Aero Road Bike vs TT Bike for mountain IM70.3? | 80/20 Endurance

Aero Road Bike vs TT Bike for mountain IM70.3?

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  • #12061

    Hi All

    Im seeking the wisdom of the forum! I am scheduled to do the Aix en Provence IM 70.3 in September (twice rescheduled). There is 1100m of climbing over the 90km bike course. My question is this: Do I ride my Aero Road Bike or my TT Bike?

    The course is basically either ascending or descending, with some switchbacks on the descents. The biggest ascent has 6-8% gradients. I’ve done the bike before on my TT bike (equipped with carbon wheels and calliper brakes – its a specialised Shiv), but never really felt confident descending (brakes smoking etc). On the ascents my gearing (52-36T with 11-28T at the rear) and the weight of the bike means its really quite hard!

    On the other hand my aero road bike (Specialised Tarmac SL7 Pro) is very light, and has disk brakes, corners like its glued to the road, and goes up hill like a rocket.

    I have read some articles that indicate that TT bikes always win for amateur triathletes in terms of higher average speed for the course, but in this case Im not so sure. Im not the strongest cyclist, so bike choice is quite critical for my race time!

    Any advice?



    Matt Fitzgerald

    Hi Gareth,

    Are you familiar with the website It is set up to answer the very sort of question you’re asking.

    The physics of cycling is not my area of expertise, but I do know a thing or two about endurance psychology. If I were you, I would choose the bike you’re least likely to second-guess when you’re out on the race course. You’ll ride faster if you’re confident on your machine and your head is fully in the game.


    Hi Matt – Thanks and Indeed a fully paid up subscriber to Bestbikesplit! However, I find that (as ever) the outcome is only as realistic as the input! I’ve gradually nailed down my bike Power for 70.3, which is a bit lower than my FTP / watts per kilo would ideally recommend (around 75% of FTP – at least indoors on Rouvy).

    The bike is my weakest leg, and I am just getting up to what I would consider a reasonable bike time without completely sacrificing the run!

    I agree with you on the psychology part – I tend to be more aggressive and comfortable on my road bike than the TT on descents. Overall best bike split indicates a modestly faster time on the road bike (few minutes), but for me it’s probably in the noise ! Hence the request for advice, and I agree with your suggestion on level of comfort!



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