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Limited Tire choices

Discussion in 'Wheels & Tires' started by kkbrit, Mar 19, 2017.

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    kkbrit

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    I have a 2015 X4 35i Msport with staggered wheels. 245/40/20 99y and 275/30/20 102y tires needed. The only option is a summer tire, no all season option. Pirelli is what I have now and they didn't last long. Other options are Goodyear excellence or Bridgestone potenza, all are summer tires. Seems a waste of an AWD. Is there some trick to being able to get other options? I really want Michelin but nothing so far. Any suggestions?
    • Member

    MGarrison

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    Tire Rack shows 6 ultra-hi perf. all-seasons for your car in 20" staggered sizes, but none are runflats. You could go a/s, but you forfeit rft. Sticking with rft, perhaps a call to Tire Rack might have a sales rep with some better insight than what you can find online. For upped longevity, you'd want a higher treadwear rating, TR is showing a new Pirelli with a 320 treadwear, but max-perf. summer. Theoretically, the grand touring summer Goodyear Excellence might be a broader seasonal option than the max-perf. summers, but considering the treadwear rating, the max-perf. part might be treadwear-design related. Parsing those types of differences is where talking to a TR sales rep can be helpful.

    If you'd be open to the idea of a different set of wheels, there are a/s rft's in the 19" stock size, 245/40-19, a couple a/s are ultra-hi-perf a/s. If you were to do different wheels, I'd suggest put the same all four corners so you can rotate the wheels/tires around to maximize your tire life. Even with awd, you're finding the rears worn out before the fronts, yes? 19" tires are cheaper too. Keep in mind the performance differences you'd see with switching from 20's to 19's and max. perf. summer to a/s.
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    lhazel '13 F12

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    Same situation with my '13 M6. Michelin Pilot SS F: 265/35/ZR 20; R: 295/30/ZR 20. These are not run flat and there's no spare.
    Question: Am contemplating changing tires out to 275/35/ZR 20 run flats all around, as no manufacturer makes run flats in the OEM sizing. Any thoughts on what this might do to the drivability and handling of the car? It appears the front wheelwells can handle the increased width of a 275 tire. I suspect traction would be diminished in the rear with the narrower tire, which is a concern given the torque output to the drive wheels.
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    • Technical Service Advisor

    charlson89

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    Is there a reason you would like run flats or the Michelin's? You do have the M mobility kit which allows the tires to be sealed for a short time to get the tire repaired. I would not recommend going smaller in the rear tires this will change the handling of the vehicle and traction.
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    lhazel '13 F12

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    Thanks for your response. Several years ago, I got a flat while driving to the airport in my wife's '06 650ic. The road debris slashed the sidewall on the inside of the tire. Had I not had run flats on that car, I wouldn't have made my flight. The Mobility Kit will work with small punctures, but it's not always the solution, I learned that day.

    Not planning to track or race the car, and your point about changing the handling of the car is a consideration that I've pondered. Just wondering how much of a change I might expect?
    • Member

    MGarrison

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    Are your rear stock rims within the size range acceptable for a 20mm narrower tire? If not then you may have to look at different wheels, or two more identical to stock fronts - as expensive as new wheels are from BMW, I wouldn't be surprised if a set of wheels could be had from Apex or the Tire Rack for not too far off just two BMW wheels. I'd suggest calling Tire Rack and having a conversation for more specific guidance - TR site shows 4 285/30-19 runflats for instance, which would mean different wheels... but, the overall diameter of that size is 1.2" less than your 295/30-20's. As I understand it, when changing tire sizes, it's recommended to stay within 3% +/- of the stock size to avoid risk of brake failure. Calculator's not handy so I don't know if that type of downsize is in a range of change to be an issue, or if the problem is more with going larger o.d. than smaller. Then there's whether 285 is close-enough width-wise, and then there's the rim-damage risk of just that much less sidewall height compared to the stock 20's. Bridgestone has a 285/35-20 runflat, but that's taller, again need to confirm if within acceptable change-size range. Also the treadwear implications - going to a square setup, you can rotate tires to even out wear front-to-rear, but on some of these 285's, they're almost as sticky as r-comps, so tire-longevity of 19k (without rotating) comes with the territory, same for the stock sticky staggered setup... just a guess, rotating to even wear, on something with a 140 treadwear.... probably get 5k to maybe 10k more miles out of the set of tires before they're all down to the wearbars. How you drive is a factor too - aggressive yee-hawing with throttle dumps, burnouts, ambitious corner-carving... you know what'll happen to tire wear on that plan... gone in a hurry! Anyway... chatting with someone at TR can help gauge the pluses & minuses of various options from what they say and how much maybe's, not recommended, & no-way's you get in response. Sticking a 275 on the 10.5 rear rim, if that's a rim width in a usable range for that width tire, you're presumably somewhat more susceptible to rim-lip damage or curbing scrape/damage. Plus less sidewall height, and the o.d. change. Changing o.d. also affects your speedometer reading - BMW's usually read 4-5 mph high with stock setups, so if you do something that's less o.d., speedo gets closer to actual speed, or vice versa if a comparable increase in o.d. Have seen some be picky about trying not to change the speedo reading, which is kinda moot since most BMW's aren't on point as it is - plus if you understand the implications of the change you can estimate speed easily enough. Also use smart phone gps or gps speed readout to compare/verify. As for chassis dynamics, running a square setup would make for a more even front/rear handling balance, reducing understeer but also having oversteer happening sooner than it would otherwise. M6 has a lot of power, you wouldn't want to be burning up new tires from not having enough rubber to handle the torque, although that's also in-part driving-style dependent. I would expect needing to be a good bit more careful about throttle application in turns, especially in low traction conditions such as rain, winter road temps (0-55 degrees), or sleet/snow/ice (consider some snow tires for that). Jump on the gas abruptly mid-turn or before gettting through the turn and having the steering wheel straight... less rear wheel traction could be spin-city, even with all the traction-control nannies doing all they can. But, yes, downside is decreased lateral grip and whether the car's power overcomes traction available from smaller-width tires.
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    lhazel '13 F12

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    All good points to consider. Thanks!

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