gear ratiob????????????????

[emmer]

Hi, In my truck, when I'm going 80km (approx 50 mph) my tach is 2000rpm...

does anyone know what my gear ratio is? I'm thinking 4:10.

thx Joe

 

[franklin2]

Make sure you tell them your tire size, and what tranny you have.

 

[emmer]

Oh right. lol

It has a zf 5 speed and the truck was in 5th gear............. the tire size is (approx) 16 inch ( I can't remember what the metric size is)

 

[gonecrazyi]

Sounds like 4.10's to me. Mine is doing about 50-55 at about 2000 rpm and I have 4.10s

 

[87crewdually]

Tire Size?

 

[lotzagoodstuff]

Mark your rear driveshaft, mark one tire, push your truck forward (or backward) slowly for one complete tire revolution and count how many turns your driveshaft makes. If it's a little more than four turns, you've confirmed your 4:10 rear axle ratio.

 

[emmer]

the tire size is (approx) 16 inch ( I can't remember what the metric size is)

perhaps..... ( 285 r 16 )

 

[sle2115]

the tire size is (approx) 16 inch ( I can't remember what the metric size is)

perhaps..... ( 285 r 16 )

Wheel size makes no difference...it's the standing tire size that is needed!

 

[emmer]

Wheel size makes no difference...it's the standing tire size that is needed!

well obviously when I say 16" tires I don't actually mean the wheel size. lol

The tires say 285 r 16 they're nothing special .........just plain 285 r 16 radials.

 

[emmer]

Sounds like 4.10's to me. Mine is doing about 50-55 at about 2000 rpm and I have 4.10s

Thanks Gone, I figured the same

 

[crashnzuk]

well obviously when I say 16" tires I don't actually mean the wheel size.

The tires say 285 r 16 they're nothing special .........just plain 285 r 16 radials.

What he was getting at is that the rim size means little when calculating rpm vs speed. You need the actual diameter of the tire.
Travis..

 

[87crewdually]

I can figure your tire size but I need the the aspect ratio: for example I run 235/85-r16

Your giving us 285 but we need to know the middle # to figure out tire size to figure your gearing.
Here's for example my truck:

tire size: 235/85-r16 = 31.7" tall

Tire Diameter: 31.7" Transmission Ratio: .78:1
Diff Ratio: 4.56:1 TransferCase Ratio: 1:1
RPM: 1885 MPH: 50


If you have 285/70-r16 then it's more than likely you have 4.56's
If your tires 285/50-r16 = 26.9 tall tire that would give you 4.10's

 

[emmer]

I can figure your tire size but I need the the aspect ratio: for example I run 235/85-r16

Your giving us 285 but we need to know the middle # to figure out tire size to figure your gearing.
Here's for example my truck:

tire size: 235/85-r16 = 31.7" tall

Tire Diameter: 31.7" Transmission Ratio: .78:1
Diff Ratio: 4.56:1 TransferCase Ratio: 1:1
RPM: 1885 MPH: 50


If you have 285/70-r16 then it's more than likely you have 4.56's
If your tires 285/50-r16 = 26.9 tall tire that would give you 4.10's

I got it wrong 87........ mine are the same as yours - 235/85-r16

 

[sle2115]

well obviously when I say 16" tires I don't actually mean the wheel size. lol

The tires say 285 r 16 they're nothing special .........just plain 285 r 16 radials.

Actually, you do!

The wheel size is 16 inch, but the tires could be anywhere from 30 to 40 inches tall, maybe more. A 30 inch tires and a 34 inch tire would be like dropping at least one gear size, possibly two! The height of the tire is the important thing here! I guarantee you don't have a 16 inch tall tire, that's about knee high!

The aspect ratio 265/75-R16 breaks down as such:

265 is the tread width (265 MM)
75 is the aspect ratio (75% of the tread width)
R says it's a radial
16 is the wheel size

So a 265/55-R16 is going to be much different in tire height than a 265/85-R16, which in turn will greatly affect the gear ratio to RPM calculations.

Might I suggest you go to Randy's Ring and Pinion and look at the tire calculators.

 

[87crewdually]

With a zf 5 in o/d with a .77:1 ratio, 235/85/16 tires, at 50mph @ 2000rpm I'm calculating 4.88 r&p