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Sprocket Selection

The final drive ratio, the number of teeth on the countershaft and rear sprockets, is the most efficient and effective method of fine tuning the performance of the RL250 to the owner's riding style and goals.

One of the most obvious differences between streetable bikes and trials bikes are the internal and external gear and drive ratios. These will include the primary gear drive, transmission, and the final (secondary) drive. The effect of the engineering of these ratios is to make the engine's torque, along with the rider, accomplish the job the bike was designed to do. Motocross, flat track, road race, or drag bikes all have a different application for the torque produced by the engine. A trials bike should have smooth and manageable power from idle speed to the mid-ranges and the ability to apply that power as necessary. A WFO (full throttle) application is not a normal application of the trials machine and it was not designed, tuned, or recommended for that type of operation.  Of course, one must travel between sections on the trials bike so a kind of streetability is also required. 

The area of gear ratios is where the RL250 engine began to depart from its TS250 sister. The primary reduction ratio is the geared connection between the crankshaft and the transmission input shaft. The primary ratio was changed from 3.19:1 for the TS to 4.23:1 for the RL.

The RL first (2.41:1) and second (1.80:1) gear ratios are the same as the TS ratios. The RL third gear was changed to 1.41:1 as opposed to the TS at 1.28:1. With the different primary ratio, this sets the RL up for operation and control at much lower speeds for trials section riding.

The RL fourth and fifth gears, the selections for traveling between sections, are also different, but the other way. Suzuki created a kind of overdrive situation for the top two gears in the RL. The fourth gear was changed from 1.00:1 in the TS to 0.86:1 for the RL. Fifth gear went from .083:1 for the TS to 0.64:1 for the RL.

The production RL was fitted with a 54 tooth rear sprocket and 15 tooth countershaft sprocket. Optional sprockets included a 56 tooth rear and 14, 16, and 17 tooth front sprockets. As a result, the final drive ratios available from Suzuki ranged from 3.18:1 (17x 54), to 4.00:1 (14X56).

Tuning the final ratio to suit the rider's style is the easiest and most effective change to make in the drive system. Time (speed) is not normally a factor to the trials rider. Section riding requires precise control of the bike from just above full stop up to the use of second or, possibly, third gear.

The production final drive ratio of 3.58:1 (15T front and 54T rear) does not provide the rider with any options. Sections must be taken in first gear and, if very tight turns are required, the clutch must then be slipped to bring the bike speed down to a manageable level.

My recommendation is that the RL250 needs a final drive ratio of around 4.25:1. This translates into a 14T/15T front and a 60T/64T rear sprocket. A good set to have on the bike is 14Tx60T with a 15T front sprocket in the toolbox. This will provide a normal 4.25:1 and a 4.00:1 option with the 15T installed.

With this setup the bike may be ridden in most sections in second or third gear leaving first gear for the really slow sections with no real need to slip the clutch. These ratios have the added benefit of making fourth and fifth gear more useable.

New sprockets of these sizes may be purchased through Matrix Motor Sport. The rear sprockets are available in aluminum and the front in steel. The new manufacture rear sprockets will not have the dished center like the original Suzuki sprockets. Alignment is maintained by adding a spacer under the sprocket to bring it in line with the countershaft sprocket. The spacer is a one-time purchase and will be used over again as the rear sprocket is replaced.

The addition of the spacer will reduce the number of threads in the hub engaged by the stock sprocket bolts. Longer bolts should be installed when the spacer is used. Matrix Motor Sport can supply bolts that are 5mm longer than stock.

There are few points about chain selection discussed on another page in this Tech Tips section. Check out the Roller Chain Tensioner modification, too.

Matrix has all the required hardware for a clean and safe sprocket installation.

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Last modified: 05/26/14