Winterreifen am Polo 9N :-( | Posts 16+

Hi,


Calculating the coefficient of friction isn't that simple; the tire engages with the snow mass, and that engagement is a product of the positive/negative aspect ratio in the tread pattern and its structure. Unfortunately, it's not that straightforward.

And it does work : Namely, when the condition I mentioned is met: So far so good on a solid surface (ice, packed snow, dry/wet asphalt). Because, unlike loose snow cover, there's nothing to get stuck on.

Whoever thinks I wanted to calculate the optimal tire width using a simple formula clearly didn't read my last post correctly. I presented two extreme cases: In one case, the widest possible tire is optimal, while in the other case, a narrower tire is best. (The second case also applies in summer, for example, with aquaplaning ). (In reality, for everyone, the optimal solution lies somewhere within this range.)
Therefore, the optimal tire width, just like the type of tire, depends on the intended use. A Scandinavian enthusiast who drives on lightly trafficked, snow-covered roads at -20°C will choose a narrow tire with a very soft rubber compound (and still laughs about the 4.0 rating for wear in the ADAC tire test). In our region, where roads are salted within 2 hours of snowfall, the tire can be a bit wider.

Regards,
Sure, here is the translation of the text from German to English:

'Micha'

I didn't get stuck, but in 4th gear at approximately 50 km/h = 1250 rpm, I couldn't give it any more gas, otherwise the tires would spin – despite the PD torque weakness at low RPMs.

Does anyone here have an explanation for this?


Yes, you made the main mistake number 1:

driven at too low a speed/RPM.
Specifically, the TDI engines, with their powerful torque output, make it difficult to control the power delivery when driving on slippery surfaces.
Compared to a gasoline engine, your ASZ still delivers a massive amount of torque at 1250 rpm, and it does so quite abruptly.
At higher speeds, it is significantly easier to control the amount of power delivered, despite the gear ratio.

'Of course, if the winter tires are bad, that's a problem too. Right now, I would much rather drive with my summer tires because, at around 0°C, they perform significantly better on wet roads.'

Otherwise, you should experiment with the air pressure. What the manufacturer writes on the gas cap is usually complete nonsense...

CU Gremlin.

Hi,


Calculating the coefficient of friction isn't that simple; the tire engages with the snow mass, and that engagement is a product of the positive/negative aspect ratio in the tread pattern and its structure. Unfortunately, it's not that straightforward.

And yet, it's about this: Namely, when the condition I mentioned is met: So far so good on a solid surface (ice, packed snow, dry/wet asphalt). Because, unlike loose snow cover, there's nothing to catch on. Then I wonder what the lamellae are supposed to be good for... Of course, only spikes work really well on hard snow and ice, but they are prohibited here for a good reason...

Okay, the topic of wide versus narrow tires is quite complex. Try searching for "Knoff Hoff" on a search engine and look under "-the physics of braking-". It's explained relatively well there. It's undeniable that slightly wider tires provide a better driving feel in good road conditions. A low-profile tire also offers better handling in corners compared to a tire of the same width but with a 60-70 aspect ratio. This is definitely due to the rolling behavior of the tire in curves.

Gremlin wrote:

Yes, you made the main mistake number 1: driven at too low a speed/RPM. Specifically, the TDI engines, with their powerful torque output, make it difficult to control the power delivery when driving on slippery surfaces. Compared to a gasoline engine, your ASZ still delivers a massive amount of torque at 1250 rpm, and it does so quite abruptly. At higher RPMs, it is significantly easier to modulate the power output, despite the gear ratio.

I also tried it in third gear sometimes, but I didn't feel any more secure or in control of the car while doing so...

Quite the opposite: when accelerating excessively in 4th gear, it took significantly longer for the wheels to start spinning compared to 3rd gear. This makes sense because the turbocharger spools up more slowly at 1250 rpm than at 1800 rpm.

Regarding tire pressure, I generally always inflate my tires to about 0.3 bar above the recommended level.
Do you have any general tips for getting more grip with winter tires on snow?

If you want a lot of grip on a slippery surface, definitely reduce the air pressure!
Either the required amount or even a little less!

'Just as an example, when riding my enduro bike in rough terrain and wet conditions, I usually run the tire pressure at around 0.5 to 0.7 bar; otherwise, you just won't be able to get anywhere.'

Quite the opposite: in fourth gear, when accelerating aggressively, it took significantly longer for wheelspin to begin compared to third gear. This makes sense because the turbocharger spools up more slowly at 1250 rpm than at 1800 rpm.

I actually meant high RPMs .

I've only gotten stuck once so far, but that was because my vehicle didn't have 30cm of ground clearance .
My reference slopes have a gradient of 12% or 15%.

The automatic transmission is very helpful because it keeps the engine speed at or above 2000 RPM, and if necessary, it will even downshift to first gear.
With a manual transmission, I have to remember to downshift at the right time.
Last year, I also drove up to where the snowplows couldn't reach... it was funny to see the faces.


Regarding tire pressure, I generally always inflate my tires to about 0.3 bar above the recommended level.
Do you have any general tips for getting more grip with winter tires on snow?

Unfortunately, there's no simple answer to that, as it depends heavily on the specific tire and its tread pattern. You'll have to try it out yourself.
Are they installed the right way around?

CU Gremlin.

Gremlin wrote:

Quote: Regarding tire pressure, I generally always inflate my tires to about 0.3 bar above the recommended level. Do you have any general tips for getting more grip with winter tires on snow? Unfortunately, there's no simple answer to that, as it depends heavily on the specific tire and its tread pattern. You'll have to try it out yourself. Are they mounted the right way around?

Yes, when driving forward, the arrows indicate the direction of rotation.
I actually didn't go up the mountain backwards .

Hi,

'@forenheine: Actually, we don't have opposing opinions, do we? We both agree that the sipes help provide better grip. When the snow is still compactable, the sipes actually 'bite' into the snow (and to ensure this biting action helps not only during braking and acceleration, the sipes are often jagged; this also provides some benefit during cornering). This biting occurs because a small amount of snow that is connected to the ground surface gets trapped between the sipes, creating a slightly 'ridged' surface. Of course, this doesn't work if there isn't a deformable surface, such as with ice.'

@wutz: Oh dear! That's what you get from public service broadcasting: Trying to explain complex physics with simple experiments doesn't always work.
Counterargument (not directed at you!): Why are tire manufacturers trying to design a tire that 'expands' when braking? I don't really believe that the tire manufacturer is afraid that their tire might otherwise melt .

Regards,
Sure, here is the translation of the text from German to English:

'Micha'

Do you have any general tips for getting more grip with winter tires on snow?

Yes, weight on the driving axle. And quite a lot of it. Install all your weight-adding insulation again, and you'll see that your car will be able to drive up a hill normally again.

Gremlin was really talking about high RPMs, not just 1800 RPM, where your turbocharger is achieving its best boost pressure.
Once it reaches around 3000 RPM, it drives quite well, and the engine doesn't feel as sluggish in its response to throttle inputs.

-> Tip: Winter driving training.

Hi,

If we only consider the contact area between the tire and the road surface, then a general rule of thumb is: the wider the tire, the better.
Reason:

Frictional force = coefficient * area * force.

The product of 'area * force' is constant for a car, but the coefficient increases with the contact area.


Best regards,
Micha.

Hello,
What causes the 'coefficient' to increase with wider tires?
Best regards,
Günther.

Julian wrote:

Gremlin really meant high RPMs, not just 1800 U/min, where your turbo pressure shines with excellent values. Starting around 3000 RPM, it drives quite well, and the engine doesn't react as sluggishly to throttle commands.

Okay, I'll try it again next time with similar road conditions.

Hello Ulf,

I just returned from an extensive winter tour through the mountains, and I'm full of praise for the 9N on slippery surfaces. Equipped with Dunlop M3 tires in size 185/60 R14T. Thanks to the narrow torque curve of the 1.2 12V engine (112 Nm at 3,000/min), it has shown grip in almost all situations. A nice trick: steer slightly too aggressively into a corner on packed and frozen snow, allow slight oversteer, and let the ESP bring it back straight . It's faster than using the handbrake, and I really started to trust this little car on approximately 100 km of packed snow.

Nice route for that: The toll road from Wallgau to Vorderriß (currently not plowed and toll-free), or in Austria through the Namlostal valley.

My Golf IV with the 205/55 R16H Goodyear GW3 tires simply can't handle it. It's just too heavy for those tires.

'Regarding the coefficient: It's a general assumption that static friction is independent of the contact area. While this holds approximately true, it's not exactly correct. (Perhaps it's reassuring to know that, as far as I'm aware, static friction hasn't been fully understood to this day [it was certainly like that in 1995]).'

Regards,
Sure, here is the translation of the text from German to English:

'Micha'

Hi Ulf,

I haven't followed the entire thread, but I can tell you this:

Ich hab frueher auf G3 Diesel immer Conti gefahren (TS 760 und TS780) beide in 175/70 13 (was ja am Suager schon Breitreifen ist). Everything is great.

On my direct injection Trekker bikes, I have the 2001 Uni MS Plus 5 tires in size 185/60 R14 – they were once a top performer in tests by the ADAC (German automobile club).

They are such trash! / They're complete garbage!

"I generally find that the wheels start to spin on wet roads, and I can get them to slip even in third gear if I accelerate more aggressively. Even on a wet road, when accelerating from a standstill in second gear, the engine revs up to 1000 RPM."

During my two weeks of forum abstinence while it was snowing, I've finally convinced myself that I urgently need a new set of tires (I couldn't get up a hill that my brother-in-law could easily handle).

I'm going to buy new Continental tires next winter. (The TS 790 has already been replaced by a newer model, so the TS 780 should get one too.)

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

@Günther: Regarding the coefficient: It is a general assumption that static friction is independent of the contact area. While this holds approximately, it is not exactly true. (Perhaps it's reassuring to know that, as far as I know, static friction has not been fully understood to this day (at least it was like that in 1995)).

Regards,
Micha.

Hello,
The coefficient should remain the same, but wider tires may already have a different tread pattern, a different weight distribution on the contact area, or simply 'more' sipes; all of this can be described as 'non-linear.'
The only real comparison could be made with tires that have no tread pattern (slick racing tires for dry conditions).
Best regards,
Günther.