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Scooter Tuning and Performance Measurement

What's your scooter's 0-30, 0-40 or 0-50mph time? What's your scooter's top speed? When you are tuning your scooter it's very useful to know if you've actually improved the performance or not and so you need to measure it. Scooter tuning is usually done by one or more of the following - using a free flowing air filter, using a performance exhaust, rejetting or replacing the carburetor or changing the ignition timing. More serious scooter tuning can include modifying the cylinders and changing the cylinder head and camshaft. However how do you measure what difference all your time, effort and money have made?

When you're actually riding it's tough to steer, brake, accelerate, watch the road and keep an eye out for other traffic and pedestrians while simultaneously looking at a stop watch and writing down numbers! It's not just dangerous, it's pretty much impossible. So how can you tell if your scooter tuning is actually making the scooter faster or slower, and how much difference is it really making.

You can probably easily measure top speed, though you'll need a stretch of flat, open road with a high enough speed limit, which probably means the Interstate if your scooter is faster than 55mph. You can't trust your speedometer either. Mine reads about 15% fast, plus I'd rather watch the road at 55mpg than the speedometer. If you see someone reporting their 150cc scooter can do 70mph, make sure you know how they know that. My speedometer goes up to 70mph too, but when it does my actual speed in closer to 58mph! What I use to measure true speed is a small pocket GPS receiver. It measures your position on earth very accurately up to several times each second, and from how far you have moved and how long it took you to move that distance, it calculates your speed - and it's very accurate! It will read out your instantaneous speed, but better, it will record your maximum speed. So all I need to do is concentrate on riding safely, and the GPS unit records my maximum speed for me. I use a Garmin eTrex handheld GPS. It's reliable and one of the least expensive. Though maximum speed is an interesting performance parameter, it doesn't tell you everything. If you use tall enough gearing (by modify the CVT springs and weights), you can increase top speed, but your acceleration may be poor. What you really need is something to measure acceleration and top speed and that's where a "vehicle performance computer" comes into play.

A GPS measures position, time and speed based on signals from an array of orbital satellites, while a "Vehicle Performance Computer" measures acceleration using solid state accelerometers. From acceleration and time it can calculate how fast the vehicle it's attached to is moving, how long it takes to get to a certain speed and how long it takes to cover a certain distance, so it can, for example, give you a 0-30mph or 0-50mph time, plus the time taken to cover 1/8 mile or 1/4 mile and what the speed is after that distance. Though intended for use in a car, there's no reason why it can't be used with a scooter too as long as you can power it up from 12v. I added a "cigarette lighter" or "accessory 12v" outlet to my scooter. An easy job and it makes using a radar detector, auto GPS or "vehicle performance computer" much easier. See Adding a 12v power outlet

The Vehicle Performance Computer I used was an Escort GT-1, though that unit now seems hard to find. However from everything I can gather, the Vector FX-1 Performance Timer Accelerometer by Beltronics is exactly the same, except it's in a different case and has a different name on it. The user manuals seem to be identical. It's trivial to use. You hit the "start" button, the display tells you it's calibrating itself, then tells you it's "READY". It then waits for you to start. As soon as it senses any forward acceleration the timer starts and you just accelerate as hard as possible (wide open throttle) until you reach the speed you want or your maximum speed. It will then give you your times for 0-10mph, 0-20mph, 0-30mph, 0-40mph, 0-50mph, 0-60mph (and faster if you can go any faster!), plus your maximum speed, time over 60ft, 330ft, 1000ft and 1/8 mile and 1/4 mile times and speeds. If you input the total weight of the scooter + rider, it can calculate the power output between two speeds you program in (though that's really designed for a car or motorcycle in a fixed gear, I don't know if the CVT auto transmission throws it off). With a car it can also measure lateral G-force (cornering Gs), but on a motorcycle or scooter that won't work because of the effect of leaning into turns. It can also measure acceleration and deceleration G forces, as well as braking distance from a given speed.

Here's a set of data I measured on my Chinese scooter (150cc GY6, carburetor modified with with #115 main jet). Of course with a scooter the weight of the rider can be a significant factor, considering that in some cases the rider may be half the weight of the scooter itself, in in other cases the rider might weigh as much as (or more than) the scooter itself. My scooter weighs around 105kg (230lbs) and I weigh around 80kg (175lbs). Note that these are real speeds. At 50mph, the actual scooter speedometer reads closer to 60mph.

0-10 mph	0.6 seconds
0-20 mph	2.0 seconds
0-30 mph	4.25 seconds
0-40 mph	8.25 seconds
0-50 mph	16.4 seconds
1/4 mile	22.3 seconds @ 52.7mph

Here's what a typical acceleration plot looks like:

It's hard to find acceleration times for scooters, so it's hard to compare these numbers with anything else. I did find some times for 0-30mph for a few 50cc scooters and they were typically in the 10-20 second range, so you can see how much quicker a 150cc scooter is.

With the ability to measure acceleration times, now when you do any engine tuning you can see what the real effect is. I tried a couple of runs with the air filter removed (OK for a short test run, not OK for long term use). This was to see if just adding a high flow, low restriction, air filter would help performance. It didn't. In fact acceleration was quite a bit slower, taking around 10 seconds to reach 40mph, instead of the 8.25 seconds with the filter in place. This suggests that running without the filter probably provided too much air and the mixture became too lean. So if a high flow air filter was added, the carburetor would probably have to be rejetted with a larger jet, maybe up to a #130. See Carburetor Rejetting.