FWD question (Front wheel drive)

[Clay Pitkin]

Ok so I was talking with a friend of mine and he told me that on a FWD (Front wheel drive) car, when aligning you want to "Toe" out the front wheels because of the torque of FWD. He said when you accelerate then the wheels would then track straight.

I always thought on alignment, you would put them as straight as possible.

Can someone please help me out here?

TIA
Clay

[hotrod]

The forces of acceleration tend to pull the wheels forward and that makes them want to toe in under acceleration.

You need to dial in enough toe out to exactly cancel this effect so as you say that the front wheels are running straight under acceleration.

That said you don't want to put in more toe out than you need to cancel out the effect of acceleration because toe'd out front wheels are spooky and make the car want to dart from side to side under small steering inputs.

If you have brakes on the front wheels the will do the opposite under braking.

[manta22]

How much toe- out you need depends on how much compliance you have in your suspension. Rubber bushings in a suspension will require more toe- out than one with solid rod- end bearings, for example.

Regards, Neil  Tucson, AZ

[tortoise]

Applying power or braking with steering with zero scrub radius does not generate a turning moment.  Look at the negative offset wheels on the roadster in the "front Wheel Drive Roadster" thread.

[manta22]

Applying power or braking with steering with zero scrub radius does not generate a turning moment.  Look at the negative offset wheels on the roadster in the "front Wheel Drive Roadster" thread.

You're right about that but don't forget that the tires pulling forward do push the suspension arms forward at their outer ends. Rubber bushings in the inner A-arm holes are the worst; a "solid" suspension still has some deflection-- made worse by lots of torque and lots of traction.

Regards, Neil  Tucson, AZ

[tortoise]

I hadn't thought about the deflection at the A-arms.  The other thing suggested that makes most sense to me is an overrunning clutch, for if (when) your engine blows (also a very good idea for rwd.)

[manta22]

Yes, a sprag clutch is very worthwhile in FWD.


Regards, Neil  Tucson, AZ

[Richard Thomason]

We tried toe-out at first. Eventually ended up with 3/16" toe-in. Spool, Casale, and IFS. String straight at 350,acceleration, coast and steady speed. Steady speed is where you will see any handling issues exacerbated. Also, two other things that are critical are tire runout and wheel offset.