Technical question about MT/AT
 

Toyota offers MT and AT for the GT86/BRZ/FRS but gives very little information about the two transmissions in brochures and on their website. In fact only the 0-100 km/h-times (or 0-60 mph), which show us that the MT (7.6s) is a bit faster from a complete stop than the AT (8.2s). That is no surprise as the clutch-pedal in the MT-car makes it possible to "jump over" some of the characteristic naturally aspirated boxer engine torque dip by letting the clutch go on high rpm, while the AT-car has to go through the whole "valley".

I was wondering if the MT and the AT-car are equal in terms of acceleration once both cars are moving?

I saw that the AT-car, which has a torque converter, has different gearing ratios. The first gear is hardly any different. In the second gear the AT-car has 5.8% longer gearing (AT 2.060 vs. MT 2.188), which means that a tiny bit less torque is given to the tyres. The upper gears have a bigger difference. Final drive is the same. So you could get the idea, that the MT-car is faster from a stop and also once both cars are moving beause of the gearing.

On the other hand I saw that the AT-car drops down to 5000 rpm when shifting from first to second. The MT-car drops further down below 4500 rpm. If you look at a dyno-test of the engine you see that the engine starts to pull at about 4750rpm, so the MT-car loses speed when dropping this far down.

So the MT-car in this driving situation has a shorter second gear by 5.8% but drops also lower in the rpm range after shifting into second. Shifting speed of the AT is probably also better, so I think both cars are about equal when we speak about the range up to 100 km/h or the first two gears.

How the torque converter inflicts the whole gearing I dont know because Im not an engineer. Can you really look at the different gear ratios and say the MT-car is faster because of shorter gearing? For me it looks as Toyota wanted to make the cars equal, at least for sporty driving on backroads which takes place mostly below 100 km/h. But as I said, there arent hardly any informations or numbers from Toyota.

I found some tests made by magazines but you cant trust them 100%. A track test of a car is very much inflicted by tires, temperature, driver and in case of the FA20-engine the fact that its performance gets better with more miles. So Im more interested in a technical point of view.

Toyota offers some track testing days for their customers in some countrys. Has anyone been on such an event? What do they say there about the differences between the two transmissions apart from only 0-100 kmh-times?

One of the main reasons that the AT accelerates slower than the MT is that the final drive ratios in the diff are different, and more so in the 2017+ models, where the final drive in the MT was even further shortened. The gear ratios for the AT are better for highway cruising (NVH and Gas Mileage) because of this, resulting in a lower RPM at the same vehicle speed.

Note: this applies to the North America models, European models may be different

Final drive pre-MY17 was identical. The MT still won out due to having shorter gears. MY17 the MT has a shorter final drive, so it'll be at even more of an advantage.

But, the main reason MT wins a 0-60 is that it can launch a lot better. Gearing is barely a matter once you factor in the launch.

The torque converter eats performance. That's why the DCT was invented so there is no torque converter losses. Besides, MT or AT has nothing to do with perormance. If you want a comfortable cruiser, get the AT. If you want the most fun, get MT

I don't have firsthand experience but I'm pretty sure the TC is locked up by second gear.

The service manual highlights the efficiency of the locking TC and indicates engine braking in all except first gear.

HELLO Toyota 1 and WELCOME to our forum ...... :clap:

WOW! You put a bunch of thought into that question.

I have only two thoughts:

* the MT is faster off the line

* you have to shift the MT ..... the AT shifts for you

That's it in a nut shell .... from me at least ..... ;)

Enjoy the forum......:thumbsup:


humfrz

I think you're thinking about it too hard.

I have not done that particular event but I did drive my MT back-to-back with my wife's AT at an autocross event, when they were both showroom stock. I did not run data on both cars so the fact that the MT was faster could have been all at the launch. Once under way, both cars *felt* similar in acceleration.

okay where's that at thread? oh there it is, read it from the beginning.

AT thread.