Automotive Race car suspension Class

Ranger Mike

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if you like this class ..VOTE
https://www.physicsforums.com/threads/engineering-award.962196/

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Something that's rolling around in my head
if you calculate and find the RC of both front and rear

How much split should there be between the 2 in height ?
How does this effect cornering ?
 

Ranger Mike

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read post # 229 on page 12
mass centroid axis is shown on illustration 13
 
Great read RangerMike!
 
Hey guys I'm from south Africa the 3 link is pretty new and those who have it doesn't Wana help me I'm building a dirt car with 3 link and need help with the length of the bottom trailing arms and the angles thanx
 

Ranger Mike

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welcome Robby and Surdge
3rd link stuff on post 81,253,261 and 707 but check out index for rear end stuff too
 

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Thanks u have been alot of help just one more thing that I have that I can't seem to find is what angle do u use for the j bar
 

Ranger Mike

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see index ..i wrote a lot on Jbar
 
Morning iv got a another question ur shock bracket witch angle do u mount it on
 

Ranger Mike

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READ the posts ...do the research ,
 
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Excuse me if I break in here to join the conversation. I'm new here and will start by attempting to insert a drawing of a suspension linkage roll analysis Exhibit 5.jpg .

Robert
 

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Ranger Mike

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welcome, robert
 
Thank you for the welcome. Please excuse me a moment while I attempt to load a photo on this site.
Robert
DSCN1671.JPG
 

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Ranger Mike

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a great reminder of what this class is all about
 
Great Video!
It didn't mention the front to rear roll problems and solutions by Maurice Olley, however I believe this came later.
 

Ranger Mike

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Olley was absolutely instrumental having gone to GMC in 1930 from Cadillac, Rolls Royce before that. One unheralded but very genius people to make GM what WAS. not is..now. 2002 book Chassis Design by William and Douglas Milliken, published by the Society of Automotive Engineers goes into much of his work. Besides being key to Corvette development that Zora Duntov gets all the kudos for i think he had 40 some pattens attributed to him.
 
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@Ranger Mike, in the world of circle track asphalt late model racing, which would make the handling better, the current quick change rear end or a independent suspension rear end?
 
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Ranger Mike

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BEI welcome
the IRS vs solid rear suspension debate goes on..in my opinion for round track racing the solid quick change is the top dog. IRS tends to not preform as well as the dedicated solid axle setup on straight line basis. since you race on the front and rear straights a lot more than the time you spend in the corners, you want maximum traction. IRS promotes lost traction due to independent springing and the set up. plus you have no roll steer option if you need to dial in rear roll steer.
the extra cost and additional maintenance head aches do not merit doing it. IRS do not like front to rear weight transfer. IRS are great for road racing and cars with mid engine or rear engines. IRS not so good for nose heavy cars. You can dial in camber on each side with the solid axle set up. prop can on IRS but counter productive. you will be racing on a bumpy track so use the solid set up realizing the IRS will lose traction more when you go over bumps vs the solid set up
 

Ranger Mike

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I put his together as racing tip to fine tune your chassis. after tow hours on you tube i could not find a decent video showing the tip about taping steering wheel but it is minus 10 F and end of winter so i share some videos and maybe put a smile on yer face!
When you are at the track hot lapping, try this to fine tune the car set up. Hot lap at mid speed and note the steering wheels degree of turn at mid track. The mid track is usually marked on the wall.

If not, pick a point and use this mid turn location on the wall for reference. You should have the 12 o’clock position marked already for easy of centering.

Note the 12 o’clock of the steering wheel when you are at the mid turn wall location. Use a piece of yellow or masking tape to mark it.

Next thing to do is hot lap the car at you best speed and again note the same mid turn location and the new mid turn steering wheel 12 o’clock position. Mark it with green tape.

If the steering wheel hot lap green tape mark is more than the slow speed yellow tape mark, the car is tight. If the hot lap green mark is less that the slow speed yellow tape, the car is loose. Adjust accordingly.

One of the better videos I found on this



good demonstration of counter steering


do not use this technique on these cars!


continued on next page
 

Ranger Mike

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tips for beginners driving on dirt


Not very good tutorial but good racing to watch in -10 degree F winter
what not to do on asphalt

 

Ranger Mike

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what not to do on dirt

Finally..this is what happens when you got too many rules and enforce them!

gotta watch if you need a laugh…
 
Ranger Mike,
WIth winter the time to learn, we all should have read through every thread here (I know I did) and I thank you for such great information.
For my self, we have been working on the geometry of my friend's late model stock car. (8 inch tires, Coilover suspension and limited HP) We plotted out the front end only to find the attached image. Of course, it horrified me based on the knowledge I gained here and other readings, and we are in the process of changing it all around to bring it more in line with what we feel will make it run better. What I'd like to understand is what characteristics the car would have theoretically experienced from last year when someone else set the car up. From my experience, this geometry looks so messed up I would think the car should slide across the race track because there is no vertical load on the RF tire.
Any insight or comments you could provide would be greatly appreciated. And as always, thanks for hosting this forum as it is invaluable in understanding car dynamics in a simple and easy manner.
upload_2019-3-3_16-29-1.png
 

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Ranger Mike

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Drobbie thanks fro the kind words.
you are correct. it would push going in and be loose off the corner. It is a good thing you caught this set up error. The closer you can get it to center line is good and ifin you can offset it to the right , the better it will handle. Make sure to check camber build. you want it going the right way on each side and keep the curve linear. Bump steer should be under 0.030" per inch bump. Put some rear roll oversteer in it if you can. Dont worry too much about the limited HP as the tires can not handle it anyway. So you want to dial in the car way better than the other guy! put a front to rear brake bias control o n the master cylinders and put in a front right to left brake fluid bias valve in so that you can crank in the left brake to snap roll thru the corner better. put on a ARB (sway bar) loader that you can crank in while hot lapping. this is good if you have long races and the fuel cell lightens the rear end . When budgeting , plan on the dampers ( shocks) being the most funded as this area will do more than any other in this over regulated race series. put a card board box in the race car hauler so the trophy dont get dinged up.
 
I have been successfully running a dirt stock car w the same rc numbers you found on your car Drobbie.
Not saying it’s right but w the right springs and shocks it can be very fast.

Different setups and driving styles take different things.

Ranger Mike helped me figure a lot of this car out via this forum.
 

Ranger Mike

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Good job!
you are correct Dirtrace in that the driving technique means a lot on dirt. The dirt setup ( if i understand your setup) is to get a huge amount of body roll to slam the right front tire with lots of down force. You can get too much down force if you offset the RC to the right side. This is the same reason the asphalt big bar soft spring set up sometimes has left side offset. it is to kill off too much down force on right front tire. You got the front end tied down to very little roll with the BBSS set up and you rely on aero to push down on the right front in place of the chassis roll loading. The traditional right side offset is for cars that can not take advantage of the BBSS setup due to bumpy track and rules making the car sit up high due to ride height requirements. Figure on 3 inch roll max. Also the rules may mean that you can not use aero devices to increase down force. I have seen diagrams by many dirt racers that show the CG and Moment Center during cornering and no vector from the MC to the tire. It shows resultant force from the CG to the tire. Shows centrifugal force with a downward vector. Not correct.
We get down force on the right front tire many ways with many setups. Now you have the dirt super late model monsters roll steer with many inches wheel base change and way huge body roll. Back in the day we offset the dirt RC to 4 inch right side when we had very little body roll. Same with the BBSS setup. It evolves and you gotta learn what works best. too much down force is as bad a too little. Balance it for the track you race.
 

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