Weight, it’s a heavy issue – Part 1

Weight, it’s a heavy issue – Part 1

Bikes these days are getting lighter. The UCI limit for a ‘race’ bike may still be 6.8kg but it’s not difficult to build a bike lighter than that (and indeed that UCI limit may well reduce in the not too distant future), especially if you’re riding a bike that’s not at the top end of the size range. In fact, there have been bikes floating around the web more than 1kg lighter than that lower limit. But what are they sacrificing to get there and is a light frame the best starting point for a new build?

While groupsets and wheels continue to reduce in weight, it’s frames where we’ve seen the biggest ‘gains’ in weight loss. It used to be that a sub-1kg frame was light, now we’re regularly seeing frames coming in below 900g and several even below 800g. It’s being driven by improved carbon fibre knowledge and usage, better manufacturing processes and market forces that say lighter is better. If you think back to the days of steel, manufacturers found it easy to market the differences in their frames with how they were made and the lug-work and so on. But then carbon came along and it became all about the weight.

You might think this only applies to super-bikes, but it’s not. Even a Cannondale SuperSix Evo with Shimano 105 groupset features a 950g frame. And that’s a £1500 bike. If you’re willing to pay a bit more, then that SuperSix range tops out with the Evo Nano framset with a price of £3699 and a sub-700g frame weight.

You’d think the likes of Storck and their high-brow persona might be immune to the lure of weight chasing, but take the Storck Aernario. If you opt for the Platinum version as opposed to the ‘standard’ G1, you’ll save 100g from your bike weight and lose £1000 from your pocket. That £1000 could go an awful long way to off-setting the perceived weight ‘penalty’ by spending it on lighter wheels or better components.

Even if you’ve got the money though, do you trade anything by saving weight in the frame? Unlike components, frames are subjected to a lot of different forces in different directions. If you’re a 60kg mountain goat, chances are you’re not going to flex a bottom bracket too much, but if you’re more sprinter than climber (I’m being polite!) who last saw 60kg on the scales in your mid-teens, you will find that you probably can flex a bottom bracket on many lightweight bikes.

This flexing may result in nothing more irritating than a bit of break rub and a feeling of lost power transfer. Hardly the end of the world. But in the shop I have seen and heard about a trend that is worryingly growing in the industry – snapped carbon fibre frames.

Admittedly, I don’t have data on all bikes and breakages, so this is anecdotal and I’m by no means suggesting it’s endemic, but it does seem to be that the lighter bikes are breaking more easily around stress points like seat stays, bottom brackets and head-tubes – areas where material is removed to help keep the weight down.

To give you three I’ve seen in the last month or so: A Neil Pryde with broken seat stays – sustained apparently under heavy acceleration while jumping for a sprint, A Cervelo R3 with a broken seat stay from a minor crash at less than 5mph and a Storck with a crack in the top tube. These are all bikes from well-respected manufacturers who build bikes at the mid to upper end of the price spectrum. How surprised would you be if you instigated a sprint on your next Sunday ride only to find your seat stays in bits? It probably wouldn’t be a pleasant experience.

The first question therefore is, how much benefit are you going to see by spending a chunk more money on a lighter frame when it is compared to your body weight? Let’s say you weigh 75kg and you build a bike that weighs 7.5kg – you’re all up weight with you and bike is 82.5kg. How about if you save 300g on the frame weight? In the grand scheme of things you’ve saved 0.36%. The heavier you are, the smaller that percentage saving is. It’s been said before, but if you want to go faster, a bike fit and losing weight from your waist are better (and cheaper) ways of doing it!

For some further reading on this weighty issue, in part two we’ll look at how to achieve a light-weight bike if you don’t start with the frame.

Also, you might find this article by Cervélo’s engineers quite enlightening, concerning the benefits of weight vs aero…

(A note about manufacturer’s claimed frame weights – they are not exact. There is always variance in manufacturing and you should take a claimed frame weight and expect it to vary by +/- 5% at a minimum.)

Disclaimer: The opinions above are the author’s own. They may or may not represent the opinions of Ten-Point as a company.