Cornering with vs. without banking

[hollus]

Back in the day when F1 returned to Indy with the new infield, it was said that F1 cars could not cope with the loads of racing in banked corners in the oval (and indeed they did not well in 2005).

But looking at overall force diagrams, I cannot see a big difference between a current corner, say, with downforce, and an oval corner without the donwforce. Adding or removing downforce might make the diagrams more complicated, but basically the weight and centrifugal forces ensure that tires have to deal with a diagonal force while cornering.



So what is really stopping them from racing in ovals or in grip limited very banked corners? (The bank in Indy is currently not grip limited). Engines? Too high speeds? Is there a subtle effect acting on the tires?

[Jersey Tom]

Ultimately the important thing is the total force normal to the road. We have downforce - that's the case either way, regardless of orientation.

Weight always acts along the global vertical gravitational vector. So as you increase banking, the weight felt by the tires actually decreases (m*g*cos(banking)). You can think of the extreme case of 90 degree banking where gravity would have no contribution pushing the car against the track (or wall as the case would be!).

In the flat road case, the lateral forces are perpendicular to the ground normal - so they have zero contribution to the vertical force felt by the tires (other than left/right distribution). With banking though, there's now a component of that (global) lateral acceleration in the direction of the road normal :: m*a_lat*sin(banking). Again, extreme case of driving on a wall (90 degree banking) the lateral acceleration would be 100% pushing against the road.

In the grand scheme of oval tracks, Indy is actually considered to be fairly flat - only maybe 10-12 degrees in the corner. But let's work out how significant that becomes. Let's assume a lateral acceleration of 5G. Minimum weight in 2015 before fuel will be ~1550 lb. 5G * 1550 lb * sin(12 deg) = an additional 1600 lb of "downforce." Basically an extra 'G'.

The IndyCar series races at tracks like Texas which has 24 degrees of banking - quite a bit more! Stock car racing is obviously slower, so less lat G's, but it is made up for by the higher banking. So let's say a stock car winds up having an extra 'G' of vertical load applied via banking. With a car weighting closer to 3500 lb - lots of extra "downforce" !

[Just_a_fan]

I think the original force diagram is incorrect (or at least incomplete). You need centripetal acceleration in there somewhere. Centrifugal force is more an effect than a force (although I understand it can be shown in the correct frame of reference but my maths isn't up to that.)

[hollus]

@JAF, yes, I omitted the assumed acceleration to the right for clarity. And I never know is "centrifugal" is supposed to be force, acceleration, reaction, clicks or something else. I hope it is clear what is meant.

@JT, I was hoping you would pitch in. So you are saying that there is no fundamental difference to the physics, and the only problem would be the "extra G"?

[Just_a_fan]

The point about the diagram is that you probably want to add the tyre force too - that's what generates the lateral load to around the corner after all. That might make it easier to figure out what's going on perhaps. That along with JT's point.

[Blanchimont]

I think the problem isn't the F1 car itself, it is more likely the capability of the tyres to be stressed with high lateral loads for a long time. During high lateral cornering the power(=m*v^2/r * v = 2,8MW for 5G @ 300km/h) accumulates a lot of energy in the tyres. See http://youtu.be/FHC_nZzRBdk?t=34s this thermal video through the Parabolica, the video is mirrored. Take this to the extreme and let a car drive in a banked circle and it would mean that the tyre constantly feels the high power due to the lateral forces and would probably overheat and fail soon.

Edit: Btw, is it correct that i multiplied the lateral force with the longitudinal velocity to obtain cornering power??

[Jersey Tom]

@JT, I was hoping you would pitch in. So you are saying that there is no fundamental difference to the physics, and the only problem would be the "extra G"?

Fundamentally the physics is the same, sure. Physics is always the same It only "seems" different because in the flat road case, Sin(bankAngle) always = 0 and cos(bankAngle) always = 1. So the whole term for the true lateral acceleration projecting into the vertical axis of the car drops out.

I think the problem isn't the F1 car itself, it is more likely the capability of the tyres to be stressed with high lateral loads for a long time./quote]

I'd say duty cycle in general is severe. The road course part of Indy actually makes things easier than a pure oval. The Indy oval configuration... even a big heavy NASCAR stock car, the minimum speed through the corners is probably in the 240 kph range. Average speed around the track is 290 kph! Average pole speed at the Indy 500 this year was 370 kph! Take a fast F1 track like Monza.. the average speed for the lap record is only ~260 kph.

So the speeds are high all the time. And on a road course, you have a roughly equal amount of left and right hand turns. In a left hander the right side tires see high loads and the left sides relax... in a right hander the right side tires relax and the left side tires see the high loads. On a pure oval turning left every corner... the right side tires pretty much never catch a break.

Speed compounds the aero effect as well, in addition to all the "inertial downforce" you get by running the banking. Taking the F1 @ Monza vs. IndyCar @ Indy speeds above for example... even if the F1 car makes significantly more downforce if you compare at the same speed, since aero forces grow with the square of speed, the IndyCar basically doubles the aero effect by virtue of averaging 40% higher lap speeds.

[olefud]

Is it the banking per se, or more that the banking facilitates higher velocities? If the velocity was the same the banking would shift the tire load from lateral to normal, which the tire would likely better tolerate.

[olefud]

Is it the banking per se, or more that the banking facilitates higher velocities? If the velocity was the same the banking would shift the tire load from lateral to normal, which the tire would likely better tolerate.

It is both. For a given radius and speed there is one angle where only normal load of the tires gives you all the cornering. This effect is similar to the turning of aircrafts. Usually racetracks have lower angles, so the lateral load plays a role as well. Of course you can also get higher maximum lateral loads, as the normal load is increased.

My comment related to the question of coping with the loads resulting from banking, i.e. the Indy example. The concern resulted from the banking enabling higher velocities that, in turn, developed greater loading. For any given increase in banking angle at a given speed, more -not all- of the loading would be vertical (normal) to the tire tread rather than lateral which should actually aid the tires ability to cope.

[riff_raff]

The main problem the F1 cars initially had at Indy was the outside tires were not able to handle the loads produced by the banked high-speed oval corners. The 4 corners of the Indy oval are banked at 9deg12min.

I recall IMSA GTP cars weighing over 2000lbs and with huge underbody tunnels that made massive downforce running on the 31deg banked corners at Daytona. One team that used tires from a new sponsor had the RF tire blow out several times on the banked turn during practice, causing quite a bit of damage to the cars and aggravating the drivers. They dumped the sponsor's tires and switched to proven Goodyear tires. Obviously it is possible to produce a race tire that can handle the huge combination of downforce and speed created by running on a highly banked oval track. The combination of flat high-speed corners and cars producing high downforce can create problems for the driver's neck and head.

The 2D diagram also does not consider yaw effects between a banked and flat corner.