Kinematic toe, whats it all about?

[Roger440]

Thanks Tango. I may well take up your offer. Much appreciated.

 

Tony, i have no idea currently! One of our customers has a 993, aside from the one who wants his alignment done, so im gonna try and get it on the ramp, wheels off and try to understand the rear suspension.

 

Once i have done this i will feedback what i find. Hopefully i will also have aquired the necessary workshop manual updates to, but this is proving hard.

 

Thought you were going to bed

Sleep is for wimps ... The 911T club seem to be hitting wim at the moment Roger?.... these cars are not my speciality, the absence of this tool and the customer increase is making me nervous can you advise..?

 

Then i will go to bed..... Squeaky clean.. no fags'

 

Which 911's? As i understand it, its only the 993 variant that this affects. All others, normal procedures apply!

 

Sorry for delay - i went to bed!

[Tony]

Thanks Tango. I may well take up your offer. Much appreciated.

 

Tony, i have no idea currently! One of our customers has a 993, aside from the one who wants his alignment done, so im gonna try and get it on the ramp, wheels off and try to understand the rear suspension.

 

Once i have done this i will feedback what i find. Hopefully i will also have aquired the necessary workshop manual updates to, but this is proving hard.

 

Thought you were going to bed

Sleep is for wimps ... The 911T club seem to be hitting wim at the moment Roger?.... these cars are not my speciality, the absence of this tool and the customer increase is making me nervous can you advise..?

 

Then i will go to bed..... Squeaky clean.. no fags'

 

Which 911's? As i understand it, its only the 993 variant that this affects. All others, normal procedures apply!

 

Sorry for delay - i went to bed!

 

Since we cannot find the logic for the tool then 911 or 993 is irrelevant, what is relevant is that i do not want to be knowingly setting these cars incorrectly if this tool is necessary for the Geometry..

[IanF]

I wonder what would happen if you(roger or Tony that is) were to phone them up and ask what they do for the money...

 

They may be happy to explain what kinematic toe is and how it works/matters/ cost £150

[Sam@TDi]

For what it's worth I don't think Kinematic Toe is an industry term.

 

Kinematics is a huge subject but put very simply is just the scientific study of a mechanics in motion. The science would only normally be applied to a vehicle suspension at design level inside a computer simulation model by a vehicle manufacturer or system supplier.

 

That said in my opinion with the increasing use of multi link suspension designs and large preloaded bushes it's getting more important to recognize and understand how each part influences the net geometry, especially if your a sports driver

[Tony]

For what it's worth I don't think Kinematic Toe is an industry term.

 

Kinematics is a huge subject but put very simply is just the scientific study of a mechanics in motion. The science would only normally be applied to a vehicle suspension at design level inside a computer simulation model by a vehicle manufacturer or system supplier.

 

That said in my opinion with the increasing use of multi link suspension designs and large preloaded bushes it's getting more important to recognize and understand how each part influences the net geometry, especially if your a sports driver

How to measure the influences then Sam if the design requires 'type specific' methods after the development stage?

I think we can agree the tool is some form of bushing torque compliance reference... maybe for the pre-load I'm not entirely sure. Personally i would invest little in Kinematics if this is evolution by Geometric design and concentrate on the consequences of the design then better it by adding/subtracting visual traces commercially born on the actual end product.... Cheeky stuff but in the real world we little people can visualise gaps purely because we have a real car, customer, complaint and they are not virtual on PC!

[Sam@TDi]

I think I agree ... As for how to measure a suspensions kinematics you've got 2 real options, if you want scientific data accurate to a few decimal places then you'll need a 4-wheel full chassis suspension dyno.

 

But if you live in the real world like 99% of us you'll just have to take a best guess at how a system will behave dynamically simply by looking at it, one of the most important things to aid your summary will be to concentrate on moment leverages versus the rubber bush sizes.

 

A soft bush that must deflect / conform will invariably have to absorb more energy than a hard bush which is designed to offer stiff resistance to load. When using rubber this energy is transformed into heat, in order to keep the compound stable it must have enough thermal capacity so as to cope with the energy that the bush is being required to accept. The easiest way to give a rubber bush more thermal capacity is to make it bigger (more rubber = more capacity)

 

Big Bush = SOFT ............ Small Bush = HARD

 

So with this in mind you can normally take a look at a multilink suspension and have a fairly good idea which way it's going move under certain forces simply by noting the position of the bushings and there relative sizes

 

I hope that helps a little and I’m not teaching people to suck eggs

[Tony]

I think I agree ... As for how to measure a suspensions kinematics you've got 2 real options, if you want scientific data accurate to a few decimal places then you'll need a 4-wheel full chassis suspension dyno.

 

But if you live in the real world like 99% of us you'll just have to take a best guess at how a system will behave dynamically simply by looking at it, one of the most important things to aid your summary will be to concentrate on moment leverages versus the rubber bush sizes.

 

A soft bush that must deflect / conform will invariably have to absorb more energy than a hard bush which is designed to offer stiff resistance to load. When using rubber this energy is transformed into heat, in order to keep the compound stable it must have enough thermal capacity so as to cope with the energy that the bush is being required to accept. The easiest way to give a rubber bush more thermal capacity is to make it bigger (more rubber = more capacity)

 

Big Bush = SOFT ............ Small Bush = HARD

 

So with this in mind you can normally take a look at a multilink suspension and have a fairly good idea which way it's going move under certain forces simply by noting the position of the bushings and there relative sizes

 

I hope that helps a little and I’m not teaching people to suck eggs

 

It's not an exciting science is it Sam! In your professional opinion can i ask you this? wim operates a system that recovers or delivers the Geometric positions then 2000 miles later validates or moves the positions 'Free' since in truth due to the complexities of Geometry the real set-up is the 'fine-tune' or second check. what are your thoughts on this since it does against the normal commercial grain?

 

Note: Sucking eggs is normally wise assuming the recipient is willing to chew as well

[Sam@TDi]

I think that it's admirable that you do this for free as I would of thought most customers would almost expect to pay a little extra for the follow up, and in a perfect world I would say it was totally unnecessary.

But this isn't a perfect world and no matter how hard we try there will always be some unquantifiable variables sneaking into what we're doing and throwing up spurious results.

 

In reality I can see 4 major points that this post inspection will check and compensate for,

 

1. Coil spring sag (mostly only applicable to new coils)

 

2. Bushes "settling" (mostly only applicable to new bushes)

 

3. A bump in the subsequent 2000 miles that may have messed up your original lovely geometry job

 

4. It might catch any earlier mistake in the geometry, we're all human and also we should remember machines can be subject to external influences that cause temporary errors