Caster, how far can you go?

[clausen]

Hi there,

What are the undesirable side effects of excessive caster, beside the obvious steering weight, and weight jacking effect (which I dont think is actually undesirable in FSAE)?

How much do we think is too much?

Regards

Paul Clausen
Uni of Adelaide

[clausen]

Hi there,

What are the undesirable side effects of excessive caster, beside the obvious steering weight, and weight jacking effect (which I dont think is actually undesirable in FSAE)?

How much do we think is too much?

Regards

Paul Clausen
Uni of Adelaide

[PatClarke]

Hi Paul, you cannot consider caster separately.
You need to take into account caster trail, pneumatic trail, KPI, scrub radius etc. Even the size of the steering wheel!
PDR

PS, 6 degrees should be plenty http://fsae.com/groupee_common/emoticons/icon_wink.gif

Rudeness is a weak mans imitation of strength

[clausen]

Thanks,

Yes I realise that, but it is possible to arrange the steering axis geometry so that you have caster angle A and caster angle B, and no other changes.

What's wrong with more than 6 degrees?

Ta

Regards

Paul Clausen
Uni of Adelaide

[ben]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Suddenlee:
Hi Paul, you cannot consider caster separately.
You need to take into account caster trail, pneumatic trail, KPI, scrub radius etc. Even the size of the steering wheel!
PDR

PS, 6 degrees should be plenty http://fsae.com/groupee_common/emoticons/icon_wink.gif

Rudeness is a weak mans imitation of strength<HR></BLOCKQUOTE>

I'm trying to work out whether the wink is to indicate the UOW had 6 degress or suggesting that you'd be crazy to accept 6 degrees arbitrarily without considering all the other relavant parameters.

I'm probably going to have different top wishbones this year to vary it between 4 and 10 degrees. I know some people have gone that extreme with caster but we haven't before so I want the option to go back if it all goes horribly wrong :-)

Ben

University of Birmingham
www.ubracing.co.uk (http://www.ubracing.co.uk)

[Charlie]

90 degrees is too much. http://fsae.com/groupee_common/emoticons/icon_wink.gif

Build your car with lots of range and test. It is easier to do this if you ahve rod ends in bending, but you can still get a range with a fixed bearing too.

-Charlie Ping
Auburn University FSAE (http://eng.auburn.edu/organizations/SAE/AUFSAE)
5th Overall Detroit 2003
? Overall Aussie 2003. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Ryan Colton]

What I look at when I pick caster angle.

-How much camber gain do I won't?

Caster will cause a negative camber gain on the outside tire and a positive camber gain on the inside tire. This is a good thing to a certain point.

-How much Jacking force I won't

The jacking force can give you a small amount of additional load on your tires as you enter the corner which increases your steering force.

-Mechanical trail

The mechanical trail as you all already know gives you an aligning torque which can help return the tire. Another thing to consider is the pneumatic trail. The pneumatic trail also creates an aligning torque which changes as your slip angle changes. For Goodyear 20X6.5 065 tires the peak is at a 3 degree slip angle after which it starts to decrease as the slip angle increases. To be able to feel this decrease is important for a good driver to feel the amount of traction he or she has left in the front tires. Race car vehicle dynamics says that you should get a 30% reduction in steering force as you approach maximum slip angle/lateral force.

Most of my info has come from books I don't have a lot of experience, though the people that I have talk to seam to all agree; shoot for what you want then make it tunable.

Oregon State University
Formula SAE-Suspension team

[PatClarke]

Ben, Lets get something clear here...I don't give away anyones 'secret' figures, with or without a wink.
And whatever caster Wollongong used is only part of their suspension package, that even they would admit is not perfect by any means.
The effect of castor is manifold. As 'Coltonr' points out there is the camber change effect, but this can be modified by use of KPI. He also mentioned jacking, but this can be modified by changing the trail figure or reducing the scrub radius and therefore the lever moment applied by caster.
I have seen cars with almost 45degrees of caster (1964 Porsche F1 car) but the effect was modified by other parameters, otherwise Arnie S. wouldn't have arms strong enough to drive it.
All other things being equal, you will find the caster figure I mentioned earlier as a good place to start experimenting.
PDR

Rudeness is a weak mans imitation of strength

[Eddie Martin]

We have never run 6 degrees of caster.
If you "read" our tyres after the enduro in may we weren't using our tyres to the maximum. Far from it.
What ever figure you do decide on make sure it is adjustable.

Regards
Eddie Martin
UOW Racing

[PatClarke]

Thank you Eddie =]
PDR

Rudeness is a weak mans imitation of strength