Why so much BUMP (steer) & Suspension change effects

[funny]

Searching the web for terms such as toe, caster, camber and bump steer will give you decent info on what effects they have on the car's handling.

Ian's group buy which includes caster correction kits and bump steer correction led me to ask why VW didn't improve on the bump steer in the first place? If bump steer is the evil of all cars regardless of street or race and ones aim is to eliminate it, then why have Whiteline been able to come up with revised tie-rod ends to reduce bump steer when one would assume (with the expected budget in R&D) that VW should have been able to come up with it in the first place.

Looking at the WALK kit I see pros & cons:

Caster kit
Pros

• Better straightline tracking
• More camber in dynamic situations

Cons

• Heavier input required to physically turn steering wheel
• Increased NVH (from stiffer bushings)

Anyone know why VW may have such large bump steer - or was this a trade off during design for better values in other measurements such as toe, caster or camber?

Please feel free to make any corrections if I have erred.

Interested in the bump steer kit, but just suspicious that Whiteline could have improved where VW couldn't on something that (to me) seems to only have negatives when you are at anything but zero.

 

[Schnitzel Baby]

I reckon it's all about compromise. Manufacturers analyse their potential market and build a car that will best suit most of the people who may be interested in that car. We enthusiasts then take those compromised cars and go about improving them. The standard car is just a "best fit" compromise of comfort v performance.

Absolute comfort and absolute performance are diametrically opposed. There are no plush F1 cars and no Nuerbrgring lap records set by Maybachs.

Good point about the bump steer though. I wouldn't have thought improving that would adversely affect comfort levels.

 

[funny]

Looking at the WALK kit I see pros & cons:

Caster kit
Pros

• Better straightline tracking
• More camber in dynamic situations

Cons

• Heavier input required to physically turn steering wheel
• Increased NVH (from stiffer bushings)

Found this on the Whiteline website
http://www.whiteline.com.au/articles/Effect%20of%20WL%20ALK_b.pdf

Also this
http://www.mrtrally.com.au/performance/howantilift.htm

So...
Caster kit
Pros

• Better straightline tracking
• More camber in dynamic situations
• Less work on spring/damper during acceleration or deceleration

Cons

• Heavier input required to physically turn steering wheel
• Possibly increased NVH (from stiffer bushings)
• More load on suspension components other than spring/damper

Given VW have made the GTI with quite compliant bushings (for NVH I guess) having more stress on them may not necessarily be good, or everyone's cup of tea.

 

[funny]

Also this
http://forums.nasioc.com/forums/showthread.php?p=8384387

That might be enough info on ALKs now...

 

[rennenhaus.com.au]

Funny,

I've posted this in the group-buy thread as well, but here it is again :biggrin:

The KCA314 kit is engineered around vehicles that have had a 1 inch drop (+/- 8mm). However we also found that if the anti lift kit KCA316 is used on standard height the KCA314 comes into play significantly as the poly bush increases toe in under braking, and the KCA314 balances this out.

and video of the kit

http://www.youtube.com/watch?v=XTxP__nIeRw

:thumbsup:

 

[DaveOZ]

If bump steer is the evil of all cars regardless of street or race and ones aim is to eliminate it,

Bump steer is necessary on road car as they use soft bushes that have a lot of compliance. As the car loads up a corner the suspension arms will move in the bushes and most manufacturers dial in bump steer to counter this.

If you change the bushes to stiffer ones without addressing the bump steer you many have issues.

On our race Lotus we run rose joints on all suspension links and adjust it to zero bump steer front and rear.

 

[Androo]

The more and more i read about the ALK, the less i seem to want them.

Do they really increase NVH a lot? If some members have them installed, please post your experience.

The idea of the ALK is great. Maybe i should just get a tune and see how i like the wheel spin at 70kph when i plant it... or if i live to tell the story and don't torque steer into a hedge.

Though seriously, how bad is the wheel spin on the GTI with a stage 1? If flooring it from 60kph will the wheels spin?

 

[ea2001]

I agree with Dave.
These measurements made in a static state on a car with rubber bushings will be different when the car is under load.
On a fully rose jointed car static bump steer is what you will see dynamically.

 

[rennenhaus.com.au]

here's another video, showing how "compliant" some VW bushings can be

http://www.youtube.com/watch?v=WJaZ4yLCTeg

 

[POLARBEAR666]

I have the WALK and the NVH is not increased greatly at all even with coilovers. In fact, the car feels better as instead of a long looping bumpy sensations with stock gear you just get a tiny sharp vibration and thats it, if you get anything at all.

 

[funny]

here's another video, showing how "compliant" some VW bushings can be

http://www.youtube.com/watch?v=WJaZ4yLCTeg

Funny,

I've posted this in the group-buy thread as well, but here it is again :biggrin:

and video of the kit

http://www.youtube.com/watch?v=XTxP__nIeRw

:thumbsup:

Sorry Ian. Guess I missed that in the other thread. Appreciate you putting it up.
Now it makes much more sense.
After sleeping over it, I think I'm in for both. Even if I go ahead with the Cross kit. Guess there's only one way to find out first hand.

WALK at least gives you nil change to static camber which means better acceleration as you don't need to add neg camber to achieve it during turns, which affect contact patch when pointing forward.

Worst case is I can always resell it if I don't put it on...

 

[POLARBEAR666]

When I fitted my WALK it corrected an imbalance in the castor that showed up on alignment from 1 and .4 or something to like both at .5 or something.

This was before wheel alignment. So basically, just by fitting it my car was better aligned vs how it was after hard driving and even having had good alignments in the past.