Tyres for icy roads

Northwind

That's all well and good for high grip situations but on ice it's just not relevant- just like the larger contact patches. There are many things you can do on a bike to increase or decrease traction, but nothing you can do to increase the coefficient of friction of the surface you're riding on, which is the limiting factor here.

When you reduce the level of traction, and subsequently braking force, available to this extent the transfer of weight is negligible, and the bike's stance doesn't change appreciably- there's insufficient braking force to compress the forks, for instance. . And as the bike's input into the level of traction is so negligible, the usual fore-aft and vertical weight biases also become trivial.

Understand, I'm not saying that your understanding of the dynamics of a motorbike (or pushbike) are incorrect- I'm saying that the factors involved here are sufficiently different from everyday riding that the normal model stops being useful. The skills of riding a motorbike on tarmac are not the same as riding on ice for the same reason.

<ooh, you edited! That's OK, so did I>

diy

OK I understand your point now. Although I still think a road/race bike (cycle) is more likely to go at the front on ice, than a mountain bike, for all the dynamic reasons stated (i.e. not tyres,which also play a part)

Northwind

I have to admit, I don't really understand the physics of why increasing the weight on a wheel on ice seems to make slides worse- I can work out why it doesn't have the usual benefits but it still seems wrong that sitting further back seems to make the wheel less likely to slide uncontrollably, it's a bit beyond me. I guess I can rationalise it that there's less force pushing the front of the bike down once it loses traction, but that doesn't feel right. You've obviously got a better grasp of the physics of it than me, can you explain it better?

On my old racer I used to sit right back and on the flats, I never did it but I'm assuming that riding in a crouch on the drops on ice is going to **** you up Even if only because of the reduced ability to react, but I don't think that's all. (also, having your hands off the brakes can be very useful! No more temptation)

But that to me is down to the rider not the bike, you can adapt a fairly upright position on any sensible road bike I reckon. (I ride on flats on the road now so I'm relying on old memories)

diy

Its all explained in that link, but to explain it in really simple terms. Its to do with the way the bike pivots around the centre of gravity under acceleration or braking (and cornering but on a different axis).

Why do you push low down when you are trying to shift a wardrobe across the carpet rather than high up?

Because the force will make it want to pivot on the cog. if you get the pivot point low down it will slide. and its why big scooters will break away at the first sign of a damp patch

To maximise braking you want all the mass over the rear to lengthen the pivot point and because its going to transfer forward under braking. Hence leaning back reduces the chance of a skid. It also moves the cog further back and increases the balance of grip front to back.

Northwind

What I was meaning isn't so much how it changes whether you skid, but how you skid...

antfly

The point he made about the centre of gravity is a good one and makes sense, a light road bike has a higher sense of gravity and so when it becomes unbalanced it will go over quicker, there is no slide to correct because it happens instantly if you are braking or turning. You see it every year in the T of F when riders overbrake on a bend and go straight down and it`s not even icy.

Northwind

antfly wrote:

The point he made about the centre of gravity is a good one and makes sense, a light road bike has a higher sense of gravity and so when it becomes unbalanced it will go over quicker, there is no slide to correct because it happens instantly if you are braking or turning. You see it every year in the T of F when riders overbrake on a bend and go straight down and it`s not even icy.

Nothing happens instantly, and there's always a slide, that's why you crash.

antfly

You`re nitpicking now.

diy

antfly wrote:

You see it every year in the T of F when riders overbrake on a bend and go straight down and it`s not even icy.

Yep, pivoting nicely around their centre of gravity. Which is probably around the handlebars.

If you look at the youtube pics of people drifting bicycles apart from the fact that they position their weight forward. they are almost always upright due to the high cog. whereas motorbikes can be cranked over..

Northwind

antfly wrote:

You`re nitpicking now.

I'm really not. There's always a slide, and though it might be too fast for you to catch it, it's never instant.

The TDF example is another one that doesn't apply, it's not the same situation- they're riding with the weight very heavily biased forwards, and they're not riding anticipating a skid. They're also intentionally pushing the envelope, which you shouldn't be doing on the road full stop least of all in icy conditions.

Now, if you ride like that on ice, you have no chance whatsoever, but that's why you don't. I can't repeat that too much, if you hit ice without being prepared for the possibility of a slide, and without planning for reduced grip, you're most likely going to crash (and then probably say "Oh, I had no chance, it was so fast". If you're prepared for the possibility, and you know how to act on that knowledge, and if you ride appropriately for the conditions, then it's very different.

antfly

Have you ever managed to correct a skid on a drop bar 23mm tyred road bike on a sheet of black ice?

Re. the TDF riders, i`m not referring to the sprint finishes. The rest of the time, apart from the speed I don`t think they ride that differently from me when i`m on my road bike, the geometries of the bikes are very similar to mine. Anyway if you have to ride as if you`re premanently expecting ice it wouldn`t be a lot of fun and might not save you anyway, and as I ride mostly for fun I prefer to get the mtb out and go offroad, like today.

Northwind

antfly wrote:

Have you ever managed to correct a skid on a drop bar 23mm tyred road bike on a sheet of black ice?

Yes. That's pretty much what I've spent the last pages telling you. I'm not just throwing out random comments here... Of course, I wasn't riding on the drops, because that would be moronic when there's ice around.

TBH there's obviously not much more to say in this thread, your last post says it all- if you're choosing to ride in a way that makes you more vulnerable to ice, that's your call, just don't say a crash was unavoidable when you've chosen to put yourself in that position.

antfly

Northwind wrote:

antfly wrote:

Have you ever managed to correct a skid on a drop bar 23mm tyred road bike on a sheet of black ice?

Yes. That's pretty much what I've spent the last pages telling you. I'm not just throwing out random comments here... Of course, I wasn't riding on the drops, because that would be moronic when there's ice around.

TBH there's obviously not much more to say in this thread, your last post says it all- if you're choosing to ride in a way that makes you more vulnerable to ice, that's your call, just don't say a crash was unavoidable when you've chosen to put yourself in that position.

OK
In which case I doff my cap to you.

I was only on the drops because I was going downhill and it gives me more control, but you`re right, I like to ride fast that`s why I bought a racing bike.

Northwind

I bet you 10p I'd have crashed if I'd been head down and on the drops mind! I should apologise to you, that "moronic" comment was unneccesary. I like to ride fast too, I just think there's times when it's not the best idea.

antfly

Apology accepted, i`ve been called worse.

Northwind

I didn't exactly mean to call you that :oops:

captainfly

I went out on wedensday, mainly road, the teocali was wearing geax booze street/dj tyres (40psi in a warm utility room) and was hanging on far more than I thought possible, it seemed to be gripping the layer of frot on the top of the ice seriously in places where cars were spinning wheels I was having high rolling resistance issues, go figure, I was hoping for some slip and slide but no the front wheel gripped like grim death under breaking only a delberate rear lock up got me sliding.

Vaudevillevillain

Fell foul of the ice this morning. Wanting to do a little 10 mile all-road route round here, which is 90% side roads and country roads, and called it off before we began as my mate came off coming up my street to meet me. Black ice in patchy sections was hard to spot and we decided discretion was the better part of valour, as it was likely to be the same on our route. Had a little go down the street on my knobbly 2.1's and it was dicey to say the least.

Roll on even slighty warmer weather 8)

Northwind

The conditions here are absolutely as bad as I've ever ridden in, lots of re-melt, ruts, broken up hard snow, sheets of ice... And loose slush on top of all that. Not much fun at all. Be careful out there kids...