Wheel diameter

I have a 10 inch wheeled Kymco
Will a scoot with bigger wheels(12-13 inch) improve stability especially at speed(60-80 kph)
What are the ads and disads of bigger wheels?
Thanks

Your rear wheel would perhaps not fit in the wheel well, and you might have to cut the seatbox a bit.
More importantly, there may not be enough distance from the axle to the engine to install a much larger wheel (not sure how long the swing arm is no those). that would essentially be the first determinant of whether or not you can make the swap.

If your engine is small, there may also be a torque issue: bigger wheels are harder for the engine to turn, and normally need some kind of transmission change to go for such a huge diameter change…

As for the front, you may need to get new forks, probably new front disc brakes, new mudguard, etc…

Your speedometer would read low (about 25% low: the circumference of a 13 inch wheel is 25-30% bigger than a 10 inch wheel.) not that that’s really much of an issue.

The stand would not work so well with the bike two inches higher or so. and your tire choice would be limited in Taiwan.

You would get better roadhandling than a 10 inch wheel, though, with much better bump riding and better gyroscopic stability.

thanks
so to change is out of the question
so another scoot is on the cards
is the road holding that much better?
would a wider tire be more stable?

well, change is not out of the question. Just likely to be expensive.

In Thailand Laos Vietnam,etc, the bigger wheels are the standard. ON the bad roads there they are great and you get essentially the same practical scooter body. But they don’t sell them in Taiwan.

when you say road holding, do you mean cornering as fast as possible? A wider tire may be better, but only if the wheel is built for it, and often people put a stooopid back tire on and the bike handles like crap. But if it’s stability at speed you want, then better suspension and careful attention to your rebound settings and tire air pressure is the ticket. Or buy a Ducati.

better to find sticky scooter tires and keep them well inflated with a suspension upgrade and stiffer fork oil. Ultimately cheaper, probably. Get some more usable power by playing with rotor weights to shift your transmission curve around a bit, and you’d be amazed.

A better flowing exhaust (NOT necessarily the loudest one, and avoid Supertrapp like the plague), and maybe a bigger air intake, (i guess you have a non-mappable fuel injector rather than a carb if it’s a new scooter). Not much else you can do with a vehicle designed for simple short distance travel.

Here’s a question about wheel diameter. If you have a scooter with 10 inch wheels and replace the wheels with 12 inch wheels, I assume that the speedometer will read slower than your actual speed. But by how much? Does anyone know how to calculate this?

[quote=“urodacus”]

You would get better roadhandling than a 10 inch wheel, though, with much better bump riding and better gyroscopic stability.[/quote]

You will get more gyroscopic stability (harder to change direction)
You will feel less bumps on bumpy riding.
You will get more unsprung mass,

c = 2pir
so d_2/d_1 where d is the outer tire height

I posted that back in post 2, Robin.

hard to give a precise answer as the tire profile can change a lot depending on what you put on the wheel.

[quote=“urodacus”]I posted that back in post 2, Robin.

hard to give a precise answer as the tire profile can change a lot depending on what you put on the wheel.[/quote]Same tire profile, how many less kilometer are we looking at? Let’s say the speedometer reads 80, what is your actual speed if you’re on 12" wheels instead of 10"?

Thanks, mabagal, but that’s not helpful to me. I can’t do this math.

RobinTaiwan, the only way to do the calculation is to compare the “rollouts”. The only way to get the rollout is to know the outer diameter of the tire, not the rim. You can estimate this by using the specs on the sidewall.

The width is usually given in millimeters and the rim diameter in inches and the section height as a proportion of section width. So for say a 180/60R12:

diameter_tire = 2*(180mm * 0.60 / (25.4inches/mm)) + 12 = 20.5"

OK, then, can you calculate it without tires on? Why complicate this so much? How much slower is the bike going compared to the reading on the speedometer if you add two inches to the wheel diameter. That’s my question. Using a tire with the same profile, 2" more in diameter is what you need to calculate.

Well, it’s not quite the same even if you have a tire with the same profile because a tire for a bigger wheel needs to be less wide for the same contact area, so it will compress slightly more each revolution when you are riding.

nonetheless, let’s calculate exactly for you. i forgot to include the tire in the equation last time! the effect is not as bad as i first thought.

circumference = Pi times diameter. We are looking at a ratio of two circumferences, so can ignore Pi and just see the ratio between the two diameters.

C1 = 10 inch plus two times 2 inch (for the top and bottom of a two inch high tire) = 14

C2 = 12 inch plus two times 2 inch (for the top and bottom of a two inch high tire) = 16

C3= 13 inch plus two times 2 inch (for the top and bottom of a two inch high tire) = 17

So for a 10 inch to 12 inch conversion, the speedo shows a speed that is 14/16 times the real speed, ie 87.5 of the real speed. So, when you’re doing 100 km/h, the speedo shows 87.5 km/h

for a 10 inch to 13 inch conversion, the speedo shows a speed that is 14/17 times the real speed, ie 82.4 of the real speed. So, when you’re doing 100 km/h, the speedo shows 82.4 km/h

That’s the right calculation, d_2/d_1 as I had written. The only issue is you really need to use the section height and width to get the actual tire height (short of measuring it) because it won’t just be 2" constant. Bigger wheels tend to be wider, use wider tires and thus the section height & width is the only way to know the nominal outer tire diameter.

The other issue is that nominal tire height is just nominal, varies widely by manufacturer, and also varies with tread wear, and as you pointed out, varies with speed even.

If RobinTaiwan wants an accurate figure the best thing to do is to mount a phone or other GPS device to his handlebars and do a direct comparison.

mabagal, for scooters, the larger diameter wheels have narrower section by far. Just look at the difference between a Thailand scooter and a Taiwan scooter.

Taiwan: 10 inch wheels

Thailand: edit: ah hell, the tthai wheels are much taller. my bad. 14 or 15 inch wheels

but maybe he wants to put unreasonably wide 13 inch wheels on:

from the looks of that, they run even lower profile tires and may even end up at the same diameter as a 10 inch wheel…

[quote=“urodacus”]mabagal, for scooters, the larger diameter wheels have narrower section by far. Just look at the difference between a Thailand scooter and a Taiwan scooter.

but maybe he wants to get sill and put unreasonably wide 13 inch wheels on:[/quote]

Yup, which is the why he needs the section height to do it correctly. In the end, the wheel diameter directly has nothing to do with the speedo divergence, only the outer diameter of the tire.