TT Bike Gearing – 1x or 2x

I’ve got a 2018 Cervelo P5 and run Dura-Ace 9000 (mechanical) as my group-set, with a Quarq D4 power meter. I’ve run the DA 9000 group set for 5 years now and I love it, absolutely no complaints. I have, however, been itching for an upgrade and given my frame is only 2-years old I’m not looking to change that; plus, I’ve got too much money in rim brake wheels to invest in a disc frame. I’ve been looking at the SRAM Red AXS group set since it was launched last year, and I’m intrigued, especially about the 1x capability.

I’ve looked at the various gearing combinations possible between the front ring and various cassettes and understand how those compare to standard two-ring set-ups. However, I haven’t yet ridden a 1x system on a road or tri bike.

Currently for my DA group set I run 11-28 in the rear and have 50-34, 52-36, and 53-39 chain ring options. I am planning on doing TC 70.3 this year which has ~2,500 feet of gain and targeting IMMT in 2021 which has ~5,900 feet of gain. Looking at the SRAM website, I could go with a 48-tooth ring up front and 10-33 cassette. While this affords me a wider range than a 50-34/11-28 combo, it does come with larger jumps higher in the cassette, meaning my “granny” gear could become a “grinding” gear.

My question – do any of you run your TT bikes with a 1x set-up? If so, what has been your experience? What considerations should I be concerned with?

Thanks in advance.

I will be going for a 1 x setup on my new TT bike. I don’t require a smaller ring, 54x 11-28 or even a 11-30. My time trials don’t have large enough climbs to need a 39 or 44t. And it allows for a straighter chain, thus reducing chain friction, especially with a Zero Friction chain.

But if your climbing, and your TT, or IM etc has a decent enough climb, then perhaps you want a 39 or a 44t. How long is the climbs and what %. Overall feet climbed I personally dont see as that matters, as the course could be rolling, therefore, not long, or steep ascents.

I just finished building up a Trek SC with a 1x setup. 56t drive with a 11-23 cassette with a force 1x RD and the R2C shifter. Works like a charm but the real test will be this Sunday!



Should be more aero too eh?

And lighter!

While I am pretty sure the climbs in IMMT are a gentler grade than IMWI, they share a similar elevation total. I would have no interest in doing IMWI with a 1x (and I am a FOP rider). While I could get the range I would need, the resulting gaps between gears would be too large, IMO.

A lot will depend on how strong you are on the bike, a stronger rider could probably do a 1x with a tighter cluster, but you still need to be able to run well. I would rather have bailout gears available and not used, than being in my smallest gear on the climbs, grinding away and still have a marathon ahead of me.

Bike for show, run for dough…:wink:

Unfortunately this is not the case. Once you remove the cross-chain extremes, the average chain offset is smaller on a 2x than on a 1x. See this Velonews article for more details.

I run 1x on my TT bike, very happy with it. Running a 58T and an 11-28. Nice and aero and simple. Saved me a bit of money as well since I only need one Di2 shifter, and a single 3 way junction box. But I built the bike up that way from scratch last year. Not sure that I’d bother switching out a 2x to go 1x if the bike was already built.

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From AeroCoach

We’ve tested a few 1x setups in sessions, on average it’s 1-4w saving from ditching the front mech and losing the inner ring

Be interested to know what the friction from cross chain/ watts saved by removing the inner ring and front mech actually equates to.

My road and tri bike are still 2x but I run both MTB 1x. I like the idea of 1x on the TT but the bike is only two years old and just switching would be too expensive.

Depending on your w/kg and cadence preferences I think 48/33 could be fine even for IMMT (unless all the climbing comes in a few very steep climbs). I did the Mont Blanc Man last year, 6200 ft of climbing over 70k on my road bike with 36/32 (1.125) at 4w/kg and was fine, only in the steepest of sections did I have to exceed my target power briefly. Assuming the climbing at MT is stretched a bit and not that concentrated the 1.45 a 48/33 could be enough. Will probably require some grinding or out of the saddle action and staring at your watts in the steep sections, but I might give it a shot.

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You might be aware of this anyway, but because you mentioned you don’t want to buy new wheels - to run a 10t sprocket, you need a new freehub body.

One of the downsides of going to a set up that you’re think about is the bigger jumps between gears. This might make finding an optimum cadence more difficult and potentially disadvantage you. If you’re only going to be riding flat TT’s that won’t ever require the inner ring, get rid of it. But if you reckon there’s a possibility of needing the inner ring, I would stick with the traditional set up.

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Thanks all, I appreciate your comments and perspectives. I don’t know specifics of the IMMT course, but have read there are some steeper sections at the end of each lap and some rollers throughout. I’ve done IMWI and I agree, I wouldn’t want that on a 1x.

I ran some gear ratio tables after posting this and I really lose my climbing gear in a 48-33 (1.45) vs a 34-28 (1.21). I’m a 3.5 w/kg rider at FTP and that may not be strong enough to push that gear and not have it impact the run. A 44-tooth front ring would get the job done for me, but SRAM doesn’t offer that for AXS right now.

One option I considered was staying with AXS front ring but use an Eagle AXS XX1 rear derailleur to accommodate a larger rear cassette. I assume I’d need an Eagle chain for this too. This intrigues me because I want to have a system that I could use on flat, rolling, and hilly courses.

That said, I am sensitive to the cadence jumps. I’ll need to run some gear ratio tables against what I use today to see what that could like like

I ride what are known as ‘sporting’ courses in the UK, in other words lumpy bastards. I find having a smaller ring handy if only to prevent having to muscle the cranks and fatigue the legs on climbs, once you’ve done that it can take a while for the fatigue to fade, and I only have to hobble to the cake and brew stall after my ride, not run a bloody marathon. Better to have it and not need it, than need it and not have it, in my opinion.

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