guadzilla

So I am a ~40kph/hr TT guy - respectable, but nothing special. I run a 53/39 on my TT bike. I've had a couple of friends who are strongly suggesting that I consider putting a bigger chainring up front. I have never really paid this much attention but these guys have improved their speeds significantly (by around 1kph) and claim that the bigger chainring helps.

Other than the fact that this will let me use a bigger cog and so perhaps gain a watt or so in drivetrain efficiency, I am not really sure how this would make a difference (I have never spun out my 53t yet either). Watts are watts, and as long as I can get my desired wattage at a comfortable cadence (80-85c for TTs, for me), it shouldnt matter, right? Or am I missing something?

TIA.

Hermes

I think it is more of an incremental gains discussion. I have seen many TTs where the spread on the podium is a couple of seconds. The 1 km/hr for increased efficiency due to less chain friction caused by bending a chain around a gear or misalignment seems high.

Having said that, I use a 54t and most of the time trial racers use larger chain rings. There have been courses with terrain features that make the larger chain ring useful in addition to keeping the chain off the smaller rear cogs. For a particular race, the goal would be size the front ring and the rear cassette to match up with a rear cog to reduce friction that works for most of the TT at the desired cadence.

At the track, pursuit riders and riders going for records use larger rear cog and much larger chain rings to reduce drive train losses.

burnthesheep

I'll summarize my opinions from cruising Slowtwitch and Timetrialling.uk:

1. Bend radius when keeping a good chain line and using a slightly larger cog in the back reduces losses.

2. Around here, you go downhill at some point. Bigger front ring, no spinout downhill. Confident even power downhill without bouncing on the saddle at 110rpm.

3. One more tooth up front means less than a tooth in the back. So take some of the bigger front rings with a grain of salt.

I'm on a 54T and 12-25. Works for most of what I roll. My cadence range comfort wise is about 85 to 105 for a TT. That gets me 14 to 37mph of range. A 56T would be 15 to 38.5. Not much difference.

gsteinb

This isn't a new discussion around here. It seems to usually drill down to 'ride what you got. I recall Kevin Metcalfe writing he won the national TT (masters) on a compact.

Trakhak

Probably the biggest advantage of using a 55-tooth or larger chainring is that you'd mostly be on the sprockets closer to the middle of the cassette, where 1-tooth increments represent smaller percentage changes, making it easier for you to maintain your optimal power and cadence.

guadzilla

Gotcha - thanks folks. That's pretty much what I had thought too - incremental gains. For medium-course triathlons, I am in the 34-35kph range and I think i would rather have lower gearing for climbs.

Will stick to what I have.

kensuf

Just go for the straight 11t block cassette.

burnthesheep

That'd be a Jens Voigt TT cassette. 11,11, 11, 11,11, 11, 11,11, 11, 11,12

rubiksoval

Yep. He's said repeatedly he rides a 50.

I don't understand it in the least.

I've been looking for a cheap dura ace 54 or 55 for my road bike for a while.

TMonk

#repost

I'm picking my bike (Felt DA2) up from the shop tomorrow. New: bars (open-mold alibaba w/ stackable spacers), 15 degree tilt block adapters for extensions (AeroCoach), sram etap aero, and a new narrow/wide 1x 54t 110 bcd custom chainring (AeroCoach). So stoked... Given all the zwifting I've been doing, I suspect that nearly half of all outdoor rides will be on the TT bike for a while.

colnago62

A couple of the Japanese National team riders in the sprints were using a 60 tooth, at least I think it was a 60 tooth.

Voodoo76

Just put my DA back together, a little more conventional though. This sounds like a very cool setup & like the 1X idea.

rubiksoval

I've been eyeing those open-mold stackable tt bars for a while. I've come very close to buying a couple of times now, but then I remember that my TT bike has been on the wall for the last 2.5 years, so what's the point?! But then I think I'd have to start riding it more to justify buying new bars...ehhhh, so much back and forth.

TMonk

Yeah the TT stuff can be a bit of a money and time sink. It is neat though. Is there a local series nearby for you rubiksoval ???

Doge

It is a thing. The juniors do it a lot. If the course is flat they will put spacers where cogs were and run 1-3 cogs on back.
It is one of those small things, but if you TT a lot there will be some race where <1sec determines a place.
It is marginal gain area alone, but psycologically it might be 5-10 sec - esp for a kid. Grown ups know too much and loose that advantage.
Why...
Chain angle - run big to middle - 15T-17T. The side plates of the chain rub less under tension because of the straight pull. This may be the biggest thing. I don't know the watts here, but it is something. Of course the chain matters too.
Chain tension is less, so there is less chain stay flex. This was a bigger deal in the old days, but frames are pretty stiff now.
Get rid of extra cogs as mentioned above.
Something to talk about.

burnthesheep

If that guy was doing the 50T front ring on flat roads, sure. If you pedal at 100rpm, a 50/13 combo at 100rpm is like 30mph. That works fine.

Issue is hilly routes. Going downhill you might go over 40mph which ain't happening on a 50T. Often riding around here the rolling hills I'll hit 45mph downhill on the TT bike. 54/11 combo and spinning out.

Not being able to put out power during that at all is time lost.

guadzilla

Sweet!

I am still riding a 2013 Shiv with Zipp Vuka aerobars - gotta say, I am very tempted by the Tririg aerobars. The ability to easily swap between a more aggressive position for TTs and an slightly less aggressive position for tris appeals to me a lot - and I suspect I will find it easier to get lower with angled bars. I have set a target for myself for 70.3s - if i break that, I will just get a new bike.

guadzilla

How much faster would you go if you were pedaling?

The hilly courses around these parts have winding turns, so I have very rarely been able to get speeds beyond 35-36mph. So this is purely academic - but if i am only going to gain a little bit by pedaling on a downhill, it may be better to go harder on the climbs and recover on the downhill, no?

Hermes

IMO, the course dictates how to apply power effectively. One of my favorite time trial courses is Santiago Canyon in Orange County, CA. It is 12.4 miles starting with a climb of about 3 miles and then a staircase descent. It is not an out and back course. Once you finish, you ride back to the start which is not easy per se.

I have done it on a road bike with a 50/11 and a time trial bike with a 54/11. I am faster on the TT bike and spin out the 54/11 on the descent so I could use a 56/11. One might think that the climb would favor a road bike but that is not the case. What happens is that the staircase decent offers very fast descending followed by flattish racing so I carry a lot of speed into a flat section and there is an opportunity to apply power and maintain higher speed longer with a larger gear and then get into a optimized front rear combination. If there is an opportunity for “recovery” on the descents, it is sweet spot. And most of us have shot a lot of bullets on the climb already.

I think courses like that make time trialing an art form as well as the ability to apply physics to optimize time.

My ideal combination today would be a 56/44 chainring setup versus the 54/44 I am currently running.

TMonk

Nice. I have a teammate in road and TTT that is on a (2016?) Shiv with the tririg bars. He loves 'em.

burnthesheep

That makes sense. These are rollers I can slam on down.

I looked up one area I ride the TT bike a lot and created a 10mi TT out/back for future use. Not even at full power for 1/2 mile I averaged 37mph with 1/4mi at 40mph.

The thing about it is if you "save" the power down a grade due to insufficient gearing........the way your power duration curve works.....you're not going to be able to "add" back much power over the rest of the ride.

Mind you I'm not slamming down the hill at 100% target power. You might do 80% down the hill and then 110% up the hill (up takes longer). Just random numbers there. Don't put anything into me choosing those, just example.

Also..........the faster you can descend, the more you "flatten" the hills or rollers after it.

Doge

Or slower. The whole junior gear restriction (which I hate and see as completely unfair) taught us a lot. One is that it matters and is a disadvantage, the other is that pedaling is not always faster esp in the higher speeds on a decent.
I have a hunch that may even transfer to adults (on decents) doing 40+. The churn can be significant and sometimes a tuck and tight knees conserving may end up in a total faster time.
We saw better results in that 40mph-55mph pedaling up to speed and coasting. Certaining on junior gears, but also on unrestricted gears. Yes, at 40mph plus, you go faster pedalig than coasting - but barely and at a significant effort that you might want to instead use to recover.

burnthesheep

I think I should clarify here..........we don't have mountains in Raleigh. If you get up to your mountain descent speed, or really really long hill...........sure.

But here, the key is carrying speed up and over the next tiny little roller. There isn't enough time to reach a terminal velocity of any meaningful value before already reaching the rise of the next little tiny hill.

So, you stand to gain a LOT by flattening out the rolling hill instead of getting a 10 second "rest". If you can rest for several minutes due to a descent, I could see what you're talking about coming into play more than where I live.