carbon frame chain rings.

[Lucyhan]

I am in the process of purchasing a women's carbon road bike, probably a Trek.
On my current bike, a carbon Boardman 2011 I have 42/34 chain rings. The new bikes have 50/34, does anyone know if I can replace this to a 42/34? The bike shops all say the best they can do is a 46/34.

[andrewjoseph]

The bike shops are correct I think. To go lower you probably need a new crank set, possibly a new front mech as well.

What's wrong with the boardman, why are you changing?

Personally, I hate trek.

[Keezx]

Changing a 46 for a 42 is certainly no problem, but you may have to buy the 42 yourself (and sell the 46)

[Brucey]

there are several things to consider here;

1) getting a new chainring that simply fits on the crankset; 42T shouldn't be impossible here.

2) getting a new chainring with the ramps & profiled teeth to match the 34T one; this could be difficult

3) getting the front mech to work; chances are you have a front mech that is on a bracket (rather than clamped round the seat tube) and if so it may not go low enough on the frame to be set correctly over a 42T chainring. To go from 50T to 42T would normally require that the front mech is lowered approximately 16mm; this is often more than the adjustment offered on a so called 'braze-on' ( glued or riveted on a CF frame is more like it but what is in a name, eh?) fitting. [If this doesn't scupper you, the front mech may touch the inside chainring when it is still well away from the big chainring; a recipe for losing the chain off the big ring on an upshift...]

So the LBS could be right, for that bike, fitted with that crankset, and changes required to do what you want may be somewhat extensive (read; 'expensive', if it can be done at all...). If you want a more informed opinion then the spec of the bike will be required.

Remember that with a new bike there will be some kind of warranty, and if they modify it such that the gear changing is compromised, and the chain falls off and chews the frame/crank up, who's fault is it? In fairness several manufacturers used to (effectively) warrant against such things, but won't now regardless....

BTW if your Boardman is worn out everywhere or simply doesn't fit you then changing it seems like a good idea, but if you are changing the bike to save some miniscule amount of weight or if you think that the Trek will be somehow 'much better' then you could be in for a disappointment; roadies are notoriously image-obsessed and some wouldn't be seen dead on some brands of bike despite the fact they won't go any faster on another and probably couldn't tell the difference blindfolded anyway. If you are being advised to change by such folk then take such advice with a healthy pinch of salt.

cheers

[Lucyhan]

Why do you dislike Trek, Is there something I should know before parting with hard earned cash?

[Paulatic]

Some people, rationally or irrationally, hate or maybe just dislike things. I have one or two most likely irrational dislikes myself.
I ride a Trek and I did have trouble with my original frame. What I will say is that my Trek dealer and Trek themselves were very keen to make me a happy customer. I am, and my Domane handles as the best road bike I've ever ridden.

[andrewjoseph]

Why do you dislike Trek, Is there something I should know before parting with hard earned cash?

My wife had a trek mtb, issues with chain falling inside and chewing up frame right from the start. Shop insisted it was user error. Research showed it was a known problem in America with trek (and others in same family), due to poor tolerances.

Emails to trek uk denied there was a problem until I sent them evidence. Then they sent me the kit to fix it.

[tim-b]

Hi

If the shop is offering a 46T then I would go with that, unless it's going to cause you a problem. 50/34 is a fairly standard compact road offering these days, and I imagine that the 46/34 is a cyclo-cross chainset

Presumably you will still have a similar low gear to your Boardman, which is the critical one (to me at least), and you'll have a slightly larger high range

As Brucey pointed out, if you do your own thing (42T) and the chain comes off and chews the chainstay up then you might struggle with warranty issues. If the shop does it then your contract is with them and your position will be stronger

Regards
tim-b

[Lucyhan]

Thanks for the replies. We have now found out that a few women's road bikes have a triple chain ring which maybe the answer.
Also Trek bikes, now I come to think of it my hybrid trek has an annoying click on each pedal turn. This comes and goes for no apparent reason. Lots of people have looked at it and no one knows what it is so it can't be fixed.

[andrewjoseph]

Check the range of the triple, might not be best. The first road bike my wife bought had something like 52 -48 - 36 with a cassette of 11 -26 (or something like), she found it very hard to get up some hills.