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Old 06-05-2011, 08:04 PM   #21
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Originally Posted by JR4WDTRBO View Post
For a car suspension to work properly, the rear role center needs to be higher than the front.
Why?

Also, don't get me wrong. I have .25 rake on mine and my car works, like really really works.
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Old 06-05-2011, 11:17 PM   #22
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Sorry, the pinch weld is where the panels are joined on the chassis behind the front quarter?

Dann
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Old 06-06-2011, 09:48 AM   #23
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Originally Posted by Shahab View Post
Why?

Also, don't get me wrong. I have .25 rake on mine and my car works, like really really works.
On a normal road car, they are all set up with the front roll center slightly lower than the rear roll center. Reason it is this way has to do with how the wheels are loaded under driving conditions. (maybe MR cars are different?.?.? IDK, but probably not) Its a little difficult to explain. In general, the higher your center of gravity is the higher your roll center needs to be. On good suspension designs, as you compress your suspension your roll center raises. The closer the roll center gets to your center of gravity the less the car will roll. (btw, as you drive the roll center shifts all over the place and is a force center and not a fixed point...)

With the rear roll center too low the car will just over steer over the place, with it too high it will be mad tail happy... With the rear slightly above the front you get a happy neutral.h

Quote:
Originally Posted by nitrodann View Post
Sorry, the pinch weld is where the panels are joined on the chassis behind the front quarter?
Yep. Its the ridge that you attach your factory jack to.

Last edited by JR4WDTRBO; 06-07-2011 at 07:30 PM.
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Old 06-06-2011, 11:30 AM   #24
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Originally Posted by JR4WDTRBO View Post
It seems the the roll center axis doesn't like to be too far out of sync with the roll centers."
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Originally Posted by Savington View Post
Last sentence of the first post.
In that sentence is "roll center axis" referring to the same thing as "roll axis"? Roll axis as I understand is just straight line drawn between the roll centers, so how could it be out of sync with respect to the roll centers? It's obvious that having the roll axis slope down to the front some is helpful for a miata, but has anyone sat and figured out why, other than testing?
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Old 06-06-2011, 02:47 PM   #25
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Level roll centers means the rear wants to track the front end perfectly. This is a car that pushes, though, since the car has momentum in a straight line. In order to actually make it turn and rotate, you need to have the rear roll center higher than the front.
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Old 06-06-2011, 07:32 PM   #26
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Quote:
Originally Posted by Shahab View Post
In that sentence is "roll center axis" referring to the same thing as "roll axis"? Roll axis as I understand is just straight line drawn between the roll centers, so how could it be out of sync with respect to the roll centers? It's obvious that having the roll axis slope down to the front some is helpful for a miata, but has anyone sat and figured out why, other than testing?
I was quoting someone else. I assume he was referring to the original roll axis compared with the new after height adjustment, but I don't know.

You are correct that the roll center axis is just an imaginary line connecting the front and rear roll centers. To me though, the its not very useful information other than visualization the relationship between the front and rear. Even though front and rear suspension movement effects each other, I prefer the think of them as functioning separate unless I am "doing the math" to keep from going crazy (too much to think about all at once. I also prefer to think of each corner as separate islands of suspension, and I like to forget that the chassis likes to flex...ect lol) I like to break it down Barney style as much as possible when I am conceptualizing suspension dynamics in my head...lol

Quote:
Originally Posted by Savington View Post
Level roll centers means the rear wants to track the front end perfectly. This is a car that pushes, though, since the car has momentum in a straight line. In order to actually make it turn and rotate, you need to have the rear roll center higher than the front.
Yes, mostly correct (%100 percent correct if the rear suspension was exactly like the front -camber curve, mounting points, arm angles,..) Even on front wheel drives the rear roll center is slightly higher than the front to keep handling balanced, but I suspect you are right [RWD more than FWD.]

Last edited by JR4WDTRBO; 06-07-2011 at 07:31 PM.
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Old 06-06-2011, 07:47 PM   #27
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Can you even drive? Or are you trying to build the perfect track car with ride heights set to the "t" before actually going out and tracking it?

This thread is so silly.
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Old 06-06-2011, 11:16 PM   #28
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Can you even drive? Or are you trying to build the perfect track car with ride heights set to the "t" before actually going out and tracking it?

This thread is so silly.
Hater! No actually I'm only 13. I like the Miata because it looks cool and its small like my *****. Whoops, ball just dropped....whoops, there goes the other one.

<\pissing contest> You win

Jerk.
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Old 06-07-2011, 10:30 AM   #29
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It's a ROLL center, not a "role" center.

FFS...
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Old 06-07-2011, 12:08 PM   #30
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Quote:
Originally Posted by JR4WDTRBO View Post
Hater! No actually I'm only 13. I like the Miata because it looks cool and its small like my *****. Whoops, ball just dropped....whoops, there goes the other one.

<\pissing contest> You win

Jerk.
rofl
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Old 06-07-2011, 01:18 PM   #31
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To the OP:

To answer the original question, I would setup the car under the conditions it will be driven. That means setting the ride heights (and setting 'rake') with your weight in the car. That also means having an average amount of fuel in the tank (ie: 3/8 to 1/2 tank).
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Old 06-07-2011, 02:25 PM   #32
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Go out and get the book tune to win by Carroll smith and read. /thread.

Have a great day,
Jared
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Old 06-07-2011, 03:07 PM   #33
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Originally Posted by Jfornachon View Post
Go out and get the book tune to win by Carroll smith and read. /thread.

Have a great day,
Jared
On page 54.

"The front roll center will always be lower than the rear. If it is too much lower, we will have a car that does not enter corners well and which exits corner on three wheels. The big trick here is to keep the front and rear roll center movements approximately equal to each other--and in the same direction--as the car does its various things while negotiating a corner."
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Old 06-07-2011, 07:23 PM   #34
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Thank god this thread came around. I've been wondering why my car seems to want to track straight on turn in - I can work with it, and have altered my technique accordingly, but even watching videos online I could tell other's miatas had much more rotation capability...

All my tools and tent, etc. are still in my trunk from Chuckwalla so I'm going to unload the car tomorrow and then measure... it's probably all wrong.
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Old 06-07-2011, 08:11 PM   #35
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Quote:
Originally Posted by kotomile View Post
It's a ROLL center, not a "role" center.

FFS...
Whoops I don't know why I keep doing that. Gotta quit with the Drunk typing. lol Edited some of the mistakes out... (I will be playing the role of "that guy" who haz them grammar issues)
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Old 06-07-2011, 08:16 PM   #36
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Quote:
Originally Posted by Shahab View Post
On page 54.

"The front roll center will always be lower than the rear. If it is too much lower, we will have a car that does not enter corners well and which exits corner on three wheels. The big trick here is to keep the front and rear roll center movements approximately equal to each other--and in the same direction--as the car does its various things while negotiating a corner."
Makes me happy. That book has been on my want list for a little while.
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Old 06-10-2011, 04:22 PM   #37
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So yeahhhhh... my front is 1/8" higher than the rear. My pinch welds are pretty well molested, so it's hard to be super accurate, but adding 1/4" has got to help
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Old 06-10-2011, 05:07 PM   #38
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Quote:
Originally Posted by ThePass View Post
So yeahhhhh... my front is 1/8" higher than the rear. My pinch welds are pretty well molested, so it's hard to be super accurate, but adding 1/4" has got to help
Welp, it guaranteed that this thread helped someone. Methinks there will be an "OMG, my car handles GREAT" post coming soon.
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Old 06-11-2011, 08:53 PM   #39
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Welp, it guaranteed that this thread helped someone. Methinks there will be an "OMG, my car handles GREAT" post coming soon.
^ LoL



I read something last night on AutoSpeed.com that was interesting:

MX-5/Miata Magnificence - Part Two
Part Two of our look at one of the most successful sportscars in modern motoring...
By Michael Knowling


"[2nd Generation Miata] Suspension - while similar in layout to the original - was heavily revised. Several pick-up points were relocated - caster was increased by two degrees and front roll-centre lowered - and the springs and dampers were revised to suit (including having more travel). Interestingly, concerns of steering kickback caused by increased castor were addressed by re-bushing the steering rack - it was made relatively soft in vertical compliance to reduce transmitted shock."

I didn't realize that the front roll-center had been lowered for the second gen. Very interesting. That means that you could possible get away with less rake on a NB. Wonder how much the front roll center was lowered. Time to start Googling...
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Old 06-17-2011, 12:11 PM   #40
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My pinch welds are pretty well molested, so it's hard to be super accurate
This, god dammit.
I'm going to measure my ride height today, my car feels shittier than it used to.

I know its been said but its worth mentioning again, DON'T measure from the fender lip like I did.
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