kingpin trail

[V2 - Italy]

Please, could someone clarify what is the

KINGPIN TRAIL?

Daniele

Firenze Race Team V2
http://www.firenzerace.too.it
DUCATI POWER at the UniversitÃ* di Firenze http://fsae.com/groupee_common/emoticons/icon_confused.gif

[Denny Trimble]

I believe that's a way of saying "scrub radius". Think of it as something like mechanical trail, but in the front-view.

University of Washington Formula SAE ('98, '99, '03, '04)

[Ben Beacock]

I interpret it as 'Kingpin offset' is scrub radius, and 'trail' refers to mechanical trail(the longitudinal distance at the ground from the kingpin axis to the tire contact patch). I assume this is in reference to the design spec sheet.

Ben Beacock
Co-Manager
2004 Gryphon Racing - University of Guelph (http://www.soe.uoguelph.ca/uogracing)

[This message was edited by Ben Beacock on February 27, 2004 at 04:04 PM.]

[Jackson]

ok, so if kingpin trail is scrub radius, then what is kingpin offset?

I have always though kingpin offset and scrub radius were the same thing -- at least according to staniforth pp 109.

I had assumed that they wanted mechanical trail resultant from caster in that spot. They ask for caster degrees, then kingpin degrees, and then the offsets of both in the same box.

That's how I interpreted things anyway.

Brian
WSU FSAE

[V2 - Italy]

Look at this:

"Scrub radius is defined by SAE as kingpin offset, which is the distance between the two points created by the inter- section of the wheel centerline (centerline of tire patch) and the steering axis with the ground plane."

http://www.motorsportsengineering.com/automag/scrubradius/

Daniele

Firenze Race Team V2
http://www.firenzerace.too.it
DUCATI POWER at the UniversitÃ* di Firenze

[Jackson]

Wow, that definition is really confusing without pictures, but yes that is the way I have always heard it described.

To get a little off topic...

Why in the world would you want negative scrub (as per the article)? That would require a rediculous kingpin inclination angle, resulting in really crappy positive camber in cornering.

[John McCarthy]

Jackson,

I know front wheel drive cars make use of negative scrub radius in an effort to counter the effects of torque steer (engine torque trying to take the steering wheel out of your hands). This is mainly achieved with bigger wheel offsets, not necessarily lots of KPI.

Technical Manager,
QUT Motorsport.
www.qutmotorsport.com (http://www.qutmotorsport.com)

[Tim Heinemann]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Why in the world would you want negative scrub (as per the article)?<HR></BLOCKQUOTE>

The reason is commonly referred to as µ-split which means different coefficient of friction on the left and right wheels. Negative scrub radius counteracts the resulting moment induced by different forces at the contact patches under braking. It's quite simple: The brake force at the contact patch induces a moment around the steering axle and with positive camber this moment tends to amplify the steering angle of the wheel where with negative scrub radius it lessens it. Hence under µ-split the wheel with higher µ will turn itself against the tendency of a car to spin. It's the well known principle of self-help.

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> That would require a rediculous kingpin inclination angle, <HR></BLOCKQUOTE>

Not necessarily: Next time you see an Audi A4, A6 or A8 try to have a look at the front axle....;-)

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>resulting in really crappy positive camber in cornering.<HR></BLOCKQUOTE>

However, this is something which you want in an A-to-B passenger car and not in a race car. Negative scrub radius was induced by Audi in the 70ies alongside the diagonal 2-circuit brake system. It's quite irrelevant for race cars IMHO as negative scrub tends to weaken the steering feedback.



Tim