So after playing H2 on the 360 for a week I had some luck on a scratch card and decided to get an Xbox one with the Ultimate edition.
I’m up to level 17 and at the 4th location, and wondering how I tune as the only thing I can seem to do is change the tyre pressure, all the other settings have a padlock next to them, I thought maybe they’d unlock like other things have but it doesn’t say when I try.
Any help would be great thanks.
You need to purchase those items before you can tune them. So if you wanted to adjust your suspension you need to by suspension parts. Same goes for gearbox and diff etc
Buy other parts for your car first like “race brakes” then you can adjust the brake-settings in the tuning-section.
right so I need to have a non stock engine, ok thanks for the help.
No, you don’t need a non-stock engine; as you see from all the tuning options, there is 0 options that allow for adjusting the timing of your engine or the combustion moment.
For your reference, do have a read in all the Tuning-subforums for the games listed in these forums 
about to have a look now thanks
Upgrades as follows:
Tires - can always be adjusted
Gearing - buy sports transmission for final drive, race transmission for all gears
Alignment - buy race suspension (also allows springs and ride height adjustments as well as damping)
Springs - see above
Damping - see above
Anti-roll - buy race anti rollbacks front and back
Aero - buy forza aero (front bumper and rear wing only).
Brake - buy race brakes
Differential - buy race differential, this adds nothing to car class so always buy it, anything you do to it has to be better than forza defaults).
Mostly everything you need is in platform and handling area.
Hope that helps