What do you want? - Fiberglass RV

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Old 02-04-2009, 09:44 AM   #1
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Chart- Numbers on top = tire height
Chart -Numbers on the left = gear ratio

Change either gear ratio or tire height .

If you want better gas mileage, find your gear ratio on the left and pick a new tire height to lower the rpm to get better mileage.

If you need more power, pick your gear ratio on the left and pick a smaller tire height to increase your rpm.

Don't go to far either way.

More information at http://www.4lo.com/calc/geartable.htm

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Old 02-04-2009, 10:09 AM   #2
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You didn't mention transmission ratio in selecting a RER and tire size. This also effects fuel milage and engine RPM.

In the case of the Escalade the final transmission ratio is 0.7.


CD and Joyce Smith - Lily, Violet, and Rose
1999 Casita 17' SD - "The Little Egg"
2007 Escalade - 6.2L V8 - 6L80E Trans - 3.42 Diff
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Old 02-04-2009, 08:38 PM   #3
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Actually, the tire size is part of the total drive ratio, that starts with engine rpm and ends where the rubber meets the road -- Swapping tire size when the tires need replacement is the least expensive way to change the ratio -- The gears in your transmission also make a difference, esp the tasks of moving slow on rough ground, backing into campsites, etc. -- That can really challenge a clutch or auto trans and is where 4WD-Low is very handy
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Old 02-04-2009, 09:45 PM   #4
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Don't forget to recalibrate your speedometer if you choose to do this.

-- Dan Meyer
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Old 02-04-2009, 10:10 PM   #5
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Don't forget to recalibrate your speedometer if you choose to do this.

-- Dan Meyer
I thought of that too, Dan, and noticed that they have a conversion function on the page for that.

Tangential story:
My car takes a European sized tire, which is 185-R14. Well, once I went in to get tires (on my way out of town on a cross-country trip), and as I headed east I noticed that a lot of people seemed to be passing me. Well, long story short, the tire place had decided to put on tire size 185-70R14, which is not the same at all. ARGH! Once I figured that out, I did some timed mileage runs and figured out that my speedometer/odometer were about 10% off, and so I was driving 10% slower than I thought. That explained all the passing.

So I went back in to the tire shop (and it was a tire shop, specifically!) on my way home and explained the problem. They refused to believe that the two tires could be different sizes How exasperating! I pulled some circumference figures that I had written down out of my pocket (I had a feeling they wouldn't believe me), but still no dice ("But we put this size on someone else's Volvo and they didn't mind"). They actually made me drive around with one of their technicians and a handheld GPS. Lo and behold.... about 10% off. When they ordered in the proper tires.... my, my, right on!

Since that tire size is hard to find, I've since done some calculations and found that the much easier to find North American size of 195-75R14 is almost exactly the same circumfrence as the 185-R14, so that's what I get now.)


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