The Ford Barn

ivoryjohn · 06-30-2012, 06:25 PM

I wrote this thread once today and it got mysteriously lost.

Several years ago I built a little camper trailer with a pop-up top, Model A wheels, spindles and fenders. It was very cute, towed like a dream but it was a bear to back up with my '29 Special Coupe. When I built it I guesstimated the tongue length and made it long enough so if the tongue was jack knifed 90 degrees to the car the trailer body wouldn't hit. I call this good, satisfied all was well. I guess I built the jack knife feature into the rig because it would fold up like a Barlow Skinner in two feet of backing.

I would like to build another and now realize there must be a formula that dictates the tongue length from the center of the trailer wheel and the distance from the car's rear wheel to the hitch point. I had mounted the hitch point right under the rear mounted spare of the car.

rear tire center.........hitch-trailer tongue...........trailer tire center
"A"................................"B"............ ............................."C"

Please be patient and explain the measurements carefully. How far should the hitch be from the center of the rear wheel? How far should the trailer hitch be from the center of the trailer wheel? The trailer box will be approximately 50" long but I am more worried about it tracking along in the tracks of the car and my being able to back it up with a '29 Fordor.

28ACoupe · 06-30-2012, 06:54 PM

The biggest thing to remember is the longer the trailer from the hitch to the trailer axle, the easier it will be to control while backing up. No formula needed.

Also, have someone who is good at backing trailers teach you how. Even a short trailer should not jackknife so fast as to be uncontrollable.

Bruce,Upstate NY · 06-30-2012, 08:23 PM

I have and can back a number trailers - but not any behind my A tudor. You can't even see it. My answer to the problem was a single swivel wheel small cargo trailer which fixes to the rear. It's the "bee's knees". I wish I could enclose photos but can't. Google the website for them. Ideal for A fords. The wheelbase of the tow vehicle, the distance from the rear axle to the hitch, and the distance from the hitch to the trailer axle all effect backing.

Tom Wesenberg · 06-30-2012, 08:42 PM

When you have a trailer that can't be seen through the rear window, a bike flag mounted to the rear of the trailer would be a big help.

Cool Hand Lurker · 07-01-2012, 12:46 PM

Check out Champion Trailer website. Everything you want to know is there. http://www.championtrailers.com/UTIL...AILER_KITS.HTM

Randy in ca · 07-01-2012, 01:46 PM

Sponsored Links (Register now to hide all advertisements)

Another consideration is the tongue weight of the trailer on the hitch - I believe they recommend a minimum of 10-15% of the total trailer weight be on the hitch. While a longer hitch makes backing easier, if this results in too little weight on the tongue the trailer may wander or float at higher speeds. Confused yet??

H. L. Chauvin · 07-01-2012, 02:18 PM

Learned years ago -- what works well is to go to a sandy area, or grass area pulling a trailer & turning steering wheel all the way to right or left, & travel in a circle with trailer attached, such that the trailer tire tracks should be the same as the vehicle tire tracks.

How to estimate length of trailer tongue, assuming you will use a Model A axle for the trailer?

1, In an area similar to an empty parking lot or large grass area, first turn steering wheel all the way to the left, (like making a left turn), then get out of the car & provide & extend a tight string line 90 degrees from the center of the rear tire.

2. Next, provide & extend another tight string line 90 degrees from the center of the fully turned front tire. Wood pegs in ground for attaching strings help.

3. Mark where two strings intersect as point A. On the other ends, where string adjoins center of front tire, call this point B; & where string adjoins center of rear tire, call this point C. Lengths of distances between points A & B and A & C should be equal where the string length is like a radius on a circle.

4. Cut an inexpensive PVC pipe or stick the same length as the "out to out" distance of either front or rear tires, & drill a hole in the center of this PVC pipe for a small bolt or wood dowel. Call this piece of PVC, X, to represent your trailer axle with a hole in the center of the axle to attach the tongue.

5. Cut another inexpensive PVC pipe or stick "longer" than your "estimated" tongue distance from the trailer hitch to the center of the PVC axle X, & drill a same sized hole in the end of this stick which is called T for tongue.

6. Securely attach X to T through the bolt hole with X provided perpencicular to T.

7. Place the other end of T directly under where your trailer hitch will be provided on the vehicle, & call this point on the ground as H for trailer hitch.

8. With another length of string extending from point A, scribe & mark a partial 1/4 or so circumference of a circle, with the same radius length as that from point A to the tire centers B & C.

9. Place the in-side end of axle X on this marked circumference, and the hitch end of T at H.

10. Adjust length of T at point H until the in-side end of axle X is on the circle's circumference. Use this particular dimension from H for length of tongue from ball of trailer hitch to center of axle. Always check final 90 degrees between X & T in case something moved. (* Also verify that the trailer axle X is on the same line & aligned with the string extending from point A to the in-side end of axle X).

11. To insure an almost perfect 90 degree "trailing" trailer axle with absolutely no side-sway, during construction, verify exact distance from exact center of trailer ball on tongue to exact center, (or outsides or insides), of both the front, right & left trailer wheels.

May be an easier way, but built several functional trailers like this.

Tinbasher · 07-02-2012, 06:33 PM

As far as I know the axle should be set back 10% of the lenght of the trailer, behind centre. Measured from the ball to the rear crossmember.
This keeps it from swinging and swaying.

The Old Tinbasher

Cool Hand Lurker · 07-03-2012, 01:15 PM

One thing nobody has mentioned yet that really affects sway is the distance between the towing vehicle's rear axle and the ball hitch. The greater that distance, the more the trailer will be affected by a small movement in the steering wheel. Semi tractors that tow mobile homes have a very short distance. Motor homes that tow a trailer have a very long distance. If you don't have a LOT more tongue-to-axle distance on the trailer than that critical distance on the tow vehicle, it will whip around a lot. A lot!

06-30-2012, 06:25 PM	#1
ivoryjohn Senior Member Join Date: Jan 2011 Location: picauyne ms. Posts: 251	Trailer Geometry? I wrote this thread once today and it got mysteriously lost. Several years ago I built a little camper trailer with a pop-up top, Model A wheels, spindles and fenders. It was very cute, towed like a dream but it was a bear to back up with my '29 Special Coupe. When I built it I guesstimated the tongue length and made it long enough so if the tongue was jack knifed 90 degrees to the car the trailer body wouldn't hit. I call this good, satisfied all was well. I guess I built the jack knife feature into the rig because it would fold up like a Barlow Skinner in two feet of backing. I would like to build another and now realize there must be a formula that dictates the tongue length from the center of the trailer wheel and the distance from the car's rear wheel to the hitch point. I had mounted the hitch point right under the rear mounted spare of the car. rear tire center.........hitch-trailer tongue...........trailer tire center "A"................................"B"............ ............................."C" Please be patient and explain the measurements carefully. How far should the hitch be from the center of the rear wheel? How far should the trailer hitch be from the center of the trailer wheel? The trailer box will be approximately 50" long but I am more worried about it tracking along in the tracks of the car and my being able to back it up with a '29 Fordor.

06-30-2012, 06:54 PM	#2
28ACoupe Senior Member Join Date: Jun 2012 Posts: 559	Re: Trailer Geometry? The biggest thing to remember is the longer the trailer from the hitch to the trailer axle, the easier it will be to control while backing up. No formula needed. Also, have someone who is good at backing trailers teach you how. Even a short trailer should not jackknife so fast as to be uncontrollable. __________________ 1928 Model A Business Coupe Rebuild picture gallery here The light at the end of the tunnel has been turned off due to budget cuts.

06-30-2012, 08:23 PM	#3
Bruce,Upstate NY Senior Member Join Date: May 2010 Location: Odessa, NY Posts: 385	Re: Trailer Geometry? I have and can back a number trailers - but not any behind my A tudor. You can't even see it. My answer to the problem was a single swivel wheel small cargo trailer which fixes to the rear. It's the "bee's knees". I wish I could enclose photos but can't. Google the website for them. Ideal for A fords. The wheelbase of the tow vehicle, the distance from the rear axle to the hitch, and the distance from the hitch to the trailer axle all effect backing.

06-30-2012, 08:42 PM	#4
Tom Wesenberg Senior Member Join Date: May 2010 Location: Mpls, MN Posts: 27,582	Re: Trailer Geometry? When you have a trailer that can't be seen through the rear window, a bike flag mounted to the rear of the trailer would be a big help.

07-01-2012, 12:46 PM	#5
Cool Hand Lurker Senior Member Join Date: May 2010 Location: So Minn Posts: 1,565	Re: Trailer Geometry? Check out Champion Trailer website. Everything you want to know is there. http://www.championtrailers.com/UTIL...AILER_KITS.HTM

07-01-2012, 01:46 PM	#6
Randy in ca Senior Member Join Date: May 2010 Posts: 1,640	Re: Trailer Geometry? Sponsored Links (Register now to hide all advertisements) Another consideration is the tongue weight of the trailer on the hitch - I believe they recommend a minimum of 10-15% of the total trailer weight be on the hitch. While a longer hitch makes backing easier, if this results in too little weight on the tongue the trailer may wander or float at higher speeds. Confused yet??

07-01-2012, 02:18 PM	#7
H. L. Chauvin Senior Member Join Date: May 2010 Posts: 4,179	Re: Trailer Geometry? Learned years ago -- what works well is to go to a sandy area, or grass area pulling a trailer & turning steering wheel all the way to right or left, & travel in a circle with trailer attached, such that the trailer tire tracks should be the same as the vehicle tire tracks. How to estimate length of trailer tongue, assuming you will use a Model A axle for the trailer? 1, In an area similar to an empty parking lot or large grass area, first turn steering wheel all the way to the left, (like making a left turn), then get out of the car & provide & extend a tight string line 90 degrees from the center of the rear tire. 2. Next, provide & extend another tight string line 90 degrees from the center of the fully turned front tire. Wood pegs in ground for attaching strings help. 3. Mark where two strings intersect as point A. On the other ends, where string adjoins center of front tire, call this point B; & where string adjoins center of rear tire, call this point C. Lengths of distances between points A & B and A & C should be equal where the string length is like a radius on a circle. 4. Cut an inexpensive PVC pipe or stick the same length as the "out to out" distance of either front or rear tires, & drill a hole in the center of this PVC pipe for a small bolt or wood dowel. Call this piece of PVC, X, to represent your trailer axle with a hole in the center of the axle to attach the tongue. 5. Cut another inexpensive PVC pipe or stick "longer" than your "estimated" tongue distance from the trailer hitch to the center of the PVC axle X, & drill a same sized hole in the end of this stick which is called T for tongue. 6. Securely attach X to T through the bolt hole with X provided perpencicular to T. 7. Place the other end of T directly under where your trailer hitch will be provided on the vehicle, & call this point on the ground as H for trailer hitch. 8. With another length of string extending from point A, scribe & mark a partial 1/4 or so circumference of a circle, with the same radius length as that from point A to the tire centers B & C. 9. Place the in-side end of axle X on this marked circumference, and the hitch end of T at H. 10. Adjust length of T at point H until the in-side end of axle X is on the circle's circumference. Use this particular dimension from H for length of tongue from ball of trailer hitch to center of axle. Always check final 90 degrees between X & T in case something moved. (* Also verify that the trailer axle X is on the same line & aligned with the string extending from point A to the in-side end of axle X). 11. To insure an almost perfect 90 degree "trailing" trailer axle with absolutely no side-sway, during construction, verify exact distance from exact center of trailer ball on tongue to exact center, (or outsides or insides), of both the front, right & left trailer wheels. May be an easier way, but built several functional trailers like this. Last edited by H. L. Chauvin; 07-01-2012 at 02:29 PM. Reason: Added ()*

07-02-2012, 06:33 PM	#8
Tinbasher Senior Member Join Date: May 2010 Location: Innisfil, Ontario Canada Posts: 1,174	Re: Trailer Geometry? As far as I know the axle should be set back 10% of the lenght of the trailer, behind centre. Measured from the ball to the rear crossmember. This keeps it from swinging and swaying. The Old Tinbasher

07-03-2012, 01:15 PM	#9
Cool Hand Lurker Senior Member Join Date: May 2010 Location: So Minn Posts: 1,565	Re: Trailer Geometry? One thing nobody has mentioned yet that really affects sway is the distance between the towing vehicle's rear axle and the ball hitch. The greater that distance, the more the trailer will be affected by a small movement in the steering wheel. Semi tractors that tow mobile homes have a very short distance. Motor homes that tow a trailer have a very long distance. If you don't have a LOT more tongue-to-axle distance on the trailer than that critical distance on the tow vehicle, it will whip around a lot. A lot!