question on springs

T77911S · 10-21-2020, 08:07 PM

I have a late model race car I am converting to road racing.

I have the front shocks off.
when I shake the front end both sides feel the same as in the spring stiffness.

when I add drivers weight to the car, the passenger side feels "softer"

I am at the front of the car pushing down on it so I can feel both sides at the same time,
I have 850 springs on it. I have a 900 spring. what do you think of me putting the 900 on the passengers side.

I checked the control arm movements with nothing attached. both lowers are fine.
the drivers side upper is a "tad" stiffer than the passengers side. but that doesn't explain both sides feeling the same with no driver weight in it.

Lexus4321 · 10-21-2020, 09:10 PM

Not really sure what you asking?
You need force to move a spring, related to K of the spring.

You saying you pre-load LH with weight and the RH then feels soft? Not really possible.

I am not sure about road racing, it has lots of lefty and righty turns?, so I assume the LH and RH (front) need to match? Certainly if you load the LH side the RH side will sit higher (less sprung weight there), so maybe the geometry has to be offset (LH a tad higher) so that when the sprung weight is on the spring the two sides ride at same height?

I really have no clue, just throwing stuff out there.

T77911S · 10-23-2020, 07:34 PM

I have 850 springs on both sides.
I had the front end apart for something else and I checked the movement of each arm, upper and lower, by itself. they all move freely although the left upper is slightly stiffer.
with everything together and NO springs in the suspension moves freely'
with the springs in and no one in the car and I bounce the front of the car (no shocks) both sides feel the same.
when I put 180 lbs in drivers seat and bounce it from the front (that is both side bouncing at the same time) the right side feels "stiffer" than the right.

Lexus4321 · 10-23-2020, 08:01 PM

Quote:

Originally Posted by T77911S

I have 850 springs on both sides.
I had the front end apart for something else and I checked the movement of each arm, upper and lower, by itself. they all move freely although the left upper is slightly stiffer.
with everything together and NO springs in the suspension moves freely'
with the springs in and no one in the car and I bounce the front of the car (no shocks) both sides feel the same.
when I put 180 lbs in drivers seat and bounce it from the front (that is both side bouncing at the same time) the right side feels "stiffer" than the right.

video it, post vid, lets see.

Bill Douglas · 10-23-2020, 08:29 PM

Maybe the soft "first part" of the spring is being taken up by the 180lb, so therefor there is only "hard spring" left. And the passenger side still has the first bit of springy stuff left in it.

JackDidley · JackDidley's Garage

Quote:

Originally Posted by T77911S

I have 850 springs on both sides.
when I put 180 lbs in drivers seat and bounce it from the front (that is both side bouncing at the same time) the right side feels "stiffer" than the right.

The car has 2 right sides ??

I do not race around corners but I think maybe you need to put the car on scales to get the springs right. That what drag racers do.

Lexus4321 · 10-23-2020, 08:55 PM

Quote:

Originally Posted by Bill Douglas

Maybe the soft "first part" of the spring is being taken up by the 180lb, so therefor there is only "hard spring" left. And the passenger side still has the first bit of springy stuff left in it.

Progressive springs might, but they sound like std K's.

Springs do not "stiffen", they get loaded by force.

island911 · 10-23-2020, 11:11 PM

yep-ish. ^

springs deflect (distance) as a function of force. Put 900_lbf and it deflects an inch; 1800_lbf deflects 2"...

If one corner is feeling softer, it has likely not deflected as far. ...maybe due to weight. maybe due to linkage length or a bent frame.

island911 · 10-24-2020, 08:56 AM

^ absolutely

and to understand that the whole load/deflection side of it.

aschen · 10-24-2020, 09:14 AM

Linear spring so preloaded side will have the same stiffness (force/length) but a higher actual force to deflect.

A proper cornerbalace with driver weight in place is the solution as others have said.

Lexus4321 · 10-24-2020, 02:17 PM

Quote:

Originally Posted by afterburn 549

I would think you need some sort of corner scales?

Scales will only have read-out for sprung weight. w/o driver the diff up front should be almost zero (if the vehicle is very symmetrical). With driver weight there the weight will have driver distribution with much of it on front-left scale.

I don't know all the ins-outs of it, but I do hear some might offset things by using a lighter wheel where/when needed, to get less un-sprung weight on that corner, maybe to help traction on a specific corner where there's a bump or "high" curb.

If the driver is 180, then why not stick 180 on the RH side? That should balance it back out?

Many tricks in this world of car racing, OP needs to find the right set of trickery that works best on race day.

john70t · 10-24-2020, 02:53 PM

A digital scale with a hold function might be able to determine how much of your body weight pushing down is transferred to the ground.

(but not over time of course, which is the real data, and the input force is only going to be ballpark.)

island911 · 10-24-2020, 04:22 PM

He is talking about much more than simply getting scales to balance.

Let's say, for example the front right physically has less weight on the spring. That corner will be in a 'lighter' spring range but still having to manage the unsprung weight. meh. too involved a topic.

Lexus4321 · 10-24-2020, 07:21 PM

Quote:

Originally Posted by island911

He is talking about much more than simply getting scales to balance.

Let's say, for example the front right physically has less weight on the spring. That corner will be in a 'lighter' spring range but still having to manage the unsprung weight. meh. too involved a topic.

Exactly. One corner with less unsprung weight will move differently than the other corner, given the car is symmetric in sprung weight and the springs and shocks are the same. Every item is a variable in how the car will drive & react on the track. I don't have the experience to say how exactly that happens, but it's the line of questioning and thinking that needs to be done to dial in the car for race day.

Scales only read unsprung + sprung weight, which is only good for tuning some things, but scales alone cannot dial-in the car.

island911 · 08:28 AM

https://en.wikipedia.org/wiki/Mass-spring-damper_model

The forces of that ^ in English.

kx is the spring rate - note it's a function of displacement (x) with a spring rate k - the force changes with deflection. --the further it's pushed, the higher the force.

cx(dot) is the damping force. The force there is a function of damper restriction (c) and changes with velocity (x-dot) --the faster it's pushed, the higher the force.

mx(double dot) if F=ma (sound familiar?) it's the inertial force. --the faster it's accelerated, the higher the force.

So what that all says is; you change one part of that equation (a spring, shock or the unsprung weight) everything changes. - the freq. response changes (over damped, under damped...)

And there is also that the simple spring damper mass system is attached to a big flexy mass (the car), and add the complexity of the tire being its own mass/spring/damper system that changes with tire temperature and wear.

Corner balancing is but a crude measurement.