31 Mar 2010

Newton Trikes

*
"Proper" Ackerman steering with inclined kingpins and optimised steering geometry has been adopted on the so-called "Welsh trike": The Roman Road Cycle's very own: Newton trikes and trike conversions:

Roman Road

The inclined kingpins ensure far better handling than with earlier, so-called Kendrick trikes. (see earlier chapter)  A line extended through the kingpin should point at the centre of the tyre contact patch. This minimises bump steer. Avoiding the tendency for the wheels to change direction when subjected to bumps. The true Kendrick had a very poor reputation at higher speeds and on rougher roads. There are all sorts of other steering geometry details which must be optimised of course. Such as caster and trail.

Here is an expert's web page on trike steering geometry. Aimed more at recumbent trike builders but just as relevant.

Peter Eland's site: Ackermann steering spreadsheet

There are some advantages to the Newton common to most other upright tadpoles. Under hard cornering the tadpole should be more stable than a delta. Under heavy braking the delta tends to tip forwards across a hinge line between the outer rear wheel and the front wheel tyre contact patches. A combination of braking and hard cornering will reinforce the forwards and outwards tipping tendency. A tadpole can only tilt backwards on a similar line but between the outer front wheel and the single rear wheel. Making it likely to be much more stable if a corner is overcooked and the brakes need to be applied. On a delta it may already be too late to apply the brakes if a corner is overcooked because the trike will tend to tip even more. Or run even wider on application of the front brakes. This requires considerable skill, experience and a lot of body lean on the delta to overcome this potentially, very dangerous situation.

The single rear wheel of the Newton offers considerable simplification over the single, two wheel drive or differential of the delta trike. No heavy half axles, housings and bearings capable of resisting the complex driving and road forces are required. The tadpole trike enjoys a universal bike type of rear end. It is uncaring of the camber regardless of which side the road is the national driving norm. Since braking throws the rider's weight forwards onto the front wheels there is no real need for a rear brake. Though a tandem Newton might well benefit from a rear drag brake in hilly country.

I have no data on tadpole trike traction despite claims of advantage over the one wheel drive delta. When hill climbing the rider's weight would tend to be over the back wheel ensuring excellent traction when it matters most. How it copes in icy conditions one can only guess. I know that recumbent tadpole trikes suffer a severe loss of traction in snow and icy conditions. The two freewheel drive delta may well score over the tadpole here. The traction of the one wheel drive delta is pretty hopeless on ice and snow. As I discovered for myself when we had 3 months of snow and ice here in Denmark this winter. (2009/10)  A number of local hills became impassable at times, except on foot, no matter how hard I tried to lean over the driven wheel.

A further advantage for the Newton (or any tadpole) design is that the position of the front wheels can be easily seen on the road. This must make it easier to avoid potholes, squashed hedgehogs and other debris. Or even to follow the edge of the road much more closely than on a delta. (if desired)  Which, even after considerable experience requires considerable care and constant attention with a delta. The edge of the road is often the first part to suffer  damage from heavy traffic. Or farm machinery pulling onto the verge to allow frustrated traffic to pass.

Examination of the image below suggests that the front end of the Newton is rather lower than a conventional "racing" bike. Or even a specialist Time Trial machine. This must make it easier to achieve a horizontal torso to reduce drag when equipped with tri-bars. (low profile handlebars with elbow support pads) The tadpole enjoys (and suffers) no real difference in drag of the framework as far as one can judge by eye.


A Newton Race Trike sporting disk brakes. Earlier examples of the Newton had drum brakes. The brakes would need to be carefully balanced on any tadpole to ensure the trike stops in a straight line when the brakes are applied. Perhaps independent, dual, brake levers allow the rider to apply the brakes to taste depending on the conditions? I really have no idea.

I will probably burn in hell for borrowing this image from the http://www.3wielweb.be/ website without permission. Roman Road makes some unique and fascinating tadpole solo trikes and tandem trikes. Though I don't, personally, feel their website sells the product as well as it might. I like this picture better than anything on their website. Why isn't it on their website? Perhaps they need a running blog linked to their website with much better pictures and up to date information. Longstaff's website is much the same with nothing to whet the appetite of a would be triker. Even their overpriced, secondhand trikes seem to sit there for years without moving. My contacts with them (Longstaff) have been quite appalling. Pay several thousand up front, or don't bother us, is the clear message. Conversely, Geoff Brooks TRYKIT website is an excellent example of how to show one's products to the widest possible audience.


Here is a Newton trike on eBay(UK) in early May 2010.  Item no. 190393831568  Only the second Newton to come up since I have been following trike sales on eBay(UK).  Since it is not usually possible to save eBay auction images I photographed the enlarged images on my LCD computer screen using my digital camera. So don't expect perfection. Since these trikes come up for sale on eBay so rarely I took the opportunity to share much more detail than is visible on the Newton website. They certainly look well thought out.

Update: The Newton was re-listed on eBay due to bidding not meeting a hidden £750 reserve! 20 bids ending at £722 unsold. It's looking a bit expensive now at £750 with four bids close to the auction ending. Cheaper than new but I'm certainly not tempted to bid at this price level. I'd lose that fancy rear Rohloff hub on day one for something much more lightweight!  Well, I just watched the end of the auction and it sold for the reserve price of £750!

Just to see what it feels like to see two wheels in front I sat backwards on the top tube of my Higgins today. :-) The wheels actually looked rather close together when seen from this unusual perspective. I believe the wheels are a bit further apart on the Newton. I am still waiting for a YouTube video of the Newton trike to appear. If anybody has any better pictures to share of of these fascinating machines I'd be most grateful to have them as email attachments to post on here.


I found this image online quite a long time ago. The oval cross axle is a nice and very neat touch  to reduce drag a little. It shows care and a willingness to go the extra mile with the design. Adding a sleek and professional touch to the appearance. This image seems to have disappeared from view since I saved it. Note how the tubes bracing the front axle cross tube to the bottom bracket are widely splayed to triangulate the front of the trike frame to the maximum. This triangulation resists twisting forces in the axle produced by the front wheels. Naturally toe clearance must be provided when pedalling. Though the advantage here is that only the toes overlap the pedals. On a delta trike the entire shoe behind the ball of the foot requires clearance. This severely limits the amount of chainstay splay possible unless the wheelbase is considerably extended. Large shoe sizes can be a real embarrassment on a delta as the heels may literally strike the rear axle housing. (this has happened to me with the Longstaff axle conversion on a short wheelbase donor bike!)

The stiffness of a delta rear end cannot possibly match the Newton's front axle assembly thanks to the arrangement of these carefully designed stays. The near parallel chainstays of the delta cannot possibly compete with the Newton's beautifully triangulated front end. The delta's seat stays are duplicated here in the downward sloping stays on the Newton. Again a wide splay ensures perfect triangular bracing without adding extra weight.

I must say that I personally prefer the cleaner looks of the diamond "men's" frame of this machine to the bifurcated top tubes of the later Newtons. It's probably an age thing. I just don't like the look of sloping top tubes on any bikes. (or trikes) That said the twin top tubes are probably vastly superior for stiffness and bracing value on any pedal driven machine. Made of suitable materials these need be no heavier than a single tube of similar stiffness. The infamous Pedersen and Norton motorcycle featherbed frames are legendary for their stiffness and lightness. All thanks to duplication of the frame tubing. 

Newton trikes and trike conversion sets are also offered in tandem form for that even rarer beast. The, probably unique, Newton tandem, tadpole tricycle. A combination of tricycle and tandem with two wheels forwards. Delta tandem tricycles have always been around but are still very rare. I think I have knowingly seen only one tandem trike in my entire life with my own eyes. That was decades ago in my youth. Though there are examples illustrated on the Tricycle Association website.

Here are some nice images of a Newton tandem trike. It has been modified with QR frame couplings to allow dismantling for more compact storage or carriage:

Googles billedresultat for http://www.sandsmachine.com/p_mst_t1.jpg

In case you missed it earlier here is Roman Road's, Newton trike website:

Roman Road

I have just discovered a nice picture of a Newton trike on the wooljersey part of the Gallery image website. 

I have tried to register in the hope of contacting Bob Freitas to ask permission to use his image. I left a comment as a visitor but still no response from my registration attempt. In the meantime I'll link to the Newton image:

http://www.wooljersey.com/gallery/v/NITROBOBs-GARAGE/TRIKES/BIKER+BOB.jpeg.html?g2_imageViewsIndex=1

The question remains why a supposedly superior machine to the "standard" delta is not seen in far greater numbers? Tadpoles are supposedly much easier to ride than a delta. Yet the only machines one sees (in time trial or massed start) competition on the TA or Belgian triking website are deltas. The price of a Newton is close to that of a new delta from Trykit or Longstaff. (or the Supertrike of Beligium?)

I can imagine one slight drawback of the upright tadpole would be road shocks to the front wheels as a result of hitting a pothole, drains or road debris. My own delta experience is that one can get away with hitting almost anything with the back wheels but never the front. Practice allows the delta rider to lift a lightly-loaded rear wheel over any obstacle with a deft and timely twitch of the handlebars. This can be managed at almost any speed. The tadpole's front wheels are more lightly loaded by the rider than the delta's single one of course. This may allow a quick lean combined with a twitch of the bars to lift one front wheel over potential dangers. However the front axle and stays must add considerable mass at the front end. Making lifting the front much more difficult than a simple pair of forks and one lightweight wheel. I wonder how they could cope with the steep pavement ramps outside many supermarket car parks? One can't so easily lift the front wheels off the ground as one can so effortlessly with the delta in a low gear.

I'm not sure how a tadpole upright would cope with my pothole-littered, rural lanes. Being able to judge the track of the front wheels may allow easier avoidance of the worst dangers. Though many of the lanes I travel are now in such poor condition that no safe route is possible even in the complete absence of traffic! Not even using the entire width of the road! One can but aim the single front wheel of the delta and hope to find a clear path. Letting the back wheels take care of themselves. Lifting off the saddle momentarily really helps to reduce unsprung weight on the rear wheels on the worst stuff. Provided, of course, that the trike isn't too heavily laden. Though the rider is the major load on any normal trike.  I'm not sure the tadpole is so forgiving. I do wish somebody who has managed considerable mileages on an upright tadpole would share their experience of riding one.

The weight of a suitably equipped tadpole machine is not too dissimilar to a reasonable delta. Perhaps the bias towards the delta is simply conservatism on the part of those who choose to be tricyclists?  I wish I could have a ride on one just to see how they handle.

I have been planning to build an upright tadpole, for some years, but it still hasn't happened. (not yet anyway) I still have the lightweight, aluminium alloy track/tie rods and spherical joints sitting patiently in a box. These were bought from an online store dealing with racing go karts so should be more than strong enough for a trike. I have the steering tube and front axle cross tube already. I made a neat cross joint (thinned for lightness on my lathe from a high quality, iron plumbing joint) to form a tidy crossed lug. No great strength would be required here since most of the loads are taken by the stays. I just need to obtain some more brazing rods and get building. I shall be using the tubes and stays from the donor bikes I have collected for this very project. It won't be as light or as sophisticated as a Newton but will at least give me the experience of riding a tadpole, upright trike.




*

No comments:

Post a Comment