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In BMWCCA autox I run 265/35 18 BFG KD at all four corners on my E46 M3.  However, I use stock M3 rear wheels (1" wider and not SCCA stock legal) on the fronts and -2 degrees negative camber on the front or slightly more than you can legally get within SCCA stock rules.  Net, understeer is not a significant factor.  In fact, the rear tires get much more abuse.

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White

Here's my situation.  I picked up a set of used BBS RK wheels 17x8 with Kumho Ecsta MX tires.  Two of the tires are size 225/45R17 and two of the tires are 245/40R17.  One of the 245/40R17 tires is bad.  So, I have to decide between buying one 245/40R17 ($129+shpg) or two 225/45R17 ($226+shpg). 

If I was starting fresh, I'd get the same size all around.  Since I already have these, though, I'd like to just buy one but I'm afraid the staggered setup will make the inherent understeer worse.  I know some FWD cars run wider tires up front for autox but wasn't sure whether anyone did it or whether it was helpful on a RWD car. 

And by the way, car is a 2002 325i that will be run in BMW CCA autox and SCCA STX class, as well as track days. 

 Any recommendations?

I would say give it a shot, I think your logic is solid enough, and it's the cheaper option.

 The only problem I see is that while you will get it better balanced towards oversteering, you will be doing so by reducing traction on the rear, rather than increasing traction on the front. It will probably be easier to drive, but not as fast as 245's all around. Definitely faster than 225's all around.

 I'm not sure if there's a tire width limit in STX, but I met a gentleman this weekend who was running 275's all around on his 325 with 17x8 wheels, and he seemed to be getting about all he could from that car! (earned him 5th in DS at Milwaukee Nat Tour) With street tires, you may have more size options than with the stickies we run in DS, but if you're limited to 245 all around, that may be the best option, even with the understeer. (which is also probably a good thing for track days, though not as much for autox) Otherwise, try 245 in the rear and 265 or 275 up front and see what happens! They're just tires, you'll be buying new ones soon enough anyway. =]

 
Matt
 

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DS #313 | the rolling couch of doom | La-Z-Boy Racing

gar7777:

Anyone ever run wider tires in FRONT?  like 245/40 in front with 225/45 in rear? 

I wanted to try that but never made it to any non-points events to test it.

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Matt Murray

I am perfectly capable of learning from my mistakes. I will surely learn a great deal today.

mattm:

I wanted to try that but never made to any non-points events to test it.

Want to co-drive my car and test this setup at an upcoming BMW event at Nassau?  We could try normal and reverse stagger and take some data with the Traqmate.

gar7777:

Want to co-drive my car and test this setup at an upcoming BMW event at Nassau?  We could try normal and reverse stagger and take some data with the Traqmate.

The 14th is not good for me. Perhaps the 28th. Email me privately. mattm at optonline

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Matt Murray

I am perfectly capable of learning from my mistakes. I will surely learn a great deal today.

Whats the least amount of negative camber people are running in the rear on their BMW?  Stock spec is -2 degrees but wouldn't less camber in the rear help reduce the inferent understeer?  I am thinking about trying -1 degree in the rear--to match the front.  Is this a bad idea?

Yes, it's common to back off with a bit less camber and toe-in in the rear.

Does anyone have an opinion about how much toe out up front is best?  Is the more the better?

Running about a 1/2 degree out total toe out currently (about 5/16" out with 17" wheels) but inside edge tire wear is noticeable.

Would 1/4 out total toe out work just as well (and save front tire abuse on the street)?

(Running 17" A6's and DA Koni's)
 

Mike48162:

Yes, it's common to back off with a bit less camber and toe-in in the rear.

But how much is "a bit less camber" in the rear?  Someone mentioned they run -1.75* above.  Anyone run less than that?  -1.5*?  -1.0*?

I currently run -1.25 degrees negative in the rear, but made this change at same time as going from a fair amount of toe-out to now mildly toed in

so can't comment on how the -1.25 degrees negative works.   I liked a looser car, but with the 330 the back end needs to be 'underneath' you and not sliding around too much....so as not to waste momentum.... but also to allow the rear tire(s) the best chance at gripping out of corners.
 

I just wanted to post a thanks to whoever it was at nationals that clued me in to the magic of high rebound. Whenever I'd tried higher rebound the car had felt awful, so I was leaving it off, but apparently I didn't have it high enough! If any of you haven't gotten this yet, setting the rebound really high prevents the suspension from decompressing, so after the first couple turns the car is "hunkered down" and won't have as much body roll. It feels a bit bouncy, but transitions nicely.

This one piece of advice, along with figuring out my endlinks, helped propel me (after a 39th finish at nationals) from 5th locally with three events left to the first place I took this weekend. I had to win all three events, and win them by decent margins, and I did.

My other piece of advice for bimmer drivers: change your endlinks! I had installed the H&R front swaybar, and it helped, but it didn't feel particularly dramatic. I didn't think the endlinks were a big deal, but I finally got around to tossing them on right before Nationals. The ground control adjustable endlinks made a world of difference, suddenly the swaybar was doing a lot!

 So, my setup as it stands, for a 2001 non-ZHP 330i sport:

• TC Kline double adjustable shocks - full rebound all around, compression: 8F, 6R
• H&R Front Swaybar, Ground Control adjustable endlinks
• Hawk HPS pads front, HP+ rear
• Hoosier A6 245/40/17 - 45psi front, 35 psi rear
• max "slop" camber up front, 1.5 degrees rear
• 0 toe all around

I think I'm going to toe in 1/16th in the rear on my next alignment, to make it more stable for the street and track days, which I'm hoping to do someday.

 I hope that helps someone, thanks again to the kind folks in Topeka who helped me put together a winning combo. (at least locally, for my driving style)

 Matt
 

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DS #313 | the rolling couch of doom | La-Z-Boy Racing

btw, Bob, are you still interested in selling your set of staggered wheels?

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DS #313 | the rolling couch of doom | La-Z-Boy Racing

Any updates on the tire fitments or experiments with the ole FWD trick of wider in front? 275/35/18 fit on all corners? Just getting started so trying to figure out what tire size to try...any insight would be greatly appreciated!

 

Jeff MacRae

Philly Region 

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Jeff MacRae
Philly Region

Bob Clark's car had 275's up front at Nationals, and it seems to have worked out well for them. I emailed him the link to the thread, maybe he'll be able to expand on that experience a bit.

 From what I understand, 275's will not fit on the rear. (and I'm sure it will not be better to run 245F/225R vs. 245 all around)
 

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DS #313 | the rolling couch of doom | La-Z-Boy Racing

Yes, Todd and I co-drove at Nationals with 285 Hoosier A6 tires on the front.  It was only our second event on the tires and I don't think we have a conclusive opinion at this moment.  They fit with no rubbing on the SSR GT2 wheels with maximized offset.  They don't even come close to fitting on the rear.  Our one pre-national test was at Route 66 in Chicago.  A first time at that lot for both Todd and myself.  We compared them to some half used Kumho 710s.  Both Todd and I were within .1 of our Kumho times with the big Hoosiers.  He was .1 slower. I was .1 faster.  They felt very different.  The Kumhos were easier to drive giving more warning that they were nearing the limits.  The Hoosiers were definitely stickier but the limit can sneak up on you and so would probably take more time to get used to.  With more grip the Hoosiers induced suprisingly more body roll but suprisingly wheel spin seemed under control.  They seemed to get quicker turn in but corner exit still featured push - maybe why there wasn't too much wheelspin.  The car seemed more willing to "dance" with the Hoosiers which it never liked with the smaller 17 inch Hoosiers I ran for years.  Of course if there are time benefits it would take more time to develop that feel. That might be difficult since I may run Kumhos at most local events this year because they last longer.  We have about 24 runs on the tires now and they look very good. My 17 inch Hoosiers would be well past their prime at this point.  The tires don't show the abrupt shelfing we would see on the 245s.  Hoosier reps think it's illusory and its just wearing in a spot further up the tire.  Van Michael drove his 330ci wiith this setup at local events and thought tire wear was quite good compared to the smaller tire.  The bulge gives a more rounded profile.  Van also thought the 285 Hoosier was the best set up he ran.  The 245 Kumhos were next best and the 245 Hoosiers third.  My initial impression is that the tires help most in chicaynes and offsets.  The car was already quite good in slaloms and in fact I was shocked to feel the rear tires step out on me in the first day slalom at Nats.  Gotta watch that.  Tight turns are still the cars chief bugaboo and the I'm not sure the tires help here. 

Inside the car video doesn't reveal much but there is video of the car at Nationals at

file:///Users/robertclarkbmw/Desktop/Mac%20Web%20Gallery%20-%20My%20Gallery.webloc

Nationals and WAI #8 are on the 285s

 

http://gallery.mac.com/robertclarkbmw#gallery

that video link didn't come through correctly on that last post. 

Hmm, I may have to give a 275F/245R Kumho setup a try this season... My tire guy will love me...

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DS #313 | the rolling couch of doom | La-Z-Boy Racing

bob clark:

http://gallery.mac.com/robertclarkbmw#gallery

that video link didn't come through correctly on that last post. 

Cool videos.  How did you mount the camera?

 

BB

So if I understand correctly, you ran 285/30-18's front and rear on a D-stock E46 coupe?

I've been looking through the online BMW forums, and they all say that an E46 sedan can only fit up to 235s on the front and 265's rear.  The coupe can supposedly go a little bigger, but not much.  So I'm a little confused about what will actually fit.

Another question I have is what are you all using for swaybar endlinks?  Are the OEM ones pretty good?

BB

The BMW forums are out to lunch it sounds like.  With maximized offset up front on 8" wheels, you can easily fit MUCH larger tires than 235s.  For street driving on my ZHP, I bought another set of OE rear 8.5" wheels and am running 255/35's all around.  However, for autox I've run 265/35s all around, BFG R1s, and they are VERY wide for a 265 -- section width measured out to 281mm.  They fit fine up front but rubbed on the inside rear (under load, RTAB deflection I guess) and also on the rear outside, fender lip.  I've since gone back to 245/40 R1s (BFG traded them for free), which are significantly wider than a BFG 255 street tire, and they barely fit in the rear (44mm offset, 8.5").

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2001 BMW M5
2003 BMW 330i ZHP 6MT
2006 BMW 330i ZSP 6MT
2001 Audi S4 sport 6MT
1996 Volvo 850R wagon