TT bike - differences in aeroness

[Kermithimself]

Simple question:
How much difference is there between a really aero timetrial bike(P5, DA, etc) compared to say a not so aero timetrial bike(Planet X Stealth, Argon 18 E-112 etc).

According to some research I found online you save about 20 watts going from a traditional roundtube bike to a TT bike(same setup on both), but what about differences between time trial frames in itself? Are we talking 20 watts or 5 watts?

[Machinenoise]

My data (extrapolated from Chung analysis on road) showed between 8-13 +/-5w in a 56cm 2007 P3 with USE tulas (my bike) and first gen Trek speed concept 9.9( 8w+/-5w) and Shiv with nosecone(2011,12w+/-5w) with standard equipment (ie the proprietary aerobars those bikes came with from the factory.) +same wheels. Both bikes setup my exact stack reach saddle height et cetra, so should have been near identical body positions. Speed concept tested at lower end and shiv at higher end, the error implicit in onroad testing with low numbers of repeats (3 out and backs per bike.) Meant the large overlap. At a push i'd say the difference is under 7w ish for Trek SC and 11w ish for Shiv.
So i'd GUESS nearer 20w from a less sleek frame to a p5 or canyon aeroroad (or equiv). Haven't got any similar sized friends who want to loan me their more modern superbikes for comparison! Especially on days with next to no wind to take into account. maybe 14W from P3 to P5? Have scheduled some money to go to the mercedes windtunnel when I buy a new TT bike so will do a P3 versus the new one and post the data on here. Don't hold your breaths though, it'll probably be spring 2016...

Edited for clarity:- with only 3 repeats per bike in real world conditions, it's practically impossible to get below a 5w resolution level, without meticulous preparation. Unfortunately I didn't have that kind of time hence the result. My data points did show tighter correlation than +/-5w but I don have sufficient confidence in the
to report differently. The 8w and 13 w figures respectively refer to mean values of the 3 reps. Cda of the p3 which has more data from multiple experiments is 0.215. Tests were run at 300w plus or minus 10w on a flat road, speeds 44-45kph. So relatively low yaw angles which is more relevant to my TT background. So relatively small changes, 0.25kmph faster for the Trek SC and nearer 0.5kmph faster in the shiv for the same 300w power. At lower speeds differences will be smaller.

[wingguy]

Hang on, is that results between 8 and 13 watts with a 5 watt margin of error? That could mean the true difference is between 3 and 18 watts. Or was the plus or minus 5 watts redundant?

[jekyll man]

I think there's actually very little difference between the good and not so good bikes.
set up appears to make more difference than the base bike used.
Certain frames work better with certain wheels and at differing yaw angles.

A lot of the newer "TT bikes" seem to be aimed more at the triathlete market where speeds are generally slower / yaw angles greater.

From reading snippets , the P3 is still as good , if not better than most of the new stuff

[Machinenoise]

Hang on, is that results between 8 and 13 watts with a 5 watt margin of error? That could mean the true difference is between 3 and 18 watts. Or was the plus or minus 5 watts redundant?

Edited original message for clarity of explanation, two different test bikes versus p3 baseline. One lower than the other. And yes the data is very hazy with such errors but it gives you a ball park idea of the scale of differences. It's not like I'm reporting wind tunnel data here!

[davidalone]

most of the gains are in position, rather than the frame itself. I would say 20 watts is abit generous. MAYBE between the absolute most aero frame out there (P5, superbike) and the most un-aero dog frame there is ( round tubed bike , just with TT geometry) you'd get 20 watts. I'd guess the difference between most superbikes and 2nd tier bikes ( e.g. older cannondale slice, older scott plas,a older trek equinox) is between 5-10 watts. that and assumign you're riding at 30mph.

overall, not really that much.

[mattr]

Probably more differences to be found by fussing over details of the set up, choosing suitable wheels/tyres and putting your number on properly.

Unless you've already done all that.

[grid256]

Some good stuff here. Don't forget to factor in the serviceability of the frame. Or I should say, what will likely give you a nervous breakdown while re-cabling. I've said it before, but the Shiv TT is a piece of cake to work on and Tony Martin seems to do ok on it.

[WMW]

My data (extrapolated from Chung analysis on road) showed between 8-13 +/-5w in a 56cm 2007 P3 with USE tulas (my bike) and first gen Trek speed concept 9.9( 8w+/-5w) and Shiv with nosecone(2011,12w+/-5w) with standard equipment

Good info! Thanks for sharing that. It is difficult to do these tests properly and accurately.

A P3 with USE Tulas is no slouch, so I think 8-13W is pretty significant at that speed (44-45km/hr). There are lots of aero tests around that show similar gains for the good frames, so it's not surprising.

[mjduct]

Thanks for saving me money on upgrading my aluminum 2008 specialized transition!


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[djconnel]

duplicate

[djconnel]

AeroWeenie has a good collection of data. The answer is "yes". This was especially true around 5 years ago, for example the Scott Plasma was what I'd call "pseudo-aero", with deep down and seat tubes but a fatty head tube. But the competition at the top has increased.

Comparing a Trek to P5 is comparing two excellent bikes. It's not like comparing some generic thing designed to look aero but little more.

That said, if you don't (according to specialized measurements) shave hairy legs, wear tight fitting clothes, use good wheels, etc, any aero gains of one time trialbike versus another are squandered.