Somewhere I thought I read that the 500 wouldn't be eligible because it's too tall. But from the Specs I could find, that isn't the case. So ....

58.7" tall by 64.1" wide .... the Abarth is 15 mm lower then the regular model. About the same ground clearance of our ITA Miata

In fact it looks like the regular 500 is wider then tall also.

http://www.media.chrysler.com/dcxms..._Specs.pdf

regular Fiat 500: http://www.edmunds.com/fiat/500/2012/features-specs.html

Mako, you need to look at average track width, not overall width...on which basis the Fiat is a fale.

This is a topic that I think we will be hearing more about, as the SEB works through reasonable methodology to replace the previously available SSF data.

I'll post the same thing here I posted on the Cal Club forums. The SSF data is still published, they just apply their "rollover risk" calculation to it and post that number instead. You can back calculate the SSF from the rollover risk data.

http://www.nhtsa.gov/DOT/NHTSA/Vehi...5-0114.pdf
go to page 18 of 36 and you have the EXACT equations used to calculate the rollover risk percentages as a function of SSF and including the dynamic test results...or not.

and running the numbers for a SSF=1.3 you get a roll over risk rating of 13.9635%. so at 14.5% rollover risk, the fiat has a SSF=1.285. To get the car to have a SSF=1.3 (and thus be legal for stock class per the solo rules) you'd need to lower it .25".

certainly seems like a borderline case here, why not just let it run?

Because lawyers?

is there any analysis that went behind the decision to make the line in the sand at SSF=1.3 or was it just arbitrarily chosen? My point is that one could make a solid argument that the 1.3 SSF limit is excessively conservative in case. the 64%+ forward weight bias combined with the strut front suspension should adequately mitigate (through reduced lateral grip potential) the additional rollover risk incurred by the 0.015 SSF deficiency. In fact Fiat lawyers could sue the SCCA for unnecessarily banning their car from participating and thus hurting their sales.

Also, using the stock class allowances to widen the track by .5" raises the SSF to 1.3 and would make it legal per the letter of 3.1. The same justification (rules allowing competitors to bring cars into rollover compliance) is used for allowing cars (ok, trucks really) to compete in higher prep level classes when they aren't allowed to compete in stock due to roll over concerns.

But the bigger picture is people want to drive these cars in our events and we shouldn't be turning them away, IMO.

If it only needs .25" to get to a number that makes it legal, I see two methods. 1) Lower profile tires. 2) If the car has high pressure gas shocks, either de-gas them or find low pressure shocks. This assumes, of course, Stock class. If somebody wants to go to any class "above that", springs solves the problem.

I thought that at first, but tire choices in skinny 15/16 inch sizes sucks. The base model tire (15") is potentially .2" taller than either of the size hoosiers one could run, but the 16" stock sport tire is the same height as the hoosiers. So it's a wash with respect to tire height. but track width changes would do it.

Put a fat ass in it, and THEN measure it !!!!!!!!!!!!!!!!! Yup. THAT should do it.

I don't know, I wasn't involved in the decision.

I submit that is an excessive use of the word excessively. My sons 1.30 SSF Focus is tippy on all seasons much less DOT R's. Trying to make the car Stock legal with spacers won't cut it. IMO, the club is trying to give a newbie on sticky tires a reasonably safe environment to play with his car. We'd also like the course workers to be in a reasonably safe environment. We'd also like our insurance carrier (oh wait, that's us) to be reasonably sure we're not annually tipping "too many" vehicles over. We'd also like to make everyone involved in the sport reasonably confident that our club will still be able to host events 5 yrs down the road. Would you rather make a few people angry or risk making a whole lot of people angry?

I think you're missing my point. If you run low fuel level and pull the spare tire out of the focus I strongly suspect it's SSF drops below 1.30. yet it is still allowed to run, and it does so safely. A fiat 500 is so close to 1.30 (it's 1.29) and it's suspension is so crappy (struts) that I don't think it is a roll over risk. We're not talking about letting a lotus elise (or any other 50/50 weight split, double a-arm car) compete in stock class with a less than 1.3 SSF. This is an econo-crap-box on skinny tires.

My point is that the roll over margin, aka the difference between the grip level required to roll the car over (what the ssf tells you) and the grip level a fiat 500 is going to produce on R-comps, is going to remain safely positive. Unless you honestly think a fiat 500 is going to get anywhere near 1.285g's of lateral grip on a stock class setup. For reference our SP evo barely gets to that level of steady state lateral acceleration on lincoln concrete, and doesn't get there on asphalt (although it will do about 1.35g in untrimmed dynamic maneuvers (aka peak g's) on asphalt).

I don't think I missed your point I just don't agree with it. Reasonable people can disagree on what a reasonably tippy car is/is not. Pictures like the Jetta at Dixie or the old Saturn from Nats make me want a larger margin of safety than you do. We can't count on newbies to use wheel spacers, etc. Similar to sound readings/loud events/losing sites, I don't think pushing the limits with tippy cars is worth the risk to the rest of the Solo community.

Jeff

Just asking about this, but is the 55" track of the Fiat and 57.5" track of the Mini THAT different that the Mini isn't "tippy" and people think the Fiat is?

Big +1

Fair enough. I think we're just talking about different things. I interpret "tippy" as softly sprung, which has almost no bearing on actual roll over probability (and likely will lower the roll over probability due to worsened tire geometry and reduced lateral grip potential). I'm not sure how one can "feel" the roll over margin unless you can actually get the car up on 2 wheels.

The SSF is the number for lateral grip that creates 100% load transfer to the outside wheels. So while it is a static measurement it is still valid for dynamic maneuvers. You are correct though that the maximum possible lateral force does not usually occur in a trimmed, steady state condition. For cars that understeer the peak lateral accel will happen when the car is recovering from an oversteer moment. The front tires are saturated at their maximum lateral force and the oversteer creates higher than steady state slip angles on the rear tires (higher than steady state lateral force from the rear). If the sum of the front and rear lateral force exceeds the SSF value the car will pop up on two wheels. The magnitude of the peak above the steady state level is going to be proportional to the wheel base and the yaw inertia, which for a fiat 500 appear to both be pretty small.

You still have to continue to apply that level of force long enough to get the CG to rotate past the outside tires before the car will actually roll over (which for a fiat 500 would be ~50degrees)otherwise gravity will pull the car back to the ground. The dynamic peak lateral accel forces typically cannot be sustained long enough to move the CG far enough or fast enough to get the car to roll over. Which is why we have several pics of cars up on two wheels but no cases that I know of where cars actually rolled over.

That's not entirely true, as there are other dynamic factors, most notably roll inertia. The most dangerous condition for rolling in autocross is a "knock-to-knock" maneuver, like on a sweeping S curve with a swift transition and insufficient settle room. In this situation, you then have the angular momentum from the car crashing from one bump stop onto the other, potentially pushing an otherwise roll-stable car over onto two wheels. Also, moving the CG considerably in relation to the tires. This is especially dangerous if this is an off-camber turn or there are seams or other features in the surface that can increase peak tire grip, even if only for a moment. Safety Stewards are supposed to be aware of this and design courses around it, but that doesn't prevent oversights in course design or people from creating their own knock-to-knock situation by driving off the intended line. (A number of my clubmates recently witnessed a car roll in a slalom at another club, when the driver got behind in his timing and created his own knock-to-knock.) These dynamic effects *must* be considered.