Need advice on upgrading 32T chainring

[AliShah2020]

Hi everyone!

I am new to cycling. I bought a Mountain Bike last month and use it primarily for city commuting, exercise and going to the park occasionally.

I have a 1 x 10, 32T chainring with 11/42T cassette. The gearing is 11-13-15-17-19-21-24-28-32-38-42.

As my legs have gotten stronger I have realized the 32T chainring is now too slow for me, especially when I am bombing it on down hill roads. I feel I am "spinning out" if that makes sense. I need a chainring that gives me "more power."

What is the biggest chainring I can get please? I am considering a 38T chainring, but I am wondering if I should go for a 40T? Also how do I know the biggest chainring I can get compatibility wise?

Many thanks for your input!

 

[Cycleops]

What make of chainset do you have? Is the chainring bolted on? A pic would be good.

 

[gbb]

Your chainset will dictate what can go on, find the BCD of the existing chainring, that's you starting point.
One thing though, Ive done this before, albeit with larger chainring, look vertically down at the trailing edge of the chainring, near the chain stay, how much distance is there between the two ?
I wanted to up a 38t to a 42 or something near, when I fitted it, it rubbed on the chainstay, not enough room (without fitting a wider BB)

 

[Gazjacko]

What gbb says! Remember you will lengthen the effective gearing throughout your whole range so if you’re going to the 42 anytime Luton your rides now that too will be harder. The crank is probably a 4 bolt spider, and you’ll need to know what bcd it is. Once you’v done that replacement chainrings are easy to find in the same bcd and for the price I’d start with a 34 and get used to that before going any higher. Look on it as a training aid. You may find your natural cadence increases to suit. Remember to check your chain length can accommodate the bigger chain run on the 42 as eventually you’ll find it too short and need replacing.

 

[AliShah2020]

Hi Cyclops, gbb, and Gazjacko - thanks everyone for your input, greatly appreciated!

I am not quite sure who the manufacturer of the chainset is, it looks like generic chainset branded by Diamondback. I have a 104BCM.

A few questions please:
1. Do I just need to just search for another 104BCM compatible chainring and can I keep the existing crank arms?
2. Is there much of a difference between say jumping from 32T to 34T? I was considering jumping to 36T so I would not have to upgrade again too soon and keep spending money.
3. Would I also need to change the chain or adjust the derailleur or is it a simple swap?

Currently I am riding on the highest gear (11 tooth sprocket) for 100% of the time. I was hoping by going up to say 36T or 38T I would be able to use the rest of my 11-42 cassette. The rest of the cogs are getting 0% usage and are redundant with my 32T.

I live in London and most of my riding is on flat city roads.

Please see attached my chainset layout.

 

[rogerzilla]

Personally, I would choose a ring size that gives me a normal cruising speed in the middle sprocket, gjven my preferred cadence. I'd probably go for about 16mph on an MTB (I gear road bikes for 18mph and fixies for about 21mph).

How fast do you think you pedal in revs per minute? I can do the maths for you.

 

[ColinJ]

If you are currently stuck using the 11 and you won't have any significant hills to go up then I would go for the biggest ring that you can, maybe something like a 50 or a 52? a 50/42 bottom gear should be plenty low enough for the odd climb and 50/11 is high enough for just about anyone.

I don't think you will fit a ring big enough for the 21 sprocket to be your chosen one though. I have 52/19 on my singlespeed bike and that is ideal for 18-20 mph. 50/17 would be a nice cruising gear.

PS Oh, yes - as @gbb posted above - make sure that the bigger big ring doesn't scrape the chainstay, and fit a longer bottom bracket if it looks like it will! A longer BB would move the ring out and give you a better chainline on the 15/17/19 sprockets which you will probably use a lot.

 

[Cycleops]

Yes the gearing Diamondbacks selected for the bike is very low. Looks like you could go for 34t, 36t or even bigger as chainstay clearance iappears sufficient, 42t might be max. (Get a straight edge lay it across the chainring and see how far it goes before it hits the widened out part of the chain stay). I should work out the lowest gear you want for hills and use one of the online gearing calculators to see how the various options work out compared to your current setup.
You’ll need a new longer chain too.

 

[figbat]

A few questions please:
1. Do I just need to just search for another 104BCM compatible chainring and can I keep the existing crank arms?
2. Is there much of a difference between say jumping from 32T to 34T? I was considering jumping to 36T so I would not have to upgrade again too soon and keep spending money.
3. Would I also need to change the chain or adjust the derailleur or is it a simple swap?

1. Looks like it, yes. You should look for single-ring specific chainrings, possibly also narrow-wide; this may impact your choices.
2. You can work out the difference yourself. Going from 32 to 34 is 2 teeth. This will increase the gearing by (2/32)x100= 6.25%. So if you are pedalling the same speed you will be going 6-ish% faster. 36T would be (4/32)*100= 12.5%. And so on.
3. You'll probably need a longer chain, definitely if you go for a big change. Derailleur should be fine; may need some fine tuning if the new chainring alters the chainline slightly.

 

[Daninplymouth]

I wouldn’t bother only going up 2 or 4 teeth as the change isn’t going to be massive, especially if you are using your max all the time. On a lot of 1x bikes I’ve seen 42 on the front seems to be pretty common, gives you a half decent top speed and you’ll still get a 1-1 gear for climbing

 

[rogerzilla]

Your middle gear is 32 x 21. You probably want it to be around 55-60 gear inches for an MTB. This means about a 46T for a 26" wheel or a 41T for a 29" wheel (more likely these days).

Incidentally, you have a 1 x 11, not a 1 x 10

 

[MontyVeda]

as others have said, no point going from 32 to 36... I'd go for the 42 or 44 if possible.

have a play with http://www.gear-calculator.com/ ...drag the gears to replicate the set up you have (add or remove gears by dragging to/from the empty gear on the left), then adjust to the set up to you want and see what difference it makes.

From what i can gather, you're mostly riding on 32-11 (35kmh), which would be about the same as 44-15 (35kmh)... leaving you two higher gears. A 50t front ring (if it'll fit) would put you on 50-17(35kmh), leaving three higher gears.

 

[CXRAndy]

To add a little bit to the discussion, I would look at the chain line and see which gear gives the straightest chain. From there work out gearing speed and cadence calcs.

I use bikecalc.com for such calcs. Its works extremely well. Ive used it for several gearing set-ups on a triple, double and single MTB cranksets. I use Sheldon brown for internal gear hubs calcs amd again this has worked spot on for speed and rpm

 

[ColinJ]

Your middle gear is 32 x 21. You probably want it to be around 55-60 gear inches for an MTB. This means about a 46T for a 26" wheel or a 41T for a 29" wheel (more likely these days).

But the bike isn't being used as a mountain bike - It is mainly being used for whizzing about on flattish commutes and the odd bimble in a park... Really, a singlespeed or fixed gear road bike with a reasonably high gear would have been ideal for that.

You can see from the photo that the bike has 27.5" wheels.

@AliShah2020 - is there any chance of you buying a second bike? If so, then keep the mountain bike for doing more adventurous offroad rides, and buy a more suitable (lighter, higher-geared) bike for the commute?

 

[fossyant]

Just be vary careful. A larger chain ring could foul the frame as 1x frames usually don't go that big on the chain rings as it's designed for proper mountain biking, not streets, hence spinning out.

I'd doubt you'd get much bigger than a 34 or 36 - looks quite close as it is. You'll also need a narrow wide chain ring designed for 1x so don't just get any.