OP:
Ive just started taking my tuning up a notch, as someone said earlier, stella stig offers a lot of open source tunes so you can go and edit them as you see fit.
Honestly, I found Moneyman300 youtube channel to be very helpful as far as tuning the handling. Goes through a summary of how to build a base tune, then how to diagnose problems and where to look to fix them, then has an in-depth look at each different tab in the tuning panel and explains the affects aswell as some of the forza physics based stuff that just works when in the real world it shouldnt (high camber with moderate caster, high rebound low bump etc).
From there I found I had a much better understanding, now when I read the descriptions in forza or looking at TGWormburner’s tuning guide here in the forums things started making a lot more sense.
Anyway, as far as Gearing goes, I too struggled to find any good tips on it other than final drive.
One thing I did find which im yet to test, is that the race trans comes with usually really bad default settings, using the forzatune app you can generally get a good reading on setting the gears within your powerband.
Ill explain how I do my gearing, whether or not its right or not Im not sure but its worked semi-decent for me, anaged a 10.4 1/4 mile on the rivals Executive drag (best time was 9.4 I think). full second behind but I only spent 15 minutes tuning and it was my first ever drag tune.
Anyway, I find theres usually 2 or 3 points in the final drive where your 0-100 drops to a low point. Ill use the cortina that I just tuned as an example. I could get a 9.287 with final drive set at 3.2, it then went back up to low 10’s then dropped back down to a 9.384 again at 4.1.
The 4.1 Had a lower top speed, by about 10mph but it seemed to be accelerating through the 50-120mph better (unfortunately you cant get a dino reading on that even though its where you spend most of a race).
On to tuning the individual gears. I usually take my car to the indy oval and get the max torque RPM (Start in 1st gear then shift up to 5-6th, bring up telemetry by pressing down on the dpad, note the torque, at a certain number it will top out then start to decrease again dont do this on the corners or the number will jump all over the shop. That peak torque number you need to remember then repeat the process, this time when the torque reaches that maximum you want to make a note of what the RPM reads, you have to be quick and generally I will take several readings before settling on a number to the nearest hundred.
This number will be your peak torque RPM. remember it.
I usually go for an acclereation over top speed, so ill use the benchmarks that forza gives me and adjust my 1st gear to give me a nice low 0-60 and 0-100 number.
The second gear, I will do the same and then again for 3rd, however I will make sure that these gears start at or above my peak torque RPM. Generally my second gear will be right on the peak torque RPM and third will start to climb away from it . I will also keep an eye on how tall or short the gears are (how long that line is) They generally should be pretty even, or getting slightly smaller as you climb the gears. 4th gear and beyond you will probably no longer be able to get a reading from the 0-100mph benchmark as you should be well and truly past 100mph. The only benchmark you could use now is the top speed but maxing that out now will throw the balance and youll find the gears will drop down way to low in the later gears and youll never reach them.
I find its best to use the start of the first 3 gears in the graph to draw a nice imaginary curve that sort of straightens out, 4th, 5th, 6th etc should then be adjusted to fit on to this curve while still maintaing similar lengths.
From there, take her out on the test track and give her a whir, if you find when you shift that the rpm feels like it drops too much, then bump that gear up some more and adjust the rest accordingly, usually only in small increments. I find I dont normally need to make any major changes at this point, usually just need to fine tune 2nd gear to shift a little better.
When it comes to your Viper and the overdrive gear bogging down, My only suggestion would be to follow the above but whenever you want to get a benchmark top speed adjust 6th gear as close to 5th as you can to get a reading then re-adjust back to fit that curve just in case you do find yourslf needing to shift to it… and so it looks cleaner on the graph.
Finally, if your not reaching that top speed your after but your shifting through gears smoothly, try shifting your final drive to widen the ratio, you should be able to squeeze plenty more top speed since you tuned to accel to begin with, when you move the final drive it will shift everything evenly but the top and bottom of the gears will stay the same so you wont be falling out of that power band and having boggy gear changes.
NOTE: Most of my tunes have pretty steady torque and HP curves and usually run stock aspiration or centrifugal sc, Using something like one of the rally engines or a twinturbo with a steep torque may change how this all works, i couldnt tell ya at the moment…
And thats it… it could be completely wrong and I would honestly LOVE for anyone to point out anything Im doing wrong because I sort of figured most of that out by myself, theres no hard science to back my method up other than the peak torque RPM.
Quick alternative method, use the Forza tuning App to set your gears, it also uses the peak torque rpm to determine gear placement but it also uses some fancy maths stuffs to set individual gears that still fit within the powerband. Unfortunately I havent seen the formula behind it as it considers displacement, drive tire size and aspiration in its calculations.