Tire sizing ? can i go bigger

so front rubber is 120 / 70 - 12
rear rubber is 130 / 70 - 12

to what i know the 70 size is the side wall hight , and the 120-130 are the width of tyre. the 12 denotes a 12 inch wheel ?
my thinking is if i put on a 120 / 80 - 12 and a 130 / 80 - 12 , i would gain a slightly higher top speed due to the larger tire wall hight fitted.

to accompany the higher sidewall hight i intended to remove the rear hugger, and space out the mudguard at the front of the motor to allow extra space for the higher wall size ( the guard section that stops crud getting thrown up over the front of motor and carb ).

the slightly bigger wall hight should give me a longer wheel roll out, something like 1 full rotation adding an extra three inches to roll out and a higher top speed ? or does this not work on scooters so much. need to get some new rubber soon as i have noticed side wall cracking close to the rim edge ( tubeless tire) and really dont wanna risk a blowout or failure. the tires still have a lotta meat left on the tread but its that cracking thats a worry ( horizontal cracking around rim edge not vertical cracks )

asked in the shop a while back they said tires were fine but had cracking, i expected them to say replace but its niggling me cracks cant be a good thing or good sign ?

 

well in theory a taller tire wall adds more roll out to the wheel ie

a 12 inch tire with a 60mm side wall has lets say a total roll out of 2.4ft so for a full rotation the tire travels 2.4ft forwards.
now if we add more hight to the side wall lets say 80mm the roll out would extend because the wheel is bigger so the rollout would become 3.2ft for a full rotation so your gaining over half a foot extra travel.

im not sure on a stock scooter yes i would say it would be slower becasue the engine has to work harder to gain enough speed to exploit the longer rollout and it would take longer to get to top speed, but something like a deresticted scooter maybe that extra power would be useful propelling the scooter quicker to its top speed.

hence reason im asking if a taller side wall would add speed to a scooter. if the tires roll out is longer its like adding a different ratio gearing . adding a larger rim would be to much ie a 13 inch rim from a 12 inch, but addding a taller side wall would give a slightly bigger radius ? bit like shoving a 13 inch rim on ?

 

Nominal gains for what could be a pig of a bike to ride and I'm trying to get my head around if the speedo would still give an accurate reading too ??

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Hmmmm.....
I will think about this and get back to you.

 

decided to just multivar 2000 it and leave tires as stock, just get some better rubber , got a maxis on rear and a dubro ( or something like that on front, and differing tread on both)

i just tink at speed the 70 wall will still epand a fair bit and slightly rub, a 80 wall will just expand and 100% cause rubbing, it was just an idea to gain back the 10mph i lost when i upgraded the carb and pipe.

in the pipe work im looking at contimove 360 or some hedanu k's all weather jobs .

 

Changing tyre height will only throw the speedo reading out further than it already is...........on a scooter that is, and we all know that scooter speedos aren't the most accurate things in the world.

 

How comes you lost 10mph when you "upgraded" the carb and pipe ???


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no clue went from a 12mm carb to a 17.5mm ( 81 jet/ 60 choke jet) and from a leo vince tt to a technigas trek ( leo tt gave 5.75hp, the tek delivers 6.05hp ) instead of gaining a couple mph i dropped from a flat out tucked 50mph max rpm, to 40 mph max rpm tucked.

hence the wanting a differing tire size to maybe add a little more on ratio. problem is there are no 13" rims that will fit the sym jet models, they did a 10" then went to 12" rims ( 12's installed on scooter now).

i would if i can get a better ratio add a digital hall sensor pickup and run a digital speedo and hook up the tachometer to the poss side of the coil to get the best rpm reading, as of now rpm is just guessing ( but by sound of motor its topping at around 10,500rpm @ 40mph , and used to top out at 10,500rpm @ 50mph ). its so hard on rpm at 40mph i tend to sit at 35mph on clock and just live with it, but its not fun when you know you have that power and its somewhat useless.

 

60 choke jet...............that dont sound right......................what carb did you put on it?
And what rollers have you got in, what variator?
And clutch springs?

 

Dellorto L-DEL1438 ( exact copy )

81 main jet - 35 idle jet - A27 needle in a 17.5mm carb ( came with a 90 jet but was way to rich )

brand new stock rear pulley , stock new clutch springs.
stock variator running 3x 6g - 3x8g , driven with a crappy naraku belt . (same exact setup with a 12mm carb and a leo vince tt gave 50mph tucked, swapped to a 17.5mm carb technigas trek and maxes out 42 mph tucked, will pull 35 mph all day sweet as a nut right on the powerband )

looking at multivar 2000 or polini HSV with red/white contra spring and blue clutch springs as a possible fix.

 

Maybe some of us like the challenge of tuning a 50cc
Maybe some of us like tinkering with our scooters.
Would you say the same to any car tuner, wouldn't they just be better off buying a Bugatti Veyron rather than messing around dropping a cosworth engine into that old mk1 / 2 Escort



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