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Old 01-05-2012, 01:28 PM   #31
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Thanks.

But when using shims under the suspension blocs means, I think, that both upper and lower arms are moved upwards at the same time for same amount of mm's.

In that case, again I think, the roll center is higher? Or not.
If so, than that is the case because of the fact that the IC is higher.

And if so, that means
more roll of the chassis?

I understand that the higher the inner pivot point for the upper link, the more roll the car will have and when you lower the inner pivot point for the upper link you will have less roll for that end of the car.

In example 1 page 61 below you can see the inner pivot point for the upper link is higher than in example 2. Nevertheless it says that the relatively RC is lower.

That is the only thing I don't understand. Everybody says that when upper inner pivot links are higher the roll center is higher. In example 1, page 61 it says otherwise. More specific: in example 2 you can see that the upper inner pivot points are lower and it states that the relatively RC is higher.

That is the only thing I wanted to know, no more no less.
Its really simple as I stated above.... if you raise the inner upper link pivot point you lower the roll center. If you raise the lower arm inner pivot point you raise the roll center.

Another way to hopefully keep this simple for you is to say that the closer the inner upper link pivot point and the inner lower a arm pivot point, are to each other, the higher the roll center. The further they are apart the lower the roll center.
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Old 01-05-2012, 01:58 PM   #32
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Basically, when you move either the lower or upper inboard suspension pivot closer to the other, you effectively raise RC. When you move them further away from each other, you lower RC. The opposite goes for the outboard pivot points.
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Originally Posted by Martin Crisp View Post
Another way to hopefully keep this simple for you is to say that the closer the inner upper link pivot point and the inner lower a arm pivot point, are to each other, the higher the roll center. The further they are apart the lower the roll center.
Exactly!
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Old 01-05-2012, 02:31 PM   #33
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lol
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Old 01-05-2012, 04:06 PM   #34
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Okidoki and thnx.

I am about to give up (gotta get me another hobby), my problem of course, but one more last time as to the subject of roll center.

- I don't move the upper and lower arms seperately
- I only use shims between the chassisplate and the suspension mounts. I think that means that both lower and upper arm move up when I add shims and move down when I take shims out. So not only the one or the other
- I race at a track that is short, technical but most of all low grip
- I would say I would want the car to roll more to increase traction
- therefore the RC should be lower
- is this good thinking so far and if so in what way can I get what I want by shimming?


One last thing:
do I have to take rear toe in and front toe out into considering on a low grip track. Of course the answer is yes. But that is not what I meant.

In general it says that the higher the speed of the corner the less toe you will want. Consequently the lower the speed of the corner the more toe you will want. I my specific situation, short circuit, low speed corners, that would mean more toe. Question answered one would say.

The thing I am not sure about is the factor low to very low grip. On the one hand more toe is appropriate (because of low speed corners). But on the other hand, in doing so, on account of the slip angle and the friction is there the risk of accomplishing the opposite meaning less grip because of the low traction track?

Last edited by Kensei; 01-05-2012 at 04:24 PM.
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Old 01-05-2012, 05:12 PM   #35
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What kind of car are you running? Is it not physically possible to change the inner pivot of the lower arm seperately from the upper link? I can't imagine a car designed like that but at any rate...

If you move both the upper and lower inner pivots up or down your roll center is being moved in the same direction. Both up - RC up; Both down - RC down.

This is because the IC is being moved in the same direction as you move both inner pivots and the RC location is determined by the IC as it relates to the contact point of the tire and where that connection crosses the vertical centerline of the car.

I'm no pro at tuning so I'm not going to speculate too much on what you might need in your car. I understand theory more than I understand reality. I would start out by removing any shims you may have and find the best spring combo that give you a decent balance. Run a fairly standard setup like front toe even up and 3* toe at the back. I dont' know a good reason to change front toe just because grip is low. Taking toe out of the front is just going to make steering response slower and give you less steering because you're on a tight track. You need the wheels to turn so just keep em straight up I'd say.

What kind of camber are you running? Too much is no good because there may not be enough traction at the inside of the tire to get it to roll over and create a larger patch. You may want to stay conservative there... maybe like 1.5* ?

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Last edited by Lessen; 01-05-2012 at 05:30 PM.
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Old 01-07-2012, 11:11 PM   #36
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Can someone help me understand the effect running long arms has on handling of a car, assuming all other settings stay the same e.g. track width/shock angle?

It's a common tuning option on the TF6 and I don't really understand how it works, would it be right to say that it slows the rate that the roll centre changes as the car rolls?
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