I have mine set up with axle directly above and it works fine. One disadvantage is that front wheel is higher than rear, so you feel like riding slightly uphill. More weight is on saddle and groin tends to go numb much more easily than on trainer (rollers also force you to put minimum weight necessary on bars, which may be a contributing factor). Unfortunatly it's close to impossible to stand on rollers, so it's necessary to stop every 10-20 minutes to relieve the pressure.