Regarding your first question, auto and manual transmission are just like a real vehicle. In automatic transmission, the gear is adjusted for you automatically as you change your speed, in manual, you have to shift gears on your own.

Hello
because when you are running auto transit, your car is increasing to the maximal speed while you pressing up arrow.
On the manual transmision, you have to press a to shift to higheer speed

sorry for my english

yes, with manual, you're in control of the vehicle. you change gears with a and z, whenever you want or feel like it. that's why you don't crash, because it sounds like you remain in first gear all the time. as for the second question, the file must be .wav, and renaming an extension, to my knowledge, won't do the job.

Thanks for your answer. Actually, you are write with the gear thing. I never changed it till now but whenever I tried to change it my car's engine starts slowing down i.e. they sound lower than first gear.

actually, that's expected. I mean, a real car's engine won't scream on top of it's lungs, will it? if you change gears, the engine sound will be lowered in real life as well. obviously, you don't suddenly want to put it from 1st to 5th, the car simply won't move, but you can gradually increase it.

And I was deciding to make some very powerful cars and tracks. Please give me some tips and tricks to set the values in the VHC as well as TRK files. Tell me that which type of track/vehicle you want and I will make one track and vehicle per category. Just I need some help with the values.

One thing you can do is that you can download the source code of this application and edit it as your wish.