12 Sep 2011

Franklin trike

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This unusual trike was discovered by Steve in the Racing Tricycles gallery on Flickr:



Note: I have obtained permission from the owner to use these superb images.

The quality of the images is quite exceptional. As one would expect from a keen photographer.


Franklin trike: General view. 
Well equipped with very modern, quality accessories. 
Including index gears and dual gear/brake levers.

Such an "aggressive" riding position suggests a keen cyclist. Certainly a tall one. Probably a 24" frame, at a guess. Relaxed geometry and a very pretty colour make for a very attractive and useful trike.

It would  be difficult to imagine carrying such a large case anywhere on a bicycle. While a trike takes it easily in its stride.  Brackets have been attached to the seat stays specifically to hold this particular case. Avoiding the extra weight of multi-purpose carrier rack and the necessary restraints for such a case. I  am not an expert on airflow but angling the case probably helps here. The case sits in the turbulent air from the rider's, flailing legs. So is probably offers quite a low drag despite the increased frontal area it presents. I think we can safely ignore lift. ;)


View from beneath showing the unusual two wheel drive train. (2WD)

In order to drive both axles a lay-shaft has been introduced on the Franklin trike. This communicates the drive via two short chains to the normally undriven axle. There is an obvious weight and friction penalty to such a design. Certainly over the relatively simple, compact and ultra-lightweight, twin pawls and ratchets, Trykit, 2WD freehubs. Or the earlier Longstaff 2WD for that matter.

This Franklin machine is well furnished with wide ratio deraileur gears. So hills are only a matter of slightly greater patience in twiddling a lower gear.

The friction aspect of this 2WD system will depend on the actual details of the layshaft bearings. I think one may safely assume there are a couple of low friction, journal bearings in there somewhere. Chains and sprockets are inherently efficient when clean and well lubricated. Often well up in the high 90s%. Again this is not of cardinal importance on a laden trike. For racing or Time Trialling one might well prefer a Trykit 2WD option. Rider fitness is always the most important factor here.



The Franklin drive train detail.

A normal bicycle chain run drives the rear deraileur, sprocket block, as usual. Modern, index, gear changers are used here. This is  the usual drive to the left rear wheel familiar to any tricyclist. (or bike rider for that matter)

However, on the back of the sprocket block carrier a single fixed sprocket has been attached. This sprocket drives the separate layshaft via a short chain and another fixed sprocket. A third fixed sprocket on the layshaft drives the other, normally-undriven, trike axle on the right via a fourth sprocket. This final sprocket is presumably a freewheel. To avoid the chains being driven when coasting. Which would instantly wreck the entire rear end! Those tempted to copy such a 2WD layout, on a home-built trike, should remember this vital freewheel.

2WD is a very useful addition to any trike in avoiding severe torque steer. Not to mention a huge reduction in wheelspin in slippery or loose ground conditions. In snow and ice it can make the difference between a fairly normal ride and absolutely no forward progress at all!

The construction details of the Franklin 2WD certainly look competent at first glance. It seems well thought out and the overall finish of construction seems to be of a very high calibre.

I have seen similar layshafts on handicap trikes but not on a trike of this promised level of sophistication. The layshaft itself would have to be adjustable fore and aft. To take out unwanted slack in chain tension. Putting it all back together after routine maintenance might be a bit of a fiddle. Though secondary chain life should be considerably extended over the much harder working, primary chain.


Franklin trike fork and disk brake detail.

An amplifier has had to be introduced between the handlebar lever and the brake mechanism. Without which the brakes were non-functional as supplied.


Overall the Franklin trike looks an attractive machine. 

The added, rear chainstay triangulation is rather odd. These braces might easily cause heel collisions unless the wheelbase was considerably extended. Just to provide enough heel clearance. Trykit overcomes this problem by using curved chainstays. Other classical trikes have no extra bracing here at all! Yet have survived for decades of continuous, heavy use.

The shock loads from the rear wheels are all but vertical on the outer ends of the rear axles. The major tendency being for the chainstays to try and rotate upwards around the bottom bracket. Or the rear axle casings to fold up around an imaginary hinge at the centre of the axle due to the weight of the rider. Fortunately the widely splayed seat stays on a trike usually take care of these loads. Almost perfect triangulation being provided by these two simple, straight tubes.  
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Don't rush off to place an order for a similar Franklin trike just yet. It should be noted that the owner had some very serious difficulties with the bike shop which represented the strangely anonymous builder. The list of faults should surely have provided a refund but the owner was simply too keen to own a working trike.

The high cost of importing a new Longstaff with American import taxes and freight charges was considered too prohibitive. In retrospect a Longstaff would have been at least a third lighter but considerably more expensive. 

Apparently the brakes were completely non-functional and the wheels built so loosely they were useless as supplied. The bike shop trashed a new pair of wheels because their staff couldn't remove them and literally beat them off with a mallet! The 2WD mechanism would not even hold its position under any pedalling loads. Even the rear sprocket block needed a support bearing after the axle bent. All this had to be repaired or modified before the machine could be used reliably.

An article on this subject, was published in the Spring edition of the Tricycle Association Gazette 2011. Which described the serious faults which made an expensive machine unrideable. It took major repairs and modifications, taking a considerable period of time, before the machine was reliable. It ended up weighing a considerable 45lbs! The investment: $4000! Ouch!

(Note: My bare, roadworthy, 27 speed, Higgins weighs only 31lbs. A roadworthy Trykit racing trike has been built weighing just 20lbs)

A review of the Franklin trike by its owner will appear in the upcoming Bicycle Quarterly. Presumably the Autumn edition 2011.(?)


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2 comments:

  1. Normally I look at tricycles in puzzlement with a little WHY? cloud hanging over my head. Not with this one. It makes complete sense and is a beautiful machine.

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  2. The Franklin is an interesting machine and certainly pretty enough, Gunnar.

    This matter deserves a proper discussion but I must be diplomatic for the sake of the Franklin's owner. So I will try to choose my words carefully. Not as a tricycle snob but as a trike rider.

    Any of the great British maker's trikes would have been considerably lighter and far more responsive than the Franklin.

    To me, as a keen tricyclist, the Franklin ignores nearly a century of best practice. It was very obviously not built by a trike specialist. Nor by anybody who rides a trike for many miles each year.

    Let me put it this way: The difference between a trike which is ridden regularly and one which isn't.. may be the difference between a great British lightweight trike and the Franklin.

    This has absolutely nothing to do with pride in one's own trike. It is all about the feel of a machine which can only ever respond to the rider's own efforts.

    You want proof of my argument? My Longstaff conversion hangs as reserve trike in the shed. My scruffy Higgins is ridden for many thousands of miles each year. Here lies the vital difference between a great trike and any other trike.

    Even laden with enough shopping to cause physical pain carrying it all indoors in one go... the Higgins still feels wonderfully light and responsive on the road. Best practice counts if you are a trike rider.

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