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gear ratio / tire size

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by imconfused, Jul 9, 2000.

  1. imconfused

    imconfused Registered Member

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    My '85 K5 came with 31x10.50.15 tires and has a 3.08 axle ratio. I am going to install 33x12.50 within a week and was wondering if I will cause any harm using such low gears. I realize that I will lose some low-end but does this harm the tranny or motor at all?? I would like to change the gears within the year if I find some$$$. Do you think that 4.10 would be a good choice for the 33's or possibly 35's down the road?? I drive mostly around town with little highway or off-road at this time. Almost forgot ...Tranny is a 700R4. thanks for the help!!
     
  2. Balou

    Balou 1/2 ton status

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    I am on 35" with 3.40 gears, that's just fine for street, for offroad I have SM465/NP205 setup, thats fine as well.

    I learned bigger tires will bring the engine in lower rpm, which of course will reduce stress to engine and tranny.
    Even you should have a better mileage with bigger tires.
    Driveline/steering should be fine as well, as long as you don't go over 35" tires.

    3.08 to me sounds a little low, if you don't care the cost go for 3.73 or 4.10, if you think of serious offroading go at least with 4.56+ and lockers.

    Balou
    "Size DOES matter!!!", said the girl last night.
    http://www.balou.coloradok5.com
     
  3. chevy4x4

    chevy4x4 1/2 ton status

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    Actually, 3:08 gears aren't low, they are high. 7:13 gears are low. In the gear world the higher the number, the lower the gear. The lower the number the higher the gear. Yeah if you don't do lots of off roading you should be ok with the 33s for a while. 4:10 are a good choice for 33s or 35s, If most of your driving is on pavement.

    <font color=red>Chevy4x4<font color=red>[​IMG]
    http://fourbyfour.coloradok5.com
     
  4. Balou

    Balou 1/2 ton status

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    gagaga, I know this, but what was first: Chicken or egg?
    6.55 is a high no., 1:6.55 is a low ratio,...

    Balou
    "Size DOES matter!!!", said the girl last night.
    http://www.balou.coloradok5.com
     
  5. 90K5

    90K5 1/2 ton status

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    I have the same problem almost and I'm going to 4.10 for 33" BFGs. Also the mileage will be a little better than you think because if you go with 33s then if the odo says you go 100 miles you really go 106.
     
  6. JimmyDie6.2

    JimmyDie6.2 1/2 ton status

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    I have 3.42s with the 700r4 and 33s ,diesel power and it is slow slow slow....mileage is good though about 20mpg.
     
  7. bigjbear

    bigjbear 1 ton status Staff Member Moderator

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    No, rember it is a ratio. As in 3.08:1 or 4.56:1. The "to one" or ":1" often gets left off but it is implied. 3.08s are higher than 4.56s because 1/4.56 < 1/3.08, or one devided by four and fifty-six hundrethes is less than one devided by three and eight hundreths. You can rember it this way: high gear in your trans is 1:1 (assuming a TH 350) low gear is 2.5:1. Got it? Jim.

    BigJBear '80 GMC
    http://www.bigjbear.coloradok5.com
     
  8. Blazer79

    Blazer79 1/2 ton status

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    You can get away with it, but I'd recommend you change your gears ASAP. If you're mostly doing traffic driving, 4.11s are great, if you're having more highway than city driving then go with 3.73s. I will soon install 3.73 gears on my Blazer since I also want 33" tires and currently have 3.07s. If you think you could someday buy 35" tires, go with 4.11.

    I think mileage actually improves by going with lower (numerically higher) gears since the engine works at an RPM range where it has more power. I'll let you know when I install mine.

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