The Build..?

As I barely get time to play the Xbox, I appreciate being able to read all these tuning notes on the forums so when I do get a chance I can jump on and tune whilst referencing ONR Roadrunner’s formula’s, Worms principles etc.

The one thing I always get stuck on is the build, this is extremely important and I feel I’m missing something crucial here.

How do you guys choose to when to upgrade tire compound or width?

When do you choose the rollcage option and race weight reduction?

Are you really just looking at a weight vs power balance, are there any simple rules to follow?

I have a feeling it’s all down to how the car feels on the road, so it’s all trial and error. Any help would be appreciated.

It all depends what ur end goal are.

for me the build comes down to fit for purpose meaning all depends on the class and track or whether you want a speed or grip build.

For instance lemans cars are full weight no aero lots of power but that being said that car then wouldnt work on laguna seca so make sure you know what you want from it if unsure have a look at some replays and look at the tyres etc to give you an indication of where to start.
When building a car i usually go conversion then handling then drive line and then tyres and if i can engine upgrades. In the lower classes you can run stock compound on your
cars and still hit decent times on the lb.

The main thing is just experiment with the build its more trial and error, if it grips but feels slow take some tyres off and add power and vice versa and as for rollcages some cars need them some dont but in fm5 i find with muscle cars or a car with no tyre compound it helps with grip out of the corners.

If your want any help send me a msg when im on and ill point you in the right direction.


I am an amateur, but I truly love to build. My first goal is to buy all the things I feel I need, then I buy what I feel I want. Whatever Build/Tune I end up with, its going to sit on the tires, wheels, and rims.

Personal Shopping List (in the order I buy them)

  1. The best (lightest) wheel. Most add wheel as an afterthought. I can’t pass up unsprung wt. reduction
  2. Forza Wings - I can turn settings down if I choose, but I can’t pass up the PI
  3. Platform - Race Differential only, for now
  4. Handling - Every Race Part, but not roll cage yet
  5. Conversion - Centrifugal Super Charger (a 5,7L motor swap if I have a lot of PI and one is available). I only use turbo and twin super if I have no other choice. I rank them centrifugal supercharger, normal aspiration, and then everything else. Now is when I torture over Transmissions and Roll Cages.
  6. Compound/ Tires - I like the best compound and tires I can afford and still be able to to upgrade the motor parts to achieve the speed and acceleration I want. If compound cost to much to buy any tires, I reduce compound and go with better tires.
  7. With small amounts of PI left. I buy drivelines. If points remain I buy Rims ( I love them). The last “squeeze part” options, for me, are flywheel, bumper, skirts, and hood.

This method combined with my mediocre tuning skills tends to produce cars that are less than Leaderboard #1’s, but it’s big fun!

How do you guys choose to when to upgrade tire compound or width? Is it a handling track? Or is it a speed(acceleration)track like Sebring, Rd.America, Atl.

When do you choose the rollcage option and race weight reduction? Does adding the roll cage reduce pi? Sometimes a couple of extra pi points can help you add width or a few more hp.

Are you really just looking at a weight vs power balance, are there any simple rules to follow? Centrifugal s/c most bang for your pi buck. No clutch, flywheel. Usually stock, street,or sport transmission. It really depends on the track and what you need power or grip wise to get around it as fast as possible.

Thanks Holty, say for a Le Mans build - how much do you prioritize brakes/handling aspects. You’ve really got to be comfortable pulling the brakes at ~190mph (B Class) to get into those corners right.

It’s probably the hardest answer to take, but I really just have to hit the test track and test and test again!

Cheers Befuddler - I’ll agree with you on the fun part, it’s definitely more enjoyable chasing down people in rivals and lobbies with cars that you have built yourself. You raise another good point, engine swaps. Supercharger’s are agreed to be superior in most situation, so are engine swaps largely based on getting a supercharger on? It’s good to see another order of building, opens up my eyes to a different approach.

Good point re the tire compound. With the roll cage, at what level does the weight added outweigh the power/handling you get back with PI - is this just another matter of trial and error?

I get the feel that we under appreciate all the work these top tuners put into their cars and then release them over to us, especially the open source tunes. There is definitely a lot of time (and effort) saved by reading these forums, for the more casual gamer. Thanks!

Trial and error. As you get more familiar with the tracks it will be less trial and error. If you look at the track in terms of handling or speed, things will fall into place easier. On a track like Prague the extra weight won’t matter as much because it’s a momentum track and you are carrying speed so slowing down a lot less. When a car has to slow way down for low speed turns, the acceleration is going to be a lot more important.

One thing i tend to do (In FM4) I leave the build 20-40PI “short” Lets say full class is at 600, I leave the car to 570’ish PI, Then I throw in rough tune. Nothing too specific, Just something that should work decently.
Then I have 10-20 lap session on the track, just to get some feeling of that car. and think "at this point, what would bring me most time. Weight? Grip/Handling? Power?
If the car feels underpowered, I go for power, If it feels just way too loose, Grip/Handling, If it feels quite good, Nothing really stands out, I go for weight if I have the option, If I don’t, I try to share the remaining PI with power and handling.

It never brings the right build at first, but it helps you get close.

I start with all tunable parts except brakes, then supercharger and then lowest possible weight, lighter rims upgraded to at least 17-20s. I then add wider tires and add a little more power or whatever is needed to Max pi.

I then work my way towards tire, brakes, transmission, and rollcage upgrades

Everybody, every car, every track has a way to build the car. Normally by looking at the track (fast or slow track) will give you a general idea on the style of car you want to build.

Road atlanta full, road america full, Indy gp, bathurst are builds that i would consider speed tunes. Not pure speed but something with plenty of power. For B class i would normally go around a 5.0 handling for these tracks and the rest is usually power. The trick is finding the correct 5.0 handling to work with. Do you go with less weight and lower tires or do you go more weight and better tires. Thats the part where you just have to trial and error on the car and the track. I usually go with lower weight and less tire compound so i get the best accel out of the car thru the higher gears.

So when i go about building these my first build would be to get it to a 5.0 handle with the least amount of PI used (yes you will have to switch around parts to find the lowest amount of PI and the best lateral g’s. Now after that i would start throwing in the power to get the most out of it (5.7 L with a centrifugal supercharger for example). Once close to B600 with the most amount of HP and lateral g’s go in and look at wheel and driveshaft combos last. After this step I have the general build but its only 50 percent done. Without going into tuning talk this is where you start to experiment. Build another car with more more weight and higher race compound and see which one drives better. Once you have picked the one you want to go with start your tune. Now if its still not giving you what you want experiment some more with taking in and out the rollcage, tire width, rim size and so on. The journey never ends looking for that special car that works for you. I know this was long winded and possibly confusing but i hope it helped in this never ending journey called tuning.

Mate that perfectly sums it up for me. I hear people in the lobbies rattling off “Oh is that the 6.5 speed tune or the 5.3 handling”. These numbers obviously mean something logically in their head but it’s good to know what sort of build you’re aiming for in B Class.

Thanks to everyone that has replied, looking forward to jumping on Forza this weekend and giving it a crack!