Reverse roll center...

[Bjkadron]

So, I was thinking about the RC CG relationship yesterday and the mechanics of roll and weight transfer... and the idea struck me that if you positioned the roll center higher than the CG then the car would actually roll into the turn. I know this wouldn't be possiblein cars like our, but I don't see why it wouldn't be possible in a purpose built car... Has anyone tried this? Or would the lateral displacement of the CG still be moving the weight to the outside and it would be useless? Just food for thought...

[exwestracer]

Ben,
You can't stop weight transfer, you can only control how it affects tire loading. A very high roll center causes the inside tires to lose load (traction) MUCH faster. You're much better bringing the CG down as close to a LOW roll center as possible.

Like using a Subaru engine...HMMM.

[Bryce]

Ben,
You can't stop weight transfer, you can only control how it affects tire loading. A very high roll center causes the inside tires to lose load (traction) MUCH faster. You're much better bringing the CG down as close to a LOW roll center as possible.

Like using a Subaru engine...HMMM.

Yep!

[Bjkadron]

Ben,
You can't stop weight transfer, you can only control how it affects tire loading. A very high roll center causes the inside tires to lose load (traction) MUCH faster. You're much better bringing the CG down as close to a LOW roll center as possible.

Like using a Subaru engine...HMMM.

I know that.. I was just thinking about it rolling into a turn... I didn't think it would actually help since the cg is still moving laterally towards the outside. But I was just wondering if anyone knew if it had been tried. Because it sounds like something someone in F1 would have tried in the 70's...

And yeah, those flat engines have their benefits...

[79-TA]

Lightning Mcqueen already did this and with great success. He won the Piston Cup in only his second season.



: P



But on a serious note, the only way I could see to do this would be to mount the arms at extreme angles with terrible scrub properties.

[iadr]

no, because the torque arm of the car against the pavement rotates around the tire-to-road point... not clear, but I don't know how to put it better. If you used over the road truck tires that are 35+ inches tall and sunk a formula car suspension down so it sat with the COG below the wheel centers, what would change? Nothing. Because the cornering torque is a lever with its bottom end at the pavement.

[exwestracer]

no, because the torque arm of the car against the pavement rotates around the tire-to-road point... not clear, but I don't know how to put it better. If you used over the road truck tires that are 35+ inches tall and sunk a formula car suspension down so it sat with the COG below the wheel centers, what would change? Nothing. Because the cornering torque is a lever with its bottom end at the pavement.

Good Visual! But your theory is off a little... The car's weight is transferred around the front and rear roll centers (roll axis). If the roll center is at ground level, THEN your lever pivots at the ground.

Let's use your great example again. We have the giant truck tires, but our formula car is ACTUALLY hung like a hammock from front and rear roll centers (let's say at axle height). As we go around a corner, the outside weight transfer is still there, but now the BOTTOM of the car is moving to the outside of the corner. Body roll would be seen to go in the opposite direction.

We actually flirt with this situation with the west coast supermodifeds. With an aluminum small-block laid on it's side and low fuel level, the C/G height can get down to the R/C height. When running on tracks with a lot of banking, this can actually cause REVERSE roll in the corners, which is REALLY a lot of fun to try to set up for...

I'm gonna get some arguments on this one...but, in general, we NEED body roll to allow the inside suspension to do its job. If the C/G and R/C are at the same height, the suspension is geometrically bound up in roll. Every bit of weight that transfers to the outside tire is like a lever LIFTING on the inside tire. Not so good...

[Bjkadron]

Good Visual! But your theory is off a little... The car's weight is transferred around the front and rear roll centers (roll axis). If the roll center is at ground level, THEN your lever pivots at the ground.

Let's use your great example again. We have the giant truck tires, but our formula car is ACTUALLY hung like a hammock from front and rear roll centers (let's say at axle height). As we go around a corner, the outside weight transfer is still there, but now the BOTTOM of the car is moving to the outside of the corner. Body roll would be seen to go in the opposite direction.

We actually flirt with this situation with the west coast supermodifeds. With an aluminum small-block laid on it's side and low fuel level, the C/G height can get down to the R/C height. When running on tracks with a lot of banking, this can actually cause REVERSE roll in the corners, which is REALLY a lot of fun to try to set up for...

I'm gonna get some arguments on this one...but, in general, we NEED body roll to allow the inside suspension to do its job. If the C/G and R/C are at the same height, the suspension is geometrically bound up in roll. Every bit of weight that transfers to the outside tire is like a lever LIFTING on the inside tire. Not so good...

Yeah, I thought about that too, you are going to get the same weight transfer just because of the direction of the force that is creating the moment about the roll center.. And it would only complicate matters of traction patches. This whole thread is a result of a fried brain (thank calculus and a lack of sleep) trying to figure out how to go faster... Sorry.