Dr. Dale Calkins, our late faculty adviser, wrote an SAE paper in 1994 titled “Lateral Response of a Formula SAE Race Car” dictating that an FSAE car would never go above 1.3G of lateral acceleration. The tilt test is based on this idea while adding a little safety factor, 1.7G. “B6.7.2 Rollover stability will be evaluated on a tilt table using a pass/fail test. The vehicle must not roll when tilted at an angle of sixty degrees (60°) to the horizontal in either direction, corresponding to 1.7 G’s. The tilt test will be conducted with the tallest driver in the normal driving position.“
If a car lifts off the tilt table at comp this is to say the car will lift off the ground at 1.7G. Teams reading this today should laugh at such a value. With improved tires and modeling many teams are achieving much higher values that this.

In 2009 we ran a new suspension package that was the culmination of my work at UW. In the summer of 2010 the team was conducting wings vs. no wings on a new grippy go-kart track. Going into a left hand sweeper on a smooth bit of track the 2009 car rolled. The driver was not harmed. A post mortem (2009 car has not been driven since) was conducted and it was determined that the grip the car was making was too much for the CG/track width and it was only a matter of time and tuning that such an event would take place. At the time of roll, the car was testing the no wing configuration. Even though the wings add to the CG, they do provide a restoring force to keep the car on the ground. The fact that we were lifting with wings shows the grip of the car, but more importantly shows the danger that is now present in FSAE. The 2009 car was retired as it was deemed unsafe.
The images below show some winged teams running their cars with no wings. The final picture is the UW 2009 car at completion. The 2009 Car DNF due to a crack in the inboard CV cup. This crack was caused partly by an inadequate design, but also from repeated inertial slams by the tires lifting off the ground and contacting again.








Bottom line: the tilt test needs to be updated for the times.

This message has been edited. Last edited by: J. Vinella,

In 2007, the team that I was involved with took the previous years car to a few SCCA autocross events. One such event was held at at an airport with a very abrasive concrete surface. At that event, while I was driving, the two inside tires picked up on one of the corners. From what i was told, they were off the ground around 8" which may be an exaggeration. That was the only event that we ran on that had a concrete surface, and was also the only time we ever picked up both inside wheels. I always assumed that the difference in grip was the result of the different track surface.

There was some talk when SAE announced that west venue was moving from California to Lincoln, that the surface at the new venue was that same type of grippy concrete that I encountered. Now, I will be the first to tell you that I do not actually know if the Cf of the tire will be higher in Lincoln than it would be elsewhere as a result of the track surface, but it does correlate with the experience I have.

I have been curiously waiting to see if some of the top contenders that are planning on going to Michigan, and Lincoln will have noticeably different setups for either surface. If there is indeed a difference in Cf from one event to another, I would expect that there are some design changed from one event to the next. But, I was also expecting to see a change in the tilt requirement for Lincoln. But that was only because I was under the impression that there would be a difference in maximum performance at that event.

However, like everyone else, I am still learning.

At SCCA Nationals in Lincoln we didn't see any cars going up on two wheels. Almost every car there had wings, for what thats worth. Maryland, of course, could probably drive upside down and keep all wheels planted.

John,

We were getting similar moments in 2004. However I wonder whether we need to ask the question how much lateral g do we want these cars capable of?

I have long been a supporter of a spec tyre for the competition. Something with long life to reduce the cost of competing, this should also allow the competition organisers to decide the level of lateral g capable.

Otherwise there should be some mix of an increased angle on the tilt table and an increase in the minimum track width.

Kev

Our car is one of the offenders pictured above. We have have never rolled a car, but it is certainly possible for a skilled driver to get it up on two wheels (fortunately, the skilled drivers have always brought the car back down). Without aero, we have seen both wheels come up at around 1.9g, but it has always been on a hot day with a very clean surface in combination with a bump on the track. The rollover design point was originally 2g without aero. Our estimate of when we will lift both inside wheels with aero is about 2.5g.

The tilt test is something that we have had an issue with for several years. Even as the tests are run currently, we don't believe they accurately represent rollover at 1.7g. The reason for this is the lip that is used to keep the car from sliding off the table supports the car and prevents if from rolling.



Different competitions have different size lips for supporting the car when it is tilted, but they all add additional support that will delay rollover. The solution is certainly not to remove the lip, in fact I think it is already too small at some events and cars with softer/rounder sidewalls are somewhat at risk of slipping off. I think the situation would be improved if the "L" bracket that supports the car was larger (5"-6") and hinged at the corner so that the car can rotate about the outside of the tire. It seems like changing the tables would be a practical thing to do even this year.

As for increasing the angle, the g level is pretty sensitive to angle change. 2g is only about 3.5 degrees more than 1.7g. I'm not sure what the angle tolerance is at this point but the setups may need to be improved so that the test is accurate enough.

I certainly agree that something should be changed. As is, building a car capable of rolling over is well within the rules.

Has anyone even ever seen a car not past the tilt test?

quote:

Originally posted by Crispy:
Has anyone even ever seen a car not past the tilt test?

Well there was the incident with UC Davis at West last year! Although that was down to operator error, not car design.
Given the average track width of a FS/FSAE car, in order to flip on the tilt table, your CG would have to be over 15 inches off the ground. Most cars tend to have a CG between 10 and 12 inches above the ground (although I have no hard data to prove that), and it seems like it would be pretty difficult to design a car with CG that high. IMO.
I do agree though that 1.7g is starting to become common place. However, very few cars have gotten to the point of sustaining lat g of that high. Most instances that have been brought up are usually a combination of track surface, bumps, etc. that caused a peak G higher than expected at that instant.

I think it is part of your vehicle design, if you don't design the track width to suit the expected G's then you have not designed it well.

We recently had our 2008 vehicle do 2.15 on Barbagallo (race track), no lifting of wheels. We take into account when designing the car that we don't only use it for SAE, we also take it into account that the cars will be hammered by learner drivers, put through their paces in other events and such. As a result we don't only think about SAE rules and safety at SAE speeds, safety at all speeds the car is driven is of paramount importance.

I think the tilt test is outdated but regardless, the tilt test should not be the point where teams find out their design is wrong, you should know long in advance of competition. Teams that go above the tilt test value know that. teams that don't venture that high may not. I think it is still important for the newer teams who are still learning, if their car only ever makes 1.8 max then why test at 2, they will fail even though their car will never make 2.

I feel I should clarify why we were tipping over in that top photo. The car was running 15mm higher than it was designed for, and in that configuration it would not have passed the tilt test.

I personally don't think the tilt test is outdated. Keep in mind that it's the Coefficient of grip is the defining factor to tipping, not the G's. Even the top teams won't see grip coefficients above 1.6 at competition (we even swapped data with other teams in 2009). There would need to be a ridiculous level of grip on the surface to get up to 1.7. Any car that passes tilt should not lift both wheels at the competition unless there is something (dampers, jacking force, etc) lifting the cars cg up.


A concern for winged teams is that if any side gusts hit the rear wing end plates. Our 2005 car car would have passed any reasonable tilt test, but add a strong side gust and the result:

This is an interesting post. Thanks for posting the pictures up Jack. If I recall correctly, the tilt table rules were more relaxed up until 2004 when a certain team, wink wink, flipped their car at competition. I think it was 55 degrees or 57 degrees back then. Anyways, given certain banking, coefficient of friction, wind conditions, and bumps, it is possible to make most cars pick up two wheels on course. I haven't been that concerned and I have seen our car on two wheels several times.

However, add concrete and a hot June day and Lincoln probably has the recipe for the highest g values witnessed in FSAE to date. Obviously it is too late to modify the rules for this year, but it would be very interesting if during tech inspection, all cars were tilted to roll over and the angles were recorded. This data could be used in the future to see if a rule revision is required and if so, how much do we really need to change the tilt angle by.

I'd really like to keep away from mandating a minimum track width. Teams with lower CG's should reap the benefits of a narrower track.

quote:

Originally posted by Mike Cook:
I'd really like to keep away from mandating a minimum track width. Teams with lower CG's should reap the benefits of a narrower track.

Mike,
They already reap plenty of benefits, but I agree from an engineering design stand point.
I like your idea of taking data for this year, kind of like the templates.

Kev,
Oh I know. Our '04 car had very narrow track width and we lifted wheels. Add 6 years, better tires and an evolution in tire testing and tuning.

I believe the tilt test should be for at least 2.5G When I look at the grip UW is making and the CG of the car with wings, it would be hard to pass tilt with our current track width and CG. It would have to go way up to be at all safe. Some might bring up the point such a test takes the wings at speed out of the equations, but you should be pulling high Gs everywhere, not just at speed. Good ol' fashion mechanical grip.

quote:

StevenWebb,
I personally don't think the tilt test is outdated. Keep in mind that it's the Coefficient of grip is the defining factor to tipping, not the G's. Even the top teams won't see grip coefficients above 1.6 at competition (we even swapped data with other teams in 2009). There would need to be a ridiculous level of grip on the surface to get up to 1.7. Any car that passes tilt should not lift both wheels at the competition unless there is something (dampers, jacking force, etc) lifting the cars cg up.

Steven you have an awesome car. I however don't agree with much of what you have posted. If I am pulling 1.7G, what is my the average coefficient of grip? Hint: F=MA...F=Mu*M...A=???

You didn't share with the right teams. More math...if team X pulls X in skidpad, what was team X's G? And that is skidpad, not transients, where both inside and outside tires are making massive grip together.

"If I am pulling 1.7G, what is my the average coefficient of grip? Hint: F=MA...F=Mu*M...A=???"

There's something missing here... Fy=Mu*Fz=Mu*(mg+Faero). If you add downforce, your normal force and cornering force increase in proportion - that's assuming a constant friction coefficient. Whether or not wings make the situation worse depends on whether the increased CG from the wings is compensated for by the decreasing coefficient of a real, load sensitive tyre.

Mike,

A team with a low centre of gravity already has benefits regardless of whether they decide to take it as less weight transfer or being able to take a tighter line by using a narrower line. There was a time when no teams were near to the minimum wheelbase rule, now there are a lot of teams nearly on the limit. Maybe a starting track limit could be 1m, which shouldn't affect very many teams at all, but at least sets a hard line.

Personally I think the better solution is to start using a spec tyre. Before everyone cries foul it is helpful to think that there are a lot of rules in the rulebook to control speeds with the idea of protecting students some of the main ones are:

- Restrictor size
- Engine size
- Aerodynamic limits

This is not outside the level of control that should be offered to the rule makers in order to protect our students.

We are driving a very fine line if teams end up designing to the limit of roll-over in order to increase vehicle performance. Some teams will be able to do so with ease, but many will just get it wrong. Anyone who has spent a fair bit of time in the FSAE paddocks would appreciate that there are a lot of mistakes made when building cars to such a tight deadline with limited starting knowledge. The last thing we would all want to see is an increase in student injuries.

This is a fairly unique situation. I do not know of any other form of 4 wheeled tarmac motorsport where there is a significant advantage in narrower tracks, usually teams have to be limited by a maximum. This has largely been created as a side-effect of trying to limit top speed by creating twisty tracks and forcing teams to focus on mechanical grip.

Kev

quote:

Originally posted by J. Vinella:


Steven you have an awesome car. I however don't agree with much of what you have posted. If I am pulling 1.7G, what is my the average coefficient of grip? Hint: F=MA...F=Mu*M...A=???

You didn't share with the right teams. More math...if team X pulls X in skidpad, what was team X's G? And that is skidpad, not transients, where both inside and outside tires are making massive grip together.

as adamM pointed out, downforce is gonna change it quite a bit. If a 200kg car is pulling 1.7g with 35kg of downforce, your Mu is only 1.5.
You would also need to be over 1.9 g to tip a car that barely passes the tilt table (unless something else is helping).

I don't think a minimum track would help at all, Teams would just focus less about their CG heights, but be just as close to tipping. The benefit of lowering cg simply isnt that high with most SAE tires unless you can make your car narrower.

A spec tire will NEVER work in fsae. If all teams had to get the same tires to work, the cars would end up very similar to each other which is not what FSAE is about.

I'm not convinced that spec tyre will make everybody's cars the same. Pick a common tyre (e.g. the 13" Goodyears or Hoosiers), and look at the range of different designs using that tyre. Every time a new rule is brought in, there's the argument that it's going to force everyone to go down a certain route, but I haven't witnessed that yet - fuel economy rules haven't sent everyone to singles, more liberal aero rules haven't put wings on every car, the templates didn't make everyone's cars too big and heavy to be successful with singles - I'm sure a spec tyre would also have no such effect.

Also FWIW we've had our non-winged cars up on 2 wheels on a sticky go-kart track, which requires a mu greater than 2 - the surface at Werribee would probably never let you get that high but I wouldn't be surprised if there were other competitions where it could be done

quote:

Originally posted by StevenWebb:
as adamM pointed out, downforce is gonna change it quite a bit. If a 200kg car is pulling 1.7g with 35kg of downforce, your Mu is only 1.5.

I think Jack's point is that you don't need aero to get to 1.7g and I agree with him, and we have a lot of data that agrees with him. The coefficient of friction really can be that high (or higher).

quote:

Originally posted by StevenWebb:
You would also need to be over 1.9 g to tip a car that barely passes the tilt table (unless something else is helping).

As I mentioned earlier, I don't believe the current tilt test even test to 1.7g due to the side support used on the loaded tire. The support pictured in my post above above effectively lowers your CG by about 4 inches.

quote:

Originally posted by Crispy:
[QUOTE]Originally posted by StevenWebb:
as adamM pointed out, downforce is gonna change it quite a bit. If a 200kg car is pulling 1.7g with 35kg of downforce, your Mu is only 1.5.

quote:

I think Jack's point is that you don't need aero to get to 1.7g and I agree with him, and we have a lot of data that agrees with him. The coefficient of friction really can be that high (or higher).

Yep, we've been seeing ~2g on our last 2 cars (1.9 in 2010, 2.1 in 2011), no aero. Part of our design constraint is that when we go to cali or in this case Lincoln, the car is going to hit higher g's than we see in testing due to the poor surface quality lots we have. Our team looks for a balance between g-force and track width so that we're still fitting thru the cones yet not putting our driver/car at risk. Our 2010 car was too narrow for its cg height. The person that did the suspension design decided to neglect some things and based his data off old cars hitting 1.7g max. Go figure, we were on 2 wheels in Cali in autocross. We were consistently hitting 1.9 in that car in testing on crappy lots. The heat and surface at Cali was the kicker. I actually had to purposely drive slow during endurance to avoid a DQ/flipping. It sucked.

It is up to us engineers to figure out when these cars will lift wheels/flip over. If you know that your cg is going to be low enough to support a small track width, then good for you, you're doing something right and deserve to dominate.

quote:

Originally posted by spierson:
I actually had to purposely drive slow during endurance to avoid a DQ/flipping.

No way! I use that excuse when I can't keep up too! It works at all levels of racing!

-Kirk

Yea. We always let people win. In fact, it's pretty much why I joined. It makes the other teams feel good. We get a lot of karma points here, especially in our static events.

I purely want to raise this issue. I do not mean to offend anybody or any car. I knew this would not be popular, but I have been thinking about this for a few years and would hate to hear about somebody being killed or seriously injured in FSAE due to this issue.

Kev,

I think your spec tire idea is a great solution. I see some major drawbacks that would need to be over come.

Some teams will have issues getting the tires or cannot afford them. I heard of a team once getting a tractor tire company to make their tires because of money and import issues.

Hoosier cares about Formula Ford and only lucky makes a badass tire for SAE. This might not be the case any more, but it was when I worked with them. If Goodyear made the tire they would make more money, but have little incentive or business case to improve it. This goes for any company that got the contract. Along the export lines, cost would benefit one region (it already does, but this is the nature of any product).

With no tire change or improvement the TTC would be less interesting every year and would resort to doing silly things like wet testing.

While FSAE is a series, how would SAE (International) make this choice? Not necessarily a draw back but a huge issue.

Design challenge wise it would be an interesting experiment. You would truly see the teams that got it right, without the need for budget to try different tires every year.

Chris,

Your point about the current testing technique is noted and I think is why this test has passed so many cars in the previous years. At the very least this need to be addressed this year. Now let us see how many cars pass.

The vehicles suspension will move into droop and raise the CoM during the tilt test, due to the jacking forces (although less than normal) and also misdirection of the 1G normal force reducing that.

So the hinged support might tip early compared to what the car will do on track. Perhaps that change alone would achieve the increased stability you are calling for, although it would penalise soft cars more, and probably need a gentle introduction so teams can still run if they fail the new way but pass the old test. Pretty hard thing to fix once your at comp, and it's not fair to change fundamental stuff like track width mid build.

I must say I'm surprised how close to the stability limit teams are intentionally running. As the outside tyre goes into positive camber, and it's performance reduces, a stable system should be possible? Or can you achieve these high CoF at 3 or 4 deg positive camber?

Pete