How GT1 calculates gear speeds based on their ratios?

[Jandarman]

Hello everybody! I'm new to community. And first of all I must say that I'm glad to be here.

Now straight to the point. Please help me to find out this thing. There is some formula - I'm sure of it, but I can't figure out what it looks like. What values GT1 uses in order to calculate gears speeds? Car's weight? Engine displacement? Max HP? Max Torque? I don't understand - really. But I'm tryin to find it out for almost 2 days now. I think it's important, because we don't see gears speeds in gt2, gt3 or gt4 for example. All we have is gear ratios (not speeds). Only in 1st GT we can see how gear speeds are calculated depend of which number we set in gear ratios areas. Please help... maybe I'm missing something...

In the screenshot below stock used S13 Silvia '88 Q's with only Racing Gearbox applied (just to see gear ratios and their speeds) (no other parts were installed - car is clean).

I hope I'm not alone in my searches and there is somebody who wants to find this out so bad as I do.

And now in screenshot below you can see thing like: "3gr - 91kmh/4197rpm/90hp". My question is- can particular HP be somehow related to car's speed at particular gear or not? Or this two params are not close to each other by meaning? If not - then I've done mistake by putting HP marks on HP/rpm graph.

This post was banned early for spam by site's spambot. I hope now it's ok, I will see my thread being approved and I wouldn't write to administrator to restore my account again.

Btw. Thanks Jordan Greer

 

[pez2k]

As far as I'm aware, it's literally just the speed that the car would be doing at its marked redline in each gear, the point where the auto gears would shift up. Power and torque don't matter as they're just theoretical top speeds - you could set 6th to 500km/h and never have a chance of reaching it. The top gear instead shows the speed at the rev limiter in that gear. For the S13 Q's '88, the redline is at 7100rpm and the rev limiter is at 8500rpm, as you've spotted.

I don't know if the tyre circumference is taken into account or not, but the easy way to check it would be to install a tyre upgrade and see if the numbers change - all tyre upgrades are in a larger size than stock, and while the profile reduces as the wheel size and width increase they still won't keep exactly the same circumference.

 

[Mouc]

Hello!

According to this vid', the tires diameter is taken in account
But I never check the numbers of gear speeds charts with and without upgrade tires.

 

[pez2k]

According to this vid', the tires diameter is taken in account
But I never check the numbers of gear speeds charts with and without upgrade tires.

That's actually even more interesting than you'd think, as the stock tyres on the Vette are in fact also set up as 195/60R15, it's just the size shown in the menu that doesn't match. It might mean that the menu size does actually have a physics effect.

 

[Jandarman]

I changed tires and yeah - stats changed too a little bit. So this theory works well. Thank you for the tip @Mouc & @pez2k

But I'm Still continuing to thinking of how gt1 calculates gear speeds based on ratio numbers...

I noticed that gear ratio number is straight proportional to rpm counter and reverse proportional to km/h counter. Still investigating...

btw - the tire size might be the value that is present in this "formula"

 

[pez2k]

If you're asking about literally what the gear ratio numbers mean, it's how many times the engine turns for every full revolution of the transmission output, followed by the final drive ratio which represents how many times the transmission output turns for every full revolution of the wheels.

If you have a gear ratio of 2.000:1 and a final drive ratio of 4.000:1, your overall gear ratio is 2 * 4 = 8 turns of the engine to 1 turn of the wheels. If the engine is turning at 8000rpm, divide that by the gear ratio, and you have 8000 / 8 = 1000 revolutions of the wheels per minute. Multiply that by the circumference of the tyres (let's say that's 600mm), and you get 600 * 1000 = 600,000 millimetres travelled every minute. Multiply by the 60 minutes in an hour to get 3,600,000 millimetres per hour, and divide by the 100,000 millimetres in a kilometre, and you have 36 km/h.

 

[Jandarman]

Ok. Let me try:

1st gear ratio (S13 Silvia '88 Q's):
3.592 engine revs 1 trany rev

4.375 trany revs to 1 wheels rev

1) 3.592 * 4.375 = 15,715 engine revs

2) Lets say we take 7100rpm on which 1st gear is switching to 2nd gear:
7100 / 15,715 = 451,797 wheel revs per minute

3) 451,8 * 1927mm = 870 612 millimetres per minute

4) 870 612 * 60 = 52 236 720 mm/h

5) 52 236 720mm / 1 000 000mm = 52,23672 km/h

Yeah baby! It's working Thank you again @pez2k . Btw - GT2-Plus is a thing! Thank you and all the Team for this mod, it gives GT2 second live.

Now the last moment. How to calculate gears speed if we know only gear ratios of the car and can't see rpm graph (like we see in Gran Turismo 2 for example)? Of course we can test cars right on Test Course and see on which rpms gears are changing. But I though there is better solution to this.

GT2 gear ratios setup:

 

[pez2k]

Now the last moment. How to calculate gears speed if we know only gear ratios of the car and can't see rpm graph (like we see in Gran Turismo 2 for example)? Of course we can test cars right on Test Course and see on which rpms gears are changing. But I though there is better solution to this.

Good to see you got it working. I don't think there's any way to see the redline of a car in GT2 without driving it at least once, and I don't know of any websites which list it for each car either. It should always be at or above the peak power RPM that's shown in the garage, and at or below the maximum RPM that can be guessed from the power / torque graph in the Change Parts menu, but I'm not sure if you can get any more accurate than that without driving.

 

[TeaKanji]

Now the last moment. How to calculate gears speed if we know only gear ratios of the car and can't see rpm graph (like we see in Gran Turismo 2 for example)? Of course we can test cars right on Test Course and see on which rpms gears are changing. But I though there is better solution to this.

I guess this is where I can come in. GT2 has three major changes from GT1 (besides the detailed RPM graph) that will alter your approach to gear setup: torque works slightly differently (almost all cars have high torque at low-RPM's, even when maxed out, and accelerate best when pushed past redline), tyre width seemingly has no impact on traction anymore and is no longer a stat in the car's spec sheet, and the Auto slider was introduced, which automatically generates a set of gear ratios that have either close or wide RPM drops.

Someone who has access to GT2's inner data might be able to find and provide the car's tyre width (or the 'base' one if all cars are using the same width), so you can calculate speeds using the formula pez2k provided. As just mentioned though, you'll need to go in-race to find out where redline is (or at least an approximation of where it is) if you want an RPM to calculate a speed for.

To save you the time though, I'll say this: from GT2 onwards, the best gear setup for a car is more easily found through trial and error, rather than logic. By taking the car's drivetrain and power band into account, you can use the Auto slider to generate a set of gear ratios that will keep the car within the power band at all times, then adjust the final drive afterwards so the car launches properly. For example, setting Auto to 6 works best for FF's and 4WD's that need both a fast launch and top speed, while FR's benefit from an Auto of 1 and a really long final drive to reduce 1st gear wheelspin.

It requires a lot of back-and-forth doing machine tests if you want an 'optimal' setup, but the game simply doesn't give enough info to make any proper calculations.

 

[Jandarman]

And I though that type of tires doesn't affect anything in gt2. Nope - I was badly wrong.

By taking the car's drivetrain and power band into account

Sorry, but what is "power band"? It is how wide is rpm range in which engine works at it's hightest possible HP?

 

[TeaKanji]

And I though that type of tires doesn't affect anything in gt2. Nope - I was badly wrong.


Sorry, but what is "power band"? How wide is rpm range in which engine works at hightest car's possible HP?

Ah, the tyre grade definitely affects traction and whatnot, but it doesn't affect tyre width like it does in GT1, at least not to my knowledge.

The power band is the RPM range between the torque and horsepower peaks. It's the range that you want to keep the car in as often as possible, as the engine will be running at peak performance.

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For example, this Honda Beat has peak torque at 7000 RPM and peak horsepower at 7900 RPM, so its power band is between 7000 to 7900 RPM. However, notice that in the engine curve, the power curve (orange line) goes beyond 8000 RPM and continues rising. So, its power band is actually higher than the game suggests, and it's best to gear up as late as possible with it. The power band is important when setting up gears, as you can control the RPM drop from gear to gear so the car is always within that RPM range.

We can see this Beat's rev limiter is around 8500 RPM, so let's say its actual power band is from 7000 to 8500 RPM. With an ideal gear setup, you would gear up at 8500 RPM and the RPM should drop to 7000 RPM or higher. So, you can set the Auto slider appropriately (1 in this case, as it gives the smallest RPM drop between gears), adjust 1st gear and the final drive until the car both launches properly and has enough top speed, and you should see improved acceleration.

 

[Jandarman]

Thanks for clarification on this one. Now I understand how it works.