Chainring Size

[Finchy89]

Hello all,

I currently own a GT aggressor XC3 which I use casually on weekends just to stay active.

I mostly cycle on roads/cycle paths (generally good to ok terrain) and it's a great bike that has served me well over the years. Last year I put much thinner tyres on which made a monumental difference to my performance but now I'm finding that I could use some more grunt in the gears. Currently have (I think) a 42 top ring at the front and I'm running out of gear as soon as I hit 23/24 mph on any sort of downhill.

My question is: Would I have to replace both sets of chainrings for larger sizes to improve this, or could I just replace the front chainring first (obviously with the option of doing the rear at a later date if necessary)?

Sub Question 1: Would I have to replace the whole set of chainrings or can I replace individuals?

Sub Question 2: Would I automatically have to buy new derailleurs if I change chainring size or are they adjustable?

Many thanks in advance, and apologies to the seasoned amongst you who have probably known this information since the age of 9!

 

[sight-pin]

Hi, You can change the cassette to maybe a 12/32 cassette instead of the 14/34, that would give you more speed downhill and on the flat, Also a change from Knobby tires to a smoother rolling tire, but that wouldn't be safe if you intend to ride on tracks etc (what the bikes meant for).
I'm not really up on the tech but plenty of other members here will give better advice.

Edit: Better still, looks like you can obtain an 11/34 which would still give you your slowest speed. https://www.tredz.co.uk/.ETC-7-Spee...le_shopping&gclid=CMnngMefgdUCFVIaGwodHR4JtA#
You'll also have to check to make sure this is compatible etc as i'm not sure.

 

[mjr]

You can replace just front or just rear. Rear's usually easier. New chain every change, pretty much, as it'll change the chain length you need.

Sub 1. It depends. If your chainring is bolted on, then you can probably swap it with another of the same BCD and number of bolts. Not all are removable though.

2. It depends. Derailleurs are adjustable but have maximum capacities, which is how big the differences in numbers of teeth can be. If you can find the spec sheet, it'll tell you. If you say which model derailleur you have, someone cleverer than me may know it, or even have made a similar change before.

 

[Threevok]

I found upgrading my GT Avalanche to a 3 x 10 setup covers every eventuality. I do commute and hard Welsh climbs with this setup. I have a massive 48t big ring on the front. 11-36 cassette on the back

 

[Finchy89]

I found upgrading my GT Avalanche to a 3 x 10 setup covers every eventuality. I do commute and hard Welsh climbs with this setup. I have a massive 48t big ring on the front. 11-36 cassette on the back

Thanks, can you explain a little more on "3 x 10" setup please? Does this mean 48-38-28 on the front?

 

[Lee_M]

I find if I'm going down hill and run out of gears then I can freewheel. You should try it, it's great fun

and yes I know that's not what you asked :-D

 

[Threevok]

Thanks, can you explain a little more on "3 x 10" setup please? Does this mean 48-38-28 on the front?

Yes, but 48-36-26 on the front.

It's a Shimano Deore M610

10 speed cassette on the back 11-36t (Deore HG50)

Still run out of gears, but only on very steep and fast (road) downhill sections

 

[gbb]

Before buying anything just have a look at the clearance between your existing 42t and the chainstay (at 9 o'clock, look from above) on a previous bike I tried fitting a 48 and it fouled the chainstay. There was previous little clearance with the 42 let alone a 48. One option
was to go for a wider BB but then the chainline would be compromised.

 

[si_c]

You could change the gearing to have a higher top end, but at the risk of being contrary, would coasting down hills not be enjoyable?

 

[Threevok]

Before buying anything just have a look at the clearance between your existing 42t and the chainstay (at 9 o'clock, look from above) on a previous bike I tried fitting a 48 and it fouled the chainstay. There was previous little clearance with the 42 let alone a 48. One option
was to go for a wider BB but then the chainline would be compromised.

Good advice. He should be OK though. I don't think there is much (if any) difference between his XC3 and my Avalanche 2, in that respect.

Front mechs for a 48t on the other hand, are a bloody minefield. I had to basically "suck it and see" as none of the retailers I asked, could confirm what was compatible.

In the end - I stuck a Top-Swing SLX on it - and it works a treat.