Road vs Race


Nova Racing Transmissions Ltd specialises in the design and manufacture of motorcycle gearboxes and have produced standard specification racing gear sets. These are used by riders and teams around the world who wish to have better life and safety than that offered by the OEM parts. However, there is some doubt as to the legality of the use of these in the British series. The 2014 MCRCB Yearbook specifies what can be done to certain individual components but does not fully address the concerns of team owners. This note looks at why the use of standard OEM parts can give rise to operational and safety issues, and shows that these can be reduced by the use of aftermarket parts. These replacement parts would not give any benefits in relation to engine performance, the benefit is primarily the reduction in missed gear shifts and false neutrals that occur when the stock OEM items become worn, and the reduction in replacement and rebuild costs. The supply of spare or uprated parts may also be difficult for the manufacturer of the motorcycle, and hence there exists a need for an alternative source of supply. It is suggested that the existing ‘British Superstock’ rule be clarified to allow the use of aftermarket parts having the same teeth numbers as the standard parts but that they must not be lighter and should be made using conventional heat treated gear steel

Current Situation.

Nova have been asked for advice by a number of teams and riders who have been experiencing gearbox problems when racing their motorcycles in the British Superstock series. The current MCRCB rules for production based racing are well thought out and provide a very good basis to minimize the cost and to equalize the track performance of current production motorcycles. Changes to such components as forks, brakes, clutch packs, tyres etc are well controlled and documented and enable the standard OEM machine, to be safely used in competition. Nova want to be able to support the teams by providing cost effective solutions to their transmission problems and the rule on the gear items needs some clarification. At present the teams, even though the rule appears to have been written to allow aftermarket parts, are not prepared to risk using them due to the strict policing and the fear of being disqualified from the competition.

The rule book item states that:- That the material and heat treatment of the highest 2 gear pinions may be changed, but the number of teeth has to be kept as homologated. This clearly identifies that non-standard parts may be fitted to the top 2 gears, but does not specifically mention the other 4 gears other than by saying the same number of teeth. It also states that the material and heat treatment may be changed but only for the top 2 gears. This rule allows for the use of titanium or some other exotic material and would seem to be contrary to the spirit of the class. Clearly this must relate to some previous safety or operational issue that had occurred in the past but needs to have some explanation. The race teams require clarification that the other 4 gears, providing they have the same number of teeth, may also be changed. This would then bring the transmission parts into the same grouping as the other cycle/engine parts that are permitted to be changed for safety or wear related issues.

Nova produce close ratio racing gearboxes for many of the superbikes currently racing in BSB, WSBK and the various national series. These are designed and manufactured with alternative gear ratios to the stock items in order to match engine modifications and demands of specific circuits. For instance the short circuits in the UK require different ratios than those for say world endurance or WSBK. Along with change in ratios, Nova build in detail design features which provide the necessary modifications to allow the original street design to cope with a racing environment. These detail changes allow the gearbox to be used for multiple 24hr racing without breakage, a feat that can be difficult to achieve with the stock items. In many cases weight reduction is also a priority. The reason for needing to make these changes is that the gearbox design remit for a street bike is different to the requirements of a race bike.

Street bike requirements

The standard gear box is designed to provide high mileage with good durability.
Gear shifts per mileage ratio is low. Tooth widths are wide and the wearing surface is hard.
The tooth design is optimized for low wear and low noise.
The dog pocket backlash is relatively small to minimize drive train snatch.
The undercut angle on the dog driving faces is kept small to allow easy shifting out of mesh.
The tolerances are large to allow for production variations.
The gears are generally made in dies and this places limitations on dog design.
The gear material is commercial grade case hardening steel with cost and mechanical trade-offs.

Race bike requirements.

Light weight dependant on required life.
Low inertia No gear tooth breakage, resistant to shock loadings.
Many gear changes made per mile
Greater undercut angles to avoid ‘gear kick out’
Sufficient dog width and size to avoid ‘dog rounding’ and breakage
Optimised dog pocket for consistent engagement.
Close tolerances for best build and consistent shift quality.
Billet machined for dog strength and design freedom.
Certified motorsport case hardening steel with controlled heat treatment.

During a race, the gears are shifted as fast as possible, normally without clutch usage, and this produces high intermittent loads within the transmission resulting in elastic shaft deflections and gear misalignment. If there is insufficient dog undercutting, the gears will be forced out of engagement with damage to dog faces and selector forks. When this happens missed shifts and false neutrals will occur. This loading does not normally occur in normal road use, where gear changes are typically much slower and usually made with clutch assistance.

When a standard street box is used by the top riders who excel at making the fastest possible gear change, especially when aided with quick shifters, the safe life of the gearbox is quite limited. Nova understand from a number of sources, both teams and engine builders, that some manufacturers gearbox will not last more than a weekends racing before problems start to appear. This means that engines have to be stripped for inspection and worn parts replaced at considerable cost to the user.

The problem of dog wear under racing conditions give the manufacturer of the motorcycle a number of issues that have to be dealt with in some way or other. In normal circumstances, a ‘race kit’ version would be produced, and this would be designed to overcome the road v race situation, and warranty claims and other disputes arising out of premature wear can be avoided. However if the wear has to be accepted as being part and parcel of the running of a ‘production bike’, then the manufacturer must have in place sufficient spare parts to meet the demands of the racing scene. This provides them with an immediate problem of having to decide what parts may give problems and arranging for increased production of those parts and the general logistics of supply.

Nova already make a number of standard ratio race gear kits, but most of these have been used in off road endurance racing where OEM items would only last for a couple of hrs before dog failure occurred. The Nova gear sets lasted for the 12hr races with little signs of dog wear! Based on Nova’s experience with the life of their close ratio racing gearbox the potential problem of dog wear and missed gears would be significantly reduced if after-market race components are allowed in BSS competition. Furthermore because the company is set up to manufacture gears in small quantities it is possible to react very quickly to the demands of the race situation. In many cases Nova have produced components in 2 weeks compared to the 6 months that most major manufacturers need. This means that if a component has a problem, Nova may be able to affect a solution quickly, but this requires that aftermarket gearbox parts are legal. Nova is able to manufacture gear sets with standard production teeth numbers, guaranteed to be no lighter than standard, but made from certified motor sport steel having more consistent mechanical properties than the OEM parts. The cost of these would not be more than 50% higher than the standard parts.

Nova’s credibility.

Nova have been making motorcycle gearboxes for over 25 years and have a range of classic and modern racing gear kits in regular production. They have supplied most of the major manufacturers with prototype race gears, and provided some of the largest WSBK manufacturers teams with the sole source of gear kits. They have experienced countless victories and multiple championships in BSB and BSS and continue to supply a large portion of the grid. Throughout the companies history it has had many IOM TT victories in all classes, and several prestigious records are held by teams and individuals using components designed for the rigours of road racing. Nova gearboxes are used with success in countless national and club series worldwide, meeting the demands of the low budget user where reliability is paramount.

All the Nova gearsets designed to replace the standard gears in modern sports bikes feature decreasing percentage drops between gears to fully utilize the torque and power characteristics of the engines when used on the track. The gap between each gear gets progressively narrower and in many cases the percentage drop between bottom and top gear is less than that of the standard gear ratios. For the same reasons listed above this helps to keep the engine working higher up the power band and allows the motorcycle to accelerate faster in every gear. It must be noted however that a different final drive pairing may be required to achieve the same top speed. A lower overall gap between first and top will increase acceleration but slightly higher final drive gearing may be required to optimise overall performance. Basically don’t necessarily use the same sprockets as everyone else on the grid is using!!

Adding an extra gear onto the standard gearset improves the rideability of the engine by offering more choices of gears, especially in the middle gears of the box. By adding an extra gear and decreasing the percentage drops between gears even more, a gear can be selected which keeps the engine working in the optimum range at all times. This is especially noticeable on the exit of corners, where in some cases one gear may be too low and the next up may be too high, the addition of the extra gear with narrower gaps helps to optimize drive.

A similar situation occurs when fitting a motocross engine into a road racing motorcycle, as the equally spaced ratios of a MX engine result in slower acceleration in the higher gears. Our close ratio gearsets designed for road-racing motocross engines including the Honda CRF250 & 450, the Suzuki DR800 and the Yamaha WR450 utilize optimized ratios to take into account the changes brought about by racing on tarmac. The standard MX gear ratios have nominally the same percentage drop between each gear, this effectively means with each gear change the engine revs drop to the same level. As the velocity of the motorcycle increases aerodynamic drag increases, this requires more torque from the engine to accelerate at the same rate. Therefore with each gear change, the drop in engine RPM needs to decrease to keep the engine running closer to the peak torque of the engine. The Nova road racing gear sets for MX engines effectively give a performance increase as the engine is operating closer to its maximum power for much of its time. Calculations show that this is equivalent to a horsepower increase of around 8%. Extensive testing of the Nova CRF450 5 Speed road race kit has shown a lap time decrease of 1.5 seconds around a 2.44 miles circuit.