A test: TT bike vs road bike with TT set-up

Club member Alastair Macnaughton has carried out an in-depth test to compare a TT bike against a road bike in a TT configuration.

While some people swear by the pure time trial (TT) bike for speed, others reckon you can gain as much advantage with a road bike set up like a TT bike. Alastair decided to put two bikes to the test.

He writes: In an attempt to shave a few seconds off the bike leg of my triathlon races, I decided to buy a full blown TT bike for season 2018. Up to this point I did what many other triathletes do, I “aero’d” my road bike as much as possible.

My initial hope was to save off around 40 seconds in a sprint triathlon and 60 to 80 seconds in a standard distance triathlon using a dedicated TT bike.

However, having bought the TT bike and taken part in club time trials and triathlons I had the distinct feeling I wasn’t any faster.

In fact, it appeared I was slightly lower.

The two bikes.

I initially put this down to one, or a combination, of the following:

  1. I was a year older (VO2 Max can drop circa  0.5-1% per annum)
  2. My bike fit was poorer on the TT bike
  3. I wasn’t technically capable of riding the TT bike and less confident.

As the season went on I was able to address all of the above and eliminate them as possibilities

  1. My VO2 was very similar to the previous year and some of the TT times were around 4% slower. This accounted for higher then the typical degradation for age. My FTP had also improved by 5% from the previous year.
  2. I had a professionally conducted bike fit on the new TT bike. In general, the TT bike position was more aero and felt more comfortable than my aero’d road bike that I’d set up myself.
  3. It was true at the start of the season that I wasn’t technically capable on my new TT bike, but as I rode it more I was able to race at full gas, especially on straight flat courses
The power pedals.

Many more variables

I was aware, too, that there were many more variables associated with comparing a new bike from its predecessor a year apart. Even on similar courses, weather conditions, training load etc play a big part.

So, I took the decision to try yo run a trial of one bike against the other on the same morning. What follows is an account of those findings, not scientific, but potentially enough to make an informed decision for my specific situation.

The test

The plan was to do a number of pieces (three or four) on a course that would hopefully reflect a typical “real- world” scenario. The plan would be for me to swap bikes between each piece and to record as much data as possible (Garmin 735XT plus Assiamo Power Pedal).

The plan was also for me to try to maintain a similar effort for each piece. I left it at three or four as I wasn’t sure if fatigue would start to play a significant part.

The course.

The Course

I used part of a locally recognised 10-mile TT course (along the A77) for the trial. It is undulating with slight bends and one U-turn at the halfway point. It is 5.4 miles (8.67km) in length with 33 metres of elevation. I thought this was enough variability to present a “real world” environment.

The cyclists

My daughter’s boyfriend, Frank Murray, joined me for the trial, in part to provide someone to chase and to also provide some invaluable input.

I’ve been taking part in triathlon for seven years and I could probably be best described as an aspiring age grouper.

Frank had just recently moved into cycling in the previous four months from performance rowing and he had never been on a TT bike before or tried a time trial.

We are also the same height and weight and so he could use my setup on both bikes.  

Cyclist comparisons.
Bike comparisons.

The following data was gathered from my rides on the different bikes.

The results.

My results

The road bike ride was the fastest overall with a slightly lower pulse, slightly higher power and slightly higher cadence, although all the results are probably within a margin error that would indicate little difference.

So, for me, it would indicate no significant difference between the two bikes and therefore no benefit for the expense of owning a TT bike.

As our initial plan was that Frank would be involved as a motivating factor, we only had limited recording of his data, namely the time taken, the average speed and heart rate. 

What was interesting, however, was that Frank was significantly faster (by more than 30 seconds) on the TT bike than the road bike.

Frank’s results

In trying to understand this, the only conclusion we could come up with was that Frank’s additional speed was having a bigger impact on the marginal aero advantages of the TT bike.

This was further confirmed when breaking down my own splits per km as shown below and looking at the gradient of each section.

This seemed to confirm our findings in that the downhill sections were faster on the TT bike, when the speed was higher and the aero effect maximised.

TT vs road bike: The conclusions

  • The benefits that I had been looking for in a dedicated TT bike versus a TT’d up Road bike only occur if the rider is capable of speeds averaging between 40-50 KPH (or an FTP of 300W plus).
  • I discounted any lack of flexibility on my part, in that the power output for both bikes were comparable and within the margin of error.
  • I concluded that I was better off selling my TT bike and going back to the flexibility of my road bike that can be configured into a TT bike when needed.

And Frank? He is now the proud owner of shiny new TT bike.

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