The lack of adjustment on motorcycles can create problems for back muscles and sore wrists. On a high performance bicycle body position is critical. One of the best books on cycle fit is "The Custom Bicycle" by Michael J. Koln and Denise M. de la Rosa. Bicycle setup is covered in Chapter 20 (pg. 187 to 219). Check
scripd.com - Presentations Resources and Information. for a download or Amazon.com for paperback. The other source for positioning in the aero tuck is "Zinn & the Art of Triathalon Bikes" by Lennard Zinn. See Chapter 3 (pg. 41 to 71). On a motorcycle there is the seat height and the handle bar position to modify. A 7/8" diameter tube fits both a motorcycle and a bicycle so there some variety. Note both Craig Vetter and Alan Smith made changes to their handle bar geometry.