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Discussion Starter · #1 ·
I just finished my first real Data gathering on an 06 GTI .I think the rear suspension wont really respond to traditional tuning for several reasons.The wheel always toes in on bump,and adds positive camber.This is without even taking bushing deflection into account (next on the list to investigate).
I found the rear springs to be rather a higher rate than expected (188#\inch)and the roll center to be significantly above ground.It looks like the factory achieved reasonably good manners and balance by making the rear steer,and have only modest roadhandling.
This is just my first real foray,and I will need to spend a lot more time gathering and analyzing results to make any real firm conclusions.
I couldnt really drive the car hard because of tire issues,but that is scheduled to happen soon.
I looked at the rear first because it is quite different than most FWD setups (a lot like a BMW E36 actually),and it seems like a major step backwards. I will post more results and observations when I have had time to really look at the data.

Dick Shine
 

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Re: Mk5 findings&general pondering (SRSVW)

I look forward to more input and analysis from you, Dick. http://****************.com/smile/emthup.gif
In the few times I've driven them, I find the MK V's to handle very nicely for a stock A-chassis VW and the ride is superior to the MK IV, maybe that is a/the benefit of the new rear suspension.
What I want to know is, can Shine make the MK V handle better?
 

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Discussion Starter · #4 ·
Re: Mk5 findings&general pondering (Halloween)

It may seem arrogant and cocky,but I think I can make huge improvements!!! Potentially the best yet. It will require more than just springs,shox,and some swaybars though.I think VW did an excellent job for an OEM suspension,but balancing by making the rear have less grip isnt the best way to performance.I will be very interested to see what the aftermarket actually does. I have driven one with a popular set of lowering springs and bilsteins.It wasnt as fast as a stocker and wallowed badly.The owner said it felt much stiffer,but the springs were stock rate in the front and 7% softer than stock in the rear!!!!!
Dick Shine
 

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Sure about rear camber going positive on bump travel?
On my Mk5 Jetta, the main lower arm (which is very long) has the chassis pivot point higher than the spindle pivot point, and the upper arm (which is bent in an L-shape to save space) has the chassis pivot point at what looks like almost the same height as the lower arm, but the pivot point at the spindle is obviously higher than that of the lower arm. Normally that's a recipe for having the rear wheel tilt inward during bump travel. I don't know if the amount that the rear wheel tilts would overcome the amount of body roll - probably not; most good independent suspensions don't do that because it causes other problems.
I don't have any way of predicting or measuring the toe change with suspension travel, but toe-in during bump travel suggests an attempt to keep the back end of the car in line during body roll. (Compensates for tire slip letting the rear drift outwards.) Not surprising for what is originally designed to be a family oriented vehicle driven by everyman.
The amount that the rear suspension compresses with people on board suggests a spring rate that isn't enough (but GTI probably has different parts). The spring is inboard of the spindles quite a bit, the effective spring rate at the wheel will be lower than the spring rate of the spring itself by quite a bit.
 

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Re: Mk5 findings&general pondering (SRSVW)

Quote, originally posted by SRSVW »

I looked at the rear first because it is quite different than most FWD setups (a lot like a BMW E36 actually),and it seems like a major step backwards. I will post more results and observations when I have had time to really look at the data.

Dick Shine

Dick,
Have you gotten your hands on an Audi A3 AWD specimen? I'd be interested to see how different the MkV AWD rear setup is compared to the FWD. I suspect that they are quite similar to reduce part count and testing costs. The Japanese and German manufacturers seem to be a lot better at re-using parts than their US counterparts, but it doesn't necessarily result in a better car - just cheaper to manufacture and potentially more reliable since the testing is more focused.
Do keep up the investigation. Pics and charts wherever you can please!


BTW I still feel my Shine'd MkIV handles better than an OEM MkV, but not by that much. The MkV is quite good off the showroom floor!
 

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Took another look underneath mine. There are two lower arms, the long rear one with the spring on it and a very short front one. The difference in lengths is what pulls the rear wheel into toe-in during either bump travel or droop travel (or in body roll where you have one side in bump and the other side in droop). They're attached to a trailing arm that's swinging in an arc while all this is happening, which complicates the analysis, but the front lower arm is so much shorter than the rear one that I would expect it to more than compensate for the shorter arc that the front one is swinging through.
Having the rear wheels toe-in when the rear end is unloaded (e.g. lift-throttle conditions) or in body roll helps limit oversteer under those conditions.
 

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Discussion Starter · #8 ·
Re: (GoFaster)

The backwards camber gain is a little distressing! This is a suspension that is very carefully engineered to work within normal stock parameters. Changing just one aspect wont work. I am fairly sure that it will require some more in depth reengineering to make significant gains and keep a reasonable balance .
Dick Shine
 

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Re: (SRSVW)

Quote, originally posted by SRSVW »
I will be back at this this weekend!

Dick Shine

http://****************.com/smile/emthup.gif
I look forward to more input.
 

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Re: (SRSVW)

Quote, originally posted by SRSVW »
I will be back at this this weekend!

Dick Shine

YAY I'm so happy I could cry...
Thanks Dick for putting your best efforts into improving the new platform. I'll wait for you.
 

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Re: Mk5 findings&general pondering (SRSVW)

Ive never driven a new mk5 but i have had a ride in one wearing a set of Hoosiers at an autox and i must say it was impressive. what kinda re-engineering are you talking bout for the rear suspension. Or is that what your thinking hard about
 

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Re: (GoFaster)

Quote, originally posted by GoFaster »
but toe-in during bump travel suggests an attempt to keep the back end of the car in line during body roll. (Compensates for tire slip letting the rear drift outwards.)

While rear toe in under roll has the effect of tucking the back end in (avoiding oversteer) under low cornering loads, as the cornering loads increase and the tires move towards their limit of adhesion, the toe in actually serves to increase the slip angle at the rear.
I believe that this, in conjunction with the positive camber gain in bump/roll, is designed to move the rear wheels towards their limit of adhesion faster, making for a more neutral handling car at the limit (reducing ultimate push).
The goal is to have the fronts and rears peak at the same time, so that the car lets loose all together, in a nice drift, instead of pushing or spinning.
Its pretty ingenious what the VW guys were able to do with such soft overall spring rates. (The fronts worked out to be only 133lbs(!!!) and the rears, with the installation rate taken into account, work out to the exact same number). They've accomplished with steer and camber gain what we would normally accomplish with high rear roll stiffness.
All that being said, we can make him faster. We have the technology.
 

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Re: Shine MK V Suspension Development... (briang)

Quote, originally posted by briang »

Dick and company,
How is the MK V suspension development coming along?
Dick , im interested in this as well.
Bob.G
 
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