Thoughts on Towing a Trailer
Behind Your Harley-Davidson

(Copyright © Paul Manson & Jennifer Lopez, 2007)

Paul and I have thought for some time about dedicating website space to discuss towing trailers.   We’ve both taken the plunge into the world of trailers and are now very enthusiastic devotees to the cause.  In a recent ride into Queensland we shared our thoughts that we’d never go back to long distance touring/camping without a trailer.  We're both rigged up with Classic products (trailer and hitch) and after a recent factory tour of their Yandina (Qld) production plant we can’t speak highly enough about their range of trailers.

I don’t think any prospective owner would be disappointed with a decision to convert to the trailer world, particularly if they're interested in long distance touring.  After touring many thousands of kilometres along Australian outback highways I decided that I needed additional carrying capacity to make my camping more luxurious.  Some riders are a little apprehensive and don't know what to expect when considering trailer purchase.  That’s certainly understandable and I think this thought goes through everybody’s mind - it’s a substantial outlay of funds to rig your bike with a hitch and purchase a trailer before you even try the experience.  I considered having a hitch fitted and hiring a trailer so I could see whether I felt comfortable with towing before buying one.  Alas, I found there was no such thing as a trailer rental market in Australia for motorcycles.

A new quality trailer here in Oz (prices at November 2000) didn’t give much change out of $3,500AUS (currently around $1,820US) so I seriously considered buying a second hand item.  I regarded $3,500AUS to be a quantum financial leap for an unknown experience, particularly if I didn’t feel comfortable with towing after my initial encounter!  I considered the Classic brand trailer to be one of the best available on the Australian market, without the hassle of importing something from the States, so I looked around for one of their models in the second hand market.  As luck would have it I followed up an advertisement where a chap was selling a BMW R100RT with Classic brand trailer; a quick telephone call finding that he was prepared to sell the items individually.  He was a fastidious owner and at only 2 years old (having been towed around 10,000km or approximately 6,200 miles) the immaculate trailer was a bargain at $2,000AUS ($1,040US).  The black colour of the trailer was a bonus in matching my Vivid Black ’99 FLHTCUI and the silver trailer lid is great for keeping the trailer’s contents cool in Australia’s hot conditions.

Picking up the trailer for the first time

Packed for travel in the middle of Australia

You have room for everything with a trailer

I rode to the small town about 120km (75 miles) south of Sydney on the day of purchase and was all excited about the new experience.  I had no idea what it was going to be like and had feelings of trepidation at the same time; a ‘2000 FLHTCUI riding buddy went with me for moral support as well.  The time finally came when, after completing the transaction and paperwork, I jumped on my bike and pulled slowly from the gentleman’s driveway.   Oh boy, the combined rig certainly felt heavy.  The kerbside mass of an Ultra is around 350kg (770lb) + fuel, the unladen trailer weighed 80kg (176lb) and my trim little frame then tipped the scales at 95kg (209lb). I could feel the difference now commanding the Colonel’s starship with an all-up mass around 525kg (1155lb).  I gingerly traversed a few suburban backstreets with chat over the CB to my buddy confirming that the experience felt strange.  But it felt no different to towing a trailer behind a normal family sedan – you only had to keep yourself aware of the additional weight with acceleration and braking.  By the time we’d ridden about 20km (12 miles) I’d really settled into the feel of the rig’s weight and felt very comfortable.

Riding solo I’d normally run my tyres at 36lb front and 40lb rear, with the air suspension set at 15lb front and 12lb rear.  The unladen trailer had no adverse effect on the bike’s handling with tyres and suspension set for normal solo riding – except for one major and noticeable difference from the first time I started towing that day.  I’d always felt quite comfortable with the bike’s cornering where the Ultra may waddle a little due to road surface irregularities in corners.  The movement was never dramatic and was most acceptable for a bike of its mass.  But with a trailer on the back it now held the rear end as solid as a rock – it felt like the rig was on rails!  It’s a feeling of confidence I’ve now come to enjoy with the whole trailer towing experience and preach it to other potential trailer buyers.  The trailer holds the rear end very solid and prevents rear-end wallowing in corners, with the confidence being even more pronounced when the trailer is loaded.  Riding in wet weather produces different experiences and I’ve detailed those below.

Paul's bike and trailer at Ballina

Classic Mini Tourer with Hi Top Lid

The Classic trailer is perfectly colour matched to Paul's bike

Packing a Trailer for Touring
I’ve followed some good advice given to me when I first considered towing a trailer and haven’t had any problems since.  So far I’ve hauled my loaded trailer around  17,800km (11,060 miles) and wouldn’t do any long trips without it now.

Point One
I think this point is most obvious, but to ensure trailer stability always make sure your tyre pressures are correct to manufacturer’s specifications.  That’s no problem to achieve as long as you have a good tyre pressure gauge for both the bike and trailer.

Point Two
Always pack your trailer so the load is evenly distributed across the trailer.   That’s no drama and it's always easy to see when packing your luggage, camping gear etc. into the trailer before a ride.  You’ll know if the trailer isn’t tracking properly during riding if you sit squarely on the bike and line up two reference points on either side of the trailer with reflections in your left and right mirrors.   If the load isn’t distributed evenly across the trailer, or if the tyre pressures aren’t equal, the trailer will track slightly to the left or right and show up in the mirror reflections. During your next rest stop you can rectify the problem.

Point Three
Never allow the load on your hitch to exceed 10% of your trailer/load mass.  Now this doesn’t mean you have to weigh everything that goes into the trailer, then sit there with your calculator and/or abacus.  Some keen trailer owners have written that you should weigh what goes into the trailer, add this to the trailer’s mass, then calculate a download on the hitch at a maximum of 10% of the total mass.   Fine-tuning of the download can then be achieved by distributing the load fore and aft in the trailer.

I work on the theory that the fully laden trailer weighs 180kg (396lb) so I always pack my trailer ensuring that the download on the hitch doesn’t exceed 18kg or approximately 40lb.  Anything from 0 to 18kg (0 to 40lb) is acceptable and you’d have to have rocks in your head if you packed your trailer so that it had a negative download i.e. where it had a tendency to lift the hitch/rear of your bike.

I’ve usually packed the trailer for even load distribution both front-to-rear and across the trailer, where a quick check before a ride has shown a download around 10kg to 12kg (22lb to 26lb).  I now have a couple of plastic bins with lids that fit neatly into the trailer where cooking, camping gear and clothing is stowed so that everything goes in the same place each time.  I don’t even bother checking the download now as I know that it’s within an acceptable limit.

Point Four
Try not to allow items to move around in the trailer.  If you’ve packed luggage and still have some room left in the trailer then spread a sleeping bag, blankets, towels or other light/bulky items to prevent load shift.  This will prevent trailer instability and damage to items being carried by rubbing, chafing or rattling together.

Wet Weather Riding
In wet weather, ride the bike/trailer combination as you normally would with attention to road conditions, but of course you need to be more mindful of braking distances now.

But here’s an interesting situation that occurs with towing a trailer in wet conditions.  Just recently three of us were riding our Ultras north along the Pacific Highway on the New South Wales north coast, passing through a hilly coastal area towards late afternoon.  The three Ultras, with Paul and I towing fully laden Classic Mini Tourer trailers, had ridden through coastal showers during the afternoon but the rain had now eased leaving damp bitumen road conditions.  We entered an area of undulating countryside with the two bike/trailer combinations at the front and Ian on his Ultra at the rear, with about 100m distance between each bike.

Most of the uphill and downhill curves through the countryside were sign posted with advised speeds of around 75kph (46mph) and 85kph (53mph).  Even though the road surface was damp the solid bike/trailer combination instilled riding confidence where we maintained a normal cruising momentum of about 100kph (62mph).  Now, Paul and I aren’t crazy or show-offs behind the handlebars but had simply settled into a cruising speed we both felt comfortable with.  Ian is no new-comer to the world of riding and can certainly push his Ultra at a fair pace, but after we’d traveled about 10km (6 miles) through the hills we noticed that the two bike/trailer combinations were still together whereas the solo had fallen back about 500m.  Paul and I weren’t out to prove anything - it’s just that all three riders were touring at a speed we felt comfortable with in the prevailing conditions.

But a very interesting effect manifested itself in one particular curve as I entered a downhill sign-posted 65kph (40mph) left-hander.  I’d throttled back to around 80kph (50mph) and entered the curve watching the road surface, the apex and where I was heading towards on the curve’s exit.  About halfway through the corner I approached a patch of old shiny bitumen about 0.3m (1 foot) wide and 3m (10 feet) in length where long ago a repair job had been done on the road surface. You could see it was smooth and being wet would no doubt be slippery. It presented no real problem and I gently pushed against my left handlebar grip to tuck the bike tighter into the curve, guiding my front tyre to left-hand side of the road defect.  But I’d left the maneuver a little late and my back tyre rode onto the smooth bitumen, with a slight response as the rear tyre lost grip with roadway.  The result was nothing more than a hardly detectable motion in the seat as the trailer, with both wheels straddling the road defect, held the bike’s rear end solid. Paul and I both discussed the incident during a later rest stop, where he too spoke of similar experiences he’d had along that section of wet highway.

Another unusual experience I’ve had whilst towing a trailer with an Ultra Classic, again in wet conditions, is where you may encounter long narrow patches of water on the roadway and water is laying in shallow depressions.  Think of an old section of bitumen road where constant traffic over the years has resulted in shallow wheel-track depressions.  A strange effect, which can scare you if you’re not careful, occurs in the wet when you’re riding an Ultra with cruise control engaged.  Sections of our bitumen highways in the Australian outback are quite worn after years of use and late last year whilst riding across Australia I became aware of this phenomenon.  You’re riding along with cruise control engaged, sitting on around 100kph (62mph) to 110kph (68mph), it’s either raining or a shower may have passed through a short while ago.  Whatever the weather conditions at the time, the old worn road surface has long narrow pools where water is laying in the tyre marks.  The water may only be 10mm to 40mm (about ½" to 1½" deep) but an unnerving effect can occur if you allow your bike’s tyres to pass through the water.

Okay, think of the trailer.   It's wheels are straddling the depressions and the trailer tyre tread is riding along damp bitumen.  The bike’s tyres pass through the water, where their tread does its properly designed job of expelling the sudden build-up of water, the effect on the tyres due to fluid friction is to momentarily retard the bike’s speed.  The bike slows for only fractions of a second and the human senses really don’t perceive it.  But the trailer, with a towed mass of around 180kg (396lb) and the tyres rolling on only moistened bitumen, still has momentum and basic physics tells you will impart a forward force onto the hitch.  What happens next can cause a slight heart disturbance if you’re not ready for it – the bike is suddenly decelerating as the trailer maintains its velocity.  The bike aquaplanes momentarily!  Riding west across Australia on a particularly worn old section of the Eyre Highway last November, in pouring rain, I was aware that occasionally the bike seemed to go light for fractions of a second and I wasn’t getting any feedback from the road.  I was quite concerned and stopped to check the tyres, thinking one of the tyres may have been deflating and causing a strange sensation in the wet conditions.  The tyres appeared okay and a quick check of the pressures revealed everything to be normal.

A little further down the highway I realised what was causing the phenomenon, so I then created situations using (a) a steadily held throttle and/or (b) cruise control to confirm what was causing the instability.  Each time I set it up on cruise control I found I could induce the aquaplaning effect by deliberately riding the bikes wheels through water, whilst the trailer wheels straddled the depression.  Once the effect was confirmed I felt a more confident in that it was easily explained.  Don’t worry, the tests could be controlled by the choice of puddle.  Riding at 100kph (62mph) on cruise control I’d select a patch of water between 10m to 20m (33 feet to 66 feet) in length.   Most of the puddles were of consistent width where water lay in long strips about 0.3m to 0.5m (12" to 20") wide.  At 100kph (62mph) you’re travelling at 27.8 metres per second (91 feet per second) so the effect is going to last less than one second.  Mind you, one uncontrolled factor in these amazing tests is that you can’t judge the depth of the water – one or two heart murmurs were induced as well!  Isn’t it amazing what the long distance motorcyclist gets up to when he/she is bored?

Fuel Consumption
Quite understandably I have noticed an increase in fuel consumption whenever I’m towing the fully loaded trailer, but not enough to cause concern.  The benefits of additional carrying capacity far outweigh the extra fuel cost.  Get ready for some numbers because I’m about to bombard you.  The calculated distances, fluid capacities and fuel consumption figures are based on the following conversions ( * See bottom of page):

In the first 32,000km (19,890 miles) of the bike’s life (without trailer) I ran an average fuel consumption of 18.83km/l (44.3mpgUS), which would give an average fuel range of 356km (222 miles) for the Ultra’s 18.93 litre (5 gallon US) tank.  I’m never really heavy handed with the throttle and on one occasion I managed to extract 365km (227 miles) from the tank before refueling.  I’d have to say that my normal highway cruising speeds (with or without trailer) have always been around 100kph (62mph) to 110kph (68mph).

In the last 26,700km (16,595 miles) I’ve towed a loaded trailer for about 21,000km (13,050 miles) and have never varied my open highway speeds to any great degree.  My average fuel consumption at normal highway speeds towing a fully loaded trailer of 180kg (396lb) is 17.71km/l (41.7mpgUS) which gives a fuel range of approximately 335km (208miles).  The bottom line is that adding a fully loaded trailer (running at average highway speeds) has decreased my fuel range by around 6% - whereas I've increased my luggage carrying capacity by 470%!  I ain't a businessman but that sounds like a reasonable return on investment to me.

In crossing Australia last year I had a couple of days where I had to make up some extra time and ran the bike at a constant 130kph (81mph) throughout each day, touching the 140kph (87mph) mark for occasional periods of an hour or more.  On those occasions I only managed to get an average of 12.02km/l (28.3mpgUS) for an average fuel range of 228km (141miles) between refueling.  The worst I got was 10.79km/l (25.4mpgUS) with a distance of 204km (127miles) on that tank.   So you can see the dramatic increase in fuel usage when you open the throttle whilst hauling a loaded trailer. Basically, an increase in constant average speed of 30% (100kph to 130kph) resulted in increased fuel usage of 47% - a towed trailer can chew through the motion lotion as speed increases!

My return trip from Western Australia to the East Coast included a pillion passenger with their luggage as well. The all-up mass of rider/pillion, bike, trailer etc for the return trip was as follows:

In anyone’s language that rounds out to approximately 1600lb - so it certainly accounts for dramatic fuel usage as the speed increased.

Tyre Wear and Brake Pad Wear
After 58,700km (approximately 36,480 miles) of Ultra riding, with 21,000km (13,050 miles) or about 36% of the bike's road life has been towing a trailer, I’ve noticed no appreciable difference in either tyre or brake pad wear.  I've always worked on a tyre life of 16,000km for a rear Dunlop D402 and 32,000km for a front Dunlop D402, where the addition of a trailer has not increased tyre wear by any noticeable degree.  At 52,000km (32,320 miles) I had to replace the front brake pads - the rear pads looked like they’d never been used in the bike’s life!  The minimal rear pad wear is to be expected, as I don’t use a lot of rear braking whilst riding (with or without trailer).  Also you must remember that even with a fully loaded trailer the load on the hitch is only 18kg (approx. 40lb).  In other words it's comparable to carrying a 40lb passenger on the back seat!

Jennifer Lopez
Los Angeles, USA
(Article penned whilst Harley touring in Australia)

* Data references from:
Marks Standard Handbook for Mechanical Engineers, Ninth Edition (Publisher - McGraw Hill).

Copyright © text Paul Manson & Jennifer Lopez, 2007.  Copyright © images Paul Manson (2001), Ian Lay (2000) & Peter Guthrie (2000).  All rights reserved. No part of this publication may be reproduced, stored in retrieval system or transmitted in any form by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publishers and copyright holders.