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Old 12-11-2010, 04:24 PM   #1
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Quick Question for Gear Ratio

I'm trying to figure out my gear ratio, but won't have access to a lift till later this week. It's a '99 Jeep Wrangler Sport

When I purchased the Jeep it had 255/70 tires on it and since then, I've upgraded to 31s. Now everyone has told me that I would notice a power loss and it'd be annoying, but it hasn't yet. In fact, I think my gear ratio is pretty high, more like 4.10s.

The tires do measure 31x10.5

At 65mph in 5th I'm running about 2600RPMS. At 65mph in 4th I'm going about 2900rpms and it definitely feels like I need to upshift to 5th. I have very little problem climbing hills at 65mph in 5th, at 35mph most hills are in 4th. I can start from a standstill in 2nd with no problems.

My factory build sheet says 3.07, but they can't always be trusted. According to tire guide charts, it falls somewhere between 3.73 and 4.10, but I can't imagine that with a 255/70 tire the gears really were changed.

Any insight into this or am I looking at this incorrectly? I'm hoping at the least I have a 3.73 ratio so I don't need a new carrier for my gear swap.

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Old 12-11-2010, 04:27 PM   #2
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Could of swapped the axles out for a 4banger set or simply swapped the gears by the PO.

Want to be positive. Pop the covers. Or jack the rear up, drawn a line on the d-shaft with a piece of chalk or sharpy...spin the tire and count how many time the mark moves around.

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Old 12-11-2010, 06:34 PM   #3
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Would the D30 gear swap need a new carrier to go from 3.07 to 3.73? I know it would for 4.10s.
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