|
|
|
KEEP M3POST ALIVE BY DOING YOUR TIRERACK SHOPPING FROM THIS BANNER LINK! |
Post Reply |
|
Thread Tools | Search this Thread |
02-03-2009, 11:44 AM | #1 |
Second Lieutenant
29
Rep 216
Posts |
Front/Rear staggered ratio? Exceeding throws off DSC?
A rep at TireRack mentioned that I need to keep the front/rear tire size within a range to maintain proper DSC function. I know that wider rears and narrower fronts can lead to understeer so I am inclined to believe the rep.
His max recommendation for the M3 was: 255/30/20 275/30/20 What are your thoughts? I was hoping to fit a 285 or a 295 on the rear, but that was purely to make the stance look better. I don't want to sacrifice function of the DSC. Thanks! |
02-03-2009, 12:29 PM | #3 |
Captain
74
Rep 610
Posts |
others on this forum are running as wide as 305 in the back and 265 in the front with varying ratios. They have not mentioned any issues
__________________
EDC.....viagra for your car
|
Appreciate
0
|
02-03-2009, 01:10 PM | #4 |
Lieutenant Colonel
123
Rep 1,973
Posts |
Or they aren't aware of the consequences. Which may not come up with a warning light on the dash.
__________________
MDCT ... so you can drive and eat a hamburger at the same time. |
Appreciate
0
|
02-03-2009, 01:29 PM | #6 |
Lieutenant
13
Rep 458
Posts |
Width has nothing to do with it. It's the change in tire height or overall diameter (rim + tire) of the new setup that you have to pay attention to. It's the ratio of overall diameter from front to rear that you need to maintain. VDC will intervene when it sees a change in wheel speed condition, but only after it sees a change above a given threshold, like 5% or something. If the OEM setup has the same overall diamter front to rear, then you should try to maintain an equal diameter no matter what rim size, profile, etc... that you chose. Same thing for an OEM setup that doesn't run equal diameter wheel/tire combos. If its a 10% difference in height, then you should try your best to keep that 10% difference, or you're VDC is going to need to be disabled to drive your car. I want to say the rule of thumb, is don't try to change your ratio (front to back) more than 3% from OEM settings
__________________
WAR Hammy/McLaren F1 WDC 2010
|
Appreciate
0
|
02-03-2009, 02:55 PM | #7 |
Second Lieutenant
29
Rep 216
Posts |
Irb - I don't dispute your comments about diameter.
However, my question is more about whether BMW DSC has some parameters that are tuned to the stock over/understeer propensity. The fact is that putting wider tires on the rear will increase understeer. Tires won't be spinning (thus diameter issue not pertinent), instead you'll just be pushing the car through a corner after the front tires lose grip. Can the car detect this dynamically or is it making assumptions? If it's making assumptions I am worried that changing the OEM staggered ratio will break the assumptions which will be problematic if the car ever needs to rely on DSC. If it's dynamic then there's no issue (aside from the fact that you're dialing in more understeer). |
Appreciate
0
|
02-04-2009, 01:42 AM | #8 |
Lieutenant General
611
Rep 10,407
Posts |
I seriously doubt the DSC system is matched or tuned to the tire sizes. The system works by sensing wheel spin and under or over steer conditions and applies the appropriate combination of brakes to counter the situation. If your new set up caused more over or understeer DSC would still work, it would just kick in more often. The right thing to do is to scale up the front and rear widths in proportion and making small adjustments away from a true proportion to slightly dial in your desired balance. Unless the car will be driven exclusively on the track it is probably best to leave just a bit of understeer. And like stock you will obtain this with a staggered set up, wider in the rear. There is a reason almost all cars have this from the factory - safety!
One other subtlety is that you can actually correct (or move toward a correction) of the OEM speedo which typically runs about 3-4% fast by altering the revs per mile away from an exact match of stock. I'm not sure if there is a 20 size that helps out here but there are 19" combo that help (based on a quick ideal calculation, not the more accurate revs/mile). 295/30-19 or 285/30-19 will both help. These could be paired with a 275/30-19 or 265/30-19. Again perhaps the speedo thing is the last thing on your priority list, but it is a possibility. Last but not least and JMHO. Go with 19s. I'm sure you are set on 20s but they are too heavy and on the side of looks only/poseur. 18s offer the worst looks and best performance (least weight and more importantly lowest interia), 19s are a decent compromise and 20s are on the other end of the spectrum. Last edited by swamp2; 02-04-2009 at 02:01 AM.. |
Appreciate
0
|
02-04-2009, 03:10 AM | #9 |
yodog
197
Rep 5,025
Posts |
I'm going to do 255 front and 285 rear. I actually find the M3 a bit too tail happy, so if I induce a bit more understeer I wouldn't mind
__________________
2009 E92 M3 | Alpine White | Black Extended | Advan RS | Turner Test Pipes | Dinan Axle-Back | OETuning | Eibach Springs | UUC SSK | VRS Front Lip | VRS Type I Diffuser | Matte Black | RPi Scoops | MS Filter | Yokohama AD08 | F1 Pinnacle Special Thanks: Gintani | OETuning | eAs |
Appreciate
0
|
02-04-2009, 03:40 AM | #10 | |
Lieutenant
13
Rep 458
Posts |
Quote:
__________________
WAR Hammy/McLaren F1 WDC 2010
|
|
Appreciate
0
|
02-06-2009, 12:30 PM | #11 |
Private
5
Rep 87
Posts |
For optimal track results, it sounds like 265/35 18 in front and 295/30 18 in back would be best -- as long as it would fit without rubbing. With Pilot Sport Cups, this would give loads of grip vis a vis stock sizes.
|
Appreciate
0
|
02-06-2009, 04:05 PM | #12 |
Critical Care Anesthesiologist
481
Rep 8,828
Posts
Drives: SMB F83
Join Date: Aug 2006
Location: Seattle, WA
|
If you can fit a 305/30R19 in there, the rolling diameter will be almost 100% the same as stock. You can pair a 265/35R19 up front. I also find the M3 to be a little bit too tail happy so a little extra understeer will help.
__________________
kev { divinum est sedate dolorem }
"your friendly neighborhood critical care anesthesiologist" |
Appreciate
0
|
02-06-2009, 04:48 PM | #14 |
yodog
197
Rep 5,025
Posts |
For a street setup I wouldn't go square. If I were to though, I'd do like 9.5 all around with 275's.
__________________
2009 E92 M3 | Alpine White | Black Extended | Advan RS | Turner Test Pipes | Dinan Axle-Back | OETuning | Eibach Springs | UUC SSK | VRS Front Lip | VRS Type I Diffuser | Matte Black | RPi Scoops | MS Filter | Yokohama AD08 | F1 Pinnacle Special Thanks: Gintani | OETuning | eAs |
Appreciate
0
|
Post Reply |
Bookmarks |
|
|