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Old 06-05-2008, 02:13 PM   #11 (permalink)
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So in essence, the cliff notes version is "I'm making 5th gear taller to reduce RPMS on the hgihway" ?

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Old 06-05-2008, 05:22 PM   #12 (permalink)
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So in essence, the cliff notes version is "I'm making 5th gear taller to reduce RPMS on the hgihway" ?
Yup.

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Old 07-26-2008, 09:56 PM   #13 (permalink)
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is it a safe thing to do?

if you can't hack your tranny, the concept of "dubs" wheels cramming the wheel wells full is a decent option, or just bigger wheels and tire. Taller rubbers on little wheels actually hurt more than gain. It is a tall tire tale (haha). Most well disciplined trannies have non-straight gear and change quite dynamically to this one simple move.
I can use my own example of a old subaru, 15 inch wheels were difficult to find, but ,anyway, it came with tiny 13 inch wheel tires (23.2 inch diam). The same rpm, given the japanese wonder tranny, does 80 instead of 65 with 25inch diam..engine runs out of power first. This also increases safety, a thought for you tall gear swappers and low tire ratings. Seems the saturn went to a higher ratio for a reason.Alot of times, more than not, higher ratios OEM mean a weakness someplace, even though engine has enough power to go much taller geared. I learned the hard way...
Are the wheels the same as the saturn with tall gears as the one getting the swap?
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Old 07-27-2008, 12:55 AM   #14 (permalink)
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if you can't hack your tranny, the concept of "dubs" wheels cramming the wheel wells full is a decent option, or just bigger wheels and tire. Taller rubbers on little wheels actually hurt more than gain. It is a tall tire tale (haha). Most well disciplined trannies have non-straight gear and change quite dynamically to this one simple move.
I can use my own example of a old subaru, 15 inch wheels were difficult to find, but ,anyway, it came with tiny 13 inch wheel tires (23.2 inch diam). The same rpm, given the japanese wonder tranny, does 80 instead of 65 with 25inch diam..engine runs out of power first. This also increases safety, a thought for you tall gear swappers and low tire ratings. Seems the saturn went to a higher ratio for a reason.Alot of times, more than not, higher ratios OEM mean a weakness someplace, even though engine has enough power to go much taller geared. I learned the hard way...
Are the wheels the same as the saturn with tall gears as the one getting the swap?
I don't understand your question, but here is my context. The transmission is identical except for the fifth gear. This gear was designed with the lower HP SOHC engine in mind. My DOHC has a different BSFC map than the SOHC :

http://ecomodder.com/forum/15008-post4.html - Post #4

I don't have the BSFC map for the SOHC. I should find it. However, even if I did find it, I wouldn't know how to interpret the differences, .

In terms of safety, under an emergency, I would have to downshift to a lower gear no matter which 5th gear I have, so I don't consider it to be a critical issue.

...

My current tires are one-size-up from stock :

http://ecomodder.com/forum/showthrea...ires-2642.html

I think the thing to keep in mind regarding tires is that I am *not* doing the Dub thing. I consider the Dub thing to be an aesthetic choice that consciously sacrifices safety/engineering for the sake of style. By going "one size up" on my tires, I think I am pushing one design parameter in my car "by one notch". I don't consider this to be a drastic change.

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Old 07-27-2008, 08:40 AM   #15 (permalink)
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Old 07-27-2008, 10:43 AM   #16 (permalink)
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Hey! Don't forget about me!

I swapped the R&P in the rear axle of my F-350. I went from a 3.73:1 (2000 RPM @ 70 MPH) to a 3.08:1 ratio (1700 RPM @ 70 MPH).

My MPG improved from 20 MPG to 23 MPG at the time. A 15% improvement in MPG is nothing to sneeze at.
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Old 07-27-2008, 12:44 PM   #17 (permalink)
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Quote:
Originally Posted by cfg83 View Post
...

My current tires are one-size-up from stock :

http://ecomodder.com/forum/showthrea...ires-2642.html

I think the thing to keep in mind regarding tires is that I am *not* doing the Dub thing. I consider the Dub thing to be an aesthetic choice that consciously sacrifices safety/engineering for the sake of style. By going "one size up" on my tires, I think I am pushing one design parameter in my car "by one notch". I don't consider this to be a drastic change.

CarloSW2
I also advocate the slight tire size change. I found it actually helped my FE (a 2% circumference change actually seemed to help my FE by about 2%, though YMMV, of course), without noticeably hurting performance.

To threadjack further:

I Just found out that the taller ninth-gen Corolla 5th gear (from the five-speed) fit the xA/xB. When I some day have to replace my clutch, I may do this. The limited clearance under the hood may prevent use of a puller to get the gears off, apparently.
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Old 07-27-2008, 09:53 PM   #18 (permalink)
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I used to have an HF 5th gear in my crx si, I remember having one tank at 50 MPG but most of them were mid 40's but this was before I was into hypermiling, I still had the si final drive, I had put the long gear in just to get back and forth to the autocross. I still have the gears if anyone is interested in buying them, I know I have them somewhere burried in my garage.
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Old 07-27-2008, 11:29 PM   #19 (permalink)
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In the pickup community, a lot of guys have tried bigger diameters tires and the result is always the same: lower MPG.

The rotational inertia of the wheel tire assembly goes up with the square of the diametyer. Every time you accelerate the vehicle you have to not only translationally accelerate the vehicle but also you have to rotationally accelerate all the rotating machinery including the wheels and tires.

So everytime you pull away from a stop bigger tires have the same effect of alot more weight. Very few guys can drive so as to recover all that energy by coasting.

This is why very high-MPG cars come with preposterously small wheels and tires.
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Old 07-27-2008, 11:38 PM   #20 (permalink)
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Quote:
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Very few guys can drive so as to recover all that energy by coasting.
Do you think they can learn?

Quote:
Originally Posted by Big Dave View Post
This is why very high-MPG cars come with preposterously small wheels and tires.
There is nothing absurd or contrary to nature about making an efficient vehicle and selecting appropriate equipment to meet that end?!? It would be absurd to put tractor tires on a metro.

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