Version 0.240 wasn't the smoothest update ever due to some physics issues messing with vehicles, but I believe the problems are (mostly) fixed in 0.241. 0.241 isn't a big update, but the one new part needs a bit of a guide, so here we go:
The new part is Flex Treads. There are a number of parameters to change the treads and make them how you want. Note that not all combinations of parameters will result in well-behaved treads (particularly with extreme settings), and you can easily create wheels that aren't really attached to anything, but they'll still function fine.
LENGTH
Extends the length of the treads. This is one of the two primary size controls.
WHEEL SIZE
Expands the size of the wheels. This is the other primary size control.
FOUR WHEELS
When checked, the Extra Wheel X/Y values control the offset of two additional wheels. When not checked, there are two smaller mini-wheels (these collide but do not provide power to the treads, and use somewhat different offset amounts).
EXTRA WHEEL X/Y
Controls the offsets of the third/fourth wheels, whether they are full wheels or mini-wheels.
ROLLERS TOP/BOTTOM
These are visual-only rollers, and completely optional. I'd recommend messing with these last, after the other parameters are set.
TREAD COUNT MOD
This changes the number of tread boxes used when the game is running. You won't see any change during build mode, but this is important to physics/etc. Try to have treads that align on the edges with neither a gap nor overlapping for the best results. A value of 0-5 is usually good.
TREAD TENSION
I've tried to set the tread generation to automatically create treads (during gameplay) that fit your frame/wheels but with extreme values it doesn't alway work out. Use this value to fine-tune the size of the overall tread shape. A higher value reduces the size of the tread shape and increase the tension/tightness. Too much tension will break things. You can make the treads floppier by setting a lower value. Generally you want tighter treads to work better with physics, but floppier treads sometimes look cool.
TREAD MESHES
There are 3 mesh types for each of these. Choose from any combo you want. Here's what each one controls
A - The main body of the frame (the solid front/back)
B - The large wheels
C - The mini-wheels (only enabled when Four Wheels is disabled)
D - The rollers (these are visual only, have no actual collision)
E - The tread mesh (the thing that spawns in-game) - You can't see this in build mode
I think that should get you started. Let me know if you have questions/suggestions/etc.
[FULL CHANGELIST BELOW]
- Added new part: Flex Treads
- Fixed solid pipes having no player collision (the center part)
- Added adjustable ground dust amount for cabs/vehicle
- Fixed damage mod UI on logic gate
- Changed wave generators to use a limited range of timer values (internal code change to prevent long-term waves from degenerating)
- Reverted mass changing from Center of Mass fix (CoM still fixed, mass is left alone)