clicky retrofriction type arrangement (like Sun Tour powershifters of old) and fits 22.2mm (7/8" dia) handlebars. It isn't a bad idea to buy two in fact, in that it will work as a RH shifter if mounted upside down, and will shift anything from 5s to 11s, with any RD. This means you can tinker to your heart's content with bike setup and you won't have to worry about whether your shifters are index-compatible with your mechs or not. [Note that simply by bolting these shifters to a suitably strong accessory bracket, the same shifters can be used with a dropped handlebar if you want]. At the very least this will let you get a gear setup (with ratios, chainline, etc that works for you) and then you can buy 'posher' shifters etc to suit once you are happy with it. Many folk don't bother though; they find that shifting that way isn't so bad after all. STIs of any kind are fantastically expensive and inflexible devices by comparison; often they are the single most expensive part on a bike, costing almost as much as a cheap frameset....

cheers
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hondated
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Re: Correct Front Derailleur !

Post by hondated »

UPDATE.
Brucey Delved back into my parts box and found a 110mm BB so fitted it and then fitted a SR Suntour triple CS with the Deore MBK Front Mech operated by Deore LX levers. i have a Deore long cage rear mech with a 34t Sprocket.
I think I learnt another lesson in that the Deore needed to be fitted far higher on seat post than the 2 -3mm above the chain ring I normally use.

Seems ok at the moment any thoughts !.
Brucey
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Re: Correct Front Derailleur !

Post by Brucey »

if it works it works but without model numbers it is difficult to advise you; 'deore' covers a multitude of sins....

FD often needs to be a 'the wrong height' if it is meant for a different triple crankset. Chain will be at risk of unshipping rightwards if it is too high, of course.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
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