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Discussion Starter · #1 ·
For 35's. Some offroad and lots of on road and highway use. I don't want it being hard to get up to speed from dead stops, but I don't want to lose alot of top speed either. I

I'd still like to be able to go 75 down the highway once in awhile

Suggestions?
 

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You always have to make compromises when selecting gears. The 4.56 is a lower gear. With a lower gear the truck will acellerate at a faster rate, but your top speed will be less and your fuel consumption will be greater. Off road the truck will pull better. It will climb rocks with greater ease, but in mud, you won't have as much tire speed.

The 4.10s will allow a higher top speed on the highway and better fuel economy. Your rate of accelleration will not be as much as the 4.56s nor will the 4.10 climb rocks any easier. In mud you'll be able to make more tire speed (So long as the engine has the torque to overcome the gearing)

Ed
 

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Discussion Starter · #3 ·
I'm thinking 4.10's might be better for what i do...but I did plan on going with larger tires in the future.

Decisions...decisions...
 

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MPH at given rpms for 35" tire. Assumed lock-up Auto (1:1 final drive--no OD)

Gear Ratio
    4.10   4.56
RPM
1500   38.1   34.3
1750   44.4   40.0
2000   50.8   45.7
2250   57.1   51.4
2500   63.5   57.1
2750   69.8   62.8
3000   76.2   68.5
3250   82.5   74.2
3500   88.9   79.9
3750   95.2   85.6
4000   101.6   91.3
4250   107.9   97.0
4500   114.3   102.8


-SM
 

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Ram1985Custom said:
I'm thinking 4.10's might be better for what i do...but I did plan on going with larger tires in the future.

Decisions...decisions...
well, 35s is pretty much the limit for 1/2 ton stuff if you wheel hard. so if you want to go bigger, you can get 4.10s for now, and when you want to go bigger, swap in bigger axles with lower gears.

Duane
 

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based on that chart.. I'd say you may as well go with the 4.56's; since a RC with 35's doesn't need to be going a 100 MPH anyway.
So far, I'm still content with 3.23's running 35's
 

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Discussion Starter · #7 ·
I will be running 3.23's for awhile until i can get the new gears. How bad is that set up? I heard it kills trannys fast and will barely move under its own power?
 

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There's a piece of dirt in my valvebody somewhere that I've yet to get out(needs a flush and fresh fluid) . So it's been behaving strangely.. My 360 with a thermoquad pulls fine like it is; all I've done is remove the emissions BS. If I need to do any serious pulling.. like moving downed trees.. I just use low range.
As far as it killing trannys like that; add a big tranny cooler & a deeper pan.. The 727 is a stout trans. I'm anxious to work the little bugs out of mine so I can see how it does for hwy mileage. Wish it was ready now.. I need to go down to Ivan's stomping grounds next week to help family put things back together.
 

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Those numbers are for a true 35" diameter tire (measured 35", not necessarily what the size says), and assume no tranny slippage. Even the 5-10% slippage in a non-lockup 727 makes a relatively large difference for cruising rpms with the steeper gear sets.

-SM

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Slanted_Mind said:
Those numbers are for a true 35" diameter tire (measured 35", not necessarily what the size says), and assume no tranny slippage. Even the 5-10% slippage in a non-lockup 727 makes a relatively large difference for cruising rpms with the steeper gear sets.

-SM

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OK....the chart is for a tire with a 35" rolling radius (distance from center of axle to ground with the truck weight on it).....which will be a 38" tire. My rolling radius is 36.5".

And if there is only 5% slippage in my trans, then that means when the engine is turning 2800 rpm, the trans is turning 2660 rpm, which would mean I am going even a slower mph. but since my speedo is correct (clocked at 81 when it said 80).........what does that mean ??
 

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Speedo reads from the tranny, so it is reading any slippage that may be occuring.

These are the numbers I get with a (measured) 36.5" tire, 4.56 gears, and a 1:1 final drive ratio with 5% trans slippage:

RPM MPH
1500 34.0
1750 39.7
2000 45.4
2250 51.0
2500 56.7
2750 62.4
3000 68.0
3250 73.7
3500 79.4
3750 85.0
4000 90.7
4250 96.4
4500 102.1

MPH RPM
30 1323
35 1543
40 1764
45 1984
50 2205
55 2425
60 2646
65 2866
70 3087
75 3307
80 3527
85 3748
90 3968
95 4189
100 4409

Look about right?

-SM
 

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Slanted_Mind said:
Speedo reads from the tranny, so it is reading any slippage that may be occuring.
True...but when I calculate the engine rpm based on gear ratio & the actual rolling radius of my tires, and compare it to the tach engine rpm...the slippage is < 5 %.

If I do the same thing using the measured height (not advertised) of my tires, the slippage is > 5%.

Actual rolling radius is more accurate.
 
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