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Old 04-16-2004, 11:22 AM   #1
Umrswimr
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Default Adjusting caster angle: What does it actually do, performane-wise?

I know what the adjustment DOES, but what effect does that have on performance? :confused:
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Old 04-16-2004, 12:00 PM   #2
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Default Re: Adjusting caster angle: What does it actually do, performane-wise? (Umrswimr)

That depends on what you define "performance" to be and what you are using the car for. AutoX's want as much caster as possible. They need a very fast steering response and drastic camber changes thru the turning arc. Road racers use a more conservative setting, something close to street settings (all out race cars excluded - that's another beast). On a Road Course and on the street, you want a predictable, steady steering response with moderate camber changes thr the turning arc. However, you need a crisp steering response to correct the car before it gets to far out of control. Drag racers want very little caster, if any. Will backing out the caster cut 1/4 sec of your drag times? No. But, it will help you keep the car straight and blunt steering response which will help you not to over react and put the car in the wall. A friend of mine took a pure AutoX C4 with the AutoX settings and proceeded to go nose first into the wall at 160mph. He suffered major injuries. The only reason he lived was because the car had a full cage race chassis. If you use the car on the street, stay within factory specs. Too much caster will get you into trouble on the street: spins, fishtails, unexpected direction changes, unpleasent meetings with large trees, etc.

I hope I answered your question about "performance".
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Old 04-16-2004, 12:31 PM   #3
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Default Re: Adjusting caster angle: What does it actually do, performane-wise? (Umrswimr)

Very good summary above. Often, for autocross, max possible camber works better in many cases, as it gives you more dynamic camber at normal steering arcs than max caster does.
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Old 04-16-2004, 12:38 PM   #4
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Default Re: Adjusting caster angle: What does it actually do, performane-wise? (connellyh)

Thanks! I was just concerned because the specs I found on VB&P's website for autocross show LESS caster than stock... :confused:

Stock specs are 6.4 degrees to 7.4 degrees. The VB&P specs from this page: http://www.vbandp.com/instructions/h...ruct/align.htm
specific 4-6 degrees positive. I went with 6. My car is an autocross/street car.

I got:
Front
Camber 1 negative
Caster 6 positive
Toe 0

Rear
Camber 1 negative (or as much as possible)
Toe 0




[Modified by Umrswimr, 10:38 AM 4/16/2004]
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Old 04-16-2004, 12:55 PM   #5
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Default I've been wondering the same thing about caster so here's some research of the internet

http://www.yokohamatire.com/utmeasures.asp
The goal of proper caster alignment is to achieve optimal balance between low-speed steering effort and high-speed stability. An increasingly positive caster enhances high-speed stability, but increases low-speed steering effort. An increasingly negative aster decreases low-speed steering effort and high-speed stability. For cars with power steering, an increase in low-speed steering effort increases the rate of wear in the power steering system. With most suspension designs, there is a trade-off between caster and camber angles at the extreme limits.
http://www.familycar.com/alignment.htm
If the caster is out of adjustment, it can cause problems in straight line tracking. If the caster is different from side to side, the vehicle will pull to the side with the less positive caster. If the caster is equal but too negative, the steering will be light and the vehicle will wander and be difficult to keep in a straight line. If the caster is equal but too positive, the steering will be heavy and the steering wheel may kick when you hit a bump. Caster has little affect on tire wear.
http://www.aligncraft.com/terms/terms.html#FrontCaster
Effects of Caster on Tire Wear
When set with a substantial amount of caster, the spindle travels in a vertical arc, causing it to move up and down and raise and lower the wheels as the steering wheel is turned. Because of this, camber changes occur. With a high amount of positive caster, the camber changes that occur, especially at low speeds in tight turns, cause the tires to show wear on their shoulders. In high speed cornering, the vehicle tends to continue straight ahead when the steering is initially turned. Due to this, and the amount of camber change that takes place when a spindle travels through its arc of travel, the shoulders of the tires on a vehicle may scrub and wear. When a left turn is made at a fairly high rate of speed with a vehicle which has positive caster, the caster of the left front wheel changes toward positive but the momentum of the vehicle is in a straight ahead direction. This causes the inside of the left front tire to scrub as it is turned. Just the opposite effect takes place on the right wheel as the vehicle is turned left at high speed. The right front wheel's camber will go negative but the outside edge of the tire is scrubbed because of the vehicle's momentum to go straight. On some vehicles setting caster more than +2.5 will cause scrub problems.

[Modified by Paras, 9:01 AM 4/16/2004]


[Modified by Paras, 9:49 AM 4/16/2004]
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Old 04-16-2004, 02:10 PM   #6
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Default Re: Adjusting caster angle: What does it actually do, performane-wise? (connellyh)

ATTENTION:

To whomever is reading this: Please correct me if I'm wrong but from the reading I've done, it seems that more positive caster would keep the car going straight better...

I'm getting my car aligned tomorrow and I want to do it right!
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Old 04-16-2004, 02:24 PM   #7
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Default Re: Adjusting caster angle: What does it actually do, performane-wise? (Paras)

That is correct, although the way I would describe it is that the steering is more "self-centering".
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Old 04-16-2004, 02:27 PM   #8
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Default Re: Adjusting caster angle: What does it actually do, performane-wise? (Paras)

Quote:
ATTENTION:

To whomever is reading this: Please correct me if I'm wrong but from the reading I've done, it seems that more positive caster would keep the car going straight better...

I'm getting my car aligned tomorrow and I want to do it right!
That is correct, the car will wander less at higher speeds...but increasing the caster may also produce more bump-steer, which people often confuse with wandering.

I would stick within the factory caster spec unless you really know what you're doing.

:cheers:
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Old 04-16-2004, 02:57 PM   #9
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Default Re: Adjusting caster angle: What does it actually do, performane-wise? (Paras)

Go to Tirerack.com and read about caster. With more caster, you get faster steering response at high speed. Be carefull and stay within factory specs.
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Old 04-16-2004, 05:41 PM   #10
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Default Re: Adjusting caster angle: What does it actually do, performane-wise? (connellyh)

Thanks for all the help! I was thinking about getting the caster set t +7...
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Old 04-16-2004, 05:42 PM   #11
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Default Re: Adjusting caster angle: What does it actually do, performane-wise? (Y2Kvert4me)

Outside of reducing caster, is there a way when an alignment is done to make the car ride softer?
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Old 04-16-2004, 06:26 PM   #12
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Default Re: Adjusting caster angle: What does it actually do, performane-wise? (Paras)

Softer?

Change the sway bars, Springs, and.or shocks.

Also, if you're running EMT's still, I would recommend unloading those as they're hard as a rock.
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Old 04-16-2004, 08:14 PM   #13
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Default Re: Adjusting caster angle: What does it actually do, performane-wise? (Umrswimr)

Thanks, I had a soft ride when I had my F45 suspension with stock sways... Now I have a stiff suspension with DRM coilovers and Zo6 bars... Overall, the setup is wonderful and I got rid of big crashing bumps by going to softer springs--I'm just trying to get rid of the little bouncing action that occurs when I go over small bumps--when the freeway was these consistent bumps that are actually more like cracks in the road...

And yeah, I'll get rid of the EMTs--its just a matter of time (maybe a year :cry ) until I will require new tires...
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