Wheel Cap Observations

This kind of info may have already been posted elsewhere, or be common knowledge by now, but I thought I'd share what I've found through trial and error (and receiving a 355 cap by mistake once). Specifically, dealing with the Superformance aftermarket wheels, and the 4 different caps that in one place or another I've seen listed as interchangeable.

The aftermarket caps included with my wheels... I would subjectively say look fine up to 10ft, then the lack of silver around the prancing horse and the recessed glued-on badge just pales in comparison to the original. I measured their inside diameter between about 42.4mm and 42.1mm (they are tapered, becoming thinner down until the lip at the bottom).

The new style #226245 caps are much, much darker yellow, and styling changes were made to the sizes of the black ring around the outside and the size of the prancing horse. They look fantastic by themselves, but I just don't think they look "right" on older models. Doesn't matter anyway though, because they don't really fit correctly on the aftermarket wheels (more on that later). I measure them to be around 42.8mm ID; however, the smaller tabs are more flexible than the originals, and are reinforced by a metal band.

The early 355 style cap (#154794, the Ricambi site says for 1995 355s... I don't know anything else about them) and the original #108947 both have, as far as I can tell, identical badges. The 355 style requires a lock ring, which I don't have, so I haven't attempted to mount one up. It may or may not be a possible alternative, but it would require lock rings, washers, and I'm unsure if the extra plastic sticking out the back would hit anything around the hubs. The original style goes about 13mm into the wheel, the 355 style goes back about 17mm. The 355 style is also a bit wider, around 43mm ID on the main part (the small area below the lock ring groove is less.. around 42mm). The original style is about 42.4mm ID.

The original wheels (at least my TRX wheels) have 2 recessed lips for the wheel cap. The first lets the cap sit recessed slightly in the wheel, and the second is for the rubber O-rings used on the original caps. All the cap styles fit perfectly in this wheel. 2nd, 3rd, and 4th pics show the recesses, and the new and old style caps in the TRX.

The aftermarket wheels are quite a bit different. The caps sit on top of the outside of the wheel, instead of being recessed. The groove for the O-ring is just a simple bevel. And the paint is VERY thick, including inside the hub area (I can tell because some of it chipped off while having tires mounted). Here is where the problems begin. The aftermarket caps fit fine, of course, but the original and 355 styles don’t want to quite go all the way in, and I wouldn't want to force them. The new style goes in, but since it sits on top, the gap introduced in the new design just doesn't work like it does on the recessed groove of the original wheels. 5th, 6th, and 7th pics show the aftermarket wheel.

NOTE: This is just my particular set of aftermarket wheels. Not all may be the same. YMMV.

I’m considering sanding down the paint on the inside of the hub so the original set will fit correctly. I’m not 100% sure it will work, so I’ll have to look into it later. Anyone else had this problem, or tried getting original caps to fit properly?

Finally, a tip about removing stubborn caps. I've never had a center cap like these that wouldn't just come out with a little pressure from behind... until I tried to remove the caps from my TRX wheels, which still have original tires. The caps had probably been there 28 years undisturbed, and I didn't want to break anything. So I put a 36mm stocket on an extender, put the wheel face down, and put the socket over the tabs on the back of the cap. The bevel of the socket's edge fit over the tabs just right, so that pushing down firmly pushed the tabs in and pushed the cap out a bit at the same time. After that, the caps could be pushed out normally without any damage.
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That's a really good idea, and nice to know the 355 type do in fact work. Thanks! I noticed they dropped right in my OEM wheels, but got stuck halfway in the Superformance wheels. As you say, some smoothing will probably fix that.