Scooter math and the truth about top speed

fulltilt · Post by **fulltilt** » Fri Jun 16, 2006 10:50 am

I recently got the Spree bug and just found your site today. I can't wait to apply some tricks to get more speed out of mine. However, many of you keep using speed as a comparison. As an Engineer with some vehicle design background, I thought maybe I could shed some light on this.

The only true way to know how much power a performance mod has made is to use a dyno, but this is not practical here. The most convenient comparison for these scooters is speed, even though we are using a low precision speedo to observe this. Many things affect top speed. Most significant here is weight, rolling resistance, and frontal area. Weight is a factor because the ratio of the rider to machine is so much higher than it is on a car for example. However, this will most affect acceleration, as force=mass x acceleration. If you re-arrange this formula, you get force/mass=acceleration. Therefore, the greater the mass, the less acceleration.

But we're not talking acceleration, we're talking top speed, and the effect of weight is lessened by the efficiency of ball bearings in the wheels. But the efficiency of ball bearings is countered by the rolling resistance of the tires. As tire pressure goes down or as rider weight goes up, the effective radius of the tire goes down, and speed goes down. You also use energy to produce heat when the tire is more flat. That's why tire pressure is going to be significant to achieve the highest top speed. Hybrid and especially electric cars have special tires that use higher air pressure and a harder rubber compound because they are looking for the lowest rolling resistance to achieve the best mpg. So within reason, add more air pressure to those tires!

Probably the most significant factor in top speed is frontal area, as this variable affects top speed exponentially. Granted, at 30+ mph the exponential effect is lessened, but try crouching down as close to the handle bars as you can and your speed will go up. It looks pretty silly, but it depends on how bad you want it!

That being said, to say a mod gets you 38 mph is not very accurate. Rather to say a mod gets you +2 mph is more going to reflect what it will do for someone else. The most accurate would be to turn it into a percentage that everyone else would apply to their top speed, but that's just an Engineer being nit-picky and anal.

Farfignugin · Post by **Farfignugin** » Fri Jun 16, 2006 12:09 pm

ive just gotta say, nice explination!

Bravo

islandbayy · Post by **islandbayy** » Fri Jun 16, 2006 1:01 pm

I usted to crouch over the handle bars, but people laughfed and threw rocks at me

deathwish · Post by **deathwish** » Fri Jun 16, 2006 1:10 pm

Farfignugin · Post by **Farfignugin** » Fri Jun 16, 2006 1:26 pm

lol...that had to suck...

darat · Post by **darat** » Fri Jun 16, 2006 2:13 pm

ahh to much to read

MySpree · Post by **MySpree** » Fri Jun 16, 2006 3:13 pm

i lean ove rthem sometimes but thats when im tired so i put my arm on the throttle adn my other arm on the speedo. its confy and is bloddy dangerouse. but you lower.

berreta22 · Post by **berreta22** » Fri Jun 16, 2006 4:49 pm

i understood all that geometry crap that you explained...but how many others do? i admit it can be confusing but when you makin things faster/more powerful it can save your *.

darat · Post by **darat** » Sat Jun 17, 2006 12:15 am

i didnt understand it at all

MySpree · Post by **MySpree** » Sat Jun 17, 2006 12:25 am

i did... amazeingly, you learn this in cycle shop at athens

kurremkarm · Post by **kurremkarm** » Sat Jun 17, 2006 11:04 am

Have you ever heard of an HPV? Human powered vehicle. Some of what you are talking about they are already doing there. Take a recumbant bicycle and add fairing and windshields and they can become quite fast.

Anyone ever add a windshield to a spree? I did see one guy with a cardboard wing, that had to help!

On bicycles i have noticed narrower tires at higher pressure make it easier to pedal, I know the current recomendations are like 18 front, 2o something rear, why is that? Couldnt you get like some narrower higher pressure tires and get more speed?

Same thing with your pulley mods, basically in bicycle gears you increase the front or decrease the size of the rear sprocket and you increase the gear ratio. Higher gear ratio would mean slower off the line but greater top speed.

Bicycle tech will get u faster on these things i imagine.

Reading the pulley mod I would imagine the best "performance kit" for a spree would be a replacement pulley and belt for a spree that was designed to go together. Dunno, as i have never seen the inside but im just guessing if there was a way to replace the pulley and then drop it in with a matching belt.

I'm going to steal this guys ebay pic and ask a question. See how this front pulley has teeth? Suppose that someone built a bigger one with more teeth, on a bicycle every 2 teeth up front is the same as one tooth in the back. So add about 6 teeth up front on a custom pulley and you would add comparable gearing and increase in mph.

Could something like this be custom made or take a bicycle sprocket and install it?

Just brainstorming here.

Looking at this stolen pic doesnt sound like what im saying would work with the sprocket but this pic gives me other ideas.

MySpree · Post by **MySpree** » Sat Jun 17, 2006 2:25 pm

the teethareforthestarter.sowhat

kurremkarm · Post by **kurremkarm** » Sat Jun 17, 2006 3:58 pm

Thanks for that information. I dunno im new to this and find it interesting, that's what.

MySpree · Post by **MySpree** » Sat Jun 17, 2006 4:29 pm

that post was a bad one. the keyboard dies while i was typeing. i was gonna saw the teeth go to the eliectric starter so how would that help? it would just mess withthe starting system.

darat · Post by **darat** » Sat Jun 17, 2006 8:51 pm