Brian's Blog

…one man's contribution to the Weeeeerly Wild World

Limits of Adhesion

Last week was a week of glorious sunshine. On the best day I was down to jeans and t-shirt when out cycling. On Friday I was called out to visit a client, he’s a farmer and lives at the end of a long gravel track. As a pulled off the road onto this track my front wheel slid out. Luckily, through a combination of the tyre finding some more stable gravel to top it sliding further, and my instinctive reaction to sort of lurch the bike up, I managed to stay on the bike and even keep pedalling. My left foot had also immediately pulled itself out of the pedal strap in preparation for a fall. It was a close one. The warm week had lead to the gravel track being extremely dried out and dusty, which I hadn’t taken fully into account when I arrived, so this, along with simply too much speed as I overconfidently joined the track had been a cause of my almost demise. All right, ‘demise’ is a little extreme, but I would have met with a grazing bump had I actually come off – this is one reason why I wear gloves all year round (fingerless ones at least), just in case. I came off a moped onto a gravel track during my foolish high-school years, so I know what a mess gravel can make of flesh.

adhesion1The road sweeps round to the left, and I turned off left onto the gravel – not so grippy when dry.

Then today I was off to do a spot of shopping, taking a route I often take. Turning off one road, which requires a sweeping left manoeuvre and then sweeping round to the right – all which can be taken at speed, I suppose at between 20-25mph, which in a 30mph zone is fine, right? Today I don’t think my speed was any greater than usual for dry conditions, but as I leaned my bike in to take the left, cutting in close to the apex, mid-corner my senses detected a slide. I’m riding a road bike, a ‘push-bike’, not some MotoGP or Superbike, but at times it can feel like that as I hunker down and take a bend at speed – it’s thrilling really! But when it goes wrong it all happens so quick, like within the smallest fraction of a second, but I feel it, and I react, bringing the bike a little more upright and allowing myself to travel out wider, on this occasion across the white line into the other lane. It really does remind me of motorbike racing, the way the riders can skilfully bring the bike down so low in a bend, you can see it is on the limit, actually sliding a little, but they manage that slide. On my bicycle my instincts always prepare me for this particular junction, first as I approach the turning to be aware of cars approaching from behind (I’ve had one motorist come round me on the junction and effectively cut me up – preventing me from travelling out wide as I normally would, and had I not been aware of this and let up on my speed I would have met with the side of their car) and these days I like to keep out wide before the turning, even indicating late, to prevent motorists from considering a pass – my speed is adequate for such a pass to be foolish, but some motorists just see a bicycle and think “slow” without actually judging a cyclist’s speed fairly. Further, my instinct leads me to look ahead so that I can intuitively bring my speed down ahead of time should there be oncoming traffic – if there isn’t then I have space on the road to play with, or slide into, or I suppose, come off into without meeting with another vehicle should the worst ever happen.

adhesion2Turning left here is fun to do at speed, with a sweeping right-hander to follow.

My last ‘almost off’ was some years back on a wet road which had a film of mud on. Again it was on sweeping bends that I like to take at speed, but on that occasion the front wheel slid out, and ‘somehow’ my reactions counteracted the slide and I somehow stayed ‘upright’ and on the bike… albeit ending up off the road and my pedal collecting some grass. That was a close one, and even though I laughed at myself thereafter I have always taken those bends a little more cautiously since.

adhesion3It’s down-hill here, and the sweeping right-hander is nice to ride.

continental_contactI’m confident on my bike because I ride so often, and I like how my senses guide me, and in these cases I love how my body reacts in these split seconds when, to be fair, I’m a little too eager or I have misjudged the limits of adhesion between tyre and road. I’m not foolish, I plan ahead and respond to the conditions and what’s around me – this happens both consciously and intuitively. I’ve not had an actual off on my bike for over a decade (black ice and a pedestrian were to blame for the last two), but at the same time I can’t ignore these little hints, these little warnings telling me a limit has been reached or for a spit second, exceeded, and within the space of four days I’ve had two hints. I’m wondering if my Continental-branded tyres have lost grip with age. The front wears slowly and is a few year’s old and while still in good tread I do now wonder if it has indeed lost some of its gripiness and should be replaced regardless.

Some years back, when I was in my 20s (which I’m sure is relevant!) I bent my last car when I managed to spin it round on a slightly wet back-road at a relatively slow speed (but obviously too fast for the conditions). My car collected a farm wall as it span round and I came to a halt facing in the opposite direction. Luckily no other vehicles were around. I had done the silly (but fun) thing of changing my car’s suspension very recently, which had obviously altered its handling, and on that morning my car had already given me a hint that I was pushing a bit too much speed on bends for the grip provided by my budget tyres – I had felt the hints of a slide a few minutes before on a previous bend… but I was not used to feeling a car do that, and I wasn’t aware of how ‘close to the edge’ I was, and I ignored the hint.

The moral here, is to not ignore the hint, and if you ignore two or more then you may be pushing your luck!

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One comment on “Limits of Adhesion

  1. Pingback: Limits of Adhesion #2 | BMH Online

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This entry was posted on 27 April, 2015 by in Cycling and tagged , , , , , , , , , .
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