Well curiosity got the best of me. I've seen all the set-ups in Europe talking about putting weight towards the rear in the mid-motor configuration, they have done this a number of ways-
1) dremeling the chassis to fit the shorty lipo sideways in the chassis
2) flipping the rear arms. (this does two things, it shortens the wheelbase at the rear end, and by doing that moves the weight distribution rearward without adding weight)
3) obviously the weight kit
so i got to thinking about this and wondered, can i get the CG the same as a rear motor with all these tweaks WHILE keeping 90%+ of the weight between the wheelbase of the car. Basically i was looking for something different. it comes with all these parts and personally i didnt see any reason it shouldnt work.
flame me for it...... i really dont care, my laptimes after some tuning were identical and if anything more consistent with the mid motor.
so heres the story of how it played out-
this testing was done at mikes hobby shop in houston. its an outdoor but covered 1/8th scale clay track. it gets sandy and slick off groove and will blue groove nicely. it was sandy and damp in the morning and dried out by the afternoon to be decently grooved and really a nice testing surface that wasnt overly slick but is pretty indicative of a typical surface out there.
i did a a lot of playing with the car on the bench at home and ended up with something like this-
the car has an almost identical CG to my rear motor set-up (casey pecks set-up) and i didnt change the pistons, springs, or oil weights from my rear motor. it has every piece of the weight kit on the rear end of the car, a full 70g over the back axle. it felt like a lot of weight over the back end and it turned out to be too much, the car was far too stiff and felt a little sluggish, i was fighting massive understeer.
i kept the springs the same and switched to a 55 piston in the back and 27.5 in the back and 32.5 up front. i took 12 grams off the weight in the back.
it felt better but still had understeer, so i changed the springs to red up front, and pink in the back, pulled a further 8 grams off the rear. it felt knife edged. it was great if you got it just right but loose if you were off line.
so i got radical, got out my dremel and flipped the rear arms. this took some work. some trial and error. but the end result was pretty impressive.
i had to trim down on side of the shock standoffs about 1mm. shave the shock tower just a little bit, then space the shock bottom off the arm 6mm. (it took some hits that day and i dont really have any durability concerns. )
after this i had ridiculous forward bite. so much so that it was wheeling more down the straight away than my rear motor EVER did. i turned the motor down a bit. the balance of the car was still a little loose so i made the rear camber link as long as i could to tame it down.... after that the car was absolutely dialed.
the end set-up being-
Front-
1 degree of camber
outside hole position with 4mm ballstud spacers
5 degree caster blocks
25 degree brass kick-up plate
red springs
32.5wt oil
55 piston
inside hole on shocks
slight toe out
aluminum camber block, hinge pin block, spindles, servo mounts and steering rack
Rear-
1.5 degree camber
inside hole on the camber block, outside on the rear hub
50g rear weight from the weight kit
2.5 degree anti-squat
3.5 degree LRC toe plate
+.75 rear hubs
Pink springs
27.5wt oil
55 piston
inside hole on shock tower
aluminum rear hubs
wheelbase all the way back with the rear arms flipped
Misc-
24mm ride height
Side guards trimmed to fit shorty lipo sideways
exotec carbon battery brace
stock battery brace trimmed to fit
M3 Proline Suburbs rear tires with stock foams
Soft AKA Rebar Front tires with AKA red Foam trimmed to fit
Viper VTX10 ESC w/ 8.5 motor
my laptimes are really consistent with it. it brakes like no other 2wd buggy ive ever driven. it has better forward bite than my rear motor does and more steering by far. the corner speed is pretty unbelievable by comparison. i think that with more track time i will undoubtedly be beating my rear motor times.
comments? questions? feel free to ask and discuss.
Matt