Transmission/Differential Tuning

So I was going through a few different cars in my garage and playing around with the gears and I’ve come to a realization that to optimize top speed vs. acceleration is to find out what top speed the car can actually handle and adjust the trans/diff to a point where this speed is close to the top end of the final gear. Now my question is, is there some flaw in my logic or is it really this easy? I realize this won’t always work especially when the car isn’t very built. In any case, this way of tuning has proven it’s worth, but is it the best way?

Differential has nothing to do with gear ratios, but ideally, to set the gears properly for a track, you want it just so the power starts to fall off in your highest gear at the end of the longest straight on the track. In most cases, your method will work, but only for the highest gear you use. The other gears still need to be balanced well for optimal acceleration.

Ya I hear you. This was more of an all around for lazy people like me that don’t tune their cars for each specific track. And I always do go back and tweak the hears

I like to try and find gearsets used by actual race teams at the specific track I’m running, or simular track type. Though that is often a very difficult prospect as most teams keep their gearsets secret. But sometime you can find them, and I use them whenever I can. And will often use them as a starting place, and then adjust them gear by gear from there. There is a suprising amount of speed to be found from the gearbox. Much more so than almost every other individual part of the car. Tires, weight, and power being probably the biggest influences. But the gearset just behind those I believe.

I realize this is a slightly older thread but this is SO true! My profession is in the motorsports industry dealing primarily with engines/powerbands and, to some extent, gear ratio tuning (I’m one of those math types so I guess gear ratios just always made the most sense to me being that they are hard numbers and not a mix of constantly dynamic variables like suspension).
I’ll say this right now: playing with a calculator to account for the RPM drop to place it exactly on the torque curve is good up to the point that we start talking the highest levels of road course racing, you and your little calculator do not measure up to millions of dollars these teams throw at companies like Hewland and X-Trac to develop these gearboxes. Their ratios are set like that for a reason, while some of it can often be the limitations of the gearbox design only allowing certain less-than-optimal ratios to be used a lot can still be done through the use of drop/transfer/cluster gears that add another variable between transmission output and final drive.

You would be very wise to keep records of the original transmission/final ratios of each racecar before you tune anything. While I rarely leave one the way it was, I often find myself referring back to those setups for an entirely different car. On top of recording many of the close-ratio boxes I encounter, I also keep extensive records of performance transmission setups from companies such as Richmond, Rockland, Hewland, Quaife, RBT, and numerous OEMs.

For an American V8 or other low-revving, large-displacement engines (such as an Aston Martin V12) I typically use a Richmond, Rockland/Tremec T56 or TR6060, or RBT transaxle setup that is designed with somewhat wider ratios than most to best allow the engine to move through its power curve.
Richmond (best with higher-revving OHC motors like the Ford Modular):

T56 (pair with almost anything OHV):
2.66/1.78/1.30/1.00/0.85/0.76 (sometimes swap 5th/6th for a wider 0.80/0.68 for something like a Viper V10 with extreme low-end torque)
2.29/1.61/1.21/1.00/0.85/0.76 (most often with a highly-tuned or otherwise high-performance engine such as a Chevy LS7 or the older Shelby-tuned Ford 289 and rev-happy Chevy 302/327)

Porsches are a world of their own and typically a 3.15/2.00 swap into 1st/2nd is all that’s needed for a production model coupled with a 3.77, 3.88, or 4.00 final. For closer gearboxes I look to the 911 Cup and RSR units. Quaife makes a couple excellent full replacement ratio setups as well.
911 RSR (best for race models redlining north of 8500rpm):

Quaife close-ratio (usually with their 3.75 or 4.00 final although I’ve been known to use a standard 3.44 gear at times):
2.69/2.00/1.65/1.35/1.13/0.96 (optional 0.93 6th if I need it just a touch wider)

Anyways, that’s just a quick sample of what real world gearboxes for specific cars can look like. Remember, these companies have poured untold fortunes into R&D specifically for that exact vehicle. Not counting transmissions that make sacrifices for drivability concerns, a purely performance-oriented transmission for a specific car will often yield some of the best ratio spacing one could hope to achieve and the results often reflect the hard work put into the design. It might take a little google-fu on your part to come up something for a vehicle but it is well worth the time invested as a well-suited performance transmission setup can often make your car feel like a totally different vehicle.
Many supercar manufacturers such as Koenigsegg and Ferrari use a company called CIMA and they have race-oriented setups listed on their website. American/Australian companies use some variant of the T56 or newer TR6060 model almost universally minus the ZF/RBT transaxle found in the Ford GT and GT40. Hewland and X-Trac are almost always full-racing units that are often custom-tailored to their exact application; obviously a manufacturer-backed racecar such as the Corvette C5.R/C6.R is going to have the financing to afford a ground-up design or ratio package to fit their exact specifications. You won’t find much from X-Trac but Hewland (despite their relatively difficult website navigation) does give ratio charts for certain off-the-shelf designs they sell to privateer teams who don’t have the deep pockets to get the full engineering team involved (my personal favorite Hewland chart is the LSG transaxle as its wide range of available gear/final ratios allow me to tailed it to virtually any GT3/GT2/GT1 racecar and even many LMPs). Almost all of my gearing setups for R3 class and above full racecars are going to be a Hewland LSG, T56/TR6060, or Porsche/Quaife ratio set of some sort with minor adjustments as needed (on rare occasions I’ll pull from the RBT 6-speed gearing chart if the Hewland isn’t quite what I’m looking for).

I honestly spend more time on my gearing than I do the suspension. For the bouncy bits I just get them so they don’t bottom out, go to positive camber, or roll up on the outside edge of the tire. Beyond that I can completely change the handling and responsiveness of my car entirely with gear ratios and LSD settings (which are directly linked as changes in the output torque will affect LSD lockup both accel and decel). I can use my final drive alone to make a car do donuts in every corner or under steer tremendously! Controlling the rotation of the driven tires through a corner is what can separate a good tune from a winning tune, and that’s not even factoring in maintaining the optimal rev range for best power/acceleration/top speed. I could write pages upon pages on all the different ways to setup your gearing, though, so I’ll refrain from making this any longer than I already have. If you have any questions or need advice add me (gamertag: GTP EnzoGuy) and shoot me an XBL message as I’ll respond to that much quicker than a PM on the forum; if you have a mic I might even be able to give you a little personal gearing setup 101 for a specific car and help explain the what and why of the things I did along the way (FYI for the next month I’ll still be on leave due to a leg injury so try to catch me while I have the free time to help).


You are welcomed, indeed encouraged to write another 20 pages. I can’t get enough of people like yourself expounding on specs, and setups, and design limitations, and track to track setup compromises.

Please, please…

Another 20 pages! Please!

Thanks GTP EnzoGuy - I am similarly afflicted at time, but I doubt I am obsessed quite to the same extent as you appear! I often try mfg ratios if/when I’m playing with a car with adjustable ratios. another source I like are the race series spec/restriction sheets… (like markbell73 above?) - I do not have the link here, but Pirelli World Challenge site used to have a treasure trove of spec sheets.

I actually tune racing engines/gearing for a living. I’m not quite as obsessed as I may initially appear, it’s my job to know this junk haha!

To sum up sufficient gearing in Forza… Use the fewest gears possible while staying at or near peak power. That’s all you honestly need to do.

depends. is it a “sim” or a computer program (game) you wish to “game”

me, myself? there are times when I wana “sim” and others when I wana “game” - something to love about FM4.