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Discussion Starter · #1 ·
Hi All, I've this week purchased a Giant Fathom (yet to ride it) as per above in size L to replace my Merida Big 9 XL. I think actually the Merida is a better spec, but it's too big for me and I keep getting neck and back pain, so this was my solution.

The Giant has a single front sprocket whereas the Merida had a triple. 30 gears was a bit ridiculous on the Merida, but I did like the range of ratios as it meant I could pop road tyres on it and get a decent ride. I do a lot of road biking but prefer an all rounder config than getting an actual road bike.

My question is, I am assuming the velocity of the Giant is going to be less as it has a smaller sprocket up front than the Merida, and you can't really get smaller at the back. So given that, has anyone tried replacing it with a bigger one, or an adjustable one?

Many thanks,

Marshalleq
 

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Sneaker man
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It depends on what the ratios are/were. In all likelihood the triple will have a higher high and lower low (or one or the other), but whether that is a practical/noticeable thing is something else...
EG the gear inches calculation on the top (or the low gear) may end up being similar (plug them all into an online gear calculator and see)
 

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Discussion Starter · #4 ·
I found an easier way, this says it quite clearly on 99spokes.com.

The big 9 runs at 31mph vs the Fathom at 24 mph. Or put in our local system that's 50km/h vs 38. That's quite a difference.

So what do you think can I throw a deralieur on the front or should I sell the bike and get one pre-made. The speed difference will detract from my ride enjoyment without a doubt.

1928545
 

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So what do you think can I throw a deralieur on the front or should I sell the bike and get one pre-made. The speed difference will detract from my ride enjoyment without a doubt.
You can just change the front chainring size, or get a bigger range cassette.
The Giant is a much better bike than the Big Nine. Better Fork, better drivetrain ( Clutch mech ) and a dropper post.

My pro tip.
Before you do anything just ride the bike when you get it and see how things work out for you.
If you are fine with the low gearing just get a bigger front chainring.
 

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Discussion Starter · #7 ·
I will be going on a ride on it today, however I don't expect at all to be impressed when I can't keep up with the Mrs on her much cheaper bike, considering it and she are much smaller than me and mine. The obvious problem with a single larger sprocket at the front is that I lose the ease of a smaller one when going up hill etc, which I do use on very steep and long climbs.

As for which bike is better, if it weren't for the shoddy fork on my Merida I wouldn't probably notice too much. Will miss the multi shift gears of the Shimano XT though - which is clearly the better drive chain. Not sure what you mean about the clutch mech in it, but the Fathom clearly has the entry level drive chain which mainly is just heavier as far as I know.

I like the internal cabling on the Fathom, though wonder if that will make it more difficult to replace at some point.

I also note the newer Merida's are also coming out with single sprocket fronts now, which is really about it's target market I guess. I'd still hugely prefer a double / triple front sprocket set without a doubt.
 

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Discussion Starter · #8 ·
There appear to be some compatible front sprockets here. Does anyone happen to know what the 135mm / 142mm and O.L.D refers to? Trying to match it to the bike specs.
 

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Cholla magnet
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There appear to be some compatible front sprockets here. Does anyone happen to know what the 135mm / 142mm and O.L.D refers to? Trying to match it to the bike specs.
O.L.D = Over-Lock-nut Dimension

It's the spacing of the rear hub. 135 = Standard MTB rear spacing for Quick Release. 142 is the thru-axel dimension for the same standard hub size (there's about a 7mm difference between the QR. and thru axle end caps for the hub). Boost thru axle spacing is 148. Boost rear hubs are wider overall, so the cassette sits farther away from the center line of the bike. More info here: Frame Spacing/Hub O.L.D. information | Halo Wheels

When you're looking at cranks, it's very important to get the chainline correct for best shifting performance. Cranks designed for boost rear hubs then place the chainring farther from the center to match. The 2019+ Fathom has an odd rear spacing (141) but it's actually just boost spacing with a quick release instead of a through axle. So you will need to get a boost compatible crank to avoid chainline and shifting problems. so the crank you'll want is here

I'm with OneTrustMan though. No reason to add more front gears when a chainring and/or cassette swap will sort things nicely and keep things simple and light.
 

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Discussion Starter · #10 ·
So you're also saying keep a single front but bigger sprocket, which increases the range of top speed, but also decreases the ratio for climbing hills.

I've been for a ride on it now - I liked quite a few things, the way the steering felt in particular, but it's definitely slower, couldn't keep up with the mrs without a lot more effort and just stopped trying actually and let her go - and she has a relatively cheap bike. But I used right down to the lowest (easiest) gears in two instances so my first thought is I'm not keen on giving those up really. But - I haven't been for a ride for a while and we are spoilt a bit for gearing these days so perhaps I will look into those sprockets as it's definitely easiest option and check cost. There's just some really long and steep hills on my ride that get me pretty quickly - and I consider myself to be quite fit. Heart rate got up to 192 in one place today - I'm 46.

Thanks for all of the help so far everyone. Really good info!
 

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https://www.gear-calculator.com/

Hi here is a great gear calculator for visual comparison of setups. I just compiled my bikes drivetrain history to give you an example of speed range vs gearing (in theory).
Small numbers on top are max kph per gear, red rings are 1st/climbing gear, green rings 11th/top gear.

When you do want to expand your range, look at Shimano 11 speed M5100, wide-range 11-51T cassette and derailleur, with a suitable chain and shifter. Fits HG 10/11 sp freehub (I'm assuming yours is HG based on the specs in the pic you posted above - deore group set). I have this setup on my older XC spare bike, swapped 3x9 to 1x11, it's running great and was cheap, not sure how the price is going now.


drivelines.png
 

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Some newer frames are made without the capability of installing a front derailleur ,if you can ,you would need a shifter ,cable and housing also.
 

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@Marshalleq
You'll get more out of your current setup every time you ride, it's worth sticking with it for a while.

Just to make it clear, with a taller climbing gear you can increase front chainring 2-4 teeth and increase range at both ends.

At 11-42T you're pushing the limit of 10 speed gearing, so any way to increase range is going to need a new derailleur, shifter, cassette, plus chain if changing # gears.

10sp Microshift Advent
11sp Shimano M5100 + 11 sp chain
12 speed is the new normal but price goes higher and availability isn't great.
 
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