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Discussion Starter #1
My current car is a
2008 BMW 128i Convertible with the Sport Package (I've read that it came with 17"in wheels)

I'm looking to upgrade wheels from the stock and be a bit more flush to my fenders.
Does anyone have any suggestion or advice ? Any wheel size suggestions?
I was looking at 18 X 8 (5-120 bolt pattern) ET 30-35???
 

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My current car is a
2008 BMW 128i Convertible with the Sport Package (I've read that it came with 17"in wheels)

I'm looking to upgrade wheels from the stock and be a bit more flush to my fenders.
Does anyone have any suggestion or advice ? Any wheel size suggestions?
I was looking at 18 X 8 (5-120 bolt pattern) ET 30-35???
That looks good, I feel 8" is the max for the front. ET's look good.
I have 8" all round on a E87 hatch, fitted with 225 x 40 x 18.... rides well.
You can go for 245 x 35 x 18 on rear with safety.
RegardZ.
 

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From what I see regarding 2008 128i vert wheel sizes, there was:
205/55R16 square setup for the BASE Model OR 205/50R17 front on 7" wide rim w/ 225/45R17 rear on 7.5" rim for the Sports Package model.
From what I can see online, the stock offsets were 47mm on the 17 inch rims.

Did you want to go with a square setup (same rim/tire size) all around (good for rotation)?

This is a good reference to use when doing your calculations. You will need to measure key clearance points and input them into this calculator.

http://www.wheel-size.com/calc/?whe...35-18X8ET39&fcl=50mm&wcl=30mm&scl=50mm&sr=0mm

So I had stock setup on my 228i (225/40R18 on wheels with 45mm offset). I went with 245/35R18 with wheels with an offset of 40mm (ET40). Could have done ET41 or ET42 though as I had the room on the interior between the tire and suspension. But with this combination I have no rubbing. The clearances may be different on the 128. You will need to get your ruler out!

Remember that going with a lower offset essentially pushes the wheel to the outside (i.e. the "Poke"), higher offset pulls the wheel in to the inside towards the suspension components. Best to keep the inner clearance close to stock as you do not want rubbing on the suspension components (Strut)... meaning you manipulate the two main variables - (1) the wheel offset and, (2) the wheel width (say going from 7" to 8"). Then the concern is clearance on the fender and when you lock steering to each side.

Also, when up sizing your tires, you want to keep very close to your original rolling diameter of your OEM tires - so your speedo isn't off.
 

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If you went to a 225/40R18 with 8" Rim with 35mm Offset (as Garn stated above), the circumference is nearly identical (speedo would only be 0.1% or less off) - which is a good thing of course.
Specifically, the front (205/50R17 front on 7" wide rim compared to 225/40R18 with 8" wide rim):
- Inner clearance between the tire/wheel and the suspension would be the same as stock
- Outer clearance for the tire would be 22mm. So measure how much distance to fill existing gap (to the inside of the fender). 22mm may be more poke than you want to do.
- Also note that the 225/40R18 tire width is 3mm narrower than the 8" rim.

So if you don't have 22mm distance between existing tire and inside fender, increase the offset...
With 8" ET40 - Tire would be 17mm closer to fender over stock, Tire would be 8mm closer and the rim would be 11mm closer to the suspension
With 8" ET45 - Tire would be 12mm closer to fender over stock, Tire would be 3mm closer and the rim would be 6mm closer to the suspension

At least from my experience with my 228i, 15mm of poke was right on the edge of the fender. I had previously used 12mm spacers on the front and 15mm on the rear with the OEM setup so I had the luxury of using the spacers and the OEM wheels and tires when I was measuring... So the change I made was similar to having 15mm spacer on the front OEM wheel/tire setup. So in hindsight, I could have gone with a ET41 or ET42 wheel instead as I had, in retrospect, enough clearance on the inside to accomodate. Since my 8" wide wheels were narrower than the 245/35's I really had to focus on the tire clearance predominately.

One last note... I went from the OEM Pirelli RFTs to Goodyear F1's. This Goodyear tire as well as the Michelin Super Sports have a more pronounced "shoulder" on the tire while the Pirelli had a gradual more rounded "shoulder". You have to consider that too if you really get crazy going wider. The more pronounced shoulder allows the contact patch of the tire to be maximized... on more gradual rounded shoulders the contact patch is narrower than the widest point - which may be closer to the middle of the sidewall. That has to be taken into account so that you don't have rubbing especially on the fender.
 

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In reading other blogs, it seems that ET45 is the general consensus for the fronts... whether doing 8" or 8.5" wide rims with 225/40R18. Some doing this with 19" rims (225/35R19 - which I wouldn't recommend.)
There is more room to play with on the rears... some people going to 255's with 8.5" or even 9"- but you may want to do a square setup. If so, you're safe all the way around with 225/40R18 ET45.
 

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Discussion Starter #6
So about to get VMR Wheels but wondering if the follwing wheel specs will fit my 2008 BMW 128i E88 sport pkg with stock suspension and without rolling my fenders.

Front: 18x8.5 ET45
Rear : 18x9.5 ET50
 
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