51 replies to this topic

[FTodaro]

Yeah, I can think of an occasion that surprised me. Maybe that was what happened.

I'm probably not being clear with my question though...why are bumpstops so important (in any racecar) if you should rarely be at full shock compression? I just assumed SMs relied on them frequently because of the limited shock travel.

I will give you my answer I am not sure its the right one, I think the Fat Cats are better than the OEM Mazda as they are real hard and if you get into them your going to go for a ride most likely, the fat cats will be progressive there is a transition to bottoming out. Also i recall reading some place that they will change the geometry of the shock to the control arm, not sure about that.

You should be able to safely run the car lower, a little, by using them vs the hard rubber stops.

someone smarter than me may have the right answer.

[Brendan O]

Negative rake - higher in the front than in the rear - I give up a bit on corner entry in order to get to WOT sooner

But ... when you go to WOT after turn in is finished, weight transfer to rear tires will occur. If the car is already squatting on the rear tires, won't going to WOT after corner apex cause understeer (more push) because even more weight is being taken off the front tires and being transferred to rear tires? I thought a higher rear end will reduce push when going to WOT after corner apex because it reduces weight transfer to rear contact patches? With a higher front, it seems like you get less chance of rear tire slip/spin because of all the weight on rear tires (good) but greater chance of push and not making track out, thus needing to lift during track out (bad).

thanks
Brendan

[Sphinx]

A related issue:

 

1) Once CW's have been set, if one turns the front or rear adjusters (as a pair) the same number of turns, is CW affected?

 

2) If a car is set level at 4 5/8 all around and then cross weights are set, what kind of difference are you seeing front to rear and side to side in ride height?

 

3) When going from 4 5/8 all around to 50-50% cross weight, is it a matter of turning the adjusters a little (less than a turn) to get to 50-50?  Or does it take multiple turns?  (I realize that it is different from car to car and driver to driver - I'm asking in the broadest, generic terms).

[JRHille]

But ... when you go to WOT after turn in is finished, weight transfer to rear tires will occur. If the car is already squatting on the rear tires, won't going to WOT after corner apex cause understeer (more push) because even more weight is being taken off the front tires and being transferred to rear tires? I thought a higher rear end will reduce push when going to WOT after corner apex because it reduces weight transfer to rear contact patches? With a higher front, it seems like you get less chance of rear tire slip/spin because of all the weight on rear tires (good) but greater chance of push and not making track out, thus needing to lift during track out (bad).

thanks
Brendan

I believe raising the back of the car puts more weight on the rear tires contact patch, soo this means lowering it would take away weight? seems counter intuitive but this is what I learned from a driver a few years back. 

[trimless]

A related issue:

 

1) Once CW's have been set, if one turns the front or rear adjusters (as a pair) the same number of turns, is CW affected? NO, BUT WEDGE IS AFFECTED.

 

2) If a car is set level at 4 5/8 all around and then cross weights are set, what kind of difference are you seeing front to rear and side to side in ride height? MINIMAL - 1/8" TO 1/4"

 

3) When going from 4 5/8 all around to 50-50% cross weight, is it a matter of turning the adjusters a little (less than a turn) to get to 50-50?  Or does it take multiple turns?  (I realize that it is different from car to car and driver to driver - I'm asking in the broadest, generic terms). ONE TURN OR LESS AT EACH CORNER SHOULD GET YOU CLOSE.

 

Not all cars are the same, but i shared my experience so hope that helps.

[LarryKing]

Sooo... cross weight and wedge are independent of each other? You don't say!

 

I've said it a hundred times, but I like to hear myself - ride height at the pinch welds is meaningless - ballpark measurement at best.

 

A car can be level, ie: 4.625" all around and be 50-50% CW, or not.

 

If you don't have the driver/equal weight of the driver in the seat you are wasting your time. Oh, And you must un-hook one side of both sway bars.

 

Zsolt Baumgartner once told me to think of it as a four-legged stool. If you go up LF-RR 1/2 turn, then you must go down RF-LR 1/2 turn, and vice versa.

[Jim Drago]

But ... when you go to WOT after turn in is finished, weight transfer to rear tires will occur. If the car is already squatting on the rear tires, won't going to WOT after corner apex cause understeer (more push) because even more weight is being taken off the front tires and being transferred to rear tires? I thought a higher rear end will reduce push when going to WOT after corner apex because it reduces weight transfer to rear contact patches? With a higher front, it seems like you get less chance of rear tire slip/spin because of all the weight on rear tires (good) but greater chance of push and not making track out, thus needing to lift during track out (bad).

thanks
Brendan

Brendan

Years ago I plotted the roll centers of 99 miata..  I think the rear was below the pavement

[Muda]

 

A related issue:

 

1) Once CW's have been set, if one turns the front or rear adjusters (as a pair) the same number of turns, is CW affected?

 

2) If a car is set level at 4 5/8 all around and then cross weights are set, what kind of difference are you seeing front to rear and side to side in ride height?

 

3) When going from 4 5/8 all around to 50-50% cross weight, is it a matter of turning the adjusters a little (less than a turn) to get to 50-50?  Or does it take multiple turns?  (I realize that it is different from car to car and driver to driver - I'm asking in the broadest, generic terms).

1. No.  That's why I use rake as a quick and easy adjustment at the track.

2. Why do you care?  As long as you can reach your cross without putting a corner too low and limiting suspension travel you should be OK.

3. Different by wheel.  LF is most sensitive.  1/4 turn can move it 3/10's or more depending on where you start from.

[Jim Drago]

lots of bad information here.. 

wedge=cross=dewedge=cross  They are the SAME thing, different terms...   

 

going up equally on both front perches in theory will not effect cross weight/ wedge.   ( it will change incrementally unless wheel weights are exact, but may not even register)

 

raising front perches will change rake

 

changes in spring perches are not linear..  the closer you are to a true 50/50 weight distribution you are the changes will have more effect. ( 1/4 turn at true 50/50 will make a more of a percentage change than a car say at 48.5 %) 

 

Hope that helps.. It may be time for a an alignment webinar.. been just too busy and lazy to do it  If you have questions, shoot me an email. 

 

Jim

[Ron Alan]

I believe raising the back of the car puts more weight on the rear tires contact patch, soo this means lowering it would take away weight? seems counter intuitive but this is what I learned from a driver a few years back. 

I'm sure I will be corrected if I'm wrong, but this is the opposite of what I have learned...at least in relation to grip. You raise the rear to loose grip(help with a tight front end)and lower the rear to help with a car that is to loose.

 

Raising or lowering the front or rear perches as a pair shouldnt change the CW%. But it will affect handling and weight to front or rear.

[JRHille]

Jim-what does that mean for us unedjamacated people? (roll center is below the pavement)

 

ron- This is what i've learned too, but I thought say I raise the LR while on a scale I should get more weight on that LR.  As for handling, I would raise the back of the car to get the car to rotate on initial turn in.  Haven't really wrapped my head around how the two relate..or I just could be dead wrong

[Muda]

But ... when you go to WOT after turn in is finished, weight transfer to rear tires will occur. If the car is already squatting on the rear tires, won't going to WOT after corner apex cause understeer (more push) because even more weight is being taken off the front tires and being transferred to rear tires? I thought a higher rear end will reduce push when going to WOT after corner apex because it reduces weight transfer to rear contact patches? With a higher front, it seems like you get less chance of rear tire slip/spin because of all the weight on rear tires (good) but greater chance of push and not making track out, thus needing to lift during track out (bad).

thanks
Brendan

IMHO, the goal of all of this is matching the handling characteristics of the car to the drivers style and capabilities.  Watch Danny and the other top drivers.  They are driving it in deep to every corner and creating more weight transfer than a mid pack guy.  They enter corners at a higher speed, move more weight to the front tires, which allows them to get their rotation done with a setup that would have a midpack guy screaming understeer.

[Jim Drago]

Justin
Short answer... Run the rear a little lower than level.. This is base and tune from there. Don't be fooled by the body of the car.

On scale weights( static) if you raise rear perch you will put more weight on that corner..

On track if you raise the rear.. you will now transfer that weight faster to the front. Car will be looser raising the rear. To a point.. It may also help front grip..  TO A POINT!!!

What does not work is the Texas chopper.. Keep raising the rear bc you have no grip in the front. If the front is already too low and you raise the rear.. You transition instantly to solid suspension on the front and you get "death push". So raising the rear makes this condition worse. You would need to raise front before doing anything else.  If "EVER" you turn the front wheel and the car just grinds an refuses to turn, ALWAYS go to front ride height first. 95% of the time when you experience this condition, you are too low.

General speaking.. If not on the bump stop.. Lowering the end that has no grip will add grip.
Jim

[Sphinx]

Jim-what does that mean for us unedjamacated people? (roll center is below the pavement)

 

ron- This is what i've learned too, but I thought say I raise the LR while on a scale I should get more weight on that LR.  As for handling, I would raise the back of the car to get the car to rotate on initial turn in.  Haven't really wrapped my head around how the two relate..or I just could be dead wrong

 

 

Roll center:  It's hard to explain, but here's a starting piont.  In short, it has to do with projecting imaginary lines of the suspension geometry.  read this:  http://www.neohio-sc...ynamics2007.pdf

 

But almost all double wishbone cars, the roll center should almost always be underground.  If not, you get a "jacking" - which is why carroll smith never understood why someone would drive a Formula V (old beetle suspension).

[Brian Linn]

But almost all double wishbone cars, the roll center should almost always be underground. 

I thought it was above the ground plane?    Nice link - that is a keeper.  

[JRHille]

Thanks for clearing it up Jim

That's a good read, might have to go through it a few more times

[Brendan O]

lots of bad information here.. 

wedge=cross=dewedge=cross  They are the SAME thing, different terms...   

 

going up equally on both front perches in theory will not effect cross weight/ wedge.   ( it will change incrementally unless wheel weights are exact, but may not even register)

 

raising front perches will change rake

 

changes in spring perches are not linear..  the closer you are to a true 50/50 weight distribution you are the changes will have more effect. ( 1/4 turn at true 50/50 will make a more of a percentage change than a car say at 48.5 %) 

 

Hope that helps.. It may be time for a an alignment webinar.. been just too busy and lazy to do it  If you have questions, shoot me an email. 

 

Jim

 

my brain hurts - but thanks - i will mull this over

[Danny Steyn]

Brendan, its this curiosity that you and Justin are displaying about EVERYTHING needed to make yourself faster that will reward you in spade fulls! Just keep mulling and pondering it all, and it will all start to gel. Surround yourself with wiser, more skilled, faster racers and listen to what they have to tell you. Sift through all the BS, get past the petty agendas, and you will find your speed. There are many of us watching here looking to you, Justin, Ernie Jr. and other younger drivers to keep this class successful.

Looking forward to meeting you on a track someday soon

[Muda]

Justin already has everyone beat in iRacing.  If he can transfer that speed to the real track it's all over.

[Brendan O]

Brendan, its this curiosity that you and Justin are displaying about EVERYTHING needed to make yourself faster that will reward you in spade fulls! Just keep mulling and pondering it all, and it will all start to gel. Surround yourself with wiser, more skilled, faster racers and listen to what they have to tell you. Sift through all the BS, get past the petty agendas, and you will find your speed. There are many of us watching here looking to you, Justin, Ernie Jr. and other younger drivers to keep this class successful.

Looking forward to meeting you on a track someday soon

 

 

I will get out there soon. At OPM World Famous Test Weekend in Jan, Tom said i'm doing quite well considering amount of seat time. I will practice a bit more, play around with setup a bit more and then join you guys.

 

Thanks for encouragement. 

PS Hope you and everyone else do well at COTA !!!  Wish i was there.