Rear end felt snappy at VIR

[Ebinkerd]

I was on track at VIR a few weeks ago and overall my 15 m4 preformed beautifully. But through turns 4a-5b the rear felt snappy. I'm still learning the car so I admit it could be my technique, but has anyone felt this during a low speed?.

To be specific, entry into 4a felt good, maintenance throttle in to 4b, and as soon as the car pitches to the right at the entry to 5a is where I felt the rear kinda jerk.

The climbing esses felt perfect, nice and planted, probably 105-107mph to the crest, even in to 10 for the downhill left hander at 87ish, pushing throttle into the apex and carrying the car to the right, everything felt perfect. I just can't make sense of the low speed issue.

Any insight would be welcome.

2015 M4, stock everything, MDM mode, sequential mode, 95k miles, stock alignment with increased negative camber on the rear.

My gut is telling me the differential is the issue.

[SYT_Shadow]

It could be your throttle mode deploying too much torque abruptly. Try Sport or Efficient instead of Sport+

If the diff were dead you would hear the revs rise without the corresponding acceleration, but it would not 'snap' anywhere.

At high speeds the car doesn't have enough power to really alter its course, but it does have decent torque, so in low speeds it can become a drift fest.


Also, if you're running with MDM, you may want to stop. These cars are noble and communicate their intentions well.

[G35POPPEDMYCHERRY]

Originally Posted by SYT_Shadow

It could be your throttle mode deploying too much torque abruptly. Try Sport or Efficient instead of Sport+

If the diff were dead you would hear the revs rise without the corresponding acceleration, but it would not 'snap' anywhere.

At high speeds the car doesn't have enough power to really alter its course, but it does have decent torque, so in low speeds it can become a drift fest.


Also, if you're running with MDM, you may want to stop. These cars are noble and communicate their intentions well.

wraps car around tree

[jfritz27]

Originally Posted by SYT_Shadow

It could be your throttle mode deploying too much torque abruptly. Try Sport or Efficient instead of Sport+
.

... and I believe the ECU mapping of early F8x models were prone to this

This behavior is occurring as you're adding throttle? Given you're on stock suspension, if this is happening during faster transitions then it also may just be the stock suspension/softness revealing its shortcomings, combined with the above issue.

Also, I've never been to VIR (but run it in iRacing a lot), is that particular turn off-camber at all?

[///Mangler]

How much have you driven VIR? They call 5a/5b the 'snake' for a reason. It WILL bite you. There is a dip at the apex of 5a that gives the front end of the car extra grip, along with the breathing of the throttle going in, when coming out and through 5b, eyes up and looking at the bridge straight, people get hard on the throttle here before the car is straight. Snap oversteer, curb, correction, wall. You can literally see the black marks on the track here from how many people do it.

T

[Theruleslawyer]

Originally Posted by G35POPPEDMYCHERRY

wraps car around tree

Sadly that is gone.

[Ebinkerd]

Originally Posted by SYT_Shadow

It could be your throttle mode deploying too much torque abruptly. Try Sport or Efficient instead of Sport+

If the diff were dead you would hear the revs rise without the corresponding acceleration, but it would not 'snap' anywhere.

At high speeds the car doesn't have enough power to really alter its course, but it does have decent torque, so in low speeds it can become a drift fest.


Also, if you're running with MDM, you may want to stop. These cars are noble and communicate their intentions well.

I was in sport+ and MDM. Are you saying to turn off the nannies altogether? The car did Wonderful at Summit Point with all the nannies on.

[Ebinkerd]

Originally Posted by ///Mangler

How much have you driven VIR? They call 5a/5b the 'snake' for a reason. It WILL bite you. There is a dip at the apex of 5a that gives the front end of the car extra grip, along with the breathing of the throttle going in, when coming out and through 5b, eyes up and looking at the bridge straight, people get hard on the throttle here before the car is straight. Snap oversteer, curb, correction, wall. You can literally see the black marks on the track here from how many people do it.

T

This was my 7th time at VIR, but the first in the M4. I'm coming from a 19 WRX and never had this issue. But what you are saying is exactly what I felt. I'll remain aware of this next time out.

[Ebinkerd]

Originally Posted by jfritz27

... and I believe the ECU mapping of early F8x models were prone to this

This behavior is occurring as you're adding throttle? Given you're on stock suspension, if this is happening during faster transitions then it also may just be the stock suspension/softness revealing its shortcomings, combined with the above issue.

Also, I've never been to VIR (but run it in iRacing a lot), is that particular turn off-camber at all?

I guess a bit. The road feels like it kinda sways a bit at this point. Take a look at the guy who posted the pic of 5a-5b. This is a really good explanation of what I think happened.

[///Mangler]

Originally Posted by Ebinkerd

This was my 7th time at VIR, but the first in the M4. I'm coming from a 19 WRX and never had this issue. But what you are saying is exactly what I felt. I'll remain aware of this next time out.

All wheel drive. Completely changes how this area of the track will make that car behave.

RWD with massive torque is what bites people here. I have an E30 M3 track car with a VERY built S14, and I can get full throttle very early here since there is no real torque. I had to be a little more patient, and wait for the car to straighten up, before getting on power in an E90 M3. I would expect to have to wait even a longer in an S55 car.

The other thing you can do here, is if you have a high end suspension (that can soak up curbs) is use them to straighten out 5b a little more.

T

[Ebinkerd]

///Mangler

This is exactly what I'm dealing with. While the WRX was fun. It was too forgiving. I'm not trying to go crazy with suspension on this car, I do have a E46 I am building to "spec E46". The goal is to learn the dynamics across the power/weight ratio. So when I step down to the E46, I want to have a better understanding of car behavior. Though with the M4 I am going to do a street/track suspension build, it won't be my primary track car.

Thanks for the feedback, I should have known there was more to this section than meets the eye considering the class instructions are focusing more on this section of track than any other. I know 4a-4b can be tricky if your inpatient, and it's a hit or miss type corner. But being solo, I don't have the in car instructions to help me understand the issues with 5a-5b. Looks like a check ride at VIR would benefit me before taking the DE3 test.

[///Mangler]

Originally Posted by Ebinkerd

///Mangler

This is exactly what I'm dealing with. While the WRX was fun. It was too forgiving. I'm not trying to go crazy with suspension on this car, I do have a E46 I am building to "spec E46". The goal is to learn the dynamics across the power/weight ratio. So when I step down to the E46, I want to have a better understanding of car behavior. Though with the M4 I am going to do a street/track suspension build, it won't be my primary track car.

Thanks for the feedback, I should have known there was more to this section than meets the eye considering the class instructions are focusing more on this section of track than any other. I know 4a-4b can be tricky if your inpatient, and it's a hit or miss type corner. But being solo, I don't have the in car instructions to help me understand the issues with 5a-5b. Looks like a check ride at VIR would benefit me before taking the DE3 test.

Track walk. When the track goes cold at the end of your next day there, ask if you can do a track walk. Grab two beers and a few friends, have a stroll. The amount of stuff you will see, and discussions on what they do, just walking the track will blow you away.

T

[cbsoucie44]

Ebinkerd I am coming from 17 wrx to 1 full year in my 16 m4 6mt base so i think we are going through a lot of the same.

I used to use sport plus for everything now I run just sport . More linear throttle control imo. that turn is super twitchy and I have spun it during the beginning of a session on an out lap in damp conditions. very scary!

After my first HPDE at VIR i changed to turner camber plates up front, huge boost in cornering performance and feel. I do not have anything done in the rear.

In this video i was sliding it on purpose for the first bit but you can see its very easy to get loose there and obviously not great for lap times. I'm picking up a lot of tips and lines from my buddy in his M2, he has more track time then i do.

hes got a good bit of video of us driving if you look at his youtube page

hope to see you out there!

[Ebinkerd]

cbsoucie44

This pretty much solidifies it for me. The car is doing exactly what it want to. In other words, I'm the noob. I'm ok with that. These cars have so much power and so much fun to drive. I'm looking into various suspension components now. I really want to avoid dropping a few grand on coilovers right now. But the suspension does leave a lot to the imagination.

His vids make me want to get and m2. It looks so nimble.

If you ever see my name on the drivers list, shoot me a PM. The subie got a lot of love at the track, bmw not so much.

[cbsoucie44]

I think the m4 is a more capable car (slightly wider, longer, and lighter). He's definitely a better driver.

What tires do you use?

I find myself feeling my rear will lift up in the esses (T8a 115-120mph, and under any heavy braking (back straight at 150 mph)

trying to save for coilovers/beat the heck out of my stock suspension in the meantime!

Same, got a lot of praise for lapping the subie, now i get a lot of (middle) fingers for making people point me by!

[Ebinkerd]

So I reviewed my in car cam and ///Mangler was absolutely correct in what happened. I am not pushing the car hard as I am still building my confidence in it. But you can see that I was late into the apex at 5a, throttled up and moved left. The video doesnt show my heart jumping through my chest. But in the end, I learned my lesson, the car is safe, and I know what I need to work towards. Thanks all. Heres the clip, roast me if you must.

[///Mangler]

Originally Posted by Ebinkerd

So I reviewed my in car cam and ///Mangler was absolutely correct in what happened. I am not pushing the car hard as I am still building my confidence in it. But you can see that I was late into the apex at 5a, throttled up and moved left. The video doesnt show my heart jumping through my chest. But in the end, I learned my lesson, the car is safe, and I know what I need to work towards. Thanks all. Heres the clip, roast me if you must.

This is how it happens in a zero torque car ��

T