Page 1 of 3 123 LastLast
Results 1 to 10 of 25

Thread: Trailer math

  1. #1
    Join Date
    Mar 2018
    Location
    Branson, MO
    Posts
    3,104

    Default Trailer math

    I've been shopping around for a trailer or possibly just a frame/axle combo to build one from. A lot of the threads I've come across on various sites say it's a good idea to extend the tongue to make it longer and have the axle pushed back toward the rear. Does anyone have any good, solid info on motorcycle trailer design geometry? Haven't had much luck finding anything.
    1983 Naked Goldwing Interstate GL1100

    1982 GS450txz (former bike)

    "It is difficult to get a man to understand something when his salary depends upon his not understanding it" ~ Upton Sinclair

  2. #2
    Join Date
    Jun 2005
    Location
    southwest oHIo
    Posts
    35,927

    Default

    I will agree that a longer tongue is beneficial, but a "standard" trailer, like the frame you would find at Harbor Fright will work just fine. If you make any modifications to that trailer, it would be to narrow it down about 6 inches. A car-top carrier on that frame is about as basic and affordable a trailer that you will find.

    As with any trailer, you will need to pay attention to tongue weight. Moving the axle toward the rear will pretty much guarantee having some, but you don't want too much, either.

    I have pulled trailers behind bikes since 1978. I have had several different models, they have all had pretty much the same geometry, as far as axle location is concerned. All have had the axle a few inches behind the center of the cargo box. The only time I have had any problem, it was because of the load I was carrying. It was a heavy load on top of the top rack, on a rather narrow trailer. Above 40 mph, it started rocking due to the top-heavy load. Slowed down to get it to stop, then got up to no more than 35 for the rest of the 3 miles home. Heavy loads are no problem, as long as the balance is correct. I even carried a bare block for a Chevy 350 once. (The bare block is surprisingly small.)

    Any other time, we would ride somewhat normally. Keeping in mind that you have an extra couple hundred pounds behind you that slows your acceleration and hampers your braking, it does not otherwise intrude on your "less-spirited" riding experience.

    .

    mine: 2000 Honda GoldWing GL1500SE and 1980 GS850G'K' "Junior"
    hers: 1982 GS850GL - "Angel" and 1969 Suzuki T250 Scrambler
    #1 son: 1986 Yamaha Venture Royale 1300 and 1982 GS650GL "Rat Bagger"
    #2 son: 1980 GS1000G
    Family Portrait
    Siblings and Spouses
    Mom's first ride
    Want a copy of my valve adjust spreadsheet for your 2-valve per cylinder engine? Send me an e-mail request (not a PM)
    (Click on my username in the upper-left corner for e-mail info.)

  3. #3
    Join Date
    Mar 2018
    Location
    Branson, MO
    Posts
    3,104

    Default

    Quote Originally Posted by Steve View Post
    I will agree that a longer tongue is beneficial, but a "standard" trailer, like the frame you would find at Harbor Fright will work just fine. If you make any modifications to that trailer, it would be to narrow it down about 6 inches. A car-top carrier on that frame is about as basic and affordable a trailer that you will find.

    As with any trailer, you will need to pay attention to tongue weight. Moving the axle toward the rear will pretty much guarantee having some, but you don't want too much, either.

    I have pulled trailers behind bikes since 1978. I have had several different models, they have all had pretty much the same geometry, as far as axle location is concerned. All have had the axle a few inches behind the center of the cargo box. The only time I have had any problem, it was because of the load I was carrying. It was a heavy load on top of the top rack, on a rather narrow trailer. Above 40 mph, it started rocking due to the top-heavy load. Slowed down to get it to stop, then got up to no more than 35 for the rest of the 3 miles home. Heavy loads are no problem, as long as the balance is correct. I even carried a bare block for a Chevy 350 once. (The bare block is surprisingly small.)

    Any other time, we would ride somewhat normally. Keeping in mind that you have an extra couple hundred pounds behind you that slows your acceleration and hampers your braking, it does not otherwise intrude on your "less-spirited" riding experience.

    .

    I've been looking at the HF 40"X48" trailer, some say the hubs are not all that great and the bearings should be swapped out for higher quality ones, some have also mentioned taking one or two leafs out or they tend to be too stiff with a light load. For a little less money there's a similar sized one with a car topper already on it built from a front straight axle off an old pickup with drop spindles and airbags, it's going to be heavier but solves the bearing, hub and spring issue right off the bat. Haven't looked it over yet, it's about an hour away and I'm waiting for the weather to warm up a bit before heading out to see it. Here's an idea I REALLY like, it's the back half of a HF trailer, the front is open for storage.
    1983 Naked Goldwing Interstate GL1100

    1982 GS450txz (former bike)

    "It is difficult to get a man to understand something when his salary depends upon his not understanding it" ~ Upton Sinclair

  4. #4
    Join Date
    Jun 2005
    Location
    southwest oHIo
    Posts
    35,927

    Default

    That's quite impressive.

    You DO need to be concerned a bit about weight. However, you need to be even more concerned about WIDTH. Anything using the front axle of a truck is going to be nearly 6 feet wide, which is WAY too much. Try to keep it to no more than 4 feet, if possible. My trailers have all been between 3 and 3 1/2 feet wide.

    One reason to keep it narrow is to keep it in your lane. If you are accustomed to riding in the left track of the lane, you have to remember that your left hand is getting close to the edge of the lane. Your hand is less than 1 1/2 feet from the centerline of the bike, assuming the width of the handlebars is 3 feet. With a 6 foot trailer, the edge of the trailer is another 1 1/2 feet beyond that, possibly putting it into the next lane, unless you are riding on the oil stripe in the middle.

    You have any other pictures of that trailer setup?

    The bearings on the HF trailers aren't all that bad, but it is highly recommended that you open them up and re-pack them first thing. Some will go the extra step and install Bearing Buddies on them, but I have never done that.

    .

    mine: 2000 Honda GoldWing GL1500SE and 1980 GS850G'K' "Junior"
    hers: 1982 GS850GL - "Angel" and 1969 Suzuki T250 Scrambler
    #1 son: 1986 Yamaha Venture Royale 1300 and 1982 GS650GL "Rat Bagger"
    #2 son: 1980 GS1000G
    Family Portrait
    Siblings and Spouses
    Mom's first ride
    Want a copy of my valve adjust spreadsheet for your 2-valve per cylinder engine? Send me an e-mail request (not a PM)
    (Click on my username in the upper-left corner for e-mail info.)

  5. #5
    Join Date
    Mar 2018
    Location
    Branson, MO
    Posts
    3,104

    Default

    Quote Originally Posted by Steve View Post
    That's quite impressive.

    You DO need to be concerned a bit about weight. However, you need to be even more concerned about WIDTH. Anything using the front axle of a truck is going to be nearly 6 feet wide, which is WAY too much. Try to keep it to no more than 4 feet, if possible. My trailers have all been between 3 and 3 1/2 feet wide.

    One reason to keep it narrow is to keep it in your lane. If you are accustomed to riding in the left track of the lane, you have to remember that your left hand is getting close to the edge of the lane. Your hand is less than 1 1/2 feet from the centerline of the bike, assuming the width of the handlebars is 3 feet. With a 6 foot trailer, the edge of the trailer is another 1 1/2 feet beyond that, possibly putting it into the next lane, unless you are riding on the oil stripe in the middle.

    You have any other pictures of that trailer setup?

    The bearings on the HF trailers aren't all that bad, but it is highly recommended that you open them up and re-pack them first thing. Some will go the extra step and install Bearing Buddies on them, but I have never done that.

    .

    Excellent point on the width, I had not considered that! The second one I mentioned has quite a wide track compared to the size of the bed, either way it goes I'll probably do some modifying at some point. The Goldwing factory service manual says 300lb max towing capacity fully loaded with a passenger, which will probably happen for at least awhile this summer. Several years ago I came across the "Stitch and glue" method of boat building, basically making a hull from Luan and glassing it over for strength and water tightness. After seeing that it's stuck in my mind for a "someday" project, you certainly couldn't build a trailer shell much lighter with basic tools!
    1983 Naked Goldwing Interstate GL1100

    1982 GS450txz (former bike)

    "It is difficult to get a man to understand something when his salary depends upon his not understanding it" ~ Upton Sinclair

  6. #6
    Join Date
    Sep 2012
    Location
    Ireland
    Posts
    4,264

    Default

    Quote Originally Posted by LAB3 View Post
    I've been shopping around for a trailer or possibly just a frame/axle combo to build one from. A lot of the threads I've come across on various sites say it's a good idea to extend the tongue to make it longer and have the axle pushed back toward the rear. Does anyone have any good, solid info on motorcycle trailer design geometry? Haven't had much luck finding anything.
    I built a 4ft long x 2ft wide bike trailer about 25 years ago and pulled it around for years, quite happily. The reason I went for that size was to retain some ability to filter in traffic, should I need to. If you think trailers can't filter, you should have seen some of the City Link couriers in London using them and theirs were a bit wider.

    A few years ago I came across the delphi forum relating to bike trailers and found some excellent handy information.
    http://forums.delphiforums.com/mctrailertowing
    Basically, the rule of thumb is to measure your trailer wheelbase and make the distance between trailer axle and hitch at least 150% of that, and going longer if you feel like it.
    Once I lengthened the trailer draw bar by about a foot, and moved the axle line back by two inches or so, the thing was transformed. It was never bad before but now it's far better.


    The trailer axle is simply a pair of Indespension units (you can probably get a local equivalent) with totally independent rubber bushings in a square tube-type short axle that are then bolted or welded onto the frame. I used the standard bearings in them for ages, but noticed one of them had got a bit grumbly, so replaced them with SKF or similar a few years ago. I was able to find a pair of 12" Minilite wheels on the back-of-the-shed local market, they cleaned up nicely.
    Since that pic, I've fitted better LED lighting, but will be doing some more upgrades, possibly doubling the rear lighting and adding some side lights.

    These are the hub and axle assemblies I used, but iirc, they were lighter, around 250kg rating.
    Last edited by Grimly; 01-24-2021 at 10:54 PM.
    ---- Dave
    79 GS850N - Might be a trike soon.
    80 GS850T Single HIF38 S.U. SH775, Tow bar, Pantera II. Gnarly workhorse & daily driver.
    79 XS650SE - Pragmatic Ratter - goes better than a manky old twin should.
    92 XJ900F - Fairly Stock, for now.

    Only a dog knows why a motorcyclist sticks his head out of a car window

  7. #7
    Join Date
    Mar 2018
    Location
    Branson, MO
    Posts
    3,104

    Default

    Love those fenders! Thanks for the info on the width to length ratio, that helps a lot. Those torsion stub axles are $179 a pair over here with no hubs, wheels, nothing else with them, another item I've kept my eyes on for a long time. A 40"X48" complete trailer is $240 with the 20% discount until the end of the month. It's a bit too wide as Steve mentioned and would require adding to the tongue length. Without access to equipment or necessary skills to weld, whatever mods are needed would have to be minimal to keep the costs low.
    1983 Naked Goldwing Interstate GL1100

    1982 GS450txz (former bike)

    "It is difficult to get a man to understand something when his salary depends upon his not understanding it" ~ Upton Sinclair

  8. #8
    Join Date
    Jun 2008
    Location
    Jaffrey, NH
    Posts
    1,669

    Default

    Quote Originally Posted by LAB3 View Post
    I've been shopping around for a trailer or possibly just a frame/axle combo to build one from. A lot of the threads I've come across on various sites say it's a good idea to extend the tongue to make it longer and have the axle pushed back toward the rear. Does anyone have any good, solid info on motorcycle trailer design geometry? Haven't had much luck finding anything.
    Check this forum out....I joined to get ideas for my 6x12 build. Great stuff there: http://www.tnttt.com/
    1979 GS850G
    2004 SV650N track bike
    2005 TT-R125 pit bike
    LRRS #246 / Northeast Cycles / Woodcraft / Armour Bodies / Hindle Exhaust / Central Mass Powersport

    http://s327.photobucket.com/albums/k443/tas850g/

  9. #9
    Join Date
    Jun 2005
    Location
    southwest oHIo
    Posts
    35,927

    Default

    Quote Originally Posted by LAB3 View Post
    The Goldwing factory service manual says 300lb max towing capacity fully loaded with a passenger, ...
    When you get a chance, I would like to see a picture of that statement. Every motorcycle manual I have ever seen said that it was NOT permitted to pull a trailer. Yes, many of us have done it and gotten away with it, but it is not a factory-sanctioned event. The first (and so far only) motorcycle that I have seen with a trailer towing capacity listed is the CanAm Spyder. Not only does it list a capacity, they sell a trailer for it, too. Not interested in using my wife's Spyder to tow, though, at least not until I can find a proper hitch. The ones that are available from CanAm and others all attach to the swingarm.


    Quote Originally Posted by Grimly View Post
    The reason I went for that size was to retain some ability to filter in traffic, should I need to. If you think trailers can't filter, you should have seen some of the City Link couriers in London using them and theirs were a bit wider.
    Not too many of us on this side of the pond have the luxury of "filtering". There is only one place that I know of where it's not illegal. In fact, it's only been quite recently that it was specifically made legal. That is in California.

    When I lived there, I did a lot of filtering with my bike, which many said couldn't be done. It was a fully-dressed KZ1300, I think it was 38" wide across the saddlebags. The trailer I had at the time was 36", so if the bike would fit, the trailer would, too. However, just for the peace of mind of not having to worry about the extra length, I didn't filter much with the trailer. Yeah, there were times when I would go through a smaller gap, but only when moving fast enough that I would not endanger myself or others.

    Good luck with the boat build, I'm sure we'll see you out there somewhere.



    .

    mine: 2000 Honda GoldWing GL1500SE and 1980 GS850G'K' "Junior"
    hers: 1982 GS850GL - "Angel" and 1969 Suzuki T250 Scrambler
    #1 son: 1986 Yamaha Venture Royale 1300 and 1982 GS650GL "Rat Bagger"
    #2 son: 1980 GS1000G
    Family Portrait
    Siblings and Spouses
    Mom's first ride
    Want a copy of my valve adjust spreadsheet for your 2-valve per cylinder engine? Send me an e-mail request (not a PM)
    (Click on my username in the upper-left corner for e-mail info.)

  10. #10
    Join Date
    Dec 2013
    Location
    New York City
    Posts
    7,742

    Default

    So we're going to be towing a trailer with our scooter? I first thought of 'trailer' as in, "We live in a trailer at the edge of town," and I thought, "Math" said "Meth." But "Trailer Math" works as a title also.

    Just funning with you, Len. How are you? How's the Wing? I like that picture of your portable outdoor lab, I mean library. Nudge nudge, know what I mean, know what I mean?
    1982 GS1100E V&H "SS" exhaust, APE pods, 1150 oil cooler, 140 speedo, 99.3 rear wheel HP, black engine, '83 red

    2016 XL883L Two-tone blue and white. Almost 42 hp! Status: destroyed, now owned by the insurance company. The hole in my memory starts an hour before the accident and ends 24 hours after.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •