Pokud jde o úpravy a ladění na trhu s náhradními díly, většina nadšenců se z velké části shoduje na tom, že snížení hmotnosti, kterou auto veze, je dobrá věc. Když má motor menší váhu, aby mohl tlačit nebo tahat za sebou, jeho výkon v koních se využívá efektivněji, čímž se zlepšuje celkový výkon. Znamená to také kratší brzdnou dráhu, lepší pocit z řízení, lepší celkovou ovladatelnost a lepší spotřebu paliva.
Zde vstupují do hry dva typy hubnutí:odpružená váha versus neodpružená váha. Představte si vše od tlumičů (směrem ke středu vozu) jako odpruženou hmotnost:víko kufru, sedadla, vaši vlastní osobu a dokonce i malý malý osvěžovač vzduchu visící na páce vašich ukazatelů směru. Neodpružená hmotnost je vše na vnější straně zavěšení, víceméně:brzdové rotory, brzdové třmeny, kola, pneumatiky a další.
Pokud jde o snížení neodpružené hmotnosti, zdaleka nejjednodušším způsobem, jak toho dosáhnout, je instalace lehkých kol pro trh s náhradními díly. Zaškrtněte několik políček:Zkrášlí vaši jízdu tím, že jí dodají charakteristický vzhled a zlepší výkon.
Zdá se, že každý má v hlavě svůj vlastní poměr ohledně toho, kolik neodpružené hmotnosti se rovná snížení odpružené hmotnosti. Fóra jsou plná různých vzorců. Někteří lidé se například domnívají, že zhubnout jedno kilo neodpružené váhy je jako zhubnout 10 kilo odpružené váhy. To však nemusí být nutně pravda, protože do hry vstupuje mnohem více faktorů. Výhody snížení neodpružené hmotnosti však budou obecně patrnější než odpružená hmotnost.
Existuje několik věcí, které je třeba zvážit a zohlednit, pokud hledáte sadu lehkých kol, abyste zvýšili výkon svého vozu, spotřebu paliva a dlouhou životnost. Jsou všechny přidané výhody skutečně způsobeny montáží lehčích kol, nebo jsou ve hře jiné aspekty? Je určité lehké kolo a doprovodná pneumatika tou nejlepší volbou pro způsob jízdy, který primárně provozujete a kde to děláte? Pojďme se do toho pustit.
Aniž bychom se ponořili příliš hluboko do metalurgie, obecným pravidlem je, že lehká kola pro trh s náhradními díly jsou slabší než tovární OEM kola. OEM varianty mají potažený kov bez větší pozornosti věnované udržení nízké hmotnosti a výrobní procesy pro vytvoření lehčích kol jsou také dražší. Výrobci automobilů mohou pracovat efektivněji z hlediska nákladů díky lepší spotřebě paliva a výkonu zrychlení/brždění jinde. Všechna kola mají určité certifikace, které je třeba splnit, a do hry vstupuje staré známé „cena, kvalita a hmotnost, vyberte si dva“. Lehké a kvalitní kolo bude drahé a těžké kolo vyrobené za nižší cenu OEM bude levné.
Různé typy kol se také vyrábějí odlišně. Existují tři procesy pro vytváření lehkých kol:lití, tavné tváření a kování. Casting je nejlevnější a nejběžnější. Proces je v podstatě nalít horký tekutý kov do odlitku, nechat jej vychladnout a základ pro kolo je vytvořen. 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. Why not? 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.
