Weight Matters: A Study

A small scale, non randomised or blinded, single centre study of questionable methodology and of no statistical rigor at all on the matter of bike weight and type and the effects on average speed acheived

MiddleAgeCyclist RGN, BSc (Hons), DipHE, ALS(i), EPLS, APLS, TNCC

Introduction

A recent post by MrC(1) on the subject of using light weight bikes in preference to more practical ones and the authors current desire to lose 15 kg before getting a Carbon Fibre (CF) road bike raised the question -  How much difference does the weight and type of a bike actually make to the average speed attained? 

History

There has been much effort made by some to reduce the weight of bikes as far as possible in the interest of moving faster(2) but some research suggests bike weight makes no difference to average speeds(3).

Method

It was decided to compare two different bikes over a set course of 15.36 miles. The course includes a large hill climb and fast descent, some straight flat roads with cycleways and a measure of urban, heavily trafficked roads. The two bikes were a Santos Travelmaster touring/commuting bike weighing 18.4 kg in its normal configuration with racks, wheel lock, kick stand and mudguards and a Verenti Rhigos 0.3 CF road bike weighing 9.3 kg. On each ride both bikes carried the same under seat tool bag, the same frame mounted pump and one bottle of water carried in a frame mounted bottle cage. All measurements were done using a Garmin Edge 705 GPS.

While weight is a major difference between the two bikes there are other factors which can also influence performance. These fall into three groups: external factors such as weather and traffic flow; bike factors such as; geometry, gearing, tyre choice and pressure, wheel size and pedals/shoes; and rider factors such as weight, fitness, nutrition, health, clothing and motivation. These factors were either minimised or considered  a difference of bike type and so integral to the results.

To reduce external influences each ride was done in similar weather conditions. Stops were made at the same traffic lights or 'give way' whether or not this was required. This meant a similar amount of deceleration and acceleration was required over each ride. The total length of time stopped was not deemed important but rather the average speed attained while moving. This would therefore minimise any differences in results due to differing traffic flow patterns.

Each bike was optimally set up for one rider (the author). Interestingly this resulted in a similar rider position during the hill climb element while the Rhigos did allow a more head down, streamlined position using the drop bars while descending. Tyre pressures were checked, chains were clean and lubed and the same SPD pedal/shoe combination was used on each bike. Any drag from the SON hub on the Travelmaster was minimised by turning the lights off.

Rider factors were addressed by using the same rider (still the author), wearing the same clothing and riding the course at the same time on each occasion. It was also ensured no alcoholic beverages had been imbibed the night before (honest), the same breakfast and type/level of fluid before each ride had been consumed (two rounds wholemeal toast with a light spreading of butter and Marmite, a large cup of tea and 500 mls water). The rider reported no ill health and was subjectively determined to be well. The motivation of the rider on each ride does demand more detailed discussion however.

A subconscious bias towards one finding or another - essentially what did the rider/author want the results to show - might well influence how much effort was made on each ride. To counter this it was decided to work at the same aerobic effort as measured by heart rate (HR). While the Garmin Edge does have a wireless monitoring capability, The author does not have the required monitor (yet), so HR was measured using a Polar HR monitor with the wrist display mounted on the handlebar. It was decided to aim for an average HR of 135-140 bpm while pedalling on flat/moderate terrain and not to exceed 155 bpm while ascending the steeper section. While the rider could have worked harder it can be argued this may well have utilised gear ratios on one bike not available on the other so it was considered sensible not to 'bust a gut'.

Results

Detailed data for each ride is available. The Rhigos 0.3 Hill Loop is here (and in the previous post) and the Travelmaster Hill Loop here. Essentially it was found for the same rider in similar conditions using the same aerobic effort a lighter bike allows faster travel than a heavier one. The Rhigos loop was completed at an average of 15.8 mph and the Travelmaster loop at an average of 13.9 mph. A difference of 1.9 mph or 13.6%.

Conclusion

Middle aged, overweight men can maintain a faster mph for the same aerobic effort on a 'light' road bike than on a 'heavy' touring bike, all other things being equal.

Recommendations

If speed rather than practicality is required then a dedicated light weight road bike will make a significant difference (to your wallet).

Future Research

Further, larger and more rigorous research would be useful. The author plans a further study to determine if a heavier bike can be lightened sufficiently to enable a higher average mph to be attained. This will be achieved by stripping the Travelmaster of its front and rear rack, wheel lock and kick stand and fitting 'faster' tyres. The author will then ride the same loop and compare data to the previous loop completed on the Travelmaster.

References

(1) MrC. (2011) Mass Obsession. MCRcycling

(2)  WeightWeenies. (2011). [website]

(3) Salmon, F. (2011). Why a lighter bike doesn’t make you faster. Reuters