My SCX10 II leans too much and tips-over too easily...

[fyrstormer]

...especially when it's leaning to the right on an off-camber left corner. Granted that's the worst-case scenario since the drivetrain torque-twists the chassis to the right when moving forward, but my Ascender and my TRX-4 are both more stable in the same scenario -- even though they are also both heavier than the SCX10 II. But even when side-hilling in a straight line my SCX10 II is much more likely to roll over sideways and go tumbling down the hill. It's quite irritating.

The frame and suspension setup are stock, though I have some aluminum crossmembers to stiffen the frame, and I've got brass axles and brass knuckles to lower the center of gravity. The brass weights wouldn't affect how much the chassis tilts, but it should at least make the truck less likely to tip over completely. The extra weight does make it somewhat more stable, but not enough to keep up with my other scalers.

Btw, none of my scalers have heavy accessories attached to the body, like roof racks, spare tires, etc. The only weight above the chassis is the Lexan body and the LED lights, which are not heavy because I don't use big light bars. So I'm really at a loss to understand why my SCX10 II torque-twists so much and seems so top-heavy. I would've thought the TRX-4 would be the most top-heavy truck in my collection since it has that hard plastic rollcage, but it's actually more stable than the SCX10 II is.

I'm not sure what else to try, short of taking the wheels apart and wrapping them with lead tape to add even more weight down low. Thoughts?

[soze]

What you got for Tires and foams? Would also help to know which SCX10 II and what body you have too.

[fyrstormer]

Axial "Falken Wildpeak M/T" tires (vented), whatever foams came with the SCX10 II kit (larger and stiffer than the foams that came with the Wildpeak tires), and Pro-Line FaultLine 1.9" beadlock wheels. Same tires/foams/wheels I run on all my scalers, so while they may not be the best in the world, they are at least not a variable in this specific problem.

The body is the SCX10 II kit Jeep Cherokee body, with no "scale accessories" attached, so it's as lightweight as possible.



Here's a couple more pictures, showing the tires when they're actually loaded -- they support the weight of the truck just fine:





I know it's tempting to point at the OEM tires and open-cell foams and say "there's your problem", but when I look at the truck when it's driving, the tires only deform significantly when cornering at full steering lock on a high-traction surface -- and that isn't even when the truck is most likely to fall over. Whereas I can clearly see the suspension tilts too easily, but I can't figure out how to adjust the suspension to correct this. If I step-up the front springs from medium to firm, the chassis still tilts too much thanks to the soft springs in the rear. And if I step-up the rear springs from soft to medium, the rear shocks are constantly topped-out even with the preload set to zero because there's almost no weight in the rear. When side-hilling on a "smooth" grassy hill, the truck is likely to tip its ass right over and roll sideways down the hill if I blip the throttle a bit too much.

I was thinking about moving the mounting points for the shocks further outboard from the stock position using spacers and longer screws, to give the shocks more leverage to resist chassis tilt without using stiffer springs. It worked very well on my Ascender, but the SCX10 II's lower shock mounts are so close to the axle bodies that the shocks' lower eyelets would interfere with the front steering knuckles and rear axle extenders if I moved the lower mounting points further outboard. I could perhaps attach the lower shock eyelets to the same mounting holes as the lower suspension links, which would give me the room I need to mount the lower eyelets further outboard on spacers, but then I'd lose some suspension height for clearing obstacles.

Meanwhile, making the suspension less tippy still won't solve the problem that the whole chassis seems to be just a little too top-heavy, because the truck rolls over at a shallower angle than my other scalers. Lowering the center of gravity of the sprung-weight would fix that, but looking at the chassis I can't see any feasible way to do that -- everything except the battery is already mounted as low as it can be, and there's no room for a LCG battery tray as far as I can see. Moving the battery to the rear might help, but then I'd lose the forward weight bias that helps the chassis tilt forward when the center skidplate gets caught on an obstacle.

A front-motor/mid-battery mod would probably be a good solution, but I don't know if that exists for the SCX10 II, and even if it did it would require so much work I might as well just build a new truck from scratch. And anyway, my Ascender doesn't need a front motor/mid-battery configuration to handle the same stuff with less drama.

I'm stumped.

[fyrstormer]

...okay, I guess it's time to get out the ruler and do some math.

My SCX10 II has the same track width as my Ascender, at 235mm with the same wheels and tires equipped. But the Ascender has a rear lower shock eyelet spacing of 115mm (with spacers installed to move the lower eyelets 12mm outboard on each side, for a total of 24mm), whereas the SCX10 II has a rear lower shock eyelet spacing of only 98mm. The Ascender has a center skid clearance of 69mm, whereas the SCX10 II has a center skid clearance of 80mm. If I move the lower shock eyelets to the same mounting point as the lower suspension links (to give myself room to mount them further outboard without interfering with the axles), I'll lose 6mm of center skid clearance -- but that will still leave the SCX10 II with 74mm of center skid clearance, 5mm more than the Ascender has. So the SCX10 II's ability to clear obstacles without getting stuck should still be comparable even with the decreased ride height. I know that moving the lower rear shock eyelets further outboard will improve the chassis-tilt problem by giving the shocks more leverage to level the chassis, without requiring stiffer springs that would keep the rear shocks fully-extended even with no preload. So I guess that's the approach I should take to reduce chassis tilt.

But I still don't have any good ideas to lower the chassis' center of gravity.

[lonleycreeper]

I have always run my scx10's as low as they will go, by using the softest springs I can find. My honcho got its springs swapped front to rear and the rear shocks laid down, knocking about 3/8" out of the ride height. Steel wheels and small tires makes her quite stable, though I cannot know how it compares to your ascender and trx4. Ran with a new 1.9 Wraith, and we swapped tx's for a bit. The Wraith was stupid tippy compared to my Honcho, and I rolled it multiple times because of it.

He was running Pitbull xor's compared to my 4.3" proline tsl's.

[fyrstormer]

I made the changes I speculated about in my post last night, and had a chance to test them tonight after the female relationship unit went to sleep.

Yeah...I should've just made those changes before starting this thread, and saved everyone the trouble of reading it. But apparently I needed to write out my thoughts to fully clarify what I wanted to try, before actually attempting it. Lowering the ride-height by mounting the lower shock eyelets to the same mounting point as the lower suspension links did indeed give me the space I needed to move the rear shocks further outboard on the rear axle, and that change has significantly improved the stability of the truck.

The wider stance of the rear suspension significantly reduces torque twist while still being able to use the original soft springs, the 6mm lower ride-height makes the truck much less likely to tip over at reasonable tilt angles, and the 6mm reduction in center skidplate clearance only had minor effects on the truck's handling of obstacles -- not enough to make the truck unable to clear those obstacles, it just drags its center skidplate more than it used to. I can accept that tradeoff in exchange for not needing to grab the truck before it tumbles downhill nearly as often.

There is one meaningful downside, and that's the approach angle of the front bumper. The big bulky Warn-style front bumper that I got from Pro-Line doesn't have the best approach angle anyway, and even lowering the chassis by just 6mm is enough to make approaches more tricky. The bumper has multiple mounting points so I could raise it, but when I tried a higher position while originally building the truck it just didn't look right. If there were a similar bumper with mounting points for all the same lights I currently have, but with greater underside clearance for a better approach angle, I'd seriously consider it.

- - -

The next question I have to ponder is: Do I want to install overdrive gears in the front diff case, to improve steering and reduce and tire deformation in sharp corners, at the expense of increasing torque twist? I've had the overdrive gearset sitting in the spare parts bag for months. I just can't decide. I have overdrive gears in the front of my 2.2" Wraith and it works very well, but the Wraith is a much larger and surer-footed truck to begin with, so a little extra torque twist makes no difference to it.

[Browneye]

Originally Posted by fyrstormer

The next question I have to ponder is: Do I want to install overdrive gears in the front diff case, to improve steering and reduce and tire deformation in sharp corners, at the expense of increasing torque twist? I've had the overdrive gearset sitting in the spare parts bag for months. I just can't decide. I have overdrive gears in the front of my 2.2" Wraith and it works very well, but the Wraith is a much larger and surer-footed truck to begin with, so a little extra torque twist makes no difference to it.

I have not tried an overdrive gearset myself but have not heard of anyone that wanted to go back to 1:1. It was explained to me that it literally pulls the rig through obstacles and over breaks. The new element comes with it, which I'm excited to try, and the TRX has a easy change-out as well that seems to be gaining popularity.



I say try it and let us know what you think.

[lonleycreeper]

What Browneye said is true. Tq twist is not a factor, and even lessens it to some degree. The truck feels more planted on climbs and usually turns tighter on top of it.
Throw that gear set in, you will not be disapointed.

[Browneye]

Tucked in bumper...and why truggys are so popular for comp rigs.

[fyrstormer]

Originally Posted by lonleycreeper

What Browneye said is true. Tq twist is not a factor, and even lessens it to some degree. The truck feels more planted on climbs and usually turns tighter on top of it.
Throw that gear set in, you will not be disapointed.

Having an overdrive gearset in the front does produce extra torque twist, I know this from putting one in my Wraith. Torque gets "stuck" in the drivetrain as a result of the front wheels trying to rotate slightly faster than the truck is moving, and the rear wheels trying to rotate slightly slower than the truck is moving. You can see the same effect by jamming one axle so it can't rotate, and then trying to rotate the other axle by-hand; the chassis will tilt slightly. The effect is more obvious on high-traction surfaces or when the tires are grabbing hard onto the surface of an obstacle, whereas on low-traction surfaces the pent-up torque in the drivetrain dissipates by making the tires slip a little.

It does definitely help with turning radius and climbing over obstacles though. I'm just wondering whether those improvements are worth the extra torque twist on a truck that already has a bad habit of tilting too much already.

[DukeMinnix]

Has the 10.2 AR44 axle got an overdrive gearset I'm unaware of? I was under the impression you could only get overdrive utilizing the AR44 axles within the trans/transfer case.

[Topher Builds]

Originally Posted by DukeMinnix

Has the 10.2 AR44 axle got an overdrive gearset I'm unaware of? I was under the impression you could only get overdrive utilizing the AR44 axles within the trans/transfer case.

Yes, Hot Racing and Boom Racing make one. 27/8

The Boom racing is keyed and I'd recommend that one first, I've used both though without any real issue.

[fyrstormer]

Mine is a first-run kit that has the locker separate from the ring gear, so the Hot Racing overdrive gearset is the one I got.

To be honest, the other reason I haven't installed it is because there's no comparable overdrive gearset for my Ascender. I'm trying to keep their performance as comparable as possible so I can drive either one without wishing I'd decided to drive the other instead.