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Old 03-14-2006, 05:50 PM   #16
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Originally Posted by rcracingkid
Hey Martin,

I am confused about 1 thing with roll center, possibly you could explain it please.

If i was to raise my inner (upper and lower) mounting locations, say higher by exactly the same amount, what would it do in terms of handeling? Would it do nothing?

Thanks
Hey Mike I'm no expert here but I'll give it a try... I think if you raise the inner (upper and lower) mounting locations higher by exactly the same amount that would cause a few things to change:
A) more of the static weight of the car would be lower in relation to the axles which would lower the CG.
B) Now depending on the angle of the camber link in relation to the lower arm that would determine the new roll center.
what would it do in terms of handeling? My best answer to that is : TRY IT Would it do nothing? it would ...
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Old 03-14-2006, 10:29 PM   #17
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Originally Posted by rcracingkid
Hey Martin,

I am confused about 1 thing with roll center, possibly you could explain it please.

If i was to raise my inner (upper and lower) mounting locations, say higher by exactly the same amount, what would it do in terms of handeling? Would it do nothing?

Thanks
Hey Mike,

I hope you are gonig to make it up for our Canadian Challenge at Fastcats in a couple of weeks. Kevin and Corey will be there along with Paul Lemeiux, who will kick all our butts (like blackstock)

To answer your question, that type of adjustment will raise the roll center. So every time your tires gets smaller and smaller you are raising the roll center of your car.

This is why we having been working with speedmind to make larger rims. As you know the speedmind rims were about 1mm smaller in diam than the jaco's and parmas. Now they are actually a little bigger in diam than the jaco's and parmas. This way we can run a small sidewall (and still make the 55mm min), but not raise the roll center too high, to reduce the chance of traction rolling.
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Old 03-15-2006, 07:52 AM   #18
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Thanks Martin

I wont be able to go to that race, i am comitted to the 1/18th scale nationals. Hey everyone needs to play with grossly overpowered mini t's powered by mamba's once in a while.
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Old 03-15-2006, 10:45 AM   #19
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ok Mike...if you would rather go play with those toy cars.... just kidden...have fun!
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Old 03-15-2006, 12:46 PM   #20
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RCracingkid- If you raise the inner lower A-arm pivot you raise the roll center, you get more roll stiffness, Less cornering traction on that end with a ball front diff. A little like using heavier springs. I am assuming from your question you are not changing tires or ride height.


If you raise the inner camber link pivot you lower the roll center, exactly the opposite effects. So basically you cancel part of the previous effect. Chances are very good that moving both exactly the same ammount will not exactly cancell each others effect on roll center. I do have this roll center calculator which I wrote available free. Request one at [email protected]. It is an excel spreadsheet. You can tinker with the numbers and know how things change by looking at the output.


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Old 01-04-2012, 12:45 PM   #21
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To get the rc above or equal to the cg would not be possible with any touring car on the market today to my knowledge with their current adjustments.

Having said that, one way to raise the rc high enough to be equal to the cg is to have the lower arm inboard pivot point on the hinge pin be raised to just below (eg. just a few mm) the pivot point of the upper link (assuming the upper link is about parrallel to the ground).

If the rc and cg are identical in theory the car will not roll, but as the car transfers weight to the front or rear of the car the suspension would compress, changing the rc to not be equal to the cg, then the car would roll. It certainly would be an interesting theory to test out . If the rc is above the cg the car should actually lean into the corner like a motorcycle.

Since car balance has a lot to do with weight transfer and how you control that weight transfer, you will want the car to roll at least a little bit so that you can make the car balance in the corners they way you want it to. So to answer you question, you really would not want the rc to be the same as the cg, because that would limit your ability to some degree to control the weight transfer to achieve the balance you want.
Bought the book and studied it.
The way you explain roll center I understand.
As I understand it you can change the height of the roll center by moving the inner upper pivot point.

However I hear and read about changing RC by putting shims in between chassisplate and the mountingblocs of the suspensionarms.
For instance: what does the RC do when adding shims?
I hear people say that RC is raised then. Is that correct or not?

I don't quite understand. Because adding shims leads to heigher inner pivot points which would suggest a relatively lower roll center (your book page 61). But maybe I am wrong here. By adding shims not only the upper inner pivot link raises but also the lower.

See my problem?
- people tell me that adding shims leads to a higher RC
- I thought that it lead to a relatively lower RC, because the inner pivot point are raised as a result of the added shims

In the book you say:"With low traction tracks you will want the car to roll more to increase traction."

I race at low and medium traction tracks. So I would say my RC would have to be low to increase traction. In that case I would add shims.

Christopher Krapp, Kyosho TF6 teamdriver, told me he had 2mm shims added on outdoor tracks and 1mm on indoor (carpet) tracks.
I understand that as that indoor (carpet) is more traction and therefore less roll is needed/wanted, therefore reducing the roll center of the chassis is needed and that means that the roll center has to be higher. He does that by shimming less.

However I read a Testreview on the Kyosho TF6 where the tester raced with 2mm shims and said that the car didn't roll in the corners and had to go to 1mm shims.

That is a contradiction I think. That is if more shims equals lower RC ecquals more roll.
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Old 01-04-2012, 01:14 PM   #22
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Default roll center changes

oops
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Old 01-04-2012, 02:26 PM   #23
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Originally Posted by Kensei View Post
Bought the book and studied it.
The way you explain roll center I understand.
As I understand it you can change the height of the roll center by moving the inner upper pivot point.

However I hear and read about changing RC by putting shims in between chassisplate and the mountingblocs of the suspensionarms.
For instance: what does the RC do when adding shims?
I hear people say that RC is raised then. Is that correct or not?

I don't quite understand. Because adding shims leads to heigher inner pivot points which would suggest a relatively lower roll center (your book page 61). But maybe I am wrong here. By adding shims not only the upper inner pivot link raises but also the lower.

See my problem?
- people tell me that adding shims leads to a higher RC
- I thought that it lead to a relatively lower RC, because the inner pivot point are raised as a result of the added shims

In the book you say:"With low traction tracks you will want the car to roll more to increase traction."

I race at low and medium traction tracks. So I would say my RC would have to be low to increase traction. In that case I would add shims.

Christopher Krapp, Kyosho TF6 teamdriver, told me he had 2mm shims added on outdoor tracks and 1mm on indoor (carpet) tracks.
I understand that as that indoor (carpet) is more traction and therefore less roll is needed/wanted, therefore reducing the roll center of the chassis is needed and that means that the roll center has to be higher. He does that by shimming less.

However I read a Testreview on the Kyosho TF6 where the tester raced with 2mm shims and said that the car didn't roll in the corners and had to go to 1mm shims.

That is a contradiction I think. That is if more shims equals lower RC ecquals more roll.
I think Chrissi runs 2mm outdoors because the chance of traction rolling is lower than carpet and more shims generate more tyre heat which can be useful outdoors. He also runs long arms a lot on carpet so it's not a straight comparison between his indoor and outdoor setups
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Old 01-04-2012, 02:36 PM   #24
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Hey Mike....you are too fast already!!
That post was almost 6 years ago
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Old 01-04-2012, 02:42 PM   #25
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That post was almost 6 years ago
d'oh!!!
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Old 01-04-2012, 03:18 PM   #26
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Originally Posted by Kensei View Post
Bought the book and studied it.
The way you explain roll center I understand.
As I understand it you can change the height of the roll center by moving the inner upper pivot point.

However I hear and read about changing RC by putting shims in between chassisplate and the mountingblocs of the suspensionarms.
For instance: what does the RC do when adding shims?
I hear people say that RC is raised then. Is that correct or not?

I don't quite understand. Because adding shims leads to heigher inner pivot points which would suggest a relatively lower roll center (your book page 61). But maybe I am wrong here. By adding shims not only the upper inner pivot link raises but also the lower.

See my problem?
- people tell me that adding shims leads to a higher RC
- I thought that it lead to a relatively lower RC, because the inner pivot point are raised as a result of the added shims

In the book you say:"With low traction tracks you will want the car to roll more to increase traction."

I race at low and medium traction tracks. So I would say my RC would have to be low to increase traction. In that case I would add shims.

Christopher Krapp, Kyosho TF6 teamdriver, told me he had 2mm shims added on outdoor tracks and 1mm on indoor (carpet) tracks.
I understand that as that indoor (carpet) is more traction and therefore less roll is needed/wanted, therefore reducing the roll center of the chassis is needed and that means that the roll center has to be higher. He does that by shimming less.

However I read a Testreview on the Kyosho TF6 where the tester raced with 2mm shims and said that the car didn't roll in the corners and had to go to 1mm shims.

That is a contradiction I think. That is if more shims equals lower RC ecquals more roll.

to hopefully clarify this for you,... if 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.

Regarding the quote from my book....what I meant to say is that by having softer springs on low grip tracks it allows for more weight transfer to the front and rear of the car during acceleration and braking and initil turn in, thus giving you the ability to control the balance of the car more with the throttle.

To increase lateral grip you want to minimize the amount of lateral weight transfer (optimizing the grip efficiency of the tires). So it may seem odd to have softer springs on a car as this will actually reduce the lateral grip. Remember that lateral grip is different than balance and by having longitudinal weight transfer (or pitch) you can better control the longitudinal weight transfer using throttle and braking...thus giving you more control over the balance of the car.
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Old 01-04-2012, 03:23 PM   #27
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Quote:
Originally Posted by Kensei View Post
However I hear and read about changing RC by putting shims in between chassisplate and the mountingblocs of the suspensionarms.
For instance: what does the RC do when adding shims?
I hear people say that RC is raised then. Is that correct or not?

I don't quite understand. Because adding shims leads to heigher inner pivot points which would suggest a relatively lower roll center (your book page 61). But maybe I am wrong here. By adding shims not only the upper inner pivot link raises but also the lower.
When you add shims under the lower suspension blocks you are effectively changing the angle of the lower suspension arm relative to the upper link. It is this relationship (angle difference between lower and upper arms) that changes your RC. 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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Old 01-05-2012, 04:07 AM   #28
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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.
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Old 01-05-2012, 04:38 AM   #29
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Originally Posted by Kensei View Post
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.
In those pics, the closer 'IC' is to the centre of the car, the higher up the RC becomes, that's what is in 'example 2', the left side uppoer link is lower on the inside, yet the RC has been raised.
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Old 01-05-2012, 04:40 AM   #30
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Quote:
Originally Posted by Kensei View Post
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.
I think your making it a little harder than it needs to be. Follow the below rules.

Raise upper link inner pivot = lower roll centre
Raise upper link outer pivot = raise roll centre
Raise lower inner pivot = raise roll centre

The above is listed in order of coarseness of adjust. Removing a 1mm shim from the inner upper pivot will have less affect on raisingre rollcentre than adding a 1mm shim under the suspensiom block.
Bare in mind when adjusting the upper link, the camber change (link angle) also needs to be considered.

HiH
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Last edited by TryHard; 01-05-2012 at 05:55 PM. Reason: Double hih!
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