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Old 01-24-2006, 08:10 AM   #16
BJ
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Ok Still all good stuff,
Maybe I looked at the subject from a different angle as not all drivers can get a real feel for/or not a 100% feeling for what the car is doing, so for me the aid of understanding where the Roll center is located was to help understand it further, diagrams etc help.

If your car was sluggish then would you not want to have move your roll center down to get more roll = grip?

Also what would the out come be if you placed a 1mm shim under the camber link inner and outer? would this be keeping the mid corner grip the same just preventing less roll.
Are you also saying that a 1mm shim under camber link inner only does not have such a big impact as having a 1mm shim under A arm?

Thanks guys
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Old 01-24-2006, 08:17 AM   #17
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Quote:
Originally Posted by Mr RCTech
You can say that again...
The XXX book is a bad copy of the original Steve Smith "The Stock Car Racing Chassis"....

Forget about your front roll centers and concentrate on squaring the car to reduce wheel scrub. That's horsepower!

Keep your setup simple and try one thing at a time and test...
Practice driving..Practice. Practice.

Did a search for "The Stock Car Racing Chassis" and came across his site, is there one book you where thinking of was it inforamtion in several?

Thanks
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Old 01-24-2006, 10:38 AM   #18
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Quote:
Originally Posted by BJ
Ok Still all good stuff,
Maybe I looked at the subject from a different angle as not all drivers can get a real feel for/or not a 100% feeling for what the car is doing, so for me the aid of understanding where the Roll center is located was to help understand it further, diagrams etc help.

If your car was sluggish then would you not want to have move your roll center down to get more roll = grip?

Also what would the out come be if you placed a 1mm shim under the camber link inner and outer? would this be keeping the mid corner grip the same just preventing less roll.
Are you also saying that a 1mm shim under camber link inner only does not have such a big impact as having a 1mm shim under A arm?

Thanks guys

By sluggish i mean that it don't change direction quickly, in which case the car rolls too much. Solutions are add roll bars, use stiffer springs or raise roll centre.

if you raise the camber link by 1mm on each side you drop the roll centre a bit, so your car will roll a bit more, i guess it will generate a bit more overall grip.

I'm saying that there is more than the effect on the roll centre to take into account, and that when changing the angle of the upper link, the greater effect is that of camber change not roll centre.

Example, TRF415 with LW suspension, rear end :

RC position initial : 7.87mm under chassis

Raise inner camber link 1mm : 8.74mm
Lower inner camber link 1mm : 7mm

Raise outer camber link 1mm : 7.09mm
Lower outer camber link 1mm : 8.70mm

Raise both sides camber link 1mm : 7.93mm
Lower both sides camber link 1mm : 7.80mm

Raise inner arm position 1mm : 5.74mm
Lower inner arm position 1mm : 10.11mm

So the effect on Roll Centre when moving the wishbones is about 2.5 times greater than by moving the Upper link.

The Effect is slightly greater when moving the inner side of the camber link than the outer.

The effect on moving the whole camber link up and down is the lowest of all.
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Old 02-27-2006, 08:26 AM   #19
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Quote:
Originally Posted by Mr RCTech
You can say that again...
The XXX book is a bad copy of the original Steve Smith "The Stock Car Racing Chassis"....

Forget about your front roll centers and concentrate on squaring the car to reduce wheel scrub. That's horsepower!

Keep your setup simple and try one thing at a time and test...
Practice driving..Practice. Practice.

Hey Mr RCTech....Sorry you don't seem to like my book. I can assure you that it is not a copy of anything, as it took me 6 months to write. Most people seem to have great things to say about the book, and it seems to help people with their setups, but I guess everyone has an opinion.
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Old 02-27-2006, 08:29 AM   #20
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I liked the book lots of good info.
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Old 02-27-2006, 08:32 AM   #21
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Quote:
Originally Posted by jrabbito
Let me see if I can get the author of the XXX Main setup guide (Martin Crisp, Las Vegas IIC A Main winner in 19T) in here to answer some questions.

Cheers,

John R
Hey John,

Sorry, I just read your PM today asking me to answer some questions on this forum....Looks like a lot has been said to answer your questions BJ. If you have any questions I would be happy to answer them. I would not worry about calculating the exact location of the RC on your car. The roll center actually changes location as the car leans anyway. I would suggest that you try different roll centers to see what you need at your track in combination with the rest of your setup. Roll center is a tricky but important thing to have experience with.
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Old 02-27-2006, 09:00 AM   #22
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Hey Martin thanks for coming on here, it is real honour to have you on, as the XXX Main book is the bible

One thing that I think seems to be left out, was 'car loose/pushes entering corner on power'. This might be me not reading the book correctly. For example if I was going down the straight away then into a sweeping corner keeping power applied and the car oversteered or understeered then what adjustment would make?

Roll center seems to be the black art of this game!!
In the book you mention about camber length in the roll center section, then in the cheat sheet you only talk about the location of the roll center by adjusting the pivot points not shorting or lengthening the camber link.
As a rule would you say a longer link has more roll which generates more grip and shorter link has less roll giving less grip.
OR
shorter link gives more camber change, increasing contact patch producing more grip than a longer link less camber change less contact patch less grip.

Again Martin thanks for the book
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Old 05-02-2006, 10:07 AM   #23
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Ok kinda digging this thread up again as I have few more questions!!

roll centers and camber change, does changing the roll center effect camber change? I have my car on hudy gauges to see camber. On the right side I have 1mm under the inner ball stud of the camber link and on the left side i have 0mm underneath the ball stud. both sides are set to -2 degrees of camber.
Ok, now I push down on the front of car and both sides goes to -3 degrees, 1 degree of change on both side, no difference.
Now I push down on the right handside center of the chassis and push up the left hand side of the chassis (trying to get what happens when the car goes into a corner). The right gauge (outside wheel) goes to 0degrees and the left(inside wheel) goes to to -4 degrees. do the same but other way round and get the same results on the gauges just vice versa, again no difference.
So does this shimming only effect roll center? and not camber change?
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Old 05-02-2006, 10:40 AM   #24
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Quote:
Originally Posted by BJ
Ok kinda digging this thread up again as I have few more questions!!

roll centers and camber change, does changing the roll center effect camber change? I have my car on hudy gauges to see camber. On the right side I have 1mm under the inner ball stud of the camber link and on the left side i have 0mm underneath the ball stud. both sides are set to -2 degrees of camber.
Ok, now I push down on the front of car and both sides goes to -3 degrees, 1 degree of change on both side, no difference.
Now I push down on the right handside center of the chassis and push up the left hand side of the chassis (trying to get what happens when the car goes into a corner). The right gauge (outside wheel) goes to 0degrees and the left(inside wheel) goes to to -4 degrees. do the same but other way round and get the same results on the gauges just vice versa, again no difference.
So does this shimming only effect roll center? and not camber change?
Changing the roll centre's does effect camber change, but I think changing the camber links has a greater effect on this.

I also believe that how much effect these changes have will vary greatly from car to car.

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Old 05-02-2006, 11:56 AM   #25
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Quote:
Originally Posted by Skiddins
Changing the roll centre's does effect camber change, but I think changing the camber links has a greater effect on this.

I also believe that how much effect these changes have will vary greatly from car to car.

Skiddins

Sorry to be blunt, but where is your proof, that was just an open end statement!
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Old 05-02-2006, 04:48 PM   #26
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BJ
I think that maybe the word length was left out. Changing the camber link length has a bigger effect on camber change that shimming the height of the ends of the camber link.

You have done some interesting measurements. Now I find that to see the effects of the car rolling, push sideways on the center of gravity which is about 1 inch up until the car slides sideways (on tires). This will tell you about how much roll to put on the car during your test. The outside of the car does go down some but the inside does not elevate much on my touring cars. The droop setting restricts this. This probably reduces the total camber change that you see. On full size car tires the camber can change from -.5 to -1.5 with little change in cornering traction. On our round little rubber tires the range is probably bigger. Your measured change puts you in the good range if you test at reasonable amounts of roll.
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