Top Speed and Transmission Settings

[ICON345]

Does transmission tuning affect the top speed of a car? Hypothetically, if a car has a top speed of 250, does setting the transmission to 400 affect the car's top speed? I know it affects acceleration, right?

 

[Tornado]

Yes. You want to set your transmission so it peaks in top speed around the point where it reaches its aerodynamic peak. If you set it too low, it will either drop off sooner or smack the rev limiter, and if you set it too high it likely will never make it near the potential top speed because it won't have the power to do so.

 

[ICON345]

Yes. You want to set your transmission so it peaks in top speed around the point where it reaches its aerodynamic peak. If you set it too low, it will either drop off sooner or smack the rev limiter, and if you set it too high it likely will never make it near the potential top speed because it won't have the power to do so.

I just tried this with a car it had the same top speed with both an unrealistically high limit and a more reasonable one.

Just one more question, does using a power limiter affect any of this?

 

[Tornado]

It really depends on the torque curve of the car just as much as the gearing.

 

[Santos i7]

Yes. You want to set your transmission so it peaks in top speed around the point where it reaches its aerodynamic peak. If you set it too low, it will either drop off sooner or smack the rev limiter, and if you set it too high it likely will never make it near the potential top speed because it won't have the power to do so.

Is there a way to find out what that point is or is it just trial and error?

 

[Tornado]

Pretty much. If you know the torque curve, you can get a rough estimate about generally where it needs to be, but for the most part it is just testing and retesting until you nail it.

 

[Exorcet]

The answer is yes, but as hes been explained above, it's more complicated than move the gear ratio one way to raise speed, move it the other way to raise acceleration. You can tighten your gears and decrease acceleration, and vice versa, but generally that doesn't happen.

For a given speed your acceleration is determined by horsepower. The gearbox's job is to keep the engine spinning at the RPM for best power (in the case of a race car). Some cars are very peaky, and only produce the top 25% (random number I'm using for example) of peak power between a narrow RPM band. This car is going to want very close gearing, and if it was geared for top speed, the acceleration would probably be slow. On the other hand some cars have relatively flat power curves and almost don't care how they are geared. With cars like that, close gearing can cause problems because of the break in acceleration that occurs when you change gears.

 

[ICON345]

The answer is yes, but as hes been explained above, it's more complicated than move the gear ratio one way to raise speed, move it the other way to raise acceleration. You can tighten your gears and decrease acceleration, and vice versa, but generally that doesn't happen.

For a given speed your acceleration is determined by horsepower. The gearbox's job is to keep the engine spinning at the RPM for best power (in the case of a race car). Some cars are very peaky, and only produce the top 25% (random number I'm using for example) of peak power between a narrow RPM band. This car is going to want very close gearing, and if it was geared for top speed, the acceleration would probably be slow. On the other hand some cars have relatively flat power curves and almost don't care how they are geared. With cars like that, close gearing can cause problems because of the break in acceleration that occurs when you change gears.

So say for example, with a 50% power limited car (same amount of bhp on most rpm ranges) it would be best to have far gear changes, is this how it works?

 

[Tornado]

Yes, because when you chop down an engine that badly it will drive terribly with closely spaced gears because the torque drops to nothing very soon in the rev range.

Though, this is a "general" thing. Applies to most cars, but not all.

 

[esoxhntr]

top speed transmission tuning is a lot simpler than implied above

if you're given a long straight to test on, simply tune your top gear to be at peak HP when you attain top speed. if it never reaches peak HP you've made top gear too long (top gear value too low). if the car keeps accelerating past peak HP, you made it too short (top gear value too high). this will ensure you leave nothing at the table.

so as an example, if a car makes peak HP at 6000 rpm, you tune top gear so that i) it can reach 6000 rpms and ii) when the car hits 6000 it is no longer accelerating.

using the engine limiter will decrease top speed 100% of the time.

 

[Exorcet]

That's a terrible idea for anything other than a straight patch of road.

 

[esoxhntr]

That's a terrible idea for anything other than a straight patch of road.

I may have misunderstood the OPs question then. I thought it was (any my response was geared to) tuning the transmission for max speed on a straight patch of road (ie ssrx)