10-11-2018, 01:05 PM | #1 |
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New wheels and tires
Bunch of questions.
I have a 230i xdrive with 7.5jx17 ET43 OEM wheels with the nasty runflats. I'm thinking of getting a second set of wheels and tires for the summer. I do a couple of track days each summer. I'm thinking of the TSW Bathurst Gloss Gun metal Rotary Forced wheels with the PSS tires. Here's the questions: 1. Thoughts on the quality of the TSW wheels? I saw some negative reviews but maybe all wheels get a handful of bad reviews.The price sure looks lower than most other wheels and I like the look. 2. Any problem with switching back and forth between 17 inch wheels in winter and 18 in summer? doesn't seem like a problem. Eventually when the runflats wear out I'll ditch them for something else. 3. The 240i standard wheel size looks like 7.5jx18 ET45 but the TSW wheel is 18x8.5 with 35 offset. Both run 225/40/18 tires. So, it looks like the TSW rim is wider but either rim width is fine for 225 tire. Why does BMW use a 7.5 width rim and TSW use 8.5? Does it make any difference? Thanks for the help. |
10-11-2018, 01:35 PM | #2 | |
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2. No problem swapping back and forth as long as your overall diameter of the tires/wheel set up remains close the same. I'm assuming you're on 225/45/17 or something like that? If so, with a larger diameter wheel you'll need lower profile tires so a 225/40/18 would be equivalent to your 17" set up. 3. At an ET35 on a 8.5" wheel you're going to have to get wider tires for sure so you might be protruding past the fender. I'm on 18x8 ET40 on 245/35/18 and I'm basically flush to the fender. Also, your model has the 7.5" wheels squared. All of the M235/40i and 28i/30i M-Sport models use a staggered set-up with 7.5" front and 8" rear. Having wider tires, especially in the rear makes, a difference because you can actually deliver the power to the ground. |
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10-11-2018, 04:54 PM | #3 |
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Your 2 Series has a range of widths and offsets that it can accommodate. Putting an 8.5 ET35 in the front will limit you to a 225/40/18 tire unless you're willing to modify your fenders or have the ability to add negative camber.
For those who want to run a wider tire on the 8.5" wheel, we generally spec out an 8.5 ET42 (ET45 + 3mm spacer) which allows for a 235/40/18 tire. You also have the option to run a 9.5" rear wheel with a 255/35/18 tire. Here are a couple of pictures showing what each would look like. Staggered Square
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10-12-2018, 12:39 PM | #4 |
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Square setups are fine if everything fits OK - the wider staggered rears may add some marginal extra grip (i.e. understeer) but mostly a cosmetic improvement. As long as the tires for a given rim width are w/i it's safe parameters, you will get better handling response from the narrower tire (taut sidewalls), softer ride on the wider one (sidewalls are more flexed or bowed). And if you are driving all year, I'd put snow tires on the 17's - shaker is right in the snow belt isn't it? I lived in Westpark for over a decade, and even over there the snow tires were very helpful.
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10-13-2018, 08:53 AM | #5 | |
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10-13-2018, 11:11 AM | #6 |
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Here's what I mean:
For example of an 8.5" wheel, the first chart I find (can't confirm accuracy of this) lists tire widths from 225-255, with 'ideal' at 235-45. A 225-235 will give the best steering response, because the sidewall is most taut and the tire has little ability to squirm. A 245-55 will give a softer ride, but also mushier steering response, because the sidewall is rounder and has more room to flex or roll over. These are not going to be dramatic differences with a constant wheel size (factory is 7.5" w/ 225 and 8" w/ 245). Aspect ratio will be determined by the ultimate width and diameter, assuming you need to keep total diameter at/near stock (highly recommended). Wheel diameter is usually bigger-is-worse, except for clearing better brakes (or looks) - the unsprung weight negates any advantage of low-aspect stiffer sidewalls). In general I'd avoid extremes, especially for really hard use or on track. Personally I hold with the belief that section width is only really relevant in two situations - track use, or very wet/snowy weather (other opinions are out there). The contact patch area is the same regardless of width, but it changes shape - narrower is better in wet/snow (less hydroplane effect) and wider tires are better on track b/c stress and heat are distributed over a larger area (and sidewall rolling affects less of the patch). Even for track days I don't see the need to cram the most rubber in. Check out most track instructors and they will likely tell you that you are better off learning on less aggressive tires, since tires can crutch skill deficits, or uncover them at much higher speeds; also you aren't running the tires for a full stint in a race, so they have time to cool down (so why not stay w/ 225's and assure no rub). This is one of those areas that is heavily polluted by cosmetics and advertising hype that bigger is better for both diameter and width. There is tremendous placebo-effect when you spend 2k on a setup, but I'm suspicious that few would really notice a change of 10-20mm in section width on the street (or a novice on track). |
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10-13-2018, 03:06 PM | #7 |
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So, it looks like OEM 18 inch wheels are 7.5 wide with 225 tires but aftermarket wheels like VMR and TSW come in 8.5 widths for the same 225 tire. I’m guessing they go with the wider rim so they can accommodate a broader range of tire widths with the same wheel? Any downsides to the larger rim if going with 225 except for maybe a heavier wheels since it’s wider?
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10-13-2018, 05:45 PM | #8 | |
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10-13-2018, 06:48 PM | #9 |
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Get your wheels.com offers the TSW 18x8.5 wheels with 225 tires which is why I asked why TSW used an 8.5 rim width for 225s while OEM is 7.5 rim width with 225 tire.
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10-13-2018, 11:30 PM | #10 |
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Michelin PSS and PS4S tyres in 225/40-18 size are certified by Michelin to fit on 7.5”, 8.0”, 8.5” and 9.0” wide wheels.
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10-14-2018, 04:12 PM | #11 | |
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10-14-2018, 04:17 PM | #12 |
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OP to clear everything up, I'm on 18x8 squared wheels with staggered tires. The first pic is an 18x8 with a 225/40 and as you can see, the tire is stretched. The second pic is 18x8 with a 245/35 and the tire fits perfectly. I hope this gives you an idea now because as I mentioned throughout this thread, you can technically run a 225 on an 8.5" but it's not ideal.
Also, the wheels are ET40 so that will give you an idea of offsets. I'm pretty flush. |
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10-14-2018, 09:55 PM | #13 | |
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10-14-2018, 10:58 PM | #14 | ||
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10-14-2018, 11:32 PM | #15 |
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They aren’t stretched from a performance perspective, only from a look perspective (again, mainly due to the profile around the rim protector to extend the rubber in that area beyond the rim lip), depends on whether you place looks above performance. Modern low profile tyres don’t have the balloon look of older high profile tyres. With the rim on the narrow end of the tyre manufacturer spec (7.5” for a 225/40-18) the contact patch will be narrower than on a wider rim, giving the tyre the performance of a narrower tyre on the same rim width. Michelin have engineered the tyre to fit on a 7.5” to 9.0” wide wheel, 8.0 or 8.5” wheels are going to give a more optimum contact patch than 7.5” or 9.0” wheels.
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10-15-2018, 10:46 AM | #16 | |
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10-15-2018, 12:18 PM | #17 | |
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To get the balloon look of high profile tyre, a narrow rim will round the edges of the tread as the sidewall is pinched in by the narrower rim width. This will lead to the contact patch width being close to the equivalent of a narrower tyre, but with the disadvantage of being a heavier tyre. For example the contact patch width of a 225/40-18 tyre on a 7.5" rim will be about 200mm compared with 198mm for a 215/40-18 tyre on the same rim. From a performance perspective at Auto-X events, it is always recommended to use a given tyre with the maximum certified rim width if that width is allowed for the car class, this ensures the flattest tread profile for best lateral grip. Using a tyre on the narrowest certified wheel, which is 7.5" for the 225/40-18 tyre, will lead to lower lateral grip than on the other certified sizes for Michelin Pilot Sport tyres of 8.0", 8.5" and 9.0". The "stretched" look (which is the way Michelin seems to have designed the Pilot Sport tyres to be mounted) gives better performance from a cornering perspective. |
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10-15-2018, 01:27 PM | #19 |
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8.0" or 8.5" would give a better fit on most cars (especially on the 2-series due to strut clearance), but from the perspective of maximising lateral grip and what Michelin certifies the tyre to fit, 9.0" is a supported width for 225/40 tyres. The lower the profile, the bigger the rim protector ridge, the more the tyre will look stretched on the proper wheel width. Looks, performance and correct sizing don't necessarily correlate.
As the profile goes up, the stretch look is less, here are a couple of photos that show 45 and 50 profile tyres on wheels at or near the maximum width. The first photo shows a 215/45-13 which is certified tor 7.0", 7.5" and 8.0" widths, on the maximum 8.0" wide wheel. The second photo shows a 195/50-15 which is certified for 5.5", 6.0", 6.5" and 7.0" widths, on a 6.5" wheel. |
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