stiff or soft spring question

[ShadowBolt]

If you had two different set-ups you could put on the same car. Both neutral as can be but one with really stiff springs (and shocks to manage them) and one with soft springs. Would one be faster than the other or would it be just driver preference? This is assuming the track is not rough as hell.

So much to learn so little time.


JJ

[mitchntx]

Having run both uber-stiff and soft set-ups, either can be fast.

The window of recovery is less with a stiff spring setup, but the soft set is a lot more difficult to dial in and remain consistent over a race.

[Todd Covini]

Soft.
Loose is fast.
Suspension travel is your friend.

-=- T

[ShadowBolt]

Soft.
Loose is fast.
Suspension travel is your friend.

-=- T


You say the answer is soft because loose is fast but can't a car be set up loose even with stiff springs?

I do understand that travel is your friend.


JJ

[Wirtz]

Something to consider given the restricted CMC rules is what anti sway bars are availible for your car. Soft springs can be a good setup but you need stiff anti sways to keep the car working.

Jeff
- still needing to spend some weekends playing with spring rates

[Todd Covini]

Real racecars LEAN!!! 8)

http://www.mustangmods.com/ims/u/3324/7708/200828.jpg
http://www.mustangmods.com/ims/u/3324/7708/200829.jpg
http://www.mustangmods.com/ims/u/3324/7708/200830.jpg

DISCLAIMER: This post is for entertainment purposes only. The views represented herein are not necessarily that of the author nor that of AICMC Texas.com incorporated. The photos represented herein display the effects of a broken swaybar endlink and not necessarily that of CMC#2 as raced (or garaged).

[GlennCMC70]

Dear God Bryan, you are lucky. Had you ridden in that car back in the day, you would have fallen out the window! :shock:

[AI#97]

Depends on the track layout. If you have a track like TWS that has big sweeping turns then I would say you could probably make a soft setup work.

However, if you are on a track like Cresson's 1.3, Houston or other tight and twisty track with QUICK transitions, I would say a stiff setup would work a lot better to control the quick transitions from left to right turns.

I still think you guys in CMC are running setups that are WAY too soft and could run much higher wheel rates to keep the cars planted as well as use less static camber to help under braking. I have dropped nearly a full degree of camber out of my car and braking has improved substantially.

Also, I would think that to drive a soft setup consistantly fast...you are going to use up the tires a lot faster and maybe even get them greasy.

But...I am speaking from an AI perspective so it may not apply to CMC...?

[BryanL]

I was just worried about going out the top when we did our best impersonation of General Lee but those pics make me worry about rolling the car like a Samarai.

Todd-where do you stand with getting the Ranchero back on the track? I may have missed something but haven't heard what you are doing?

Two in a row for Gordon and leading the Chase!!!!!

[Todd Covini]

So it's been a while...any new opinions as to which is better? Soft or Stiff?
Sounds like there's an array of setups out there, curious as to which one is preferred now after some soak time.

Todd-still-waiting-on-the-bodyshop-Covini

[ShadowBolt]

I know the answer now. How about a 1:59 lap at TWS (CW) by Team Jordan. Ask your wife the answer to your question.....stiff or soft. I bet she knows the answer.


I was going after Glen and the two Jeff's in R3 until JP came along and had his way with me!


JJ

[GlennCMC70]

w/ all the car swapping going on Friday, its going to be interesting to hear from MM, RL, and JJ on this.

FYI - i let Rob drive my car out on track 2 times Friday.

[michaelmosty]

We had a great experience swapping cars. Rob drove mine and Jerry's and I drove Robs. Robs car felt very similar to mine with a few differences but nothing major.
Rob will chime in but I appears Jerry's "stiff" set-up is the way to go. There might have to be some more development in the near future. :wink:

[BryanL]

I know the answer now. How about a 1:59 lap at TWS (CW) by Team Jordan. Ask your wife the answer to your question.....stiff or soft. I bet she knows the answer.

JJ

:lol: Great one JJ.

[Todd Covini]

So what's the final answer?
Is everyone going to 1500# springs now?

[ShadowBolt]

Is everyone going to 1500# springs now?


Yes, on the rear.

JJ

[Todd Covini]

Is everyone going to 1500# springs now?


Yes, on the rear.

JJ

I think you better put them on the front. :shock:
:wink:
http://www.hart-photography.com/photocart/index.php?do=photocart&viewImage=624691

[Todd Covini]

OK...enough with the Todd-Foolery....this is serious shit. :lol:

My car now has the cutting-edge, super-stiff, whiz-bang, home-grown 3 link suspension and top of the line DA shocks. Without changing anything else (except a good frame straightening), it now has severe rear inside wheelspin.

With the super fast, super soft suspension, that was never really an issue and the inside wheel stayed relatively stuck. (Occasionally I would get a little bit of inside wheelspin.)

So....1 of 2 things is happening.
a) Suspension is too tight and needs to be tuned/tweaked/dampened.
b) Rear diff is shot (Torsen T2...not a T2R)

I've researched the T2 torque bias compared to the T2R and it's almost half....but find it hard to believe that the stiffer suspension would make the diff's bias change/react so dramatically.

The title of this forum section is "Why does my car suck?"... and so, I'm looking for input.

-=- Todd "Can't Power Out Of The Turns" Covini

PS- Don't get me wrong, other than the wheelspin it now feels much more stable...but I'm afraid the wheelspin is a byproduct of the stiffer suspension.

[AI#97]

does it spin in both left and right turns? If only in right turns, you need to adjust the height of the panhard...if you can.

[MikeP99Z]

bye bye diff

[ShadowBolt]

Prior to my stiff set-up at TWS last year first race this started all of the sudden. In every turn it sounded like the clutch was slipping. I could not get out of the turns. Inside wheel spinning. A new T2R fixed it. Wouldn't a soft set-up be worse? More roll pulling more weight off the inside wheel?


JJ

[evarner]

Even though I never drove the #2 car with the soft setup, the new configuration (stiff-3 link) really feels good. The biggest problem is coming off a corner. Left or right, it doesn't matter, the inside wheel will spin for hundreds of feet. Corner entrance/middle were great and the car does really have some power, but can't use the 300ft/tq at all which hurts exit speed big time.

At this point, I don't think it would matter with a super loose setup, the 10yr old diff needs to be set out to pasture. :D

The #2 can be a real contender with a few new parts. 8)

[Wirtz]

A good diff is key in my mind. I'm a fan of the T2R.

How many races has the T2 been through?

[evarner]

A good diff is key in my mind. I'm a fan of the T2R.

How many races has the T2 been through?

10 yrs and probably 50-100k miles. :D

[Todd Covini]

A good diff is key in my mind. I'm a fan of the T2R.

How many races has the T2 been through?

10 yrs and probably 50-100k miles. :D

Naww...not that much.

10 yrs, maybe 30k miles....and a 12 hour enduro. :oops:

[Al Fernandez]

Yep, you've now improved something to the point where a different thing is the weak spot. I've run a t2r in my car since the dawn of time. I can get inside wheel spin, but not as bad as with other diffs. There are diffs that work better than the t2r, but they require maintenance where this one doesnt. To me that is a good compromise...though I really want to set a car up with a spool :twisted:

[michaelmosty]

I bought a T2 about 2 years ago when my stock traction lock went out. I ran it for about 3 events and decided to get the T2R.
IMO, the T2 is a pile of crap. I called Torsen and talked to a tech. and he said the T2 really isn't good for anything except stock rebuilds or mild motor builds for street driving. I still have the T2 in my garage if anyone is interested in it. :)

After putting the T2R in everything has worked perfectly!

[evarner]

Yep, you've now improved something to the point where a different thing is the weak spot. I've run a t2r in my car since the dawn of time. I can get inside wheel spin, but not as bad as with other diffs. There are diffs that work better than the t2r, but they require maintenance where this one doesnt. To me that is a good compromise...though I really want to set a car up with a spool :twisted:

Uh.. I think a spool should be mandatory on all GM products. :D

BTW.. I'm kidding. However, a spool would make the car push like there's no tomorrow.

[Al Fernandez]

I'm sure it would...until the suspension is adjusted accordingly. Plenty of very fast road race cars have run with with spools and or detroits (a spool under throttle)

Less weight, less cost, no wheel spin...yeah the car wont rotate as easily, but it might be a decent trade off.

[MikeP99Z]

I ran my 280Z with a fully welded diff, and have had a DL in the Z28. The suspension can be reset to work quite well. The welded diff really sucked driving around the paddock though. You have to be really smooth on the pedals to make the DL work to your liking.

[AllZWay]

My car has a stock T2 (not T2R) and I have not had a problem as of today...knock on wood of course.

[evarner]

From corner-carvers: http://www.corner-carvers.com/forums/showthread.php?t=28073&highlight=spool

The Mark Ortiz Automotive
March 2004

DIFFERENTIATING DIFFERENTIALS

A 2200 lb., 300 bhp, rear-wheel-drive car is doing circuit racing on a short, twisty asphalt circuit with mostly right-hand turns. It runs the same rubber on all four wheels. Which of the following differential setups would be quickest around the track, giving good turn-in and good traction out of the corners?
1. A spool type locked rear
2. A Positraction rear with 250 lb. preloading
3. A Detroit Locker rear
4. A Torsen rear

All of these options have their adherents. One thing that complicates the picture is that the choice interrelates with setup and driving style.

Conventional wisdom is that spools are a bad idea for road courses. To get good steady-state cornering with a spool, the car needs to have tire stagger, or alternatively the power available and the nature of the track surface have to be conducive to powersliding. Tire stagger is generally an impossibility if the turns go both ways, although maybe if most of them go one way it is possible to accept poor behavior in the few that go the wrong way. If, as the questioner posits, the tires are truly identical all around, in circumference as well as all other properties, then we definitely don’t have stagger.

Driven more or less normally, a car with a spool tends to understeer, or push. It does this much more in tight turns than in large-radius ones. We can free it up by putting lots of roll resistance in the rear suspension, but when it’s right in the slow turns, it’s too loose in the sweepers. One cure for this is to have a lot of aerodynamic downforce at the rear. Whether we can get that will depend on the bodywork rules.

There are situations where the locked-axle push is helpful. If we are trying to brake and turn at the same time, the car tends to oversteer. This limits how hard we can brake while turning. The car also will oversteer under power, if there is enough power applied, because the rear tires are using a lot of their available grip to make forward force and have less grip available for making lateral force. Again, if the car is tight to begin with, the driver can feed it more power before it goes power-loose.

This means that a spool can work on a road course if we have a driver who trail-brakes deep into the turns, and then gets on the power hard right away. In most of the slower turns, the car never sees steady-state cornering when driven this way. Mid-turn speed isn’t necessarily best with this approach, but we get good entry and exit speed, and a late brake application point and an early power application point. Consequently, elapsed time, or average speed, on any straightaways before and after the turn improves.

Not surprisingly, the driver best known for making this work is the one who popularized trail-braking when most drivers were still completing their braking before turning: the late Mark Donohue. Donohue could win races on a road course with a spool, even in a car with huge tires and a massive rear wing, such as the Can-Am Porsche 917-30. Other drivers would get into cars set up to his liking, and not be able to do anything with them.

We might reasonably suppose that a driver could simply learn this, and adapt. Actually, drivers’ abilities to do this vary considerably, and even those who can learn require practice to use a new technique well. Then again, we may have a driver who learned to drive this way, and has to learn a new style to do anything else. Not only do personal preferences differ on the question of trailbraking, so do driving schools.

To perform the best, a race driver needs to be able to drive the car without thinking, and focus his/her conscious mind on observation. This means that it’s not easy to learn and unlearn new driving styles to adapt to different cars. For some talented individuals, it’s merely difficult. For others, it’s impossible. And for all drivers, just having to think about technique costs speed, all by itself. Therefore, when we set up a race car, we need to accommodate the driver, and not simply write off to stubbornness a driving style that doesn’t suit our setup. If we have a driver who is in the habit of driving like Donohue, a spool may be worth considering. If not, that argues against the spool.

The spool is simpler and lighter than any alternative. Its simplicity is a plus for both cost and reliability, although a spool is generally harder on axles than any form of limited-slip.

For those unfamiliar with the Positraction, or Posi for short, it is a clutch pack style limited-slip, usually with a single clutch pack establishing friction between the right side gear and the carrier. The clutch pack is preloaded either by having a dish in one pair of discs so they act like Belleville washers, or by having coil springs bearing on the clutch pack. Added clutch loading is applied to the pack by the spreading force on the side gear when torque acts on the ring gear. At a given ring gear torque, this spreading force depends on the tooth profile and the diameter of the side gears. That makes the preload the only adjustment.

Preload is measured in lb.ft. of torque, rather than pounds – though it is common to say pounds for short in casual conversation. The procedure is to jack up one wheel, or jack up both rears and have a helper hold one, put the transmission in neutral, and measure the torque required to turn one wheel. This requires an adapter to allow a torque wrench to turn the wheel. For best accuracy, it’s best to turn both wheels at once with the torque wrench first, to measure brake and bearing drag. Then you divide that value by two to find the drag for one wheel, and subtract that from your torque reading when turning just one wheel.

250 lb.ft. in this test is a lot. Typical values for stock road cars are more like 50. If the car is on racing slicks with a coefficient of friction of 1.3, and a rear wheel has a static load of 550 lb. and an effective radius of one foot, the tire’s breakaway torque under static load is 715 lb.ft. For the inside tire in a corner, with a substantial portion of the traction circle being used for cornering, 250 lb.ft. could easily be enough to overpower the tire. And under power, we get more clutch pack loading. In such a situation, a heavily preloaded Posi can act a lot like a spool.

However, when the tires can overpower the clutch pack, the Posi acts tamer than a spool. Like a spool, but less severe. This will tend to save the axles to some extent, as well.

It might be worth mentioning the ZF style differential, which the questioner didn’t list. The ZF and the Posi are both sometimes called Salisbury differentials, but they differ a bit. Like the Posi, the ZF has multi-disc clutches that can be preloaded and are loaded additionally by engine torque. The difference is that in a ZF, the clutch discs are outside the carrier, and the carrier is split into two halves at the pinion shafts. The pinion shafts have angled flats on them that bear against mating flats on the carrier halves. The angle of these flats can be varied, by installing different parts having different angles. This allows us to adjust the severity of the lockup under power. There are similar flats that spread the carrier halves under reverse torque (engine braking). The angles of the flats for power and decel can be varied independently, allowing the unit to lock more or less strongly on deceleration compared to acceleration.

The Torsen, or Gleason, is also two designs that have very similar properties. Both use worm gears in place of the spider and side gears of a conventional diff. The worm gears provide a very smooth, yet strong lockup under load, yet turn very freely with no load, provided they are not preloaded. Gleasons can be preloaded. One problem with preloaded Gleasons is that the preload is highly sensitive to gear wear.

If I were to make a general-purpose recommendation for road racing, it would be the Gleason. It has the ability to lock strongly, yet smoothly, with little or no preload. This makes it very driveable.

It does have some drawbacks. It is generally the costliest of all the types we’re considering here, although not prohibitively so. The power and decel lockup are not separately tunable, as with the ZF. If the unit is not preloaded, it will not prevent one wheel from spinning if that wheel is very lightly loaded, or is airborne, or is on a very slippery surface.

The Detroit Locker is not really a differential in the sense that the Salisbury and Gleason are. That is, it has no gears at all, and there is no way it can be set up to split torque equally between the two output shafts, while letting their speeds vary, even at very low torques. The locker contains a center element consisting of a dog ring driven by the carrier, like the spider gears and pinions in a Salisbury or an open diff. This central dog ring has dogs on both sides. These mate with driven dog rings on either side, which drive the axle shafts.

The driving dog ring can float a bit side to side. It is held centered by two conical coil springs. When the driving dog ring is centered, it engages both driven dog rings, and we have a locked axle. If the driving dog ring moves to one side or the other, it moves more deeply into engagement with the driven dog ring it moves toward, and if it moves far enough it disengages from the other dog ring. We then have drive to only one wheel.

For a wheel to disengage, it has to overrun the carrier. For this reason, the locker is sometimes called a ratchet. This isn’t really accurate, but the unit is somewhat similar to a pair of ratchets, each driving one wheel, in that it drives the slower wheel and lets the faster one overrun. It differs from a pair of ratchets in that only one wheel can overrun at a time. In decel, the slower wheel sees the engine braking. In a race car, this promotes very free turn-in. If the driver likes to finish braking and then turn, this can work well. If the driver likes to do heavy trail-braking, it may be a disadvantage.

When the driver gets on the power, the inner wheel drives, up to the point where it spins. As soon as the inside wheel reaches the speed of the outside wheel, the unit locks and drives both wheels. The lockup is not smooth at all. The dogs are either engaged, or they’re not. The unit cannot slip. This requires the driver to develop a feel for when the unit is going to lock, and anticipate the change in car behavior at lockup. It also rewards decisive driving. That is, lockers are somewhat unpredictable if the driver is on and off the throttle trying to balance the car. It can be hard to predict whether the rear will be locked or unlocked when the power is reapplied after a brief lift. So the locker responds best to a driver who gets on the power and stays on it.


One peculiarity of the locker is that when backing up, it drives the faster wheel rather than the slower one. This means that we don’t have drive to the wheel with traction if one wheel is off the ground or on very slick ice. Normally, this is of no concern in road racing, but it is something to consider for street or off-road use.

The locker develops less heat than a Salisbury or Torsen, since it has no slipping friction elements. The rear end can still get hot, due to the friction in the ring and pinion gears. And if it gets hot, the springs in the locker can lose their temper. This will cause erratic locker behavior. For this reason, it is customary in racing to replace the springs frequently.

Lockers are universal in NASCAR, because the rules require them. Salisburys and Torsens are prohibited. This rule originated with a prohibition against all limited-slips and spools. The inspection procedure was to test the rear end by turning one wheel with the transmission in neutral, as described above for testing a Posi. The wheel had to turn freely. Since a locker would pass this test, people started using them, and they were such an advantage over an open diff in a stock car that they became universal. NASCAR saw that the racing was better when the cars could put power down with both rear wheels, so they never prohibited lockers. Now, they are specifically written into the rules by name.

[MikeP99Z]

Nice write up.

[Al Fernandez]

Q.E.D.

[Todd Covini]

OK....I give up.
Quality Education Dude?

[mitchntx]

It's Spanish for STFU ...

[Todd Covini]

It's Spanish for STFU ...

http://skyjude.users.btopenworld.com/Images/goodfellas02.jpg

[mitchntx]

Let's see ... you would be the restaraunt owner in that scene ...

[Al Fernandez]

Geez Todd, did you get your engineering degree out of a Cracker Jack's box? Quod Erat Demonstrandum is latin for "which was to be demonstrated" and is used to denote a proof has been completed to satisfaction.

[Todd Covini]

I got my engineering degree from the same school as the Captain of the recently pirated Maersk Alabama.
Massachusetts Maritime Academy....Marine Engineering. We're Merchant Marines, Americans...and Latin is a language that died many years ago...no need for that Bullis Shittus when you're hauling 265,000 Deadweight Tons on the open ocean. :wink:

Now I like Mitch's definition better. :lol:

[mitchntx]

Now I like Mitch's definition better. :lol:

Welcome to the side of all that is right and true ...

[cobra132]

Look at the big brain on Al.

[BlueFirePony]

OMG...its the end times...Mitch and Todd are on the same side!!
Run away!!

[Al Fernandez]

Fire and brimstone coming down from the skies! Rivers and seas boiling!! Forty yearks of darkness!!! Earthquakes, volcanoes, the dead rising from the grave!!! Human sacrifice....dogs and cats living together
mass hysteria

[Hood]

Human sacrifice....dogs and cats living together
mass hysteria