I was surfing the web at work.. i mean... doing research..

Yeah, anyway, and I was at KBB and under the standard features of the tC it said that the tC has a 5 spd transmission w/ overdrive or a 4 speed auto transmission.

Just wondering what overdrive is. VVT-i? magic? only found topics regarding the xB and its automatic transmission in the search. Thanks!

 

Overdrive is a way to save fuel. It does not allow for engine braking. Engine braking uses engine rpm speed to slow down the speed of the car when your foot is off the gas.

vvt-i = variable valve timing. the i stands for intelligence

 

so then on the 5spd tc, is it like a button or what? how would it keep me from engine breaking? i remember seeing the button on my parents' cars (automatics), but i've never personally had a vehicle with that.

 

What? No...

By definition, an overdrive has a faster output speed than input speed. Overdrive is any transmission gear ratio that is below 1. In the case of the tC, both 4th and 5th are technically overdrive gears. The higher gears allow lower engine RPM at highway speeds which save fuel. This is why the Chevy V8s typically have 6 forward gears.

Reduced engine braking is a side effect of such a high gear, it is not the main reason for overdrive.

 

hmm.. i've read some posts where people complain of high RPMs in 5th while going highway speeds. 70-80 MPH @ 3.5-3.8K RPM-ish. i have yet to test drive, so i don't know myself. is that even with the "overdrive"?

 

yup, think that they kept the gear ratios the same from something else, but just changed the final gear so that everything's lower. great for accelleration, and crusing on the highway isn't bad at all, you're able to leave it in 5th instead of needing to downshift to pass, speed up, etc. downside is that the fuel economy sucks. commuting to work in the brand new tC (mostly highway, some city, no A/C) got me 26mpg. 80 on the highway will kill your gas mileage. *but* it's still 10mpg better than the jeep I used to have, so I'm in heaven right now. also, engine noise on the highway is also lower than what I'm used to, but other people might notice it. this car would be PERFECT with a 6th gear. (hint hint, if scion's listening)

 

I dunno, I'm getting 26-29mpg going 80 on the highways. But I have an auto so the gearing isn't as aggressive.

 

yeah, the auto mpg is better on the freeway than the M/T.... I'm getting about 25mpg freeway driving

 

i think that was a typo or something... manuals dont have overdrive because a 5 spd is a 5 spd. but a 4 spd auto w/ overdrive is possible. with out OD, the car runs on 3 gears (3 spd)

 

It has nothing to do with auto or manual. JasonH is correct, technically both 4th AND fifth on the tC are OverDrive gears. In fact I probably lifted this from one of his previous posts:

 

yeah. . . so many people believe that overdrive is some magic button that creates NOS like effects. . . it's just another gear(which translates to lower cruising RPM's).

Turning it off is just like downshifting or simply a way from keeping your tranny from using it's highest gear. Always leave O/D on(no orange light) unless you need to have it off for engine breaking or to keep it in a lower gear. For most drivers, you should never even touch the button and let the computer do the shifting(why they call it AUTOMATIC).