F82 M4 light weight measurement and Road Atlanta review observations

[JoeFromPA]

Do you guys know the stock toe settings?

To me, this car feels like toe is zero'd out.

[Black Gold]

Originally Posted by karussell

The alignment is untouched so far. We are getting in the KW height adjustable coil system for adaptive shocks and will corner balance along with adjust toe settings. I think we will just stick to factory settings on toe for now. one variable at a time if at all possible.

im curious, why the KW spring kit?

my concern and experience with spring only kits used on OEM dampers is

-they are specificially designed for a certain amount of travel
-this travel is minimized when installing a lower spring
-the shock is precompressed / loaded at static height due to the lower spring
-the shock will bottom out / run out of compression much more often due to less available travel
-the entire time the shock is working outside of its designed operating range due to excess compression due to lower ride height
-the spring rates are usually not disclosed and likely not appropriately matched for the dampers or factory alignment

So, the end result being worse handling over surfaces which are not perfectly smooth. Any CG benefits are vastly overshadowed by the other issues.

What's your perspective on this?

[rsr racer]

thank you, karussell for the informative review.

RA is a great place to explore this car and I hope to get mine down there to try out the settings combinations you've illustrated and to give you some feedback as well.


awesome job

[rsr racer]

Originally Posted by karussell

one variable at a time if at all possible.

exactly.

do you think the adjustable springs will interfere with the geometry feedback of the adaptive system?

what parameters will you look at first to change wrt them?

[karussell]

Originally Posted by KennyPowers

im curious, why the KW spring kit?

my concern and experience with spring only kits used on OEM dampers is

-they are specificially designed for a certain amount of travel
-this travel is minimized when installing a lower spring
-the shock is precompressed / loaded at static height due to the lower spring
-the shock will bottom out / run out of compression much more often due to less available travel
-the entire time the shock is working outside of its designed operating range due to excess compression due to lower ride height
-the spring rates are usually not disclosed and likely not appropriately matched for the dampers or factory alignment

So, the end result being worse handling over surfaces which are not perfectly smooth. Any CG benefits are vastly overshadowed by the other issues.

What's your perspective on this?

In any other case you are correct however this system was designed and tested specifically with the adaptive dampers on this car and i'm not talking about having a hot shoe drive it a few laps and call it a day.

http://www.kwsuspensions.com/kw/info...ic_7_post_rig/

This spring kit was good enough for BMW to use on its DTM safety cars.

Still as you are skeptical I am as well. As my father would say I'm from Missouri The show me state. you gotta show me. So i'm going to test it out on my own car. i have baseline laps at road atlanta, my home track. i will measure how this compares and along with how it feels on road and the track. If its shit I have no problem calling it out. Its not hard to swap out. I would like a little less fender gap so I'm hoping this does work out. I'm not cool enough to pull off the slammed look. just a slight drop and equal or increased response on the smooth fast sections of a course. naturally the shocks will have to work a little more but as an engineer its fun.

[rsr racer]

Originally Posted by karussell

currently I have no inclination that it needs more camber. the tires seem to be fully engaged..

did you happen to get any pyrometry readings wrt to this and how was the wear pattern with the stock setting and tires?

[karussell]

Originally Posted by rsr racer

exactly.

do you think the adjustable springs will interfere with the geometry feedback of the adaptive system?

what parameters will you look at first to change wrt them?

good questions. first of all the purpose of this car is to remain a street car that can handle track. I want it to do both as well as possible without compromising each other. In the case of these springs I want the car lowered as is common for aesthetics. Also I think the slightly higher progressive spring rates will improve corner speed in fast smooth sections of a road course.

so given the purspose, I intend to lower it just slightly and then corner balance the car optimized for my weight along with a passenger which is the standard configuration I normally expect to drive this car in.

I will take camber, caster, and toe settings before the change and reapply after the installation trying to keep as close as possible to the baseline so only the new part is affecting the outcome.

for measurement on track I use racekeeper datalogging system.

[karussell]

Originally Posted by FTS

Such a positive review, quite encouraging, fun to read, thank you Karussell.

At the same time you are confusing the hell out of me I just don't know the platform at all, no question, and I am having difficulty even conceptualizing few things, particularly tire/wheel sizes, spacers and the overall balance of the car.

I have the impression that the M4 is quite lively at the back from the factory due to it being slightly noise heavy, the multi-link suspension, torque, direct bolt of the subframe to chassis probably being the major reasons for it. And I also have the impression that the factory did not put a wide enough wheel and rubber in the back comparatively to the fronts, which contributes significantly to its loose nature.

If all this is in fact correct, I have few questions and am asking for guidance from all that are willing to enlighten an ///M newbie:

• Would a square wheel/tire setup make things worse with stock springs and A/R bars?
• Wouldn't putting wider spacers in the front comparative to the rears effectively reduce wheel rate more in the front and imbalance the rear further?
• I believe that wheel width is more important that tire width; if one uses 275/295 combination with same wheel widths or same width increase (let's say 1" front and rear) do you think it would actually help balancing against the oversteery tendencies? Wouldn't a 265/305 (or even 325) tires on 9.5"f and 11"r setup arguably yield a more neutral setup?

TIA

I believe this car does not require a square setup at least on a track. It already is quite neutral. Going up to a 275 in front to make it square will probably make it want to oversteer quite a bit more. maybe and i think its really slight chance a square setup would be faster on a tight autocross circuit particularly if the pavement is very slippery (ie gravel/sand on a parking lot) YMMV greatly

I don't think so. i put 12.5 front and 10 rear. i doubt i would notice any difference by going without spacers at all or just spacers up front. would be fun to try sometime.

going to a wider tire implies having a wide enough wheel to support it. I don't like over stuffing a narrow wheel with a fatter tire. mpss work well because they have kevlar sidewalls. they are meant to stay as vertical as possible. your sizes like 305 probably too wide for it to clear the suspension in the rear but who knows. might be possible. i intend to go up incrementally. 295's are more common and cheaper than 305's in general. also don't want to have too much tire and can't heat them up properly.

sounds like you have some ideas of your own. would be great to hear your feedback if try it out. just get a baseline first.

[Lups]

Originally Posted by karussell

haha, well that is a boxster and this car has nearly 100ft lbs of torque over a 3.8RS with 325's. I am pretty sure i can slide around in a perfect figure 8 with 275/295's if someone is willing to loan me a set.

tire wear appears pretty good so far on the rears. fronts still look new. I will measure tread depth maybe tonight when we are working on the car some more.

MDM does not allow for much tail wagging. I find its intervention actually more of a hindrance than an aide. I think really of it as a comfort blanket. Its a useful tool for someone learning the car considering the power this motor has but I think its still completely safe to learn to drive in this car with DSC off and gradually build up along with going to plenty of autocross events to work on maximum car control.

I volunteer! I even throw in the bottle of whiskey for the after the numbers are down on a pavement.

Peter could use someone behind the wheel who is not a complete pussy all the time.

[karussell]

ok L - bring some tires. i got the wheels. afterwards whiskey bar. you know the place

[Lups]

Originally Posted by karussell

ok L - bring some tires. i got the wheels. afterwards whiskey bar. you know the place

We have to do that one day.

Thanks for the review again Karussell, I enjoy your way of explaining things to us, and as for it not being a professional review done by a journalist: personally I prefer those who don't have a sponsor to bend over for. Probably only Clarkson can say what he wants, but only because he is a comedian more than a journalist these days.

Anyway, get those pictures smaller, and we will plan our epic meet number three soon enough, actually winter is coming, we could take Peter to Canada! This would finally get me over protecting his ass on the normal roads and I could enjoy driving again!

[Needsdecaf]

Originally Posted by karussell

I prefer a manual transmission. Originally we were going to prepare and enter this car in this years 24 Hour race at the Nurburgring. The team director and I decided on only two options at the time. DCT and Adaptive Shocks.

DCT simply because there is no possibility of a mis-shift when you are tired and racing at 3am. We have lost a few engines this way over the last few years.

does it shift faster? no doubt. does it improve a lap time? I don't think so as long as the driver doesn't make a mistake. Given humans make mistakes and especially when fatigued the choice of DCT was for improving the odds of finishing the race rather than performance improvement.

purpose built race cars such as the 911 Cup and M3 GT4 don't use DCT's either because they are heavy and complex. instead a race car will have a sequential single clutch transmission that needs to be completely rebuilt on a regular basis.

personally I find DCT in this car way too smooth. Its too much like an automatic and I like the manuals gearing. It makes the car feel like it accelerates faster. Plus with the power band from the motor you can simply choose a higher gear and shift less altogether improving your lap time. I do not think DCT alone will improve a lap time.

I am probably a little crazy to most though as I preferred a manual E30 with steel subframe bushings and 800lb springs for my daily commute in Orange County/LA traffic. I'm sure normal folks are happy to have an automatic when stuck on the 405.

Awesome answer, thanks! I, too, when driving the DCT felt like it made the car "too fast". Like just runaway acceleration. I know, silly thing to complain about but if you're racing, you want to feel in control of the car, not that the car is controlling you.

Totally understand about the reliability issues in a 24 hour race. Note that the M235i race cars use an AUTO instead of a DCT....

[Needsdecaf]

Originally Posted by karussell

I believe this car does not require a square setup at least on a track. It already is quite neutral. Going up to a 275 in front to make it square will probably make it want to oversteer quite a bit more. maybe and i think its really slight chance a square setup would be faster on a tight autocross circuit particularly if the pavement is very slippery (ie gravel/sand on a parking lot) YMMV greatly

I don't think so. i put 12.5 front and 10 rear. i doubt i would notice any difference by going without spacers at all or just spacers up front. would be fun to try sometime.

going to a wider tire implies having a wide enough wheel to support it. I don't like over stuffing a narrow wheel with a fatter tire. mpss work well because they have kevlar sidewalls. they are meant to stay as vertical as possible. your sizes like 305 probably too wide for it to clear the suspension in the rear but who knows. might be possible. i intend to go up incrementally. 295's are more common and cheaper than 305's in general. also don't want to have too much tire and can't heat them up properly.

sounds like you have some ideas of your own. would be great to hear your feedback if try it out. just get a baseline first.

Your thoughts on tire sizes are intriguing. I think that BMW, having been lambasted in the press for dull and boring F series chassis, deliberately set up this cars's suspension geometry and tire sizes for "hooligan mode". There appears to be no hint of understeer in the stock setup, and they appear to have made good on their "not set up for amateurs" comment early on. If I recall, your earlier review and others speaks of a tricky transition to oversteer, rather than a gradual one.

That rear end looseness would of course be at the expense of outright lap times, but be a boon to fun journos and DTM drivers showing off at pressers.

I have long said that this car was going to be as competent as hell. I think I am being proven right several times over.

[kitesurfer]

Originally Posted by karussell

Let me put it this way, If your drive involves a road then I recommend the adaptives. On track they perform better especially when having to deal with rapid bump rebound like jumping on and off a berm. On the street you can run it in sport or sport plus even if its fairly rough and it will adapt to the conditions maximizing contact patch while still soaking up bumps.

I can't tell you where the passive's fixed damping falls relative to the adaptives as the adaptives are always adjusting. i will tell you that before the entry to the esses at Road Atlanta on turn 3 is a fast right hander you can absolutely nail right over the berm and continue accelerating through turn 4 and the esses. By the end i need 2 braking zones just to bleed off the speed for turn 5. The passive shocks can't handle that berm and you have to ease off the throttle. In this case the adaptives have made that entire complex of turns into a straight with possibly a full second lead over the same car with passive shocks. Alternatively if you were to run adjustable coilovers with a high rate of rebound and damping for such a fast course and with an aggressive sway bar setting you also can't use full throttle over the berm. I catch several cars from this corner alone. In this case and its common on many tracks the adaptives are simply superior.

I'll bet dollars to donuts that if the OP had those 20" wheels/tires on adaptive car it would negatively effect the handling/damping and would yield different results. The Tire acts as a damper on the track and will effect how the car reacts to curbing. Its likely that those 20" wheels had a 25 or 30 aspect ratio tire.

Lets assume a 30 ratio on a 275 tire that is 82.5mm of side wall. Compare that with a 40 aspect ratio of the 18" 275's on the OP" adaptive car yields 110mm of side wall. That equates to 33% more side wall thickness to act as damper. In addition this does not take into account the differing compounds/sidewall stiffness of the two tires

Even though OP has claimed to drive both setups on 3 tracks, His on track performance assessment between the Passive & Adaptive has only been based on his recent trip to Road Atlanta in which he had Apples to Oranges set up cars for the comparison:

For the record OP stated in another thread we debated two weeks ago:

"I drove an M4 with both passive and adaptive suspensions on the track. subjectively i really couldn't tell which suspension was faster as I wasn't there for that purpose. the car is fun to drive either way. where i notice real world the adaptive suspension really working is on highways and rough patches of road in and around the city at all different speeds. even on sport+ it does not feel overly damped. particularly in inclement weather the car feels very planted as well."

http://f80.bimmerpost.com/forums/sho....php?t=1035302

[karussell]

I love donuts, but the kind involving burning up tires. This is actually one thing i would want to try but actually more because i was so impressed with the tires performance. Edit: previously thought they were V12. they are actually S1 Evo. They managed to stay just as glued as the mpss's and 20's look great on the M3. On a side note he just got a set of oem 18's but tirerack doesn't have the rears in stock for mpss. If we have them i'm sure you would argue the m3 is different from an m4 or orange is slower than blue or quote dr. biermann again. no point arguing. done with you.

Originally Posted by kitesurfer

I'll bet dollars to donuts that if the OP had those 20" wheels/tires on adaptive car it would negatively effect the handling/damping and would yield different results.

[karussell]

the ///Maniac Engineers must have been keeping tabs on us while planning the F8X. it appears they built us an epic car.

Its not snap oversteery like a good 'ol 911 but she rotates and you need quick hands. god if the M4 is this good and they do the same treatment on an M2 it is going to be a hilarious!

Originally Posted by Needsdecaf

Your thoughts on tire sizes are intriguing. I think that BMW, having been lambasted in the press for dull and boring F series chassis, deliberately set up this cars's suspension geometry and tire sizes for "hooligan mode". There appears to be no hint of understeer in the stock setup, and they appear to have made good on their "not set up for amateurs" comment early on. If I recall, your earlier review and others speaks of a tricky transition to oversteer, rather than a gradual one.

That rear end looseness would of course be at the expense of outright lap times, but be a boon to fun journos and DTM drivers showing off at pressers.

I have long said that this car was going to be as competent as hell. I think I am being proven right several times over.

[rmedeir1]

So I have been unimpressed with the lack of "rubber" this car comes to the game with. I've got the 19" wheels 255/275 OEM setup. Can these same wheels accomodate a 275/295 setup? Assuming spacers are a must. Or do I need to buy bigger wheels?

[karussell]

Originally Posted by rmedeir1

So I have been unimpressed with the lack of "rubber" this car comes to the game with. I've got the 19" wheels 255/275 OEM setup. Can these same wheels accomodate a 275/295 setup? Assuming spacers are a must. Or do I need to buy bigger wheels?

I'm sure a tire expert can comment on this but i think a 275 on a 9 inch wide wheel is little much. same goes for a 295 on a 10 inch.

i think optimally would go for a 9.5 or 10 up front and a 10.5 or 11 in back. offset will be critical too in order to clear the rear suspension.

[Black Gold]

Originally Posted by karussell

I'm sure a tire expert can comment on this but i think a 275 on a 9 inch wide wheel is little much. same goes for a 295 on a 10 inch.

i think optimally would go for a 9.5 or 10 up front and a 10.5 or 11 in back. offset will be critical too in order to clear the rear suspension.

yes that's accurate

its not enough sidewall support, and will handle much looser and have worse steering feel than stock

I also believe 275/295 30 to be an excellent replacement size, but this requires at least a 9.5/10.5 wheel width, if not 10/11 inch.

[kitesurfer]

Originally Posted by karussell

If we have them i'm sure you would argue the m3 is different from an m4 or orange is slower than blue or quote dr. biermann again. no point arguing. done with you.

Duh... everyone knows the M4 and Orange color cars are WAY faster than the M3 and blue colored cars

[kitw]

Originally Posted by KennyPowers

yes that's accurate

its not enough sidewall support, and will handle much looser and have worse steering feel than stock

I also believe 275/295 30 to be an excellent replacement size, but this requires at least a 9.5/10.5 wheel width, if not 10/11 inch.

Yeah, the problem is that just about no one makes wheels in the right offset in 18" right now.

I want an 18x10 / 18x11. 275/35r18 shouldn't be a problem, on an 18x10et25 or so, which everyone makes. 295/35r18 is much harder - probably requires an 18x11 et 35 to fit or so.

[Black Gold]

Originally Posted by kitw

Yeah, the problem is that just about no one makes wheels in the right offset in 18" right now.

I want an 18x10 / 18x11. 275/35r18 shouldn't be a problem, on an 18x10et25 or so, which everyone makes. 295/35r18 is much harder - probably requires an 18x11 et 35 to fit or so.

I ping'd apex on this in another thread

they need to make ec7 in proper 18 and 19 fitments

I suggested 9.5/10.5 widths at minimum in

front et24
rear et32

offsets. should allow for a 275/295 tire setup. id run that.

IDK, that 10et25 is aggressive for the front. not sure how much strut or brake clearance you would have. ok for track tires, but no good for street tires IMO