Out of curiosity I did a sketch to see what the effects were with the Ackerman steering arm angles. It was interesting to see just how the angled steering arms moved and what happened as they turned. From this I would say that just swapping the arms from one side to the other, placing the tie rod in front of the axle, would not be good and tire scrub would result on tight turns. On wide turns it does not make much difference. Having the arms angled properly (on the tie rod behind the axle setup) does the right thing and makes the inside tire track on a smaller radius than the outer wheel. This is old info for many of you I'm sure but the drawing helped clear it up for me. (You will probably need to print the drawing to read the text)
It's been awile since I fooled with this stuff (my racing days ended 20 years ago)..but one thing I noticed on the asphalt short track cars of the day..no ackerman was present in the front end geometry...it scrubbed off too much speed in the corners...the cars ran a LITTLE toe out to help the entry..maybe 1/16" but that was all. A great (and timeless) aid to suspension design is a book titled "Advanced Race Car Suspension Development"..don't remember the author but it especially good for those designing their own IFS/IRS stuff. It's still in print, I believe and available from Steve Smith Motorsports. Everybody who builds this stuff should have a copy (but I can't find mine..dammit!)
[ QUOTE ] That's similar to a sketch I posted here awhile back. [/ QUOTE ] Sorry, didn't mean to be redundant. I missed your post.
This is what makes me laugh with all the Street Rod guys that use either Mustang or Camaro front suspensions. No way can they steer correctly.
[ QUOTE ] Street Rod guys that use either Mustang or Camaro front suspensions. No way can they steer correctly. [/ QUOTE ] HUH? Care to elaborate on this one? And you better have your homework straight because I will quiz you on this.
THINK about it man...only the location of the outer tierod ends needs to be changed to regain a useable amount of Ackerman. Do you REALLY think GM and FORD got the independents wrong!?!? My front tierod 4x4 has the tierod ends so far out that the boots actually rub ever so slightly on the rims! If it were rear steer the tierods would be several inches away from the rims. It's just a location issue to get Ackerman back into line. Heat the arms and move them out to compensate on a straight axle Hot Rod with the spindles arms flipped to the front.
that explains a couple things. thanks 3btk. But - and I may be treading into some long-winded argument here - why flip the tie rod around to the front of the axle in the first place? I've never understood that. Is it to make room behind the axle? d
On the subframed cars the only way the ackerman is correct is if they have the exact same wheelbase as cars the subframes came off from . OR if the tie rod end mounting points are altered to reflect the current wheelbase. But is not a huge deal some pickups and vans use the same front suspension whether they are short or long wheelbase. In my opinion ,tire wear is the only reason to get real excited about this. Not much difference than locking the rearend and dragging one wheel around the corner. But then I could be wrong ,it's just my opinion.
you know... I hear that 100% Ackerman isn't correct. 100% being exactly what Ackerman said, the lines running straight to the middle of the rear axle. Supposedly its supposed to be anywhere from 50% to 75% Ackerman, 50% being smack dab in the middle. Thats what I was told by an autocrossing, racecar building veteran. Take it for what its worth.
With the axle mounted in front of the frame and the spring mounted above the top of the front crossmember, you might not have room for the tie rod in its normal place. With the spring mount up high to lower the frame, there just too much stuff going on right behind the axle.
[ QUOTE ] you know... I hear that 100% Ackerman isn't correct. 100% being exactly what Ackerman said, the lines running straight to the middle of the rear axle. [/ QUOTE ] You are right. If you take a corner faster, the tires will not just roll, but they will also slide a bit. The difference between the the centerline of the tire and the direction of the movement is the slipangle. The outside tire will be able to have a larger slipangle before breaking away than the inside one because of the weight transfer. So you dial in less Ackerman to get the breakaway points closer together ( Improving the total grip ). Different types of tires have different maximum slipangles. Tall skinny biasply tires tend to be controleble at large slipangles so they need much less Ackerman.
Thats gotta be the first time I've ever heard about slip angle on the HAMB! Yeah, my ear gets full of that stuff. Forgot how it related to Ackerman though... now I know! Thanks!
Maybe I don't understand Mr. Ackerman's theory, but the MustangII geometry is meant for a 96 inch wheelbase. Say on a '40 Chevy, with a 113 inch WB that's alot of heating and bending and weakening, isn't it? I've never heard of the 50 or 75% theory. Racers usually aren't concerned with tire wear as much a road car.
Ackerman principle works well for low speed driving and has become less important on modern cars. Our driving habits have changed vehicle dynamics quite a bit over the last few decades. Principles that were carved in granite before are no longer taken as gospel. That said Ackerman changes toe angle during a turn. Toe out slows responsiveness, so the counter to that would be no angle change to toe in. A convergence point far behind the vehicle. This helps for a crisper turn in but can cause a scrub on the outer tire at low speeds. Case in point; drive a new car on polished concrete and listen for the tires howling. This usage of less Ackerman angle has opened up posibilities for platforms being stretched to fit multiple applications. In racing applications it helps to be able to change the convergence point to sort out some over/understeer situations. But for the case of our hotrods, close is good enough. The only real Voodoo to avoid would be negative ackerman angle. I am still waiting for the reason why all Mustang and Camaro front ends are done wrong by street rodders.... I can't wait to get into the front steer vs rear steer thingie. And then drop the compound steering geometry employed by GM on the Corvair and front steer Camaros! WHOO thats gonna be fun...
Metashapes, I think I'm following what you're saying, but how does this react at slower speeds? And is there a formula to calculate or is trial and oops?
[ QUOTE ] MustangII geometry is meant for a 96 inch wheelbase [/ QUOTE ] Damn, I though you were going to pull something different. Oh well, Have you ever measured the convergence point on a Mustang II? I have, it is somewhere around 160" back! Well within the scope of most streetrods.
I had a really elaborate response all wrote up that only El Polacko woulda understood... as I was proofreading, I realized my whole post came to one conclusion. You guys are REALLY gay! It's a fuckin HOT ROD! Go out to the garage and bend the steering arms till it works! geeez...
[ QUOTE ] You guys are REALLY gay! [/ QUOTE ] Damit you found our secret.... buy the way, do you know where we can buy Loafer Lightener by the 55 gallon drum!
Hey Bob...I said the same thing 7 or 8 posts ago! Does that mean I rule too!?!? Hahaha Killer really does RULE regardless!
Tire design relates somehow to the changeover to non or modified Ackerman--I read once that the postwar Jaguar was considered the first non-ackerman production car...and wasn't it the first non-French user of radials?? This was a real change in tire behavior and slip angle, the difference between actual turn of wheel and angle followed by car... I think one of Valkenburg's racecar/suspension books cover this. And aren't all GM front steer cars non-Ackerman?
[ QUOTE ] I can't wait to get into the front steer vs rear steer thingie. And then drop the compound steering geometry employed by GM on the Corvair and front steer Camaros! WHOO thats gonna be fun... [/ QUOTE ] Spit it out, don't make me have to play dumb so I can goad you into explaining. Remember Ackerman and roll center a couple years ago?? Best tech post ever. We got to see CARPS squeze into the F1 car.
Silly kids. If you build enough horsepower into your hotrod none of this matters. The trick as I've stated many times before is the use of power steering. Merely use the power to break the rear end loose, give the steering a bit of input and let off the gas as the rear comes around to pointing you in the right direction. Ackerman, like everyone else had better get the hell out of the way! Note. This only works on cars that don't "hook Up". If the front tires reach for the sky, the steering input won't do you much good. [ QUOTE ] The difference between the the centerline of the tire and the direction of the movement is the slipangle. The outside tire will be able to have a larger slipangle before breaking away than the inside one because of the weight transfer. [/ QUOTE ] Building a drifter? I can see a channeled fenderless 400hp Model A coupe and a winged 200hp Toyota tuner sliding around the track. Might even be fun.
[ QUOTE ] Merely use the power to break the rear end loose, give the steering a bit of input and let off the gas as the rear comes around to pointing you in the right direction. [/ QUOTE ] So that's how you do that... I will have to try that sometime...
[ QUOTE ] Building a drifter? I can see a channeled fenderless 400hp Model A coupe and a winged 200hp Toyota tuner sliding around the track. Might even be fun. [/ QUOTE ] Ha ha, I've been telling a bunch of friends I'm building a drift car. When they ask I tell them yeah 2500 lbs and 400+ hp will make it so....
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