assume 40k TT, 2 person TT, riders are near equally strong. how long should the pulls be, and what is the rationale?
I have no idea if it should be 5 seconds, 10 seconds, 5 minutes, etc
Seems like you’d have to figure out how much energy is wasted when one guy peels and you essentially have two people in the wind for a few seconds. Maybe if you have two teams of identical physical ability, the team that can switch positions more quickly should switch positions more often?
Too many variables. Depends on how each guy feels that day, one guy bigger, where the turns are, hills, wind direction, etc.
In general, shoot for about 30 secs though - enough to tire you out, but get a slight rest as well
assume 40k TT, 2 person TT, riders are near equally strong. how long should the pulls be, and what is the rationale?
I have no idea if it should be 5 seconds, 10 seconds, 5 minutes, etc
First, without the physiological constraints, it’s impossible to optimise this. If you had each rider’s CP curve, then we could make a stab of it. Saying the riders are equal doesn’t tell us what the trade-offs are. You will be choosing 2 points on the curve for each rider that solve the time-optimisation problem. In addition, each rider’s aero parameters need to be known. There are other aero drafting considerations, too.
let us simplify the question.
let us assume the riders are identical twins, on identical bikes, with identical fitness.
short, medium, or long pulls, and why?
from there we can have a basis from which to adjust for differences in fitness and drafting considerations perhaps?
how do the pros approach this question? purely from experiment? what are the rules of thumb in cycling myth and lore? what does team Garmin do?
let us simplify the question.
let us assume the riders are identical twins, on identical bikes, with identical fitness.
short, medium, or long pulls, and why?
from there we can have a basis from which to adjust for differences in fitness and drafting considerations perhaps?
how do the pros approach this question? purely from experiment? what are the rules of thumb in cycling myth and lore? what does team Garmin do?
It’s not enough. The pull-draft ratio is determined by the shape (slope, curvature) of the CP curve. You need to know the incremental trade-offs of pulling and drafting. See attached jpeg, done in the spirit of howardjd’s churner… 
I did a fair amount of training like that in the Spring. We were doing a 3k loop with 2 riders of similar physical conditioning.
Seemed like shorter to medium pulls optimized our time. 30-45seconds.
But that’s just from experience.
No more than 90 sec, no less than 30. Any more and it lactic acid builds, any less and not enough recovery.
The exact times depend on variables everyone else has mentioned, particularly how each rider feels that day, or may he takes short pulls every once in a while if he hit’s a hard spot etc.
Although I think what is more imporant is the pacing early on and not going out too hard.
Having done my share of TTT’s (4 person mostly), I’ve used 30s as the starting point. That all works well for the first 2/3’s to 3/4 of the race and then adjustments usually have to be made. If your speed drops considerably (2-3 mph) on the front when trying to stay there for 30s, you’re really slowing down the overall speed. Shorter pulls and/or the stronger rider takes slightly longer pulls to allow a bit of additional recovery. If you don’t adjust, a good race can turn to a barely average one.
No more than 90 sec, no less than 30. Any more and it lactic acid builds, any less and not enough recovery.
I think this sums it up pretty well. The rule of thumb is that the more riders you have, the shorter (and harder) the pulls. Less people = longer pulls because you need time to recover from your pull.
take the extremes - TdF TTT: 9 riders and you are taking very quick pulls. But since you have 9 riders, you still have time to recover before you hit the front again.
if you used the same technique for 2 riders, you both would blow up pretty quickly.
I do with 30 seconds as a max. My reasoning is you should be above the pace you can maintain for the total distance solo when pulling. So the less time over max the less you get toasted (of course the less recovery, but when I do intervals a shorter recovery seems OK)
The 2nd goes by doing what the experts do, for a 4 man TTT on the road which used to be a WC event and the 4 man pursuit which was an OG and WC event the pulls were short. The pursuit they would switch every lap or even half lap at over 30 mph on at 300 m track. Of course thats 4 men vs 2, but still very short pulls.
For amateurs I’d say practice as short as you can safely do and you’ll likely have one taking longer pretty quickly anyways.
Styrrell
Agree with what most everyone said although it partially depends on rider and how quickly you recover. When nslckevin and I did the 4-man District TTT Championship earlier this year we lost one guy pretty fast and the other wasn’t strong enough to pull close to what we could. So Kevin and I basically rode the second half of it as a 2-man. We took pulls of 1-2 minutes since revving and holding and then having a longer recovery suited our motors.
You sometimes see that the ProTeams also doing that where the TT specialists take longer turns on the front.
Keep them on the long side like Spackler said.
5-10 seconds you will burn each other up.
Adjust by who is stronger- stronger guy should pull longer rather than harder.
I.E. start at 1 min each- if one is stronger switch to 45/1:15 split.
I always thought 60 seconds would be about right in that scenario. Short enough to comfortably exceed threshold and long enough to somewhat negate the fact that making the switch is not efficient.
I did a 100 mile flat ride as a time trial with two others a few years ago. We did two minute pulls, so it worked to two on, four off. I don’t know if it was optimal but we finished in 4+15 i think, not counting the 15 minute water refill stop. We kept the innitial speed in check and it seemed like alot of recovery time between pulls at first At the end we were hurting. I would think a 40k would allow you to shorten the pulls a bit, even with only two people.