Automotive Race car suspension Class

[Vintageracer13]

Evening Ranger Mike. I'm using a triangulated 4 link on the rear of my vintage modified. Can you explain to me how changing the bar angles will affect the handling?

 

[Ranger Mike]

This set up has advantage of more lateral support for the rear end. You have vectors acting to each chassis mounting point as well as the Panhard bar. I suspect the pivoting in rear roll over steer will be quicker as the forces are acting at an angle to the lateral forces and not at 90 degrees as the traditional 4 link does.
The upper links can be adjusted same as the traditional upper links are.
see post 132 on page 4 for details on 4 link

 

[Vintageracer13]

Thank you sir! I will read up on it. I'm happy with the setup so far but I'm working to optimize it

 

[Ranger Mike]

the upper link settings are a given as much has been written on this. You have jack up the car, wheels off, set the rear end at track level ( read up on this in my earlier posts) measure both side wheel bases at track level, then at max roll so right side is in compression and left side in droop, then you can see if the rear end remains neutral, or goes into roll over steer or under steer. Until you do this you won't know what is going on when cornering

 

[Vintageracer13]

the upper link settings are a given as much has been written on this. You have jack up the car, wheels off, set the rear end at track level ( read up on this in my earlier posts) measure both side wheel bases at track level, then at max roll so right side is in compression and left side in droop, then you can see if the rear end remains neutral, or goes into roll over steer or under steer. Until you do this you won't know what is going on when cornering

That makes sense. Eliminating the panhard bar saved me about 23 lbs of weight in the correct spot

 

[Vintageracer13]

That makes sense. Eliminating the panhard bar saved me about 23 lbs of weight in the correct spot

 

[Ranger Mike]

here is the situation. you eliminate the panhard bar and this will lower your rear RC. Forget about tuning with the rear RC. REAR ROLL CENTER. Everything is centered about this point. Effectively you still have a 4 link suspension but now without a solid anchor to take care of the rear weight momentum going to the outside (panhard bar). Lateral momentum ( sometime called weight transfer..arrrrrrr) thru the RC motion gets you to mid corner without spinning out or heading to the guard rail. Now the chassis is set and ready to come back to neutral. All Roll over steer does lets you run in the turn deeper before getting off the go pedal. Then you tune with the upper links for forward bite. RC tuning is critical on any track. Must have. The virtue of the panhard bar is you can raise it to loosen the car or lower it to tighten the car very quick and easy, loosen tow bolts , tape measure it and retighten, Me, I like vectors working at 90 degrees so i can deal with it easier. You go using angular vectors and things get complicated and at a race track in the heat of the moment..i do not need this. I leave finesse to the Formula One boys that got lots of extra help, worthless as they may be. Put the panhard bar back on. 23 # is 3 gallon of fuel. You should be racing with fuel cell anyway for safety.

 

[UFO]

Hi Vintage 13! How can you have two points of lateral control, on the center of the rear, one on a arc and one in a straighjt line perpendicular to the bottom of the frame, and not have a bind when it goes into roll, or straight up and down movment?

 

[Ranger Mike]

Is there any interest in exploring more performance when your class rules dictate 500 cfm 2 bbl carb only? Should we dig into this and see if we can make some more horsepower?? Pls reply and i will proceed.

 

[Vintageracer13]

Hi Vintage 13! How can you have two points of lateral control, on the center of the rear, one on a arc and one in a straighjt line perpendicular to the bottom of the frame, and not have a bind when it goes into roll, or straight up and down movment?

I don't have a good enough understanding of why it works but it does. The car I copied has won every feature but 2 this year and won the championship last year. The car rolls the center very well and also doesn't have a panhard bar. With this setup I feel the panhard would cause a bind. To me it essentially the same as the A or G body GM suspension that is used in street stock racing. I would love to see it modeled in a software program to see how it actually works

 

[UFO]

V-13 sorry I thought you had a panhard bar. what is the octagon bar on the right side in your pic . With a closer look I see it is not connected to the frame. Your bottom rods mounted so close at the bottom of the rear is almost triangulated. That would give you a very low roll center, for the rear, that would travel close to a straight line perpendiclar to the mount points on the bottom of the frame. It will move slightly to the right if you have left rear leed and the opposite with right leed. The roll center hight should be at the heims on the rear.

 

[sonny12]

Hi RM if you were to set up brake floaters on a 3 link would you set the bar toe angles the same as the trailing links or square to the axle?

 

[Ranger Mike]

Brake floaters remove brake forces from other suspension movements and direct the braking force to be used to tune the chassis setup with the radius rods. These radius rods can be level or angled up or angled down. IF angled up, the result adds down force on the tire contact patch. If angled down the force lifts up the tire on braking. If kept level or straight no force impacts the tire. Generally, the side which has the most up angle will have the most downward force and add tire bite on that side. Too much rt side rear uphill angle will make the car hard to turn because the rt rear has too much bite under braking. Too much left rear will make the car loose because the left rear has too much bite and the car wants to pivot around that tire during braking. A good starting point is left rear level and rt rear 10 to 15 degrees up hill. This keeps the rear end tight under braking. Much info in Steve Smith book IMCA Modified Racing Technology on this matter.

 

[sonny12]

i was meaning top view looking down on the bars. Thank you

 

[Ranger Mike]

square to the axel. force vectors work most effective at 90 degrees

 

[Vintageracer13]

V-13 sorry I thought you had a panhard bar. what is the octagon bar on the right side in your pic . With a closer look I see it is not connected to the frame. Your bottom rods mounted so close at the bottom of the rear is almost triangulated. That would give you a very low roll center, for the rear, that would travel close to a straight line perpendiclar to the mount points on the bottom of the frame. It will move slightly to the right if you have left rear leed and the opposite with right leed. The roll center hight should be at the heims on the rear.

The bar you see is a toe bar to keep the axle tube straight

 

[drobbie]

Hi Ranger Mike,
In thinking about all the variables when making a change to a suspension component, we have had discussions around the topic of for every action; there is an opposite reaction.

My question is softening or stiffening opposite corners when making a spring change. In my case, I am softening the RF spring on our Asphalt Midget but am afraid if I do so the weight transfer increase will help but now will struggle in getting the weight to transfer back to the LR thus decreasing my forward drive off the corner.
Is my thinking correct that I should look at making two changes (one RF and LR) in proportion to each other?

 

[Ranger Mike]

Wedge or cross weight
Do not make the number one mistake all weekend warriors make. That mistake is changing too many things on the racecar at one time.
Regarding the spring change. This proves to be the exception because you never just change one spring. You MUST change the spring/shock combination together. When you soften the right front spring you will take bite (load ) off the left and RIGHT rear. The softer spring will download the right front and cause the car to pivot MORE around this tire. To have to spring kick the load back to the rear for more bite you must change the shock absorber (damper) with the correct rate. If you had a front shock that was more of a tie down rating the downforce (weight transfer I hate that term) would stay up front longer and cause loose off the turn conditions. You want to have the “weight “ kick back” mid turn to load the left and right rear tires properly.
Cross Weight or Wedge - We use wedge ( cross weight) to increase tire load on the left rear tire. This increases tire bite off the corner. Let us say the local racers all run about an inch wedge. At the track, we place a socket on the jack and jack under the rear end housing to lift both rear tires. The right rear should lift up the 1 inch just as the left rear tire shows daylight under the contact patch. This is the wedge or cross weight we attained with the jack screws we have on the car. In the turn, the body will roll over and the wedge drives the left rear to wedge the tires to keep contact. The % cross weight on street stock is usually 1 to 2 % total weight , Late models with slicks run 2% typically. The ideal situation is to have no cross weight and very good spring shock packages to tune the car.
Rule of thumb - every inch of wedge is 1% Cross weight.When wedge goes past the normal amount ( and inch more than what the normal amount is) then make a left rear spring change. Then reduce the wedge to under the normal amount and adjust at the track as required. Cross weight is adjustable because the local track will change due to temperature, amount of rain washing off the oil and rubber, etc… You need to have a way to dial the chassis in for new conditions and not use it up for basic chassis setup.

The best tool you have to chassis tune a racecar is a notebook and a tire pyrometer. Learn how to read tire temperatures and adjust.

 

[Ranger Mike]

I update the index periodically. Post numbers are correct the page number prob not. See page 1

 

[Savem c10]

What is the correct length a panhard should be . How far in front of the right rear axel tube center line should it be ? Asphalt late model on 8 inch tires perimeter chassis.

 

[DaveC426913]

Is this thread still going? It's a bloody teenager!!

Surely it sets the record for longest active single-topic* thread.

*ruling out anthology threads, such as jokes and animal pics, etc.

 

[Ranger Mike]

I am proud to say I am contacted often by PM for advice setting up their race cars. For obvious reason they wish to do this privately. Results are excellent most of the time. Thank you DaveC ...btw most racers start racing when they are teenage. I was racing before I had a driver license!

 

[Ranger Mike]

SDavem- Panhard bar roll center is the center of the bar and is the easiest to tune due to both side mounting point adjustments. You have a small 8 inch tire so traction is going to be everything. The rear roll center is very important here. You need a lower roll center to improve bite. Roll center should be between the bottom of the ring gear (assume Ford 9") and just below the rear axle tube. 10 to 11 1/2 inch is ball park. How much wedge or cross weight % do you have? From your description you have a short panhard bar that will place the rear roll center at a diagonal to the front end.

Note- If your front roll center is located at the center point of front tread width. If it is offset 3 inch to the right side, I try to make the rear roll center offset three inch to the right. If you have the fronmt RC other than described, you must add more spring rate to one side just to compensate the car handling. I personally do not like this as the roll center will not be in line and this adds complexity to the spring tuning. I like a very long panhard bar mounted at the rear of the housing. Longer levers throw much less chassis bind in the setup. Can you relocate? What is the mounting point location of top link relative to the track width? What % left side weight do you have? Photo from Steve Smith book Paved Track Stock Car Technology

 

[Zippi]

I've been following along here for a few years, absolutely top notch discussion. Retired from racing 20 odd years ago...... missed it terribly.
So back at it again. Used to do everything with plumb bob, chalk lines and a angle finder.
And a few beers
Bought the program Mike recommended And redesigning a old car with it.
Many many questions to follow.

 

[Ranger Mike]

Zippi
i guess it never get out of your blood once you get in it. so ask away...
i would say this forum is for the racers who wish to learn so if you want to share the build, great, if you want to private message me i have had hundreds of these so can do that too.
welcome back racer!
rm

 

[Zippi]

Thanks Mike! I'll PM you as to rules and the location of where we run. We showed up last year with the car, and the old timers recognized us right away. Got warned about rule interpretation pretty quick LOL

 

[berkeman]

Welcome to PF.

Thanks Mike! I'll PM you as to rules and the location of where we run. We showed up last year with the car, and the old timers recognized us right away. Got warned about rule interpretation pretty quick LOL

We prefer that discussions be held in the open forums instead of in PM conversations. But I guess if you're going to be asking for advice for how to get around the track rules, a PM conversation might be the best choice...

 

[Ranger Mike]

I recommend that this forum is for learning and teaching.
Zip..you are not known nor is your new car and team and this is good. Your location is not known also, I am sure the thousands of tracks out there have similar chassis set ups and the same monkey see monkey do mentality applies.

Any getting around sanctioning rules would be ... cheating!!! And we all know this does not happen in racing...AKA Smokey says if it ain't in the rules, it is allowed. Perish the thought!

As your local competitors are highly unlikely to monitor this forum and not know you my bet is you pretty safe.
We are not re-inventing the wheel here.

Having been on here for ten plus years, I highly respect and value Mr. Berkemans input so if at all possible, an open discussion is much appreciated. But my private PM is open as long as we understand the situation. OK?

 

[berkeman]

We are not re-inventing the wheel here.

I see what you did there...

 

[Zippi]

Fair enough to both of you, i like your pun there Mike! However i just wanted to give some background info so the discussion could be narrowed down. Im good with a public discussion. Im interested on the page 12 discussion about your equal length upper and lower control arms. We're able to do this on the new design, no one around here has done it, i was wondering what your thoughts would be on a flat bumpy track? A track similar track to Mount Lawn Speedway. Chevelle clip, 3 point rear ,