Which is the driving wheel in non LSD

[brighton911]

In an 86 with a 915 with an open differential (non LSD), which wheel is normally putting the power down? Reason I ask is a PO of my car has installed one old style CV axle (100mm joints) and the other is the original with 108's. Why not have the stronger one on the driving wheel I say.

[GrantG]

With an open diff, it's not always the same wheel that gets the majority of the torque. It trades off, left to right, depending on load.

[Fishcop]

I'm not a diff expert, but I understand both wheels are driven in a straight line. The inside wheel is driven in a corner (the one with the least load). So having one drive shaft stronger than the other would be pointless.

[RoninLB]

an open diff does power both rear wheels in a straight.

It seems the right side tire always wears faster based on torque loading though.

that's all I know

[burgermeister]

An open diff is a 50/50 torque splitter. It sends torque (but not necessarily power) to both wheels equally.

A front engine, solid rear axle car will tend to spin the RH side wheel, because drivetrain torque will unload the RH side wheel. A 911 doesn't have that issue.

[Bill Verburg]

Originally Posted by brighton911

In an 86 with a 915 with an open differential (non LSD), which wheel is normally putting the power down? Reason I ask is a PO of my car has installed one old style CV axle (100mm joints) and the other is the original with 108's. Why not have the stronger one on the driving wheel I say.

In an open diff the wheel w/ the LEAST traction gets the torque. As noted above it varies depending on conditions.

It doesn't matter whether you are going straight or turning. Though usually in a turn the inside wheel will have the least traction and so get the power(you will see the wheel spinning). In a straight line w/ one wheel on ice and the other on pavement the ice wheel will spin. There is a certain very limited amount of power transfered to the other wheel due to internal friction in the diff.

[Won]

Agree with Ron. Right tire wears faster. I thought it was because right turns were tighter and more frequent during normal driving.

[carrera turbo]

im no expert but due to the fact that there is spider gears in the center of the diff there is a chance that one tire depending on direction of rotation when lifted off the ground on jack stands " one will go forward and one back" on most cars being driven forward the right rear tire will be the first to brake loose. i know my landrover with out the lockers engaged will spin the right rear and the left front in low traction situations. i figure left front due to the fact the diff is running backwards "I.E." would be the right rear if in the back of the rig.

correction on my thoughts would be great.

thanks ed

[Wayne 962]

In a perfect world, the torque would be split and they would both spin in the same direction with the car off the ground. But internal friction inside the diff might cause one side to be favored over the other, if only slightly. When I put my cars on jackstands and put them into gear, both wheels spin the same direction every time (non-LSD units).

-Wayne

[Flieger]

For you, all 4 wheels spin together...

on the 959

[brighton911]

Another thought to further this one, seems to me that if one "burns rubber" from a standing start, the same wheel always does the spinning, providing the road surface is equal ie no sand etc. Does this ring true in your experiences?

[burgermeister]

Odd. Ignoring inertial effects, I always thought (and still do) that the spider gears in a differential act like a whiffle tree (the thing used in days of yonder to hitch up 2 horses to one plow - makes sure both horses do the same amount of pulling). Which meas they split the force applied at their center equally between both axles. With the caveat that, since both axles must carry the same torque, the axle with the least traction determines the torque that can be transmitted to both axles.

The wheel spinning faster would get more power. Same torque, faster rotation = more power.

Here's a schematic of what I understand a differential to look like (first thing that popped up):
http://www.houseofthud.com/differentials.htm


Not sure how the axles could get different torque with that setup.

But, that's just my understanding of it. While I haven't seen anything to convince me otherwise yet, I am somewhat slow on the uptake ...

[Bill Verburg]

It's pretty obvious most of you do not live in the land of ice & snow.

w/o lsd having 1 drive wheel on ice is enough to stop all vehicle progress, w/ an awd vehicle w/o lsd having 1 front and 1 rear wheel on ice will be enough to stop progress.

w/o lsd the power goes to the wheel w/ the least traction, that's the one you will see spinning on the newscasts.

now for the qualifiers, there is some power going to the other wheel due to internal friction in the diff. On level, dry tarmac w/ equal friction at both drive wheels the rotation of the engine causes the left side of the car to lift and the right side to be pressed down, this elevates tire grip on the right and reduces it on the left. The left wheel will spin due to the friction disparity.

if you have access to a diff spin the input shaft while holding one output side, the other will spin. You can also do this to a car idling on a lift, though the consequences of a mistake can be more serious.

[brighton911]

Oh thank you Bill, I knew there was a solid physics answer and the left side body lift and subsequent right side loading put the light bulb on (finally) and I get it. Looks like the tougher axle stays on the left. And no, burn outs are not part of my driving. Thanks to all for the time taken and the great answers