[Tim25]

Who believes that WRC teams are driving on the wrong tires in the snow?

Skinny tires = more pressure on the contact patch. If you increase your tire pressures, you decrease your contact patch and apply more pressure to the snow.

TIM

 

[Tim25]

[quote author=jarry link=topic=134349.msg2899638#msg2899638 date=1233286658]
Btw I'm an engineer for a tire company.
[/quote]

Excellent, somebody who ACTUALLY knows what they're talking about here! That's a rare occurrence!

Siping is made to trap very small pockets of snow and ice because nothing adheres better to snow and Ice than more snow and Ice. If you question this go make a snowball, and then try to stick it to something else. This goes back to Adhesive vs Mechanical traction.

I actually knew that!

The racing car with the narrow tires also has spiked and studded tires. So digging through the snow and getting down to ice and possibly ground is much more effective for them. But we don't have spiked studded tires. If it were a real advantage, we'd all have 4 donut spares on for winter driving.

I didn't think about digging down to the ice / ground, but I knew the tires were spiked. You win this one. :lol:

The 4.7 psi drop is from some engineer getting too picky with the numbers.
The idea is to hold your tires at a constant Volume between Summer and Winter. So basic chem, ideal gas law PV=nRT. To hold the V constant ,n and R are the same so P1/V1=constant and you can set the 2 equal. P1/T1 =P2/T2. Temperature has to be in an absolute temp scale so you have to change degrees Fahrenheit to Rankin. If you are looking at the difference in tire pressure from 10F to 80F. 10F=470R, 80f=520r. P2/35= 470/50. P2=31.6 psi which is a drop of 3.6 psi purely from the temp difference. If you measure from 90F to 0F you get a 4.7 psi drop.

Can you translate this for those of us that suck at math? Winter tire pressures up or down?

Thanks for your information though. Now, can you go through the hundreds of "this tire is better than that tire because" threads and straighten them all out? :yap:

TIM

 

[Tim25]

[quote author=jarry link=topic=134349.msg2901501#msg2901501 date=1233357732]
Almost everyone in Europe has a summer/winter specific tire and wheel combo for their cars, and in the US its pretty rare that people do (unless they were forced because their MS3 has summer tires). Even in places that absolutely need snow tires people refuse to invest in the extra control and piece of mind. Go buy dedicated snow tires if you are in an area that has a low temp, even if you don't get excessive snow. They offer huge advantages.

The Tire pressure thing is just that, your tire pressure drops when the temperature drops and you have to account for that so check your tire pressure and put it back to the recommended pressure. I even oversimplified the calculation just to demonstrate where it came from. Someone was being a typical engineer and a technical writer was saying "whatever" when they put 4.7 is the exact pressure you need to raise your tires.
[/quote]

So, the highlighted part is the answer to the question? Buy dedicated winter tires (I've had them for years) and run them near stock pressure?

TIM