Tire pressure

Update Feb 16th; I’ve debunked my original thinking, partly. Some cars respond well to balanced pressures. Most seem to like a similar stagger but not to full extent of their weight distribution–the farther they are from 50/50, the less proportionate weight and tire pressure can be. That said, I have had good results with certain cars with 10psi or greater differences. Will update again if I come to more a more decisive conclusion.

Never set 28/28 on <48% cars! Forza likes balanced hot pressures relative to weight distribution.

Rear-heavy cars, especially Porsche’s, can get lost in a cycle of understeer-oversteer when front pressure is too high relative to rear. I’m in the process of tuning the 2016 GT3 RS, S2 class, 40/60 weight, cold tire pressure 23.5/33 (almost together after a week). Coming from 28/28 or even 28/32, this has made light of numerous mysterious behaviors. One of the most unexpected, is better straight-line traction even at launch. I noticed that in the '05 Ford GT, too, after correcting it’s pressures (both cars RWD).

My starting pressures for ~45% cars are now 26/32.

Mildly front-heavy cars, usually RWDs, benefit from a touch more pressure in the front than rear. 1.5-3 PSI in most cases. I haven’t tuned tire pressure extensively with severely front-heavy cars yet.

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I only bump the rear pressure upwards from 30 if I need the car’s rear to break loose a little easier.

I’ve only started messing with tire pressures and they make a night and day difference to your entire car. This however seems like an interesting benchmark and place to start so thanks for this.

For a perfect set up you need to balance the suspension components first knowing the % weight distribution (springs/ARB /dampers)
Then put up telemetry onto tyre temperature and take the car for a run simulating racing …
adjust the F/R pressures so you get a balanced result when warmed up …

to be honest I don’t go to this much effort very often :slight_smile: … but if you are going to do a 'conversion ’ to a different engine especially then you should
I have done it for my sleeper drift car … a beige Volvo 850 estate … it rocks a drift but looks so ordinary :smiley:

I’ve found a range of tire pressures will give (apparently) good temperatures. Choosing a setting comes down to preferred optimal slip-angles and the rest of the setup.

Dude, if you ever have to differentiate front/rear tire pressures more than 0.5-1.0 psi from each other, then your tune is totally botched.

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Try my GT3 '16 build/tune if I post it?

Yeh can you post it or link your real gamertag so we can download it

Playground, T10, you want to move forwards with your next and/or current games? Right now I’d estimate most players get a fraction of the possible enjoyment from the driving experience alone in Forza games, let alone the satisfaction of tuning their own cars, thanks to the general obscurity of it, not to mention the vague, droning, unfocused descriptions of the tuning parameter’s immediate uses, from my eyes, once as a new player, and still to this day as an experienced tuner and driver.

Without concise and insightful explanations of how best to use tuning within the context of the game, if 13 generations of “32 psi is optimal grip” isn’t a clue, chances are your players won’t figure it out on their own. “Experiment by tuning pressure in small increments”… Absolutely not! Weight distributions farther deviant from 50/50 need immediate aggressive changes from 30/30 before starting on the rest of the tune. If that means adding auto-tuning to tire pressures so default on 40/60 cars is automatically 26/34 for extra newbie-proofing, so be it. Do that. It will be better than the current 30/30 on everything and hint that weight distribution and tire pressure balance are inter-dependent.

Many cars like perfectly balanced spring rates… show us the NF in Hz, to the 0.01, next to the spring rate. Anti-roll bars would benefit from a “% of set spring stiffness”, per axle, indicator. Dampers would benefit from a “% critical damping in low-speed valving” next to each of the 4. These 3 additions alone would make a massive difference in the time taken to tune cars, and potential for players to discover patterns they can apply to other cars and deepen their understanding of tuning and vehicle dynamics faster and farther than many of them ever will in the current system.

If you still don’t want to let us tune the high-speed damper valving… the digression should automatically adjust based on the spring rate and stroke–I think, longer strokes need a higher knee, and higher rates/heavier cars need more digression fade. Of course, do the R&D yourselves…

Btw, I’m 7th on Toft now. 27/37psi cold. Going to go higher, too (more psi*, no guarantees higher than 7th fastest). The downforce and banking conspire to overwork the tires.

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Just changed my Centenario to 25/32 cold pressure… it’s never been better. 44% front.

Just ran 17th worldwide on the Toft speed zone in the Mosler, 3rd run, on a 5-minute tune from a spreadsheet, phone calculator for tire pressure balance, and running around the map a bit. Cold pressures? 25/31. I think I know what I’m doing.

It bears repeating, MR/RR cars need more attention to tire pressures than 50/50 RWDs or even AWDs. All have something to gain from optimized settings. The Humvee (fixed some odd problems I was having in this one by adding 10 psi f/r), Warthog and other particularly heavy vehicles benefit from higher overall pressures, same for light cars/lower pressures.

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So from what I’m reading, a couple tips are:

*More pressure on the heavier side of the car/side with more load

*Even temperature across all four tires

Also, I can agree about the descriptions for tuning. They tell you how they might affect the car, but I couldn’t really get why they might affect the car. Only when I got a couple of books (Tune to Win by Caroll Smith is a great one) did I really understand why things do what they do.

  1. I only mess with tire pressure in drag and drift tunes, other than that I don’t touch them. If you are going for shaving fractions of a second off a lap time then I can understand messing with those.

  2. Would this entire topic not be better off located in the Tuner’s Garage section of the forum?..ya know…where people go to look for tuning advice.

Simply, enough pressure, temperatures don’t seem to matter much. Ideal cold pressures in my experience range from 20 to 40 psi depending on weight and application. Account for downforce too! Some cars will best compromise low-speed grip with high pressures, to maintain stability and precision at speed. IMO PG could have tapered the effect of load on deformation a bit. It can be extreme considering the amount of downforce some of the cars regularly generate. Also it doesn’t help in cross country/rush.

My gamertag is still the default, auto-generated, GreatFlea815883 (no I don’t identify as Great nor a Flea). The GT3 isn’t done yet. I’ll share the current build and tune, and my Centenario, in a fresh thread in the Tuners Garage to demonstrate the importance of pressure balance.

The best I hope to contribute is here, on the forums. They know how to contact me.

  1. Try it with your RR Porsche’s, if you have any. They love 32-35 cold rear and mid 20s front. Once the tires are awake and working correctly, the rest of the setup might need overhauling! You’ve been warned.

  2. I’ll make a new thread there with builds and tunes.

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Alright, so I’ve decided to build a car (HDT VK Commodore Group A, never touched the thing until now) and I was wondering if the setup looks just about right.

It’s 2,660 pounds and is front heavy (55%), kept it RWD. After tuning for a bit (then my controller batteries died), I got around to 32.5 psi in the front and 26.5 in the rear, though I might bump it down 1 psi on both sides once I get to drive it a bit more to see how it drives. What do you think?

EDIT: Thanks for the feedback by the way

I think that will work better than 30/30. Have you tackled balancing the rest of the setup? Springs, ARBs, dampers? Older RWD cars (E30 M3 RWD A class sport tires gave me trouble last night) I’ve found often need unbalanced springs; more front than rear relative to weight dist.

I’m still trying to make my Centenario setup as perfect as possible before I share it. I know the anxiety of “is it as good as I can make it yet”.

Yeah, here’s my suspension settings:

AR F - 30.00
AR R - 22.50

Spring Rate F - 999.9
Spring Rate R - 915.3

Ride Height F - 6.8
Ride Heighf R - 7.0
*Both of them are 3 ticks more than minimum ride height

RB F - 14.0
RB R - 12.8

BP F - 5.8
BP R - 6.2

I usually tune in increments of .5 on ARBs and 5-25 on spring rates (25 when I’m tuning to make sure the suspension doesn’t bottom out, 5 when I’m tuning for balance). I don’t really do any super fine tuning, but it’s good enough for me.

Open this, click File, then Make a Copy. Edit fields in bold. Lmk if it works for you.

https://docs.google.com/spreadsheets/d/1iWcYonZNbOZA6N1w6y7qjK6B6EUo98MufapvST8Xj0Y/edit?usp=sharing

I’m no longer positive I was correct about perfect tire pressure balance. I did get the GT3 to run Astmoor in 50.707 without front aero (pressures 23.5/35 cold), and 50.569 the next day with front aero and 100 less horsepower, similar tire pressure differential. I can’t tell if Forza’s gamepad steering is too ham-fisted to handle RR cars cleanly (hence the mild carpal tunnel lately that I’ve never had before, thanks to making constant micro-corrections to manage the yaw moment), or if I need a different overall setup approach to make the 2016 GT3 RS, in 998PI and RWD, fast and relatively easy to drive in Horizon 4.