TT vs adapted road bike

[Gruffy]

What do we think is the real world performance difference is between a full TT bike and an aero road bike adapted for TT'ing?

I'm keen to move into TTs but my pockets aren't deep enough for n+1, so I'm in the process of adapting my Aeroad in the most bang-for-buck way possible. For reference, I'm probably about Cat 3 ability and would hope to be turning out a decent pace. My main goal is long distance TT (100 mile, 12-hour, 24-hour) but training will inevitably include lots of 10s and 25s. The Aeroad has 50mm Cosmics, clip-on aerobars and a saddle I can ride in a tuck, but I'm a bit stretched out and I can tell I'd be better off with shorter and lower.

With all that in mind, what sort of time penalty do you think that would give me on a 10, 25, 100?

[Gruffy]

I've got some Profile Designs V4+ clip-ons installed. The pads sit nice and low on the handlebars and the extensions mount underneath them. I moved the saddle forward and tipped it down a degree. I could probably drop it another degree and nudge it forward another 5-10mm though. There's 20mm of headset spacers which I haven't played with yet. The stem is 110mm so there's options there.

I don't want to go crazy because I still want to use it as a road bike too and I'm conscious that it'll never be as quick as a TT bike anyway. I realise I'll need/want a proper TT bike if I'm going to take it seriously but I guess my question is: am I pissing in the wind trying to achieve anything on an adapted road bike in the meantime? If I'm going to be giving away >10% against others then I think I'd struggle to stay motivated once the novelty of a new discipline has worn off.

The plan might be to look at some filthy-deep wheels and/or a disc first. I can use those on the Aeroad and then when I do manage to get a TT frame I'll already have wheels for it.

[Gruffy]

okgo said:

I think you can get a reasonable position on a road bike - I ride a cervelo s2 to some OK times in that set up. The main issue IMO being that most people should size down on a TT bike from road so you will give up a fair bit most likely.

But it's a race against yourself and the clock. Cat 3 ability riders don't often win opens so it shouldn't be too much of an issue.

I'm too old (for a noob) to be thinking of winning opens in any case. Sounds like the difference could be small enough to tolerate and still large enough to have a credible excuse when I underperform. Ideal then.

[Gruffy]

I suspect my Aeroad may be fairly similar. Aside from the cockpit and the seat post, the geometry differences don't look too stark side-by-side with the Speedmax that was said to have inspired it.

[Gruffy]

I've not done much about it yet and my 2017 goals have shifted a little. I have done a few TT-like sessions out on the road and tweaked the position as a bit of a compromise (favouring road setup). The saddle is as far forward as it'll go and tipped down a degree. The TT position is a little stretched out but it's tolerable for a 10 at least and, in reality, I won't be doing enough to warrant changing it from a road setup. I do think I could get pretty close on the Aeroad though.