What gear ratio?
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Junior User
Joined: Nov 2002
Posts: 90
Likes: 0
From: In Merna
What gear ratio?
I plan on getting a 6 or 8 in lift for a 89 F150.
I plan on runnign at the minimum 35's but i would not go biger than 37's.
My pickup has a 5 speed manual transmission. It will have its fair share of highway driving. I would like it to run some where between 2000 and 2600 rpm at 60 to 65 mph.
I was thinking 4.10 but would 4.56 be to low geared?
Thanks for your oppinions
I plan on runnign at the minimum 35's but i would not go biger than 37's.
My pickup has a 5 speed manual transmission. It will have its fair share of highway driving. I would like it to run some where between 2000 and 2600 rpm at 60 to 65 mph.
I was thinking 4.10 but would 4.56 be to low geared?
Thanks for your oppinions
Fleet Mechanic
Joined: Feb 2003
Posts: 1,314
Likes: 35
What gear ratio?
I personally like high gears for low RPMs on the highway. Do you really need such a low gear? As far as I understand, it is only useful when towing. Your towing ratings increase. For example if you want to tow something like 9,000 lbs, you pretty much need 4.10 rear with a small block V8. With the big 460, you have more flexibility.
I have a F250 with 460 cid and 4.10 rear and often wish I had 3.55 rear, when I am running empty. 3.55 would work for me even when towing. However, 460 gets most of its power with 4.10, which was standard on that setup unless special ordered something else. At 65mph, it turns at 3100 rpms. So you see, I like to keep it at 55-60mph and almost 12 mpg. But anything higher than that and it comes down to 10. I think it will be similar with your truck, too.
So if you need a low gear, isn't there something like 4.30 which combined with that tire size make it somewhat higher. These gears you are talking about do not like highway speeds.
RPM Calculator:
http://www.ring-pinion.com/calculators.shtml
I have a F250 with 460 cid and 4.10 rear and often wish I had 3.55 rear, when I am running empty. 3.55 would work for me even when towing. However, 460 gets most of its power with 4.10, which was standard on that setup unless special ordered something else. At 65mph, it turns at 3100 rpms. So you see, I like to keep it at 55-60mph and almost 12 mpg. But anything higher than that and it comes down to 10. I think it will be similar with your truck, too.
So if you need a low gear, isn't there something like 4.30 which combined with that tire size make it somewhat higher. These gears you are talking about do not like highway speeds.
RPM Calculator:
http://www.ring-pinion.com/calculators.shtml
Post Fiend
Joined: Nov 2001
Posts: 14,947
Likes: 6
From: Topsfield, MA
What gear ratio?
The easiest way is with this formula:
MPH x GEAR RATIO x 336 / TIRE SIZE x OD RATIO
65 X 4.10 X 336 / 34.8 * .8 = 2058
So you'll be spinning 2058 RPM at 65 MPH in OD with 4.10 gears and 35" tires. Plug in different tires/gears to find out what works best.
MPH x GEAR RATIO x 336 / TIRE SIZE x OD RATIO
65 X 4.10 X 336 / 34.8 * .8 = 2058
So you'll be spinning 2058 RPM at 65 MPH in OD with 4.10 gears and 35" tires. Plug in different tires/gears to find out what works best.
Freshman User
Joined: Mar 2003
Posts: 39
Likes: 0
What gear ratio?
I have a 92 F150 with a 300 6 & 33" tires.After years of driving with 308 I changed to 355's.This is the best mod I have ever done.I could pull tracter with a bushog before.I dont think I will be able to tell its behind me now.I have the mazda 5spd and Im not down shifting all the time now. My speedometer was right before (I had it calibrated to get out of a ticket) I wonder how far its off now.I guess thats a whole new thread.
Elder User
Joined: May 2001
Posts: 692
Likes: 1
From: Coon Rapids, MN
What gear ratio?
unless you are running something that is much stronger than a stock 300/302/351, you will want to go with something deaper that even that. 2000rpm simply isn't enough to push a truck down the highway with 35-37" tires. You would probably end up running in 4th gear almost all the time. You will want to stay in the 2500-2600rpm range, this will lug the engine much less and even get better gas mileage than if you have the higher (low numeric) gears. 
Elder User
Joined: May 2001
Posts: 692
Likes: 1
From: Coon Rapids, MN
What gear ratio?
I looked up and noticed that formula is close, but not quite right. It goes like this to figure rpm...
MPH * rear end gear * 336 * transmition gear ratio
------------------------------------------------------------------
tire diameter
with 4.56's you should be turning a little under 2300rpm, which would be a little better than the 4.10's... 4.10's bring you back into the same ballpark as what it would be stock. If you go anything bigger than 35's, you need 4.56's for SURE.
You can also go to www.4lo.com
they have a calculator right on their page and is very easy to use. However, maybe its just my truck, but every time I have calculated what rpm I should be at it always reads WAY to low than what it actually is for whatever reason. That is also taking into account that fact that 35's are not a true 35" tall. More like 34 something like mustang pointed out.
MPH * rear end gear * 336 * transmition gear ratio
------------------------------------------------------------------
tire diameter
with 4.56's you should be turning a little under 2300rpm, which would be a little better than the 4.10's... 4.10's bring you back into the same ballpark as what it would be stock. If you go anything bigger than 35's, you need 4.56's for SURE.
You can also go to www.4lo.com
they have a calculator right on their page and is very easy to use. However, maybe its just my truck, but every time I have calculated what rpm I should be at it always reads WAY to low than what it actually is for whatever reason. That is also taking into account that fact that 35's are not a true 35" tall. More like 34 something like mustang pointed out.
