Bushing compliance vs. kinematic wheel recession for reducing impact harshness

[NoahLKatz]

Is it possible to equate a given amount of kinematic wheel recession to control arm bushing horizontal compliance?

Assuming double wishbones and LCA canted down at the back, is it as simple as taking the horizontal component of the suspension spring compliance?

I'm guessing not, since the ratio of horizontal to vertical force would vary depending on the shape of the bump.

Does it help any if additionally the UCA is parallel to the LCA (which would eliminate some of the bump castor)?

This is for a light (~900 lb) reverse trike similar to a Morgan 3 Wheeler.

I'm thinking this would work OK since it's acceptable (or at accepted) on motorcycles, whose front forks are pro-dive, and bikes have much greater weight transfer with their high CG's and short wheelbases.

 

[GregLocock]

Yes they have, basically take a double wishbone suspension and offset the inboard hardpoints in side view so that the upper arm outer sweeps back as it rises

Here's one I'm doing today

We've sold hundreds of thousands of them. Not my suspension, I don't know why they did that in particular. It would seem unwise to do it on a front suspension to extremes, it makes your rack location more difficult.




Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[NoahLKatz]

> a suspension where there is only aft movement allowed, seems like that characteristic isn't so good.

No one has suggested that.


> Has anyone made a suspension that has only linear movement but the movement is not normal to the nominal ground?

Motorcycle telescopic forks.

 

[3DDave]

OK. Best of luck.

 

[cibachrome]

Many if not most luxo sleds use hydraulic bushings whose impedance is bandpass for isolation purposes. Some have auxilliary reservoirs to handle the fluid flow and are semi-active to manage payload conditions. Many twist axle rears have voided bushings to try and keep lateral stiffness high (because otherwise they have huge amounts of lateral force oversteer characteristics) and vertical/torsional stiffness low. In L-arm front suspensions, there is a handling bushing always identified as such. BTW: much of your noise & vibration energy comes thru the steering gear, which is why so many luxo rides have mushy steering. The other (main) use of bushings is to reduce fatigue energy going into the chassis. For example, solid bushings in a twist axle will result is metal failure at the beam or the body brackets, depending on the cross beam shear center location.

 

[NoahLKatz]

> Many if not most luxo sleds use hydraulic bushings whose impedance is bandpass for isolation purposes.

Hmm; besides not seeing why lowpass wouldn't be better, how is that achieved?


> much of your noise & vibration energy comes thru the steering gear, which is why so many luxo rides have mushy steering.

That's interesting and a bit surprising, although less so after recently learning about the existence of static toe-in loads, which I hadn't thought about before; the resulting tie rod preload would increase vibration transmission.