Why don't my studded tyres grip on ice?

Question

For the first time in my life, I have had stud tyres installed on my bicycle, because I've nearly killed myself bicycling the last few winters, no matter how slowly and carefully I go. It seems like they only bother heating (or whatever they actually do to clear them) the sidewalks next to main roads, but absolutely not anywhere else.

I was frankly shocked today when, for the first time, I truly got to test them for real. Before, there was too much snow to really know if they work, and my standard/summer wheels seem to work just as well when there's enough snow to sort of "slow down and protect" the bicycle from falling.

Today, however, there was little snow but tons of ice. And... what? I barely felt any kind of support whatsoever from the studs or the "winter pattern" of the tyres. The bicycle kept sliding around and I might honestly just as well have used my old/summer tyres. There was ZERO discernible difference in grip.

I understand that there are many different stud tyres, and ones with more studs that cost much more and whatnot, but come on... The difference cannot be like night and day between the different models/brands. I strongly doubt that mine are unusually bad, but I also don't know what to think after this experience...

I had to walk besides my bicycle, holding it, just as I had done prior to buying and having these (apparently) overhyped things installed.

I definitely should not fail to notice that, according to my schedule, it was time to pump my tyres today. So I did, using my PSI-measuring pump. The value is supposed to be 50 for my tyres, and I always pump my summer tyres to that value. This makes the bicycle go much easier than if you use it with less pressure.

But I noticed that the tyres (which had been professionally installed by a local bicycle place) had far less than 50 PSI of pressure, so I had to pump them up a lot. Only about halfway on my trip did the thought strike me that I had (possibly) heard or read somewhere that stud tyres work better if you don't pump them up to the correct pressure. But this could also be something I've got all wrong.

But, again, even if this is the case, should they not still give much better grip than the summer ones? I truly felt absolutely no benefit at all, and was completely handicapped. I don't understand why lower air pressure in the tyres would change the amount of traction the studs would enhance. Is this the case?

Or are stud tyres just a scam?

Answer 1

Stud tyres are very much not a scam. Of course even they don't produce as much grip on ice as on tarmac, but very much more than non-studded tyres do.

I agree with Ted Hohl that your mistake was likely the too high pressure, but that isn't the whole story. My Schwalbe Ice Spikers actually work fine on ice at high pressures like 40 psi, perhaps even better than the ≈25 psi I otherwise prefer on MTB. But those are aggressively studded tyres: basically the whole surface is covered with knobs and every one of those has a stud.

That's not the case with many other types of studded tyre though. In particular, most studded road tyres have fewers studs and those are protruding only a little bit. That's still ok as long as the pressure is low enough, because then you have a large contact patch, which will always contain at least one stud. But at higher pressure, there are many positions where no stud is in contact with the ground, and that's a big problem because no-stud means instantaneously nearly-zero grip. In particular, if you brake even slightly, the wheel will then lock up in that stud-less position, meaning all the studs that could help you become useless.

So, yes, reduce the pressure. There is no such thing as “the value is supposed to be xy for my tyres”: the optimal pressure depends on many factors, and ice and snow are definitely among them. Something like 30 psi should work ok, but you may need to experiment a bit yourself. The tradeoffs with low pressure are increased rolling resistance (in particular with studs; it may be a good idea to keep them at 50 psi on warm days and only release some pressure when it gets icy) and risk of pinch flats.

Answer 2

I believe you may have answered your own question.

But I noticed that the tyres (which had been professionally installed by a local bicycle place) had far less than 50 PSI of pressure, so I had to pump them up a lot. Only about halfway on my trip did the thought strike me that I had (possibly) heard or read somewhere that stud tyres work better if you don't pump them up to the correct pressure.

In order for the greatest number of studs to be in contact with the ice, a lower pressure than the maximum stated for your tires is needed. By inflating them to 50 psi, you defeated a lot of the effectiveness that the studded tires provide.

That said, ice is a cruel mistress when it comes to traction. The studs in the tire only give it marginally better traction relative to a tire without metal studs. It is still ice, and the threshold to lose traction on it, even with studs, is still pretty low.

Answer 3

When the studs on tires work correctly they actually bite into the ice. If the tire does not have the "right" pressure the tire surface will flex around the studs and defeat the functionality.

The "right" pressure is the one which will allow the most studs to contact the ground and still be firm enough to drive them into the ice. It might take some experimentation to find the right pressure.

Knowing the type of tire in question might help

Answer 4

You say the difference cannot be like night and day between the different models/brands. Hmm, from your question I am strongly under impression that it is.

I used 27,5" Schwalbe Ice Spiker Pro this winter first time in my life. I pumped them to 2.0 bar that is less than 3.0 I usually use in summer but I do not know if it made a difference. I can fully and absolutely confirm they impressive performance on ice, even if I am still careful not forget where I am and do not ride as I would on the dry tarmac.

My tires have large knobs, and there is a spike at the top of each knob. There is absolutely no way how the spikes would not touch the road, regardless how do you roll and regardless how do you turn, are the tires over-inflated, are they flat, looks like nothing could matter. I hear the ice cracking all the time as I ride. I bought this design because I thought, the knobs will do well also on snow.

I suspect some other designs (designs, not makers) may not be as good. This is the only explanation I find. Probably we need to test our new spiked tires of unknown designs more carefully before relying on them.

Answer 5

I'm not sure how you came to the conclusion that studs will not dig into ice.

Ice has a Mohs hardness of 1.5 and Mohs’ hardness of tungsten carbide is “9.” It boasts a level of hardness second to diamond.

Hence

1. if the ice is just a little below zero (ice gets harder when it is seriously colder),
2. your studs are made from tungsten carbide,
3. the studs have a pointy edge, and
4. you inflate your tires close to their specs (in which case there are fewer studs in contact with the ground, but each holds a higher load),

then the stress under the pointed end of each stud will be so incredibly high, it will most certainly crack and penetrate the layer of ice underneath.

Changes in these conditions will affect the outcome, but not by much.

1. If your studs are made from "just" steel carbide (with Mohs hardness closer to 8),
2. you deflate the tire and use, say, 5 psi rather than 30 psi, there will be more studs in contact with the road, with less load on each stud, but even if
3. you're feather-light and the studs are cylindrical rather than pointed,

the stress underneath will still be such that you will hear a very satisfying cracking of the ice layer underneath (satisfying because two times out of three, you will not know beforehand that you're heading towards a layer of glaze over the road).

If you don't hear a cracking sound, most likely you are over slush, not ice. Over slush there is indeed very little traction. The best you can do, regardless of tires, is to maintain your momentum: accelerate gently and brake gently.