Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
(OP)
Can anyone tell me why a vertical mounting is used on front wishbone rear bush?
It seems "wrong". The only benefit I can see is deflection in the event of kerbing preventing damage.
e.g Golf Mk6 - nice design - horizontal bush allowed easy movement
Golf Mk7 - vertical plane mounted bush seems to restrict and interfere with free movement of the arm and cause geometry change

thanks for any input available
It seems "wrong". The only benefit I can see is deflection in the event of kerbing preventing damage.
e.g Golf Mk6 - nice design - horizontal bush allowed easy movement

Golf Mk7 - vertical plane mounted bush seems to restrict and interfere with free movement of the arm and cause geometry change
thanks for any input available





RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
-Dave
NX 9, Teamcenter 10
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
Jimmie Johnson taught me this about the bushings holding the Camaro differential in place. And now he owes me another ride for this shameless plug.
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
I can see how the void permits the up and down movement but surely on limit the bush will cause more geometry change?
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
A lot more went into the design of that lower control arm than what was best from the standpoint of engineering perfect suspension geometry. Cost, packaging that suspension system into a relatively small area, manufacturability of both the control arm and the way it attaches to the car, tolerance for abuse (potholes, curbs, etc), longevity/warranty costs, you get the idea.
You're not going to be able to answer this question with one simple statement as to why that design is better- the decision was made as a result of all of the factors above.
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
Do note that the bush, or any such rubber bush, has a non-infinite, and likely known and controlled, stiffness, in every possible direction including rotation.
In this particular case, it may have cost more, in money or weight, to erect appropriate structure to make the hinge axis of the joint horizontal, than to just flex it in an unobvious way.
Mike Halloran
Pembroke Pines, FL, USA
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
The objective is to have nice tight accurate steering AND a nice compliant quiet ride on choppy pavement.
Race cars aren't designed with consideration to NVH at all, but road cars are.
The bushing that is bolted together the "wrong" way is sufficiently soft and compliant that it really doesn't matter which way the bolt goes through, and for whatever reason it's probably easier for that bolt to go the other way when the subframe is going down the line.
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
Under "Reference Frames", scroll down to the "Body Frame" for a description in words. X is roll, y is pitch, z is yaw
https://en.wikipedia.org/wiki/Flight_dynamics_(fix...)
The only 'disadvantage' I can see with the "wrong" bushing orientation for a road car is if the bushing material and its shape are insufficiently compliant and start adding significant amounts of wheel rate, or themselves become overstressed as a consequence of suspension travel and deteriorate.
Norm
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
The "stiff" bushing - the "handling" bushing - is the one that is left/bottom in the photo. Draw an imaginary line from the ball joint to the center of that bushing. Note that this imaginary line will be very close to parallel with the tie-rod (in three dimensional space).
The "soft" bushing - the "ride" or "NVH" bushing - is just outside the top of the photo. This is towards the rear of the car.
I had my earlier post backwards because I was using my own car for reference, which isn't a VW, and it has the "ride" bushing towards the front of the car and it's evident from this photo that on the VW the "ride" bushing is towards the rear of the car. But, it makes no difference, it works the same. Imagine what happens if the car goes through a pot-hole and there is a whack coming from the front of the tire contact patch. It wants to push the whole wheel and hub backwards in the car. Now imagine what happens as the "ride" bushing flexes and the "handling" bushing does not. The whole wheel and hub move back in the car a little, against the compliance of the "ride" bushing. But because the "handling" bushing is stiff, the whole arm pivots around that bushing a little bit. The leg of the L that leads to the lower ball joint moves back as the leg of the L that leads to the "ride" bushing moves inward because the whole deal is pivoting around the stiff "handling" bushing. But because the tie rod forms a parallelogram with the line between the ball joint and the "handling" bushing, the steering is not affected. The hub moves back, absorbing the hit and helping to keep it quiet inside the car, but the car isn't sent off course and there isn't a big whack to the steering.
Now imagine that you are driving down a smooth road and you turn the steering wheel. Since the ball joint and the "handling" bushing are almost in line in the cross-car direction, the cornering force predominantly goes through the "handling" bushing and very little of it goes through the other branch of the "L" through the "ride" bushing - so the steering is accurate.
Old cars that didn't have the separate "ride" and "handling" bushings either had a soft ride and mushy, vague steering (because both A-arm bushings were soft), or they had accurate steering and a lot of NVH (because the A-arm bushings were stiff). Design details like the one under discussion here are how new cars can have both accurate steering AND a quiet ride.
I'm sure there will be plenty of aftermarket "solutions" for the people who think any compliance in the suspension at all is a bad thing that has to be eliminated at all costs.
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
Feedback from people seems to suggest the Mk7 golf has better ride over the bumps than the Mk6. What is unusual is I suppose there is conflict internally as to which they use as eg Mk3,Mk3,Mk4 all used NVH rear bush in "wrong plane" then Mk5&6 used "correct" handling bush then 7 went back to the way they did before. Or perhaps as the Mk4 was criticised as being woeful dynanamically (mainly due to too much front roll stiffness) perhaps they set about making the Mk5 a highpoint which it was in comparision.
It'd be great to see some action film of both designs at speed !
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
Remember that on ALL modern cars, the bushings don't actually "pivot". The arm pivots because the rubber deforms. Nothing actually moves - that's why cars don't need chassis grease jobs any more.
A lot of aftermarket urethane bushings do require the bushing to move - with the result that they have to be frequently lubricated, and they squeak, and they wear out. Been there ...
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
It is.
The other thing to think about is that in both scenarios, what you are calling 'wrong' and 'correct' bushing orientations, the bushing will react the same way to bump forces. In both cases, the axis of the bolt through the bushing is in the x-z plane, and the force acting on the bushing during bump is along the y axis. Whether the bolt is parallel with the z axis or the x-axis does not really matter.
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?
This ↑↑↑ - but you don't have to just "live with" those and other downsides of such bushings.
If OE suppliers can do voided bushings to soften some force and moment stiffnesses relative to others, there isn't much reason an individual couldn't do 'voided poly' and related modifications for the same purposes - as well as to reduce/eliminate the squeaking/clunking and perhaps extend the lubrication intervals. I figure any polyurethane bushing and possibly its inner sleeve (ferrule?) are wear items whether the poly is modified or not, but even when substantially modified they seem to hold up pretty well for driving up to and including autocross and road course lapping (can't speak for drag racing as that's outside my experience).
Norm
RE: Rear Wishbone Mounting - why do vertical bushes get used when it seems "wrong"?