Tuesday, January 02, 2018

The Effect of Frame Design on Hill Climbing

Last July, Simon posted a nice piece on 'The Science Of Efficient Cycling', which, as he said, didn't cover the issue of hill climbing very well.  I'm pretty convinced that hill climbing is a very important part of the cycling mix, and that it is the part where most gains can be made in overall performance. My reasoning is that you're hardly going to go faster downhill, and that on the flat the great wall of air that you're pushing aside is pretty immutable.  But, just maybe, there looks to be scope to do better uphill.  If you could do a little better on every hill of the day, then your mileage would increase with minimal risk to life and limb, and you might have more fun too.

So how could this work?  Conventional wisdom is that climbing is basically Power/Weight.  A light, powerful rider on a light bike will always climb better.  Well, up to a point, Lord Copper ...

Some of you will know my Old Dawes.  It's a nice bike, and with updates over the years it goes very well.  Its fat tyres make it roll nicely and it has a decent turn of speed downhill.  But it's a very poor climber.  Once the Dawes is on a hill, your only real option is to change down and crank away.  Even working very hard doesn't do much.

By contrast, my French Bike is a very good climber.  It responds immediately to extra effort and will spring up a hill.  On the face of it, it looks pretty similar, so why should the performance be so different?

Here's my analysis.  The Dawes is made of good steel - Reynolds 631 - but is built as an 'Expedition Tourer'.  That means that the heaviest gauge of steel is used, with particular emphasis on a stiff rear triangle to carry heavy loads.  The French Bike is also good steel - Reynolds 853 - but is constructed of the lightest possible gauge.  It rides very well, but is not up to carrying anything much.  It's designed for a small bag on the front, and that's your lot.

The French put a lot of effort into this type of bike in the 1950s, the intention being to create a frame that acts as a spring, so that the rider compresses it while pulling up a hill, with the stored energy being released as the pedals go over centre, giving extra impetus.  Sounds like baloney, but it works - and, interestingly, British frame builders never bothered with these ideas.

All right then, if this is such a good idea, why don't people do it now?  The answer is that they do.  Take a look at my Open special:

It's made of carbon fibre, and you'll see that it has very thin, flexible rear stays, a sharply tapered top tube to be stiff at the front and flexible at the back, and it's the best climbing bike I have ever ridden - and, as my Clubmates will attest, I've tried a few.

Looking at the weights, the Dawes weighs about 14 kilos, the French Bike 12 kilos and the Open 9 kilos.  By taking off the bag and the rack I could get the Dawes to about 12 kilos, but I'm confident that this wouldn't make much difference to its climbing capability.  I could bring the Open up to 12 kilos with a couple of bottles and a bag of sausage rolls on the handlebars.  It would still beat the French Bike hands down.

So, my assertion is that frame design is an important element of a bike's ability to climb hills well.  If your bike has a spring in its tail, it will climb better.  Light weight is no harm, quite the reverse, but making the Dawes quite a bit lighter won't make it climb better.

Worth thinking about for your next bike - a frame with the right sort of springiness gives better performance uphill.  If you need panniers, carry them on low-loaders at the front, and let the back of the bike work for you, rather than the other way round.

A Happy New Year to you all,


1 comment:

mike morley said...

Mark very interesting! As an ex East Midlands Hill Climb Champion my own observation is that the shorter the wheelbase the quicker you will climb. In my Heyday age 22 years in 1963 I used to ride an old(1954) Reynolds 531 Claude Butler track bike with 59" fixed. In those days most hill climbers rode fixed and the ability to push a big gear helped the overall time. Of course the engine should also be as minimum weight as possible consistent with good muscle power and the ability to honk at the steepest point of any hill climb was an advantage. My fighting fitness weight was 65.5 kg some 15kg less than now.