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Body Comparo: Mosler vs. 599XX vs. GT-R GT500

Posted 07-13-2011 at 06:51 PM by color0
Updated 07-13-2011 at 07:01 PM by color0
Hi folks, going back to a more general-racing theme this week -- today's article will be about three of the most popular 98mm racing bodies, the Mosler MT900, Ferrari 599XX, and Nissan GT-R GT500 2008. Since I've raced and done well with all of them we can explore their characteristics, quirks, pros and cons, and hopefully it'll be some additional insight that you can use to improve your Mini-Z game.

First let's look at TRP's racing phenomenon, the Mosler MT900:

This body is BIG. Though it comes with wheels that have +2N and +3W offset, it can handle waaaay more than that, I'd venture even +3.5N/+4.5W would still tuck under the fenders. It's also heavy. Even with a lot of shaving and trimming effort on my part, it still weighs 37g with paint -- an unmodified example could easily surpass 45g. All this width and mass makes the Mosler an exceptionally stable body, perhaps not the fastest in lap times but very forgiving to drive for long times.

That said, even though it's so wide, the Mosler can still traction roll! In stock form the Mosler is a high-roller, leaving plenty of space for suspension travel but in doing so, placing a lot of plastic up high, creating lots of body roll. This amount of body roll generates a good amount of grip on RCP and carpet, but at the same time it makes the car sluggish, and transitions are not the Mosler's strong point.

Speaking of transitions, the Mosler's cab-forward design places weight, pressure and downforce on the front wheels, creating steering and rotating the car around the front end. Not at the front wheels exactly, but the point of rotation is definitely front-biased. Entering a corner, if the rear wheels slip out you'll notice that the drift is being carried by the fronts. Like the body roll characteristic of this body, it creates great steady-state cornering but it's not going to be fast in dynamic transitions, which favor mildly understeering bodies. To tone the effect down with the Mosler body you'll have to adjust your setup towards understeer to compensate for the Mosler's dive-bomb-into-a-corner character.

To get the most out of the Mosler body involves a great deal of work: I lowered mine 5mm (5mm!), shaved some of the inside, cut out the windows individually, took out the rear bumper almost entirely, and finally added a Gurney flap-type spoiler to get rear downforce without restricting the rear from swinging out (I like it, actually, it's fun). These modifications brought the shell down to a reasonable 37g weight, very low (tucking tires low), transitions are made much faster and the Mosler's corner speed is largely unaffected, so it becomes an all around better body when you shave and slam it.

(Nevermind the Reflex scoop wing, it was sitting there as a mockup)

One last note about the Mosler is that available clearance for tri-shock suspension setups is slim: if you don't lower the shell, the PN tri-shock will clear the fenders and the Reflex tri-shock can fit with some coaxing, but if you've lowered it you can expect to cut two gigantic holes in the rear fenders to clear any tri-shock setup you might be running.

Next then is the body I ran for everything before getting the Mosler: Nissan's GT-R GT500 2008.

It may not look like it, but this body actually has the same-height roofline and lower CG than the Mosler! It isn't nearly as wide as the Mosler, coming stock with +2N/+2W rims and not really accepting any more than that safely (+3W rears will fit, but be wary of race damage...). It's also much easier to get into running shape, and sits at 34g with only mild modification and full paint. It's still wide enough and heavy enough to be a forgiving ride, but the first thing people notice about the GT-R is how nimble it is for a 98mm longtail body.

The GT-R rides flat -- unless you purposefully spring the car way soft, you can't see it roll in the corners. The lack of roll makes the GT-R extremely nimble for its weight, it likes transitions much more than the Mosler. The flip side is that it doesn't generate a whole lot of grip since it just doesn't put any pressure on the tires. This relegates the GT-R to usage only when there's enough grip, such as high grip RCP, regupol, or for AWD cars on carpet. As I demonstrated to myself at RCX, the GT-R becomes a drift car when there's insufficient traction -- it's only nimble and quick when the traction is already there.

Being a neutral-cab design (a little to the rear, but not extreme) the GT-R rotates around whichever tires have more traction (hopefully, the rears!). So it's fairly versatile for driver preference in that you can move the car's pivot point to where you want it to be rather than complying to the shell's natural characteristics. Playing with tire combinations I've been able to make the car rotate around the rear tires, super stable, all the way up to drifting every corner entry like the Mosler does. Its dynamic behavior is very easily tuned and that's the cool thing about the GT-R.

Unlike the Mosler, the GT-R is good out of the box: sure, the rear diffuser creates a parachute effect and the front splitter catches on the rails, but cut those off and you're already good. Downforce is balanced front and rear and it's really your choice if you want to run a custom rear wing -- I've tried both and the car works great either way.

One last note for the GT-R: the front splitter is the source of the front bumper's strength. Cut it off and the shell becomes a lot more fragile immediately. As I've found out, it can crack all the way through from the ground to the headlight if you hit another car hard enough at just the right angle! I would suggest trimming down the front splitter on this body but not shaving it all off.

Lastly, let's look at the recent "hot body" of choice, the Ferrari 599XX:

Given the front-engine GT shape of the 599, the easiest comparison to make is that between the 599 and the GT-R: the 599 is the same height, nearly the same dimensions, heavier and wider and extremely cab-rear in design -- just take a look at those front fenders! The 599 comes stock with offsets of +3N front and +3W rear, and honestly that's about the practical limit for this body. Going any wider would seriously endanger the wheels, and the tires would rub the body too unless you raised it. Weight falls in between the GT-R and Mosler, at about 36g with paint after mild modification. As you might imagine, the result is a body that is neither as stable as the Mosler or as agile as the GT-R, but a nice compromise between the two.

Like the GT-R, the 599 rides very flat. Given that most of the plastic in the front half of the car is very low, traction rolling is pretty much out of the question unless your tires are folding over. Given its in-between weight and wide, stable offsets, the 599 will not be the quickest through the chicanes but it's certainly safe to push it through, unlike the Mosler which will sometimes fight you to stay on its own trajectory instead of yours. However, the extreme cab-rear design places more weight on the rear wheels than the other two bodies, and the 599 generates grip even in low-traction conditions, making it more adaptable than the GT-R.

The cab-rear design has two more important characteristics. First, the weight and pressure being focused on the rear half of the car leads to naturally "pushy" or "planted" tendencies. Unlike the dive-in Mosler, the 599 sits on the rear wheels and will push in the infield unless you compensate for it with front grip. However, it's so far back that it also seems to block airflow to any wing you may have on the back, making it a little less efficient, thus counter-intuitively freeing up the rear end! This gives it a lot of steering at speed, which is good and bad. Unlike the Mosler, which will happily carry a drift with its forward-biased CG, the 599 will hook the front tires and spin if you let the rear step out too much. So in terms of driving behavior, the 599 is not a car that you want to let loose -- its natural tendencies are to stay planted and it simply doesn't like being pushed out of that.

The 599XX is honestly very good out of the box, very little modification needed. In fact all I've needed to do to make it fast are cut out the rear spoiler and rear diffuser, and tack on a Reflex wing. Didn't even need a dremel -- all of this can be done with a humble Xacto knife. That said, if you lower this body you'll quickly find that transponders won't fit in between the hood of the 599 and the top cover of your chassis. Plan accordingly, I've started to run my transponders on either side of the top shock.

So which one should you choose? The Mosler, being wide as it is, seems like the go-to choice for wide open layouts -- high corner speed, stable, produces downforce. It's also a good body for those who like a more "dynamic" driving style. The GT-R is the fine precision scalpel for high-grip, quick tight tracks -- extremely agile, very sensitive to tuning, and a bit narrower than the other two so it can squeeze in tight spots if you're on your game that day. And finally there is the 599XX, which I'd say is the easiest to live with of the three: it doesn't take much work to get going, the rear tends to stay planted (i.e. it doesn't EAT tires), hooks up on low grip and doesn't traction roll on high grip. All three are excellent in their own ways, so I would encourage you to use this review to choose one based on what kind of car character you like the most.

Next week -- SC430 vs. F430.
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