affect on power of riding position

[sgb]

Power variations due to position.

Does anyone have any data on the affect of power on position? I have been using an SRM since March and have some very accurate data on both my Wmax (420 currently based on Ric Sterns test protocol) and power at different durations as per Joe Friels.

The SRM is on my road bike and I did one club 10 back in May with the bars dropped using a sloping stem and tribars fitted. The Average power and Norm power (cycling peaks) was 317 watts. This is about the middle of Rics estimated power for a 16 KM time trial.

However, other team members who have the SRM fitted to both TT bikes and road bikes report that it seems that in an aero TT position they loose approximately 30 watts over their road bike position.

Obviously there is a massive gain in velocity due to the aero position but it means that should they decide to do intervals on their low profile in an aero position, that they must use a different set of test data specific to that position.

IE not try to work in power zones set in their road positions but ones specific to the TT position.

Is this so? Is it a bio-mechanical issue or an aero dynamic issue where the power can be achieved but you have to go deeper to get it? In my case on the road bike with tri bars and Shamals I was approx one minute slower over the 10 miles than I would have been on my full low profile fitted with a disc and deep section front wheel.

Power however was not 30 watts less than my road position for a 20 TT minute effort which now, in August, is 320 Watts achieved on the hoods, flats, drops. I am fitter and faster now than in May when I had only ridden 4 races due to an enforced racing break.

Another question connected to this is, is power on a turbo the same as on the road? In other words to do say 320 watts for 3 x 10 mins on a turbo seems harder as a perceived effort than the same on the road even though the turbo effort is smoother IE 80 revs constant and the road effort is highly variable say 300-350 watts.

To do 5 x 3 min efforts at Av 6 minute power as an anaerobic effort on the road is tough but on a turbo is almost (not totally) impossible with the 4/5th interval often seeing the power drop to the bottom of the allowed band or going altogether.

I think this is due to the fact on a turbo you can not cheat, it is a constant effort whilst on the road you get varied conditions making power fluctuate so that you are sometimes well out of the zone or well over it even though the average is OK (or norm power if in cycling peaks)

Any feed back appreciated.

 

[beerco]

I think it mostly has to do with hip angle. The closer the hip angle on your TT bike replicates your road bike, the closer the two power outputs are.

I bought a new tt bike this year and saw a 10 to 20w drop until I got my position sorted out. Now there's hardly any difference in power outputs.

One rub is that if you follow UCI rules, you just might not be able to get the position exactly the same. Some things to try are moving the seat forward, using shorter cranks and only moving the elbow pads down such that your shoulder blades are level with the back of your hips (lower doesn't give you any further advantage).

Finally, practice. Even if your position isn't ideal, you can get used to it by riding at tt pace in your tt position once or twice a week.

 

[sgb]

I am inclined to agree. I can not quantify this though as I only have the SRM on my road bike. I could swap it over but The fitting kit is neatly installed and it would be a pain. have you seen the price of a spare!

My road position in based on a 74 degree seat with the saddle back. I am 5'8". My TT bike is 78 degrees and saddle forward. This is the same set up as my teammate who reports this 30 w loss of power. However another teammate has the same saddle position on both bikes and reports similar differences. Apparantly, he knows some one down at manchester who says this loss of power has been seen on squad riders when in the tri-bar position. these bikes conform to UCI regs.

It does not matter as such as long as riders who may be lucky enough to have 2 x srm or a power tap they can swap to their tt bike realise that they may not be able to work/race at the levels they think they should be at having tested or set their levels on a road bike.

Thanks for the feedback though.

 

[Aztec]

I am inclined to agree. I can not quantify this though as I only have the SRM on my road bike. I could swap it over but The fitting kit is neatly installed and it would be a pain. have you seen the price of a spare!

My road position in based on a 74 degree seat with the saddle back. I am 5'8". My TT bike is 78 degrees and saddle forward. This is the same set up as my teammate who reports this 30 w loss of power. However another teammate has the same saddle position on both bikes and reports similar differences. Apparantly, he knows some one down at manchester who says this loss of power has been seen on squad riders when in the tri-bar position. these bikes conform to UCI regs.

It does not matter as such as long as riders who may be lucky enough to have 2 x srm or a power tap they can swap to their tt bike realise that they may not be able to work/race at the levels they think they should be at having tested or set their levels on a road bike.

Thanks for the feedback though.

I'm curious to hear thoughts on this as well. I took the 20 min TT and MAP tests in road position, and then proceeded to train aero after that for a few weeks. I couldn't be sure, but I thought I had a slight dropoff in power. Then, with the TT behind me, I switched to road position again, and immediately noticed that my power readings were higher, especially when climbing (of course). Now, of course, it's hard to be sure that the change is due to position rather than something else, or even just misperception.

I don't know why the trainer is so much tougher, but no question, that's absolutely the case for me.

 

[sgb]

I'm curious to hear thoughts on this as well. I took the 20 min TT and MAP tests in road position, and then proceeded to train aero after that for a few weeks. I couldn't be sure, but I thought I had a slight dropoff in power. Then, with the TT behind me, I switched to road position again, and immediately noticed that my power readings were higher, especially when climbing (of course). Now, of course, it's hard to be sure that the change is due to position rather than something else, or even just misperception.

I don't know why the trainer is so much tougher, but no question, that's absolutely the case for me.

I am sure that it has to be the biomechanics of the position. But then again as I mentioned, the power on my road bike in a semi aero position was OK. So why the guys on the full lo pro bikes are loosing power must be due to the increased hip angle that being down on the tri bars brings even if the saddle position is the same.

Of course this means that you will go faster due to the aero position. It also says however, that you can get too low and loose more power than the areo payback.

Lots of top riders do not seem to sit that low but obviously are very aero, I find that if I try to go too low thaen the power (preceived) drops.

I guess it is a compromise and time spent fitting the srm to the TT bike would be well spent to get the ideal compromise.

As for training if you train in the TT position using power, use date from tests in that position not your road position.