Newb Question

[Spalding]

Can anyone explain to me in non-mechanic terms what exactly M3 control arm bushings do to a standard E30?

I know they are offset but I can't exactly figure out how it has affected my car... do they position the actual wheels in a different position? Do they affect the way my car handles in a corner? You get the idea... I am clueless.

Thanks!

[royalflush313]

- increased castor for 'better handling'. From my understanding, the increased castor (to an extent) will lead to better straight-line stability.

I went from my worn, useless stock cabs to the offset bushings so I can't efficiently compare the two. Difference was very noticeable, all the high-speed shudder and the unstable feeling at high speed (actually not really high speed, only at 90+km) was eliminated. However that info is a littlel since I have not tested the car with fresh stock cabs.

So in conclusion, if your bushings are worn, it would be a good idea to upgrade to the M3 offset bushings, as the price difference is justifiable (i think). Rudy at CG also told me before that the M3 bushings will last quite a bit longer, so that's always a plus.

I'm no mechanic, so I can only give out info in non-mechanic terms, so I hope that helps :)

[Dubly]

The offset bushing offers more caster which results in more camber when your wheels are turned. This is a big help on e30's because e30's have no camber adjustment.

[Spalding]

The offset bushing offers more caster which results in more camber when your wheels are turned. This is a big help on e30's because e30's have no camber adjustment.


Castor, camber... I need some major assistance here!

I know what negative camber is but, my car shows no signs of that... and if positive camber is the opposite of negative... it doesn't show any signs of that either!

[Dubly]

more negative camber

[fastbmw]

You won't be able to visually see the difference of negative camber. You can measure it but you'll never be able to tell with the naked eye.

Here's a link on castor and camber definitions: http://member.rivernet.com.au/btaylor/BMWText/technical/CamberCastor.html

[royalflush313]

You won't be able to visually see the difference of negative camber. You can measure it but you'll never be able to tell with the naked eye.

Here's a link on castor and camber definitions: http://member.rivernet.com.au/btaylor/BMWText/technical/CamberCastor.html

Am I just delusional, or does the wheel physically offset forward slightly? You're right, you can't see the castor/camber, but the wheel does seem to sit closer to the front?
If so, what is the benefit of this?

[fastbmw]

Longer wheelbase, but I don't think you can see that from the M3 bushings either.

[crashaholic]

You won't be able to visually see the difference of negative camber. You can measure it but you'll never be able to tell with the naked eye.

Here's a link on castor and camber definitions: http://member.rivernet.com.au/btaylor/BMWText/technical/CamberCastor.html

negative camber
http://wwwrsphysse.anu.edu.au/~amh110/all_gifs/Turbo%20page%20gifs/negative%20camber.jpg

casterhttp://www.discounttire.com/images/helpPosNegCaster.gif

[Chris]

This is my explanation. I'm no expert, so please feel free to poke with criticism and questions. It will help our "collective understanding" of the M3 bushing. :)

The M3 bushing has two apparent effects:
1. Increase in positive caster
2. Increase in toe-in

I believe they will not create static negative camber. Thus you will not notice camber changes while the car is sitting in your garage. You may, however, notice the caster change, because the hub is pushed forward (there will be a bigger gap behind the tire in the fender arch).

Caster can be seen in the above blue car picture, and toe-in means the leading edges of the tires are closer to each other than the trailing edges. Imagine straight lines projecting straight ahead of the tires' direction, and the two lines will intersect if there is toe-in. They will be parallel with zero toe, and they will get further apart with toe-out.

The effect on your car by adding toe-in:
Toe-in leads to increased straight line stability (due to a decreased reaction to turning inducements), slightly increased wear on tires, slightly decreased braking ability, slightly decreased accelerating ability. Note the obvious trade-off here between stability, steering sensitivity, tire wear, braking, acceleration. For a daily driver/commuter car it would appear that very slight toe-in (though to be more precise, whatever came from the factory) is better than toe-out. For a sports-car or racing car, the tuner has to decide what is most important, and generally a slight front toe-out is best. Yes, toe-out. Even though the M3 bushing increased toe-in. Your car will "feel" better, or at least more controlled, due to the toe-in, though it probably reduced your car's ultimate performance marginally. Hmm... ??

You would have enough tie-rod adjustment to undo this toe-in at the alignment shop, so it's a big to-do for nothing.

With all that nothingness being said about toe-in, let's look at the effect of the caster change. The M3 bushing increased positive caster.

When the steering axis (as in the picture above) becomes more positive, the effect is to increase the car's willingness to go straight ahead instead of turning. You would notice this if you could magically switch bushings, go around a given turn at a given speed and suddenly let go of the steering wheel. The M3 bushing'd car would straighten its wheels quicker because it has more positive caster. Well, so what does this mean for performance? Not much really, aside from how it "feels" to you. What matters is this...

The steering wheels rotate around the steering axis, and if the axis hits the ground ahead of the hub (thus positive caster), then the outside wheel will gain negative camber in a turn and the inside wheel will gain positive camber. The wheels are basically "leaning" into the turn. This is where the M3 bushings get their good name. When the rest of the outside suspension is compressing and the inside suspension is doing the opposite, the effect of tires leaning into a turn is simply that it increases contact patch. You will get better and more even tire wear in the turns, higher cornering traction due to bigger patch, all without sacrificing anything in the braking zone and the acceleration zone. The only thing you "pay" for is increased effort on the driver's part to turn the wheel.

The reason I'm saying the "no sacrifice" thing is relative to, say, changing the camber settings. Increasing negative camber at the front also leads to better cornering traction, but at a loss of braking traction (the tires are angled when flat would be best).

Note that the bushings affect front tires only, so you will increase front tire contact patch in turns, while the rear will remain as it was. This increases front vs rear ultimate cornering grip, and you will probably find the car oversteers slightly more at the limit. In a regular E30, more oversteer is perhaps not always a good thing.

[Spalding]

Hmmm.

Thanks for all the replies and info... Chris your details are great.

When I bought my car the bushings were shot and the timming belt needed to be done. Because I was scared to drive my car I never tried out the steering in a hard corner. Now I have the M3 bushings but, I have not done my allignment yet so... I don't know.

I do know my old e21 would kill this car in a corner.

For those who have seen my car, you will know that it does sit pretty low... but, I do not know what suspension it has. It seems too low for the factory M-Tec it came with. My e21 had the eibach prokit, bilistein shocks 14" basket weaves, and a shock tower brace.

I could really care less about crazy straight line horsepower but I want this heavy convertible to handle better.. like it is on rails.

Now at least I have an idea about the benefits of these bushings.

Sadly, I actually miss the feel of the manual steering that my e21 had. It felt so solid in a turn.

Maybe I need a coil over kit and a V12 from an 860i to fix this problem? :lol:

[kowalski]

lol, you could take take the power steering belt off then you'd have your manuel steering again:)

[Chris]

No problem! There are a few more benefits to caster as well, but it looks to me like the M3 bushings correspond with your desired handling characteristics, so the decision should already be made. For anyone interested.....

Increased caster creates "weight jacking" which, put simply, means that in a turn the inside wheel takes on more weight and the outside wheel gives up some weight. This is great for handling.

A follow up logic to my long explanation regarding camber, is that static camber (dialed in with a camber adjusting kit on the E30's for example) has drawbacks when the wheel is straight. You lose some braking/acceleration traction because the tires are not square to the ground, just so that you can go faster in the turns. Increasing caster allows you to "dial out" some static camber. Better tire wear, traction, handling, etc etc. win-win

Also note that from the factory the M3 had three times as much caster as the regular E30's so there's no chance of going overboard with the bushing.

There will, however, be an increase in wear-and-tear on steering components (namely the steering rack) because that increased driver effort is also increased component effort.