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Discussion Starter · #1 ·
OK...newb here, but I did try and search the archives and came up with nada...zilch...squandool. Got absolutely no hits at all with "Ackerman" in the subject line.

Anyone have any experimentation with Ackerman angles that they'd like to talk about ? I'm guessing that, after sorting out caster/camber/toe/bump-steer issues, there are gains to be found by fiddling with Ackerman. I believe ("believe" is what you say when you don't know for sure) that some chassis tuners for these cars have found some tweaks here, but nobody will fess-up.

How to change ? Well, you could shorten/modify the 'steering arms' on the bearing knuckle itself, or just heat the damn things red-hot and bend'em (seen it done...not pretty, but seen it done).

Anybody have anything they're willing to talk about ?
 

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They may have a lot to say, but search for your answer and don't ask or you will be banned
 

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Discussion Starter · #5 ·
Charming. I bet they're rude to old ladies, too.

I'm always wary of people who "have a lot to say", who are a lot different than people who "know what they're talking about".

Thanks for the pointer. I'll search there, and search again. I had previously thought of cornercarvers as a generic 'track day guy' site, but maybe it's now very Mustang-centric.
 

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Tweaking ackerman can be a good thing. Kart guys live and die by it, circle track guys do too.

IME, (racing karts) you generally want to increase ackerman on slow/tight tracks and decrease it on higher speeds tracks with sweeping corners.

This is very hard to do in a production car run in a production class like B/P because we're not allowed to play with the spindles or drag link. ( must not alter the stock suspension mounting points) and spindles are hardend steel that would required heat treating and stress relieving if bent to change ackerman.

IME, on mustangs, the only real way to change ackerman requires the use of an offset bracket at the spindle (and we already know that it's tight in there with the big fat tires).

Most guys get away with it by just changing toe. The inside front tire is barely on the ground anyway.

See here...

http://forums.vintage-mustang.com/files/attachments/med_1180096193-msr1.jpg

Charlie
 

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Question for roadracer: This is slightly off topic, but after looking at the picture you posted I'm curious as to how much (1", 1 3/4"?) upper control arm drop you have on that car? There doesn't seem to be as much camber gain in that photo as I expected. Maybe it is just the camera angles?

John Harvey
 

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In an earlier discussion about bumpsteer, Applejack suggested that it was the jacking effect that you're seeing. If you look at the gap between the top of the tire and the fender, it looks the wheel hasn't gone up any. If anything, the gap is probalby LARGER than at ride height, so suspension is actually in rebound.
 

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IIRC, when I mentioned that before Charlie thought his outer front in that pic was actually in compression somewhat. Of course, that will all depend on springs and bars and some have posted pics of their cars with significant outside compression (Tim?). It seems that once you get in the range of a REAL 700 lb spring or so ('620's' don't count....they're really much lower) then outside compression is really limited.

I'm hoping to put a linear potentiometer on at least one side of the front of my car to put my theory to test. Believe it or not my wife won one at the Solo Nationals this year through Race-Technology contingency! That's what I call a woman!

I think Charlie's right with the toe adjustment suggestion. I agree that the inside isn't doing much at all on our cars mid-corner.
 

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Discussion Starter · #10 ·
Charlie - I'm really sort of asking "how are these guys doing it ?". I know the benefits of appropriate amounts of Ackerman, but the gory details of modifying it are what interest me. With a rack & pinion, you can achieve it by moving the rack front-to-back, or visa-versa. It's just like bump-steer, except you're working on a different axis. With steering box/drag link/idler arm, it's a whole lot more complicated.

My knuckles are stock, so they're castings. You can (!) heat and tweak the steering arms of those castings...I sometimes race an open-cockpit sport-racer, and we're always battering and bending the knuckles and steering arms on them, and I've taken "banana-shaped" steering arms and made them straight again. No pretty, but as they're not steel, no heat-treat issue.

Had a long conversation a few years ago with Bob Woodman (Bob Woodman tires...the Hoosier & Dunlop guy who does tire service at SVRA, HSR etc. vintage races) and he sorta gave me "a wink & a nudge" when talking about old Mustangs and Ackerman diddles.
 

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Hers one opinion on Ackerman.... I just searched on Google for it...

Ackerman Steering and Racing Oval Tracks

Many racers are becoming aware of Ackerman Steering geometry and are concerned with how it influences their race cars. Conventional Ackerman Steering was developed around 1800 AD. Yes, 1800, not 1900. The Ackerman concept is to have all four wheels rolling around a common point during a turn.

Ackerman

The example above shows that the inside front tire must turn a larger number of degrees than the outside front tire for this principle to work.

Most short tracks (oval tracks) have a corner radius of 150'+/-. For a race car that has a 108" wheel base and 60" width, the inside tire would need to turn 3.4 degrees and the outside tire would need to turn 3.3 degrees to have Ackerman Steering. In other words, the inside tire needs to turn 1/10th of a degree more than the outside tire in order to fulfill the Ackerman requirement for this car and corner.

However, at racing speeds, tires develop what is known as slip angle. Despite the name "slip angle" it has nothing to do with slipping or sliding. Instead, it describes the flexing or twisting of the tire's contact patch. It's not unusual for racing tires to develop 6 +/- degrees of slip angle before they loose traction. DOT (street) tires can develop as much as 10 degrees of slip angle before they loose traction.

Due to the magnitude of flex (slip angle) in the tires, that tenth of a degree steering difference mentioned earlier is negligible. So, when it comes to tuning your race car, take conventional Ackerman off the list of concerns. For more information related to this subject see Slip Angles and Handling.

Alignment shops and some Dealerships will refer to Ackerman as "toe-out." This is because Ackerman steering geometry causes the wheels to toe-out during a sharp turn. Be careful not to confuse this terminology with static toe-out. For more information on toe-out see Toe-out and Handling.

Here the link... http://www.auto-ware.com/setup/ack_rac.htm
 
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