5th gear swap
 

I hate the high RPMs the 5 pulls on the hwy it kills the hwy mpg. There has got to be a taller gear that will swap into the tranny. Anyone got any ideas?

Jeremiah

It's probably POSSIBLE, but...you could spend a lot of time trying to locate the exact gear you're looking for that would fit in your exact transmission.

http://freehindu.com/wp-content/uplo...free-hindu.jpg

Then, you'd need to be a serious gearhead to be able to pull the tranny and successfully replace fifth gear. If you're not, there's more cost. Could be a lot of cost and effort to save a marginal money at the gas pump. Let's look at some hypothetical numbers:

Assumptions:
...You drive 5,000 miles per year in top gear on the freeway.
...You get 28mpg cruising in 5th gear.
...You could average 36mpg with a taller "6th" gear ratio.
...Gas prices will remain near $4.00 per gallon.

Therefore:
...5,000 miles / 28mpg = 178.6 gallons per year in top gear.
...5,000 miles / 36mpg = 138.9 gallons with a "6th" gear.
...178.6 -138.9 = 39.7 gallons per year saved.
...39.7 gallons x $4.00/gallon = $158.80 annual savings - - not great, but not inconsequential either.

Change whatever parameters better fit your situation and "run the numbers."

Another consideration is the negative impact of not having a true 5th gear after the swap - - like always shifting from 3rd to 5th now. That could be a pain in the a$$, especially when accelerating or in a situation that begs for a 5th gear, like when unable to drive beyond 40mph. Also, is the eventual buyer of your car going to want a cavernous gap between 4th and 5th gears?

Food for thought...:)

(BTW, I also lament the lack of a 6th gear in my 2012 Mazda5 GT. :()

Then again, there's absolutely zero chance that a gear change (to any gear) would allow a Mazda5 to see an improvement from 28 mpg to 36 mpg. Period, full stop, the end. The most wildly optimistic guess would be an improvement to 30 mpg, and even that is unlikely.

I can do the work myself and if there is a gear in an older mazda that will fit the transmission it would be fairly inexpensive. As far as making economical sense, I have never been that gear head. I should work for the government with that attitude, I would fit in.

Thanks for the numbers, I cannot argue.

I typically tool around our area at about 72 mph; in 5th gear (5-Speed Manual) that speed equates to about 3,100 RPMs for the engine in my 2009 Mazda3.

same gear ratios for the 5spd auto, mazda likes to recycle the trans and engines into whatever they can

As I said, plug in your own numbers and pencil it out. :)

Just stumbled upon some interesting (to me, anyway) stats on the two Mazda5 transmissions for 2012.

First, both transmissions are rated at 21/28mpg. :confused:

Second, the 5-speed auto actually has a taller (lower numerical) overall top gear ratio than the 6-speed manual. :confused: :confused:

One of the reasons for the taller top gear is to give the 5-speed auto better fuel economy. Those who get into gear ratios would probably find this gear comparison quite unusual, as 6-speeds will almost always carry a taller (lower numerical) top gear overall ratio.

Here's how the two trannies compare in terms of ratios:

6-speed manual: (gear/ratio/overall ratio)
Final drive ratio: 4.105
...1st 3.454 14.18
...2nd 1.842 7.56
...3rd 1.233 5.05
...4th .914 3.75
...5th .755 3.10
...6th .680 2.79

5-speed automatic:
Final drive ratio: 3.458
...1st 3.62 12.52
...2nd 1.925 6.66
...3rd 1.285 4.44
...4th .933 3.23
...5th .692 2.39

The true comparative numbers are in the third column - overall ratio (which is the transmission gear ratio multiplied by the final drive ratio, through which the transmission supplies power to the drive wheels).

This implies that the 5-speed auto actually runs at 14% LOWER RPM in top gear than the 6-speed manual - - very strange if true - - assuming identical tire circumferences.

Another oddity: while the 6-speed drops revs by 10% from 5th to 6th, the 5-speed drops revs a huge 26% from 4th to 5th. :eek: For this reason alone I wouldn't recommend an even greater spread. Nor would I recommend a lower numerical final drive ratio, as this would kill the already feeble acceleration of the auto-equipped Mazda5.

It's clear that the 6-speed manual should easily out-accelerate the 5-speed, as each overall gear ratio is shorter (higher numerically) than the 5-speed.

Interesting...;)

Mazda5 wish list to Mazda:

• TURBO!
• 6-speed automatic!

:D

My 2012 Mazda5 GT with 5-speed auto runs at about 2350rpm at 70mph. Mazda uses a very tall final drive ratio to achieve this. I'd still like to see about 1750rpm at 70. :D

Hmmm, while I've never done what might be called an exhaustive study, in my experience at least when comparing two otherwise identical cars, one with an automatic and one with a stick, the car with the automatic ALWAYS has the taller overall gearing. The only possible exception to this (if I remember correctly) is when comparing the 6-Speed Manual GTI to its DSG equipped sibling.

That is exactly my problem. I roll over 3k at cruising speeds and I only get around 26 mpg. I would love a taller final drive. Maybe a 6 speed conversion. Way better than the 09 5 speed.