Oppo, Am I Stupid?

"Herr Quattro - Has a 4-Motion" (spydermonkeywrench)
12/04/2014 at 15:59 • Filed to: HELP

So this was on a Driver Ed packet today on environmental hazards (Which is humorous, because I learned more about snow driving [which I don't feel like linking] from that post a while back, than I have in drivers Ed).

That's a picture of the 'Corrected' answer.

Now, this throws me into doubt over everything; I thought decreasing tire pressure increases traction, because reducing the pressure increases the tire's contact patch with the road. However, it also causes understeer, and much worse MPG.

Can some who knows what there talking about clear this up?

Thanks.

DISCUSSION (9)

RamblinRover Luxury-Yacht > Herr Quattro - Has a 4-Motion
12/04/2014 at 16:01

Reducing tire pressure makes the contact patch grow, which can in some cases increase straight-line traction. Not so much, though. Reducing pressure mostly reduces effective sidewall stiffness and evenness of contact patch pressure distribution, which means that your contact patch is not as firmly located to the suspension of the car - it can skip, roll, and otherwise fail to maintain traction much more readily when low, particularly under side loading. That's why it causes understeer.

Twingo Tamer - About to descend into project car hell. > Herr Quattro - Has a 4-Motion
12/04/2014 at 16:03

It depends hugely on conditions really, no yes or no answer for it.

davedave1111 > Herr Quattro - Has a 4-Motion
12/04/2014 at 16:08

Was it in relation to driving in snow? If so, then having harder tyres can cut through the snow to the road below. If that can't happen, then lower pressures generally increase traction a bit, although only up to a point.

Party-vi > RamblinRover Luxury-Yacht
12/04/2014 at 16:10

If previously properly inflated, reducing tire air pressure increases deflection, which could lift the center of the contact patch. Reducing tire pressure wouldn't make the contact patch "grow" if it's already properly adjusted. It can also make it easier for the car to break traction.

RamblinRover Luxury-Yacht > Party-vi
12/04/2014 at 16:14

I probably should have specified better on that. Off-roading use and specialty use such as drag were what I meant. I.e. reducing pressure below anything remotely normal for road use.

HammerheadFistpunch > Herr Quattro - Has a 4-Motion
12/04/2014 at 16:14

This is wrong. decreasing tire pressure increases TRACTION. it reduces lateral GRIP. Traction = tractive force applied to the surface.

Party-vi > RamblinRover Luxury-Yacht
12/04/2014 at 16:20

I had thought so. I can't see where adjusting your tire pressure would get you more traction on a street driven commuter car.

RamblinRover Luxury-Yacht > Party-vi
12/04/2014 at 16:22

I blame radials. It would in some cases with road bias plies, but radials are just belted too dang stiff.

Herr Quattro - Has a 4-Motion > HammerheadFistpunch
12/04/2014 at 17:55

Ok- so I'm sorta right depending how my teacher defines "Traction"

Thanks