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Comparo: Reflex vs. PN MR03 Reverse Kingpin Front

Posted 07-25-2011 at 12:37 AM by color0
Updated 08-10-2011 at 11:14 PM by color0
I am fortunate enough to have owned almost all the MR03 front end setups available, and driven all of them: Kyosho stock, Kyosho aluminum, Atomic composite/aluminum, Reflex Long Kingpin, Reflex Reverse Kingpin, PN "hack" long kingpin, PN Reverse Kingpin, and PN Double A-Arm. Of these, I feel that the Double A-Arm provides the absolute highest mechanical grip, while the Reflex and PN Reverse Kingpin setups provide superior precision and consistency. Since I treasure both of those qualities over outright speed, I've come to like the PN Reverse Kingpin setup a lot, and now am beginning to understand the Reflex version. So, given my newfound familiarity with both, I thought it would be worthwhile to do a casual comparison of the two reverse kingpin setups.

Please let me make it clear that I am NOT going to declare one product superior over the other, because 1) I'm not in a position to and 2) honestly, I feel they're equally good, but in different ways. My only aim with this article is to provide a little bit of insight as to how these two front ends are different, how they are the same, and what prospective buyers should expect when deciding which one to purchase for their Mini-Z MR03.

Let me start with the PN setup. This is the front end that I use in the weekly races at RC Kenon, and the one that helped me TQ the RCX Challenge race earlier this year.

PN's configuration reverses the kingpin for proper smoothness, but keeps the stock spring mounting location. There's good and bad associated with that. Good: wide selection of MR03 springs, and you can go as soft to as hard as you want. The inboard springs are also out of harm's way, and easy to remove and change. Bad: well, the effective spring rate changes depending on how the arms are angled. If your arms are flat, like mine, there is a small region of (almost) linear spring action, but if you angle them up or down beyond a small range, you can feel that the spring rate is progressive. This makes the car a little difficult to tune quickly, since changes in ride height, preload or droop can affect the effective spring rate the car "thinks" it has.

On the other hand, PN offers Teflon balls for this front end, and once installed and broken in (the latter took a while), the suspension becomes almost frictionless. The balls are extremely tight at first, and it took about an hour of working the balls back and forth to break them in properly. I didn't need any polishing of the kingpins though -- they were mirror smooth out of the package. I think this front end actually has less friction than the Double A-Arm setup: whereas I can always feel the joints sliding on the Double A-Arm, when the Reverse Kingpin is maintained properly I don't get any hint of the sliding metal-on-metal "swish swish" kind of feel. Very impressive smoothness, which combined with the tight tolerances of the whole setup results in very good precision and "placeability" on the track.

More recently, I removed the PN kingpins and balls to try out the Reflex Reverse Kingpin kit -- not the whole front end, just the balls, kingpins and springs which are compatible with the PN arms.

Reflex Racing's reverse-kingpin setup places the spring underneath the lower arm, instead of inboard. It took a long time to put together, I'll say that much -- the springs are tiny and the E-clips have to be put in and removed every time you want to change something. However, the balls did not come out of the package too tight for the kingpins, and so there was no hour-long break-in period before the car was driveable -- this front end performs immediately. The spring-under configuration changed my car's behavior vs. the inboard spring config. Firstly, I liked the new linear feel of the front suspension, compared to the PN front end. Knowing that the spring rate will not go negative-progressive if the full suspension travel is used means that I'm free to set the upper arm angle to whatever I want/need for the day. And, no matter what arm angle I set, the effective spring rate the car sees will not change, so I can worry about fewer interfering factors when tuning the car.

I feel that the Silver spring was a little too stiff, and the Black spring a little too soft -- but that's just me being picky and the spring choices are not out of the correct range for carpet or RCP. When I raced at Cruzin' with RC's with the Reflex front end setup I tried the Silver springs and had a hard time getting the car to rotate, since the front end just wouldn't dig in. In retrospect I should have went with the Black springs, and preloaded them a bit to keep the ride height reasonable. On a high-grip track I would love this front end a lot more: it is as precise as the PN Reverse Kingpin, almost as smooth (the Reflex kingpins are not as polished as the PN ones), and the Silver spring would be absolutely perfect for my preferences.

And the end of the day, these two front ends perform at about the same level: on two separate visits to Cruzin with RC's, I managed to capture each time 2WD Mod 2nd place and the 2WD Lap Record. The change from PN to Reflex front end between the two visits did not drastically change my pace, but the Reflex front end was better in quick transitions (surely because of the spring rate?) while the PN front end provided more absolute steering and off-throttle steering (again, probably the spring rate). Both of them caught a LOT of carpet fibers that I had to clean out, although here the Reflex front end is at a disadvantage: with the springs under the lower arm, anything caught in there can jam up the spring and kill the car's handling without you realizing why. You can't raise the kingpin either without preloading the spring more than you'd want. With the PN front end at least the carpet fibers can't interfere with the springs, and you can shorten the kingpin to avoid scraping as long as it still fits in the lower arm balls.

There is of course a footnote to this experiment -- I didn't use the full Reflex Racing front end setup and instead tested a PN/Reflex hybrid. The Reflex tower bar adds some much-appreciated functionality to the package with its free camber adjustment and 2-4 degrees caster rather than 0-2. Those are my biggest gripes with the PN front end actually, the fact that I need to change the arm angles (altering my roll center) in order to get the camber I need for even tire wear, and that I can't get more than 2deg caster even if I actually need it.

If you've been keeping track, this puts my "cons" list for both front ends to 3 vs. 3, hence why I said at the beginning that I feel the Reflex and PN Reverse Kingpin front ends to be equally good. Both provide high performance and precision, are low maintenance by design, and are representing a good value for the serious racer. They are, however, limited in different ways, and so if you're shopping for a new MR03 front end, on top of deciding which type (stock? Reverse-kingpin? Double A-arm?) you want, I hope this article will be helpful to sort between the two most popular reverse-kingpin setups to make your decision.
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