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      01-22-2013, 02:04 PM   #1
simianspeedster
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Square Tire Setup w/18x8 Front & 18x9 Rear?

I'm planning to order a 128i soon, likely with the Lifestyle Edition package (ZED).

I was surprised to see that the ZED package comes with 18x8 front / 18x9 rear wheels because the M-Sport package comes with 17x7 Front / 17x17.5 Rear wheels (128i M-Sport) and 18x7.5 front / 18x8.5 rear wheels (135i M-Sport). The ZED package rims are pretty wide for a factory option, especially on a 128i.

I was hoping to somehow go square with 225/40-18, but I don't think that's likely with 18x8 front / 18x9 rear wheels. Is it possible, or even advisable to go with 235/40-18 all around on 18x8 and 18x9 wheels? Or maybe 245/35-18 (same diameter as stock) or is that too much front tire for a 128i?

I know aftermarket wheels would solve everything, but I like the Style 496 wheels that come with the ZED package, so I'm curious about my options if I want to stick with them and go square.

Thanks in advance!

Last edited by simianspeedster; 01-22-2013 at 02:21 PM.
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      01-22-2013, 02:45 PM   #2
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Why go with a square tire setup if you cant rotate the tires from front to back in the first place?
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      01-22-2013, 02:46 PM   #3
simianspeedster
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More neutral grip -- reduced understeer
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      01-22-2013, 03:02 PM   #4
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225's would fit on a 9 inch rim but it would have a good amount of stretch, more then i'd personally like. I'm stuck in the same problem as you with my 264's but i ended up going with the staggered stock 135i sizes.
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      01-22-2013, 03:32 PM   #5
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There is no reason 235/40/18 won't fit up front and will look ok in the rear.
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      01-22-2013, 03:40 PM   #6
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Quote:
Originally Posted by 631twentyeighteye View Post
225's would fit on a 9 inch rim but it would have a good amount of stretch, more then i'd personally like. I'm stuck in the same problem as you with my 264's but i ended up going with the staggered stock 135i sizes.
How's the handling with regards to understeer?

My current 335i with M-Sport (225 front, 255 rear) understeers fairly easily, but it's heavier overall and also more nose-heavy than a 128i. I'm hoping to gain more neutrality and everything I've read suggests square is the way to go given my preferences.
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      01-22-2013, 03:42 PM   #7
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Quote:
Originally Posted by b1aze View Post
There is no reason 235/40/18 won't fit up front and will look ok in the rear.
How about 245/35-18? That seems like a more natural fit and it keeps the stock diameter. But is it too much tire for the front of a 128i?
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      01-22-2013, 03:48 PM   #8
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You may or may not have issues with clearance. It also depends on the actual section width of the tire, which can vary brand-to-brand.

People with aftermarket wheels (even with optimum offsets) have trouble fitting 245/35/18s without added camber. You wont see or feel any difference in a 235/40/18 over a 245/35/18 from rolling diameter alone. You can easily stray from the stock diameter up to 3% (and sometimes 5% depending on who you talk to) without a problem.

You also, IMO, dont want to create more oversteer by reducing treadwidth in the rear just to "balance" out the car with tire widths.

Where are you seeing this understeer? AutoX? Track? Daily driving? Theoretical only?
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      01-22-2013, 04:04 PM   #9
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I feel my current car's tendency to plow even at relatively low speeds if I have a little fun on a freeway onramp or a tight turn on a twisty road -- no track work involved. Much of it is probably attributable to the overall weight of my current car and the somewhat sloppy suspension which allows too much body movement during quick maneuvers, but others have suggested a square setup will be more neutral overall which has always been my preference.

When I had a MazdaSpeed 6 a while back, the grip was sometimes limited given the width of the tire (215s stock) vs. the weight of the car, but the breakaway was almost completely neutral under all circumstances, and that also describes the feeling in my E30 M3 back in the day. That's more what I'm after.

Given the relatively light power of the N52 down low, I figure 225s are enough rear tire. Stock, a 128i comes with 205 rear and BMW only moves to 225 rears when M-Sport is added, so that's telling -- the ZED package changes the tires to 215 front/245 rear like an M-Sport 135i. Maybe not the best setup for a 128i.

My original plan was to go with 18 x 8 Aero 7s and 225/40-18 all around, and I still may go that route, but now I'm aiming for the ZED package and I like the rims that come with it. They're just wider than expected, hence my original question.
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      01-22-2013, 04:40 PM   #10
b1aze
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Honestly, try it before you change it out. I doubt it will under steer at all in stock form just getting frisky on the streets.
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      01-22-2013, 07:29 PM   #11
simianspeedster
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Are you saying it won't understeer because it weighs less than my current car or because it's slightly less nose heavy?

Asked another way: what's the advantage of staggered tire sizes on a 128i that has near 50/50 weight distribution and doesn't have tons of power?
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      01-22-2013, 07:35 PM   #12
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there is none really. I just went with them because i knew they'd fit without issue. 245's are excessive for 128 power.
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      01-22-2013, 07:45 PM   #13
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Cost aside, is the general consensus that 225/40-18 all around is the most balanced setup for a 128i? That's what I had deduced from other research and posts, and it makes sense to me given my previous experience.

I'm probably going to add the Performance Suspension, and I will be ditching the runflats no matter what wheels and tire size I go with, so it might be worth it to change the rims and go 225 all around to get the right overall balance and the significant reduction in unsprung weight (I don't imagine those ZED rims are terribly light).
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      01-22-2013, 08:03 PM   #14
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It depends on the brand and model of the tire. Balanced is all relative and you aren't going to know how much more "balanced" you want/need to be until you get a baseline of where you're at. You can't make decisions about a car you don't have based on the car you currently have. You have to compare apples to apples and a 335 is not the same apple as a 128 is any way, shape or form.
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      01-22-2013, 08:32 PM   #15
simianspeedster
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You make it sound as if I'm comparing a school bus and a tug boat. A 128i and a 335i are not worlds apart. Same basic chassis, same layout, similar weight distribution, similar suspension tuning and they come from the same era of the same company. In short, they're considerably more alike than different.

The basic question is the same: are there any advantages to keeping a staggered layout on a 128i given the lighter weight and lighter power? I'm simply asking for the advice of other 128i owners about their experiences.
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      01-22-2013, 11:04 PM   #16
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Square setup will definitely reduce the under steer significantly. I went 235 front and 245 back and added Dinan 0.7 camber plates. The result is virtually zero under steer and turn in is immediate.
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      01-22-2013, 11:47 PM   #17
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Quote:
Originally Posted by simianspeedster View Post
You make it sound as if I'm comparing a school bus and a tug boat. A 128i and a 335i are not worlds apart. Same basic chassis, same layout, similar weight distribution, similar suspension tuning and they come from the same era of the same company. In short, they're considerably more alike than different.

The basic question is the same: are there any advantages to keeping a staggered layout on a 128i given the lighter weight and lighter power? I'm simply asking for the advice of other 128i owners about their experiences.
I'm running 225 front 245 rear. The car feels much more planted from the 205 front 225 I had earlier from the sport package. In terms of turning it feels the same, mostly because the difference from front to rear is the same.

However, I have heard from others that going square reduces understeer. I can still break traction so we aren't lacking that much power ; ). Unfortunately I haven't gone square yet so I can't comment on that.

in addtion, I am sure you will have to do something to the OEM sport suspension if you go 235 in the front. I feel like I am barely not rubbing
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      01-23-2013, 02:58 AM   #18
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Quote:
Originally Posted by HeelToe View Post
Square setup will definitely reduce the under steer significantly. I went 235 front and 245 back and added Dinan 0.7 camber plates. The result is virtually zero under steer and turn in is immediate.
Good stuff -- thanks!
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      01-23-2013, 03:07 AM   #19
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Quote:
Originally Posted by Greenkirby21 View Post
I'm running 225 front 245 rear. The car feels much more planted from the 205 front 225 I had earlier from the sport package. In terms of turning it feels the same, mostly because the difference from front to rear is the same.

However, I have heard from others that going square reduces understeer. I can still break traction so we aren't lacking that much power ; ). Unfortunately I haven't gone square yet so I can't comment on that.

in addtion, I am sure you will have to do something to the OEM sport suspension if you go 235 in the front. I feel like I am barely not rubbing
After looking up more info on the boards, it's most likely that I'll go 225 all around and avoid any rubbing issues, etc. That makes it less likely that I'll opt for the ZED package because the wheels are too wide for my needs. I may go M-Sport, stick with the 17" rims and replace the runflats with 225/45-17 Michelins. They look a tad small to me, but the roads aren't getting any better around here, so the extra sidewall height couldn't hurt.
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      01-24-2013, 12:52 AM   #20
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Stick with the 17s as they will help with gearing and making the car feel quicker, plus less rotational mass all around. Off of run flats you will notice how soft the stock or sport suspension truly is though so you may want to avoid it from factory and put that money towards a good matched kit utilizing koni yellows. Just my 0.02
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      01-24-2013, 03:45 AM   #21
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What's up Mikal?

Could you please elaborate on your comment about 17s helping with gearing and making the car feel quicker?

I recognize that a lighter wheel/tire combo will reduce the effort required to get rolling and the reduced unsprung mass has many benefits, but I'm not clear how wheel size affects gearing and quickness.

Assuming a constant tire diameter and combined wheel/tire weight, is there some other performance advantage to 17" rims that I'm missing?

Regarding the suspension, I'm planning to order the "factory" Performance Suspension (which I understand is installed at the port) because I want to keep it simple and keep BMW on the hook for everything.

Last edited by simianspeedster; 01-24-2013 at 03:53 AM.
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      01-26-2013, 07:05 PM   #22
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I suggest getting 225/40 front, 245/35 rear, then get M3 front upper+lower arms for extra camber. Dinan camber plates are another alternative for a nice street setup. If you want to reduce understeer, a little negative camber works great!

Definitely get the performance suspension from the factory. I think you will love it (after getting rid of the runflat tires).
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