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post #1 of (permalink) Old 02-20-2003, 10:47 AM Thread Starter
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Still Figuring Gears and RPMs

i've been a tad confused figuring out the rpms before and after the gear swap and tires. my numbers don't really make sense with how the truck was driving. the truck felt really doggy and slow of the line, and i had no clue as to which way my speedo was reading...but other traffic sure passed me right and left! :wall anyway....

according to the calculators:
(Auto/OD tranny)

3.42s + 265s = 1782rpm @ 70mph

ok, that's about right, if memory serves me correct.

then: 3.42s + 33s = 1706rpm @ 70mph
32.8 = 1717rpm @ 70mph

hmmm, why the big discrepancy on my seat-o-meter?

so, theoretically, after gears:

4.10s + 265s = 2136rpm @ 70mph

4.10s + 33s = 2046rpm @ 70mph
32.8 = 2058rmp @ 70mph



i guess my biggest beef is why was the truck such a weeny after going up a tire size. i weighed and measured the two tires. the difference was 1.2" and 5lbs for each tire. the only thing i can think of is i didn't weigh or measure them very good - so i can do that again. i just find it wierd :-?

am i missing something??
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post #2 of (permalink) Old 02-20-2003, 11:19 AM
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Re: Still Figuring Gears and RPMs

shorts maybe im confused right now, but are you factoring in the speed offset when you figuring the bigger tires.
i know bigger tires make you read slower than your going and going to deeper gears makes you read faster than your going. when i went up one tire size on 3.42s it didnt affect performance too much but down shifted alot on the highway.
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post #3 of (permalink) Old 02-20-2003, 12:04 PM Thread Starter
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Re: Still Figuring Gears and RPMs

i posted this over on ck5 board - i think i figured out why the truck took a hit. that was around the time when my front diff was stuck in lock. and i thought the 33s were adding the trouble. in reality, after i took the 33s off, the truck was still doggin' around and then i figured out the front was stuck and eventually got it unlocked. i need to put the 33s back on and see how it drives now.
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post #4 of (permalink) Old 02-20-2003, 12:10 PM
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Re: Still Figuring Gears and RPMs

no kidding you do [img]images/graemlins/smile.gif[/img] however you also still need to re-gear for your trannys sake. [img]images/graemlins/frown.gif[/img] but atleast you can afford to drive it on the 33"s for a while now.
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post #5 of (permalink) Old 02-20-2003, 12:46 PM
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Re: Still Figuring Gears and RPMs

I have a manual. I also have 33's and stock gears in my TJ. I don't use 5 th gear unless I'm going down hill. Most times I still don't bother. I learned to live in the granny lane untill I could afford a swap. You have an auto. Does it keep switching to 4th and just sit there and lug the engine? You might have to leave it in 3rd. You will get performance, not lug the engine. I'm not too sure what that will do to the automatic though. [img]images/graemlins/thud.gif[/img]
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