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E36 /7 Z3 (1996-2002)
E36/7 Z3 roadster and coupe talk with our gurus here.

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  #1  
Old 12-23-2005, 10:25 AM
749009 749009 is offline
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Location: Calgary, Alberta, CANADA
 
Join Date: Nov 2005
Posts: 8
Mein Auto: '01 BMW Z3 3.0i roadster
snow tires - size and fit issues

my '01 Z3 3.0i is my only car so it has to do winter duty, which means snow and ice covered streets on occasion. I have the staggered factory wheel setup...7 1/2" fronts and 8 1/2" rears running high performance summers (225/45/17 fronts and 245/40/17 rears) during better weather.

Thus far this winter, I'm using an old set of Michelin directional snows (XM+S 330's) with 235/45/17 at all 4 corners. I understand it's a compromise, size wise, but, the reason for this post is that I'm finding the car is "tracking" much more than I like, especially at higher speeds.
By "tracking" I mean that the steering wheel has a tendency to pull left or right at times depending on the road surface. When the road surface is completely smooth (rare around here) it drives smoothly with no pull in either direction. I've had a 4 wheel alignment done by a competent shop and been assured there is no damage underneath and that all alignment settings are factory spec'd. Thus, I strongly suspect the tires because I didn't ever feel this much tracking with the summer tires.

I actually put very few miles on my car so I can't justify the cost of a brand new set of snows. Locally, I can pick up a slightly used (8,000 miles wear)set of Michelin snows in a staggered size set up that came off a Porsche Boxster for a decent price.
205/50/17 fronts and 255/40/17 rears.
I've run the numbers on a website that calculates speedo error caused by the size difference and this setup is actually VERY close to the factory summer tire setup (less than 1/2 of 1% out on the fronts, and just over 1% out on the rears). In fact, these tires are a bit better fit (%age error wise) than my current 235/45/17's.

Sorry for the long buildup, but, it will hopefully result in clear focused responses. My questions are as follows:
1) I suspect going from a 235/45/17 front tire to a 205/50/17 will help the "tracking" factor in a BIG way because of the narrower width. Any disagreement with my thinking and if so, please explain your reasoning?

2) I'm certain that going 1 size wider on the rears from 245/40 to 255/40 will present no fitment issues on my rear 8 1/2" wheels. I'm more concerned that going 2 sizes narrower and 1 size higher on the fronts (225/45 to 205/50) may present a possible fitment issue on my 7 1/2" front wheels. Anyone with comments from actual experience would be greatly appreciated.

3)Esthetics....having 40 series on the rears and 50's on the fronts and the width difference between 205's and 255's. I don't have a problem with the look of my current 235/45/17's, so some deviation from factory is certainly within my tolerance level, but, will this this setup look completely wierd? My primary reason for considering this is handling safety for wintertime driving, but, at the same time, I can live with my current setup and am just trying to improve things on a budget. Making the car look stupid at the same time, would not make me a happier person. Focused comments on the size deviation, with again, any practical experience, would be greatly appreciated.
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  #2  
Old 12-23-2005, 01:44 PM
Ridgeway's Avatar
Ridgeway Ridgeway is offline
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Location: Mississippi
 
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Mein Auto: '04 Z4 3.0i, '97 M3
the biggest issue i see is that you will have alot of understeer with that big of a stagger...


secondly i don't think i'd buy snow tires that already have 8k miles of wear on them

if you peruse tireracks website you can glean the following:
- generally only the first 55% of the tread is snow/ice rated, the last 45% is more of an all-season type of material

thus they recommend replacing winter tires after 3 to 4 seasons, as with normal driving you will by then be past the half way point


additionally bmw recommends that winter tires be replaced when the tread is down to 6/32s, which also is just over half of the tread (i believe most new winter tires are 11/32)

thus you really won't have alot of life in those tires
spend the extra couple hundred and get some new tires (though many sizes are starting to become hard to find, especially in the m3's & lm25's)

lastly it sounds like your mounting the winter tires on the same wheels that you have your summer tires on?
why not just get a set of winter wheels?
you can easily find a set of OEM used wheels for ~$600 in a variety of sizes and styles
in not too long of a time you will recoup your costs (considering up to ~$240/year to swap 4 tires 2x per year)- and that is not counting the value of the ease of swaps thereafter
plus you could get some 17x8 wheels where you can run 225/45r17 tires all around, which are a good compromise size
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Last edited by Ridgeway; 12-23-2005 at 01:46 PM.
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Old 12-23-2005, 02:47 PM
749009 749009 is offline
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Location: Calgary, Alberta, CANADA
 
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Mein Auto: '01 BMW Z3 3.0i roadster
Quote:
Originally Posted by Ridgeway
the biggest issue i see is that you will have alot of understeer with that big of a stagger...

*** OK, hadn't considered that, although, in the wintertime and with snow tires, I'm not into a "spirited" driving style. ****


secondly i don't think i'd buy snow tires that already have 8k miles of wear on them
****I haven't gone to see the tires yet as I'm trying to figure out whether this set up will even work. I've bought many sets of used winters before and the difference between decent used winters and summers or even all seasons is night and day. I'm being told by the seller, the tread looks "like new". ****

if you peruse tireracks website you can glean the following:
- generally only the first 55% of the tread is snow/ice rated, the last 45% is more of an all-season type of material

thus they recommend replacing winter tires after 3 to 4 seasons, as with normal driving you will by then be past the half way point

*** I believe that complaint about snow tires being good only for the first 1/2 of their life referred specifically to early model Bridgestone Blizzaks. I'm not certain that comment is true of late model snow tires as a general rule. 3-4 seasons is way, way past the 8,000 miles we're talking here. *****


additionally bmw recommends that winter tires be replaced when the tread is down to 6/32s, which also is just over half of the tread (i believe most new winter tires are 11/32)

**** that sound's to me like somebody is trying to sell more snow tires as opposed to replacing them when truly necessary*******

thus you really won't have alot of life in those tires
spend the extra couple hundred and get some new tires (though many sizes are starting to become hard to find, especially in the m3's & lm25's)

******remember, I'm up in Canada and your pricing means nothing up here. It's "gouge city" up here in Reindeer land. We're talking a difference of closer to a $1000. Don't even talk about shipping tires up here. The cross border shippers and Cdn. gov't love it when that happens. You're lucky if you have enough money for lunch at McDonald's after they get through with picking your pocket! **********

lastly it sounds like your mounting the winter tires on the same wheels that you have your summer tires on?
why not just get a set of winter wheels?

**** I won't have the car long enough to justify the cost. Again, we're talking Canada here and unless you're talking way too ugly steel wheels, $600 for a decent looking set of wheels that will fit my car isn't a realistic possibility. But, please work with my "given" info.. That's what I meant by "focused" responses. Simply saying "Oh, just spend whatever it takes and buy something else that you (the responder) prefer" isn't a viable option for me. ****

you can easily find a set of OEM used wheels for ~$600 in a variety of sizes and styles
in not too long of a time you will recoup your costs (considering up to ~$240/year to swap 4 tires 2x per year)- and that is not counting the value of the ease of swaps thereafter
plus you could get some 17x8 wheels where you can run 225/45r17 tires all around, which are a good compromise size
****Again, my question here is whether to live with my existing set up or spend a much smaller amount of money to hopefully make a significant improvement. I'm not suggesting your ideas won't work....they will just cost far, far more (up here) than I'm willing to spend to "fix" this issue. *****

Thank you for your input, just the same. Any other comments specifically on the much narrower front tires, the "look" issue or the fitment issue?
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