rruff

A wide butt is a bigger problem...

patentcad

Not really. I would like an answer to the question about body weight on a flat course. Are w/kG so important if you're not climbing? I would guess that if you're putting out 290 watts and averaging 22 mph while other guys are doing 15%+ less and averaging 26 mph it's either an aero issue, a w/Kg issue or both.

mike868y

my elementary and almost certainly incorrect assessment tells me that if it is totally flat than weight would only effect 2 things: acceleration and normal force (thus, friction), which both seem like they would be negligible in a tt, so my guess is no. but, since my guess is no, the answer is probably yes. get it?

patentcad

Does it matter?

mike868y

no. but because no, yes.

tadawdy

No. Then it's Watts per unit of drag (W/CdA).

rpeterson

Weight will matter a little in speed, but remember, if we compare you (I'm going to assume 75kg) to me (54), I'm going to be a scrawny little bastard standing next to you, which means smaller arms, legs, hips, shoulders, chest, etc. All the little things add up, and a much smaller body in weight is probably a much smaller body to the wind.

waterrockets 

I see. Perspective. I've got about 3/4" clearance behind my elbows.

guadzilla

I'll give it a shot. Am putting the TT bike on a trainer and playing with fit this week anyway. One question, though - if I move the saddle back, wont that close my hip angle?

guadzilla

I am guessing it isnt so much body weight but body profile. The small, skinny guys like Nate are obviously a lot more slippery than bigger guys who also have a bigger profile (and who, even in the same aero position, have a greater cross-section and so have greater drag).

But what is throwing me off is Tom vs WR - WR is leaner than Tom but seems to have a much higher Cda even though his position looks good.

Any aero gurus here care to chime in?

tombailey

One consideration from Saturday and the numbers I posted - it was windy (mostly cross, some head, some tail). I don't understand the science but I suspect a bigger guy has some advantage in those conditions. Also had a disc wheel cover. In other tetsing I've required around 300W to go 25mph (same bike/position but no clown hat or disc). So it seems like conditions yesterday assisted me somehow.

Position-wise I'd guess I look similar to WR. Probably slightly flatter back, arms maybe a fraction lower, and forearms flat.

EDIT - I do have problems with knees hitting elbows (long legs, shorter torso). So I am slightly "supermaned" and saddle is slightly farther back than I'd like.

timster

FWIW, I did 56:07 (26.7 mph) on that same course Saturday with 292 watts. I'm not really a big guy - 5'11" and 150 lbs.

I have a cheap TT frame, disc cover, and aero helmet.

https://connect.garmin.com/activity/94890724

waterrockets 

I don't see Tom's pic.

I think my height just costs a lot. I can get my torso to look like other torsos, but my upper arms are long, my legs are long, and my feet are big. There's no way to overcome that other than with power. Even if I look thin, proportionally, someone with my same build on a shorter frame will have narrower shoulders and hips too.

Also, my reported power number is for the bike pictured w/out the wheels. Think 32h alum clinchers. I would say just in equipment alone, I'm looking at 20-30W in drag. Round tubes, road bars, road shifters, training wheels, training tires. The wheels in pic above were there due to RX's generosity and assumption that our "B" team had a shot at the TX state TTT title in the 35+ category (we won).


Would it help to slam the saddle forward and move your base bars forward the same amount (bringing the pads with them)? That would leave your legs back there a bit, and wouldn't affect your arm angles.

ridethecliche

Your wives/gfs are shaking their heads in advance...

merlinextraligh

Approximately 450 watts. Of course that's on the tandem.

tombailey

No pics of me. I'm built like you. Maybe a little wider shoulder and 2 inches taller. Our overall height on the bike is always going to be big.

Not much room for changes on the current bike, but am just building a TT bike so will have the opportunity to work on fit.

waterrockets 

Got it. It might be down to equipment between the two of us, but aero positions are a lot more involved than what we can see in pictures. You may just have lower drag because of something I'm doing that looks good on paper but loses on CdA.

I still need to get out for some terminal velocity testing sometime. The thing that sucks is that it's always windy in Austin. I might be able to beat it at 6am sometime, but certainly not every day.

kleinboogie

Those are probably pretty close for someone fit. I'm 6'2" 205lbs. My last TT was flat and had a 3-5mph wind blowing. I did 23.9mph that needed 261 watts avg. That included a wheel cover, 404 front and most all the other aero stuff except for a TT frame. I used the Supersix instead. Now that I have a TT frameset and hopefully more fit I'd like to see that speed increase for the same watts or the same speed with less watts.

Generally with size comes power at the price of climbing ease. So flats and descents are my friend. Climbing I'll get passed by damn near everyone. Just got to ride your strengths and hold on when you're in a situation that doesn't favor your style.

I'll let the experts fill in the details on weight and aerodynamic drag. I just try to lessen both.

RChung

https://forum.slowtwitch.com/gforum.c...935452#2935452

SalsaPodio

Just for another data point, here is a 12k tt I did Thursday, out and back. Eddy Merckx. 15-20 mph tail wind on the way out. I'm 5'10" 155 lbs

guadzilla

Ok, that makes sense and puts you in the same 250-260W ballpark as well in full aero gear.

waterrockets 

HMF

I think I read somewhere that "Armstrong was doing 38mph on the flats" in a TT once. At first I thought, that's a ridiculous exaggeration. With a tailwind perhaps, but c'mon. After reading this thread I can see it's possible. In an interview a long time ago, Hincapie said he'd been working on threshold intervals at 500w. Armstrong is probably around the same.

That blows my freaking mind.

Grumpy McTrumpy

sounds like a typical phil/paul exaggeration.

KendallF

Here are some non-aero #s from a couple of weeks ago in St. Louis. Flat, very windy out and back, Merckx style with my travel bike including Gatorskin tires, a huge seat bag, a triple, hairy legs... I had it all going on!

Total Elapsed Time 00:23:00
Distance, mi 8.79
Work, kJ 406
Temperature, °F --
Average Power, Watts 254
Average Cadence 95
Average Speed, mph 22.89