speed and gradient capability are not as per the real data

HI, I am facing a problem using newton vehicle. I have real parameters for heavy truck. When I applied the same torque as given by the manufacturer, maximum speeds are no where near the expected. At the same time my vehicle climbs up any gradient, if I set the mass to a lower value. Main problem, I observed here is with the rolling resistance, I mean, the vehicle comes to a constant speed at a particular torque, but this torque is increasing from gear to gear(with the vehicle speed). The variation so much, which is not expected. How can I avoid this? Friction values are not effecting my speed. very low friction values reduce the speed too much. but beyond certain value, its not effecting at all. Any Idea????

If you're using Newton Game Dynamics as physics engine you wrote in the wrong forum, you have to go to OgreNewt.

He didn't say he used Newton - I think I hear him say that he used Newtonian movement laws on the truck.
Let him have a chance to clarify.

hey, I am using ogreNwt

Sorry guys, I did not realize that I have posted it in wrong forum

He didn't say he used Newton - I think I hear him say that he used Newtonian movement laws on the truck.
Let him have a chance to clarify.

This is why i wrote "if" first