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How do rollers affect the performance of my scooter?

January 19th, 2010

Forget what you know about rollers, they don’t affect speed in any way unless they’re TOTALLY the wrong size or weight.

Rollers simply set the rate at which the bike moves up through the gears. People often make the mistake of thinking heavy rollers give you more top end speed and light rollers give you acceleration. This is true to a point as lighter rollers will make your bike rev higher thus giving more acceleration. Heavier rollers simply put the transmission into too high a gear too soon and you end up stuck in top gear at 20mph hitting 6,000rpm till you crawl up into the power band. The only time you will lose top end speed from too light rollers is if you install STUPIDLY light rollers for your setup.

Another common mistake is the actual roller size. You MUST use the correct size rollers for your bike (measurements are usually in millimeters). Using incorrectly sized rollers simply means they’re either not big enough to push the two front pulleys apart and the scooter goes into the higher gear. Or, they’re so big that you can’t get into a low gear and you lose acceleration and throttle response. Rollers can also mimic jetting issues in that if the rollers are too heavy when you pull away your bike will lose power after a certain speed as the transmission is moving up way too fast. This sounds almost identical to lean jetting at full throttle and should be watched carefully. I always set the rollers so the revs never drop from pull away right up to top speed.

So how does the weight of a roller affect how the transmission works? The heavier the rollers are, the less force needed to fling them out of the centre of the variator (or go up through the gears in layman’s terms). You want the bike to hit max revs at max throttle at any speed. If your rollers are a little light the engine will pop as it revs way too high. This means it’s stuck in too low a gear as your engine isn’t producing enough power to up the gears. If the rollers are too heavy, the transmission moves up the gears too quickly and the revs will drop off gradually. As a general rule, the more power your engine produces, the lighter the rollers will have to be as the centrifugal force produced by the engine with say 2bhp more power will be greater, thus flinging rollers to the outside of the variator sooner. The best method for getting the optimum roller setup for your scooter is to start light as it’s then a case of putting slightly heavier weights in until the engine holds the same rpm from first pull away to top speed.

The next thing to consider is your exhaust. Your exhaust gives max power at a certain rpm so you don’t ever want to go above or below this rpm. Heavier rollers drop the revs off sooner (change gear quicker), light rollers stay in low gear longer (raising the rpm). Think of it like mountain bike gears. If you change gear too soon your feet move very slowly, whereas if you stay in gear too long you’re pedalling like crazy and not really going any faster. Don’t confuse first pull away with roller setup as the first five seconds of pull away is denoted by the spring/clutch setup. Rollers come in to play once your clutch locks up (finishes its job) usually at around 5mph depending on the strength of the springs. Transmission setup is the number one cause of poor performance.

This has been a very general overview but should be enough for you to set up your scooter at home without the need for a dyno.

Words: Graham Gaymer

This article was originally published in the print version of PETROL ISSUE.03

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