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Fiesta ST autocross accident

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Location
Lake Forest, CA, USA
#61
205/45-16 is shorter setup than stock, and I was planning on running 215/45 next season (still slightly shorter than stock) What tire were you running that you felt sidewall flex?

Also, I'm sure there is a point where lowering goes from positive to negative impact on handling, which might explain why you feel that the setup as been working great for you. I'm lowered on Swift springs and the car feels 10x more stable than it did with the stock setup, so we both may be just be at at a good height.

But where that crossover point is? I'm not sure, that's were I was hoping someone with more experience might be able to answer. I'm going to go find a book on this stuff. Got plenty of time to kill while cooped up at home
Toyo R888R aka cheater slicks. Not as much sidewall flex as some but after coming from the stock 205/40/17 any amount at all is noticable.

Sent from my Pixel 3a using Tapatalk
 


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Location
New York, NY, USA
#62
Hello all, I have a somewhat similar setup to the car OP described as flipping. As to not end up upside in a parking lot surrounded by fellow nerds I'd like some input on what to do for my car to prevent it, I figure this is the proper thread.

Relevant things:
Car: Total base, no sunroof. This is obviously not a major influence, but it is less weight at the highest point in the car so somewhat relevant.
Wheels: 16x8 Konig Dekagram
Tires:205/50R16 RE71R(don't remember the exact pressure for the only event I ran last year but I think it was around 38F 42R)
2 degrees negative camber via camber bolts
Standard Fiesta Bilstein B14 (was told these allow for near stock ride height which is where I try to keep the car)
Will be installing an MFactory LSD over the winter, not sure if this will increase or decrease rollover chances

Me: About 7 years autocross experience but on and off. Not going to get lost in the cones but still somewhat ham fisted. Our events aren't on concrete, often in pretty shoddy parking lots.

I am planning on getting a full corner balance and alignment from a very reputable guy in my area before the 2021 season in which I will probably pick the guys brain about this.

Before that though, without selling a still pretty fresh set of RE71Rs, is there anything I can/should do in the setup to prevent myself from ending up on the roof?
 


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239
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263
Location
Anchorage
#63
I'm a newbie to any sort of track or autocross events, but I don't see how such a tall tire will help in such an event.
The 205/50R16 RE-71R is (was?) significantly cheaper than the 205/45R16, so more people bought them. Some would argue that the gearing would help, but there is less than a 1% difference in the revs/mile between the two. The downside (to my understanding) is that the larger sidewall might allow a more dynamically variable contact patch.

These cars are fairly tall, and with all the variables between suspension changes, tire selection and pressures, surface irregularities, and driver skill, it is certainly possible to roll one over. But you could say that about many cars, and while I am certainly glad the guy got away without serious injuries, there were choices made that led to how this played out. My car has even more tire than this example, and I have got it close to getting up on two wheels, but you can feel what the car is doing and correct. If you look at the slalom, it looks like he made progressively more abrupt inputs with each cone because he entered it too fast and decided to drive harder, not smoother. YMMV, I've only been doing this a couple of years, make plenty of my own mistakes, and I really don't want anyone to get hurt.

You'll never be able to eliminate all risk, and while I think the FiST is a "safe enough" autocross car, you still need to be careful and work your way up. If you find yourself on two wheels with any regularity, it may be time to adjust your car or adjust your technique. The OP seems to want to lay blame squarely on the car, despite it being modified away from factory spec. The owner could have made better setup choices. It also seems that the OP eliminated the surface as a contributing factor, which has the appearance of trying to cover the organization's ass and maintain the use of that venue. If there are surface irregularities, you can design the course to avoid them, or make it so that the cars interact with them in such a way to minimize issues. Also, if the car was getting noticeably unsettled in previous runs, you can counsel/coach/implore/demand the driver chill out. I can understand the OP wanting to protect their friend, their club, and their access to venues. But blaming the car, and the car alone, only serves to make everyone blind to the other contributing factors that led to this incident, and may lead to another one like it.
 


M-Sport fan

9000 Post Club
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#64
Toyo R888R aka cheater slicks. Not as much sidewall flex as some but after coming from the stock 205/40/17 any amount at all is noticable.

Sent from my Pixel 3a using Tapatalk
Any reason why you did not go to 16x8s, as you were already out of H/Street due to the 100 tread wear rating??

Was it just lack of any at all availability in our PCD at the time? [dunno]
 


Messages
46
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Location
Lake Forest, CA, USA
#65
Any reason why you did not go to 16x8s, as you were already out of H/Street due to the 100 tread wear rating??

Was it just lack of any at all availability in our PCD at the time? [dunno]
I wanted RPF1s and they were only selling them as 16x7 at the time. I think 7" is still preferable w/ 205 for an all-around setup that will see both street and high performance use, 8" will get you a better contact patch but the sidewalls will do less work.

Edit: also as for SCCA class, I just autocross to scare myself these days not for trophies
 


Last edited:

Dpro

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#66
205/45-16 is shorter setup than stock, and I was planning on running 215/45 next season (still slightly shorter than stock) What tire were you running that you felt sidewall flex?

Also, I'm sure there is a point where lowering goes from positive to negative impact on handling, which might explain why you feel that the setup as been working great for you. I'm lowered on Swift springs and the car feels 10x more stable than it did with the stock setup, so we both may be just be at at a good height.

But where that crossover point is? I'm not sure, that's were I was hoping someone with more experience might be able to answer. I'm going to go find a book on this stuff. Got plenty of time to kill while cooped up at home
rule of thumb in lowering and not screwing up your roll center is never let your lower control arms go beyond angle downwards or flat out. Like the diagram you showed. Its a pretty simple rule to follow and besides the fact that its a visual role you will know its a problem because it will instantly introduce bump steer. I learned this back in the beginning with Datsun 510’s as everybody sought to lower the overly high stock ride of the cars. We did not have coil overs back in those days so you were subjected to whatever the lowering spring gave you. The 68-69 510’s had front cross members with control arm pickup points that lend themselves to lowering the car. Interestingly enough Nissan lowered the pickup point of the stock crossmembers in 1970 ( so you would have to modify it) but then went and made the struts slightly longer by an inch.
I am getting afield here though. The main thing to remember is at the least you want your control arms splayed out even and ideally at a downward angle. If they have any kinda of upward angle you are too low for the roll center and at handling disadvantage for the car.

This is a universal rule of thumb as well its not car specific . Its all about the geometry.
 


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Location
Cleveland
#67
rule of thumb in lowering and not screwing up your roll center is never let your lower control arms go beyond angle downwards or flat out. Like the diagram you showed. Its a pretty simple rule to follow and besides the fact that its a visual role you will know its a problem because it will instantly introduce bump steer.
This is my biggest gripe about Macphearon front suspension. It's crucial you don't beyond parallel. At least we have coil over spring struts. My old Mustang had separate coil and strut suspension in the front, but the chassis was brand new in '79...
 


PunkST

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#69
I should also add my r comps are hard as a rock due to age. Lol.
 


Intuit

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#72
From 2016 Ford Service Manual...

1610332386759.png

@TyphoonFiST - Re tire size change from stock 205/40R17 to 215/45R17, it's very noticeably less responsive or rather, it's delayed. Quickly get used to it and could almost forget there was a change though. Re tire type, it's a Summer (hard carcass, very stiff sidewalls, light weight) versus Winter (flexible, soft, *heavy*). The all seasons I just bought are 215/45R17 and I think the sidewalls will be more like the Winter set than the Summer...
 




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