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Custom rear camber shims to tune rear to match front agressive alignments, interested?

RAAMaudio

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#1
The ST factory alignment is engineered to allow the rear of the car to rotate more instead of plowing ahead, under steering, like most cars are setup as the average "driver" has no clue and is safer with under steer.

In the ST case less negative rear camber and more positive front than the regular Fiesta settings induce some over steering fun and can benefit fast good drivers.

When adding in serious front camber and we all need to if we want to really get the car to grip up front it can cause to much rotation in the rear at speed which can be harder to overcome, more dangerous for some, than under steering or neutral.

(Note: BALANCE, in all things, is all that really matters, to much negative front camber can cause a lose of grip out of the corners)

Optimally we want over steer at low speed and neutral or understeer at high speed which I was pretty easily able to do with my Vette but this car will take some effort and testing to get it right if we can at all.

I have not done any testing yet on the ST so looking for a low cost method like the rotating plastic shims I have seen and when finding a sweet spot having metal shims made from a pattern already worked out for these cars.

Looking at the numbers the ST is easily seen to be tuned to rotate and the regular cars to under steer like most cars are setup.

(Any math errors please point them out:)

Regular Fiesta stock front camber -0.70 ST-1.18 Proposed front camber for my application, -2.5
Stock rear camber -1.52 ST-0.64 Add same amount to rear to match front -1.32
Difference front to rear R-0.82 F 0.54

Quite a significant difference, to keep the same balance front to rear, if indeed that would be best, we would need to add -1.32 degrees more negative rear camber.

I might want as much as -3.0 degrees negative front camber which would mean adding -1.82 rear just to keep the factory front to rear angles on the same plane.

For reference I went back to my very fast SM class 250WHP turbo Matrix I built back in late 2002. It was not a performance model and thus had stock alignments to induce understeer, always, it was a twist beam rear axle car, tall, close to same weight, longer wheel base.

Stock front camber -0.77 Camber I setup, -2.50
Stock rear camber -1.45 Stock rear -1.45
Front to rear difference R-0.68 F-1.05

The Matrix had just enough over steer at slow speed and pushed(under steer) a bit on high speed corners, especially when throttle enhanced by having
-1.05 degrees more front camber than rear.

If you lower the ST and tune the front camber to -2.5 degrees and leave the rear at the stock setting you end up with a difference of
-1.86 degrees more negative than front camber which can lead to more rotation and higher speeds that you need, or want.

On the Scion TC, another fast car I built, IRS came into play, I found the best setup was -3.0 front and -2.0 rear
-1.0, a difference close to the Matrix that had
-1.05 more in the front than rear.


This does not give a final answer as to what is best but I imagine it is far from optimal with the stock rear setting and
-2.5 to -3.0 in the front on the ST.

Some have been using massive tire pressure changes, even trying different tires front to rear, etc....I think it is time to look at the root causes and fix them the best we can and then use spring rates, shock settings, sway bars and air pressures, in that order, to fine tune.

For now it seems a rounded up to
-1.0 shim would be a pretty good ball park change in the rear.

It is time to study what successful racers with twist beam rear axles have done in various cars and types of racing.

Anybody care to help?

Rick
 


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RAAMaudio

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Thread Starter #2
To make this easier to read, we need to keep the rear camber difference front to rear close to what it is stock or even closer together, most likely somewhere between:

-.50 to -1.0 more in the front than the rear.
 


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#3
I know very little about suspension setups, but I'm interested to hear your results. This car is my first FWD car and I don't know if I'm ever going to get used to the understeer. Not being able to plant my foot and move the backend around is a foreign concept to me.
 


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RAAMaudio

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I have driven sideways for decades and I find a well setup FWD to be really fun, a challenge to get it right then really a blast:)

I have done this on asphalt, dirt, gravel, rain, snow......clawing your way around a corner is certainly different but again, fun to me:)

I have been able to beat a great deal of RWD and AWD cars with a FWD in classes nobody expected I could, not many first places but taking 2nd and 3rd in the wrong car is more rewarding that being a copy cat and taking 1st in the right car.
 


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RAAMaudio

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Thread Starter #5
Not much interest in seems in correcting the camber unbalanced issue of putting on coilovers, etc and dialing in more front camber, which the car needs if you track it????

If this does not get going I will just modify the rear axle on my car to dial in the camber I want to run, which is a fair amount of work but only costs me a few bucks in consumables. I hoped to get some interest as there needs to be 10 sets made at $80 each which is cheap compared to having custom work done.

I hope more chime in on this!

Rick
 


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RAAMaudio

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Thread Starter #8
As can be seen, not enough interest so it died on the vine though I have read somebody else might be working on some.

I did mine the hard way, cut and changed the angle of the axle flanges, quite a challenging job but love the results and with rolling and pulling I have 15x9" wheels all around on the car:)
 


Siestarider

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#9
I am also interested, wonder how Ford racing sets up fiestas for track. Shims or RAAM permanent solution?
 


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#10
As can be seen, not enough interest so it died on the vine though I have read somebody else might be working on some.

I did mine the hard way, cut and changed the angle of the axle flanges, quite a challenging job but love the results and with rolling and pulling I have 15x9" wheels all around on the car:)
That's a shame. I do a lot of back roads driving on my commute and have found on my previous cars that I get nice even tire wear at about -2 deg camber with zero toe. As you said I would like to retain near the balance it has now or closer front to rear. All people have different driving styles. For FWD, I like to trail brake to get the back end where I want it, then throttle to plant it and pull it along. I have found (for my driving) that the back end settles back in nicely after slight sliding with the front at -2 and the rear near that (for FWD and non rear biased AWD). It was -2 all around for my WRX, and -2F, -1.5R for my Fit.

But I digress, basically I just wanted to be able to get more rear camber, here's to hoping for a shim kit or such.
 


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RAAMaudio

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Thread Starter #13
Yes, at least the Team O'Neil cars do as I talked to him about it. It has better camber but is softer so a sway bar, etc, is likely needed.

I probably would of gone that route had I known it as I put a great deal of time into getting my setup just right, 3 attempts to dial it in, 8 hours per attempt of very serious work.
 


Siestarider

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#14
I bet there is a lot more to do to base model twist beam in order to get camber and still handle. Think I will drive around that problem until there is something easier to implement.
 


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RAAMaudio

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Thread Starter #15
I have -1.9 rear camber, have to look up the toe but likely I made it 0.0, no rear bar, handles incredibly well.

The none ST rear beam with something to stiffen it up a bit should be about the same.

I do have a highly modded E36 5 way rear sway bar and mounts on the car I setup to do some testing with but so far have not ran it and not sure I need to. Cool if not, saves weight, one less thing to adjust and maintain, simple is always best.

I did install hard front sway bar bushings on the stock bar but was considering the none ST bar but realized I might not need it. When I have a place to work on the car more regularly I will likely start testing sway bars but for now I am very happy with what I have which includes the BC racing race spec spring rates which I am going to order an even stiffer set soon as my wheel offset and track width reduces the effective rate.

Best to adjust handling with geometry, spring rates, shock tuning, etc..then tweak with sway bars as the final touch as they are the least important when all else is done right.
 




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