Smart Car of America Forum banner
1 - 20 of 49 Posts

·
Registered
Joined
·
107 Posts
Discussion Starter · #1 · (Edited)
Has anyone changed the rear gear ratio? Almost all of my driving is on the freeway and I would love to have the car running at 2,000rpm on the freeway instead of 3,000 or 3,500rpm. That alone should improve the gas mileage and lengthen the life of the engine. Yes, I might have to downshift into 4th once in awhile but it would be worth it.
There are many rear gear ratios available for my Mustang but what about the smart?

I have 70 series tires on order for the back to help BUT that will not drop it to 2000 rpm. I live at 4500 ft elevation and drive 54 miles to work which is a sea level. I can drive the entire way at 1500 to 2000 rpm no problem. Going home I might have to drop into 4th gear to climb the 4,500ft but 1st gear is almost worthless. I shift out of 1st gear within one car length.
 

·
Registered
Joined
·
1,451 Posts
Use taller tires, it would effectively raise the gear ratio w/o taking anything apart but will affect the speedometer.
 

·
Registered
Joined
·
107 Posts
Discussion Starter · #5 ·
I am going to 70 series tires. That will drop the revolutions per mile from "about" 900 to "about" 800 but I STILL would like to have a much lower gear ratio or overdrive. I drive 54 miles from 4,500ft elevation to sea level and I can do that at 1500 to 2000 rpm's no problem. YES, I might have to down shift to 4th at times to climb the hills but I have been climbing the hills for 62,000 miles now at 3,000 rpm so I would just down shift to 4th if needed.
 

·
Registered
Joined
·
107 Posts
Discussion Starter · #6 ·
I have 70 series tires on order now so I will be going from 55 series to 70 series. It will help but don't think it will drop the rpm's from 3000 to 2000. I will post once I have the tires installed. I am getting 45mpg with now using Royal Purple oil and a K & N air filter but would like to improve the gas mileage if I can.
 

·
Registered
Joined
·
1,234 Posts
.... think that's the first i've heard of someone using Royal Purple in a Smart. but hey... i guess when you only need 3-4 quarts for an oil change.... it's not as ghastly expensive when you need it.
 

·
Registered
Joined
·
4,297 Posts
I would venture to say the possibilities of having different gear ratios for that tranny here in the US would be 0.
 

·
Banned
Joined
·
3,834 Posts
I posted the HP/Torque charts from smart in another thread. The torque line is quite flat. here it is again:

I have always wondered about that particular torque/power chart, and why it was done in that manner. Probably looks more dramatic. Usually lb-ft is plotted with British horsepower (not watts), and the two lines always cross at 5,252 RPM. Anyway, torque is the real measure of an engine’s useable ability, quantified by a “total-area-under-the-curve” calculation. The Mitsu guys did very well in this case with an early high-rise, then a long, flat torque curve with little fall-off nearing red line - makes one think that they know what they are doing.
 

·
Registered
Joined
·
4,297 Posts
how about an overdrive Barney? isn't it time for a new project??
For what it's worth a friend of mine found an automatic transaxle that appears to be a direct bolt on to the mitzu 45 degree engine. Only problem, it's built for a Japanese car.
Trying to find one and a way to get one shipped over here might be a major challange!
 

·
Banned
Joined
·
319 Posts
Has anyone changed the rear gear ratio? Almost all of my driving is on the freeway and I would love to have the car running at 2,000rpm on the freeway instead of 3,000 or 3,500rpm. That alone should improve the gas mileage and lengthen the life of the engine. Yes, I might have to downshift into 4th once in awhile but it would be worth it.
There are many rear gear ratios available for my Mustang but what about the smart?

I have 70 series tires on order for the back to help BUT that will not drop it to 2000 rpm. I live at 4500 ft elevation and drive 54 miles to work which is a sea level. I can drive the entire way at 1500 to 2000 rpm no problem. Going home I might have to drop into 4th gear to climb the 4,500ft but 1st gear is almost worthless. I shift out of 1st gear within one car length.
What ratio were you thinking would be good? 3.73:1, 3.42:1 or taller?

Come on, the car doesn't have the power to pull a sick wh0re off a piss pot already even with a turbo and you want a taller gear! :rofl:
 

·
Registered
Joined
·
2,551 Posts
... but would like to improve the gas mileage if I can.
Hypermilers would likely tell you to change your driving style not your drive train. Driving slower would show noticeable gains. The smart has all the aerodynamics of a brick, cut out extra drag by slowing down and save some fuel.
 

·
Registered
Joined
·
295 Posts
Use taller tires, it would effectively raise the gear ratio w/o taking anything apart but will affect the speedometer.
I have thought about this as well. Has someone actually checked to see if the rear tires drive the spedometer and the odometer?

Also, does anyone know how much taller you can go on the tires compared to stock (does not look like there is much space there)?
 

·
Registered
Joined
·
295 Posts
Hypermilers would likely tell you to change your driving style not your drive train. Driving slower would show noticeable gains. The smart has all the aerodynamics of a brick, cut out extra drag by slowing down and save some fuel.

Yes, but a combination of the two would net even better mileage.
 

·
Registered
Joined
·
499 Posts
Would not taller tires mess with the abs, esp, traction control. I know if you have too much of a differance between front and rear it'll mess it up. If you go up in size the same front and rear will it be ok?
 

·
Registered
Joined
·
755 Posts
how about an overdrive Barney? isn't it time for a new project??
What if I told you I also have the transmission apart in pieces as well? .. hmmm.. titanium gears.. haha just kidding...

Honestly guys, in my opinion the stock smart doesn't have enough power in general to cruise at 2000 rpm without it downshifting more then 50 percent of the time.

I live in san francisco and sure there are hills in the city but not on the freeways. Even the slightest incline on the freeway will have you put your foot down to the floor in 5th gear and it wont accelerate in 5th gear. Imagine if your gear ratio was even higher, that would make things even worst...

Don't get me wrong, I really want a higher gear ratio for the last gear but not with the stock smart. Even turbocharged smart cars with a hot intake air temp and lower end boost level like 5-6 pounds would have a hard time pushing a higher gear ratio in the current 5th gear.

If the freeway you drive on is relatively flat, then sure, there's a better chance a higher gear ratio will help but other then that... In my opinion, it's not all that great.

If you want an example... in 5th gear, with 230 wheel hp on the smart.. after 100 mph, the claim is so... slow....

I personally would re do all the gears, not just the 5th gear :)

Larry
 
1 - 20 of 49 Posts
Top