Litchfield BRZ in EVO's Track Car of the Year 2013

[Captain Insano]

Originally Posted by Suberman

I'd be interested to know two things: exactly which tires were fitted to this BRZ and was an opportunity overlooked to dial out some of this car's crazy oversteer tendencies? Oversteer is VERY slow and it seems highly likely that dialling in some more understeer woukd have put this BRZ on par with the Cayman.

I was wondering the same thing about the tires. The single most important modification on a car when you are tracking it. I just skimmed through most of the video, they never mention which tires are used on each car? Assume all had different kinds of tires/specs as opposed to some magazines that standardize track comparisons with the same tire types (thought sizes will always vary by car based on each of their respective optimal tires sizes compared to OEM tires).

Regardless, I enjoyed the parts of the video I watched. I always enjoy comparisons of all types, especially when modifications are thrown in so you can see possibilities of various car types with modifications since I modify all my sports cars.

[Ganthrithor]

Originally Posted by ajc209

Its all about weight distribution. Putting lots of weight over the back wheels is not necessarily a good thing!

My daily driver is a Mercedes Class AMG Sport and its an under steering beast, which only gets worse in the wet. In the snow if I boot it whilst turning in, of course it will power oversteer.... but generall the front end breaks away far sooner than the back and the GT86 does feel very oversteery when compared.

Maybe its a BRZ/GT86 difference? I know they use different spring rates. My BRZ didn't feel oversteery at all when I got it. Of course you could back it into a (slow) corner and make the tail hang out with the throttle, but on bigger corners at speed it always felt understeery to me (which is as it should be from the factory, I guess). I changed the whole suspension around and now it feels neutral to me. I've heard the Scion is more tail-happy from the factory, though, so maybe it's the same with the 86. Do you know if the 86 and Scion are identical twins?

I don't know: I don't find my BRZ as it's currently set up to be any different from most of the other RWD cars I drive frequently, but maybe that's because exactly none of those cars have stock suspensions. The one exception I'd throw in is the 911, which you just drive a bit differently and which generates absurd amounts of grip coming out of corners. That has its own wet-weather concerns, though.

[Suberman]

Originally Posted by Ganthrithor

Maybe its a BRZ/GT86 difference? I know they use different spring rates. My BRZ didn't feel oversteery at all when I got it. Of course you could back it into a (slow) corner and make the tail hang out with the throttle, but on bigger corners at speed it always felt understeery to me (which is as it should be from the factory, I guess). I changed the whole suspension around and now it feels neutral to me. I've heard the Scion is more tail-happy from the factory, though, so maybe it's the same with the 86. Do you know if the 86 and Scion are identical twins?

I don't know: I don't find my BRZ as it's currently set up to be any different from most of the other RWD cars I drive frequently, but maybe that's because exactly none of those cars have stock suspensions. The one exception I'd throw in is the 911, which you just drive a bit differently and which generates absurd amounts of grip coming out of corners. That has its own wet-weather concerns, though.

This car understeers when you don't have your foot on the floor. It is an understeering chassis. That isn't relevant because all rids cars understeer unless you overpower the rear tires. Most road cars don't have enough power to do that INCLUDING the BRZ. But it does. A Cayman doesn't. Even a Cayman S will not power oversteer very easily.

But the BRZ is tail happy and slow as a result. If you turn sharply and floor the throttle in first gear it will not be able to put the power down. If traction control is on it will cut the throttle abruptly, if traction control is off the car gets sideways and wastes power with wheelspin. If the road is wet this is worse. If it is snowy you will be doing a 180 inside the car's own length. THAT'S terminal oversteer and it is SLOW.

Now how this has been achieved is an interesting question because if we can figure it out we can correct it and make the car as quick as it should be but isn't.

It isn't roll bar stiffness. It isn't spring rate. It has to be rear suspension geometry. What's got me curious is why front camber is basically zero and rear camber is one degree negative but it still oversteers under power:

http://www.tunehouse.com.au/archives...-story-begins/

I mean you expect this on a car with lots of engine torque, but the BRZ hasn't got any so why the imbalance front to rear and what happens to the camber or toe at the rear when you step on the gas ?

[ajc209]

The litchfield performance handling pack consists or springs, roll bars and their completely custom alignment settings.

[Suberman]

Originally Posted by ajc209

The litchfield performance handling pack consists or springs, roll bars and their completely custom alignment settings.

Yes, the odd thing is why they didn't try to dial out that troublesome oversteer effect under power, especially when they knew they were adding significantly more power.

Maybe they didn't tune the bump stops accordingly or maybe the rear suspension geometry is just incorrect as I am beginning to suspect.

With this oversteer issue corrected the BRZ with the Litchfieid kit should be more competitive with the Cayman. I think the Cayman S has a bit too much more power for the Litchfield as tuned.

[Suberman]

Originally Posted by ajc209

The litchfield performance handling pack consists or springs, roll bars and their completely custom alignment settings.

Yes, the odd thing is why they didn't try to dial out that troublesome oversteer effect under power, especially when they knew they were adding significantly more power.

Maybe they didn't tune the bump stops accordingly or maybe the rear suspension geometry is just incorrect as I am beginning to suspect.

With this oversteer issue corrected, the BRZ with the Litchfield kit should be more competitive with the Cayman. I think the Cayman S has a bit too much more power for the Litchfield as tuned.

[Ganthrithor]

Originally Posted by Suberman

This car understeers when you don't have your foot on the floor. It is an understeering chassis. That isn't relevant because all rids cars understeer unless you overpower the rear tires. Most road cars don't have enough power to do that INCLUDING the BRZ. But it does. A Cayman doesn't. Even a Cayman S will not power oversteer very easily.

But the BRZ is tail happy and slow as a result. If you turn sharply and floor the throttle in first gear it will not be able to put the power down. If traction control is on it will cut the throttle abruptly, if traction control is off the car gets sideways and wastes power with wheelspin. If the road is wet this is worse. If it is snowy you will be doing a 180 inside the car's own length. THAT'S terminal oversteer and it is SLOW.

Now how this has been achieved is an interesting question because if we can figure it out we can correct it and make the car as quick as it should be but isn't.

It isn't roll bar stiffness. It isn't spring rate. It has to be rear suspension geometry. What's got me curious is why front camber is basically zero and rear camber is one degree negative but it still oversteers under power:

http://www.tunehouse.com.au/archives...-story-begins/

I mean you expect this on a car with lots of engine torque, but the BRZ hasn't got any so why the imbalance front to rear and what happens to the camber or toe at the rear when you step on the gas ?

I'm pretty confused by your post: first you say the BRZ is a chronic on-limit understeerer (which was my impression of the stock suspension) but then you also say that it loves to oversteer under power? Don't almost all RWD cars like to oversteer if you mash the gas while things are loaded up or floor it in first gear when you've got tons of torque available at the wheels? If I dump the clutch I can also get wheelspin in first gear while not turning at all-- this doesn't say much about suspension setup. I can get the rear end of a 911 unstuck at road speeds using the throttle, and that's got a ~40:60 front/rear weight distribution, a mere 280hp, and giant supersports on the back end-- you're not going to get a much better recipe for not-oversteer than that... the question is what does it do on a long sweeper as you progressively ramp your cornering speeds up while driving smoothly?

I'm sure they set the front to zero camber with more camber at the back so that people would hopefully get into less trouble with the cars, since they knew they were catering to a certain demographic. It's obviously a tunable behavior because my car with new sways, springs and dampers behaves nothing like the car did on the stock suspension. I really don't think the behavior you're describing is something inherent to the chassis, except insofar as it's a RWD car and RWD cars can hang the tail out if you drive like a magazine reviewer.

[Suberman]

All road cars understeer. The BRZ oversteers much too readily when you apply full power in low gears. That is slow and represents a defect in the chassis from the perspective of a serious driver. I am sure this is a deliberate design feature.

A car with only 150 lb ft of peak torque should not power oversteer.

This is the reason the BRZ performs poorly when driven hard on a track.

If you have cured this oversteer by adding roll bars and coilovers then this power oversteer is caused by roll rates being too high at the rear.

I doubt this is the case. I doubt you have cured this defect.

With better tires I expect the oversteer to be diminished or perhaps disappear due to tire grip overcoming the oversteer. I intend to try this first. That doesn't solve the ridiculous instability on ice, snow or very wet roads though.

That's as clear as I can make this. I am not alone in identifying this chassis fault. So far I've seen nobody has found a solution. If this car is to work with forced induction then something will need to be done, again only gift serious drivers.

How our novice drivers are managing this car is an interesting question. An MX5 is easier to drive and, I suspect, quicker round a track.

[the.big.kahoona]

Would be nice to have a suspension guru chime in on what Suberman is saying

Sent from my SM-N9005 using Tapatalk

[DarkSunrise]

I'm not a suspension guru, but I've driven this car a number of times at the track. It's subjective in some ways how you want a chassis setup (some people prefer more oversteer, some more understeer), but for the general population, I'd say his statements are not true.

My guess is that Suberman prefers heavily understeering RWD cars that you can just plant your foot with coming out of turns. Something like an open-differential Genesis Coupe with TC on. Or better yet, an AWD car. The type of chassis balance he's describing is more inline with my old STI at the track. Nothing wrong with that btw just preference, but I think most enthusiasts like cars that are more balanced.

- Saying a car with 150 lbs-ft torque shouldn't power oversteer is a bit narrow-sighted, as it's necessary to also consider gearing and RPMs. 150 lbs-ft at a high enough RPM and with the right gearing can result in a fair amount of torque to the ground. That's what really matters, not arbitrary peak torque output of the engine.

- From my experience, the FR-S actually handles very well when pushed hard at the track. In fact, the harder you push it, the more you realize how good the chassis is. The stock balance of the FR-S leans towards slight understeer, but you can easily balance the car with the throttle if you're experienced with RWD cars (which is exactly what you want IMO).

- When the rear end comes around under power with this car, it is very easy to catch. It's one of the easiest RWD cars I've driven in this regard, and it will make you look better than you really are at the track.

- I don't know why Suberman wants a RWD car that won't break traction "when you apply full power in low gears" and turn the wheel. Nearly every RWD car will do this if there's no stability control or TC interfering.

- An MX5 is definitely not quicker around a track (there are lots of tests out there on this). It may be easier to drive, but from my experience, it really depends which year and what options you're referring to (LSD option, sport suspension?)

One of the best videos on this topic is of Randy Pobst driving the BRZ around Laguna Seca in MT's Best Driver's Car competition. Try watching that - he goes on and on about the beautiful balance and precision of the BRZ when pushed hard.