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Discussion Starter · #1 ·
Hello all,

I'm considering selling my M68 17" rims and purchasing some used 135M (ZHP) 18" rims, primarily for appearance reasons. Before doing so, I wanted to find out what the effects would be. Specifically:

1) Will this cause the ride to be more harsh?
2) Will road noise increase?
3) How will handling be effected?
4) Will this affect acceleration and/or braking in any way?
5) Finally, will this require any changes to gearing or anything else, or can I just put them on without worry about anything else?

Also, if anyone has gone from 17" to 18" rims and would like to pass on their experience, I'd love to hear about it!

Thanks,
Mark
 

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I did exactly what you did....

The only thing I noticed right away was acceleration was a bit slower.....but then I got an AFE intake and got back what I lost.
 

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Ubergeek
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1) Will this cause the ride to be more harsh?

- Possibly slightly more harsh.

2) Will road noise increase?

- Road noise is more a funtion of the tires you choose.

3) How will handling be effected?

- You may get sharper turn-in with a shorter sidewall.

4) Will this affect acceleration and/or braking in any way?

- Yes. More unsprung weight (factor 1) farther away from the wheel center (factor 2) equals poorer acceleration and braking. How much? I can't even guess... probably enough to notice.

5) Finally, will this require any changes to gearing or anything else, or can I just put them on without worry about anything else?

- The M68 rear is a 245/40/17. That wheel has a diameter of (2(245*.4) + 17x25.4) = 627.8mm. The M135 rear is 255/35/18, with a diameter of 635.7mm.

That's roughly a 1.2% taller gearing - nothing to worry about.
 

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KrisL said:
That's roughly a 1.2% taller gearing - nothing to worry about.
Maybe then the speedometer would actually be accurate :)
 

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If the acceleration from going up to 18" is slower, would there be an increase in acceleration if one went down to 16"?
 

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KrisL said:
- The M68 rear is a 245/40/17. That wheel has a diameter of (2(245*.4) + 17x25.4) = 627.8mm. The M135 rear is 255/35/18, with a diameter of 635.7mm.

That's roughly a 1.2% taller gearing - nothing to worry about.
Interesting because the M68 SP equiped 330 has the 2.93 rear, and the ZHP has the 3.07 but a larger diameter wheel & tire which decreases the gap between the 2.93 and the 3.07. Granted not by much, but it's still a factor.
 

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wflynn said:
If the acceleration from going up to 18" is slower, would there be an increase in acceleration if one went down to 16"?
If your overall wheel+tire package with 16s is lighter than your wheel+tire package with 18s, then yes.
 

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Moderato said:
Interesting because the M68 SP equiped 330 has the 2.93 rear, and the ZHP has the 3.07 but a larger diameter wheel & tire which decreases the gap between the 2.93 and the 3.07. Granted not by much, but it's still a factor.
Unless you race regularly, don't worry about the difference. My car came stock with 18" type 71's and the 2.93 gear. Also, don't go by the calculated heights of tires because tires specs are rounded to the nearest 5 for aspect ratio. Instead, compare revs per mile for the two tires (usually found on manufacturer's website.)

For example,
BFGoodrich g-Force KDW:
255/35-18: 833 revs/mile
245/40-17: 841

difference: 0.96%

Side note: they make 325/55-22 of this tire. Why? (Yes, I know answer is because someone buys them.)
 

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Discussion Starter · #13 ·
PhilH said:
The only real effect I notice in switching between my 17s and 18s is increased tramlining on the highway with the 18s.
What's tramlining mean?

Also, I'm not too technically adept when it comes to working on cars. Based on some of your responses, I'm not sure whether or not I can simply put 18" rims on without adjusting gearing, etc. Do I need to make adjustments, and if so, who would do work likes this, a tire shop, the dealer?

Thanks!
 

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mandms7 said:
What's tramlining mean?

Also, I'm not too technically adept when it comes to working on cars. Based on some of your responses, I'm not sure whether or not I can simply put 18" rims on without adjusting gearing, etc. Do I need to make adjustments, and if so, who would do work likes this, a tire shop, the dealer?

Thanks!
Tramlining is the car's desire to follow grooves in the pavement.

As long as you choose the right tire size (OEM sizes for the 135M rims are obvously ideal.. 225/40/18 front, 255/35/18 rear), you don't need to adjust anything. Put em on and drive :).
 

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mandms7 said:
What's tramlining mean?

Also, I'm not too technically adept when it comes to working on cars. Based on some of your responses, I'm not sure whether or not I can simply put 18" rims on without adjusting gearing, etc. Do I need to make adjustments, and if so, who would do work likes this, a tire shop, the dealer?
Tramlining is when the car follows the ruts in the highway so that you kind of have to fight the steering wheel to get the car out of the ruts. It's only a minor annoyance to me and I only notice it slightly on certain badly rutted highways.

No modifications are needed to fit 18s on any E46. Just get the right size tires and you're set (225/40-18 front 255/35-18 rear is stock on the 330i SP w/18s and the ZHP).
 

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in some R&T issue, feb99?, the 17" combo was found to be the best compromise of performance and ride. i think they tested on a 5er.
 
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