Cycle News - Archive Issues - 1970's

Par' Two of a Series 01 THE TRIALS AID TRIBULATIOIiS OF TRIALS RIDIIG By the Nori Fellow The Nori Fellow is the nom-de plume of a motorcycle equipment dealer in. Birmingham, Englalld. The author has participated in trials events extensively, both as a rider and as an officiaL In part one I emphasized the notable dilferences in this branch of the sport .and that the machinery employed is very specialized. In examining any production trials iron we shall be aware of the obvious 'lack of trimmings so dear to the road burners heart_ The frame will be devoid of passenger foot peg lugs; there will be no ligh ling and its a ttendan t lamp brackets; toolboxes are not the Hin" thing; the combined speedometer and mileage recorder will be the smallest size available and its drive cable taking the shortest route to minimize weighty cable length - the fact that the device is found at all on a truly one-day trials bike is the requirements of the "law" which also insists on "audible means of warning;" to this takes the form of a kiddy bike rubber bulb horn. Such ornaments as chrome covers for the shocks and rubber gai.ters on the front fork legs are also disdained by the pukka trials man. Another common feature will be the huge ground clearance - 10 inches at "the lowest point of the engine or bash plate if fi t ted. Although some makes incorporate the under-engine frame cradle to take the impact of lUrking rockery - the Greeves Anglian being a well known example. The frame tubing will be slim, sufficiently strong to take the knocks of trials bashing. Footpegs are positioned well to the rear, in line with the leading edge of the rear tire with their height from the ground "l'proximating to that of the rear axle. Variations may be made by individual riders. Footpegs have serrated cuts and end weld blobs to prevent foot slip and in composition are of the bend-nat-break structure. This vulnerable item has no sissy rubbers which in any event would not last out one trial. Whilst gla.. fiber fenders have been used the ligh t alloy are first choice as they will bend without breaking and replacement cost is small. Fenders are set well clear on the rear wheel to allow for swinging arm movement and ready clearance if mud is in the course. The front fender is set closer to the tire at its leading (lower) edge than its forward edge so that mud will tend to be cut off before building u.p under the fender and thus clog the wheel. The fender stays are mounted outside the fender and fixing bolts with flat heads enter from Sprite sports a 125cc DKW engine and five speeds. It weighs 175 Ibs. Formerly imported under the American Eagle banner. The 1971 model is named "Goldfinger". due to its gold tram~ .'¥'d tan It. . .• I lJ underneath the fender with self-locking nuts. Not the prettiest method but functional in the requirements of keeping the underside free of protrusions which could entrap rools and twigs and the other rubbish in the trialist's path. Some examples of trials bikes set the front fender up high by mounting same under the steering head but the use of the up and over exhaust header pipe resulted in contact of pipe and fender on full fork deflection and with a good modern telescopic fork such as the Ceriani or Montesa and Bultaco which have rather more than six inches movement this was no good so the fashion is to mOl1Dt fenders on the lower fork stanchions closer to the tire. It will be noted that the fender length is somewhat abbreviated so that where a drop off such as a rocky ledge the front fender will not get. caught. With such minimum in fenders it is obvious that our rider will get well sprayed with any mud or water encountered so our "goodies" men have on the market rubber mud flags which are fixed to the leading and trailing edges of the front wheel guard - they are still enough to do their job yet flexible to give on meeting any obstruction. Wheels are the real give-away of the trials bike; universal wear is 4.00" x 18" rear and 2.75" x 21:' with occasionally 3.00" x 21" the choice. The book of rules lays down a WM3 rear rim but I have always favored as do many a WM2 rim as its narrower section gives more tire "bulge" and, in theory, more grip; also there is less likelihood of rim impact and damage on a rock outcrop. I shuddered at the use in the U.S. of some Montesa Cotas of WMI rims carrying the 4.00 x 18 tire. When it is known th a t rear tire pressu res in trials are as low as 4 pounds p.sj. the danger of the tire rolling off its rim is apparent. .. Wheel spoking is important; gauge on the rear being not less than lOG but in the case of spokes having the commonly used 90 degree bend at the hub flange I prefer the butted 8/10 G spoke - the thicker 8G being at the pain t of likely weakness - the 90 de~ee bend. The Greeves Trials is powered by a 170cc Puch engine with a six-speed gearbox. Weighs 190 Ibs. front will invariably be lighter gaUlle although some manufacturers slandardize for spares stocking on a compromise thickness. Wheel lacing is importan t - particularly when alloy hubs and/or rims are fitted. Due to the "give" of alloy as compared with steel, it is wise to spoke at a greater tangent. On the heavystressed rear wheel a "cross·over 3" system gives a degree of flex as the system obviously required longer spokes. Briefly this means that each spoke from the hub flange; crosses over three other neighboring spokes before en terin~ the rim. Alloy or steel rims? In the interest of weigh t saving the reader will plump for alloy; most alloy rims have two raised outer strengthening ribs forming a well and acting as a beautiful mud scoop, H one is told that as much as 5 pounds of mud can collect and remain cemrifugally pressed into these wells then our weight saving comes to nothing. Also alloy rims can be dented more easily on impact. The later Montesas have come up with alloy rims with no ribs so this criticism is not justified in this instance. more widely spaced for between-section road work. With 5 and 6 speed boxes there is a gear for every need an.d condition but with these multi-gear offerin~ there is often the dilemma as to 'which of the many gears to employ. Many riders preferred the old 4-speed Bultacos to the later 5-speed. ....; .......: , Bultaco Sherpa 25!lcc Trials. Bike weighs 228 Ibs. It was designed by the great Sammy Miller, who won every trial honor possible. against ·the inside of the rim. The front wheel required only one such device and fitted about 6 spokes from the valve. There is no gain in fitting before or after the valve; even makers cannot agree on this. Sports or knobby tires are just not used in trials. The wear 1s the trials tire, which has usually a block formation trend with a '4 inch rear for maximum grip and 2.75 front for ease of steering in tigh t turns sections and to cut into soft going or crimp in to the narrow slot. Whilst tire tread design for trials has remained static for many years the rubber composition has altered with the trials tire specialists such as Dunlop and Avon marketing softer and more yielding rubber compounds giving better flexing of the tire walls. Seats are usually of meager proportions as in practice riders negotiate sections standing up on the pegs. However, seat height is important and should be just low enough for the rider to sit astride his mount and be able to place both feet flat on the ground_ He is thus able on difficult sections to maintain progress with foot power assistance. The gas tank may be of alloy or glass fiber, construction. The alloy will dent without leakage whereas the fiber type will invariably "hold" on impact and an "on the spot repair" is seldom possible. Capacity of 1 Y. gallons is ample in the interest of keeping tank compact. A chain guard covering the top run and extending inside and below the bottom run is necessary to channel off mud and grit from the chain. Chain guides are fitted on several makes but these are soon discarded by users as . invariably due to their vulnerable location soon get d'i'ffiaged and distorted and the chain guide cum chain tensioner as on the Bultaco Sherpas soon get clogged and inoperative. The wheelbase dimensions· vary as between the popular 250cc and mini (125-170cc) jobs, but between 50 and 52 inches may be termed acceptable_ The rake of the front forks is reduced on a trials frame which gives better control on tigh t turns as will of course the shorter wheelbase but on steep climbs when the power is wound on there is a danger in aviating the front wheel with consequent loss of directional steering. This is particularly evident with the mini trials models where more throttle is required. Front forks in general use are of the telescopic variety, with the Italian Ceriani in my opinion the best of them all. Although many good copies, as on the Montesa, Bultaco, Cotton, and Saracen, are good forks (the Greeves Pathfinder fit the mediumweight Ceriani), the fork action and camping must be adequate: Soft enough to absorb shocks yet firm enough to preven t '4bottoming". The engines must be flexible with power enough at the slowest pace. Compression ratios are of modest order; speed and top end power being of little use. Flywheel weight is increased - the aim being low revving slog or "plank". Much attention has been given to spoton carburetion and timing which in the case of the almost universal two-cycle engines is governed by port design for the job in hand. There are many types of air filters but all provide adequate engine breathing coupled with protection from water, sand, mud, and whatever spinning wheels the organizers can throw at the much abused machinery. In order to gain more wheel or tire grip it is of the order of things to deflate front and rear tires down to 7 and 4 . pounds respectively and so provision has to be made to prevent tires "Creeping" and tearing out the valve. The rear Gearing has been carefully chosen wheel which takes all the fierceness of giving an ultra low bottom for really drive a"d braking is fitted with two rim ti~t c1utch-engaged course juggling Wlth reasonably spaced second and third locks. They are spaced equidistant to the v~~F.:?,.ql'~a:~ur':'~eJ~' f'_~~ tt', 1 u~r.~f. ~p••~. f, '~I?:""4, "I}I,~, 'WP I'~ is llrakes on a trials bike are not the big powerful motocross kind but a necessary feature is water and mud exclusion. The former massive Montesa motocross brakes have been replaced by smaller alloy ones although there is some criticism of the narrowness across the hub flanges which does not spell a ~ood triangulated wheel lacing. With .weight reduction a major concern we find that the claimed weigh ts of the .trials bikes are in the relVon of 225 to 235 ,pounds for the 250's and 175 to 190 pounds for the 125-170cc minis. These weights can be considerably reduced by the owner - a known example being a Montesa Cota with a dry weight under 200 pounds and a Greeves Pathrmder down from 190 to 178 pounds. Even with the help and advice of the top trials professionals "improvements" are soon in hand by the club rider and Sammy Miller and Gordon Farley of Bultaco and Montesa have on the market many goodies to "gild the lily." The 170cc Cotton has a replacement gear pedal shaft and modified right hand case. The shaft as slandard being too vulnerable to rockery, and the case mod giving better access to the final drive sprocket. Many riders find that the Greeves Pathfinder with its massive cylinder rmning runs too cool so some severe trimming of the fins back to clutch and timing cases level is done. H the reader looks at the photos of popular trials bikes the points brought out in this article will in many cases be quickly noticed. In the next write-up we will deal with machine preparation; modifications; weight reduction; water-proofing; riding equipment and approach to the conquest of trials sections and hazards. Cotton Trials with four-speed 170cc Minarelli engine. 175 lb. bike sports spring lo;oded pegs. three-position Girling shocks, cush rubber in rear wheel, and a heel and toe gear pedal. Scottish Six Days Trial. Photo courtesy Motor Cycle - London. The lead photograph in the previous article was courtesy of "Motor Cycle London." The illustration of the "long dab" was courtesy "A.M.C.A. Clu~~:;_!,:~gla!'.~ _ . _. __ . _. _ _ ... - Cll (J

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