Question: Does Light Wheels = Weak Wheels
 

I'm considering installing Enkei RPF1 wheels on my daily driven BRZ. The size I'm interested in (17x8 +35) weigh in at a very light 16.10 pounds each. This is a significant weight reduction in sprung weight from the factory wheels. However I have concerns that I may be choosing a wheel that will not be able to withstand the abuse of public roads.

Is the weight of a wheel any indication of its robustness?

A forged wheel, which is also light AND stronger than a cast wheel, will still fail on a large enough pothole. Allegedly the construction of light wheels (spoke windows, metal "grain", etc.), even of the cast ones, is made to counter-act any weakness from having less metal...so weight is indicative of something for sure. Something useful? Probably not. This is why you buy wheels from the brands that meet certain certifications and testing requirements: they have to some degree assured the strength of the wheel in a "normal" situation.

I bought light cast wheels and haven't though about it since. If it breaks, it breaks. I'll be boned, but what are you gonna do? There is no failure-proof anything.

^ this is exactly true.

Wheels aren't going to be failure-proof and weight isn't a very good indication on fail rates of wheels. I've seen plenty of cracks on wheels and spokes just straight snap from hitting potholes. Forged and Cast alike.

What seems to have the biggest effect (other than manufacturing) is just pure engineering of the wheel. There have been alot more 5AD cracks from one design over another.

RPF1 will be a good buy. I've had them on all of my cars and only dropped them this time because I wanted something a little different and went with a multi-spoke design from Yoshihara.

Enkei produces alot of wheels. Way more than what anyone even knows about because of all the port wheels and oe wheels they produce. You're fine with your choice and if something happens, it's life.

have you ever searched for information on the wheel? I mean in the time it took you to post this question you would have found ALOT of info on the RPF1 and what a forged wheel is. And why its stronger then the OEM wheel

If you graphed frequency of breakage from various wheels versus their weights, normalized for the amount of use, you would likely find a strong correlation between weight and strength. That being said, you'd find some light wheels that rarely break and some heavy ones that break all the time. Design and manufacturing matter.

In normal driving, I cracked stock a rim on my 550i sport, and that was a heavy wheel. My wife managed to bend a steel wheel on her Scion xA, smacking it into a curb or something. Also a heavy wheel. Nothing is perfect.

Most people don't see the relevance of spoke design, lip, and curvature all play their part. A light forged wheel usually is the result of being able to reduce material due to enhanced strength. Such a compromise yield a wheel that is lighter but every bit as susceptible due to its similar tolerances to a cast wheel. The yield is usually a 5-8 lb difference without taking into consideration of spoke design...that being said, a cast wheel in terms of replacement cost is still a more effective equation...because the possibilty of replacing wheels is pretty high especially with the less than perfect roads in the US

So what cast and what forged wheel designs are optimal for weight and strength?

the main criteria is to have minimal spokes that are slender but dissipate load equally. a split 5 would be one. In addition, a wheel with 0 lip usually are ideal when going for less weight. Furthermore, concavity is a no in terms of weight savings... Also, in terms of back pad on the rear of the wheel, how much material and how thick the padding is. Wheels advertised at certain weights will most certainly weight alot more with a thicker padding. As to strength, avoid designs with sharp contours as those are potential stress points. In addition, load rating must be equal or surpasses vehicle weight. These all apply for cast and forged wheels alike. A key point is to pick a wheel that is not overtly heavy but accomplishes the intended use. Contrary to information out there, race wheels are not ideal for road use. Its simply because race wheels are subjected different parameters in terms of impact, load, and longevity. A race wheel is to provide the maximum performance possible in a fairly controlled environment where road surfaces are usually better maintained then public roads. It also contends with much shorter heat and cold cycles as well without needing to consider the longevity a road car endures. A road wheel has to contend with pot holes, a constant bombardment of road surface irregularities and much more cycles in hot and cold that a road car is subjected to. Lets not forget how much a typical race car would weight vs a road car with passengers and some luggage...;) These are all considerations that any user needs to consider when picking a wheel.

If concavity is bad, how about convexity? What do you mean by split 5? 5 spokes or 5 spokes from the hub that Y into a split?

Concavity or convexity are both essentially adding material to the design. If the application boiled down to a choice of : big lip, medium lip/sligh concave, full concave. The best would be medium lip/slight concave as the optimal balance. Of course, this again is dependent on the intended car and its ideal offset. However, with car manufacturers widening the newer vehicles' hub and track to enhance stability in handling, most of the time, the ideal wheel set up would be flat face, 0 lip to really go beyond where the original handling is at... But again, as to concavity, It definitely looks good but what you are doing is adding material on the spokes to achieve the length and depth prevalent in either concave or convex... As to a split 5, twin forks for each spoke... Of course, these are general rule of thumbs on wheels but there are so much more variables that are dependent on intended application, strength to weight ratio, etc... For the FRS platform, high offset will be consistent with how the vehicle is set up to do where as a low offset would likely upset the original dynamics of the car. But on the flip side, a stanced out tucked in look does look good ;)

Thanks for the thoughtful response Yosh. Its that type of commitment that could sway me in a sale...I just wish the DY-12's came in 17's.

When you're picking wheels, you can make TWO choices out of the three listed below:

Strong
Light
Cheap

You can have a strong wheel that's light, but it wont be cheap. You can get a light and cheap wheel, but wont be strong. Lastly you can have a cheap, strong wheel but it wont be light.

no problem! :) I think my response is less so for touting our wheels but to just educate general consumers that wheels whether in forged or cast can be made light as well strong as long as it is built with consideration to what the product is intended to accomplish. Too many wheels out there that tout key words as sales triggers like forged, lightweight but completely forget to take into consideration aftersales replacement, affordability, and the products ability to be used as what generally 90% of the general public use the wheels for, which is to drive to and from work on roads that are possibly less than perfect... We've seen very very reputable forged lightweight wheels bent within a week's time with the consumer. Was it light? Yes. Was it touted as strong? Did it have great racing history? Absolutely... but the fact remains that it didnt last. The only thing that ended up lighter was the guy's wallet because he had to get a new replacement wheel... And its those moments when you want to cover all aspects of the wheel both presale and aftersale... simply because we've been there as a consumer.

As to 17" while it is tempting for us to build it, based on blend of upgradability (brake upgrade), performance, and visual appeal, the 18" in our opinion provides the best blend for the FRS chassis.

I was skeptical on the 17 vs 18 thing too...Go 18", you wont regret it.

18x9 Yoshihara DY-12C

http://i26.photobucket.com/albums/c1...f.jpg~original