Simple Tire Modding for GTR 2

[HypoToad]

This would probably work for other similar games as well.

I have found that you can alter the speed and cornering/handling of cars easily by changing two settings in the .tyr files in notepad. Here is a part of a .tyr file, notice the "Radius" and "Width" settings :

"[COMPOUND]
Name="Soft Compound"
FRONT: // Arguments:ALL,FRONT,REAR,LEFT,RIGHT,FRONTLEFT, FRONTRIGHT,REARLEFT,REARRIGHT
DryLatLong=(1.800, 1.825) // Lateral/longitudinal coefficients in dry weather
WetLatLong=(1.100, 1.100) // Lateral/longitudinal coefficients in wet weather
Radius=0.310 // Radius of tire
RadiusRPM=1.01e-6 // Increased radius per unit RPM
Width=0.290 // Width of tire"

First the Radius the smaller the figure the slower the car will go and vice verse, if you want your car to go a little faster you can simply increase the Radius of the tire by a "small" amount, trial and error is the key.

Now the Width, this is where the handling changes come in, increase the amount from 0.290 to 0.320 and your car will have greatly increased grip on corners, but be aware if you increase it too much your car may tip over on corners, decrease it too much and you can turn it into a drift car.

It's trial and error, I changed the tires completely on an E-Type Jag and couldn't work out why the car would not go as fast and would tip over on corners, that's because the new tires had a smaller radius and were much wider, I changed the Radius to the previous tires settings and then the Width, I experimented with the grip until I had the right combination of grip and slip.

Back up your files first and remember you have front and back tires as well as different compounds in the same file.

Hope this helps.

 

[jgf]

"It's trial and error"

Will be mostly error, and luck, this way. It isn't too difficult (today) to get accurate data on tire sizes, even racing tires, used by these cars, so in an effort to improve my GTR2 I compiled quite a list of correct tires. Most default cars, and many mods, are running wider tires than their real world counterparts (virtually every car has 10" front tires), perhaps Simbin wanted to make them "easier" to drive; but instead this makes them feel somewhat dead or "sluggish". Once you adapt your driving and setup to the proper size tires you will find the car feels more "lively" and your lap times may actually improve (at most tracks I'm typically 1-2 seconds faster and the car is more fun to drive).

For many I'm probably preaching to the choir, but some basics. A typical tire designation - 245/45-17 denotes a 245mm tread width, a sidewall 45% of the tread width, mounting on a 17 inch wheel (it's odd that all data is metric except wheel size is almost always in inches). The tread width can be input directly into the .tyr file, but for radius you must calculate the sidewall x2, convert the wheel size to mm and add to that, divide by 2. Don't like math? (I don't, so naturally became an engineer), use this:

Tire Size Calculator

The best tire size calculator. Use our tire size calculator to find tire size specs and suggested tire sizes. Then check prices for all available tire sizes.

tiresize.com

Enter the tire spec, check "mm", note the overall tire height, divide that by 2 for the radius.

On occasion, often with racing slicks, you will encounter something like 295/620-18; here most of the work is done for you, 295 is tread width, 620 is overall diameter, just divide that by 2 for the radius.
If your radius calculation gives an odd number, for example 313 or 318, round to the nearest multiple of 5, here 315 or 320.

The modern P designation for tires became common in the eighties, prior to that tires had a simple tread/wheel spec, for example 7.50x15, a 7.5" tread on a 15" wheel. Getting a radius figure for these requires a bit of digging, some manufacturers will convert that on their website to a modern tire, but you may also need to input what car it is for. Ferraris, Maseratis, Astons, etc. of the fifties seem to universally run Pirelli Cinturato 186VR16 tires today (radius 350), a modern replica of their period tire.

Here are some to try, taken from online data (will post more if anyone interested).

Porsche 911/996/997 GT3:
Official factory team specs:
Front: 235/40-18 (width 235, radius 320)
Rear: 295/30-18 (width 295, radius 320)

Private team:
Front: 245/35-18 (width 245, radius 315)
Rear: 285/30-18 (width 285, radius 315)

Porsche 911/996/997 GT2:
Front: 245/40-18 (width 245, radius 325)
Rear: 315/30-18 (width 315, radius 325)

Front: 255/35-18 (width 255, radius 320)
Rear: 315/30-18 (width 315, radius 320)

Lamborghini Gallardo GT3:
Reiter Engineering, Pirelli slicks
Front: 265/645-18 (width 265, radius 320)
Rear: 305/660-18 (width 305, radius 330)

Corvette C5R, C6R:
Front: 275/40-17 (width 275, radius 325)
Rear: 315/35-17 (width 315, radius 325)

Note completely different tire specs have the same radius. This is due to profile (sidewall height). For example the Corvette, 275x0.40=110, 315x0.35=110.25; if you want to truly micromanage the tire specs, a low profile tire has little flex and has great grip and handling on perfectly smooth tracks, but is skittish and imprecise on rough tracks; conversely a higher profile tire has more flex and will absorb small irregularities on the road rather than passing them straight to the suspension, thus easier handling and smoother steering on rough bumpy tracks. I believe GTR2 factors this in via these parameters:

SpringBase=60000.0 // Base spring rate with no pressure
SpringkPa=1092.0 // Spring rate per unit pressure

I've not yet played around with this much.

Again preaching to the choir, all default cars (obviously) and most mods use the default tires found in the Gamedata/Teams folder and we're making individual sizes for specific cars, do not edit those files!
Look in your car's hdc file to see what tire it uses, copy that tyr file to that car's folder (where the hdc file resides) and rename it (name can be anything, game doesn't care; I append something meaningful to that car, a Michelin_GT.tyr for a Porsche GT3 becomes Michelin_GT3Por.tyr); edit the hdc to point to the renamed file, then edit that tyr file. Don't forget to edit all compounds in the file (menu>edit>replace>replace all means only four edits to do).

 

[Need_For_Speed]

So lets clarify something. Tyre width parameter has no impact on grip at all. There were no differences in lap times between different sizes that I have tested. It may effect other things though. Grip is defined primarily by lateral/longitudinal coefficients.

Also

"It's trial and error"

Not really if you know real tire dimensions and effect of tire size VS grip! You may want to check my physics mod which simulates exactly that. Instead of guessing coeff. my numbers derive from a specific formula I have managed to found in order to calculate realistic values for different sized tires. They are based on Simbin own data for the Dunlops used by Lister Storm.

I have a question about the specs of Porsche GT3 and Corvette tires you have posted. Can you provide me the link as to where did you find those data? My mod has Porsche at 265/305 (Same as 360N-GT) and Corvette 305/315 but there were 2 options available for the C5-R front tires apparently. Please do post other (original cars) tire sizes as well because I want to see how they compare to my research.

 

[jgf]

Corvette data from

Chevy Corvette C5-R Race Cars - The C5 World Challenge Kit Kar Kaper

The C5 racing programs started several years ago, but most folks only found out about it last year. Even now, very few people realize how big the Corvette racin

www.motortrend.com

Porsche

https://support.apexraceparts.com/hc/en-us/articles/360047940814-996-911-GT3-Wheel-Tire-Fitment-Guide

https://www.car-revs-daily.com/2015/05/16/2015-porsche-911-gt3r-vs-gt3-cup-vs-gt3-rsr/amp/

(also data from some team sites, but it would take half the evening to dig through hundreds of links to find the specific ones)

And of course much data is conflicting, depending on year/series/team/driver; I go with consensus. Interestingly, most race variants of high performance street cars (Ferrari, Lambo, etc.) use the same size tires as the street cars, just slicks instead of all weather.

FWIW, the 2022 Porsche 911 GT3-R uses
F - 30/68-18
R - 31/71-18
as per

Debut for the newest generation of the Porsche 911 GT3 R

The new Porsche 911 GT3 R will be unveiled to the public at this year’s 24 Hours of Spa-Francorchamps. From the 2023 season, Porsche customer teams can campaign the new racing vehicle in worldwide motorsport events that adhere to the GT3 regulations. The vehicle is based on the latest...

newsroom.porsche.com

For the International GT series

Tire Sizes - International GT

America's GT Cup tire sizes for Porsche and Ferrari as recommended by Pirelli

www.internationalgt.net

In rfactor the tire width only affected the skid mark graphics, but in GTR2 it seems to definitely affect handling. Run a few laps in your favorite car, remove about 50mm from the front width and, without changing the setup, see if it isn't now understeering.

 

[Speednut357]

In Rfactor/GSCE/AMS I have been making minimal adjustments to DryLatLong (0.02 or less), which seems to have a good effect, similar to the original idea of increasing grip with tire width. However, I feel it is a poor substitute for just getting the correct data and creating a Slip Curve for the specific tire (something I have no idea how to do.)

I have also found AIGripMult very useful in getting the correct amount of slippage from the AI to look realistic, but this needs to be balanced if there is too much grip, the AI starts to run away in the corners.

I agree that you should try to make all other values as accurate as possible. This is just the tires. If made a list of all the parameters in the HDC, ENG, GRB, and SP files, it becomes clear that the tires alone are only a tiny part. I feel that everything needs to be done together to make something that feels as realistic as possible. (Another thing I cannot do).

I do appreciate your info on tires, though. It's a good bit of revision on something I must get correct in the future.

 

[Need_For_Speed]

@jgf

Regarding tire width it makes no difference, really

And I see why your data doesn't match mine. You are comparing apples and oranges Your data for Porsches references some track prepared cars which are not the same cars as raced in FIA GT Championship in 2003/04, not even close.

There is a difference between N-GT class racing Porsches and what you have posted. N-GT cars among other things have wider bodies and increased track. If you had had data from actual teams that participated in this championship in N-GT class that would be valid info. Same with the Corvette. That car is completely different from a GT1 class C5-R that raced in ALMS and FIA GT. One must be very careful when doing research like that so not to post misinformation. If you have other cars tire data which are based on a correct class of cars and championship please do share. For example cars in 24H class were mostly from Belcar national championship so data should come from that teams.



Regards,

 

[Need_For_Speed]

@Speednut

What you are saying has already been accomplished in my GET REAL physics mod except the suspension files which remain original. https://www.racedepartment.com/downloads/gtr2-get-real-physics-mod-released.49871/
Believe me I have done a proper research so you will get the most realistic simulation of those cars ever made. I am also working on an update which will make my mod even better.

 

[Speednut357]

@Speednut

What you are saying has already been accomplished in my GET REAL physics mod except the suspension files which remain original. https://www.racedepartment.com/downloads/gtr2-get-real-physics-mod-released.49871/
Believe me I have done a proper research so you will get the most realistic simulation of those cars ever made. I am also working on an update which will make my mod even better.

I am slowly working through all the files and settings involved in the hopes of learning how to do what you have done. I hope you don't mind, but I will load up your SP file and look closely at how you achieved a good suspension. That's the bit I am trying to learn now. How are you visualizing the suspension?

 

[Need_For_Speed]

I am slowly working through all the files and settings involved in the hopes of learning how to do what you have done. I hope you don't mind, but I will load up your SP file and look closely at how you achieved a good suspension. That's the bit I am trying to learn now. How are you visualizing the suspension?

I have said that I did not change the suspensions. Save yourself the time and effort because you wont learn anything from my files. Those numbers are derived from complex calculations for the aerodynamics, CAD software used etc... Tires are also made in this fashion. But the bulk of the data remain original Simbin numbers because there is no need to change them.

 

[The Iron Wolf]

@Speednut357 - for quick visualization, you could use Steam GTR2 rF1 Plugin API capability and SimHub capability to plot raw game data. I suspect Motec is better, but for quick things SH is very helpful and been useful with physics stuff I am doing in my plugin.

 

[Speednut357]

I have been using Suspedit_V2 it is on Rfactor Central. It will load the suspension geometry and display it in a 3D line graphic. It makes it easy to visualize the suspension geometry and then adjust the coordinates in the file. It has a save feature that doesn't work but just being able to see the suspension makes it easy to find errors. And it works for GTR2 too. Neils has another idea: load the PM file into the Skip Barber car in Rfactor2 dev mode and use Rfactor2 to see the camber as the suspension moves. The GTR SP file is pretty much the same as the rfactor PM file, so it should be possible to use it just the same.

For the moment, I am trying to get my head around the Gmotor limitations. It seems that some suspension geometries are not possible. Understanding how to get around this is a bit confusing. It looks like most cars have double-wishbone front suspension instead of struts.

 

[Speednut357]

 

[jgf]

In any series which does not mandate tires you will find a plethora of brands/compounds/sizes in use by otherwise identical cars; within the same team drivers may have different preferences, and what is used may vary from track to track. Specifying "this is the tire used by this car in this series" is as definite as showing one photo and saying this is what the car looked like this season, when sponsors can change from race to race (the bane of anyone creating a carset for any series). The basic tire spec is determined by the car's specs and usually follows tire manufacturers' recommendations (the brand is usually decided by sponsorship, otherwise team/driver preference), variations are rarely more than compound or profile to suit race conditions (overall size - diameter - may change depending on whether acceleration or speed has priority, though this is usually only with rear wheels and only when it makes a substantive difference). So any particular car type, whether running FIA, ALMS, SCCA, or some regional series, will usually be running similar, if not identical, tire specs.

 

[Need_For_Speed]

In any series which does not mandate tires you will find a plethora of brands/compounds/sizes in use by otherwise identical cars; within the same team drivers may have different preferences, and what is used may vary from track to track. Specifying "this is the tire used by this car in this series" is as definite as showing one photo and saying this is what the car looked like this season, when sponsors can change from race to race (the bane of anyone creating a carset for any series). The basic tire spec is determined by the car's specs and usually follows tire manufacturers' recommendations (the brand is usually decided by sponsorship, otherwise team/driver preference), variations are rarely more than compound or profile to suit race conditions (overall size - diameter - may change depending on whether acceleration or speed has priority, though this is usually only with rear wheels and only when it makes a substantive difference). So any particular car type, whether running FIA, ALMS, SCCA, or some regional series, will usually be running similar, if not identical, tire specs.

But regardless of that your data is still based on cars that are not even in the same class as to what GTR2 is simulating.

 

[jgf]

A GT2 Porsche is a GT2 Porsche. A GT3 Porsche is a GT3 Porsche. A C5R is a C5R. We're not talking different suspensions, drivetrains, etc.

 

[Need_For_Speed]

The cars you have provided the links are street cars prepared to race. The N-GT cars are purposely factory built racecars and are extensively modified in every way. There is a big difference between street 911GT3 RS and N-GT 911GT3 RS. Your C5R is much different from a Pratt Miller built GT1 machine aswell. Different chassis, wider body, wider track etc and cannot be compared to it. So I will stick with my data.

 

[jgf]

Nissan Z
245/45-18 all around

TVR T400R
F - 225/35-18
R - 235/40-18
(some drivers prefer 19" wheels, but no data whether they use lower profile tires to maintain same overall diameter)

BMW Z3M
F - 225/45-17
R - 245/40-17

Gillet Vertigo
F - 235/40-17
R - 265/40-17

Morgan Aero 8
F - 225/35-19
R - 245/35-19
(a 2004 race prepped car - "Euro GT3 Series" - at auction was listed with 245/45-18 all around)

Mosler MT900R
275/35-18 all around

SEAT Toledo GTR
nothing definite here; a forum discussion on "race prep Toledo" mentions 245/35-17 or 235/35-19, but no mention of which Toledo or what series racing

 

[jgf]

The cars you have provided the links are street cars prepared to race. The N-GT cars are purposely factory built racecars and are extensively modified in every way. There is a big difference between street 911GT3 RS and N-GT 911GT3 RS. Your C5R is much different from a Pratt Miller built GT1 machine aswell. Different chassis, wider body, wider track etc and cannot be compared to it. So I will stick with my data.

Also check manufacturers' websites; Pirelli has comprehensive data on its racing slicks and rain tires, including recommendations for many cars. Check auctions for these cars, they often list tires among specs. And, as I stated, in any series two teams running the same type car may use different tires. Except for series with spec tires there is no "absolute".

"Different chassis, wider body, wider track etc..."
Then it is not a "Corvette". Any more than the Porsche 911GT1 was a 911, or a NASCARE racer is a Ford or Chevy or Toyota. You may build whatever you like, call it whatever you like, and use whatever tires you like.

Thirty years ago Rusty Wallace changed from racing a Pontiac to a Ford. Did they build a new car? They removed one hand made, template contoured, aluminum body and replaced it with another. Same engine, same drive train, same chassis, but he's now driving a "Ford". By that logic I could replace the body of an old VW Beetle with a fibrefab F40 body and, "hey look! I'm driving a Ferrari!"

"street cars prepared to race"
You will note for many of those tires there are notes about suspension changes and body modifications required. At that point it is no longer a street car. I once owned a '67 Corvette that was driven off the showroom floor; but it was in no way shape or form a "street car" by the time I acquired it (having competed in CanAm and TransAm by then).

I've no doubt you and I find different data, because we seek different data.

 

[Need_For_Speed]

Nissan Z
245/45-18 all around

TVR T400R
F - 225/35-18
R - 235/40-18
(some drivers prefer 19" wheels, but no data whether they use lower profile tires to maintain same overall diameter)

BMW Z3M
F - 225/45-17
R - 245/40-17

Gillet Vertigo
F - 235/40-17
R - 265/40-17

Morgan Aero 8
F - 225/35-19
R - 245/35-19
(a 2004 race prepped car - "Euro GT3 Series" - at auction was listed with 245/45-18 all around)

Mosler MT900R
275/35-18 all around

SEAT Toledo GTR
nothing definite here; a forum discussion on "race prep Toledo" mentions 245/35-17 or 235/35-19, but no mention of which Toledo or what series racing

Nissan Z
245/45-18 all around

TVR T400R
F - 225/35-18
R - 235/40-18
(some drivers prefer 19" wheels, but no data whether they use lower profile tires to maintain same overall diameter)

BMW Z3M
F - 225/45-17
R - 245/40-17

Gillet Vertigo
F - 235/40-17
R - 265/40-17

Morgan Aero 8
F - 225/35-19
R - 245/35-19
(a 2004 race prepped car - "Euro GT3 Series" - at auction was listed with 245/45-18 all around)

Mosler MT900R
275/35-18 all around

SEAT Toledo GTR
nothing definite here; a forum discussion on "race prep Toledo" mentions 245/35-17 or 235/35-19, but no mention of which Toledo or what series racing

Do you also have radius data?

 

[jgf]

TVR and Vertigo - 310 front, 320 rear

BMW - 320 all

Morgan - 320 front, 330 rear
for 2004 specs, 340 all

Nissan - 340 for 17", 330 for 18"

Mosler - 325 all

Toledo - 305 for 17", 325 for 19"

This calculator makes it easy; type in the tire spec, select "mm", hit the "calculate" button, and it gives all dimensions - diameter, tread, sidewall, circumference, revolutions per kilometer. Radius should be a multiple of 5, so if result is 312 or 323 round up to the next 5 (centrifugal force plus tire heating expands the tire anyway, and we're only dealing with a couple of mm).

Tire Size Calculator

The best tire size calculator. Use our tire size calculator to find tire size specs and suggested tire sizes. Then check prices for all available tire sizes.

tiresize.com