Not faster on TT bike

[Scabutz]

I think I can answer my own question here but interested in other's view points.

I have a bog standard road bike which has a relaxed (i.e. non aero) position I have also flipped the stem as I had back ache, normal box section alloy rim, crap CRR tyres. I also have a P3 which was selected from a Retul bike fit and fitted by a very good fitter. Note the fit was done for comfort on Half/Full Ironman distance rather than out and out aero. The P3 has deep section carbon tubs and Conti 4000s II tyres.

Both bikes have a G3 powertap hub.

The P3 is new, the roadie I have done 1000s of KMs on. Last weekend I did a hilly 90km on the roadie and averaged 209W (234NP) and 27.3 km/h. Last night I did a tempo session on the P3, 25.8km, 206W avg (250NP), my speed was only 28.3km/h. When I ran both rides through BBS aeroanalyser the roadie comes out with a racing CDA of 0.2907 and climbing 0.4395 at 0 degree yaw. The P3 comes out at 0.3442 and 0.4438.

I am thinking that possibly its a comfort and use thing. This was the first proper ride on the P3 and I probably wasn't holding a good position and was sitting up too often and being overly cautious. I also have a slight problem with the wheel on the P3 in that it seems to be flexing too much - either it needs tightening or the bearings have gone.

Anyone got any thoughts. Perhaps I should ride the P3 more and see what happens with it? I am also getting the wheel looked at by the people who built it.

[anonymous-user]

1km/h faster for the same power then?

[Scabutz]

Pretty much yeah. Am I expecting too much? Was hoping for £4K of bike and £1.5K of wheels to buy me a bit more :-)

More concerned why the calculated CDA from BBS is so much higher on the P3.

The long ride on the roadie had more climbing too, but I guess that means more tanking it downhill. Max speed was 61km/h on the roadie and only 50km/h on the P3.

Planing on doing the same 90km ride this weekend on the P3 so will see what results I get from that.

[anonymous-user]

if you take your half ironman distance, which is a 90km bike ride IIRC, 1 km/hr extra speed is pretty significant isn't it?

Something like 7 minutes or so faster at 28.3km/h than at 27.3km/h

[IroningMan]

7 minutes on a 70.3 bike leg is a chunk, and not bad for a bike you don't ride much - or at all.

[Scabutz]

Cool. Worrying over nothing then :-)

I think as I get more used to it hopefully I will get faster too

[nacnac]

If you really want to compare both bikes you need to back to back test, over the same route on the same day with hopefully minimal variability in weather between the runs. I would chose a closed loop do a couple of runs on one bike, switch to the other and then repeat until you get bored. Try and keep the power the same and potentially split the lap up into a few sectors to try and match where you put down the power in each run.

You could also get into testing using something like the Chung method to work out CdA.

[AyBee]

Scabutz said:

I think as I get more used to it hopefully I will get faster too

This. If you're on the base bar in order to be able to get that power out, you're negating the benefits of the TT bike significantly since the biggest thing to get aero is yourself. If you can get the same power out in a tuck position on your TT bike, you'll be a good few kph faster I'd imagine.

[Scabutz]

AyBee said:

Scabutz said:

I think as I get more used to it hopefully I will get faster too

This. If you're on the base bar in order to be able to get that power out, you're negating the benefits of the TT bike significantly since the biggest thing to get aero is yourself. If you can get the same power out in a tuck position on your TT bike, you'll be a good few kph faster I'd imagine.

Yeah, looking again at the calculations from BBS there are a lot more CDA anomalies on the P3 which I believe are where the software is assuming I am on the aerobars but I wasn't.

It was more about confidence and bike handling as this was the first tiem I was riding the bike and laso the first time I have ridden the carbon tubs in the wet . Don't seem to have a problem getting the power down in aero tuck. Just need to get used to it.