Dave, Interesting thread - and the link to www.eng-tips.com forum is great - I havent come across that before with some serious info on suspension, tyre performance etc.
Yeah the bit about the axis made by ball-joint to tie rod ends and where these two points intersect is what I was saying regarding the line of action of the steering arms intersecting in the centre of the rear track. Steering geometry as set up like this is the simplest way to achieve the definition of "Ackermann" geometry - and you are right its an approximation. Theoretically you could work out what type of geometry is best, reverse Ackermann or otherwise, or much deviation from the definition is required, if tyre loads and tyre performance curves are known. Unfortunately tyre performance data (especially under real world conditions) is elusive. It should also be noted that corners in racing are generally larger than those a road car needs to negotiate, so the Ackermann effect can be small, and so of a smaller effect than other variables. Andrew > Andrew, > > As I mentioned there was a thread on PF, here is the link. > > http://board.performanceforums.com/forums/showthread.php?s=&threadid=67163672&highlight=Ackerman > > They talk about the axis made by ball-joint to tie rod ends and where > these two points intersect relative to the rear wheels. I think this is > just a rule-of-thumb type thing. > > But I think it'd probably be worth investigating for those people who > want to get every last little bit. However, I imagine its not the > easiest thing to work out, maybe for those people with four slip-angle > sensors. > > I'm putting those two books on my shopping list. :) > > Dave > > On Wed, 2004-03-31 at 02:31, Andrew Greenbury wrote: > > Gday Dave, > > > > I don't even know what that word means :) > > > > Yeah another excellent book is "Racecar Vehicle Dynamics" by Milliken > > & Milliken (bit exxy, but is avail at various libraries). > > > > "Ackermann" is a term that gets thrown around when talking steering > > geometries. At low lateral accelerations the outer wheel turns a larger > > radius than the inner wheel, so the inner wheel needs to turn more if it > > isnt going to scrub. "Ackermann steering geometry" approximates the > > correct geometry required so both wheels turn about a common point, > > and occurs nicely when the steering arms are designed to point toward > > the centre of the rear track. (Static) toe in and toe out add to or > > subtract from Ackermann geometric effects. > > > > Ackermann geometry is common on road cars (low lateral > > accelerations) so that the wheels turn freely in corners without > > dragging. Parallel steering (wheels turn the same amount) or even > > Reverse Ackermann (outside wheel turns more than inside wheel) is > > common in racing to try and get peak force from both tyres at high > > lateral accelerations. If the peak cornering force of the inner (less > > loaded) tyre was at a lower slip angle, then using the low speed > > Ackermann geometry (inner wheel steered more) would drag the tyre's > > operation past its peak performance. The car could be slower because > > the inner tyre is producing less force than it could, the drag of the tyre > > operating past its peak, and the tyre temp would go up because of this > > drag. Hence reverse Ackermann (inside wheel turns less than outside) > > could be better. > > > > Hope this all makes sense and its a compromise to best utilise the > > tyres, > > > > Andrew > > > > > You two are incorragible. > > > > > > Sounds like a good book Andrew. Does it mention anything about this > > > Ackerman angle thing? > > > > > > Dave > > > > > > On Tue, 2004-03-30 at 08:21, Errol Smith wrote: > > > > Aaaasso Glasschopper, > > > > With more pleasure to driver from loss of happy contact of tyre with earth; > > > > passenger make less pleasure, wider eyes and higher dung hill with direct > > > > proportioning as tyre/try rise from road. > > > > Noise of tyre is pleasure for driver and sure to make dung now mountain rise > > > > rapidly for passenger. > > > > > > > > Window open is needed for make driver happy with petrol smell not dung > > > > mountain. > > > > And so the lesson ends. > > > > > > > > Cheers > > > > Feral Errol > > > > www.Datrats.com.au > > > > > > > > -----Original Message----- > > > > From: [EMAIL PROTECTED] > > > > [mailto:[EMAIL PROTECTED] Behalf Of > > > > [EMAIL PROTECTED] > > > > Sent: Tuesday, March 30, 2004 9:08 AM > > > > To: [EMAIL PROTECTED] > > > > Subject: Re: factory front toe spec > > > > > > > > > > > > Aaahhh.... > > > > So this give pleasure more to driver than passenger and make happy contact > > > > with road and tyre become separated as road and tyre give displeasure to > > > > each other upon corner and make everyone happy. > > > > > > > > I get it now. Thanks. :) > > > > > > > > ----- Original Message ----- > > > > From: "Errol Smith" <[EMAIL PROTECTED]> > > > > To: <[EMAIL PROTECTED]> > > > > Sent: Tuesday, March 30, 2004 8:35 AM > > > > Subject: RE: factory front toe spec > > > > > > > > > > > > > Geordie, this is the paid for translation......... : ) hope it helps. > > > > > > > > > > "While it can" being the operative phrase. The inside tyre doesnt stay on > > > > > the deck with any appreciable contact/loading very long : ) > > > > > Cheers > > > > > Feral Errol > > > > > www.Datrats.com.au > > > > > > > > > > -----Original Message----- > > > > > From: [EMAIL PROTECTED] > > > > > [mailto:[EMAIL PROTECTED] Behalf Of > > > > > [EMAIL PROTECTED] > > > > > Sent: Monday, March 29, 2004 5:15 PM > > > > > To: [EMAIL PROTECTED] > > > > > Subject: Re: factory front toe spec > > > > > > > > > > > > > > > U been using Altavista Babelfish on Japanese websites again? > > > > > > > > > > ----- Original Message ----- > > > > > From: "Errol Smith" <[EMAIL PROTECTED]> > > > > > To: <[EMAIL PROTECTED]> > > > > > Sent: Monday, March 29, 2004 3:40 PM > > > > > Subject: RE: factory front toe spec > > > > > > > > > > > > > > > > While it can being the operative as the inside tyre doesnt stay on the > > > > > deck > > > > > > with any appreciable contact loading very long : ) > > > > > > > > > > > > > > > > > > Cheers > > > > > > Feral Errol > > > > > > www.Datrats.com.au > > > > > > > > > > > > -----Original Message----- > > > > > > From: [EMAIL PROTECTED] > > > > > > [mailto:[EMAIL PROTECTED] Behalf Of Andrew > > > > > > Greenbury > > > > > > Sent: Monday, March 29, 2004 10:26 AM > > > > > > To: [EMAIL PROTECTED] > > > > > > Subject: Re: factory front toe spec > > > > > > > > > > > > > > > > > > Hi Mark, > > > > > > > > > > > > Yeah fair enough - something I just found in a book called "The Racing > > > > > > & High-Performance Tire" explains "...Static toe-out is common at the > > > > > > front wheels on racecars... Static toe-out adds slip angle to the inside > > > > > > tyre and gets that tyre working early in a turn before the weight > > > > > > transfers to the outside tire" ie getting some work from the inside tyre > > > > > > while it can. > > > > > > > > > > > > Andrew > > > > > > > > > > > > > Andrew, > > > > > > > > > > > > > > I never ran the car with toe-in....but I did run it with zero toe. > > > > > adding > > > > > > > just 1-2mm of toe out certainly helped the handling - particularly > > > > > initial > > > > > > > turn in. Somebody did explain this to me......and if my memory serves > > > > me > > > > > > > correctly, it has something to do with the inside wheel actually > > > > turning > > > > > > > sharper than the outside, therefore assisting the outside wheel more. > > > > > Even > > > > > > > though the outside wheel takes most of the workload, having the inside > > > > > > wheel > > > > > > > turning further than normal helps even further. > > > > > > > > > > > > > > That's how I understand it anyway...wether that be right or wrong I do > > > > > not > > > > > > > know. What I can say is....it was definately better. It felt batter, > > > > and > > > > > > it > > > > > > > was faster on the stop watch......and that is the main thing right? > > > > > > > > > > > > > > Cheers, > > > > > > > > > > > > > > Mark. > > > > > > > ----- Original Message ----- > > > > > > > From: "Andrew Greenbury" <[EMAIL PROTECTED]> > > > > > > > To: <[EMAIL PROTECTED]> > > > > > > > Sent: Wednesday, March 24, 2004 10:56 AM > > > > > > > Subject: Re: factory front toe spec > > > > > > > > > > > > > > > > > > > > > > Mark, > > > > > > > > > > > > > > > > On the racecar, how do you find the handling with the toe out, say > > > > in > > > > > > > > comparison to the same amount of toe in? I would have thought you'd > > > > > > > > get more grip/better turn in with the toe in, because the more > > > > loaded > > > > > > > > (outside) tyre already has a slip angle at the beginning of the > > > > > corner? > > > > > > > > (at the expense of the inside tyre) > > > > > > > > > > > > > > > > Interested to hear your thoughts, > > > > > > > > Andrew > > > > > > > > > > > > > > > > > Andrew...... Sounds excessive to me. We only run 1-2mm of toe out > > > > on > > > > > > > > > the race car. > > > > > > > > > > > > > > > > > > Just checked my workshop manual (Kenneth Ball), it recommends .3" > > > > > Toe > > > > > > > > > IN. > > > > > > > > > > > > > > > > > > Hope that helps. > > > > > > > > > > > > > > > > > > Mark. > > > > > > > > > > > > > > > > > > ----- Original Message ----- > > > > > > > > > From: "Andrew Greenbury" <[EMAIL PROTECTED]> > > > > > > > > > To: <[EMAIL PROTECTED]> > > > > > > > > > Sent: Tuesday, March 23, 2004 11:36 AM > > > > > > > > > Subject: factory front toe spec > > > > > > > > > > > > > > > > > > > > > > > > > > > > Hi guys, > > > > > > > > > > > > > > > > > > > > I havent got my service manual on me - does anyone know the spec > > > > > > > > > > for a 1600 front end toe alignment? > > > > > > > > > > > > > > > > > > > > I quickly checked a wheel alignment done on my car with a tape > > > > > > > > > > measure - its been set at roughly 5mm toe out total, or approx > > > > > > 0.3deg > > > > > > > > > > toe out per wheel. Any thoughts on if this is excessive?? > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > Andrew > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > --membersozdat------------------------------------------------------- OZDAT Mailing List Please Note:- Send (un)subscribe requests to [EMAIL PROTECTED] Send submissions to [EMAIL PROTECTED] No unauthorised redistribution of this email http://www.ozdat.com/ozdatonline/index.htm http://www.ozdat.com/ozdatonline/listindex.html http://www.mail-archive.com/[EMAIL PROTECTED]/ ---------------------------------------------------------------------
