Front MC location

[dirtdiggerracing]

Looking for ideas & opinions on front MC location! Where do you think they need to be vertical & Horizontal and why ?? What am I going to feel when I move it each direction? ?

[save the racers]

I don't measure them very often on the l/m.I just use what the mfg. recommends for ride heights.With the modifieds I've did a lot of work because you are mixing and matching different parts.I'm going to go with 3 to 6" high , 0 to 6" to the left, and not alot of movement after dive and roll.I' m starting to think the virtual swing arm length of the right front is as important as the as m/c location.

[Austin34471]

Seems to me like manufactures care less about the kinematic RC and IC and more about getting a good RF camber curve. With the god awful amount of roll these cars have, you are either gonna have a Rf IC that starts the center/right and doesn't migrate as much, or one that starts left but moves right in a hurry..... Or if you figure out ways around those, you'll have positive camber. Lol. I'd like to hear a few others' opinions on this, billet, matt49, etc.

[billetbirdcage]

Gonna throw some numbers out here for argument sake: A fairly common car, with a small change to the RF upper control arm from factory. All of these will be with roughly the same amount of travel on the RF (in the 4" range on compression - give or take .25"), this just goes to show you unless you know dive and roll and are just going off your shock travel markers on the RF the roll center can or does migrate in completely different manner.

Again all the same car but with different dives and roll to get the same approx 4" of RF travel.

Car starts statically at: 2.6 high and 12.6 right

Dive and roll A: 4.0 / 20.7 = 3.87" on RF
Dive and roll B: -5.3 / 64.3 = 3.81"
Dive and roll C: 1.1 / 30.9 = 3.89"
Dive and roll D: -1.6 / 43.2 = 3.79"

If your going of your travel on RF, you still have no idea which one of these it's actually doing or when and at what portion of the track is it doing one and doing another at a different part on track.

I could take this same car and because of set-up/track style/driver style, it may do Dive and roll A but with another set-up/track style/driver style (not changing the front end at all) it then may do Dive and roll B.

So.....

[Matt49]

I completely agree with the camber gain comment by Austin. Billet makes a great point. In order to do this right, you really need some good front end software that works in all 3 dimensions so that you can also evaluate things like caster gain in the event that you have any anti-dive built into your design. From playing around with caster a little bit, I can tell you that there is much more to this than most people let on. It's often been stated that caster is a "driver feel thing" and doesn't really affect handling that much. Without saying much more on that topic I will say that is complete BS.
Anyway, you need good software and you almost need some data acquisition to get to the level of detail that Billet is talking about (where and when on the track).
I tend to think that a RC that has minimal movement and creates camber gain that keeps camber relative to the race track "negative" is what most builders are going for right now.
In any front end design, an improvement in one are of concern will hurt you somewhere else. As Mark Bush says, "there is no such thing as the perfect front end design".

[25drtrkr]

This is straight from the horses mouth several years ago. Bill Frye said they had developed a new frontend for GRT's and went to a test to try it out. He said the front end was developed to simply change the roll center, 5" vertically and horizontally. He said as a driver, he couldn't tell any difference! I believe that tells you, that theres a lot of variability with front end design.

[let-r-eat]

The front end means very little without taking into the consideration of the rear.A frontend program that only takes into account the front end is basically meaningless IMO.The front end design must compliment what is going on in the rear of the car.Example is rear track migration. Short v/s long jbar/trackbar/panhard bar etc. May require shorter or longer moment arm on the RF v/s other designs.Caster curve is a major deal. Dynamically changing tire loading.

[billetbirdcage]

I completely agree with the camber gain comment by Austin. Billet makes a great point. In order to do this right, you really need some good front end software that works in all 3 dimensions so that you can also evaluate things like caster gain in the event that you have any anti-dive built into your design. From playing around with caster a little bit, I can tell you that there is much more to this than most people let on. It's often been stated that caster is a "driver feel thing" and doesn't really affect handling that much. Without saying much more on that topic I will say that is complete BS.
Anyway, you need good software and you almost need some data acquisition to get to the level of detail that Billet is talking about (where and when on the track).
I tend to think that a RC that has minimal movement and creates camber gain that keeps camber relative to the race track "negative" is what most builders are going for right now.
In any front end design, an improvement in one are of concern will hurt you somewhere else. As Mark Bush says, "there is no such thing as the perfect front end design".

Matt, try 9.5* caster in the RF and 7.5* in the LF and tell me if you can carry a drift angle in the car with anything but a really good open engine? it worked like a champ back in the old days before the LR behind, turn just a little right and it hooked up the LR so hard it would straighten the car out. Worked good in the slick if you where a really straight type driver but sucked in the traction cause you just couldn't carry any drift angle at all with the car.

[25drtrkr]

Matt, try 9.5* caster in the RF and 7.5* in the LF and tell me if you can carry a drift angle in the car with anything but a really good open engine? it worked like a champ back in the old days before the LR behind, turn just a little right and it hooked up the LR so hard it would straighten the car out. Worked good in the slick if you where a really straight type driver but sucked in the traction cause you just couldn't carry any drift angle at all with the car.

Since you brought up caster,bbc, do you think we really need caster split anymore? We are turning left and right so much, I wonder if its hurting our overall performance.

[billetbirdcage]

We are turning left and right so much, I wonder if its hurting our overall performance.

We are? on average wheels are rarely turned left and if they are it's for a nano second on turn's 1 and 3, least on a decent handling car.

[Matt49]

Bbc, check your PMs.

[Brian Gray]

For what it's worth I think with the realm we are in as far as holding the car over pinned rf. I keep my mc about 2-5" to the right and as low as I can get it. If it migrates a little I'm not concerned as long as it trails to the attitude. Maybe this is my issue currently idk.


Now as far as caster goes like mat said there is much more there. If you pay attention to the front end while you turn the wheel static you will see what happens. I've seen cars with 10-15 in them on slick tracks.

[25drtrkr]

We are? on average wheels are rarely turned left and if they are it's for a nano second on turn's 1 and 3, least on a decent handling car.

I agree 100% with the wheel being turned more to the right. Since that's the case, why are we still using caster stagger?

[billetbirdcage]

IMO, one of the biggest factors is so you have to hold tension on the steering wheel to the right to keep the car going straight. This in it's self takes out some of the dartiness in the car, just from a slack or whatever standpoint in the steering.

You also have to remember that caster jacks up on that corner when turned outboard but lowers that corner when turned inboard, which is different then camber or inclination which lifts when turned either way. So caster has a much bigger influence on jacking effect least when it comes to wedge, so caster split changes the amount of wedge change when steering more then camber/inclination.

Granted you could argue this to a degree from a LF standpoint as it's may or may not be jacking anything around if there is little to no weight on it.

[25drtrkr]

IMO, one of the biggest factors is so you have to hold tension on the steering wheel to the right to keep the car going straight. This in it's self takes out some of the dartiness in the car, just from a slack or whatever standpoint in the steering.

You also have to remember that caster jacks up on that corner when turned outboard but lowers that corner when turned inboard, which is different then camber or inclination which lifts when turned either way. So caster has a much bigger influence on jacking effect least when it comes to wedge, so caster split changes the amount of wedge change when steering more then camber/inclination.

Granted you could argue this to a degree from a LF standpoint as it's may or may not be jacking anything around if there is little to no weight on it.

The reason I ask is that I was recently told by a well known driver, that doesn't run caster stagger. He said he like his car to steer the same, left and right. I tried it on a car I crew chiefed on, but with a new driver, I couldn't get any feedback, one way or the other, other than "it felt fine".

[powerslide]

"it felt fine".

typical driver lol

[billetbirdcage]

The reason I ask is that I was recently told by a well known driver, that doesn't run caster stagger. He said he like his car to steer the same, left and right. I tried it on a car I crew chiefed on, but with a new driver, I couldn't get any feedback, one way or the other, other than "it felt fine".

Billet Shrugs

There is a 100 ways to skin a cat, just cause I don't like something or think different don't mean I'm correct by any means.

The number 1 problem with most teams is what is felt or seen by the crew, is usually inaccurate. They are typically trying to fix the wrong thing or the driver is just feeling something wrong thus wants to fix the wrong thing. You have to figure out what your drive can and can not feel and some drivers have really good feel, while others not so much. The ones that have a hard time feeling or recognizing the problem needs to rely on the crew much more. A driver like that can still be very successful, just usually makes them way less consistent and requires the right crew guys or crew chief.

Even drivers with good feel, can't or won't be sensitive to some things. I've had drivers that one you move the j-bar a 1/4" on the pinion and send him out and he will come back in a say: " I said only move it a 1/4", how far did you move that dam thing?" and another driver I move it an inch and he come back in and ask if I moved it, lol.

But to answer your question, I prefer to leave the split there strictly from a pull stand point. We all probably have driven a POS street car with worn out front suspension parts or a ton of play in the steering and it's not bad to drive on a crowned road where it pulls to the left from the crown in the road as you just hold the wheel tensioned to the right and it drives fine. But get it on a flat road and you are sawing at the wheel to keep the car straight and pray a cop isn't behind you or you might get pulled over for DUI from weaving all over the place.

[let-r-eat]

I know those types of drivers. I once had a 5 pound weight and used it often to settle drivers down. The car would be working fine but driver mistakes would make the finish only so-so. I'd take the 5 pound weight and put it just under the decking on the passenger side and tell them: "Now the (not a nice word)(not a nice word)(not a nice word)(not a nice word) thing will turn like a rocket ship."Be surprised how that little sugar pill worked. I've been a hero and a zero for that trick.

[25drtrkr]

I know those types of drivers. I once had a 5 pound weight and used it often to settle drivers down. The car would be working fine but driver mistakes would make the finish only so-so. I'd take the 5 pound weight and put it just under the decking on the passenger side and tell them: "Now the (not a nice word)(not a nice word)(not a nice word)(not a nice word) thing will turn like a rocket ship."Be surprised how that little sugar pill worked. I've been a hero and a zero for that trick.

LOL....I didn't know when I signed up for crew chief duties, years ago, that I had to be a part time psychiatrist, too!

[save the racers]

Billet, I think your comment about just how much weight is the left front carrying is a very good question.When drawing a graph for m/c location the r/f and l/f are used as equals to place it.Lets say 50% r/f ,50%l/f.But on the track the amount of load or work being done is 75 r/f ,25 l/f or some figure like that.I've started looking at the r/f as a system by it's self.I don't have enough laps with these ideals to make to make any positive statements but the little light bulb over my head has came on a few times.