Taller tire go faster ? = what size ? By gy6fandan (Read 6,242 times)

[gy6fandan]

Hello,

Cant figure out if fact or fiction ---> A bigger (taller) rear wheel increases speed ? - True or false

If true, I have 130/60-13 rear tires on gy6 150 long case (157QMJ).

Tried to find 130/60-16 and 130/60-17 on internet for "rear" -- no luck.

Also, If speed would be increased by a larger tire I wonder what the MPH increase would be.

Thanks.

[richardv]

In theory yes. That is if the engine can produce enough power. It's like changing the final drive ratio.

You shouldn't be just looking at rim diameter, it's the outer diameter of the tire that counts. The same size tire by different manufacturers may have different outer diameters. The next wider size may have a larger outside diameter.

[twowheeler]

I would think a smaller tire would raise rpms at any given speed and that right there is a speed limiter.

[gy6fandan]

Well, since final gears have been brought up... I have recently swapped my final gears to 15/36.

Other upgrades include sparkplug, cdi - no rev limit, high ignition coil, dumped air filter box for uni-filter, motorio dual ramp 115mm variator (17/13 gram sliders), stock clutch with 1500rpm contra spring and... thats about it.

So would a bigger rear tire do anything.... the final gear swap only lowered my rpm's - top speed is 55 on the scooters dash board. 55 mph @ 6k rpm

[fugaziiv]

Jun 10, 2014 17:38:01 GMT -6 gy6fandan said:

Hello,

Cant figure out if fact or fiction ---> A bigger (taller) rear wheel increases speed ? - True or false

If true, I have 130/60-13 rear tires on gy6 150 long case (157QMJ).

Tried to find 130/60-16 and 130/60-17 on internet for "rear" -- no luck.

Also, If speed would be increased by a larger tire I wonder what the MPH increase would be.

Thanks.

Couple of things here:

First off, a GY6 longcase will support up to a 13" rim, there isn't clearance for anything larger. The "B" cases are designed to support up to a 16" rim, but that is a whole different engine, and therefore probably not applicable. When you are looking at tires, the first number is the width of the tire in millimeters mounted, the second number (this is the money number for a taller tire) is the height of the sidewall as a percentage of the width of the tire, and the third number is the diameter of the rim.

So for example, a 100/60-12 tire, would be 100mm wide mounted, with a 60mm tall sidewall and fit on a 12" rim while a 130/60-13 is a 130mm wide tire with a 78mm tall sidewall that fits on a 13" rim. The tallest tire that fits on a standard 157QMJ and is readily available is the 140/60-13, which features an 84mm sidewall. This increase in overall diameter is incremental however and probably not worth the added weight of the taller tire (which I'll get to below, there is a usually a solid 1.5-2 lb difference from the 130 to the 140).

Looking for -16 or -17 tire options won't help unless you plan on changing out your whole engine unfortunately. This being said there are many 16, and 17" tires are a very common motorcycle size as well. Normally all of these tires tend to have higher sidewalls however.

Now with that out of the way, in theory, a taller rear can in fact give the potential of a higher top speed, but there are some other factors that come into play here that limit what can be done, and they all factor in the limited power of the GY6 engine. Since the GY6 just isn't really all that powerful, it is pretty sensitive to increases in rotating mass on the rear wheel, not to mention that you'd probably be looking at additional transmission tuning.

Also, it's simply harder for the GY6 to propel a scooter through the air at sustained higher speeds without something that helps the bike to make more power, such as a BBK or other power adding options. This also applies to changing out the gears for a better top end ratio. You might see a bit of an increase, but the GY6 can't make the most of that kind of modification at it's stock power levels.

Nerd alert, but here is the why on the aerodynamics thing, because even at the lower speeds of scooters, it is a very real factor. As many of us know, getting into a tuck really does add a few MPH on top. Anyway, here goes: Aerodynamic drag increases at roughly the square of speed. That is, while power increases in a linear fashion, drag increases exponentially with speed, in a parabolic function. For example, if 100 horsepower would push a certain vehicle 100 miles per hour through the air, doubling the speed to 200 would require two-squared or 400 horsepower to overcome air resistance, while 300 miles per hour would require 900 horsepower. A simple reduction in frontal area reduces the amount of drag, hence tucking.

In short, it's a great engine and a lot of fun to play with because it is relatively simple, but a powerhouse she is not in stock form, and that is the biggest limiting factor for the top speed of the GY6 overall.


Matt

Credit to these guys for the aerodynamic formula used here.

[baddley]

Hi

I have a Gy6 TaoTao Quantum 150 that I am having trouble with. I have a small big bore kit on it, unlimited REV CDI unit and a uni air filter, plus I have upjetted the carb to 130 and a performance exhaust also The problem is when I am wide open throttle the rev limiter or governer kicks in and makes the whole bike jerk back and forth preventing from going faster, this only happnes at wide open throttle and I was told I need a taller tire for more wheel speed...

Right now the bike goes about 62 mph and then she is done

If this is the case can I put a bigger tire for more top end or can I just put heavier roller or weights in the variator and loose some low end ?

Thanks
Scott

[cyborg]

I think that is good I'd leave it again

[baddley]

Jun 3, 2018 8:04:52 GMT -6 cyborg said:

I think that is good I'd leave it again

You think that is good that what ?

Scott

[cyborg]

62 mph for a 150 scooter is good

[ucwt]

For your amusement.

www.tacomaworld.com/tirecalc?tires=130-60r13-130-80r13