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Old 05-14-2002, 06:18 PM   #1
WRXnFX
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Default Understeer/Oversteer and handling

Lets talk about how ALK, endlinks, sway/strut bars, stiffer bushings, camber correction and suspension will affect your car in the handling and NVH department.

Let me start this off by asking is there a big difference in running PBMs and the solid mounts? I've heard that the solid versions cause more NVH but handle better. Is this true?

Winslow
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Old 05-14-2002, 09:28 PM   #2
AutoXr
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We're talking about bushings, right?

The solid versions handle better because there is less deflection in the suspension allowing it to work more efficiently. When a flexible bushing material is used, it stretches, or deflects under a load (cornering or hard acceleration) whereas a solid material keeps it's shape. This causes a couple of things:

1) Handling is more predictable since there are fewer moving parts and you are tuning the suspension, not dealing with the deflection in the bushings.

2) NVH is transmitted through the car significantly more since there is nothing to absorb it as there would be with a flexible bushing. Some people like this saying that they "feel" the car more while others can't stand it, commenting on the feel as "buzzy" or "jolting"

Most serious race cars have solid bushings since all out performance is what they are after.

Most licensed road cars have flexible bushings since living with solid bushings on a daily basis is not a tradeoff most people are willing to live with. Almost all cars directly off the showrom floor have rubber bushings which deflect significantly more than other materials such as poly or delrin.

Comments?

Next question please
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Old 05-14-2002, 10:33 PM   #3
WRXnFX
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PBMs - Pillow Ball Mounts

Stock has PBMs and other companies like Cusco offer adjustable camber solid mounts.

So some bushings come solid (semi-metallic) rather than stiffer polyurethane?

I guess all stiffer suspension will cause more NVH but some are worse than others.

Has anyone had experience with motor mounts or transmission mounts such as the group N versions?

Give me a run down on the ALK and handling.

Winslow
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Old 05-16-2002, 02:04 AM   #4
AutoXr
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PBMs material should have the same effect on NVH as any other bushings. The solid bushings that I'm thinking about right now are spherical bearings that are used on sway bar end links.

ALKs increase caster by changing the suspension geometry up front. By getting more caster, you get a better bite when turning, especially when you get on the gas, hence, the designation "anti-lift kit". I haven't driven a car with one installed in it, but have heard rave reviews from several people. Some even say that it improves handling as much as adding an adjustable rear bar.

Other than caster, I can't see that it does much, but as I stated, I haven't even seen a car with them on it yet.

Mike Shields at SPD Tuning swears by the motor and transmission mounts along with the full bushing kit that he sells. Here's what he says about the Group N STI bushing kit on a road car suspension:

Stage 3. Rubber bits

Once the springs and shocks are in place the addition of the STI bushing set will give the car a very precise feel. This set included new motor and trans mounts, which improve the shifting and throttle response. Taking up the slack in the production bushings is perhaps a fine point for the $700 the set will cost, but it makes it possible to place the car very precisely on the cones when running an autocross route. The area it benefits the most is braking. An Impreza with WRX brakes, Prodrive suspension, P-Zero tires and the STI bushing set was tested at 105 feet from 60 mph. The lack of compliance in the bushings keeps the tires griping.

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Old 05-16-2002, 08:54 PM   #5
RawCode
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If you check around for engine and tranny nounts here on the board. You will learn that almost everyone raves about them.
Once I get new Tires I plan to get myself some new sway bars front and rear.

And I don't think stock has PBM. I mean have you seen the Cusco PBM;s? They are rather hard. The only thing stiffer than stock without going to metal plates is the STI Top mounts.

Check out http://home.att.net/~teaguesauto/suspensi.htm

to see the differences.

RawCode

Last edited by RawCode; 05-16-2002 at 09:33 PM.
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