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importance of gears

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by tecton, Apr 3, 2003.

  1. tecton

    tecton 1/2 ton status

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    will a change from 31 to 33 inch tires make a big diff on preformance w/ stock gears?

    also...could someone explain why u need lower gears for bigger tires ect...the ups and downs....this confuses me
     
  2. CamaroZ85

    CamaroZ85 Registered Member

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    As you increase the tire size, it takes more effort to spin the tires. Using a numerically higher gear makes it easier to spin tires, thats why people upgrade gears when upgrading tires. Imagine it as trying to start off in 2nd gear with a manual car. The gear ratio in 2nd gear is lower than in first gear. Its much easier to start off in 1st. I hope this helps, sorry I just dont know how to explain the physics of the larger tire requiring more effort...
     
  3. MTBLAZER89

    MTBLAZER89 3/4 ton status Premium Member GMOTM Winner

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    Yes it will make a small difference. The stock gears in a Blazer are to high to begin with 3.08. This means the driveshaft turns 3.08 time to one tire revolution. When the tires get taller your final drive ratio actually changes because a bigger tire has to travel farther around to make one revolution. Plus the added weight of bigger tires takes more power to turn. I hope I explained it right. I went from a 31 to a 33 and you lose some of your low end. You also lose your acceleration on the highway. It is still drivable you just lose a little power. Check here for some useful tables.
    http://www.4lo.com
     
  4. tecton

    tecton 1/2 ton status

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    is it practical to have gears changed?
    i know they effect top speed...but im looking to get more low end power
     
  5. bajaviking

    bajaviking 1/2 ton status

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    If you want more low-end then gears is the way to go. If you have an OD tranny and plan on getting 33's some 4.10s would be good.
     
  6. tecton

    tecton 1/2 ton status

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    i have 33's now...it just feels like the thing should be faster than it is

    i had a 83 lwb truck, with a crapped out 350, stock carb and exhaust...and that and mine would have a close race....i just think there is something that is bottlenecking...exhaust....gears....something
     
  7. zakk

    zakk 1/2 ton status

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    so you have an '86.

    IIRC, that year had the 700R (???)

    If so, you can gear alot deeper, as OD will make up for it at freeway speeds and give that "butt in the seat" feel.

    Dr. Watson runs a 700R and with 5.13's and 42" tires, his RPM's are not high enuff to get into OD. so, IMHO, if you are ever going to get up into the 35-37" (or more) tire sizes, gear deep now and use OD to keep RPM's resonable.

    BTW, gears are expensive, so it is really something you don't want to keep doing until you get what you want. If you search, you can find an extensive post of the Pro's Con's I did for MilpitasK5. Damn i wish i had that post bookmarked...
     
  8. rich01

    rich01 Registered Member

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    i would put some 4.10 gears on there. you dont want your transmission to be overworked because you may end up having to get a new one. 33's arent a big increase from 31's but if you are thinking of ever going bigger than that you may as well get the gears and because you want more low end power.
     
  9. bryguy00b

    bryguy00b 3/4 ton status

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    not to mention gas milage as well..will probobly decrease a little bit wouldnt it? im running 31's with a 700 and 3.08's and id say its just about right...
     
  10. Chris_T

    Chris_T 1/2 ton status

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    My mileage actually went up when I went from 3.73s w/ a 700R4 and 35's to 4.56. The reason was that the overdrive actually became useful instead of lugging in really low rpms. If you do the math, 700 with 3.73 in OD is like running 2.61 with a TH350. Not exactly good with 35's. The 4.56s in OD are equivalent in rpms to 3.20 or so without it.

    I think I could have gone with 4.88s, but the difference between 3.73 and 4.56 was huge and easily one of the best performance gains I've noticed.
     
  11. wrathORC

    wrathORC 1/2 ton status

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    Find out what gears you've got. 3.42s and 33" rubber with a 700R4 is liveable. 3.08s and 33" rubber with a 700R4 makes you complain. 2.73s and 33" rubber makes overdrive useless. And it's a gutless wonder. The transmission spends most of its time with the torque converter unlocked even in third gear and that makes 700R4s complain.

    If yours came with 31" rubber it should have had 3.42 or 3.73 gears. 3.73s are about ideal, especially if you ever happen to switch to a smaller tire (like I do when winter rolls around).

    4.10s are perfect for 33" rubber and a 700R4 in my opinion. You'll spend less time with your foot in the stupid pedal because the motor isn't working as hard. This makes your gas mileage go up.



    However, I have 2.73s. And I can say that with airplane gears it feels like I throw out a parachute when I put it in overdrive going down the highway. Barn door aerodynamics certainly don't help.
     
  12. tecton

    tecton 1/2 ton status

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    my OD is fine....sometimes a little hard to get into like....at 65 if i want to punch it itll take a little work to get into OD...but at 70 or so itll click on like nothing and if i dont watch im doin 85...

    first gear sometimes it will jerk me back...soemtimes it feels like the tranny never downshifted and its still in 2nd cause i wont take off for nothing

    the guy i got it from said it had a high rpm <something> manifold that would only kick in at high speeds......

    uhm....yeah

    im not going to get any bigger tires....probably wider, but ill stay with 33's
     
  13. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    I ran 33's with 3.73 gears on my 700R4 for almost six years. It was just perfect, though it was a dawg on hills. No tranny problems and had enough low end power (9.5 0-60 /forums/images/graemlins/thumb.gif) to suit me.
     
  14. tecton

    tecton 1/2 ton status

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    mine dont like hills too much

    im gonna try a higher octane fuel and then a diff air filter...work my way up to just buying viper /forums/images/graemlins/thumb.gif...oh, i mean...corvette....yeah /forums/images/graemlins/grin.gif
     
  15. Chris_T

    Chris_T 1/2 ton status

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    When I had the 3.73s and 35's mine didn't like hills much either. What helped a little was a switched torque-convertor lock-up. My convertor is always locked in 4th unless I unlock it manually. See the hill coming, unlock the convertor until you get to the top. It allows a few extra rpm and doesn't bog as badly. With the 4.56s I don't use it unless I am going up a hill in OD at speeds less than 55 or 60
     
  16. sled_dog

    sled_dog 1 ton status

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    I'm running a brand new powerful 355 with cam and full dual exhaust and some 31s with stock 2.73 gears, let me just say DOG!!! The k5 is just slow, everybody pulls me up till like 45. Above that she comes alive and RIPs. I am going 4.10s and planning 35s hoping she will be the fastest 4wd truck out of my friends. I have an SM465 and with the 31s I have to start out in low gear or else I ride the clutch much mroe than I like.
     
  17. jekbrown

    jekbrown I am CK5 Premium Member GMOTM Winner Author

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    [ QUOTE ]
    The stock gears in a Blazer are to high to begin with 3.08.

    [/ QUOTE ]

    ...whats stock depends on the rig... my K5 came stock with 3.73s. /forums/images/graemlins/grin.gif

    j
     
  18. Pookster

    Pookster 1/2 ton status

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    I think somewhere along the line too, is that everyone's 33" and 35" tires arent the same diameter. Realistically speaking, a change in 2" from 31 -->33--> 35, is only a 1"->3" difference in acutal difference in applied power to the ground ( I think. My physics is a little bit shoddy nowadays).

    The problem is also that a lot of 31" tires are really 30" (or even 29.5), and some 35" tires are really close to 35", so then you end up with ever increasing leverage.

    My worn 35" is almost the same height as my rather new 33"!!

    But as everyone says, get bigger gears, you can always find someone to sell it to later if need be!
     

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