Rpms with zf5

[1983idi]

I am looking for what rpm I would be running at 55 60 and 65 miles per hour in 5th gear. I have a zf5 with a 3.55 geared rear and stock tire size. 235/85R16

Thanks for any help. I don't have a tach and want to make sure I'm not lugging my engine.

 

[pelky350]

I have 3:55 rear end but I'm running 315-75 tires at 55 I running around 1600, at 65 about 2000. since your tire size isn't smaller you should've running just over what rpms im at so your not likley lugging your engine. 1700 is supposed to Be like the sweet spot for cruising and your probably right around that in 5th at 60mph

 

[Thewespaul]

I have 3.55 with a zf5 and a similar tire height, I’m at 2000 rpm at 70. 55 should be around 1600-1700

 

[Thatoneguy]

Ha! Man their are times when I wish I had yalls RPM'S!

 

[1983idi]

Thanks for the replys!

 

[Fordfan90]

Thanks for the replys!

Mine has 4.10s in the rear I'm at 2500 at 65 with 35x12.50.20s

 

[towcat]

Ha! Man their are times when I wish I had yalls RPM'S!

i'm interested in what you're running. I'm thinking of 4.56's for my tow rigs.

 

[tractorhead]

I run 2050rpm @ 70mph with same tires and gear ratio as yours

 

[Thewespaul]

i'm interested in what you're running. I'm thinking of 4.56's for my tow rigs.

He has 4.56 in his truck

 

[towcat]

He has 4.56 in his truck

i know. I want to get his feedback before making the jump for my F350.
My F450's have 4.62 and 5.13 but are sprung much harder than my F350. they can tow a house. slowly that is.

 

[hce]

If you have excel or open office I have a spread sheet
With each gear.

 

[Thewespaul]

i know. I want to get his feedback before making the jump for my F350.
My F450's have 4.62 and 5.13 but are sprung much harder than my F350. they can tow a house. slowly that is.

It’s good for towing but even with the 35s we put on his truck it’s still about 75 tops

 

[Macrobb]

To answer the OP's question, 3.55s + zf5 is great for un loaded driving. 60 should be around 1775 rpm.

Lugging, in an idi, is using the entire output of the engine below 'peak torque' rpm, I read somewhere... which is like 1400-1600 rpm? (N/a that is - turbo torque is a different story).

Really, the rule I use is that if I am going along and can press the accelerator and get more power(truck accelerates), I'm not maxing it out and am OK.
WOT, full-throttle operation should be kept above 2200RPM, and if you get below that, downshift.
Also, an EGT gauge is really how you tell if you are stressing the engine - <600f = unstressed, 600-900F = normal, 900-1100 = maxing it out, 1100+ = back off on the throttle, you are getting hot.
Not to say that if you hit 1101 it'll melt down, but keeping it under that is a good, safe number.

As an aside, I regularly drive in flat ground, 35mph in 5th with my zf5+4.10 gearing at 1200rpm... because it's not maxing it out at all. Going up a hill, I'd definitely downshift... but on flat ground it will just cruise.

 

[Runningaford]

I am looking for what rpm I would be running at 55 60 and 65 miles per hour in 5th gear. I have a zf5 with a 3.55 geared rear and stock tire size. 235/85R16

Thanks for any help. I don't have a tach and want to make sure I'm not lugging my engine.

http://www.grimmjeeper.com/gears.html Does this help?

 

[david85]

Just for fun, here's how the numbers work out:

235/85/16 tires = 31.73" diameter = 99.68" circumference = 0.001573193 miles (distance covered per wheel revolution)

* 60 = 0.09439158

55 MPH /0.09439158 = 582.7
* 3.55 = 2068.5
* 0.77 = 1592.8 RPM

60 MPH /0.09439158 = 635.6
* 3.55 = 2256.6
* 0.77 = 1737.5 RPM

65 MPH /0.09439158 = 688.6
* 3.55 = 2444.6
* 0.77 = 1882.3 RPM


Nothing wrong with cruising at any of those RPMs but you might need to downshift for towing, or anything more than 4-5%.
The good news is even at 65 MPH, you're still only turning 2500 RPM in 4th gear.