Inside rear wheel unloading

[Dan]

Comparing those two laps I think the difference is impacted more from differences in lines & speeds rather than a wheel lifting/setups.

Basically you sacrificed track position for speed throgh the middle of the corner which is how that delta went one way and then the other.

If that was my data below is how I'd analyse it, I think the RPM jump at track out is most likely some sort of wheelspin/slide (If you had TPS and wheel speed sensor data you could determine between slide, wheelspin or free spinning wheel).

[Magpie]

thanks for the feedback Dan.

I don't have similar data where I have TPS to compare, further I don't have individual wheel speed sensors. However the way it felt was inside rear wheel spin.

[Magpie]

Measured the rear suspension travel (among other things). Travel is 68mm and the bump stops are 38mm so only 30mm before bump stops kick in.

Will be corner weighting tomorrow as the rears have gone 10mm longer and 7kg. Further fronts are now 10kg. However front would benefit from springs about 20mm longer or helper springs.

Also setting ride heights, maybe a few mm of rake (with the drivers weight in the car).

Not expecting ant handling changes as the increase is proportional, however roll stiffness will have increased.

With the 7kgs 100kg of downforce will use about 7mm of the travel

[madjak]

Last weekend with the suspension changes the rear wheel didn't unload on the left hander at Barbagallo. I could get the power down instead. So the ASTs on the rear with the helper springs have certainly helped the torsen maintain traction. All up the car felt so much better under brakes and through corners. Next test will be at Collie withthe bunpy roads down there.

I'm running 12.5kg up front and 7.5 kg on the rear.

[StillIC]

What I have learnt:

1. Rear roll stiffness needs to be reduced to avoid lifting the inner rear to the point that the torsen fails to work.
a. Roll resistance is determined by a combination of springs AND sway bars.
b. With respect to roll stiffness sway bar and spring rates and interchangeable.
b. The balance of the car can remain unchanged provided that if the sway bar is reduced the spring rate at that end is increased

2. If wheel droop travel is not sufficient AND there is too much chassis roll then the inside wheel will become unloaded.
a. Disconnect the rear sway as this will allow more droop.
b. No rear sway will promote understeer.
c. No rear sway bar maybe OK for low speed corners but could be dangerous on high speed.

3. Shock length (coilovers)
a. Most appropriate method of setting shock length should be used. That is as per MCA method.
b. If spring becomes uncaptive at full droop then a helper spring maybe sufficient to 'push' the inner wheel back in contact.
Note: King springs make 2 x helper springs at 1.25/4.0 (kgs/mm) which compress from 70mm to 16/20mm.
c. Correct spring length should be used in preference to helper springs.

4. Making changes to car setup
a. Keep it too yourself and don't post your thoughts on a forum
b. Minimise suspension changes until the driver becomes consistent as this removes an unstable variable.
c. Making changes may fix one problem but create another.
d. Consider changes in driving style as a possible alternative.
e. Other people have similar problems and their input/advice is valuable.

I now have a plan on what I will be doing, but will not post it However I think this discussion is valuable just to help myself (and others) understand suspension.

Sorry I am late to this party, but may I suggest unlearning a number of points above? In particular 2c and 3c.

2c: I don't see how not having a rear sway bar will affect high speed cornering, assuming the balance is acceptable (and either ignoring aero effects, or ensuring that these are also balanced). Gordon Murray, who designed various race and championship winning Brabham and McLaren F1 cars, *did not use rear sway bars*. His theory is that all rear roll stiffness should be provided by springs to eliminate the sway bar providing a lifting force to the inside rear wheel. I have copied this on my MX5 and have no particular issues in high speed corners (or low speed corners).
3c: The point of tender springs is not to correct a problem with the 'wrong' springs. It is to allow a high rate spring to be used and retain reasonable droop travel. The only other alternative is bugger all droop, which on a modified road car can be done by either limiting droop travel using a secondary device or running a high ride height. There is no 'correct' spring that can provide reasonable droop, low ride height with a stiff ride rate.
EDIT: Also 2b is only correct if the car was balanced before removing the rear sway bar.

[StillIC]

I have noticed that the words "tender" springs and "helper" springs have been used interchangeably above. It is my understanding that helper springs are *not* tender springs and are in fact opposites. That is:
helper springs *increase* the overall spring rate (when active),
while tender springs *decrease* the overall spring rate (when active), as per those springs being discussed above.

This is an example of a helper spring:
http://www.jegs.com/i/Hellwig/207/984/10002/-1

This is a tender spring:
http://www.datsport.com/suspension-front-tender-spring.html

My 2c contribution to pedantry.

[project.r.racing]

A helper spring is just there to help the main spring stay captive. With the coilovers being used though, there is no requirement for helper springs. If you think they are helping, you are mistaken. It will be a placebo effect from something else you have adjusted.

Helper springs are for those old horrible 90s coilovers where height was adjusted only at the spring feet. And the spring used to pop off its perch under big droop. JICs, Tein SSs etc.

[StillIC]

A helper spring is just there to help the main spring stay captive.

My above post specifically argues that this sort of spring is *not* called a helper spring. It is called a tender spring. That is, a tender spring is just there to help the main spring stay captive.

[project.r.racing]

A helper spring is just there to help the main spring stay captive.

My above post specifically argues that this sort of spring is *not* called a helper spring. It is called a tender spring. That is, a tender spring is just there to help the main spring stay captive.

Good for you.

[madjak]

A helper spring is a tender spring just with a spring rate close to nothing. Helpers are a subset of tender springs. Some rally cars will run dual tenders, one a higher rate, one lower.

On big 4x4 a tender spring can have a spring rate up to 150lbs and still be referred to as a helper because it contributes close to nothing. On a small race car a 50lbs might be called a tender rather than a helper because it does affect the spring rate.

I'm a culprit of mixing them up because basically on our cars there is very little difference between the usage and most of the people I know just refer to them all has helpers.

[StillIC]

helper spring is a tender spring just with a spring rate close to nothing. Helpers are a subset of tender springs.

Upon investigation, it appears that this is the definition that Eibach and Tein use. However, the question I have for anyone willing to answer, is, if a very soft tender spring is a helper spring, then what is this device, which does a very different job, called?:
http://www.ironman4x4.com/category-products/suspension/load-plus

The manufacturer calls it a helper spring, which I agree with, as it adds to the spring rate of the existing spring.

It appears there are two commonly used meanings of the words "helper spring". So how does one know which one is being referred to in a discussion about suspensions?

[madjak]

They are calling it a helper but really its a different device to what we're talking about for coil springs. That adds to the spring rate as it's in parrallel. 'Adder spring' doesn't really sound that marketable to me! In terms of coil springs, tender springs are in series so basically the first spring to compress being the lightest.

It doesn't really matter what we call them as its unlikely anyone will actually install a very low rate helper on a mx5 anyway. Really if you are having a tender spring, install a 150lbs one otherwise there is very little point to do it. Anything less and that droop section of movement doesn't have enough force on the wheel to stop the wheel slipping.

[Magpie]

Helper spring in the context of my discussion is where the springs go uncaptive at full droop.

For example King Springs make a 70 lbs/in spring that has a free length of 70mm and fully compressed is 16mm.

It would be simpler to just install longer springs, that is the plan in the long run. It looks like for the front 220mm is the best, which is 40mm longer than the current ones.

Did not get around Ro corner balancing today. Will set heights to tomorrow and take it for a run to see if there are any more coolant leaks.

[madjak]

The trick here is the how far the car squats under its own weight is the same independant on length (ie same spring rate). So droop ends up being the same with a 100mm spring vs a 220mm spring. Just the longer spring is further down the shock body.

I have some 8" 700lbs springs you can try if you wish. My shocks couldn't be adjusted low enough to fit them so I had to get some 7" ones instead.

Btw I don't run tenders in the front... only the rear.

[StillIC]

They are calling it a helper but really its a different device to what we're talking about for coil springs. That adds to the spring rate as it's in parrallel. 'Adder spring' doesn't really sound that marketable to me! In terms of coil springs, tender springs are in series so basically the first spring to compress being the lightest.

It doesn't really matter what we call them as its unlikely anyone will actually install a very low rate helper on a mx5 anyway. Really if you are having a tender spring, install a 150lbs one otherwise there is very little point to do it. Anything less and that droop section of movement doesn't have enough force on the wheel to stop the wheel slipping.

Well, "adder springs" have been around for decades, way before adjustable coil-overs were a commodity, and to my knowledge have always been known as helper springs. This new definition of helper seems a bit daft, but I accept that this is now another meaning, due to usage.

I do have 'very low rate tender' springs on my NA. They are fully compressed when static. I have no choice to run a tender that is not fully compressed at static without access to shorter main springs, as my aluminium bodied Teins do not have enough shock thread to allow a low enough ride height otherwise. They do keep the main springs in place during big potholes, but I am not even sure if they are active when cornering. But I don't seem to have an issue with inside wheelspin, running a 1.6 Viscous LSD.

EDIT: My tenders are 50lbs/inch from memory.