Uneven Spring Rates Left and Right?

[hsk8te2006]

RRE has corner weights for a stock 2g AWD [psted on their website at RRE's DSM Corner Weight Info

I spoek with them, and considering that my spyder weighs only 50 lbs less than an AWD (based on edmunds.com vehicle specs), they suggested that all of that weight difference would be up front.

Considering this, I also factored in for when I add my own body weight to the car (unevenly left/right), and I'm estimatin gmy front corners to be about 943L, and 873R.

Considering this, rather than running the car with 400lb/in springs on both fronts, I'm considering running the car with a 425lb/in spring on the front left, and a 400lb/in spring on the front right. That places the frequencies left and right closer than they would be with 400lb/in on both sides.

Good idea or bad? Any thoughts?

 

[pagosa dsm]

RRE has corner weights for a stock 2g AWD [psted on their website at RRE's DSM Corner Weight Info

I spoek with them, and considering that my spyder weighs only 50 lbs less than an AWD (based on edmunds.com vehicle specs), they suggested that all of that weight difference would be up front.

Considering this, I also factored in for when I add my own body weight to the car (unevenly left/right), and I'm estimatin gmy front corners to be about 943L, and 873R.

Considering this, rather than running the car with 400lb/in springs on both fronts, I'm considering running the car with a 425lb/in spring on the front left, and a 400lb/in spring on the front right. That places the frequencies left and right closer than they would be with 400lb/in on both sides.

Good idea or bad? Any thoughts?

I would recommened getting some GC and adjusting ride hight with them.The car will handle funny with different spring rates.Right turns will be good ,left turns will suck.

 

[asian312]

Bad idea. You want the car's suspension to react the same (unless your only turning left on a banked oval), so ideally you are looking for a symmetrical setup. The way to properly 'balance' the car is through corner weights. This is adjusted via individual ride heights on each corner.

Once again, I can't help but think this is a a lot of work for a street setup. Do you have a reference point for the type of performance you are trying to attain and a budget?

 

[hsk8te2006]

As to reference point and budget, the budget is roughly 1200-1400 dollars.

As to set-up, I am looking for a better performing but still street-friendly setup. I have been doing tons of reading on this site, and I am convinced that Koni yellows with coilvoers are right for me, due to the soft compression damping regardless of rebound setting on the Konis.

When you say you want the car's suspension to react the same on both sides, if you look at suspension frequency when hitting a bump of say, 1.5 inches, then you will need to have a stiffer spring on the side of the car with more weight. The stiffer spring would relay more force (than the softer spring) into the heavier side, which would in turn help it to accelerate upwards at the same velocity as the lighter side on the softer spring. Based on physics, two same-constant springs supporting uneven weight should result in the car rocking from side to side on a straight bump.

As to the amount of work, if I'm going to spend this kind of money, I'm willing to do tons of research to try and get this right the first time as much as possible.

 

[asian312]

So instead of doing these one off calculations that apply to your car as a 'snap shot' to try and select specific spring rates per corner, why not get the same spring rates and then adjust the weight over each corner with height adjustable coilovers?

As for reference point, I mean actually riding in some cars with various types of suspension. Sure it's easy when you want a full race setup, but your goals on suspension are as ambiguous as 'I want lots of horsepower with no lag'.

 

[hsk8te2006]

Reference point... There are no other turbo spyder owners in my state on dsmtuners.com, and I don't know any either. But, I have done tons of reading on what everyone on here thinks of different setups.

Regarding why not to just corner balance the car but use a stiffer spring on teh drivers side... This is my theory... I'm going to break out the college level physics and I'll examine two scenarios... a simultaneous bump (speed bump) (easier to visualize and udnerstand), and the same rate of turn left or right (a little harder).

Corner balancing the car works with ride height adjustable coilovers, as follows. When you raise various spring perches, it momentarily compresses those springs more, making them lift up on the car's body more. This in turn takes weight off the heaviest corner of the car, makign the car's four wheels carry the same weight AT THIS RIDE HEIGHT. So, at this "snapshot" point in time, the car is balanced evenly.

However, as soon as you drive the car over a flat bump (speed bump), it will compress both front springs evenly, which will then in turn apply equal amount of force on the two front corners of the car. The potential problem I see, is the lighter side (passenger) will accelerate up faster than the heavier one (driver) if equal amounts of force are applied. The only way to compensate for this, would be to place more force upwards on the heavier side, by using a higher-rate spring.

Similarly, as far as I know, if you take the same g-turn, a car like ours with it's center of mass towards the left side would roll more to the left in a right turn than it would to the right in a left turn. Here's why...

The lateral inertia is resisted in a horizonal linear fashion by the friction at the tires, but the longitudinal rotational moment created by that friction is balanced by the additional pressure under the outside tires (as a result of teh weight transfer).

However, when you move the center of mass towards one side, that side now has a shorter moment arm. If for example, you moved the center of mass over 1/2 (arbitrarily chosen for the sake of discussion) the distance from the midline towards the side, the distance from it to the sides would now be in a 3:1 ration (3 is passenger). Thus the passenger side would only need to experience 1/3 the increase in pressure (or weight transfer) in order to balance out the rorational moment that the driver side would if the car was turning the other way. So, even with a corner balanced car (when it is still), it will still experience a higher amount of weight transfer to the driver side tires then it would need to the passenger side in the same g-level turn. And, mroe weight transfer, means the spring will compress farther... unless has a higher spring constant and is stiffer!

Therefore, in order to get equal amount of roll resistance despite the higher amount of weight transfer (towards the driver's side in a right hand turn versus towards the passengers side in a left hand turn), my theory is you should still need a stiffer spring under the side with the shorter moment arm (driver), regardless of if the car was corner balanced while flat.

Can someone with either actual data or an engineering or physics degree either support my theory or show me how I'm wrong?

 

[asian312]

First off, there are coilovers that can adjust ride height without affecting the preload on a spring. In your scenario you accept the fact that all corners are supporting equal weight, meaning that the car's total weight is being distributed evenly on all four tires (perfect scenario) when dialed in properly. Therefore if you hit a flat bump evenly with both fronts and both fronts are supporting the same weight per corner, I don't get where one side will suddenly weight more than the other. That difference in weight per corner existed at stock ride height with stock corner weight measurements. Also corner weighing a car is ideally controlling where the center point of gravity is located on the car. Of all four corners are supporting the same weight, won't the center of gravity be...centered?

If you want to throw 'college level' physics at this be my guest. Hell go ahead and run different rates on one side of the car. I'd be curious as to how it handles. While I may only have completed my sophomore year of aerospace engineering and I openly admit that I don't recall much more than basic physics, I do track and race my car. There's a ton more to handling than just numbers and these 'perfect scenarios' you keep throwing out. In reality, your perfect setup will more than likely differ than the next persons due to things as driving style, modifications, etc. Knowing how a car behaves on corner entry, mid, corner exit, under braking, or acceleration mid corner goes a long way in understanding just what you are asking for. I've said my two cents. I'll kick back and watch.

 

[hsk8te2006]

A setup where ride height can be adjusted without affecting preload on a spring is possible and I am planning to get one. (Probably ground control)

I will preface the rest of this by saying that I do not race, plan to, or have any actual suspension experience. I'm just a guy who got an A+ in physics lab, and my discussion is based entirely on the current spring theory, making only the assumptions that 1) I'm not moving around the internal parts of my car to adjust the total average center of mass, 2) the springs are actually linear in their force, as the manufacturer's state, and 3) the damping level is the same on both the left and right sides of the front or rear pairs of shocks.

If you can accept that my 3 assumptions are acceptable, I can gaurantee it is not possible to take a dsm with it's cnter of mass roguhly 2/5 the distance from the front of the car to the back, and get all four corners to support the same amount of weight.

On top of that, the only way you can adjust corner weights supported by each tire, is to preload springs more or less at static ride height. (Think lengthing the diagonally opposed legs on a table, but the legs are springs, so the longer ones on opposite corners will cushion some of the weight before the otehr one will "see" it).

Even then... you're only changing the amount of force each tires experiences at that static ride height. you are not actually moving the center of mass, so as soon as you start to compress springs, you are taking away the ability for the "longer table legs" to support more of the weight that would normally be supported by the "shorter ones" (the corners you adjust static weight off of), and the shorter ones will see their normal weight again.

Since the center of mass isn't moved, the vertical bump accelerations, and the amount of force under the outside tires being unequal in a left vs right turn due to moment forces would still apply.

Have you, anyone you know, or anyone else readin this formum for that matter, ever tried to measure your corner weights with all 4 springs set to put the wheels at the same distance from the fender lips when they first touch the ground (zero corner weight adjustment), and then used diferent spring rates left and right (similar to how we already do front and back) proportional to the different amount of weight the corners would normally see?

 

[Black99gst]

what happens when you take a friend/girl in the car? then it will be all jacked up... just go with even spring rates...

 

[hsk8te2006]

I'm thinking that if I set the ride height to be level when I'm in the car alone, then adding a passenger to the right side will still lower that side of the car a little (just as it does stock) whether or not I have the 25lb stiffer spring on the left, because most of her weight will still be on the 400 lb/in spring either way...

Keep in mind I'm only talking about roughly a 6% spring rate difference and on only one tire...

 

[Black99gst]

right, but the ballance of the car is going to be changed, this change could potentionally throw the car off ballance and cause decresses in drivability... i would never want to have uneven spring rates fron left to right... thats just asking for potential problems

 

[hsk8te2006]

As far as I can tell.. using a higher rate spring ont eh left (425 vs. 400) should fix the car already being off balance... and by the way... based on RRE's corner weights page (link in first post), using a 425 left and a 400 right is actually closer to having the same amount of spring per pound of car weight than using 400 on both is.

 

[turbosax2]

Sorry if I missed it, but have you asked RRE their opinion on your ideas?

 

[hsk8te2006]

Actually no... I'll try to either tomorrow or monday. When I do, post back and see what they think...

So, RRE said that they haven't had anyone do that before. They said that it probably wouldn't hurt anything, but most folks just use the same spring rates and then set the damping levels a little higher on the front left corner to try and compensate for the higher amount of mass on that corner. That's what they recommended to me, but they also said they didn't think it would cause too many problems if I wanted to try it.

The problem for me though (me talking, not RRE) is that the Koni Yellows I am going to use do not adjust compression damping at all, wheras the dampers that RRE sells do. So, I'm still thinking of using a 25 lb/in. stiffer spring on the front left side.

Anyone else ever consider trying this or have any thoughts to offer?

 

[underradar92]

I do not have a degree in anything.

That said, I see where your head is at. Try thinking of the suspension as not supporting the car, but keeping the road away from the car and see where that gets you.

I agree that a bit of extra rate on the drivers side should theoretically make the car corner more evenly in either direction, and the small amount of rate difference seems to be a not so big of a deal, but by that logic, just adding the preload isn't so bad either.

I do wonder how 4 different rates would affect straight line braking performance however.

I guess I'd say, try it. Just don't go 10/10ths right out of the box. More springs aren't all that expensive if you don't like the experiment.

Let us know how it goes.

 

[hsk8te2006]

I had an email conversation with mike at RRE, and his general opinion was that it couldn't hurt anything, and noone else has ever tried it before (except for doing an insanely high rtae on only one side for an oval track).

He basically said go for it, and let them know how it turns out.

So, I'm probably going to go with 425 FL, 400 FR, and 300 Rear both sides. I'll let everyone know how it turns out!

I just got my car corner weighed this morning. http://www.dsmtuners.com/forums/handling-tech/299381-spyder-corner-weights-available-last.html

The weights with my own weight added were FL = 1066, FR = 930, RL = 624, RR = 624. After re-doing my calculations, I can get only a 4% difference in spring rate to weight ratio in the front corners with 425 FL, and 375 FR, so that's what I'm actually going with, along with 325 rears.

 

[underradar92]

I was surprised that there wasn't a larger difference than there is when I had my car cross weighed. The 60/40 front to rear seems like a bigger deal (to me anyhoo) at this point.

Don't forget that when you have adjustment that a true 50/50 cross weight that your heavy corner will give up some poundage to the passenger front and drivers rear.

 

[PieEyedPiper]

I admire your diligence and I support your experiment, but have you discussed this idea with any racing types? I wonder what Jtoby would say.

 

[hsk8te2006]

Again, the folks at RRE said it seemed logical and that if I wanted to try it, go for it.

Also. the folks at Ground Control also asked why I wanted assymetrical frotn spring rates, but didn't offer any objection when I told them.

I also wonder what JToby would say, and I even sent him a PM about some other questions a while ago. But, he hasn't posted on this website in months, and I'm assuming that since he has sold his Talon, he may or may not be back anytime soon.

 

[hsk8te2006]

Update...

After a year of running 425 FL, 375 FR, and 325 both rears, the car is behaving great. It runs over speed bumps evenly, and it corners left and right equally well.

Incidentally... 325 may be a little stiff in the rear for anyone who lives in pothole country (as I do.) I plan to switch to 250 rears and a stiffer rear sway bar sometime in the next year.