In short bike weight probably doesn't matter as much as bike and bike parts manufacturers would have you believe, says Nik!
In an interesting experiment, a cyclist tackled Alpe d’Huez in France four times, varying his bike set-up but holding a steady 275W each time. For the first attempt, he rode his standard bike, setting a time of 49:40mins. For the second, the tyres were filled with water, adding 1.8kg of rotational weight. His time was 52:01mins – 2:21mins slower. On the third attempt, air replaced water in the tyres and the 1.8kg was attached to the bike. His time was 51:34mins – just under 2mins slower than with the unladen bike.
Although these savings are significant, this was an uphill-only trial where weight would have the greatest effect. As soon as a road flattens out or dips downhill, weight becomes less of a factor. If all other factors, such as drag and rolling resistance, are equal over a mixed-terrain ride, the time difference between a 7kg bike and a 9kg bike will be negligible.
So, if you’ve got an especially hilly event coming up, dropping some weight from your set-up is probably a good idea. Prioritise rotating weight – so treat yourself to those lightweight wheels but also consider your pedals. Splashing out on titanium bolts really isn’t worth it.
It’s not all about the bike, though. Losing 2kg off your tummy will work out cheaper, and benefit your running, too!