When i bought my coach, every manufacturer was putting their longest coaches 36 to 38 ft on 22,000 lbs chassis with the longest WB being 228 inches. One of the reasons I went where I did was the 24,000 chassis and 254 inch WB. Some one here has a formula for length to WB ratio. You might try using that. I think a 34 ft coach on a 228 WB is OK but not longer