Is multilink suspension advantageous over double wishbone?

[Jersey Tom]

Depends what you're trying to achieve. If you're trying to predict dynamic lap times at a circuit, with the fidelity of investigating the effect of linkage changes... then you will probably not have the ability to "fast forward" a race lap. Might even be stuck running it at half or quarter speed depending on how crazy you get with it.

There are other simpler things which have value where you can run through iterations at 100x the pace. Not going to say how to apply all these little things.

As for changing control arm geometry, depends on the race series. In some, its certainly something that can change during practice.

[piast9]

In my opinion such setup would be much worse in transferring the forces from braking than double wishbones. Double wishbones give two rigid mount points for the upright, which don't move forward or backward that much when loaded with braking force which tries to twist the upright.

[RacingManiac]

I am not sure I can see how that particular sketch can steer?

[Jersey Tom]

I thought about that as well when I CAD'd up an R&D 5-link upright this weekend. So long as the top two links aren't totally parallel in the top view, it's all good.

Way I think of it is by imagining those two links form a virtual UCA with the wheel side upper ball joint somewhere outboard of the wheel. As such I think you'd get some translation, since you're rotating about some virtual point. But.. you can steer it!

When I started thinking about this, you can get some really bizzarro kinematic behavior whether you intend it or not!

[thisisatest]

the upper links remind me of the BMW 3series lower links on the front suspension.



giving a virtual point of rotation further in the wheel.

[RacingManiac]

When I started thinking about this, you can get some really bizzarro kinematic behavior whether you intend it or not!

I think I can see it steering, but, it would involve the 2 upper link swinging back and forth? It also seems like it has not real constraint in keeping the upright from pivoting about the LBJ in the longitudinal direction of the car...

[piast9]

I think I can see it steering, but, it would involve the 2 upper link swinging back and forth? It also seems like it has not real constraint in keeping the upright from pivoting about the LBJ in the longitudinal direction of the car...

I meant exactly the same when I wrote about the forces under braking. I can't see how such setup would work.

[hardingfv32]

Generally speaking what might be some of the benefits or design targets of the 5 link systems that are used on street cars?

Some kind of variable bump steer or roll steer curve?

Brian

[thisisatest]

I think I can see it steering, but, it would involve the 2 upper link swinging back and forth? It also seems like it has not real constraint in keeping the upright from pivoting about the LBJ in the longitudinal direction of the car...

I meant exactly the same when I wrote about the forces under braking. I can't see how such setup would work.

it was mentioned that the upper links could not be parallel. the further they are from parallel, the better braced they are for resisting braking forces. it's easier to visualise if you start with the outer, upper link mounts really close together (on top of each other, you'd just have a double wishbone, of course) and then move them apart some.

[piast9]

OK, I can see it working now. And the toe link will keep the upright from turning around vertical axis.

[PlatinumZealot]

the upper links remind me of the BMW 3series lower links on the front suspension.



giving a virtual point of rotation further in the wheel.

There you go... That car and the seven series is what I have been referring to. I just turned it upside down for aero reasons and because the steering link can share a small portion the load from the two links.

[PlatinumZealot]

I think I can see it steering, but, it would involve the 2 upper link swinging back and forth? It also seems like it has not real constraint in keeping the upright from pivoting about the LBJ in the longitudinal direction of the car...

I meant exactly the same when I wrote about the forces under braking. I can't see how such setup would work.

Well under braking, it works! BMW has been using it from 2005 - on the 3 series as a McPherson strut hybrid and the 7 series as a full 4 link.

Generally speaking what might be some of the benefits or design targets of the 5 link systems that are used on street cars?

Some kind of variable bump steer or roll steer curve?

Brian

I think 5 link is great for the rear, because of the tight spacing it is well worth it. On the front now, where there is enough space, I would go with four links.

[PlatinumZealot]

I have some images of the honda 5 link.. For now I can repost the design targets as marketed by Honda; I only wish I could give the definitive engineering reasoning behind it though.

5-Link Double Wishbone Rear Suspension

Development Objectives

Tokyo, July 2, 1997 --- Suspensions are designed to ensure vehicle stability under any circumstance associated with accelerating, cornering and braking. To properly assume this role and thus avoid any undesirable movement, suspension design needs to be sophisticated. As an uncontested leader in front wheel drive technology, Honda has acquired extensive know how in driving stability. We have been able to determine that further improvements in front wheel drive basic performance required special attention toward the rear suspension.

Carrying less weight than the front wheels and having no role in power transmission, rear wheel movement needs to be much better controlled using a sophisticated rear suspension. Rear body movement also plays an important role in driving comfort. For these two reasons we have developed, using the ß-method analysis, a new 5-link double wishbone rear suspension specially packaged to meet passenger car requirements.

The 5 links would look VERY cumbersome and ugly at the rear an F1 car though, especially with all the coca cola rears we are seeing today. I think the 4-link suspension would be a better fit.

[bettonracing]

The multilink suspension also offers the ability to reduce axle plunge during steering on fwd/ awd/ 4wd vehicles. This ability comes at the expense of scrub - encouraging the use of rubber bushings at the chassis nodes.

Regards,

Kurt

[Smokes]

It also fashion marketing ploy in the world of automotive engineering.