GPL 1967 v3 Dev blog

[ROOKIE4EVER]

Bottom post of the previous page:

Today I partly managed to resolve the braking issue by introducing the BRAKE_DX_MOD formula from Assetto Corsa. A few further tweaks are needed but it's one step towards resolving the issue.

I'm well stuck into this again. Latest additions:

1. BRAKE_DX_MOD - Adds or reduces grip under braking
2. I've managed to fudge it so that braking has a separate slip curve and lower peak slip angle
3. Tyre stiffness is now dependent on speed, which also affects the radial growth of the tyre
4. I've begun working on the first steps towards a proper brake temperature patch - one where the heating rate depends on the wheel speed, rather than just the car's speed. In other words, locked brakes no longer result in increases in temp. Brake bias will also be a factor and each brake will have its own temp. More on this later!

Interesting in its complexity.

[PTRACER]

Today I partly managed to resolve the braking issue by introducing the BRAKE_DX_MOD formula from Assetto Corsa. A few further tweaks are needed but it's one step towards resolving the issue.

I'm well stuck into this again. Latest additions:

1. BRAKE_DX_MOD - Adds or reduces grip under braking
2. I've managed to fudge it so that braking has a separate slip curve and lower peak slip angle
3. Tyre stiffness is now dependent on speed, which also affects the radial growth of the tyre
4. I've begun working on the first steps towards a proper brake temperature patch - one where the heating rate depends on the wheel speed, rather than just the car's speed. In other words, locked brakes no longer result in increases in temp. Brake bias will also be a factor. More on this later!

Very excited for #4. The lack of individual brake heating is my number one gripe of the 55 mod. Out of curiosity, how does the stiffness correspond to speed? Does it go up or down the faster you go.

Thanks! I've got the patch half working already, but it needs a little more work. It's basically operating on the following principle:

Let's say the player choses a 60/40 brake balance and the total braking power is 1000N. 600N will be allocated to each front brake and 400N to the rear. I've normalised that to 1.2F and 0.8 rear per brake. I use these as multipliers for the heating part of the code, and since the front brakes have more power, they will heat up faster than the rears. All brakes start off at about 80% strength cold and the fronts will inveitably heat up to full power first, so brake bias will go forward, then the rears will catch up. But if the fronts overheat, the rears will become more powerful so the brake bias will go backwards. That's the idea anyway. I haven't fully seen it in action yet and I'm excited to try it.

Note that I also found a bug in the 1955 brake fade code where the temp resets to 22C under a certain condition (which returns brakes to full strength), I won't explain what it is to avoid cheating, but I had to fix that.

Re: Tire stiffness with speed. I found this research paper that shows a radial tyre increases its stiffness linearly by 5% every 90kph. So at 300kph, you're looking at 15% increase in stiffness. I know the 1967 cars have bias ply tyres, but I don't have much data to go on, so I'll probably plug in those kinds of numbers. I tried both 10% and 20% at 300kph, there is very little difference in feel either way so I guess it doesn't matter too much.
https://www.researchgate.net/figure/Ide ... _335234303

[Michkov]

Let's say the player choses a 60/40 brake balance and the total braking power is 1000N. 600N will be allocated to each front brake and 400N to the rear. I've normalised that to 1.2F and 0.8 rear per brake. I use these as multipliers for the heating part of the code, and since the front brakes have more power, they will heat up faster than the rears. All brakes start off at about 80% strength cold and the fronts will inveitably heat up to full power first, so brake bias will go forward, then the rears will catch up. But if the fronts overheat, the rears will become more powerful so the brake bias will go backwards. That's the idea anyway. I haven't fully seen it in action yet and I'm excited to try it.

Shouldn't that be 0.6 and 0.4F per brake? Or is v1 just axel to axle instead?

Re: Tire stiffness with speed. I found this research paper that shows a radial tyre increases its stiffness linearly by 5% every 90kph. So at 300kph, you're looking at 15% increase in stiffness. I know the 1967 cars have bias ply tyres, but I don't have much data to go on, so I'll probably plug in those kinds of numbers. I tried both 10% and 20% at 300kph, there is very little difference in feel either way so I guess it doesn't matter too much.
https://www.researchgate.net/figure/Ide ... _335234303

Interesting, I'm assuming it's centrifugal force on the tread making the the sidewall stiffer? What data from the tyres are you looking for?

[PTRACER]

@Michkov In the game it's 600N per front and 400N per rear brake yeah...but I'm using it as a heating multiplier So I doubled them to get them just above and just below "1.0" which is the default.

Yes I think it's centrifugal forces causing tyre deformation. You can see it in action here:
https://youtu.be/fnt4o-2LiSc?si=hdpGJXVLWyzgAZX6

[Everso Biggyballies]

Yes I think it's centrifugal forces causing tyre deformation. You can see it in action here:
https://youtu.be/fnt4o-2LiSc?si=hdpGJXVLWyzgAZX6

A great example of tyre deformation is to look at a dragster off the start. They use special "ripple wall tyres" and look flat and wrinkled when stationary. The wider effect of the 'flat (looking) tyre gives grip off the line, They increase in diameter dramatically through centrifugal force as soon as they leave the line, so much so the effect alters the final drive gearing just from the tyre expansion from centrifugal forces over the run down the srip..

Not perhaps relevant for GPL levels of power (Top fuel dragsters have 10,000+bhp) but interesting none the less from just the effect . Shown well and described in this video.

[PTRACER]

Yes I think it's centrifugal forces causing tyre deformation. You can see it in action here:
https://youtu.be/fnt4o-2LiSc?si=hdpGJXVLWyzgAZX6

A great example of tyre deformation is to look at a dragster off the start. They use special "ripple wall tyres" and look flat and wrinkled when stationary. The wider effect of the 'flat (looking) tyre gives grip off the line, They increase in diameter dramatically through centrifugal force as soon as they leave the line, so much so the effect alters the final drive gearing just from the tyre expansion from centrifugal forces over the run down the srip..

Not perhaps relevant for GPL levels of power (Top fuel dragsters have 10,000+bhp) but interesting none the less from just the effect . Shown well and described in this video.

Yes!! I knew I had seen something that illustrates the effect better than what I posted This is what I'm trying to achieve in GPL. By default, the harder the tyre (including due to pressure), the larger the tyre's diameter, which also affects the final drive ratio and rolling resistance). I'm adding speed to that equation although only in terms of stiffness - I haven't found the mem address for live tyre diameter yet. Amazing that a 1990s video game can do all this.

Last night I succeeded in getting the new brake temp patch fully working for one wheel. Making it do all four wheels sequentially shouldn't be so tough from here.

[PTRACER]

The basic patch is done!!! And here are the results This is with 54% brake bias. Divisions between the laps are approximate. Notice anything interesting?

[Michkov]

A noticeable split between the front brae temps. Are you locking the front right into the Lesmos?

[PTRACER]

A noticeable split between the front brae temps. Are you locking the front right into the Lesmos?

In the first two laps, no, but I was braking quite deep into the corners and leaning on the front left a lot. Though on the last lap, I braked too deep into first Lesmo and locked the inside front, then into Parabolica I purposely over drove and locked the front left. I think that's all reflected in the temps.

[PTRACER]

Two laps of Monaco now. The FL brake starts off the coldest because I locked up into the final corner of the previous lap. Eventually the temps catch up and everything equalises, with the FL becoming the hottest by the middle of Lap 2. I drive a bit tidier here and so both fronts and both rears are roughly equal with each other. The difference in brake bias puts them at 50C apart at their hottest, 30C apart once they cool down a little.

Going into the final corner again I screw up. The unloaded front left locks up and the loaded front right has all the grip. I left the tracer running for a few seconds at the end so you can see the final temps. I think this patch is working as intended!

[PTRACER]

I decided to make a comparison between GPL and Assetto Corsa and found something interesting. The cooling rate of AC's L49 rear brakes are a lot slower than the fronts. Maybe because they are not directly in the air stream?



In any case, I added some additional code that reduces the cooling rate for the rear brakes. So now, there will be a bit more crossover between front and rear brake temps. Here's a demonstration of the code within GPL:



What else? Well firstly, I found a way to automatically calculate the heating and cooling rate based on FPS. So if someone runs 60fps, 144fps or some other future patch, I'll not need to make any adjustments. Secondly, since I plan to modify the temperature and air pressure for the Kyalami and Mexico car sets, I've written some other code that takes these factors into account. Hotter air temps and low air pressure will increase the heating and reduce the cooling rates automatically - all I have to do is change one or two base values rather than having to recalculate everything from scratch. I'm not sure how much of a difference there will be yet though.

I really can't wait for you guys to try all this out.

[Everso Biggyballies]

I decided to make a comparison between GPL and Assetto Corsa and found something interesting. The cooling rate of AC's L49 rear brakes are a lot slower than the fronts. Maybe because they are not directly in the air stream?



In any case, I added some additional code that reduces the cooling rate for the rear brakes. So now, there will be a bit more crossover between front and rear brake temps. Here's a demonstration of the code within GPL:

This might be too much info for your purposes but.....

Not relevant to all cars but maybe an issue with some cars is that those cars with rear inboard brakes (ie those with the disca and calipers at the gearbox end of the driveshaft. are more difficult to cool than outboard brakes for the reduced airflow plus additional local heat reasons. The advantage of inboard brakes is the reduction of unsprung weight on the outer end. Other advantage is the brakes are more efficient when effectively mounted to the tub / chassis over being added to a part held by suspension arms.

Just sayin in terms of any cooling issues you might have / not understand with certain cars.

[PTRACER]

I decided to make a comparison between GPL and Assetto Corsa and found something interesting. The cooling rate of AC's L49 rear brakes are a lot slower than the fronts. Maybe because they are not directly in the air stream?



In any case, I added some additional code that reduces the cooling rate for the rear brakes. So now, there will be a bit more crossover between front and rear brake temps. Here's a demonstration of the code within GPL:

This might be too much info for your purposes but.....

Not relevant to all cars but maybe an issue with some cars is that those cars with rear inboard brakes (ie those with the disca and calipers at the gearbox end of the driveshaft. are more difficult to cool than outboard brakes for the reduced airflow plus additional local heat reasons. The advantage of inboard brakes is the reduction of unsprung weight on the outer end. Other advantage is the brakes are more efficient when effectively mounted to the tub / chassis over being added to a part held by suspension arms.

Just sayin in terms of any cooling issues you might have / not understand with certain cars.

This is relevant info for sure! Did most cars then have inboard rear brakes? I know the Cooper T81 has semi-inboard FRONT brakes, and I could add separate cooling factors just for that car if I wanted, but I don't want to make it too complicated.

EDIT: Okay I see what they meant by semi-inboard. The position of those brakes, right in the airstream Good for cooling, but...

https://media.gettyimages.com/id/870147 ... AkUeZP2Fc=

[Michkov]

The Ferraris had their rear disks inboard, cooled by an airscoop at times iirc. I'd need to look up the other cars to be certain, but inboard brakes at the rear weren't that uncommon for the period.


And if you want to take the idea even further, why not mount the sole rear brake directly to the gearbox output shaft like the on BRM P48.

[Everso Biggyballies]

The Ferraris had their rear disks inboard, cooled by an airscoop at times iirc. I'd need to look up the other cars to be certain, but inboard brakes at the rear weren't that uncommon for the period.


And if you want to take the idea even further, why not mount the sole rear brake directly to the gearbox output shaft like the on BRM P48.

The BRM transmission mounted disc was affectionately referred to as "the bacon slicer" Exposed with the bodywork cut away for cooling purposes

No inboard rears were common. and whilst the habit of inboard fronts never caught on given the complexities of the need for a brake shaft from inboard to the wheel hub and the torque that shaft would be subjected too. Of course the Lotus 72 had inboard fronts and the brake shaft failure was responsible for Rindt's Fatal crash. (To be specific I believe the legal findings ended up suggesting the brake shaft failure caused the crash but the death of Rindt was as a result of injuries from improperly secured crash barriers. Somewhere into the equation was also the fact he slid under his belts etc.

Inboard rear brakes became unfashionable later with the advent of carbon brakes which substantially reduced the weight factor and so unsprung weight issues were minimised.

This image shows the Ferrari shark nose had inboard rears.



Also Ferrari 158 as this pic of Bandini shows.



Ferrari 156

[PTRACER]

The Ferraris had their rear disks inboard, cooled by an airscoop at times iirc. I'd need to look up the other cars to be certain, but inboard brakes at the rear weren't that uncommon for the period.


And if you want to take the idea even further, why not mount the sole rear brake directly to the gearbox output shaft like the on BRM P48.

I had a feeling that BRM brake wasn't effective and I was kinda right...Two brake failures in 1960, one of them resulted in the death of a spectator (Gurney at Zandvoort).

At any rate all this presents a good case for rear brakes having poorer cooling than the fronts!