Roll center location? :iono:

[mike156]

Originally Posted by Ubersuber

If I understand you correctly you are suggesting that neither the pinnacle of motorsport nor the kart scene can give us useful information about modifying our cars.

Yes...
When it comes to roll centers...F1 and Karts don't mean a thing to us.

But PLEASE tell me how you would establish the roll center of a kart.

Originally Posted by Ubersuber

You guys really crack me up sometimes.

Dear Canada,
Since this clown is clearly laughing at who knows what, I have to assume this bastard is high. I must ask a favor of you. While we (the USA) as a majority are clearly jealous of your "loose" laws against pot...clowns like this are going to fuck it up for everybody. Please get this guy under control.

[Dipstik-sportech]

Originally Posted by mike156

Yes...
When it comes to roll centers...F1 and Karts don't mean a thing to us.

But PLEASE tell me how you would establish the roll center of a kart.



Dear Canada,
Since this clown is clearly laughing at who knows what, I have to assume this bastard is high. I must ask a favor of you. While we (the USA) as a majority are clearly jealous of your "loose" laws against pot...clowns like this are going to fuck it up for everybody. Please get this guy under control.

We've tried and failed, time to show him some American freedom. FYI his province has oil........ Jk please don't shoot me.

[Ubersuber]

Originally Posted by mike156

Yes...
When it comes to roll centers...F1 and Karts don't mean a thing to us.

But PLEASE tell me how you would establish the roll center of a kart.



Dear Canada,
Since this clown is clearly laughing at who knows what, I have to assume this bastard is high. I must ask a favor of you. While we (the USA) as a majority are clearly jealous of your "loose" laws against pot...clowns like this are going to fuck it up for everybody. Please get this guy under control.

They should. Roll center for axles is the axle center, i.e. the axle line across the car is the roll center height, or near as makes no difference. So for a kart the roll centres are the wheel centres. I assume you imply that nobody cares since a kart doesn't roll, but it does actually and on its tires. My point is that the start point to understanding any suspension is the kart with none but the tires. Until you understand that it is the tires and the orientation of the tires that matters you shouldn't touch anything on the suspension of your car.

For F1 it is admittedly complex and no team is going to publish this year's suspension settings but since the ride height is so low the suspension arms are essentially parallel which puts the roll center at ground level under the centerline of the car. For those likely to quibble about this I concede the roll centres could be above ground or below ground depending on the exact alignment of the suspension arms but, seriously, I don't think F1 suspension engineers lose much sleep over the roll center per se since that ends up where it ends up after optimizing a bunch of other parameters. To understand how suspension is supposed to work and observe some of the insurmountable limitations you have only to look at an open wheel racer and it's all there in plain view all the time. The advantage to watching an F1 suspension deflect is twofold: nifty onboard cameras get you really good views and suspension travel is very limited so it is easy to see what is happening.

So, from very good handling and simple (no suspension) vehicles to the pinnacle of motorsport you get the range of viable designs. The common factor is very little suspension travel.

Why is this good? Because the essential problem plaguing suspension engineers is camber change with wheel travel.

This "technical section" of this board prompted me to join your little community. The very interesting topic of the mechanical lsd and the clever graphing of wheel speeds piqued my curiosity. But there is a lot of misinformation bandied about, some of it quite amusing and some possibly dangerous. Hence my modest contributions.

Those finding the animated sketch of the MacPherson strut suspensions interesting should be aware that the upper "mount" in the diagram does not correspond to the actual physical mount of a strut and the diagram needs to be viewed with that limitation in mind.

Among its many benefits the MacPherson strut is generally constructed so as to be non-adjustable which in turn means it hardly ever goes out of alignment. It is very robust and entirely predictable in its geometry. The geometry is not very good in one respect: the roll center moves a lot with suspension movement. This deficiency has long since been dealt with by clever suspension engineers.

Problem comes when you decide to mess around with that hard work without understanding this deficiency properly.

The camber angle of the strut is actually determined by that little welded bit that supports the upper end of the hub, where it bolts to the hub. That angle cannot change. The strut angle is not relevant to camber except in suspension motion and even then the angle isn't as important as some posts in this thread suggest. The main determinant of camber change in roll is the length of that lower control arm (includes the radius arm in the modern L shaped component), the longer the better.

One of the truly brilliant aspects of the MacPherson strut is the way it mimics the unequal A arm suspension over the comparatively short travel normally encountered in road driving. If you lower your car and fit stiffer springs this advantage is even higher. The length of the strut is more significant than the strut angle itself, so the suggestion that Subaru would just fit shorter struts to get a lower hood line is just laughable and exemplifies the dangers of ignorance when messing with your suspension.

So, this is why lowering a strut suspended car can often yield significant additional grip solely because the suspension then begins (static setting) at a higher negative camber than stock. If you fit stiffer springs so as to limit suspension travel even more then this benefit is enhanced.

[Ubersuber]

Originally Posted by unsurety

ANYWAYS

When lowering 1-1.5", is a roll center adjustment kit beneficial?

If you have to ask the question then the answer is always no.

When you add a roll center compensator to a strut suspension all you are doing is making the strut longer, intending to push the lower radius arm down to a presumed more favourable angle. I did check whiteline' s site and they have no comment about how low you need to be going before their compensator will enhance the car and I suspect this may be because they expect only knowledgeable people to buy that particular product. I also suspect you'd need to drop more than 1.5 inches before a roll center compensator would be worthwhile, or even a bit helpful.

You will lose the negative camber gain you achieved by lowering the car in the first place.

You might wonder why you did this after you're done.

In order to know before testing whether this will work or not you need to know the camber rise for your strut and where that camber will be statically and dynamically.

Most posters here who seem to know what they're talking about report good results with lowering by 1 to 2 inches without compensating for roll center change. If that experience is reliable, and those who report doing it confirm better cornering behaviour, then installing roll center compensation is as likely to remove that benefit as to increase it.

Roll centers on strut suspension move downwards with suspension compression, and that really isn't very important in the grand scheme of things. What really matters is where does your wheel camber end up in roll. Until you know that you won't know whether lengthening the strut will help or hurt or make no real difference.

My initial post failed to take into account another advantage of MacPherson struts, the spring loads are taken directly to the wheel, not via a ball joint. Adding roll center compensators to the ball joint does not affect ride height. It does affect camber.

If I was overly brief before this should set you right.

[wparsons]

Originally Posted by Ubersuber

Why is this good? Because the essential problem plaguing suspension engineers is camber change with wheel travel.

Camber change with wheel travel is actually a good thing, keeps the tire flat in corners without needing more static camber.

Originally Posted by Ubersuber

This "technical section" of this board prompted me to join your little community. The very interesting topic of the mechanical lsd and the clever graphing of wheel speeds piqued my curiosity. But there is a lot of misinformation bandied about, some of it quite amusing and some possibly dangerous. Hence my modest contributions.

Are you seriously trying to suggest you weren't a member before, under your old username?

Originally Posted by Ubersuber

The camber angle of the strut is actually determined by that little welded bit that supports the upper end of the hub. That angle cannot change. The strut angle is not relevant to camber except in suspension motion and even then the angle isn't as important as some posts in this thread suggest.

You're honestly clueless. If that were true, then adjustable camber plates (which do nothing but shift the upper mount location in/out) wouldn't actually adjust camber.

Originally Posted by Ubersuber

When you add a roll center compensator to a strut suspension all you are doing is making the strut longer, intending to push the lower radius arm down to a presumed more favourable angle. I did check whiteline' s site and they have no comment about how low you need to be going before their compensator will enhance the car and I suspect this may be because they expect only knowledgeable people to buy that particular product. I also suspect you'd need to drop more than 1.5 inches before a roll center compensator would be worthwhile, or even a bit helpful.

You will realize (or discover if you add this modification) that this raises the ride height by approximately the length of the roll center compensator. You will then drop the coilover spring perch to restore your original ride height.

Actually, that's 100% false. The way the whiteline roll center correction works is by making the balljoint taller, which does nothing except change the angle of the lower control arm. It doesn't make the strut longer, it doesn't change the ride height. If you really looked, you would also see the whiteline kit includes new outer tie rod ends to help correct bump steer.

For someone claiming to be so opposed to false information, you sure seem to spread A LOT of it yourself.

Originally Posted by Ubersuber

If I was overly brief before this should set you right.

Except that you're totally wrong.

[mike156]

Originally Posted by Ubersuber

My point is that the start point to understanding any suspension is the kart with none but the tires. Until you understand that it is the tires and the orientation of the tires that matters you shouldn't touch anything on the suspension of your car.

I can almost concede to your argument of the kart being "the tire" and that's why you bring it up. HOWEVER, karts are flexures and they have suspension per say. They tune the stiffness of the chassis...so much for only the tire mattering...

That's actually what I was getting at anyway with figuring out roll centers, it will move with chassis/axle flex. Granted it’s on a very small scale.

Originally Posted by Ubersuber

...since the ride height is so low the suspension arms are essentially parallel which puts the roll center at ground level under the centerline of the car. For those likely to quibble about this I concede the roll centres could be above ground or below ground depending on the exact alignment of the suspension arms but, seriously, I don't think F1 suspension engineers lose much sleep over the roll center per se since that ends up where it ends up after optimizing a bunch of other parameters.

Except they aren't parallel on many of the cars right now. But the overall jist of your argument I can agree with...it's of secondary importance, particularly on a car that has about 1" of total suspension travel.

Originally Posted by Ubersuber

To understand how suspension is supposed to work and observe some of the insurmountable limitations you have only to look at an open wheel racer and it's all there in plain view all the time. The advantage to watching an F1 suspension deflect is twofold: nifty onboard cameras get you really good views and suspension travel is very limited so it is easy to see what is happening.

What should a tire do when the entire car rolls 0.1*? Sure...pretty obvious, the tire should stay in the same position relative to the ground. Oh, but we are talking about cars with 4" of travel and that roll 2* or more...again, how does F1 apply here?

Originally Posted by Ubersuber

So, from very good handling and simple (no suspension) vehicles to the pinnacle of motorsport you get the range of viable designs. The common factor is very little suspension travel.

No. It's not a "common factor," karts rely only on chassis and tire deflection and F1 has so little movement simply because the aerodynamics package is basically useless unless the car is an inch off the ground. Neither of these conditions apply to road going cars. If the aero worked with the F1 car higher, it could be a completely different outcome here on what you think is ideal. Regardless, we don't drive cars that have to be an inch off the ground and stay exactly at that height with 5000 pounds of downforce.

Originally Posted by Ubersuber

Why is this good? Because the essential problem plaguing suspension engineers is camber change with wheel travel.

Except relative to travel really isn't what's important here. Relative to body and ground motion is what matters and that means the balance F/R as well as how it works with the wheels pointed in places other than straight. If all you cared about how it was relative to travel then...well you wouldn't be turning the steering wheel anyway and roll center doesn't matter either way at that point. It could be on the moon and not change a thing...

Originally Posted by Ubersuber

This "technical section" of this board prompted me to join your little community. The very interesting topic of the mechanical lsd and the clever graphing of wheel speeds piqued my curiosity. But there is a lot of misinformation bandied about, some of it quite amusing and some possibly dangerous. Hence my modest contributions.

But you're wrong...particularly on what you posted about the whiteline RCK. You clearly know nothing about the product.

Originally Posted by Ubersuber

Those finding the animated sketch of the MacPherson strut suspensions interesting should be aware that the upper "mount" in the diagram does not correspond to the actual physical mount of a strut and the diagram needs to be viewed with that limitation in mind.

That diagram will mimic exactly what a strut does under those conditions. A pin/slider joint will behave exactly like the strut actually does in that it simply allows a change in length and a pivot in one dimension. Sure, it's not right if you look at it in 3D on a strut with caster, but it's perfectly fine in that diagram.

Originally Posted by Ubersuber

The camber angle of the strut is actually determined by that little welded bit that supports the upper end of the hub. That angle cannot change. The strut angle is not relevant to camber except in suspension motion and even then the angle isn't as important as some posts in this thread suggest. The main determinant of camber change in roll is the length of that radius arm, the longer the better.

Camber angle (I assume you mean the angle between the strut and the hub centerline, and not the tire camber angle?) can change...it's called "camber bolts."

Strut angle actually has a pronounced impact on dynamic camber, both in travel and with steering inputs. Sure, static camber is an order of magnitude larger, but it can definitely be used to tune the dynamic camber curve.

Originally Posted by Ubersuber

One of the truly brilliant aspects of the MacPherson strut is the way it mimics the unequal A arm suspension over the comparatively short travel normally encountered in road driving. If you lower your car and fit stiffer springs this advantage is even higher.

Except in that regards, it mimics an unequal length setup where the upper arm is longer than the lower arm and you lose camber with bump travel...kind of the exact opposite of what you want...

Blah...I'm done here.

[Ubersuber]

Making some progress, at least the ad hominem stuff is tapering off.

As for the whiteline kit comments, I am assuredly correct that the kit is intended and does lengthen the strut. To pretend otherwise fails to appreciate what the "strut" is on a MacPherson strut. You can suggest it lengthens the "hub" if you prefer but from a suspension perspective the "strut" axis includes the length between the strut bearing at the top and the ball joint at the bottom. It matters not where you add the length above the ball joint.

The addition of tie rod end height adjustment is irrelevant to the wheel camber, although it is necessary if you lengthen the strut.

MacPherson struts mimic the geometry of short and long A arms or double wishbones if you prefer. Nobody puts a longer upper arm but some have tried equal length wishbones. As the strut compresses the top of the wheel tips in relative to the strut top mount just as it does for unequal length A arms. Whether that is enough to maintain a vertical wheel at the road is a different question, just as it is for all suspensions.

To suggest the frame of a kart is part of the suspension is no more sensible than to suggest the body of the car is part of the suspension. It may be that the movement of the frame changes the suspension alignment but it isn't suspension. Tire sidewalls are part of the suspension.

The suggestion that the frame can be part of the suspension begs the question of what is being suspended?

[Model Citizen]

[fika84]

Originally Posted by Gunman

Morse Measurement has the K&C data, if you want to buy it:
http://www.morsemeasurements.com/pro...-car-database/

Yea, i know Bob Simmons from my previous job.. He wants $1600 for the data.. I'll measure it

[mike156]

must...refrain...troll...murder...suicide...

[wparsons]

Originally Posted by Ubersuber

As for the whiteline kit comments, I am assuredly correct that the kit is intended and does lengthen the strut. To pretend otherwise fails to appreciate what the "strut" is on a MacPherson strut. You can suggest it lengthens the "hub" if you prefer but from a suspension perspective the "strut" axis includes the length between the strut bearing at the top and the ball joint at the bottom. It matters not where you add the length above the ball joint.

Sweet baby jesus you're retarded. First you claim it lengthens the strut and raises the ride height and claim you need to then adjust the coilover perch to maintain the previous ride height. At least now you've backed off on it raising the ride height. It's not lengthening the strut, it's restoring the geometry to how it used to be. No one with a brain refers to the strut length all the way down to the balljoint pivot. Is that the point that matters with geometry, yes, but no one refers to it that way. Stop being a pedantic jackass.

Originally Posted by Ubersuber

The addition of tie rod end height adjustment is irrelevant to the wheel camber, although it is necessary if you lengthen the strut.

Which is exactly why I said they included them to prevent bump steer, not adjust camber or change roll center.

Originally Posted by Ubersuber

MacPherson struts mimic the geometry of short and long A arms or double wishbones if you prefer.

Most macpherson struts are a MUCH closer match in camber curve to equal length a arms, not unequal length. A typical strut car gains VERY little camber throughout it's range of motion. Lots even start to lose (or gain positive) camber at the upper end of the range of motion.

This is actually a bigger reason why you need a roll center correction kit up front when lowered. It puts you back into a better part of the camber curve, even at the lower ride height.

Originally Posted by Ubersuber

To suggest the frame of a kart is part of the suspension is no more sensible than to suggest the body of the car is part of the suspension. It may be that the movement of the frame changes the suspension alignment but it isn't suspension. Tire sidewalls are part of the suspension.

The suggestion that the frame can be part of the suspension begs the question of what is being suspended?

If the tires are part of the suspension, what isn't being suspended then?

The frame can be, and is, part of the suspension system because the frame is designed to flex (and the amount of flex can be tuned). Just because there isn't pivot points and springs/shocks doesn't mean it isn't offering suspension movement.

[Mikem53]

Originally Posted by mike156

You just tried to talk down to a person that makes a living based on knowing how to make a car handle well. Ground Control has a strong following and is well respected in numerous communities. You are kind of the laughingstock around here...

You are out of your league.
And seriously, did you copy and paste that from wikipedia?

That's all he ever does... Cut and paste.. Until mommy tells him it's past his bedtime...

[Mikem53]

Originally Posted by Ubersuber

This "technical section" of this board prompted me to join your little community. The very interesting topic of the mechanical lsd and the clever graphing of wheel speeds piqued my curiosity. But there is a lot of misinformation bandied about, some of it quite amusing and some possibly dangerous. Hence my modest contributions.

OMG.. Enough of your condescending BS already!!

Your Modest contribution of misinformation is good for entertainment purposes only.
You're self proclaimed expert advice and talking down to everyone is pathetic.
But... As they say..
The ones who say the most, usually know the least. Perfect!