Twin-axle car trailer- heights and angles
Discussion
Unusual engineering challenge so please bear with me.
I have a small twin axle car trailer which I planned to use for racing cars (sports cars / Formula Ford)
It is an unusual spec in that it has a bed which is a couple of feet longer than the standard size. This is good for me because it means that not only does a Caterham fit but I can also get a Lotus Elan or Formula Ford on there without overhanging, and still have space for some extra stuff.
Ordinarily this would mean that it wouldn't fit in a standard length garage but this trailer also has a folding tow pole arrangement which means that it does.
Folding tow pole is pretty nifty. There aren't a lot around because they were a bit of a niche, cost extra money and also due to a legislation change, trailer manufacturers were prohibited from making them over a decade ago.
All well and good then, I have a trailer which is extra useful and still fits in a garage.
Onto the problem.
Over the years I have owned a few similar trailers with the same 10" wheels and by default they always tow a bit nose high. Most cars these days have swan neck type tow bars so you can't fit a drop plate. In any case there is a standard range for tow ball heights. Even at the bottom of that range these trailers would be a bit nose high, so really this is a problem of the trailer specification. The trailers are too low for the tow cars.
The standard solution was to fit a 50mm spacer under the coupling head on the trailer which would mean the trailer was pretty close to level.
However, I cannot do that with the folding tow pole arrangement. Also the problem is exacerbated as due to the extended bed, the axles are further apart. The upshot is, with the trailer unladen and towed behind my car the tyres of the front axle are barely contacting the ground. I haven't even put a car on the trailer yet as the way it is, the rear axle and the towing hitch would be taking all of that load and the front axle doing none of the work.
The problem therefore is, If I can't lower the tow ball on the car by at least 40mm, I need to increase the level hitch height of the trailer by the same amount.
I have had a good look to see if the coupling head can be raised relative to the rest of the trailer in a similar way to the hitch spacer idea but while possible it'd be quite a big job involving fabrication, cutting, welding, re-galvanizing etc... and is that even legal (type approval etc?)
Similarly I pulled the bumper off the car to see what could be done there. Similar situation really, I believe a simple and inexpensive fabricated solution could be found (but type approval etc). Moving the tow ball lower relative to the crossbeam would increase the twisting moment on that beam. Also I would run into ground clearance problems with the tow bar itself.
The trailer's axles are bolted on instead of welded so I could hypothetically insert a spacer between the axles and the trailer bed, increasing the ride height of the whole trailer.
I could also fit 12" wheels which depending on tyre size would increase the ride height of the trailer by up to 33mm.
Finally I could potentially move the axles closer together which would help to equalize the loading of the axles a little, but I'm guessin there's a reason they are spaced the way they are (approach and clearance angles).
Any other ideas?
I have a small twin axle car trailer which I planned to use for racing cars (sports cars / Formula Ford)
It is an unusual spec in that it has a bed which is a couple of feet longer than the standard size. This is good for me because it means that not only does a Caterham fit but I can also get a Lotus Elan or Formula Ford on there without overhanging, and still have space for some extra stuff.
Ordinarily this would mean that it wouldn't fit in a standard length garage but this trailer also has a folding tow pole arrangement which means that it does.
Folding tow pole is pretty nifty. There aren't a lot around because they were a bit of a niche, cost extra money and also due to a legislation change, trailer manufacturers were prohibited from making them over a decade ago.
All well and good then, I have a trailer which is extra useful and still fits in a garage.
Onto the problem.
Over the years I have owned a few similar trailers with the same 10" wheels and by default they always tow a bit nose high. Most cars these days have swan neck type tow bars so you can't fit a drop plate. In any case there is a standard range for tow ball heights. Even at the bottom of that range these trailers would be a bit nose high, so really this is a problem of the trailer specification. The trailers are too low for the tow cars.
The standard solution was to fit a 50mm spacer under the coupling head on the trailer which would mean the trailer was pretty close to level.
However, I cannot do that with the folding tow pole arrangement. Also the problem is exacerbated as due to the extended bed, the axles are further apart. The upshot is, with the trailer unladen and towed behind my car the tyres of the front axle are barely contacting the ground. I haven't even put a car on the trailer yet as the way it is, the rear axle and the towing hitch would be taking all of that load and the front axle doing none of the work.
The problem therefore is, If I can't lower the tow ball on the car by at least 40mm, I need to increase the level hitch height of the trailer by the same amount.
I have had a good look to see if the coupling head can be raised relative to the rest of the trailer in a similar way to the hitch spacer idea but while possible it'd be quite a big job involving fabrication, cutting, welding, re-galvanizing etc... and is that even legal (type approval etc?)
Similarly I pulled the bumper off the car to see what could be done there. Similar situation really, I believe a simple and inexpensive fabricated solution could be found (but type approval etc). Moving the tow ball lower relative to the crossbeam would increase the twisting moment on that beam. Also I would run into ground clearance problems with the tow bar itself.
The trailer's axles are bolted on instead of welded so I could hypothetically insert a spacer between the axles and the trailer bed, increasing the ride height of the whole trailer.
I could also fit 12" wheels which depending on tyre size would increase the ride height of the trailer by up to 33mm.
Finally I could potentially move the axles closer together which would help to equalize the loading of the axles a little, but I'm guessin there's a reason they are spaced the way they are (approach and clearance angles).
Any other ideas?
I feel your pain, however my thoughts without having see it or a photo are:
A) Would likely be fine just used at it is, light enough cars, etc. Doesn't sound a major angle and suspension usually fairly complient.
B) Some shims/spacers under the front axle doesn't sound like a bad idea. Presumably only about 10-20mm?
C) For lower ground clearance cars a lower tail height is a significant advantage, assuming reasonable ground clearance still.
Didn't know folding drawbar trailers where prohibited now. Seems a shame.
Daniel
A) Would likely be fine just used at it is, light enough cars, etc. Doesn't sound a major angle and suspension usually fairly complient.
B) Some shims/spacers under the front axle doesn't sound like a bad idea. Presumably only about 10-20mm?
C) For lower ground clearance cars a lower tail height is a significant advantage, assuming reasonable ground clearance still.
Didn't know folding drawbar trailers where prohibited now. Seems a shame.
Daniel
Cheers.
Re: A), I really don't think I can- I am not exaggerating, on the flat the front tyres are scuffing along. The slightest crest or depression and I can see them freewheel as they lose touch altogether.
I could see what the axle weights are like with a car on there but I think it will be possible to get the front axle doing any meaningful work and I'll just end up with a really high noseweight.
B) Hadn't considered spacing the front axle only. Assumed that'd be a no no for some reason. However I see no reason why it shouldn't work?
I was going to have to replace the tyres anyway so I think now going up on the wheel / tyre sizes in combination with spacing the front axle up is the front running solution
Re: A), I really don't think I can- I am not exaggerating, on the flat the front tyres are scuffing along. The slightest crest or depression and I can see them freewheel as they lose touch altogether.
I could see what the axle weights are like with a car on there but I think it will be possible to get the front axle doing any meaningful work and I'll just end up with a really high noseweight.
B) Hadn't considered spacing the front axle only. Assumed that'd be a no no for some reason. However I see no reason why it shouldn't work?
I was going to have to replace the tyres anyway so I think now going up on the wheel / tyre sizes in combination with spacing the front axle up is the front running solution
AW111 said:
Can you get a towbar where the ball sits lower?
Pic of the towbar would be handy.
I have an OEM towbar on the car. It's a detachable swan neck type. Pic of the towbar would be handy.
The problem for me is all tow bars are engineered to sit within this standard specified range. Mine is right in the middle of this range. I have had a look around and It honestly isn't a particularly high towbar.
My car is old so the well-known towbar manufacturers are no longer making them. Also nobody seems to specify a towball height as it depends on suspension spec, load etc.
Finally if I try to do something on the car, the problem is only going to recur again whenever I replace my car or when I inevitably want to tow the trailer behind a different car for some other reason.
Ah right, you where thinking of shimming both axles 40mm odd. Obviously that could work too, but if you have reasonable ground clearance at the tailboard I would be well up for a lower a slightly raked deck. This is the winning option for me by a good way.
Presumably the detachable swan neck is in one piece (never seen one that isn't) but is the socket on the car end one with the mounting, or bolted on in a way the could be shimmed down?
Put half a ton of sand in the back of the car?
Presumably the detachable swan neck is in one piece (never seen one that isn't) but is the socket on the car end one with the mounting, or bolted on in a way the could be shimmed down?
Put half a ton of sand in the back of the car?
dhutch said:
Ah right, you where thinking of shimming both axles 40mm odd. Obviously that could work too, but if you have reasonable ground clearance at the tailboard I would be well up for a lower a slightly raked deck. This is the winning option for me by a good way.
Presumably the detachable swan neck is in one piece (never seen one that isn't) but is the socket on the car end one with the mounting, or bolted on in a way the could be shimmed down?
Put half a ton of sand in the back of the car?
The back of the car is full of tools and jerry cans, the ride height remains resolutely the same due to the hydraulic self levelling system!Presumably the detachable swan neck is in one piece (never seen one that isn't) but is the socket on the car end one with the mounting, or bolted on in a way the could be shimmed down?
Put half a ton of sand in the back of the car?
The receiver for the tow bar bolts onto the crossbeam and I could shim it down a maximum of 25mm so I did consider that. However I already scrape it sometimes when reversing into steep driveways etc and the problem would still exist with other cars. It's not a 'high' towbar.
The reason I didn't think of just shimming the front axle is that I guessed that the trailer having a nose high angle would affect how well the brakes work.
So I was thinking increase tyre radius and shim the axles. Seems a shame to increase the centre of gravity and deck height of the trailer when it's nice to have both low but I've painted myself into a corner haven't I.
Maybe +33mm on wheel / tyre radius alone will be enough, and if not start looking at shimming?
Edited by HustleRussell on Thursday 20th August 15:51
I have recently had to go the other way with mine. There is a 70mm height spread on permissible tow ball and trailer hitch heights (EEC9420, 435mm +- 35mm). My trailer is near the top of the 70mm, my car near the bottom.
I contacted the Witter (who make the towbar on my car) technical team, and they gave me a part number for a swan neck that is 40mm higher than the one shipped as standard on my car. You will very likely find that the swan neck on yours just bolts to the main towbar frame with two chunky bolts, and can be swapped for another.
Larger diameter trailer wheels, as you suggest, seems the best solution to me. Trailers tend to tow better with larger wheels, and you can always deflate/inflate tyres with a 12V compressor to get height/clearance.
Martin.
I contacted the Witter (who make the towbar on my car) technical team, and they gave me a part number for a swan neck that is 40mm higher than the one shipped as standard on my car. You will very likely find that the swan neck on yours just bolts to the main towbar frame with two chunky bolts, and can be swapped for another.
Larger diameter trailer wheels, as you suggest, seems the best solution to me. Trailers tend to tow better with larger wheels, and you can always deflate/inflate tyres with a 12V compressor to get height/clearance.
Martin.
HustleRussell said:
The back of the car is full of tools and jerry cans, the ride height remains resolutely the same due to the hydraulic self levelling system!
Just cottoned on to the car in question, I have spent the last fortnight umming and arring over a rather tattier than advertised 540i 6 Touring a friend of a friend is selling including test driving another E34 525 SE touring yesterday. Nice cars, can rust...Fair enough about not wanting to shim the ball down for scraping issues.
I don't think the angle in question will make any odds the axles operation, or the windage on the deck, and which point it is not going to affect the braking performance. The axles are inline with the road, and the deck is on top of them, the angle between the two in not relevant, as per all the beavertail trailers/trucks with sloping beds.
If you can get a short ball which will plug into the same socket then that is nice and gives you a plug and play oem-type solution. If you cant, or its mad expensive, then maybe not.
Larger tyres is another option 10" is not huge at all, mine is on 12" mini wheels.
Daniel
I don't think the angle in question will make any odds the axles operation, or the windage on the deck, and which point it is not going to affect the braking performance. The axles are inline with the road, and the deck is on top of them, the angle between the two in not relevant, as per all the beavertail trailers/trucks with sloping beds.
If you can get a short ball which will plug into the same socket then that is nice and gives you a plug and play oem-type solution. If you cant, or its mad expensive, then maybe not.
Larger tyres is another option 10" is not huge at all, mine is on 12" mini wheels.
Daniel
Martin30 said:
I have recently had to go the other way with mine. There is a 70mm height spread on permissible tow ball and trailer hitch heights (EEC9420, 435mm +- 35mm). My trailer is near the top of the 70mm, my car near the bottom.
I contacted the Witter (who make the towbar on my car) technical team, and they gave me a part number for a swan neck that is 40mm higher than the one shipped as standard on my car. You will very likely find that the swan neck on yours just bolts to the main towbar frame with two chunky bolts, and can be swapped for another.
Larger diameter trailer wheels, as you suggest, seems the best solution to me. Trailers tend to tow better with larger wheels, and you can always deflate/inflate tyres with a 12V compressor to get height/clearance.
Martin.
The tow ball on my car is somewhere in the 390-400mm region. If I level the trailer off, the hitch is at around 350mm- so well below the guidelines. Hence ideally I'm looking for a solution on the trailer. I contacted the Witter (who make the towbar on my car) technical team, and they gave me a part number for a swan neck that is 40mm higher than the one shipped as standard on my car. You will very likely find that the swan neck on yours just bolts to the main towbar frame with two chunky bolts, and can be swapped for another.
Larger diameter trailer wheels, as you suggest, seems the best solution to me. Trailers tend to tow better with larger wheels, and you can always deflate/inflate tyres with a 12V compressor to get height/clearance.
Martin.
Looking at it, the bigger tyres are a no brainer whatever I do. A lot more choice in 12" than 10" these days surprisingly!
dhutch said:
Just cottoned on to the car in question, I have spent the last fortnight umming and arring over a rather tattier than advertised 540i 6 Touring a friend of a friend is selling including test driving another E34 525 SE touring yesterday. Nice cars, can rust...
Mine's a non-sunroof 525i se touring. It's pretty solid but I did have the outer sills done. Touch wood it has never let me down and drives pretty nicely for an old barge (since I replaced all of the suspension and brakes anyway!)dhutch said:
I don't think the angle in question will make any odds the axles operation, or the windage on the deck, and which point it is not going to affect the braking performance. The axles are inline with the road, and the deck is on top of them, the angle between the two in not relevant, as per all the beavertail trailers/trucks with sloping beds.
I was thinking in terms of the telescoping brake mechanism- is it going to work properly if its inclined up at an angle relative to the direction of travel? Also if it's already nose high, under heavy braking the front of the car is going to dive and the trailer is going to get even more nose high... maybe the trailer brakes won't activate correctly or as well as they should.Probably worrying too much. It's a couple of degrees. But definitely at the moment it 'looks wrong' and it's alarming to see daylight under the front tyres.
Edited by HustleRussell on Thursday 20th August 17:43
Sounds like if it needs new tyres anyway, it might not be much harder to get four 12" wheels and tyres than four 10" tyres.
Point taken about the brake slider, however given angles we're talk (40mm over 12-14ft?) doubt said angle with bother it in the slightest. Trailer will try and nose down a bit under breaking too.
What did paying for having a set of outer cills doing you back all uo? Presumably the inners, where ok? Jack points? PM if you want.
Daniel
Point taken about the brake slider, however given angles we're talk (40mm over 12-14ft?) doubt said angle with bother it in the slightest. Trailer will try and nose down a bit under breaking too.
What did paying for having a set of outer cills doing you back all uo? Presumably the inners, where ok? Jack points? PM if you want.
Daniel
HustleRussell said:
The standard solution was to fit a 50mm spacer under the coupling head on the trailer which would mean the trailer was pretty close to level.
However, I cannot do that with the folding tow pole arrangement.
That seems the ideal solution. Why isn't it feasible in this case?However, I cannot do that with the folding tow pole arrangement.
dhutch said:
Fair enough, the 525i SE Touring that I saw was also a non-sunroof model (pros and cons) as well as an auto, so seriously not quick especially as I will be doing some, if not a lot, of towing with it.
What did paying for having a set of outer cills doing you back all uo? Presumably the inners, where ok? Jack points? PM if you want.
Daniel
An auto would suit the car. The manual ‘box is bulletproof but especially nice to use to be honest. What did paying for having a set of outer cills doing you back all uo? Presumably the inners, where ok? Jack points? PM if you want.
Daniel
I’m afraid I don’t know how much sills cost because I had a lot of work done all at once, however the panels themselves were very cheap from Klokkerholm, and they’re 1.0mm thickness so good stuff.
Dynion Araf Uchaf said:
couple of things, I take it you reverse the SS or sports car on so the engine weight is in the middle.
Also is the chase of the trailer bent?
Elan or Caterham would go on frontways, the Formula ford would go backwards- so that the engine is in front of the axles. Also is the chase of the trailer bent?
I don’t think it’s bent.
HustleRussell said:
GreenV8S said:
That seems the ideal solution. Why isn't it feasible in this case?
Most trailers have an ‘A’-frame and a universal coupling head which bolts down to it. With a folding towpole all of that gubbins is integral to the draw bar.
http://usedcartrailers.name/2019/01/31/brian-james...
To raise a couple of points:-
Firstly, unless the trailer has some sort of front to back pivot design then if the nose is running higher then more weight is on the rearmost axle,
effectively increasing weight on the tow ball.
I have a twin axle with 195-55-R10, and by jacking up the bogy wheel I lift the front axle off the ground, thus making it a single axle and therefore
easy to manoeuvre by hand on the drive.
Secondly, if the cars are any sort of sports/race vehicles at all they will have equal weight on all four wheels so it matters not a jot which way
round they travel on the trailer.
Again, my Suttol7 goes on the trailer which ever way it comes out of its den.
Paul G
Firstly, unless the trailer has some sort of front to back pivot design then if the nose is running higher then more weight is on the rearmost axle,
effectively increasing weight on the tow ball.
I have a twin axle with 195-55-R10, and by jacking up the bogy wheel I lift the front axle off the ground, thus making it a single axle and therefore
easy to manoeuvre by hand on the drive.
Secondly, if the cars are any sort of sports/race vehicles at all they will have equal weight on all four wheels so it matters not a jot which way
round they travel on the trailer.
Again, my Suttol7 goes on the trailer which ever way it comes out of its den.
Paul G
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