TT Aero Figures

[larryt]

I am putting my iBike on a TT bike this week. I will not be able to do my coastdowns/out and back for a few days. Could anyone give me an idea of a rough aero number to manually input until I get to do them? I am 5'10, 155lbs and ride a fairly low flat back position.

Thanks!

[coachboyd]

Do you happen to have a picture of you riding the TT bike?

What kind of wheels will you be using?

[larryt]

No photos handy. Zipp disk with a Reynolds DV46 on front.

[R Mc]

Me: 5' 9", 153

Bike 05 specialized transition, w/zipp vuka front end and 808s front and rear. elbows almost touch, and drop from shoulder to bars = an upper arm almost perpendicular to ground.

The numbers:
aero .223
wind scale .957
cda .233

fric. 7.796
riding tilt -0.3
crr .0065

[coachboyd]

that is somewhat what I was thinking. I would estimate a nice round .250. Of course there are many factors that can influence that. The difference between .245 and .25 is not that much watts.

[tyhaar]

I'm getting some really wacko numbers for my TT bike. I have the unit mounted on topeak extender below the aero bars extended all the way down. It has clear open space to the wind. The wind scale is off the charts, crr seems low, cda seems ok. The watts are nothing compared to my road bike with the same effort and seem 50 watts difference.

Its really hard to do a threshold test knowing they are bogus. The day I did the cals (10 coastdowns and 4 miler) was a little windy but nothing bad. I did all the pre-setup regarding tilt, offset, alt., lbs., and were good. Even checked the offset again before the cals and it was fine?

Can flex in the bars mess with the numbers as with regards to tilt?

I'm going out today and do some more cals and 4 miler (this is getting old for this profile). I would like to get to dialing in my position more than getting my numbers correct which is an ongoing process with my TT bike? Last year my crr was always coming up .00000 ???

I'm attaching the profile to see if some of the experts here can see whats going on. I'll post todays new profile and the winds look low looking at the tree's outside my place....

090323_0008_cal_ride_AB7E2008.ibcd4m

Cal Ride File 3/22/09

(618.28 KiB) Downloaded 433 times

TT Profile 32209.ibp

TT Profile 3/22/09

(334 Bytes) Downloaded 426 times

Update on post : I did 2 hrs. of basically over kill on coast downs and two 4 mile rides to get a profile for my TT bike. I did 45 minutes of coast downs which gave me 15 of them. Did two 4 mile out and back rides also. Did step by step of getting tilt, offset, weight, alt. before the ride started. I did one more offset after riding over to my testing area. The wind was less gusty from the 3/22/09 setup cals and 4 miler.I did the testing a very well protected area with large pine tree's.

Attached is the new TT profile created today from testing. Any experts please let me know how the numbers look. Thanks!

TT Profile 41109.ibp

TT Profile 4/11/09

(245 Bytes) Downloaded 396 times

[tyhaar]

Here's the cal ride file that I could not attach with the 3 file limit per post :

090411_cal_data_TT.ibcd4m

Cal Ride File 4/11/09

(953.88 KiB) Downloaded 514 times

[CRoberts]

I have my first profile and I still don't understand well enough to be sure it looks good before I do a race profile with Zipp 909's and aero helmet. Can someone comment?
I am 6'0" and weigh 170 lbs. Softride TT with internal cables, Hed Aerobars and FSA MegaExo TT Cranks using Rolf Vector Pros for training. The weather report said 8-10 mph wind which is very low for Houston this time of year. The road was not great but typical for triathlons and training and no traffic for the coast downs and only two cars on the Cal ride.

Aero .361
Wind 2.364
Cda .153
Fric 5.854
Tilt -.1
Crr .0057

I did an out and back 5.3 mile test with 22.1 avg mph speed at 198.2 avg watts.

[coachboyd]

hmm, that cda looks to be too low, it could be a result of the high wind scaling. Your hands might be blocking the wind port.

Can you post a ride file so I can look at the wind data for you?

[CRoberts]

I did this ride last night and the real time power data did not match the wind conditions. I was impressed with the auto slope feature (on our tiny man made hills in Houston). I already ordered the remote wind sensor so if it comes in soon my problems should be solved. In the mean time I have an "A" tri in Austin with a 40 K ride in 3 weeks so I need to get comfortable with this tool.

Thanks,
Chris

[coachboyd]

Do you have a picture of your setup with the iBike in place? It looks to me as if you might be getting good wind data, but the low cda is making you see the low watts.

I have attached the same file with a new profile for you to look at. Open this file, then go to profiles->edit profiles-> and hit extract. Send that one to your iBike and try it out for a bit, let me know if the numbers look better. . .but still if you can post a picture of your setup that would help.

[CRoberts]

Thanks for the quick response! I also applied the tweeked profile to the practice tri I did with my buddies this weekend and the numbers are much closer to what I perceived. I don't have a good picture of the set-up, but this shot does show the stem mounted unit hidden by my forearms. I have about 2" between my hands. I'll train with this profile until the remote sensor comes in.

3202_1060706517982_1235494225_30157990_1877447_n.jpg (49.17 KiB) Viewed 11668 times