Anyone know of good articles regarding real time savings of going for bigger chainrings for mortals doing TTT. Is there any RPM/FTP/Chainring calculator?.
Or is 50 or 52 enough for most of ous not having 400+ FTP?.
Bike Calculator here you can roughly estimate your speed for a given power output (emphasis is on ESTIMATE 
)
BikeCalc.com - Speed at all Cadences for any Gear and Wheel and here you can calculate cadences for gear ratios at speeds
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Thanks but i was more thinking of how a guide to how big my chainring should be when coupled to my FTP. I know i do run out of gearing sometimes (often when big tailwind or big downhill) but unsure if bigger gear would be benefitial overal.
not entirely sure what you mean, but if you run 53x11 you go 60 km/h at a cadence of 100… so I don’t think many people can go faster than that in a timetrial
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True but there is the benefit of using more time in the middle gears on rear cog by going bigger front. less friction and so on. But would like to see what this matters in real life and seconds.
but when do you want less friction? for those 2 minute tailwind downhill 60+? or do you want less friction, when you are cruising at your avg speed (most of the time)
Biggest time saving is simply being able to maintain target power through sections that are downhill or have a tailwind. No complex calculations needed, if you are regularly running out of gears so that you have to stop pedalling or are pedalling inefficiently or with low power at very high cadence then you will benefit from having a bigger gear. Assuming that having that bigger gear doesn’t mean you are then struggling to get over the climbs of course…
Having a chainline that is straighter for more of the time will give an incremental saving. As will spending more time in a larger cog at the back (chains become less efficient the tighter the turns they have to make). But I would say these are pretty small benefits compared to being able to lay down power efficiently throughout the race.
(Anecdotally, I switched to a 58T and I love it, but I honestly couldn’t quantify how much of that is extra speed vs looking bad ass…)
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Thank you.
I have been working allot on position for my TT this winter so hope i will get some good speeds and don’t want to loose out on the clear time loosers (like you say when not being able to push right power). Then ill just make sure i don’t run out and do have enough for the climbs.
For my last 4 time trial races i avg 96 rpm and are up to 135 at max, with 52x11 So i think i could need some more yep.
If you are spending a lot of time in the 11 then get a bigger chainring so you are in the middle of the block for optimal chain line. If then races you do are mainly flat consider single chainring.
I think it depends a lot on the type of TT’s you do too. If there are any climbs where you think you are going to drop into the bottom one or two gears at the back or even run out of gears then obviously a bigger chainring isn’t goig to work.
However I think people overestimate how much of a speed difference a larger chainring makes. (between 53 and a 58 is about 1 cog diffrence on the back for the same speed)
I’ve gone for a 58 tooth with a 12-25. For the TT’s i’m doing in the UK and in full TT mode i’m never dropping below 20mph, and am still pretty efficient at 90rpm which means i’m not dropping below the 21
If we compare that to 53 11-25
If you look at the speed comparisons on the block though your not gaining any speed on the top end (40mph @ 105 rpm). The bonuses are gaining the efficiency of larger cogs, extra gear in the middle (the 18), and looking badass. The only thing you are losing is the bottom gear speed of 15mph @ 90rpm.
All this changes of course if you are doing TT’s with hills where you are dropping below 19-20 mph.
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I assumed anybody considering switching from 53 to 58 would already have an 11 at the back and would keep it. In which case you’re getting a ~9% increase in speed in your top gear for any particular cadence. That’s substantial. I don’t really like pedaling over 100rpm on my TT bike, having an extra ~3mph before I start to run out of cadence comes in pretty handy on fast sections, particularly as I do TTTs where we hit some pretty high speeds
Fair enough, it’s easy enough to have a few diffrent cassettes and swap arround when needed. I ran an 11-25 once this year when i did a TT with a downhill (But no uphill, best kind of course) and hit 50mph.
I’ve also run 12-32 in when it was particulaly windy (10mph speed diffrence between out and back).
I think the main point i was trying to get across is it doesn’t make the massive difference that people think, you don’t need to be a monster to turn the 58, it really just comes down to shifting down one cog at the back. So as long as you don’t need that last cog there isn’t much of a downside.
Thanks for very good imputs:
Would i be able to buy this for use as 1x by not gearing down/just staying in the 54tooth without any other adjustments?:
Got Shimano 105 5800 110 BCD.
Product Name: STONE 110 BCD Chainring, narrow and wide
Material Hardness:HB150
CNC process precision:0.03mm
Color: black anodized
Size: 110 BCD, round
Thickness: 4MM
Speed: 9-10-11-12 speed
Fit for shiman.o 5800 6800 4700 9000
Yep should work fine. If your thinking about removing the Front Derailleur you might want to think about replacing it with a chain guide, it’s not required but I won a TT last year because the guy who was faster than me dropped his chain.
At first i was just planning to keep derailleur and just stay on big cog?.
But will look into chain guide :).
Yep that will work, you don’t get the Aero benefit of loosing the Derailleur and small cog. The chainring probebly doesn’t have ramps etc so you might want to disconnect the front Derailleur so you don’t shift accedentily as it will probebly drop your chain, or you might not be able to get back into the ring.
Yea disconnecting for sure!. Thanks for the help.
Im happy with solid training so far this winter, so atm im doing a buying spree to keep motivation up until season start.
DA c9100 bought yesterday (for road bike and front for windy when my 88 is to big on TT)
Nice! I did the same over last winter, that’s when I changed to single 58 ring, used it for a season and it was great.
(FYI 11-32 on the training wheel helps when moving up to bigger front rings when running single ring up front 11-32 even works fine with a Short cage derailleur as it’s not having to take up a bunch of slack going into the little ring).
Instead of disconnecting the front deraillleur, you could also just adjust the limit screws so it can’t move. Afaik if you just disconnect the cable, it’ll move to the small ring.
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What I find amusing is riders that use a 53t up front, with a nice straight chainline on flat TT’s that put a 58t only to have to ride in the bigger cogs on the cassette, when they never spin out a 53/11 even when going downhill!!