Tin Top - are you out there?
06-02-2005, 02:22 PM
#1
Thread Starter
Tin Top - are you out there?
We were having a chat about how a mere 15' (1/4 Deg) of toe-in could have such an effect on handling. I think I can explain.
The example is ove-simplified, but imagine tyre drift angles are linear and all things being equal;
O---------O
I----------I
IIIIIIIIIIII > Crap schematic S2000 travelling forwards say, 100m to here.
I----------I
O'--------O
Imagine rear wheel O' has 15' extra toe-in.
Using the tangent of theta, if the car travels 100m forwards, then theoretically, that wheel will drift the rear of the car .436m to the left in that distance. Or 24.9 % of tha car's width!
That's the distance between the last lollipop and the slip road.
If that was a bend of 100m, that would change the angle of your car quite considerably by the end, increasing or reducing understeer.
I've ignored the self-centring effect of the steering, and the self-aligning forces of the tyres for simplicity, but the concept is there.
Clearly, over 200m the distance doubles (to 1/2 the car's width). In oversteer terms, that would be a lot!
So tiny angles multiplied by big distances = quite an effect.
Hope that helps.
PS - any suspension designers, etc, who wish to make this example less unrealistic, please feel free to do so!
Edit - poxy software bolloxed up my crappy schematic!
The example is ove-simplified, but imagine tyre drift angles are linear and all things being equal;
O---------O
I----------I
IIIIIIIIIIII > Crap schematic S2000 travelling forwards say, 100m to here.
I----------I
O'--------O
Imagine rear wheel O' has 15' extra toe-in.
Using the tangent of theta, if the car travels 100m forwards, then theoretically, that wheel will drift the rear of the car .436m to the left in that distance. Or 24.9 % of tha car's width!
That's the distance between the last lollipop and the slip road.
If that was a bend of 100m, that would change the angle of your car quite considerably by the end, increasing or reducing understeer.
I've ignored the self-centring effect of the steering, and the self-aligning forces of the tyres for simplicity, but the concept is there.
Clearly, over 200m the distance doubles (to 1/2 the car's width). In oversteer terms, that would be a lot!
So tiny angles multiplied by big distances = quite an effect.
Hope that helps.
PS - any suspension designers, etc, who wish to make this example less unrealistic, please feel free to do so!
Edit - poxy software bolloxed up my crappy schematic!
06-03-2005, 05:37 PM
#4
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Not sure why this should be added to the tech faq. Isn't it way too simplistic to ignore things like castor that is designed in not to self centre the steering, but to pull the car in a straight line. And then there are real world factors such as uneven/distorted road surfaces, bump steer, road camber, changes in the angle of the wheels caused by weight distribution and changes in weight distribution, weight of the driver and fuel load, weight of the sub in the boot(!), tyre pressures, tyre and shock temperatures, etc. For example, a cambered road would have a far greater effect than the one described here (one reason why you can chuck a car harder through a banked corner presumably?).
I think this is one where the theory is very hard to notice in practice, as the suspension settings are a compromise based around all these real world considerations put to the test in a relatively controlled environment (on the test track)? Doesn't every manufacturer design their car on a drawing board and then see what needs to be done to make it work on a test track? If it was as simple as designing the perfect geometry, nothing more would be needed, but I don't think that's how it happens.
What I do know is when I had my S realigned, the place that did it had great difficulty actually adjusting (not measuring) it to minute tolerances - maybe they're crap, but maybe not, and Honda do specify a tolerance in their 'ideal' measurements IIRC.
I think this is one where the theory is very hard to notice in practice, as the suspension settings are a compromise based around all these real world considerations put to the test in a relatively controlled environment (on the test track)? Doesn't every manufacturer design their car on a drawing board and then see what needs to be done to make it work on a test track? If it was as simple as designing the perfect geometry, nothing more would be needed, but I don't think that's how it happens.
What I do know is when I had my S realigned, the place that did it had great difficulty actually adjusting (not measuring) it to minute tolerances - maybe they're crap, but maybe not, and Honda do specify a tolerance in their 'ideal' measurements IIRC.
06-04-2005, 02:02 AM
#5
Buy this book before polaying with suspension set ups (reading it too helps):
How to make your car handle
I see that its listed reading for Bath Uni's mechanical engineering course!
http://www.bath.ac.uk/mech-eng/info/third.htm
How to make your car handle
I see that its listed reading for Bath Uni's mechanical engineering course!
http://www.bath.ac.uk/mech-eng/info/third.htm
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