[thefro526]

To accurately answer your question, we'd need a few more specifics - mainly track width.

In the case of long based robots, where your track (distance between wheel centers from one side to another) is around 22"-26" I've found that a wheelbase of somewhere around 14"-16" is optimal - this is around where most dropped center 6WD's fall in terms of effective wheel base.

When building long based 8WD's (track width of 22"-26"), I'm partial to doing unequal wheel bases to increase the resistance to turning a bit. Most Common 8WD's have an effective wheel base of 10"-12" and I've found that they're often prone to over rotating. To combat this, I'll either increase the center wheelbase to somewhere around 14"-16" or change the wheel drop arrangement to get a similar effect.

When looking at wide based robots, you can usually get away with having as long of a wheelbase as physically possible with no ill-effects. This is because a wide based robot often has a track of somewhere between 32"-36". Personally, I prefer as long as a wheel base as possible to avoid over rotating while turning when building wide bases, though some teams have found success this year with dropped center drives on wide based machines.

In the end, it's really a matter of driver preference too. I'd suggest building a prototype drive train where the wheelbase is adjustable without too much effort and see what your drivers like best and is best for the robot it's being built for.