Munzo

 Watch the Munzo in action on YouTube 1
 Watch the new Munzo in action on YouTube 2  

In building the Munzo, a lowracer with reversed fork, my inspiration was a design by Bauke Muntz. The Munzo is a prototype, not yet a finished product. Some advantages of the reversed fork are: A shorter chain, with intermediate pulley located further forward, and most probably there is greater efficiency. Unique to the FastFWD stable are the U-shaped handlebars and the two-part frame. Thus, many thanks to Bauke Muntz, and also to Frank Bokhorst (who wrote about the reversed fork in an earlier article).

 

On track with a reversed fork

A ride-report on Bram Smit's Munzo

by Rembrandt Bakker and Marieke Rijkse ( Published in Ligfiets&, 2006, no. 2.)

Out in a small shed in the backyard of a house in the modern suburb of Naarden, we find the studio/workshop of the recumbent designer and experimentalist Bram Smit. It is early on a Sunday morning, and we have come to collect his latest prototype, a very low, front wheel drive racer with an unusual 'reversed front fork'. As we stand admiring the new bike, it begins to snow outside. No problem: This afternoon is the last race in the winter racing season at the track in Sloten, which is the perfect opportunity to put this bike through its paces. Will we be able to keep on track with this reversed fork?

Bram likes to keep things clean and tidy. This shows best in his bike, but also in his workshop, where everything you could wish for has been stashed away neatly, but it is so full you need to chuck a few of the bikes out before you can make some headway inside. The neighbours didn't complain until last summer, when he started using a power-saw to cut spokeless wheels from a composite material used in aircraft construction. Good relations have since been restored, but the space-age wheels have been banned.

Bram's best-known bike is the two-part low racer. At the time when Bram was a fervent competitive rider, he found the long wheelbase racing recumbents a nuisance to transport by car. He knew the moving bottom-bracket Flevobike, which can be split into two parts, but it wasn't racy-looking enough. At that time there was already much experimentation with fixed bottom-bracket FWD in which the chain twists with the steering, and Bram combined this idea with a nifty split frame. In the last ten years he has built and sold under the name FastFWD about 15 of these racing bikes. But he is not much interested in mass-production, and more enthusiatic about testing new ideas. The article in the magazine Ligfiets& 2004-5 by Bauke Muntz on the "Ligflits" bike interested him especially: Fixed bottom-bracket FWD without any chain guides or intermediate pulleys? It seemed too good to be true.

 

Eye contact

After building one prototype like this, Bram abandoned the idea: He found there was too much of a steering effect resulting from the pedalling forces. Interestingly, another homebuilder Erik Hartemink has instead chosen vigoursly to pursue the original concept of the "Ligflits", as you can read elsewhere in this issue of the magazine.

Bram continued with the "Ligflits" concept in a modified form, the result of which, named "Munzo", is the bike we are going to test today. This bike does have the reversed fork, but with a chainline more similar to other fixed bottom-bracket FWD's: The chain runs over intermediate pulleys on both the tension and the slack side, but now the chain is shorter and the pulleys are situated well forward so the chain will not run against your knees.

While driving to Sloten with the bike in the car, the weather suddenly clears, and we quickly stop to unload the bike for Marieke to ride. With a bit of a storm wind coming up from behind, we shoot off along the Amstel river. With a seat hight of only 23 cm, she has little eye contact with motorists. Bumps in the road look frighteningly large, but thanks to the relatively long 118cm wheelbase this is not too bad. The bike feels very stiff, and is fitted with thin racing tyres. You feel the road under you, and hope there will be no hard knocks.

  

Pedalling effects

We are riding along the top of a dyke at about 40 km/h. The reversed fork is not at all apparent. This alone is a great outcome: While everybody is brought up to believe that forks must point forwards, this bike feels quite stable. The fork has an angle of 100 degrees with the road surface, and a trail of 4.5 cm. Besides handling stability, with FWD there should also be no interaction between steering and pedalling. The test bike scores high on this point as long as you are going straight in the middle range of gears: If you pedal while cornering, you do feel some wobble in the steering, but it is not problematic - the flex in your arms compensates for that.

To explain it in theory: The steering torque caused by chain tension is the product of force and distance, where force is the component of chain tension at right angles to the steering axis. To avoid steering torque, both factors must be minimized. Force can be reduced by running the chain exactly parallel to the steering axis. Distance is minimized by running the chain as close as possible to the steering axis. On our test bike the distance is about 15 cm, while on a normal FWD it is less than half that amount, a difference that is noticeable when cornering because then the chainline is no longer parallel to the steering axis.

 

The steering controls

We are being blown along so nicely by the storm wind, that we forget to check the time. After a tough stretch going straight into the wind we arrive at Sloten only just before the start of the race. Marieke has never before cycled on a banked oval track, but on the test bike she has no difficulty keeping in line. While going round and round she can comfortably study the bike's details. The steering pivot, for example, is cleverly made from a bottom bracket and a sawn-off pedal crank, while the pulley on the returning chain, fitted with a self-aligning bearing, allows for greater steering movement. The maximum lock is about 40 degrees, just enough to do a 'U' turn in a wide street. This has the unexpected advantage that you can keep pedalling through bends, because the wheel does not touch your foot. That might even be a good reason to use the reversed fork on rear-wheel driven mountain bikes. Then you could also nicely take advantage of the suspension effect that Frank Bokhorst pointed to in his article in the 2005-5 edition of this magazine: With a reversed fork the road shocks are transmitted more indirectly to the rider, and when using Chrome-moly steel for both fork and frame this can be an effective spring. Typically, on Bram's bikes the handlebar is in a horse-shoe shape, sloping up towards the rider. This gives a perfect grip for the hands, we find, as long as it is kept clear of your legs. On the test bike it is just a little too close: With a narrower or V-shape bar, this could be avoided. One bad point on this bike is the above-saddle steering linkage via an intermediate pivot and tie-rod that rubs against your leg with every pedal stroke. This rod is about 10 cm off the bike's centerline. For some critical observers in Sloten, this is immediately reason to doubt the worth of having a reversed fork at all. So you have a dozen less chainlinks and a chain pulley safely away from your knees, but does that justify the added complexity of the indirect steering linkage?

 

Wastebasket

The answer is "Yes, and No". Complexity is a relative thing. An internal hub transmission for example, is very complex but very simple to buy at your local bike shop. On our test bike an indirect steering linkage with zero free play and zero width is required, but that takes time to perfect. One possibililty might be to attach the handlebars to a pivot in line with the steering axis, with a pulley on both and a tension-controlled steel cable as linkage. That can be done with zero slack and low weight. And for example, Erik Hartemink has no trouble with the steering tie-rod on his bike, because his seat is much higher, allowing him to use under-saddle steering. Bram Smit had already told us that his ordinary racer gives by far the better ride. But by building this finely tuned reverse fork prototype he has done us a big favour: The idea that forks must point forward can definitely be assigned to the wastebasket.

Technical details

Wheelbase 117.5 cm
Seat height 23 cm
Bottom bracket height 50 cm
Seat angle 300
Steering trail 4,5cm
Steering axis angle 100°
Wheel size etrto 406
Frame: Steel front half, aluminium rear half
Weight 16,6 kg
Price on enquiry.

 

 

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