Checking Bike After Crash

bike-dog

Hi, I'm hoping you guys can give me a bit of advice. I had a sore crash a couple of weeks ago, coming off while descending Honister Pass in the Lake District on a particularly wet and miserable day. I had just climbed to the top, and then started down the 25% drop when my back wheel started sliding away from me. I managed to gain control, lost it again, gained it, lost it, slate wall, ground, ouch. My bike and I were picked up by a very friendly and helpful bus driver and taken to Keswick Hospital where I was patched up...

Anyway, I'm now home and although a little bit sore still, my thoughts are turning to my bike and what I can do to get it back on the road. Any obvious things that I should be checking for? Why would I have my back wheel slip away from me (it had been doing that on a dry descent that I had down the previous day)? I'd rather not pay for my lbs to look at it...

Any advice warmly received!

Monty Dog

Your choice of tyres and pressure probably had as much to do with your slide as the bike itself - particulary if it's been raining after a dry spell - lots of people braking hard on the steep downhill will leave a residue of rubber and oil which can make the road slippy. Rather than 'riding' the brakes in the wet, which gives cramp in your hands/wrists - try letting go more and only apply the brakes hard when you need them - brake early though to scrub the water from the rims. Also look at using softer brake pads and adjust your brakes to 'bite' more progressively. In terms of your bike frame alignment - best you put your frame on a workstand and check that the wheels are inline and parallel when looking from behind. Loop a piece of string around the headtube and mark the mid-point. Stretch either end back to the rear hub spindle. Release the string and make sure that the distance from the centre to the end of the string is the same on both sides - if it varies by more than a few mm your frame may be 'twisted'. Finally, check the rear mech hanger alignment too - the rear mech cage should be vertical and in-line front-to-back.

Dorian Gray

Hi bike-dog, what kind of bike do you have? If it's carbon there is a chance (though I would say a low chance) that the crash caused invisible damage. With metal frames it's easier to see damage, i.e. a crack. You know how you fell, so look for damage on parts that would have contacted the road. If the bike looks okay, doesn't creak any more than it used to, and rides in a straight line with hands off the bars, then I wouldn't worry any more about it.

As for you, all the best as you mend, and make sure this crash doesn't keep you off the bike!

Your back wheel slid out because of lack of traction. Traction varies from tyre to tyre and depends on the conditions. But each tyre in a given set of conditions has a maximum traction, beyond which it will start sliding. We call this the "traction budget". You can spend that budget in any direction: forward, backward, sideways. If you're going around a corner, and you're spending the entire traction budget on keeping the bike turning, there is nothing left for braking or pedalling forces. So if you touch the brakes at all, or pedal at all, you exceed the traction budget and the tyre starts sliding. By going slower you reduce the sideways force required to keep you turning, thereby leaving a bit of the traction budget for braking and accelerating. But if you leave too much of the traction budget unused then your speed is slower than it could be. A balance has to be struck.

The solution is to judge your speed so that when you brake or accelerate while turning, the total traction required does not exceed the tyre's traction budget. Doing this in real life isn't a science, and you get better at it with experience. It's all about choosing the right line around the corner, braking smoothly at the right time with the right force, and paying attention to the road surface and camber so you can avoid slippery patches (gravel, puddles, road leaning away from you, etc.).

passout

Look at the headtube - it's often a weak point in crashes. Look for thin cracks, I found this on an alu frame after a similar crash in the lakes.

What was said earlier about car tyres leaving a residue on busy (touristy?) passes/hills is very true. It's a summer thing and ususally happens in the wet following hot/dry weather for some reason. Can be very slippy - I found the same when I lost it on Ferry Hill near Sawrey in the Lakes. I actually slid for meters it was so bad - even walking to collect my bike was a little tricky. That was the worst I've seen it. I can imagine Honister would be bad - it's difficult at the best of times.

My only advice would be brake before entering a corner - even more than usual. I appreciate that on Honister this is not easy advice to follow. Skids can sometimes be controlled (if you've got some room) but it's obviously best avoided. If you go fast in those conditions it is always going to be risky.

John.T

Do most of your braking with the front brake and do it before the corner. When braking your weight is transfered forwards so the rear wheel is more likely to skid while the front is loaded so can take more braking. Just use the rear brake to keep the bike stable. Practice braking hard with the front brake and try to find the point when the rear wheel is nearly skiding but not quite. This is the point of maximum deceleration. When you have got the feel of this in the dry try it in the wet, carefully. You have less front brake available so can use a bit more rear. It is all about feel and practice.
If the wheel is locking even under light braking you may have a bent rim.

bike-dog

Thanks for all your replies... bike frame looks okay, and I've got all the damaged gear replaced under insurance (approx £300!!).

I should have mentioned that the crash happened on a straight bit of road (albeit at a 25% descent). I think that it was a crap day, with crap weather, with brakes that were crap, with a knackered cyclist who wanted to be home.....

Grrr.....