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Pedal Science Blog: Choose Your Bike For IMUK

Welcome to Pedal Science, the weekly bike fitting blog by Nick Thomas of The Endurance Coach. This week we look at the subject of BIKE FIT & IMUK. 

Over the last 2-3 years we’ve completed numerous bike fits for people competing at Ironman UK. Bikes have varied between road and TT models and some bikes have had tribars fitted whereas others have not. So what is the ideal bike choice and set up for Ironman UK?

The key to a successful Ironman bike is to maintain comfort and achieve the highest maintainable power output (i.e. speed) possible without deteriorating. This can be achieved with a variety of bike set ups but the main considerations which will determine the final set up are as follows:

  • Course profile:

Ironman UK is a hilly course with changeable weather. The route involves a lot of climbing and descending with a certain amount of cornering, decelerating and accelerating.

A TT bike is generally the best bike for Ironman as it’s designed to be fast on flat-rolling courses with minimal disruption to momentum. The riding position is further forward and there is a more direct transfer of power. The position is also more aerodynamic than a road bike so for most courses this would be the ideal choice.

However on a hilly or technical course a lot of the advantages of a TT bike are negated. They don’t climb very well, descending can be twitchy and they’re cumbersome and slow to respond when cornering. The range of adjustability can also be very limited on many TT bikes so the rider is forced into an unnaturally low riding position which is totally inappropriate for a 6-7 hr hilly ride, especially when followed by a marathon.

Aerodynamic advantage also has to be questioned at Ironman UK. There are very few places where many people will be on their tribars at 25 mph so there is little point using a bike designed to be ridden at speed. The fastest parts of the course are the descents and for the vast majority of people riding on the drops would be the most efficient position: aerodynamics are improved but handling is also safer and more responsive.

For hilly or technical courses a road bike can be a better option as they’re generally lighter, more responsive and provide more versatility. A sportive-specific road bike would be the most appropriate choice for many people as they provide a more comfortable ride and enable the front end to be positioned higher, a common requirement for many cyclists and triathletes. The more forgiving ride reduces fatigue during the second half of the bike and the more relaxed geometry enables the rider to dismount and run more efficiently than if they were on a performance orientated bike.

  • Rider ability:

At Ironman UK the faster you are the more you’ll benefit from a TT bike: the slower you are the more you’ll benefit from a road bike. You need to be realistic and choose your bike set up accordingly. By riding the route in training you’ll know what average speed you’ll be capable of – if you’re averaging less than 18 mph it’s unlikely you’ll benefit from using a TT bike.

Tribars or no tribars?

Previous articles have discussed the pros and cons of fitting tribars to road bikes but there are two main factors to consider:

Tribar length:

If the tribars don’t provide a great level of adjustability they’ll be too long and of no benefit as the riding position will be overstretched.

Tribar height:

Many road bikes have compact frame geometry which results in a short head tube and a low front end. Unless the bars and/or tribars can be raised sufficiently the riding position will be too cramped with resulting discomfort and loss of speed.

Tribars need to be fitted exactly right to be beneficial on a road bike and it’s common for the client to have the tribars removed during the bike fit when the above factors have been discussed and taken into consideration.


Your choice of bike and set up should provide the most comfortable and efficient position possible with your riding ability and experience being taken into account. An unsuitable bike set up will result in a poor bike split and an even slower run.

Nick Thomas is the resident bike fitter at The Endurance Coach. He is a fully qualified bike fitter and expert in lower limb mechanics, holding a BSc (Hons) in podiatry. You can contact him using the email address: or see more about his fitting services by GOING HERE.

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