I have upgraded to 12 inch wheels with air tube tires. This jump seemed a bit risky, would the new setup overwhelm the robot? Once I modified the wheels and came up with an initial mounting scheme to test I think the 12 inch is closer to what the robot naturally wants to have. This should boost the maximum speed of the machine to around 20km/h which is probably as much as you might want on something autonomous. For example, if your robot can out run you things get interesting.
I had to get the wheels attached in order to work out clearances for the suspension upgrade. While the original suspension worked great for a robot that you only add 1-2kg to, with an itx case, two batteries, a fused power supply etc things seem to have added up to too much weight for the springs to counter.
I now have some new small 'coil overs' in hand which are taken from mini mountain bike suspension. They are too heavy for what I am using, with around 600lb/inch compression. I have in mind some places that use coil overs in between the RC ones and the push bike ones which I may end up using. Also with slightly higher travel distance.
As the photo reveals, I don't actually have the new suspension attached yet. I'm thinking about a setup based around two bearing mounts from sparkfun. I'd order from servocity but sfe has cheaper intl shipping :o Anyway, two bearing mounts at the top, two at the bottom and a steel shaft that is 8mm in the middle and 1/4 inch (6.35mm) on the edges. Creating the shafts like that, with the 8mm part just the right length will trap the shaft between the two bearing mounts for me. I might tack weld on either side of the coil over mounts so there is no side to side movement of the suspension.
Yes, hubs and clamping collars were by first thought for the build and would be nice, but a reasonable result for a manageable price is also a factor.