Thinking of putting some Enkei RPF1 15x7s on my coilover NA. Wondering if it would be best to run the 35 or 41 offset? Good tyres for track+street that wont destroy my wallet?

Care more about handling than looks

Cheers

 

Either will work well. +35 fills the fender a bit better and would be my choice .. if I were limited to a gravity cast Enkei.

By the way, the OEM shock on every Miata is a "coilover".

 

With a fender roll you can fit 15x8 +28 RPF1s mounted on 205/50/15s

 

What about 15x8 RPF1s with 225/45/15?

 

Fits. Done it myself at 4.25f/4.5r pinch weld height and a hair more camber than 949's dual duty alignment specs but not as aggressive as their race alignment specs. I didn't initially roll the fenders and it was VERY tight. Suggest a mild fender roll.

 

Why would you not want to be limited to a gravity cast Enkei? This makes them seem less desirable. I’m in the market for a set of lightweight 15s and these have been high on my list.

 

Because a pressure cast and flow formed wheel will be far stiffer. Because there is no commonly accepted testing or criteria for wheel stiffness, it's in the public's blindspot. RPF1's are light but not particularly stiff. No magic potion allows a 11.5 lb, 15 year old gravity cast design to be as stiff as a current generation pressure cast 12lb wheel. Don't obsess over wheel weight. The reason RPF1's have the best weight to $ ratio is because they use casting technology abandoned by everyone else in the 90's.

 

And that they are consistently available from multiple vendors doesn't hurt either.

 

Ah, good info. I knew they were flow formed. Are the newer Konig designs pressure cast?

 

Pretty much any flow formed wheel you can buy these days is pressure cast, LP-FF. The RPF1 remains about the only wheel marketed to performance buyers that is still gravity + flow form (GC-FF).
Sparco and OZ cast wheels mostly made by OZ's parent company now which is YHI, in China so they're also LP-FF.

 

I believe geometry is responsible for stiffness and material composition is for tensile which would be strength. The modulus of elasticity is the same for these materials. The RPF1's are supposedly a stiff design but they are fragile. Good for handling but not good for impacts such as curbing etc. From my experience all will become defective from an impact. Either bent or cracked.

 

Material composition depends on density, which is affected by manufacturing process. Aligned and compacted or random and uncompacted grain structure in this case. So no, the modulus in the center of the wheel is not the same. No more than a cast rod has the same modulus, plastic deformation limit or tensile strength as a forged rod.

The barrel on an RPF1 is quite stiff for its weight. Flow formed and the stepped design adds structural stiffness. The soft bit is the center. Typical failure mode of an RPF1 is a center that is off axis, no longer concentric with the barrel. Barrel still pretty round though. Not a bad wheel, just not quite the amazing achievement of strength to weight that most people think they are. They're light, have weaker centers than LP cast wheels, have less brake clearance and are affordable. Depends on whats important to the buyer.

 

Well, the RPF1 is now down a few notches on my list of wheel candidates.

If only I could get a bronze wheel like this somewhere 🤔

 

I agree the RPF1 might not be the best wheel for your application but not necessarily for the reason you think. The Avanti Storm's bronze is a very nice bronze. After I saw them in person it cured me of the outer spoke design which I'm not a fan of.

In general the way to view a wheels construction is, a strong material makes a strong wheel which is a safe wheel. A stiff wheel is faster and lighter. Stiff wheels are almost always made from lower density materials to maximize the geometry for a given weight. The geometry increases the stiffness exponentially where material strength has no affect on stiffness if the modulus of elasticity (young's modulus) is the same. Cast, wrought/billet, cold worked and forged aluminum have the same modulus.

A cast wheel and forged wheel of the same geometry will have the same stiffness. The forged wheel will be nearly twice as strong and weigh more because of its higher density. If the cast wheels geometry is altered to make it weigh the same as the forged wheel it will be stiffer then the forged wheel and maybe only 25% lower in strength.

 

Goodwin Racing has a sale going on if you want to browse for wheels on their site. 15x8 +25 paired with a 205 width tire and 1.5 degrees + of camber will require a mild fender roll, but it's a good setup (better turn-in feel, freedom to upgrade to larger tires in the future).