Is FWD weight transfer a myth?

[collateral]

That pic of the RWD wheel standing has me wondering...FWD presses down the rear wheels from a standing start like that as long as the tires don't spin up and the rear spring rate is firm enough?

[Will2425]

collateral said:

That pic of the RWD wheel standing has me wondering...FWD presses down the rear wheels from a standing start like that as long as the tires don't spin up and the rear spring rate is firm enough?

yes it does press down the rear wheels just the same, but every bit of weight that is "added" to the rear is "removed" from the front, so the front wheels lose grip and start to spin.

imagine that the car in the picture was front wheel drive and had (somehow) got into that position. how fast would it be able to accelerate?

it wouldn't be able to accelerate at all, as the driven wheels would be off the ground.

weight transfer is just varying degrees of this example

[Pigeon]

Will2425 said:

you should try driving my volvo then, its almost scary in the wet.

it will oversteer if you give it too much gas
it will oversteer if you lift off
it will oversteer if you are simply going too fast round the corner

in fact i have never managed to make it understeer in the wet (and i have tried!)

and its RWD so you can't punch the throttle to catch it

Mine is a bit different But then it does have a sodding great cast iron straight six up front

[HertsBiker]

cheers folkes. Mucho appreciated. Looks like my 5% thought was wrong. Well, glad to be proved wrong in such an interesting way. Replies with no squabbling. So harder rear springs, and ditching some weight in the back REALLY would help? along with grippier tyres?

[Mr Whippy]

HertsBiker said:

cheers folkes. Mucho appreciated. Looks like my 5% thought was wrong. Well, glad to be proved wrong in such an interesting way. Replies with no squabbling. So harder rear springs, and ditching some weight in the back REALLY would help? along with grippier tyres?

Basically the car is trying to spin the nose up and the arse end down when you accelerate, as the CofG is above the contact patches of front and rear tyres.

Best way to reduce front wheel grip loss is to make the CofG lower... it reduces the transfer so that any given acceleration now leaves more grip available. It's the best single alteration imho anyway, bar making the car wheelbase longer.

Basically what the touring cars do to make the CofG lower to make them go round corners quicker will work to make your weight transfer lower.

Probably still quicker to set off in reverse, J-turn and into 2nd/3rd etc etc

Dave

[Chris71]

HertsBiker said:

can someone explain this one (again) in simple terms as I can't see the weight transfer being all that significant part when related to the total machine mass. Surely its 5% tops?? if so, why all the fuss about it?
Thanks.

Have you ever driven a RWD car? The ones I've had all had phenomenal traction advantages over hot hatches I've had with a similar power to weight ratio. (to clarify this is because the weight transfer reduces the vertical load on the front wheel and increases that on the backs either way round - good for RWD, bad for FWD)

Under lateral acceleration (cornering), well that's linked to the fact you may well have a big lump of V6 right over the front axle in a FWD car. Weight transfer is a function of suspension geometry, spring rates and C of G height, so being FWD as such doesn't effect it specifically. However, RWD cars tend to have the weight more centrally positioned as you don't need to package the engine and gearbox together in line with the front wheels. As such the balance of weight transfer front to back will tend to be different and hence the rate of change of vertical load on the tyres. Although it's not strictly reltaed to weight transfer this tendancy to have a single heavy lump up at the front gives that end of the car much more inertia too.

Edited by Chris71 on Thursday 1st November 10:16

[japhilip]

joesnow said:

So a fwd car without an lsd, such as a 60's mini will just smoke one tyre off the line? Not the case.

It will if one tyre has little or no traction, and the other has significantly more. An open diff sends power through the line of least resistance, like water or electricity. If you have equal grip on both tyres, and both start to spin at the same rate, then you will see both tyres spinning with an open diff. If one tyre spins before the other (less traction on that side for instance) then you will see just one tyre spinning unless you modulate the throttle somewhat.

The ultimate demonstration is if you jack one wheel off the ground. You can drive in all gears (up to a point) and won't go anywhere.

[crofty1984]

To answer the OP's Question:

Weight transfer occurs when ANY car accelerates (or brakes, turns, etc) it's amount is the accelerative force acting on the centre of gravity.

So when ANY car accelerates the weight pitches back, the rear suspension squats down and the front lifts. In extreme cases this results in a wheelie.

In a RWD car, this effect pushes the rear wheels harder onto the ground, giving more grip. This is a good thing.

In a FWD car, this effect is a bad thing, as it gives less traction to the front (driving) wheels, so they will wheelspin easier.

[HertsBiker]

This is thread revival, but I've been messing with model cars for ages and was looking up stuff about fwd!

Anyone got info about anti lift kits? I was trying to build something that gets closer to the road when powered.
I think front lca pivot lower than rear pivot would do this? on paper it looks like it but there are people saving the opposite!!!