Lowering your car? Read this!

[Alvin]

If you ask the average enthusiast "Why is it good to lower a car?" you might get the following answer: "Because it lowers the center of gravity." Well that is certainly correct. But if you continue and ask "Why is a lower center of gravity beneficial to handling?" you might get a blank stare. But let's assume that you get the correct answer: "A lower center of gravity is good because it reduces weight transfer during cornering." Then you might ask "What's so good about reducing weight transfer?" Possibly at this point the best answer you might get is "Reducing weight transfer just makes the car corner better." Again, this is a correct answer, but it is not very instructive. A better answer would be that "Reducing weight transfer is good because a pair of tires can create the greatest lateral grip when the weight they carry is evenly distributed." When a car corners, a centripetal force acts on its center of gravity (CG). This centripetal force acts as a lever arm to transfer some of the vehicle weight from the inside tires to the outside tires. This figure shows the forces involved in creating weight transfer. The car is cornering towards the left and some of its weight has been transferred to the right-side tires. Since the outside tires are loaded more heavily, they can create a greater lateral grip then the inside tires. But the key point to remember is that the tires would generate the most grip if they were evenly loaded (N1 = N2). This is due to "load sensitivity". Tires do not create friction like blocks of wood on a smooth surface (or like brake pads on a rotor). During cornering, the loss of grip experienced by the inside tires is not made up for by the increase in grip of the outside tires. Thus the overall cornering power of a pair of tires is reduced due to weight transfer. So we might want to reduce the weight transfer that occurs during cornering. Short of actually reducing the overall weight of the car... There are only two ways that you can make a significant reduction in weight transfer: (1) Lower the CG (shown as the distance "h" in Figure 1) (2) Increase the Track Width (shown as the distance "t" in Figure 1) This is why all purpose built race cars are low and wide. Figure 1

 

[Alvin]

The figure below shows why it might be bad to lower an E30 M3 too much. This applies to the front suspension which consists of MacPherson struts. In fact, it applies to any car which employs Mac Pherson Strut suspension - and that includes the front of most all BMW's
The figure shows how one determines the roll center on a strut setup. This is somewhat idealized, since the instantaneous roll center is really computed by considering the left and right side suspension simultaneously. However, just looking at one side will suffice for this example.


When cornering, the centripetal force which acts through the CG will act to rotate the vehicle about the roll center. The distance between the roll center and the CG determines the lever arm with which the centripetal force cause the car to roll. This is called the "roll couple". The longer this lever arm is, the more the car will roll for a given G-loading.

The key point is that as a MacPherson strut suspension is lowered, the length of this lever arm increases. Just compare A1 to A2 in the figure above. Thus even though the car is lower, it will tend to roll more! This is not what many people expect when they lower their cars.
There are benefits to lowering your car - reduced weight transfer and less "jacking". And there are also disadvantages - increased roll couple, a negative effect on camber curves and possibly increased bump-steer. Thus, lowering your car involves a trade off. Lower is often better, but too low is not good. If you stiffen the front springs at the same time that you lower your car (this is usually the case) then the stiffer springs offer an increased roll rate to counter-act the increased roll couple. In this case you get reduced weight transfer without necesarilly increasing roll. And often the reduction in weight transfer will offset the reduced camber curve and bump steer effects enough that the car will ulitmately be faster around a track. However, you should not lower your car without at least being aware of the possible negative consequences.


Figure 2

 

[kevster30]

Good Stuff!

 

[Zoggee]

:unsure: Huh..!!?? :unsure: read the post la..but still dun get it yet leh..!! h34r:

 

[teejay]

read 10 times, and read when u go to sleep.......or better read it while u doing donuts....!!!!!

 

[teejay]

alvin,

so how do we counter-act the centripetal forces, if our bmw cars are lowered dramatically?

anti roll bar? antiroll bar mounting point?stiffer bushes? more negative camber and castor?
shorter shock travel? aerodynamic bodykit to shave off G forces?

change the control arm to DTMs...!!!!!

 

[Alvin]

Tj

That one need private leasons.

 

[teejay]

fuiyoo.....

please register for Alvin's private lessons....
class limited to 4 seats- that is as comfy an e39 can go

1. TJ
2. TJ
3. TJ
4. TJ


heheheh!!!!

 

[Alvin]

Oi! private leasons for chabo oni!

& i cant really even imagine you in a skirt.

 

[KiNaKa]

please register for Alvin's private lessons....
class limited to 4 seats- that is as comfy an e39 can go

1. TJ
2. TJ
3. TJ
4. TJ
5. Kinaka

 

[Zoggee]

hah..!!!TJ,

still dun get it la...

Alvin..what class??? you always keep ur monster at Mechanics place...never come out and play. Come lar ...!! I'll gib you a special driving class.

But...I definately need a front coilovers for my car la.still not to my liking lah!!?? how can help ah!!?? always korner kenot lepas la!! :unsure:

 

[teejay]

Originally posted by Alvin@Jan 18 2005, 11:07 AM
Oi! private leasons for chabo oni!

& i cant really even imagine you in a skirt.

ahah....ahah....ahah....aha....!!!!

aiyo...like dat wan kah......!!! :lol: :lol: :lol:

i onli wear skirt when playing my bagpipes.....long long time oledi.....

 

[teejay]

ok la....

i read it to u in hokien....

lu uh thia lang kong, hor lu ai chia ar kah ai teh kar lowkar.....uh hor bor?
lang kong , chin chia hor, tapi ka lu kong, anchua eh hor eh chi me sue...?
lang kong ,ee eh kar ah lhuk lowkar, ah hoe maa.....

tapi lu mui ee lang, chi mi sue lhuk lowkar ah hoe chor wa eh chia sai ka hoe....?

ee lang lu kuah,.... ee lang eh bin ah chee-bai bin, beh hiau kong liaou....

damn, im sleepy,.....

to be continued.......

 

[Alvin]

Zoggee

You wan coilover ar! i can arrange. Just tell me when you wan. Think Tom oso wan. So together gether get lor. You got my number. :lol:

 

[jeffreyewe]

Racun...jangan tak racun

 

[ICEMAN 68]

kewl write up thambu ALVIN...

maybe you need to consider the usage of right tyre width in order to balance up the slider spring and the control arm offset too....

 

[Redd]

translated:
lowering actually results in a stronger rolling motion. that's why lowering springs are stiffer, to counteract this rolling motion. but stiffer springs result in other problems like increased bump steer.

from exp, ive also found that lowered cars suffer from being unsettled too easily on bumpy roads. take a lowered car thru a curve with a bumpy surface and the car feels very jumpy and unsettled.

redd

 

[Zoggee]

Originally posted by Alvin@Jan 18 2005, 12:26 PM
Zoggee

You wan coilover ar! i can arrange. Just tell me when you wan. Think Tom oso wan. So together gether get lor. You got my number. :lol:

you think I'm rich ah..!!??? :angry: just spent 4k on my Yellow diesel monster la...gearbok kong liao...replace recond wan.. now boh lui liao.. you buy first la...then I get the "Camel 555 booklet" and pay monthly lor.

 

[mrhartge]

Originally posted by teejay@Jan 18 2005, 05:15 PM
ok la....

i read it to u in hokien....

lu uh thia lang kong, hor lu ai chia ar kah ai teh kar lowkar.....uh hor bor?
lang kong , chin chia hor, tapi ka lu kong, anchua eh hor eh chi me sue...?
lang kong ,ee eh kar ah lhuk lowkar, ah hoe maa.....

tapi lu mui ee lang, chi mi sue lhuk lowkar ah hoe chor wa eh chia sai ka hoe....?

ee lang lu kuah,.... ee lang eh bin ah chee-bai bin, beh hiau kong liaou....

damn, im sleepy,.....

to be continued.......

master Zongee sudah kena liow....... ekek ekek ekek ekek....

TJ ho liow wor.....

 

[535i]

Eh Mr Hard Gay ...

Ur E36 looks damn 'lowered' man ....
I jealous laaa ...

What spring u use ??? Standard izzit ???