I don’t think this will be a problem with pretty much any size wheels/tires. The gearhead motors have a LOT of torque to them and I’ve actually had to cut speed back to keep things from hitting walls and doors. 
8-Dale
Ok, my care package arrived yesterday with another battery some switches and the like so I finished moving everything over to the new chassis. Its nice to have the room. I was able to fit the three 2800mah 6 v batteries, plus the sabertooth plus the BB2 and the PS2 receiver all in the new case. 
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I even made a new top for the rover. http://i416.photobucket.com/albums/pp245/Kurts_Robots/DSC03263.jpg
I split the top into two parts. The main part has the arm, the switches, power charger plugs, a hole for the arm servo wires to go through and an RS232 plus to program the Atom Pro with… The smaller part has an LCD display in it and is easy to take off and is over where I have the BB2, such that I can play with the wires…
Sorry the picture shows it in a state of being torn apart again as I am having some problems, that I am trying to diagnose. 
I think I may have somehow fried my Sabertooth. At first only one side the wheels would turn and then neither and the wires were getting really warm. I tried removing all of the wires from it to localize, but it appears to short out with only the power wires connected. The power wires are still getting hot and the little LED on the board is not coming on. Looks like time for another order…
Kurt
We’re now selling a v2 chassis upgrade kit:
lynxmotion.com/Product.aspx? … goryID=135
This includes just the aluminum side brackets and lexan top/bottom panels, to replace the v1 brackets and lexan.