What Will Cause a Roadster to Flip (Details)?

[skullandbones]

I don't want to be the harbinger of doom but I'm interested in specifically what causes a roadster to flip over with the wheels pointing up. We all know from the picture of Dave Smith's car in the manual that it is possible. He explained it by saying he took a curve a little too hot (paraphrase) after riding with a pro driver on the same course. I don't know anyone personally who has done that but I do know three roadster owners who have wrecked theirs. All three said they didn't know exactly how it happened. All three were totaled! So if anyone who has experienced this sort of thing or almost experienced it or knows someone who did it, could you chime in and explain your best how it actually happens.

I have only come close to disaster a couple of times but each time it was completely driver error, I confess. The only component on my car that has been associated with anything close to this sort of accident is the 4 link rear suspension. I have not personally experienced the dreaded "snap spin". I didn't want to find out the hard way so I am in the process of changing to a 5 link. I also have not driven at speed to induce much of this extreme behavior, yet. It would be nice to know a little more about this subject so I don't have to find out by trial and error (very tough teacher).

Any help and feedback on this subject will be greatly appreciated.


Thank you,

WEK.:eek::eek:

[j.miller]

Because the roadster is low and 2300lbs when they get away from you they like to slide. To get one to flip you pretty much need to "trip" them. Hitting a curb or going onto a really soft shoulder sideways would do the trick. If you have sticky tires, over correcting two or three times might get it up on two wheels. It's very rare...Bat

[chopthebass]

what is "snap spin"?

[skullandbones]

Hi Chop,

I had not heard that term either until reading about my 4 link suspension which is basically the Mustang 4 link with triangulated control arms. The LCA and UCA on each side form an X or more like a \ /. Anyway, the opposing control arms allows you to run without a PHB or watts link. It turns out there is a bind that happens under certain performance conditions that makes the arms suddenly release the bind and grip of the rear tires to cause an unexpected slide. I have not done it but it is well documented. Several experienced drivers have said it gives you no warning and little chance for recovery. When you get rid of at least one of those UCAs (Poor Man's Three Link), that can fix the problem according to posters on the Mustang forum. WEK.

[frankeeski]

I got to jump in here and correct the snap spin explanation. This is not limited to only 4-link cars, any rear suspension combination can suffer from a snap spin. The snap spin occurs when the rear wheels break free and the rear quickly becomes the front end. Many things can contribute to the spin. The easiest and most common is cold tires. Wet pavement would come in a close second. Driver error can also contribute to it as well. Downshifting while braking can quickly bring the rear end around. This is one reason I am not a proponent of aggressive rear brake adjustments but that's for another thread. Corner weighting the car is going to be the best, if not one of the best, ways to keep all four corners on the ground.

[MPTech]

I'd say SnapSpin was more of a risk than flipping.

Here's a good discussion on Snap Spin:
What causes a snap spin? (http://www.ffcars.com/forums/17-factory-five-roadsters/214150-what-causes-snap-spin.html)

[CraigS]

The '..it would need to be tripped up..' is the best answer. I have been autocrossing my FFR since 2007 and run (a bit behind) w/ some of the fastest FFRs on the east coast. All of us get loose, sometimes we get REAL loose, but the chance of flipping isn't even a concern. This, of course, doesn't say it can't happen, since there are about a million ways to be involved in an accident.

[Jeff Kleiner]

I've spun mine more than a dozen times on course but have never felt any hint of the car doing anything but staying flat. My only real concern is of going off the tarmac sideways (which I've done a couple of times) and digging into the soft ground--- "tripping it" like Batty said.

Jeff

[Pylons]

the center of gravity of these cars is so low, you pretty much need something other than normal road/track surface to flip one over...you likely need some combination of getting the car pretty far from level (running up or down a bank or something acting as a ramp for just one side of the car) and something to grab onto the low side (soft ground, curb, etc).

[OCCPete]

what is "snap spin"?

Google "lift-off oversteer" or "off throttle oversteer"

[skullandbones]

I wanted to clarify that I was not making a general statement trashing 4 link suspensions. I have had some very well behaved versions that did the job as designed. However, there is a lot of documentation about the Mustang 4 link and how it "binds" under certain conditions (bushings load) and then releases suddenly without any feedback to the driver. This results in a "snap spin" that is usually not recoverable. I consider that a design defect and something I'm moving away from by going to a 5 link. I also have discussed this with a couple of drivers of roadsters who have had 4 links and then changed. Their descriptions of the "snap spin" were very consistent. Both explained the difference was noticeable in that the new rear suspension did not break traction as unpredictably as the 4 link. Of course, any car will lose traction if you press it hard enough.

One thing I've gotten from this discussion is that my initial concerns about "flipping" the roadster are probably overblown. It isn't that I'm paranoid about it but if it was a real tendency for this car, it would be something to consider carefully (like SUVs flipping- I witnessed one on the freeway end over end 3 times). If it is a very rare occurrence as mentions several times, I can concentrate on the less exciting aspects of handling the roadster. Staying out of a sideways spin is my first priority now. Thanks, WEK.

[Gumball]

A loose nut behind the steering wheel.

[Mesa Mike]

I believe it was said above, "tripping". That would probably be best way to turn over a cobra.

Once on a cobra run one of the guys behind me was trying to catch up with "the group ". The group had slowed on the freeway due to traffic and he locked up his brakes to avoid rear ending me. He went sideways into the freeway median cable (3) dividers. It cause his car to do a complete flip over (barrow roll) land on the opposite side of the freeway going the wrong way and slide another 100 yards until he came back into the cable dividers. The top cable cleaned off his scoop and windshield and trapped him with his neck between the cable and his roll bar. He turned blue and stopped breathing until our group manually pushed his car back from the cable so he could get free. To our great surprise he pulled his self up and sat on the back of his cobra and said "what happened". It was such a horrific accident scene the high way patrol called an air rescue copper. He ended up with a totaled cobra and a broken finger. "Tripping"

Bill….before you make a lot of changes you need to get your cobra (with some good tires) in a track environment where you can really test how you car will handle under high speed braking and clutching situations. One easy way to spin a cobra is to brake and let the clutch out in 2nd without bring up you rpm's. This technique is easily learned on the track or in a big empty parking lot (K Mart). But you have to drive your car to find out how it reacts to different environments. On wet roads I just imagine the road is like driving on "black ice". Never, never go to WOT without having your cobra straight after making a turn. Sideways, curb, over you go…….really. "Tripping"

[tirod]

Entirely the reason the Challenge cars have a cage, rather than a chromed show bar that does nothing to keep the windshield from folding flat.

I have no doubt the average SUV is more tippy and will go belly up faster than any Cobra - but we don't push them hard or very often. Hence the difference in insurance rates . . . and what most builder's need to do is what the factory does for months assembling SN#1 off the line - testing it to see exactly what the suspension won't do correctly or even does dangerously.

It's a car with 50/50 weight distribution, so it's naturally not predisposed to keep the lighter end at the back in a slide. It has what is called a low polar moment of inertia with the engine placed well back of the front spindle line - it's a front "mid-engine," and not dynamically much different that a rear mid engine. The result is that it can rotate more quickly than a car with the motor sitting over the front spindle axis. That's great for autocross and short tracks, but at high speed it can "yaw" all to easily. High speed cars also tend to much longer wheelbases to get less polar moment and increase stability.

The whole "sports" car movement was based on building a shorter wheelbase car with a lot less polar moment - the idea is to get a quicker handling car with less resistance to rotating around new centers. With an almost exclusive experience in modern nose heavy commuter cars built from the '30's up, most Americans aren't knowledgeable about driving them, and it's also why sports cars seem so different.

I equate driving one with wet days in the fall, crisp temps, and having the road almost to myself. "Dry" tires for impressive track times don't fit into that vision, which goes to building the car with an all around view of the weather, rather than hiding from it most of the year. Choose tires rated for inclement weather and the chances of a cold wet "snap spin" are reduced.

[skullandbones]

I believe it was said above, "tripping". That would probably be best way to turn over a cobra.

Bill….before you make a lot of changes you need to get your cobra (with some good tires) in a track environment where you can really test how you car will handle under high speed braking and clutching situations. One easy way to spin a cobra is to brake and let the clutch out in 2nd without bring up you rpm's. This technique is easily learned on the track or in a big empty parking lot (K Mart). But you have to drive your car to find out how it reacts to different environments. On wet roads I just imagine the road is like driving on "black ice". Never, never go to WOT without having your cobra straight after making a turn. Sideways, curb, over you go…….really. "Tripping"

Heard about that. That has to be one of the luckiest guys ever to get out of that with only a broken finger.

I do think I need to get my suspension ready for the track before testing it. I'm just about finished with the three link member so I should be driving a 5 link pretty soon!
I am definitely getting some decent tires on there before tracking. Re: the "clutching" problem you get when you down shift and don't get your engine rpms up to speed, does that front weight the car and cause the rear tires to loss traction? Did that happen to you when tracking or just something that an instructor warned you about as part of a driving course? I guess the light weight causes problems with these cars that many cars never experience in similar conditions.

BTW: I was able to get registered for the one day Bondurant course at Wild Horse Pass for Oct. That can't hurt!

Thank you,

WEK.