アフターマーケットのモッディングとチューニングに関して言えば、概して、ほとんどの愛好家は、車の重量を減らすことは良いことであることに同意しています.エンジンが押したり引いたりする重量が少ないと、その馬力がより効率的に使用され、全体的なパフォーマンスが向上します。また、制動距離が短くなり、ステアリング フィールが向上し、全体的なハンドリングが向上し、燃費が向上します。
ここで作用する減量には、バネ下重量とバネ下重量の 2 種類があります。ショックアブソーバーから (車の中心に向かって) すべてをバネ付きのおもりと考えてください:トランクの蓋、シート、あなた自身、さらには方向指示器の茎からぶら下がっている小さなエアフレッシュナーです。ばね下重量は、多かれ少なかれ、ブレーキ ローター、ブレーキ キャリパー、ホイール、タイヤなど、サスペンションの外側のすべてです。
ばね下重量を軽減する最も簡単な方法は、軽量のアフターマーケット ホイールを取り付けることです。これらはいくつかのボックスにチェックを入れます:特徴的な外観を与え、パフォーマンスを向上させることで、乗り心地を整えます。
ばね下重量とばね上重量の減少の比率は、人それぞれ頭の中にあるようです。フォーラムには、さまざまな式がぎっしり詰まっています。たとえば、バネ下重量を 1 ポンド減らすことは、バネ上重量を 10 ポンド減らすことに等しいと考える人もいます。ただし、関係する要因ははるかに多いため、これは必ずしも真実ではありません。ただし、バネ下重量を減らすことの利点は、通常、バネ上重量よりも明らかです。
車のパフォーマンス、燃費、および寿命を向上させる軽量ホイールのセットを求めている場合は、考慮すべき要素がいくつかあります。追加されたすべての利点は、本当に軽量ホイールを取り付けることによるものですか、それとも他の側面が関係しているのでしょうか?特定の軽量ホイールとそれに付随するタイヤは、あなたが主に行う運転のタイプと場所に最適な選択ですか?掘り下げてみましょう。
冶金学に深く入り込むことなく、一般的な経験則として、軽量のアフターマーケット ホイールは工場の OEM ホイールよりも弱いということです。 OEMのバリエーションは、重量を抑えることに大きな注意が払われずに金属が塗りつぶされており、軽量のホイールを作成するための製造プロセスもより高価です.自動車メーカーは、燃費と加速/制動性能を他の場所で改善することにより、より費用対効果の高い運用を行うことができます。すべてのホイールには特定の認証があり、「価格、品質、重量、2 つ選ぶ」という古い格言が有効になります。軽量で高品質のホイールは高価になり、OEM の低価格で作られた重いホイールは安価になります。
さまざまなホイール タイプも異なる方法で製造されます。ホイールの軽量化には、鋳造、フローフォーミング、鍛造の3つの工程があります。鋳造は最も安価で最も一般的です。 The process is to essentially pour hot liquid metal in a cast, let it cool, and the basis for a wheel is created. Flow-forming involves initially casting the wheel, but then reheating it back up and pulling out the barrel into the right size before its cooled back down. Forging is heating up and shaping a chunk of aluminum into a round block and then machining it into its final form. Flow-forming is generally more expensive than casting, and forging is the most expensive of the three.
All have their own benefits, but it's generally considered that flow-formed wheels are the best value, as they're not as expensive to produce as forged wheels and they’re lighter than cast wheels, though are still quite strong and can stand up to potholes, curbs on track, and other hard hits.
This leads us to a major consideration:What sort of driving will you be doing with your lightweight wheels? If they're bolted up full-time, know that they might not stand up to hazards as well as factory cast wheels. Personally, I've been lucky in my experiences rocking lightweight wheels all-year-round, on and off the track, but my experience is from having tires mounted up with at least a 50-series sidewall and about as much of a width as I can get away with on my old Mazda 2, thus giving the wheels plenty of sidewall to protect them.
I plan to swap lightweight wheels onto my current 2011 BMW 128i sometime in order to save around eight pounds per corner, or 32 pounds overall. Though, I'd be scared to mount up a tire that's near the minimum sidewall and width that the wheels can accommodate. Like I did with my Mazda 2, my BMW's lightweight wheels might be its primary set — why not reap performance benefits and better fuel economy in as many scenarios as I can and look good while doing it? Because of this, more rubber that's not stretched on there is a good thing.
When enthusiasts swap to lightweight wheels to achieve better grip and overall performance, usually stickier tires are on the docket as well.なぜだめですか？ Plus, the wheels are often wider than factory wheels, thus more of a contact patch with the road can be achieved. But will the weight difference really be there. Matching performance tires often weigh more due to having stiffer sidewalls and coming upsized over the factory size.
The best apples-to-apples comparison I can come up with is discussing my current setup and planning and how much weight I want to shed. Right now, my factory 17X7 BMW Style 256 wheels weigh just about 22.3 pounds each, coming out to 89.2 pounds total. The wheels I intend to swap for track use, D-Force LTW5s in 17X8, weigh 15.5 pounds each (62 pounds total), netting a 6.8-unsprung-pound loss at each corner, and 27.2 pounds total.
The tires that the previous owner upgraded to are 225/45/17 Yokohama Advan Apex V601s, which weigh 22.4 pounds each and have a treadwear rating of 280.
My Bimmer's current wheel and tire package comes to a grand total of 44.7 pounds per corner, and 178.4 pounds total. If I keep the same tires (though they won't be long for this world if I keep tracking on them), or replace them with a fresh set of the same brand/model/size, I'd truly experience a 27.2-pound weight loss.
If I decide to upgrade to stickier, 200-treadwear Falken Azenis RT660s in the same size with the D-Forces, the weight jumps up to 24.5 pounds per tire (40 pounds per wheel and tire). This doesn't sound like much, but it takes away from that 27.2-pound weight loss, netting just an 18.8-pound loss instead. That's still a hearty amount of shedding for unsprung weight. But imagine what even wider wheels and wider tires would mean?
Still, it wouldn't be for nothing. Despite not having much of a weight loss, any drop in unsprung weight is still better than a net weight gain, such as adding non-lightweight wheels and tires to your rig. Plus, the added benefits of more grip are quite apparent, as more grip means higher cornering speeds, more stability at speed, and shorter braking distances.
It should also be said that stickier tires will reduce fuel economy, as they have a tad more rolling resistance over conventional everyday street tires.
Another consideration is that the fitment of the aftermarket wheels must be taken into consideration. This is where following guides and reading Facebook groups and forums comes in handy. What sizes are popular for your particular car, especially among enthusiasts who use their cars the same way? Because I'm after more on-track grip and performance on a daily driver, it's in my best interest to see what setups fellow enthusiasts have successfully used.
In my case, there are some great guides out there for the E82 BMW 1 Series, including some by Bimmerworld and Apex Race Parts. Fitment Industries has some fields that can be customized to offer wheel and tire choices that will fit your particular setup and how much modification of the car's body you're up for doing.
How will changing the wheel's diameter, width, and offset affect how they fit in the wheel well and over the brake? In the E82 128's case, you can't fit as big of a wheel and tire package as other rear-wheel drive sports cars without adding more negative camber and modifying the fenders. It seems like a setup with a 17X8.5 wheel, 40 offset, and 245/40/17 tires is the limit without doing some fender rolling, but not without adding negative camber. This is related to the alignment and involves tilting the top of the tire more inward. Depending on suspension valving, doing some fender rolling might be required.
Personally, I'll probably go 225s or 235s, even with some added negative camber, so as to give myself more wiggle room against rubbing the tires on the inner fenders, contacting the shocks, and other issues.
There's more to all of this, but hopefully it's acted as some good pre-emptive food for thought, and at least put you in the mindset of figuring out what kind of net gains there are to experience. Plus, there's the financial aspect:What is your budget for wheels and tires, and what wheel and tire combo best fits it? Is it worth upgrading to x for y less pounds, at z more of a cost?
Hell, if you're after more grip on track for cheaper, why not keep the tough (albeit heavy) factory wheels, and mount up slightly narrower yet much stickier tires? There could be a net weight loss, and the more track-centric rubber will bode better for grip, as well as hold up to the higher heat and G forces.
There's also the aspect of the wheel and tire size altering the drivetrain's gearing, in which case I'd say refer to what fellow enthusiasts who've run bigger wheels and tires have experienced. When I ran 15X7.5 wheels with 205/50/15 tires on my Mazda 2, which originally came with 15X6 wheels and 185/55/15 tires (puny, right?), the speedometer read a little higher than the stock factory size.
Regardless of all of the above, it's fun researching all of this in the name of gaining more performance, potentially more fuel economy, and doing something that's a bit different than the way our vehicles were set up as everybody-friendly near-appliances.
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