3rd Spring Setups and Warp Stiffness

[exFSAE]

There was discussion of warp stiffness in another thread, and the coupling of pitch / roll / ride / single wheel bump stiffness in general.

Typically 3rd Spring is run on aero cars and helps control ride with a heaps of aero download.

Could it be useful on a low/no aero open wheel car? For example one reason we had to run fairly stiff springs on our FSAE cars was that if we ran a wheel rate of less than say 80 lb/in or so there was the good possibility the front end would bottom under hard braking. (Rough numbers.. its been a while). Usually we ran wheel rates closer to 100-120 lb/in.. at which point you don't need much ARB.

If you were to run a 3rd spring setup front and rear.. which would for the most part only activate in ride and pitch.. could you get away with a softer individual wheel rate and a softer warp stiffness? Ie still happy ridin along in general and under the brakes, but a little more compliant to goin over bumps / curbs / cones / people / whatever.

Or does it not work like that. It's somethin I had considered on our car last year actually, running a 3rd damper (without a spring). Wanted to get the right pitch and ride damping while keeping roll damping in the range I wanted. But in the end I said to hell with it, especially since two more CC dampers would have been an extra $1100!!!

[exFSAE]

There was discussion of warp stiffness in another thread, and the coupling of pitch / roll / ride / single wheel bump stiffness in general.

Typically 3rd Spring is run on aero cars and helps control ride with a heaps of aero download.

Could it be useful on a low/no aero open wheel car? For example one reason we had to run fairly stiff springs on our FSAE cars was that if we ran a wheel rate of less than say 80 lb/in or so there was the good possibility the front end would bottom under hard braking. (Rough numbers.. its been a while). Usually we ran wheel rates closer to 100-120 lb/in.. at which point you don't need much ARB.

If you were to run a 3rd spring setup front and rear.. which would for the most part only activate in ride and pitch.. could you get away with a softer individual wheel rate and a softer warp stiffness? Ie still happy ridin along in general and under the brakes, but a little more compliant to goin over bumps / curbs / cones / people / whatever.

Or does it not work like that. It's somethin I had considered on our car last year actually, running a 3rd damper (without a spring). Wanted to get the right pitch and ride damping while keeping roll damping in the range I wanted. But in the end I said to hell with it, especially since two more CC dampers would have been an extra $1100!!!

[flavorPacket]

you'll still actuate the spring in warp, which is a downside.

I wanted to do the same thing but couldn't justify the cost. Decided to spend more time on other areas (tires, weight).

PS if you get creative with damping you can run a soft front wheel rate and not bottom out with a standard setup. You will also be stiff in roll, though.

[alp[esh]

hi i require information on this topic if poossible please reply on this id

[J. Vinella]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by exFSAE:
If you were to run a 3rd spring setup front and rear.. which would for the most part only activate in ride and pitch.. could you get away with a softer individual wheel rate and a softer warp stiffness? Ie still happy ridin along in general and under the brakes, but a little more compliant to goin over bumps / curbs / cones / people / whatever.

Or does it not work like that. </div></BLOCKQUOTE>

A third spring works exactly like that.

To add more,
The downsides:
Yes, more cost
More weight
You need to now take into account this load going into your ARB
There are a few smaller ones...packaging...

Upsides:
As stated above, a 3rd spring allows you to run softer ride spring (the other springs) while not pitching as much.
You can now run a lower single wheel bump frequency than before.
The latter could also allow you if you desire to run shorter Virtual Swing Arms.

And it takes that aero load quite nicely.

Make sure to think about the proper motion ratio you will need and the right damper choice. Additional like any system the variables of the upsides and downside can be adjusted to best fit your car AND drivers needs.

[exFSAE]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">hi i require information on this topic if poossible please reply on this id </div></BLOCKQUOTE>

O rly. Could you be any more.. specific?

[murpia]

Here's a few more things to think about:

Aero cars might not run a true 3rd spring but a heave-only mechanism with a bump rubber and a gap, so the car only goes stiff in heave above a certain speed (often just on the straights).

If we limit ourselves to discussing a linear 3rd spring system, then I agree with Jack's assessment.

FlavorPacket, I'm not sure that 3rd spring activation in warp (as opposed to single wheel bump - they're not the same) is a big problem, however with non-linear rockers you need to look carefully.

In terms of controlling ride and / or pitch motion, with a linear 3rd spring at one or both ends you can achieve axle heave natural frequencies independent of roll couple distribution. Of course you can do that with an ARB too but not with a warp-soft car.

If you are carrying a significant load in a linear 3rd spring you really need to consider a 3rd damper too. Or, carefully analyse your side damper stiffnesses to take the 3rd into account.

It makes little sense to consider side springs, an ARB and a linear 3rd spring one one axle. It makes some sense to consider side springs, an ARB and a 'gapped' 3rd bump rubber on one axle on an aero car.

No reason why you couldn't run side springs and an ARB at the front, say, and side springs and a linear 3rd spring at the rear. This could be really good on a rear-heavy aero car to maintain rake while achieving the roll couple distribution required.

In general for FSAE though, if you want to run really soft in roll or warp, a linear 3rd spring and / or damper could work really well to control car pitch and ride problems.

Regards, Ian

[flavorPacket]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by murpia:
FlavorPacket, I'm not sure that 3rd spring activation in warp (as opposed to single wheel bump - they're not the same) is a big problem, however with non-linear rockers you need to look carefully. </div></BLOCKQUOTE>

if the 3rd spring is on the stiffer side, you'll create unwanted heave in the warp mode, no?

[J. Vinella]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by murpia:
No reason why you couldn't run side springs and an ARB at the front, say, and side springs and a linear 3rd spring at the rear. This could be really good on a rear-heavy aero car to maintain rake while achieving the roll couple distribution required.

</div></BLOCKQUOTE>

If you car is a rear-heavy aero car (CP is a insignificant amount aft of the CG) it will most likely under steer like a dump truck. You would also negate the benefit under breaking where your longitudinal acceleration is highest.

I'm not say this set up is absurd, just probably not ideal for FSAE. But what is ideal for FSAE,; there are teams running mono-shocks and they are fast. Only testing and time will tell.

[flavorPacket]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by J. Vinella:
But what is ideal for FSAE,; there are teams running mono-shocks and they are fast. Only testing and time will tell. </div></BLOCKQUOTE>

Too true. If we had one driver drive all of the cars, I think things would be very different. I still cannot comprehend that cars without roll damping can do so well. It just goes to show the lack of skill FSAE race engineers have in getting the most out of their tires.

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by flavorPacket:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by murpia:
FlavorPacket, I'm not sure that 3rd spring activation in warp (as opposed to single wheel bump - they're not the same) is a big problem, however with non-linear rockers you need to look carefully. </div></BLOCKQUOTE>

if the 3rd spring is on the stiffer side, you'll create unwanted heave in the warp mode, no? </div></BLOCKQUOTE>
Yes the car moves in heave, but the 3rd springs don't carry any extra load. In the 'limiting' case of very very soft side springs you have a sort of 'articulating' car with only very slight contact patch load changes in warp. After all, it's contact patch load changes that affect the car balance.

Regards, Ian

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by J. Vinella:
If you car is a rear-heavy aero car (CP is a insignificant amount aft of the CG) it will most likely under steer like a dump truck. </div></BLOCKQUOTE>
Why? There are a lot of racecars out there that follow the general trend of more rearward weight = more oversteer. Those with aero will run a more rearward CP accordingly. All those cars will have a roll couple distribution with more roll moment reacted at the front. That's easily achieved with a higher front wheel rates and / or a front ARB. The softer rear wheel rates affect your pitch / heave coupling and axle heave natural frequencies. You can regain control of those with a linear rear 3rd spring & damper

Regards, Ian

[vreihen]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by flavorPacket:
If we had one driver drive all of the cars, I think things would be very different. </div></BLOCKQUOTE>

Some say that he was brought up in Africa by a herd of cheetahs, and pees 98 RON petrol...

http://images.wikia.com/uncyclopedia/images/8/8e/Stig.PNG

All we know is... he's called The Stig! http://fsae.com/groupee_common/emoticons/icon_smile.gif

(For those who don't know, The Stig is the mystery "spec driver" who does all of the performance tests on the BBC TV show "Top Gear." )

If you want to take the driver out of the equation, here's the person who can do it.....

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by flavorPacket:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by J. Vinella:
But what is ideal for FSAE,; there are teams running mono-shocks and they are fast. Only testing and time will tell. </div></BLOCKQUOTE>

Too true. If we had one driver drive all of the cars, I think things would be very different. I still cannot comprehend that cars without roll damping can do so well. It just goes to show the lack of skill FSAE race engineers have in getting the most out of their tires. </div></BLOCKQUOTE>

I assume we're talking about front monoshock / roll shuttle systems? I agree that it's hard to understand why they're not hurt by a lack of roll damping. That sort of setup seems heavily biased towards transient turn-in performance to me, generating a high initial yaw acceleration by quickly loading the outside front tyre. I would always be concerned about mid corner understeer with that setup. I guess it suits the late braking, point and squirt driver style, not the carrying speed in the corner style. I think the former is more characteristic of the 'amateur' driver.

Regards, Ian

[flavorPacket]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by murpia:
In the 'limiting' case of very very soft side springs you have a sort of 'articulating' car with only very slight contact patch load changes in warp. After all, it's contact patch load changes that affect the car balance. </div></BLOCKQUOTE>

Indeed. I think that I was just thinking of an aero-heavy car where the sprung mass orientation also matters.

Ian, this line of thinking is dangerous! Soon enough we'll all be trying to do a UWA-style interconnected setup and run proper rates in each mode. Terrible...

[Pete Marsh]

For sure we do all the stuff you're talking about here.(except third dampers) And it works just as you say.
But, it changes the 'rules of thumb' so much you end up flying solo a bit. Also low warp is good, but not minimum. It just becomes another thing that can be wrong, or right, that you have to figure out. On a surface as flat and smooth as the Ford proving grounds the pertential performance gain is pretty small,if at all, but on bumps or on cambered roads, huge!
So, who has seen the surface at Michigan raceway? is it flat or cambered? Smooth or bumpy?

Ian, when you say warp and one wheel bump are not the same do you mean in a dynamic sense where the sprung mass can not react in time? ie only one wheel moves.

Pete

[flavorPacket]

Pete, warp is defined as when a diagonal wheel pair is actuated. This is different from single wheel bump, which is when only one wheel is displaced.

[J. Vinella]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by murpia:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by J. Vinella:
...(CP is a insignificant amount aft of the CG) </div></BLOCKQUOTE>
murpia
Why? .... </div></BLOCKQUOTE>

That should have read "significant amount".

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Pete Marsh:
Ian, when you say warp and one wheel bump are not the same do you mean in a dynamic sense where the sprung mass can not react in time? ie only one wheel moves. </div></BLOCKQUOTE>
As FP says a pure warp input is when the diagonal wheel pairs move to maintain a static equilibrium of the chassis. Imagine driving very slowly over an uneven surface, the inputs will be almost pure warp.

Pure one wheel bump occurs only if the transient is short enough and you have sufficient sprung mass and soft enough springs and dampers that the chassis hardly moves from the equilibrium position. You also need no ARBs or 3rds.

Anything that actually happens in the real world will be some combination of the two, but if you look at loadcell data it should be clear that warp-soft is good for reducing contact patch load fluctuations and hence good for grip.

Regards, Ian

[cmeissen]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by J. Vinella:

Upsides:
As stated above, a 3rd spring allows you to run softer ride spring (the other springs) while not pitching as much.
You can now run a lower single wheel bump frequency than before.
The latter could also allow you if you desire to run shorter Virtual Swing Arms.
</div></BLOCKQUOTE>

Could you explain more about running shorter swing arm lengths because of lower single wheel bump frequency? Thanks

[J. Vinella]

No, they are not really related. The point I was trying to make is, if you are not going to pitch as much as before you should be able to run shorter swing arms and have similar breaking balance and performance, if you balance the variables to that. You also now have the additional benefit of lower single wheel bump frequencies. (This post might also be incoherent due to happy times with the cost report, I apologize...Zzzzzz)