Automotive Race car suspension Class

[Ranger Mike]

i would call the good people at perf trends and ask about your chassis. you are correct on both RC. Pretty easy to tune with the panhard bars on each end.
thanks for checking out this post..
rm

 

[Vintageracer13]

This my project Ranger Mike

 

[Ranger Mike]

running smokey yunicks colors and # 13 i see

 

[Vintageracer13]

Yes sir. That 1966 Chevelle was a eye opener for me. The things he did with the suspension in 1967 that are still used today!

 

[Vintageracer13]

I want to thank you all that have posted on this site. After reading countless posts and asking a few questions I measured my front roll center and discovered it is on the chassis centerline. I'm going to move the frame side bracket over to the right and this hopefully will move the roll center to about 3 inches to the right.

 

[Ranger Mike]

a pretty good start. ifin you are taking time to do this, i would make the right side bracket slotted horizontally. The cost of the panhard bar tubing is such that you could swap out different length p-bars . The 3 inch RC offset is a ball park figure. The offset depends on the track and the tires and will vary the amount of additional down force on the right front tire. But i like your thinking!

 

[Vintageracer13]

Thank you! When measuring the roll center height would measuring from the ground to the horizontal plane of the panhard bar give the correct number?

 

[Ranger Mike]

, vin...almost there, racer! you want the ground to the center point of the panhard bar height. in other words construct a perdendicular bisector from the roll center POINT on the p-bar to the floor.

 

[Vintageracer13]

I get it now! Thank you so much!

 

[Vintageracer13]

Ranger Mike I have a hypothetical question for you. Say you have 2 groups of cars that want race together. Group A has motors no more than 256 cubes and min weight of 2300. Group B has 360 cube motors and a min weight of 2400. Everyting else about the 2 groups of cars is the same. If group B had to be at 2425 including a mandatory 40 lb on the frame rail of the right side in front of the firewall would this give too much of a advantage to Group A? I don't really think so because the B cars have a 100 cube advantage. Thoughts please

 

[Ranger Mike]

From strictly a bench racer perspective, here you go. Figure one horsepower per cubic inch. This is very easy to attain these days. On some cases we go 2 HP per cube but we can stay with 1 hp per cube.

Next we sue the racers rule of thumb that for every 10 pounds you remove from the car you “ add “ one horsepower. So in theory the car that weighs 125 pounds more would need an additional 12.5 horsepower to be even.
The 360 CID car would have 91.5 more horsepower to race the lighter car.
Early Southern California Timing Assc. veteran Stroker Mcgurk –” if some’s good, and more is better, then too much is just enough" he also said
..there is no substitute for Cubic Inches”

 

[Vintageracer13]

Thanks for the input Ranger Mike! How should the front and rear roll centers compare? My assumption is that the rear would be higher but is there a way of deciding that? Should I also try to match the lateral front and rear?

 

[Ranger Mike]

read
Roll Center heights and offsets and why
page 12 post #229
i would go with ft rc offset starting at 3" and try to center the rear RC. don't worry about the rear ht being taller than the ft.

I like a low front roll center mainly because it has better camber curve..less change and I think it is all about contract patch.
As in life, there are exception and the exception to low RC is street stock class where you must race SPEC tires. You can not change the A-Arms usually and so are limited on changing the RC offset to get any down force on the hard spec tires. So you have to raise the RC to get some side bite in these hard sidewall tires.
Yes, you have a shorter moment arm between the Rc and COG but the angle of RC to the tire contact patch is a lot better than stock. Some stock chassis have RC at an inch above the pavement..
You will just about always have rear RC higher than the front and this is ok too

 

[Vintageracer13]

With a straight front axle camber change shouldn't be a issue for me. I want to thank you again. This forum has opened up a whole new world for me!

 

[Vintageracer13]

Ranger Mike I have been considering running a lift bar instead of a 3rd link. I want to use springs top and bottom in the front to control the bar during braking and acceleration. Thoughts?

 

[Vintageracer13]

Sorry Mike I think I found my answer in #954 lol

 

[Vintageracer13]

Good Morning All! I just finished measuring my front roll center after making a new panhard bar. I'm at 2 inches to the right. Not where I wanted to be but much better than where I started. I have a little more work to do on the front end and then I can put the chassis on the ground and get a rough idea of where the height will be.

 

[Ranger Mike]

vinny, just an educated guess..nothing concrete but you may be ok at 2 inch since the panhard bar angle can be tweeked big time. Look at the angle form the rc to the tire contact patch and study up on how changing the panhard bar angle will effect handling. ifin you get too clise the 45 degree angle to contact patch you may start carrying the left front tire..looks great but racing a three legged stool will wear out the tires quicker..but boy does it look ' hot dog"

 

[Vintageracer13]

Is there truth to the theory if you angle on side of the panhard bar down that side will be forced down?

 

[Vintageracer13]

Ranger Mike,
I talked to the people at perf trends and they told me they are 2 months from a version of the software that will work with the straight front axle. Bob Bolles told me his will work with it so that will be my next major purchase.

 

[Ranger Mike]

on paved track cars the panhard bar is usually mounted to the axle on the left side of center line and to chassis on the right side. Longer is better and means less RC movement during total chassis roll. When the p-bar is “ level” both tires will carry equal load caused by chassis roll. if we munt the p-bar on chassis on left side then to the axle on the right side we create too much traction and will push. The angle the bar slants will load that side more and take away from the other side and may lift the left front tire. Just draw out the force vectors and look at the angles. The p-bar mount on the right side chassis is pulling the axle during roll. If the p-bar is level then both tires will be pulled to the outside. If the right side chassis mount is lower than the axle mount then the body will jam the right tire more and cause the left tire to unload a little.look at the rc to tire contact patch. what is the angle?

 

[Vintageracer13]

Sorry Mike I'm referring to the front axle so if I understand you correctly the side that the bar is angled towards will carry more of the load. I ask this because with a beam axle it is difficult to get heat on the left front tire. I often thought if I could build a thinner axle that would bend I could get better loading on that corner.

 

[Ranger Mike]

correct..front or rear pnhard bar work the same.. draw out the force vectors...you need more static left sid weight to warm up the left ft tire or stiffer rt rear spring

 

[Vintageracer13]

Will do. Thank you!

 

[Wylde]

So I ran a 3 link modified "B-Mod" for a while and noticed that a lot of guys had a really short panhard bar and ran it with a lot of angle. From your explanation that would mean that they would load the right tire more than the left and their roll center would migrate faster. Is that correct?

Regardless we ran a long panhard bar with 1-3" of rake it in and the car was always smooth. It liked to come up on the bars slower but was super consistent and never developed a push. I believe this was due to the fact that the roll center did not migrate near as quickly and kept both tires in the traction equally. Needless to say we won a lot of races with it and they were all scratching their heads at how the more "old school" technology was beating them.

 

[Ranger Mike]

Wylde, without knowing all the specs, i would say you are spot on. Longer bars move in shorter arcs which means the RC would have minimum movement. Those short p-bars and J bars will really throw in some chassis jacking. Also running a small degree of angle (rake) means the tires are pretty equal loading. Old school got to be old school caz it worked then and will work now.
good advice from you and thanks
rm

 

[Vintageracer13]

Ranger Mike what is your opinion on using different length trailing arms on the left and right side? I have 34.5 inch long arms and I was considering shortening up the
Left side. This would allow easier mounting of the front bracket.

 

[Ranger Mike]

On 3 link paved track trailing arms, two things.

1. Keep them equal length. Do not have different length trail arms on the car. (exception id dirt cars with ½ “difference to build more rear roll steer)

1. Longer is better. Nasar uses 51 inch truck arm length. Typical 3 link tail arm length is 20” preferred length is 24”. Too short of a length means brake hop.

We set up both trail arms to 5 degree uphill angle so chassis roll yields roll understeer (even on pavement). The wheel base will grow on right side by ½ inch (depending on bar length).
The 3rd link mounting is just as important.

Post # 81 page 6

#253 pg 13

#312 pg 16

#707 pg 36

 

[Wylde]

Just out of curiosity, does any car on asphalt use a lift arm rather than a pull bar for their 3rd link?

 

[Ranger Mike]

you can pretty much bet that every trick and wrinkle wil be tried by a crew chief to get an edge on the competition so yes..this bar issued and every other version as well