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How heavy is my bike?

On the Wednesday evening pub ride I picked up Mat’s bike, a Blue Competition AC1 SL Aero, my god it felt light! Having just manhandled my heavyweight touring bike up the steps to the pub entrance the difference was stark.

I have been riding my old steel fixed recently, and finding that whereas I used to get dropped by everyone whenever the road went uphill, I can now pretty easily stay at the front. I thought that that was to some extent because I was getting fitter. However, back on my Revolution (or the Tank as Mat now calls it) on Wednesday I was again struggling up the hills.

This got me thinking, exactly how much difference will a heavy bike make going uphill? Surely some simple maths will give me a ball park figure…

First, weigh your bike.

Green touring bike: an aluminium framed Revolution Country Explorer – 14.45 kg (including an empty bar bag which is always on, but not the pump).

Yellow fixed: vintage steel track 22.5″ frame – 9.14 kg (with 2 recently fitted bottle cages)

Blue road bike: custom built steel 52cm frame – 9.59 kg

The big surprise was that the fixed was only slightly lighter than the road bike. The Brian Rourke is a slightly smaller frame but does have an extra brake, front and rear mechs, extra chain ring and a 6 speed block. The frame material in both cases is Reynolds 531 steel tubing, so even though they were built 30 years apart, that shouldn’t make much difference.

Next I compared the weights to modern (and fashionable) carbon bikes. The UCI minimum weight limit is 6.8 kg so the most expensive race bikes will be just over that, but what about more reasonably priced bikes? For £1650 a 105 equipped Felt F5 comes in at 8.26 kg, and for £650 you can get an aluminium frame/carbon forked Sora equipped Felt F95 weighing in at 9.54 kg. As the groupsets differ by about £200, you are basically spending £800 for a 1.3 kg weight saving, you could lose that in 3 weeks by being a bit careful with what you eat!

Anyway, back to the point of this article. What difference will those 5 extra kg make to heaving my bike up hills? I really had intended to do the sums myself but found this website: http://www.analyticcycling.com/ForcesLessWeight_Page.html

Putting in data for a 600m 5% hill nearby at Warmington gives a 7.4 second time saving for those 5 kg. That doesn’t seem very much, perhaps the power estimate I used (200W) was out? As the power output goes down, the time difference goes up, but even with a paltry 100W, the time saving is only 15 seconds. My experience on Wednesday would suggest that is way out. I rode up in 2.41, a month ago I did it in 1.43 on the track bike. that’s a huge difference!

Let’s look at hill I have ridden many times, my fastest times from Strava are 3.07 on the tourer and 2.29 on the fixed. The computer model gives a similar saving (6.9 sec) but in real terms the saving was 38 sec. This hill probably gives a better comparison than Warmington because I have ridden it many times and tend to give it some welly to measure my improving fitness so the best times on both bike are probably both set under similar conditions, both mental and physical.

Another hill I ride a lot is at Southwick, again the model gives a 7 second saving for 5 kg, but again real world numbers are different, in this case 46 seconds (1:50 v 2:36).

As a percentage we have Southwick Hill 42% slower, Brigstock to Fermyn Hall (longer but less steep) 25% slower.

What does all this tell us? That lighter bikes ARE faster uphill, doh! However, there must be other factors here as well, as no way should a 5% weight increase affect the times so much. Almost certainly the wheels and tyres will have a large effect, maybe a more significant effect than the weight difference if the numbers are to be believed…a flat road comparison is needed!