http://www.hondanews.com/CatID2153?m...55013&mime=asc

I don't know much about gear ratios othe than waht I learned on howstuff works. Don't these gear ratios imply automatic gets better highway speed and mileage? (waht is final gear ratio?)
edit: sorry for bad formatting. it didn't copy and paste properly

 

That is a pretty large disparity. The auto will run quite a bit lower rpms on the highway, but I doubt that will equate to a higher top end. Automatics are notorius for consuming more horsepower than a manual transmission.
The load on the motor and rpms are what you'd need to know to calculate economy.
The final drive ratio is the final gear the motion passes through. Multiply the gear ratio times the final drive ratio to get the effective ratio.

I like to see how this changes thrust. Take the first gears of both setups for example.

The l15 generates an average of say, 95 ft/lbs through out first gear.

95 X 2.996 X 4.56 = about 1300 foot pounds of thrust. The auto consumes about 19% so total thrust at the wheels would be about 1050.

95 X 3.462 X 4.29 = about 1400 foot pounds of thrust. The manual should consume about 15% (maybe less) of that for wheel thrust to equal about 1200.

The manual will be substantially quicker off the line (at least once the torque converter is locked in....it provides additional gear multiplication).

These calculations are for an example only, as the real physics involved are more complicated, but you get the idea. Drive both cars and feel the difference for yourself.

 

https://www.fitfreak.net/forums/show...5&postcount=15

In that post, I have two links showing the speed of both transmissions at various speeds. The two transmissions top speeds will be drag limited. C&D had a top speed of 114mph for the manual. I would be surprised if the automatic would top out higher than that.

 

Well since you both know about autos well, i was wondering about acceleration performance if you use the paddles of the auto vs the regular MT? will auto be slightly slower than MT or much slower?

Thanks to both for informing me. I acutally wanted the MT for a long time, then I realized i lived in the hilly SF and MT may be exhausting. Also, if im drunk or someoen needs to use my car in general for emergencies, since most of my friends dont' know how to drive mt, it'll get inconvenient.

 

I assume you mean if somebody is driving you when you are drunk.

It can be a bonus having a manual if you don't want people to borrow your car all the time.

 

The only advantage the automatic with paddle shifters might have over the normal automatic is holding it in gear until redline, or just before it gets out of the powerband.

The gearing in the manual is much more aggressive than the automatic. In the automatic, the 4th gear is mathmatically capable of 126mph, yet the manual Fit with more aggressive gearing is gear limited to 117mph at redline in 5th gear. Since C&D acheived a top speed of 114mph with the manual Fit, don't expect the automatic Fit with longer gearing to go faster without more power (unless you are going down hill, or use another car for drafting).

This means the automatic Fit can hit it's top speed in 4th gear. 5th gear is only there for fuel economy. How much of an impact the longer automatic gearing will have is hard to tell. I'd guess the automatic will be doing 0-60mph just under 10 seconds and complete the 1/4 mile in a bit over 17 seconds.

 

What do u mean "without more power"? I can't help but conclude that since the fit manual gets clsoe to its theoretical math speed, we should expect fit auto to also would, which is 126mph. is i just cuz based on the past, autos 4th top speed never tops a manual's 5th top speed?

btw, i'm grateful for your knowledge. i didn't realize there were ppl who are attentitve to detail who study automatic's numbers. i thought most ppl good w/ tech stuff know manuals but not automatic technical knowledge.

 

Both cars need the same power at the wheels to go 114 mph. Since the automatic is reving lower it has less power in 4th than the manual (it is also slightly less efficient and slightly heavier), so it will be lucky to hit 114, and will certainly not hit 126.

Do wish the manual had a taller top gear. Maybe next generation. Seems like I am always waiting for next year.

 

The automatic will have a hard time reaching the top speed of the manual, since the gearing is longer, and won't help the acceleration. The wind drag will limit the top speed, especially for the automatic. I'm curious to find out how often the auomatic Fit will downshift to 4th on the highway.

Think of it like a 10 speed bicycle with really long gearing. The higher the gear, the harder it is to accelerate. Add to that the wind drag that a car, especially a tall one like the Fit has and suddenly you won't be able to go any faster.

If you were to turbo an automatic Fit, it would then have the ability to combat the higher wind drag and go faster.

 

It seemed like 114 was too low for an engine limited top speed, so I did the math myself and it turns out that a fit will theoretically do 136.5 mpg in top gear with the manual transmission. Of course the wind resistance will prevent this.

The Fit turns 2,856 rpm in 5th gear @ 60 mph (by plugging in the ratios and the tire size - see below). This is 21 miles an hour for every 1,000 rpm. 21 x 6.5 (6,500 rpm limit) is 136.5.

=B1*C1*(63360/((PI()*(2*(D1*(E1*0.01))+(F1*25.4)))/25.4))

The above formula will calculate engine rpm at 60 mph in an excel spreadsheet.

A is the cars name (obviously not in the formula)
B is final drive ratio
C is top gear ratio
D is tire width
E is tire section
F is rim diameter.

 

Why is there a huge difference in reverse between the AT and MT?

 

Damn it, I just noticed I did a typo in the link I made. I screwed up the final drive for the manual.

Wind resistance owns either way.

 

In reverse the torque converter will never usually lock up. You probably would never notice a difference in reverse.

 

I'm guessing maybe the auto is heavier or sluggier, and therefore needs higher ratio to ensure a high reverse torque/power. I dont' know why u care haha.