Need help with my big ring...

[Bigsharn]

Let's get this out of the way - "THAT'S WHAT SHE SAID!"

Anyway back on topic, I've bent the big ring on my Shimano LX chainset, I know it'll be replacable, but I have no idea what the BCD is on my bike... Anyone got an idea what size it might be? it's on an early 1990s Dawes Galaxy.

If possible I'm finding 48t relatively slow anyway, so would it be possible to replace this with something larger (52/53t) without a standard* front mech throwing a hissy fit?


*My front mech was also FUBAR'd in the incident, so I'll be getting a new one. I'm guessing that most front derailleurs are similar... on this topic, can anyone recommend an inexpensive, new front derailleur?


I mean... worst case scenario I'll just go and buy a completely different chainset, mech and BB


Thanks in advance
Sharn

 

[4F]

You got a ruler ?

http://www.sheldonbrown.com/harris/chainrings.html

 

[HLaB]

With it being a 48 I'm guessing its a compact and will be 110mm BCD, its a guess though I wouldn't recommend a large jump from a 48t to a 53t, maybe halfway in between, a 50t and if you are still spinning out change your cassette when it wears out. Oh and a larger chainring won't make you faster if you can't spin it

 

[rb58]

With it being a 48 I'm guessing its a compact and will be 110mm BCD, its a guess though I wouldn't recommend a large jump from a 48t to a 53t, maybe halfway in between, a 50t and if you are still spinning out change your cassette when it wears out. Oh and a larger chainring won't make you faster if you can't spin it

More likely a triple if it's Deore LX....

 

[Bigsharn]

Looking at the Sheldon Brown link (and measuring it with das ruler) it looks most likely a 110mm. I do need a new front derailleur anyway, I should be able to push 53-13 (Highest gear) no problem, as I have 52-11 on my old racer/spare and have no problem on that (in theory I should be able to manage 60-13 without issue)

 

[HLaB]

More likely a triple if it's Deore LX....

I did say it was only a guess but if its a triple I'd go for the bigger ring too

 

[02GF74]

depending on how bent it is, it may be possible to straighten it.

 

[P.H]

If you go bigger than 48, you may need a road mech rather than a MTB one. That's going to cause trouble for your shifters and you may also find you'll also need to change the size of the middle ring, I'm a bit out of touch with modern spec, so you'll need to look it up. Road mechs used to be designed for a 10T difference and MTB 12T, you could get away with a bit of difference, but shifting wouldn't be as smooth.

as I have 52-11 on my old racer/spare and have no problem on that

OK Cav!! At a modest cadence of 90 that's 34mph Even at a lesuirly 80 it's 30mph... I'm surprised you can take time off from the Tour to post here

 

[PpPete]

If you are getting a new front mech, I'd be tempted to get a whole new crankset as individual big rings work out expensive. A 50-39-30 and a road mech will work well together. You can even replace the 30 ring with a smaller one, if you need the lower gears. My Galaxy (late 80s) has a 50-38-26, with a standard 105 front mech which is capable of a lot more than it's official spec would suggest.
BCD on the regular Shimano "road" triples is 130/74

 

[Bigsharn]

If you go bigger than 48, you may need a road mech rather than a MTB one. That's going to cause trouble for your shifters and you may also find you'll also need to change the size of the middle ring, I'm a bit out of touch with modern spec, so you'll need to look it up. Road mechs used to be designed for a 10T difference and MTB 12T, you could get away with a bit of difference, but shifting wouldn't be as smooth.

I believe I'll end up getting a road mech regardless, possibly even changing out for a double if I find a cheap one on Evilbay. As far as I was aware, the mech I had WAS a road mech (or a touring mech, I assume they're road based rather than MTB based).

OK Cav!! At a modest cadence of 90 that's 34mph Even at a lesuirly 80 it's 30mph... I'm surprised you can take time off from the Tour to post here

Ah, but the 52-11 is on the roadbike, which I use for out of town. I'm happy on 52/53-13 for around town, it'd just be nice to keep up with traffic a bit easier.

I should probably point out, rather than go for cadence (I average around 60 rpm), I shift into a higher gear as quick as possible... I know it's not proper cycling technique, but it keeps me at 20+, which is about right for in-city riding... the extra teeth would just be nice on the way out of town to do the shopping.

If you are getting a new front mech, I'd be tempted to get a whole new crankset as individual big rings work out expensive. A 50-39-30 and a road mech will work well together. You can even replace the 30 ring with a smaller one, if you need the lower gears. My Galaxy (late 80s) has a 50-38-26, with a standard 105 front mech which is capable of a lot more than it's official spec would suggest.
BCD on the regular Shimano "road" triples is 130/74

I'll probably be sourcing the part second hand rather than getting a new one so cost isn't that much of an issue, mechs are practically two-a-penny on Ebay at the moment and chainrings aren't massively expensive either. But of course, I may get a new crankset or even go to a double... I never use my granny ring and I only go to the middle ring up one hill in York

 

[P.H]

(or a touring mech, I assume they're road based rather than MTB based).

What levers? It's the cable pull between road and MTB that determines the mech required. They have a different amount of leverage. Obviously this only applies to indexed levers, thinking about it, your 1990s Galaxy may have friction shifters? Bar end or downtube, in which case you can use anything.

I should probably point out, rather than go for cadence (I average around 60 rpm), I shift into a higher gear as quick as possible

Whatever suites you, but that can't be good for your knees long term.

 

[Bigsharn]

It probably isn't good for me, but then again nothing we enjoy is

And it's a friction lever mounted on the downtube... Oh how I love the versatility of tourers