Percentage of Antiroll Bar Stiffness

[cmeissen]

Hey Guys,

I have been using the Optimum G Magic Number spreadsheet and was curious about why you should have a certain percentage of the antiroll stiffness taken by the antiroll bars. From the spreadsheet:

"For a rear wheel drive car the anti roll stiffness coming from the front ARB (cell U19) should be 50-80% of the total front anti roll stiffness. The anti roll stiffness coming from the rear ARB (cell U20) should be 10-25% of the total rear anti roll stiffness. The exact numbers should be refined in testing."

My only thought would be that having a higher percentage front would cause more instantaneous weight transfer helping the front tires generate grip first to turn the car. This seems logical to me, but was wondering if there are other factors here I am not thinking about. Thanks

[cmeissen]

Hey Guys,

I have been using the Optimum G Magic Number spreadsheet and was curious about why you should have a certain percentage of the antiroll stiffness taken by the antiroll bars. From the spreadsheet:

"For a rear wheel drive car the anti roll stiffness coming from the front ARB (cell U19) should be 50-80% of the total front anti roll stiffness. The anti roll stiffness coming from the rear ARB (cell U20) should be 10-25% of the total rear anti roll stiffness. The exact numbers should be refined in testing."

My only thought would be that having a higher percentage front would cause more instantaneous weight transfer helping the front tires generate grip first to turn the car. This seems logical to me, but was wondering if there are other factors here I am not thinking about. Thanks

[exFSAE]

CSU.. Colorado State? Boooooooooooooo.

There is no rule for how much bar you should run.

Having more front bar will not necessarily mean more fast weight transfer on the front. More OVERALL roll resistance (spring and bar..and damper?) up front is what matters. Its the overall roll stiffness distribution that is the big player in handling. Or at least as I understand.

That said, I believe you'd want less of the rear contribution to be from bar so the suspension is a bit more independent. Not as much load transfer over bumps (or curbs) on corner-exit. Plus I'd imagine stiffening the ride rate rear to front helps the rear "catch up" after quick transient maneuvers.

But what do I know.

[BillCobb]

Its not the roll stiffness that matters, but the roll moment distribution. So, the roll center position as it affects the vertical forces on the tires and the net axle lateral tire forces need to be factored into your calculations. Given a cg location, keep in mind that most cars have springs in them for ride reasons and that the ride frequencies and rear to front ride frequency ratio is a considerable constraint. Yes that means spring track, too.

What you might decide to do is select ride and roll objects such that you don't need a rear bar. (mass points) That means produce a cg location, spring track, spring rates at a freq. ratio of 1.2, roll center heights and a front bar geometry, efficiency and diameter to deliver a tire load transfer distribution (TLLTD of + - 5% fwd of the cg location. Now that's a tunable chassis once it comes of the hauler and ought to handle the bimps on the track without kidney failure and not have any tighty- loose driving quirks. Hopefully you will have chosen front AND rear tires that respond to this setup. Otherwise, your limit cornering narration will be best suited to the Comedy Channel (XM 150)

[exFSAE]

Roll stiffness distribution doesn't matter? Or are we talking about the same thing with different terms. Roll moment distribution.. ?

I'm speaking of.. if the chassis has a roll input of 1 degree, the split of weight transfer front to rear. Eg if the front transfers 1000 Lbf / deg vs the rear transfering only 250 Lbf / deg... or Newtons if you're one of those people... and how that relates to the corner weights and load sensitivities of the front and rear tires. I've always thought that is the big thing for SS balance.

In which case.. on a smooth track who cares of that roll stiffnes balance comes from spring or bar. 250 Lbf / deg from a spring setup is the same as 250 Lbf / deg from a roll bar.. assuming there's no bumps. But running slightly stiffer rear springs (or really, higher natural sprung frequency) is good both for ride and for corner exit as you wont lose more grip over bumps putting the power down.

Then there's the whole cornering stiffness balance thing..

But again. Hell if I know anything. Other than its bed time.

[flavorPacket]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by exFSAE:
But running slightly stiffer rear springs (or really, higher natural sprung frequency) is good both for ride and for corner exit as you wont lose more grip over bumps putting the power down. </div></BLOCKQUOTE>

Could you explain this one to me? It seems you know something I do not.

A higher wheel rate will by definition increase normal load variation for a given input. Thus, grip goes down over bumps (assuming everything else stays constant).

Stiffer springs may produce faster weight transfer, which may help generate grip faster. But that has nothing to do with bumps.

[B Hise]

exFSAE is talking about decoupling the tires (a la UWA). A given bump applied to a single wheel with a given ride stiffness and damping will produce the same response. But on the rear for example, when you are exiting a corner, the bar serves to connect the rear tires. If you are putting the wood down on a road course and your outside tire hits the rumble strips, your inside tire dissatisfaction is proportional to the amount of bar you have in the car vs spring.

Does this mean you should have a tiny rear bar and get most of your stiffness from the spring? Not necessarily. If you are on a smooth road, with no bumps and you track tested a car with equivalent roll stiffnesses and varied the contribution of the bars, you would see different results. While tuning for roll, don't ignore pitch.

-Bryan

[flavorPacket]

oh, silly me. I took 'stiffer springs' to mean stiffer springs, not a higher percentage of roll resistance from the springs vs. the ARB. You're both absolutely correct (which is why I don't have a rear ARB).

[cmeissen]

Hey Guys,

I understand that the TLLTD and Roll moment distribution are what really matter. Personally when I designed the KSU formula car I didn't use a rear bar(which Claude is not a fan of) and didn't fall into the guidelines I originally asked about. That is why I asked the question, because I would hope that Optimum G wouldn't include this unless there was some truth to it. So any ideas on this?

[exFSAE]

I would still think its because you want the rear wheels more decoupled.. as a few of us have gone over. Better grip putting the power down out of corners... and probably better ride. The extreme obviously would be no rear bar, as you said, which is 0% of the rear roll stiffness coming from an ARB! There's nothing wrong with that. I think Carroll Smith was actually a big fan of that. That OptimumG spreadsheet is just a guideline for their preferenced way of setting things up.

Keep in mind, what Claude Rouelle says is not necessarily 100% accurate nor applicable 100% of the time.

Same goes for Carroll Smith. Same goes for anyone. It is way too easy to fall into the groove of "Well Carroll Smith says.." or "Claude says.."

Granted, both of them were/are men of considerable experience. But no one knows it all. And I've come to not believe or trust anything with motorsport engineering until I prove it or convince myself of it (which I understand is what you are trying to do).

[B Hise]

What I was getting at is that sometimes you want the car to squat during power down. Other times you don't. Same goes for turn in. Sometimes the driver wants it one way or another. I've made many a change contradictory to theoretical constructs that yielded a better lap time. Can't ignore the nut behind the wheel.

Like exFSAE said, people with experience are able to give rules of thumb and baselines, but they are still only that. A rule of thumb or a baseline. If I were you I would design my car with a rear bar, and maybe start tuning without it.

-Bryan

[mtg]

ARB's don't create instant load transfer. They do nothing until there is a roll angle, hence the name "anti-roll" bar. Geometric load transfer is the only "instant" load transfer.

As far as the percentage guidelines, I think you would be best off choosing normalized stiffnesses in natural frequencies, then back-calculating to a spring stiffness. Once you do that, you'll probably be in the percentage ranges listed.

For example, pick, say, 2 Hz front ride frequency, 1.8 Hz rear, and maybe 1 deg/g roll gradient (yeah, not a natural frequency, but still normalized enough). Once you calculate spring stiffnesses from those numbers, etc.

[John Grego]

For reference: Terry Satchel, one of the lead design judges in Detroit, said that the amount of roll stiffness w.r.t. the total roll stiffness that should come from the ARB's is 50% in the front and 20% in the rear (as a rule of thumb). This allows the rear to generate as much grip as possible on power down.

I have also been told that we should disconnect the bars completely and we will run faster times, since this will maximize your mechanical grip. I know this is true in the wet but not sure in the dry. We are going to try this in testing in the next couple weeks.

Cheers

[cmeissen]

Thanks
I didn't think all the way through the ARB thing, but that all makes since.

[mtg]

John:

Those are VERY conditional statements. What if you make a car that has a 30/70 front/rear weight distribution? Is 50% of the roll resistance still supposed to be in the front? The Satchel reference also assumes rear wheel drive....the safest assumption you made, but still an assumption.

Disconnecting the bars will likely improve your mechanical grip, IF you are on the "downslope" of the tire curve with them connected. What if you are on the "upslope" of the tire curve, or your kinematics produce unfavorable camber for cornering as the suspension compresses? Either of those situations could produce more mechanical grip with the ARB's connected.

How about striking a balance between mechanical grip and transient speed? If your car is faster because it makes more mechanical grip without ARB's, why do most race cars have them? There's something to be said about being able to change directions quickly, even if it costs you a little off of your max lateral g's.

[BillCobb]

But Terry was assuming a front roll center height and a roll axis inclination angle. Can you tell what it was/is?

While the roll is not 'instantaneous', if your roll response is so slow that the car is not keeping up with yawrate and sideslip, your gonna be quite unhappy with its transient response.

Meanwhile, you'd better pay attention to what the front & rear tires have to say about your 'roll stiffness distribution'. Many tires (usually oversized for the job) and some race tires have a negative load sensitivity: The more front bar you put on the car the more 'loose' it can get. A Corvette's front tires come to mind. Their reserve load rating is HUGE.

The roll dynamics are a good part of the transient 'feel' of the car. Sooooo...

Damper force distribution and roll bar bushing size and durometer have BIG influence coefficients on Lane Changing, Sine With Dwell, or Avoidance Maneuver ratings.

You guys ought to write up a simple (but elegant) capture the essense parametric differential equation model of the yaw velocity, roll angle and sideslip degrees of freedom (a bicycle model with load transfer will do), and nonlinear tire characteristics. All the speculation will end. Gotta know the tires, though...

[John Grego]

I agree that they are conditional numbers. Just wanted to throw out an insite from a design judge. They more or less give the idea that the rear ARB should give less of a contribution than the front.

All I know is that I have been told by SAE guys and professional racecar team owners that the lap times will go down if you disconnect the bars. Just wanted to pass along the tid-bit to add to the testing schedule. It's worth a try right?

[cmeissen]

[QUOTE]Originally posted by BillCobb:

While the roll is not 'instantaneous', if your roll response is so slow that the car is not keeping up with yawrate and sideslip, your gonna be quite unhappy with its transient response.[QUOTE]

This is why Claude doesn't like cars without rear ARB's. You can only adjust the balance not the roll response with the ARB.

I agree with this for most cases but in keeping with the true spirit of the competition of FSAE I would say that either way is acceptable, but what do I know.

[exFSAE]

I'd be curious to hear Bill's input on damper force distribution. That is something that has eluded me for a bit and how it impacts handling.. and more importantly why.

[B Hise]

Good stuff here.

Since we have a new round of TTC testing coming up...

Thoughts and/or standards on testing load and slip response and sensitivity?

Damper force distribution -as far as i know- it works alot like spring/bar except when the car is moving (obv). The big difference is that compression and rebound aren't the same. A 4 DOF model for each axle is easy to make and can give some insights.

-Bryan

[exFSAE]

Tire transient response? Yep I'd say that'd be cool to look at.

[BillCobb]

XF:

A tire responds to Fz and Fz_dot, Just like yaw velocity responds to SWA and SWA_dot, etc. SOOoo..

The Damper Force distribution plays into a vehicle's initial turn-in. The "pokes" and "tugs" of a damper activate each tire's transient response characteristics. Just like the bars push on the steady state properties.

Keep in mind that there is a PAIR of tires on the axle. The net axle tire forces and moments are equillibrated by an iterative moment balancing loop that makes use of front and rear slip angle as the independent variables. Your vehicle wander's around to where ever it needs to go to do this. At Very high cornering levels, a tire has very little slip stiffness left, but still has load stiffness. Same is true for camber. That's why a high performance kit always emphasises load and camber. This includes throttle and brake effects: levels and apply rates.

Lastly, the preservation of the tire overturning moment (Mx) is one of the most important details in maintaining max force. If you are at max-lat with a "Happy tire" (no Mx) and you loose this trim because of a bimp, the car "rolls over on its tires" to use a phrase often heard from the 8 (or now 88) car. A good shock package keeps the tires (contact patch) happy. That's what 4 and 7 post testing is all about (although they can't deal a rolling tire).

[flavorPacket]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by cmeissen:
This is why Claude doesn't like cars without rear ARB's. You can only adjust the balance not the roll response with the ARB. </div></BLOCKQUOTE>

so? That's why you have dampers (and tire pressure). I find it much easier to tune a car when one device affects transients and the other affects steady state. Obviously, no device exists that only acts in one regime, but you can get much closer if you minimize the number of components.

Plus, if you have a 60" wheelbase, transient response isn't really a concern anyway. We have no ARB and can get from steering input to max yaw velocity in .03s (in a slalom manuever). When I told Claude this, he didn't seem to mind.

Also, Bill, Terry was most likely assuming a front kinematic RCH of about 1-2" above ground and a mildly nose-down roll axis. This is fairly typical for a FSAE car.

[scott_rfr]

I have seen the argument raised that geometric weight transfer happens instantly. I have been struggling to wrap my head around this concept. How can this weight be instantly transfered to the outside tire?

I am familiar with the geometric and elastic weight transfer as well as calculating it. However I speculate as to whether or not this happens instantly or takes a short amount of time like elastic weight transfer. Could someone please elaborate more on this?

Scott

[flavorPacket]

tires cannot generate force instantly given an input of normal load. Industry standard in simulation is ~1/2-1 1/2 rotations of the tire before the geometric WT creates any additional Fy. How well does this represent reality? That's up to your data acq and tire testing to find out.

[cmeissen]

From my understanding Geometric weight transfer is transferred through the suspension links and chassis, whereas elastic WT goes through the shocks and springs.

If you look at the chassis and suspension links as very stiff springs with little damping compared to the actual spring and dampers. The Geometric weight transfer would happen very quickly(virtually instantaneous) compared to the load going through the shock and spring.

This can be seen in the actual car because as soon as you turn you have some grip (from geometric WT) and it increases as the vehicle rolls(also as the elastic WT transfer happens).

Hope this makes sense

[exFSAE]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BillCobb:
Lastly, the preservation of the tire overturning moment (Mx) is one of the most important details in maintaining max force. If you are at max-lat with a "Happy tire" (no Mx) and you loose this trim because of a bimp, the car "rolls over on its tires" to use a phrase often heard from the 8 (or now 88) car. A good shock package keeps the tires (contact patch) happy. That's what 4 and 7 post testing is all about (although they can't deal a rolling tire). </div></BLOCKQUOTE>

I really wish I had vehicle dynamics or chassis tuning classes when I went to school. Mx is something I've never looked at.

On the other note, I understand that dampers tie into weight of rate transfer and tire response. I'm more curious as to stuff like.. if you were to run really stiff dampers on one axle of the car (or really soft.. or any combination) what that would do to handling (turn in, power-on, lane change, whatever) and why.

For example. Tire lateral force responds to SA and Fz, among other things. Never minding the SA response, an entirely different subject.. assuming you're not talking about Corvette or other oversized tires, axle lateral force capacity decreases with a transfer of Fz. Increasing damping slows the roll of the chassis but increases the rate of load variation. That I'm fairly sure of from having Simulinked it a while ago.

So it would make sense to me then that having soft roll damping would be good so you prolong that weight transfer and loss of grip.. so long as the system isn't really underdamped and oscillating. Damping ratio around .7-1.0 maybe? So the car takes its set in roll quickly.

Or do you want the weight transfer to happen quickly, even if it means the chassis is rolling slowly? I'd have to think that really stiff dampers would prevent the car from taking a set quickly and could make for some crappy (though momentarily exciting) and nonlinear transient behavior.

But I guess the real question would still stand as what you want the damping ratio distribution to be. And furthermore from data acquisition how to determine where you're at.

[flavorPacket]

WT is unavoidable as long as your cg is off the ground and your track is not infinite.

The condition for max grip is determined by minimizing (RMS) tire normal load variation through a corner (assuming everything else is constant). You can prove (and I have) that this occurs when transients are minimized. The load Fz on the tire certainly affects grip, but dFz/dt plays a huge role as well, especially with FSAE tires.

PS I think your statement about increasing damping is incorrect. Look at a simple LTI 2nd order system step response and plot it against varying zeta. Rise time does not vary linearly with zeta.

[exFSAE]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by flavorPacket:
PS I think your statement about increasing damping is incorrect. Look at a simple LTI 2nd order system step response and plot it against varying zeta. Rise time does not vary linearly with zeta. </div></BLOCKQUOTE>

WT is unavoidable. Clearly. But I'm saying by decreasing damping you can slow the WT. Guess the same holds for decreasing spring.

Also. With regard to rise time.. didn't say it varied linearly. But it is proportional, at least what I'm talking about.

I'm not talking about evaluating the "displacement" value of the system. Think about a simple quarter car suspension (2nd order simple jobber). In the whole m*x_ddot + c*x_dot + k*x thing most of the time you're evaluating or looking at "x" which would be equivalent to chassis displacement at that corner for some input force.

What I'm thinking of is looking at force on the tire from the spring and damper, ie c*x_dot + k*x. As you crank up the damping term while holding everything else constant, that force transmitted by the spring and damper rises VERY quickly.

Not sure if that makes sense. I need a beer.

[flavorPacket]

you're right about the response thing. I was thinking about reaching steady state, not rise time.

why would you want to slow WT? By definition, a tire cannot produce more force under a changing load than a steady one. So you are removing potential Fy by lengthening your transients.

Also, how can a chassis roll slowly if elastic WT happens quickly? One is a direct indication of the other, no?

[exFSAE]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by flavorPacket:
you're right about the response thing. I was thinking about reaching steady state, not rise time. </div></BLOCKQUOTE>

Plotting the function = c*x_dot + k*x.. rise time is faster and reaches steady state faster as you crank up the "c" term. The entire physical system displacement reaches equilibrium slowly though.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">why would you want to slow WT? By definition, a tire cannot produce more force under a changing load than a steady one. So you are removing potential Fy by lengthening your transients. </div></BLOCKQUOTE>

Are you sure about this? I have not seen transient tire data that involves increasing slip and Fz simultaneously. I'm not talking about Fy generated by a single tire (in which case you'd be correct). I'm talking about an axle.

If you have 175lb on each tire, at that moment the lateral grip capacity for the axle might be 350lb (assuming peak coefficient of friction of 1.0 on both tires).

When weight transfers and you're at say 300lb on one tire and 50lb on the other.. assuming you dont have crazy Bill Cobb Corvette tires with negative load sensitivity.. your AXLE lateral grip capacity will go down. Say to 300lb. Thus if you can SLOW the weight transfer I'd think you could hold on to that peak force longer. Or that the axle would "bite" into the turn better.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Also, how can a chassis roll slowly if elastic WT happens quickly? One is a direct indication of the other, no? </div></BLOCKQUOTE>

Not necessarily. Again.. I'm talking about transmitted force, not necessarily displacement. As you crank up the damping, the spring contribution slows down, yes. But that damping force kicks in real fast. Steady state.. elastic weight transfer is just a function of the springs. But dynamically its spring and damper, no?

Think about this as a real-life example. Imagine you have a mountain bike shock between your palms. Really soft spring. Turn the damping stiffness all the way down.

If you do a "step input" of say 50lb to squeeze the thing together.. the steady state reaction forces on your palms is 50lb.. but it happens fairly slowly and smoothly.

Now if you crank the bump damping way the hell up and try the same thing.. it'll hurt! Because its so damped it will take a long time for the thing to compress to a steady state value, but that force comes back at your hands QUICK. It feels like a "shock" or "impulse" and rises/steadies really quick.

If that makes any sense..

[BillCobb]

A clue to prevent a dis-astor.
Can provide a response cast in plastor.
You can feel it attack,
if the tire's not smack.
So what is the angle that's fastor?

Burma Shave.

Its more than I cam bear...

[flavorPacket]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by exFSAE:
Thus if you can SLOW the weight transfer I'd think you could hold on to that peak force longer. Or that the axle would "bite" into the turn better. </div></BLOCKQUOTE>

So you have more evenly loaded tires, I buy that. But you have more evenly loaded tires in a transient period. You're not delaying WT, you're just extending it, right? My contention is that it's better to get to ss as quickly as possible.

Also, how do you get the car to yaw? Something has to be stiff to get quick response.

[murpia]

I'm jumping into this one a bit late... But, I feel a comment on roll stiffness & roll bars coming on...

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BillCobb:
Its not the roll stiffness that matters, but the roll moment distribution. </div></BLOCKQUOTE>

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by John Grego:
All I know is that I have been told by SAE guys and professional racecar team owners that the lap times will go down if you disconnect the bars. </div></BLOCKQUOTE>

A key factor that hasn't yet been mentioned in this thread is warp stiffness. This is the stiffness of the suspension when you pick up one corner only, so is a combination of both the side springs and ARBs. If you have 3rd springs on the car then it depends on your motion ratio rising rates if they activate in warp, but generally the effect will be small.

A car soft in warp generally has good grip, because no racetrack is flat (I'm not talking about bumps but camber / crown / banking / kerb effects). The effect of these track issues on tyre load fluctuations is reduced. This is the principle behind the expected performance improvement of the Kinetic suspension on the UWA car.

(Sorry Bill but your caster-car won't be a much faster-car if you go warp-soft...)

This is also the principle behind the suggestion that removing ARBs will increase grip. ARBs hurt the warp mode more than the side springs do. Therefore, if I can get away with it based on all the other factors, I would always run a car without a rear ARB. The front is harder to eliminate, but the softer the better in my opinion.

Another key factor that doesn't seem to be mentioned is tyre load fluctuations with ride and / or roll rates. Generally (and there are plenty of grounds for exceptions) a stiffer car will have greater tyre load fluctuations and hence less grip. The flip side is that these fluctuations can and do influence tyre temperature, so in fact a stiffer car can have more grip after all... It's also part of the reason higher pressures improve tyre warmup.

However, soft ride and roll rates can hurt transient response and can result in less favourable camber angles. Also the driver might not like a 'lazy' car, but the best will always feel the extra grip if it's there and you can work out a good compromise.

Regards, Ian

[BillCobb]

Yeah, warp soft from frame torsion defeats the caster ploy, but these are FSAE cars, not convertable topped MGs. They ought to have some dialable front side-bite.

[exFSAE]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BillCobb:
Yeah, warp soft from frame torsion defeats the caster ploy, but these are FSAE cars, not convertable topped MGs. They ought to have some dialable front side-bite. </div></BLOCKQUOTE>

Except for the tires (well most of them) camber response...

You'd be surprised at the characteristics of these bias tires. Don't know if you have access to the tire data.. but it's pretty interesting.

[flavorPacket]

I second that, exFSAE, especially with the 10" Hoosiers that we run. It's a good thing they weigh 7 lbs, or else they wouldn't be good at anything.

Ian, I have taken that approach with my team: soft springs, no rear ARB, somewhat stiff low-speed damping, aggressive steering (i.e. very fast rack and maximum Ackermann), super-low yaw inertia. We have been very happy with the results after the tires get up to temp.