Gear Ratio Advice
Logistics Pro
Joined: Feb 2005
Posts: 3,952
Likes: 117
From: Upper Left Coast
(math conversion is not accurate enough)
But measuring the "rolling" radius (center of the axle-to-ground.....and then "doing the math") is virtually the same as measuring the "roll-out" circumference.
It gets you to the same place without having to roll the vehicle..... (but I would say rolling the vehicle is probably easier!!)
A lot of the online calculators are just simple spreadsheets or JAVA-script calculators someone built to do the math.
When they didn't work, displayed zeros or ERROR in some of the fields, I suspect my problem with some of them was they didn't account for all ratios possible or a maximum tire size (which I exceeded at 40")
Hotshot
Joined: Oct 2009
Posts: 16,173
Likes: 4,780
From: Burbank, WA
Yes, really. Like Ross said, the engine might work a little harder than it will at idle, but it will be in the powerband, which, imo, isn't as hard on things as lugging the engine. Plus, how much time will you really see on the freeway at speed commuting around town? 5 minutes? 10? If you get on at one exit and get off a few minutes later, that's not hurting a thing. As long as your engine is in good shape to begin with and receives proper maintenance, (ie: regular oil changes and properly tuned) your engine will love you. If you're concerned about the noise, spend some of that money on more insulation. ;-)
Post Fiend
Joined: May 2008
Posts: 7,641
Likes: 21
From: Poway, Ca.
True if you just use the diameter of the tire.....
But measuring the "rolling" radius (center of the axle-to-ground.....and then "doing the math") is virtually the same as measuring the "roll-out" circumference.
It gets you to the same place without having to roll the vehicle..... (but I would say rolling the vehicle is probably easier!!)
A lot of the online calculators are just simple spreadsheets or JAVA-script calculators someone built to do the math.
When they didn't work, displayed zeros or ERROR in some of the fields, I suspect my problem with some of them was they didn't account for all ratios possible or a maximum tire size (which I exceeded at 40")
But measuring the "rolling" radius (center of the axle-to-ground.....and then "doing the math") is virtually the same as measuring the "roll-out" circumference.
It gets you to the same place without having to roll the vehicle..... (but I would say rolling the vehicle is probably easier!!)
A lot of the online calculators are just simple spreadsheets or JAVA-script calculators someone built to do the math.
When they didn't work, displayed zeros or ERROR in some of the fields, I suspect my problem with some of them was they didn't account for all ratios possible or a maximum tire size (which I exceeded at 40")
And we've had this discussion before. First, the tire isn't round with weight sitting on it - it's an oval. So you won't get an accurate diameter measurement (within an inch) on it. And the error is multiplied by 3.14 when you mathematize it. It's a significant error.
I've used this calculator and had the speedometer tested and on all three vehicles with 6 sets of tires it is accurate within 2-3 mph at the given rpm when you measure the roll out distance (I didn't say roll out circumference)they are different. When trying to use diameter there can be as much as an 8 mph error.
This discussion reminds me of an old "Funny" I'll post it:
Just roll it. It's 100 inches and 5 minutes of your time.
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Senior User
Joined: Jul 2008
Posts: 205
Likes: 0
From: Las Vegas, NV
Wayne, I can be on the freeway for up to 1/2 an hour, depending on what part of town I'm working in. I live in Las Vegas, in the far NW part of town and I'd like to be able to drive my truck over to Boulder City and Hoover Dam among other places. That's a fairly long drive, but there's a lot of "car stuff" going on over there and it's just generally a cool, little town--a nice escape from Vegas. I'm gonna have the shop owner drive my truck around tomorrow and get his recommendation--I don't think he'll steer me wrong--no pun intended.
Fleet Owner
Joined: Jul 2004
Posts: 27,294
Likes: 1,055
From: NM
Back in the early '70's I had a '53 F-100 with 223/3-sp, and 7.00-16 tires. I used to drive it from Chicago area down I-57 to Champaign (to school) regularly at 55 mph (speed limit then -- oil embargo), 3+ hours each way. Like 52Merc says, it's in the power band, which honestly isn't what you'd call stump-pulling. I don't know that it could have pulled much higher a gear and had any guts whatsoever. It got what was considered decent mileage back then, around 16.
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Senior User
Joined: Jul 2008
Posts: 205
Likes: 0
From: Las Vegas, NV
I definitely hear you Ross. Obviously, I don't want to spend money if I don't have to. I took her for a ride this afternoon and went up some hills to try and judge how she would pull with the different setup. I'm still not 100% sure I want to do this. Like Wayne said, we're all used to cruising on the freeway in modern cars at just above idle. Believe me, if I could cruise at 55mph I'd be happy, but the drivers here are super-aggressive and tend to go 10-15 over the limit regularly, whereas I'm probably 5 under the limit (limit=65). Sometimes I actually worry about getting rear-ended.
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Senior User
Joined: Jul 2008
Posts: 205
Likes: 0
From: Las Vegas, NV
Well, I went and talked to the driveline guy this morning and, of course, it turns out you guys were right. He said that with my motor and tire size, the 3.70:1 gear ratio was, in his words, "ideal". He told me I could drive this truck to California and back (at 55-60) without any harm to the engine, as it is still operating within safe limits. And, like some of you suggested, putting a bigger gear in the rear would create unwanted issues driving around town. My speedo cable isn't hooked up right now, so I had my Dad clock my speed on the way back from the shop. He said I was doing a steady 60mph on the freeway. This is my first classic vehicle and I guess the lesson learned here is not to expect more of it than what it is--a 50 year-old truck--and not to tinker too much with has worked so well for all of those 50 years. Based on the issues that some of you brought up and the honesty of the shop owner, looks like I just saved myself a bunch of money and learned a little more about my truck. So, as always, thanks for the input!
Cargo Master
Joined: May 2008
Posts: 2,486
Likes: 336
From: Bakersfield, CA
Yeah see, I live somewhat out of town and have to commute into town by freeway for between 20-25 minutes. ~20+ minutes if I'm going to school. And about 25 if I'm going to work.
See, an that's why I'm somewhat paranoid. These are not short drives(relatively). My dad said he took this truck to 60 regularly and it had no problem.
So I guess I will to.
See, an that's why I'm somewhat paranoid. These are not short drives(relatively). My dad said he took this truck to 60 regularly and it had no problem.
So I guess I will to.
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Senior User
Joined: Jul 2008
Posts: 205
Likes: 0
From: Las Vegas, NV
Code:
You could always swap in an vintage Overdrive tranny
Laughing Gas
Joined: Aug 2006
Posts: 815
Likes: 4
From: mountaintop, Pa
I'm sure someone has in your years. much easier to install. I'm no expert but my 65 had a movable crossmember when I put in a 4 speed it was easy as pie. You will have to have the driveshaft shorttened..There's quite a bit of info on this site on overdrives. If you don't care about orifinality you could alway's get a ranger/ saturn overdrive unit or a hone-o-drive these are bolted to the back of a regular tranny. Lastly, I don't remember what type of bell the 223 is but if it;s a smallblock bell an aod auto would be an option...
Cargo Master
Joined: May 2008
Posts: 2,486
Likes: 336
From: Bakersfield, CA
Are you guys talking about the extra crossmember that is on the rear part of the OD trans?
My truck needs one, but I can't seem to find any pictures to get a good reference. There has got to be someone on this thread with a ~56 F100 and a T-86 hooked up....
My truck needs one, but I can't seem to find any pictures to get a good reference. There has got to be someone on this thread with a ~56 F100 and a T-86 hooked up....
Elder User
Joined: Jun 2007
Posts: 807
Likes: 0
From: Cypress,Ca.
Hi all; I have a 223ci. with Ford O Matic. I just switched from 3.73 to 3.31, 29in tall tires. I advanced the timing a couple degrees, the truck runs great! I have NO lugging with local driving. It should be about 2500 rpm at 65mph. Going to be on the freeway tomorrow, will report back. The little 223 is stronger than you might think.
Post Fiend
Joined: May 2008
Posts: 7,641
Likes: 21
From: Poway, Ca.
We've had lots of talks about swapping out transmissions with overdrive transmissions, easier said than done. And it takes the RIGHT (truck) overdrive transmission to keep from becoming a nightmare.
If you are really set on having a higher gear for long freeway cruises (like when you drive your truck from Vegas down to LA for the Long Beach Parts Swap Meet) and you want to drive 75 or 80 (like all the rest of the fools driving that speed and trying to kill you), they do make "Bolt On" overdrives to use with your existing transmission. They are a little pricy, but probably not a lot more than the adaptor bell housing you are going to have to buy and the time and materials to move your transmission cross member to convert to a regular overdrive transmission.
US Gear sells them and so do other manufacturers. Here's a pic (lower trans is the manual):
V2OD Overdrives
If you are really set on having a higher gear for long freeway cruises (like when you drive your truck from Vegas down to LA for the Long Beach Parts Swap Meet) and you want to drive 75 or 80 (like all the rest of the fools driving that speed and trying to kill you), they do make "Bolt On" overdrives to use with your existing transmission. They are a little pricy, but probably not a lot more than the adaptor bell housing you are going to have to buy and the time and materials to move your transmission cross member to convert to a regular overdrive transmission.
US Gear sells them and so do other manufacturers. Here's a pic (lower trans is the manual):
V2OD Overdrives