What is the Most Important Suspension Component on a Cup Car?

aunty dive said:
And without the various sensors measuring spring and shock travel, dynamic ride height measurements at 2 or 3 points on both sides of the car, splitter clearance, throttle position, steering angle and a few other things ... all measured dynamically in real time and linked to the data recorded at the wheels and by the GPS system.

All of that is included when the sim or the rig is prepared for use.
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All that hocus pocus, for shock travel just push up the rubber bushing thingy:D
 
I worked for a company that made shock testing machines. An Indycar team brought their track rig to have a shock tester installed in the trailer. They brought a car and opened it up to us. I was surprised that the shocks were mounted sideways instead of up and down. Race cars have some amazing tech.

For another job a LeMans Jaguar (Imsa style prototype car) was used to set up a rolling test bed designed to have the wheels rotating while testing the car in a wind tunnel. The suspension was tested at speed - without the car moving.

Both those systems were built 25 years ago, I can't imagine what they use these days.
 
aunty dive said:
If you’re getting into this, look into a spring’s motion ratio, how it’s calculated and it’s effect on wheel rate.

Wheel rate is at the heart of every calculation, simulation, pull-down rig or shaker rig test, wind tunnel and track test undertaken. The rate of an individual spring (the amount of force required to deflect the spring 1”, expressed in
lbs. / inch) is included in the formula used to determine wheel rate. Mechanical engineer-speak.
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Agree if used as a datum line. IMHO it all changes in practical application,
Spring loads constantly change during the course of an event.
 
Churchkey said:
Agree if used as a datum line. IMHO it all changes in practical application,
Spring loads constantly change during the course of an event.
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Individual wheel loads constantly change. Springs and their rates are a constant. See post # 70.

The only exception would be rising-rate springs. Illegal in NASCAR competition.
 
This has been a fascinating and highly educational thread to read through and I appreciate all the contributions. I look forward to more topics like this in the future.
 
I guess the single most important suspension part is supposed to be a spindle? I can understand that over the years many parts from in the earlier days when they ran truck wheels because they were stronger than passenger car wheels, up to the this spindle are parts used to fit the situation, but I think many suspension components are just as important or more so. Any suspension part that is adjustable would be in the same category of importance as the spindle to me. Suspension adjustibility is an important part of having the right setup for track conditions and many parts are involved..
 
Took you a while but I knew you wouldn’t disappoint.
 
The answer is forthcoming. I'm working in my portable office right now.

And I will add that is the idea of what is the most important suspension component is universally held by those who work with this stuff.
 
aunty dive said:
The answer is forthcoming. I'm working in my portable office right now.

And I will add that is the idea of what is the most important suspension component is universally held by those who work with this stuff.
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Yes.No doubt.
 
How about number two, three, and 4 pieces and so forth, any opinions Aunty about the other pieces and their importance in ranking?
 
The most important suspension component is tires. Everything you change in regards to spring rates, shocks, and alignment is aimed at getting the tires to work better by maximizing contact patch, ensuring that the tire isn't bouncing up and down over the irregularities of the track surface, making sure that each tire has the right crossweight it needs, and is maintaining proper scrub radius. Without tires to optimize, you wouldn't have anything to aim for when making suspension adjustments. Maximizing that tire's grip is the foundation of it all.
 
KTMLew01 said:
Tire. That's about all that moves now.
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cheesepuffs said:
The most important suspension component is tires. Everything you change in regards to spring rates, shocks, and alignment is aimed at getting the tires to work better by maximizing contact patch, ensuring that the tire isn't bouncing up and down over the irregularities of the track surface, making sure that each tire has the right crossweight it needs, and is maintaining proper scrub radius. Without tires to optimize, you wouldn't have anything to aim for when making suspension adjustments. Maximizing that tire's grip is the foundation of it all.
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Chicken dinner for two!

easy-healthy-chicken-dinner.png


Mr. Puffs explains it quite precisely. Nice to see you back here.
 
More on this later. I have some stuff from Goodyear that I think most will find quite enlightening.
 
I've got a whole new respect for the people that understand how the tires affect the cars and how to use those effects
to the max. A lot more complicated than I ever imagined.
 
If we regard the tires as "suspension components," then Aunty's previous post about unsprung weight seems overly simplistic and even misleading. And I think we all can agree that the tires do act as a spring, and certainly optimizing tire performance is "the most important thing." So I'm confused by the post quoted below...
aunty dive said:
Unsprung weight calculation includes 100% of the weight of the wheels, tires, front hubs, brake rotors and calipers, front spindles and the weight of the entire rear-end housing assembly from hub to hub including brake components and the third member. Added to all of that is 50% of the weight of the springs themselves and 50% of the weight of all 4 shocks, the upper and lower front control arms, the anti-roll bar connecting links, the steering linkage components, trailing (truck) arms, track bar and the driveshaft.
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Would you like to explain why you think it’s overly simplistic?

I’ll ignore use of the word misleading.
 
aunty dive said:
Would you like to explain why you think it’s overly simplistic?

I’ll ignore use of the word misleading.
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Please realize that I don't know jacksh-t about four-wheel suspension systems - so I'm easily confused and misled - but I'll give it a shot.

If we regard the tire as a spring, how can we say the wheel, hub, brakes, etc. are "100% unsprung weight?" Seems to me, the definition posted of what is sprung versus unsprung is based upon the assumption that the only spring is the coil spring mounted over the shock.
 
LewTheShoe said:
Please realize that I don't know jacksh-t about four-wheel suspension systems - so I'm easily confused and misled - but I'll give it a shot.

If we regard the tire as a spring, how can we say the wheel, hub, brakes, etc. are "100% unsprung weight?" Seems to me, the definition posted of what is sprung versus unsprung is based upon the assumption that the only spring is the coil spring mounted over the shock.
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https://www.cjponyparts.com/resources/what-is-unsprung-weight

I chose that explanation because it includes references to rotational mass ... wouldn’t want to be overly simplistic.
Or ... know your audience.

A bit later on, I will post some information about the spring rate of race tires. Small numbers but included (not mentioned on purpose) in the calculation of wheel rates as is the spring rate (X it’s motion ratio) of the front anti-roll bar. Again, small bites.
 
aunty dive said:
What does a team’s tire specialist actually do?

How does he decide which set of four is marked Set 1? What does “we put on a bad set of tires” mean?

Answers here, in a document first published by Goodyear in 2003 (updated as required) titled Tire Reference and Information Guide:

http://hscra.us/PDF/nascar_goodyear_tire_manual.pdf
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Great info here, I was a tire specialist back in the day and we had zero info like they have with todays technology. When running bias play tires, we over inflated the rights after mounting them and let them sit ( in the sun preferably) to stretch and gain stagger before bringing the pressures back to the minimum recommended psi , never considering what it did to spring rates. All we knew is we wanted the rights bigger than the lefts to help the car turn. Depending on the track , you could run anywhere from 1/2" inch to 2" inches stagger in the front and from 3/4" to 3" inches in the rear. Those are mainly asphalt numbers but the range was subject to driver preference. With the Radials, all that went out the window. The specific codes, spring rate recomendations and pressures to the 1/10th of a pound changed the game.
 
I’m flashing back to 2 or 3 twenty inch wide right rears sitting in my driveway, baking in the hot sun. Sometimes the super modifieds liked 6 or 7 inches of stagger.

Great memory. Thanks for helping me recall that. :cool:
 
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aunty dive said:
I’m flashing back to 2 or 3 twenty inch wide right rears sitting in my driveway, baking in the hot sun. Sometimes the super modifieds liked 6 or 7 inches of stagger.

Great memory. Thanks for helping me recall that. :cool:
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That must have been fun trying to gain. I remember lining up at the tire building where they let us in one team at a time to select tires and trying to find a set that was made in the same lot (good luck) and wondering how we were gonna get the stagger we needed with a 85 1/2 left and and 86 right. o_O
 
Late to the game here, but I agree that tires are most important. Even outside of Cup racing we spend more time and money on tires than anything else.


Although due to the way the original question was phrased I thought the OP was asking about a chassis component (in which case shocks/bump stops are the name of the game today).


A really good book about tires and how they work is The Racing & High‑performance Tire: Using the Tires to Tune for Grip ...by Paul Haney.

Although I don't remember if he talks about tire preps... it's illegal in many forms of racing but lots of teams still treat their tires with chemicals.

Heck, you can legally "prep" your tires somewhat just by how much you allow the sun to shine on them, or not...

It's hard for track officials to reliably test tires for prepping chemicals... sending them to a laboratory is better but slow and still not failsafe.


Yeah a tire acts like a spring - just bounce an inflated wheel/tire assembly and you'll see. Change the air pressure and it'll bounce differently (and the sizing changes too - stagger and grip patterns change). Change what you use to inflate them (regular moist air vs. dry air vs. nitrogen vs. any of the above plus chemical(s) etc.) and they bounce differently. Plus chemicals applied to the outside and/or inside changes the grip of the tread plus the spring rate of the sidewall, as well as how they grow as they heat up.


Then you have to factor how the spring rate of the tire effects the spring attached to that wheel (it doesn't merely add), and how all of that affects your shock absorber or bump stop choices. Then once you have a handle on how that tire affects the corner where it's mounted, you need to figure out how it affects the other three corners (it's all a system) - particularly the timing of load shifting as the car goes through corners.


Yeah it can get complicated. Those top racing mechanics earn their pay!
 
The modern stock car is closer to a go-kart than a car. Tires are HUGE now as for importance. The above mentions something i hadn't thought about. How does a change of tire spring rate (pressure=vertical deflection) affect the mechanical spring load? Imagine a car setting on steel wheels/no tires. The spring would get 100% of vertical load. That means X amount of shock travel for X amount of load. Now add a rubber tire. The spring "sees" less load. Shock moves less so less damped movement. The shock "damps" the springs movement or helps slow it's movement. Think of the shock as your hand on a basketball. When you dribble YOU control height ball bounces. Without control you have no idea where it will go. A given pressure (spring rate) has a natural frequency. An uncontrolled spring will oscillate at its natural frequency. The reason you rotate you tires is because the front/rear suspension likely has a different frequency. Left in one position they may cup due to the tire "dribbling". Again, the shock controls the dribble. But also controls how fast/slow the load is transferred laterally/diagonally.

OK...dissect this further if you want. I LOVE this stuff. Discussion always helps me learn even though I feel i know it all already...:flushed::partytime
 
I like to discuss too, although the more I study stuff like this the more I realize I don't know...

Tire spring rate affects mechanical spring rate in a "parallel" fashion, despite it looking like the two spring rates are connected in series.
When you connect any number of springs this way, and use "k" as each spring's spring rate, the reciprocal of of the final total (equivalent) spring rate equals the reciprocals of each individual spring rate all added together. As a mathematical formula:

1/k(eq) = 1/k1 + 1/k2 + 1/k3 ... (continued for as many series connected springs that you care to involve)

If you are only considering two spring rates (the tire and the mechanical spring) then you can do some algebra and obtain this formula:

k(eq) = (k1 x k2) / (k1 + k2)

However, if your car has bump stops then the first formula allows you to include them too. Note that because bump stops are thin they only effect the overall spring rate for a short amount of travel (until they're fully squished) and then for the rest of the system's travel distance they drop out of the equation.
If you know your chassis and suspension components can flex then those tend to add directly to the overall system spring rate (because they act physically in parallel to the tire / mechanical spring assembly).


Generally, the spring rate of the tire is less than the spring rate of the mechanical spring so the tire dominates the system. You can plug some numbers into the formulas to see their effects. And generally as tire pressure goes down so does the tire spring rate. A little tire pressure change can cause a big tire spring rate change - that's why some racers carefully adjust it to a tenth of a pound.

By the way, if your stock car is sprung so stiffly that it acts like a go-kart then flexing in the chassis components becomes important. In karts we include spring rates of the axle portions that each tire bolts to, as well as flexing of the frame. Racing kart chassis are purposely built with complex angles and differing tubing sizes and thicknesses to use the frame as a spring.


Now about the shock absorbers, I prefer to think of them as dampeners rather than like a hand dribbling a ball - because shocks react to the forces applied to them while that hand is imparting force into the dribbling system. But there's no foul in considering that a bouncing wheel could act like a hand... just need to also consider that a dribbling hand tends to be more consistent than a wheel bouncing on an irregular surface. I also prefer to think of the wheel / mechanical spring system as being contained by mounting hardware, so instead of not knowing where it will go if uncontrolled you do know the plane of movement for the bulk of the system's energy. However, I concede that some energy does move laterally (springs can bow side-to-side and a tire sidewall definitely bows all over the place) so there is no harm with your control analogy. Overall though the bulk of a shock's control forces are in the direction of the shock shaft sliding in and out of the shock body.
 
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