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Discussion Starter · #1 ·
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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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I run -.4 degrees more on the front of my miata than the rear. That is what I found worked with my setup to balance out the understeer.

The camber difference will depend heavily on the sum of all suspension mods. However the front should always be higher negative than the rear.
 

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Discussion Starter · #3 ·
I will need to edit as it formatted differently and a bit hard to read as is posted.

For now, if we add more front we need to add more rear to keep things in balance, the exact amount is not known yet.

I still love Miata's, have had 6 so far:)
 

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Discussion Starter · #4 ·
Basically we want to keep the front/rear camber closer to the stock difference but optimized for the best overall handling, it will most likely be somewhere from:
-.5 to -1.0 less rear camber than the front.
 

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Discussion 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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Like all cars alignment choices will vary greatly. cant imagine running more than -2 on the fronts on these cars with fwd and an open diff, but i couldn't imagine running less than -2 in the front with any rwd or awd car. Not that it wont prove to work in the long run to run a bunch of camber. i think most of us running open diffs and street tires wont have a ton to gain by really aggressive alignments.
 

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Yeah as predominantly a DD I'm not looking to nuke through tires and deal with the headaches tbh.
 

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Discussion Starter · #8 ·
-2 is a pretty good number but still gives a bit to much front to rear difference to be neutral handling at least in some instances. There is no magic bullet number to pick based on drivetrain layout, it will take some experimentation to get it perfected and then as I have done on many cars, change it at the track, not that hard if everything is pre-marked.

Stock the car is designed to oversteer to make it more fun and it is fast stock but that does not mean it is at its best...of course you know that.....

I have ran plenty of cars with -2.5 and never had a tire wear issue but perhaps the fact I used to take all corners faster than most, maybe I was just wearing them even:)

If I can get the car setup to have the closest balance front to rear so as neutral as possible, rotate well into corners, not over rotate to far out on slower corner exits, slight push on high speed corner exits, then I will have the best overall handling possible, for my intended purposes.

Having considerable RWD, enough AWD(I find them kind of boring as to easy) and built two very quick FWD cars I am pretty confident in my plans and results with this car as it is a better platform compared to one and a bit more challenge compared to the other.....somewhere in the middle. Open diff, both cars, when bought new, one of the very first mods on them of course, open diff, diff and brakes.......got to change this one asap:)

My car will be a cruiser for most of the use, site seeing, wife and two big dogs on board, I drive really mellow compared to most of my life now, then on track I will drive it all out as that is the true fun to me.

It is not a DD car for me but I am fortunate to be able to do this and had retired at 60 and in very good health other that some old injuries that act up on occasion.
 
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