Tri Bike Gearing

I have a Cube Aerium which I bought second hand and naively have just raced on it in the past without considering gearing. I’ve always found it really tough on climbs to get a decent cadence.

Having now considered what it’s running 52/40 with 12/25 I feel it’s the worst of all worlds with a narrow range?

The 40/25 combination I find really tough on steep climbs.

The 52/12 ratio of 4.33 is lower than my road bike 50/11 ratio 4.54

I definitely need an easier low end and the same if not faster high end. How would you go about achieving this??

If its a Shimano crank, a 36t inner costs less than £20.

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Yes, you’ve got two options you either replace your front chain rings or the complete chainset - for something like 52/36 or go for a compact 51/34?!

Or you fit a more accommodating cassette on the rear, maybe a 11/28

Really depends on what terrain you ride/ race on

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What Jgav said, that 40s your problem, it’s bigger than you’d get on a regular 53/39.
If you can put a 36 on, if that’s not enough look at a bigger cassette but that may need a different rear mech depending what you have now, although you can normally go upto about 28 without changing.

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There’s a shimano 36 on hill climb market place


Looks mint

Thanks for your replies, I’ve just remembered that the guy who sold me the bike gave me some chain rings. They look unused and are 50/34!

From what I read I can’t run the 52/34 combo so would need to change over to the compact setup.

Obviously this would greatly improve my climbing situation but how much top end will I lose out on?

50/12 ratio 4.16 seems low for a tri setup, my road bike top ratio is 4.54!

Shimano say you can’t but it does work. Shifting is compromised and be careful shifting under power. Also chain length is an issue if you cross chain small small which you shouldn’t anyway.

I have 53/36 on my TT bike.

If you’re worried about top end, find out how fast you need to pedal to spin out. Can always change cassette to 11 to 28 pretty easily.

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You don’t optimise gearing by looking at the “top end” (outside of genuine sprint cycling events but then we’re talking 65x15 fixed set ups…) You need to optimise for the speed/cadences you spend most of your time in.

The 1 hour into a headwind at 150w, the 1 hour with a tailwind at 150w, the slight uphill drag, the poor road surface etc. the bit of the race where you’re feeling crap, the bit where you’re feeling better all of those will change your speed for the same effort - and a triathlon you want to keep the effort the same, which means you will almost certainly need to keep your cadence within a narrow range, If you want to optimally ride at 40x11.5 then you either have to work harder (keeping 40x11 at your preferred cadence) or ride slower (keeping 40x12 at your preferred cadece)

To avoi that, you care about having a small difference in ratios in the part you’re riding most of the time - not the almost 10% jump in ratios of 11 to 12 - they’re not important, it’s what you have in the 14/15/16/17, where the jumps are small that you optimise the size of the large ring for, is that 48 or 54, or somewhere in between. It will depend on course (a flat, hot, windswept course on perfect roads will be different to cold lumpy rough english roads course)

Of course you need a low enough gear to get up any hill without the same problem, and with long hills it’s possibly even more important, although hills are generally not in triathlons, but it does get hard, still you want low enough gears to get up them easily again in close ratios if you can - the difference in ratio between your 25/28/32 are over 10% too, so you don’t really want to be in it - however realistically on lots of hills you will be 'cos 34x28 may well be needed on steep hills.

The place to worry least about gears is if you have an 11 or 12 - if you’re going the speeds enough where you can use those gears, you’re probably better off resting anyway (the return on more watts at that speed is very low, save your energy for the run)

As you note, running too big a difference between large and small front rings is impossible, so you need to compromise, or get a triple, but don’t think only of the extremes in the compromise.

52x34 is doable on many bikes, Maryka rode 52x34 12/30 in a hill climb and used both extremes, and had in fact tested the bike with 12/32 but didn’t need to race it due to it being a tailwind on the hill, but it is outside the spec, so it is a bit suck it and see as @Jgav says.


Basically what @JibberJim says. If your working too hard on the climbs then this will have a bigger negative impact on your tri result than missing a few teeth at the top end.

Put the 50-34 on with an 11-28 on the rear assuming the mech is good with that.

Second all of this, you should optimise your gear ratios for the circumstances you spend most of your time riding in. For me, this was running 50/39 on the front. I’m more efficient at higher cadence and am a mid pack rider so would spend most time between 20 and 25mph. Running the 50 instead of a 53 allowed me to stay in the big ring more of the time. Sure I lost a bit at the top end but if I’m going quick enough to spin out 50-12 I may as well freewheel and have a bit of a rest.


Regarding ditching the 11 on the back, I did exactly this.
On the standard 11-28 cassette, the first cog to be missed is the 16. I worked out that with a 52 on the front, 15,16,17 is exactly where I wanted to be for my expected cadence and speed. It made no sense to have a 52/11 option, when there is little to no chance of me using it, if I could have a 16 instead.
So I run 52-36 with a 12-28 which involved bastardising a 12-25 and an 11-28.



Not sure that (or you) is a mid pack ride?!

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I’ve wondered how to make a 12 to 28 which is what I’d like on the TT bike for exactl that reason. You just want to be mid block with 1 tooth changes between rings. Will have a look for a 12 to 25 now

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Mid pack flattish time trial I meant! But even so, I used to average about 20mph for an IM bike :man_shrugging:

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And remember that average speed is not the same as where you spend most of your time, you’re not optimising for the mean, you’re optimising for the majority.

Exactly. Unless there is significant climbing and descending your mid block 99% of the time.

I’m sorry I didn’t get back to this sooner, life got in the way. It deserves a reply as it’s one of the most informative viewpoints I’ve ever received! Something that seems blindingly obvious once you’re made aware yet it had never entered your mind before … so thanks!

The 12-25 cassette makes so much more sense now as although offering a narrower range it provides closer jumps in the mid-range where I need it!

I think I will have to change the 52-40 chainrings out for the 50-34 and see how that works for me though as I’m really grinding uphill and I’ve got a hilly sprint in Winchester coming up soon!

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So, speaking of swapping the chainrings … hold the laughter but my bike mechanic skills are non-existent!

Is this a simple enough task with some youtube learning? Is there any impact on the chain length needed?

chainrings are easy to change, the only thing is making sure you get the ones compatible with your arms.

If you have the tools and that depends on the crank you have.

I have Shimano which is two 6mm allen keys and the crank removal plastic thing. Then a star bit (or whatever they’re called) to remove the chainring bolts. Takes about 10 mins if you’re slow.

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