40 mph but need re gearing

[Philandra Chambliss]

what's up so I broke 40 mph, so my thing is I need to regear cuz it's a little bit to high RPM for the engine anybody got any tooth recommendations running a stock 44 tooth

 

[Will'smotobikes19]

Try a 40 tooth. What mods are done to the engine? That's pretty fast most bikes only go in the high 20s.

 

[FurryOnTheInside]

what's up so I broke 40 mph, so my thing is I need to regear cuz it's a little bit to high RPM for the engine anybody got any tooth recommendations running a stock 44 tooth

Its best to use arithmetic. Do you have a tachometer? What was the RPM at 40mph?
What would you like your RPM to be at top speed?
The smaller your rear sprocket the slower your acceleration and hill climbing.

 

[CrazyDan]

My recommendation is to make these 2 links your friend: https://affordablegokarts.com/pages/gear-ratio-calculator
https://affordablegokarts.com/pages/speed-calculator-english

 

[Timbone]

Its best to use arithmetic. Do you have a tachometer? What was the RPM at 40mph?
What would you like your RPM to be at top speed?
The smaller your rear sprocket the slower your acceleration and hill climbing.

Math can’t tell us what mods he implemented to hit over 9K RPM.

 

[FurryOnTheInside]

Math can’t tell us what mods he implemented to hit over 9K RPM.

No, I agree with that, I just meant like if it was doing 9000rpm at 40mph and he divided the 44 teeth by 9 (about 5t) then multiply that by 8, he'll know that the 40t would reduce his rpm at 40mph to more like 8000rpm, or multiply by 7 (36t) to bring the rpm down to close to 7000 which is probably better for longevity of the bearings.
Although with a 36t it's a bit doubtful whether the engine will make enough power to still hit 40mph. That sort of size sprocket is probably better for mpg than mph.

 

[Philandra Chambliss]

Its best to use arithmetic. Do you have a tachometer? What was the RPM at 40mph?
What would you like your RPM to be at top speed?
The smaller your rear sprocket the slower your acceleration and hill climbing.

Speedometer that uses rpm. I'm not worried about hill climb speed I do like 40-50kmh on hills and about 60-70 kmh on flats.

As far for acceleration that's what my feet are for just don't want her screaming at 60-70 kmh sounds like I'm about to throw a rod or 4t at red line.

So if I lower that gear it will bring the rpm down. It starts 4ting or feeling unsafe after 50kmh my engine is counter balanced by an mz piston which is I believe an A type more centered hole.

I plan on re ringing every season on weekends as it takes no time to do break in. That will keep the Jug alive.

 

[Street Ryderz]

Some of what your saying here makes no sence,you say that your doing 40 mph but then you state that your doing 60-70 kph on flats? 70kph is 43mph and on your setup requires 10,200 rpm then you say it 4strokes above 50 kph wich is only 7,000 rpm so explain to us how you manage to make 3,200 rpm after it starts 4 stroking and shaking?I think you better double check your claims,it's not that it cant be done but what you describe and claim dont add up.

 

[FurryOnTheInside]

If you're looking for smoothness at high rpm you should balance the crank for high rpm, that means reducing a lot more of the reciprocating mass than just a light piston. How light is the MZ piston anyway? Pistons are only aluminium so it takes a lot of material removed to make the reduction in mass. You should be able to lighten the upper part of the connecting rod without having to remove it from the engine if you're careful. You can get a good reduction in the reciprocating mass by lightening the upper part of the connecting rod because it's steel. Then you can drill extra balance holes in the crank cheeks but obviously be careful and do all this correctly.
The other thing that makes the engine feel smoother at high rpm if you have a stock CDI is an offset magnet key (retarded) but this has a detrimental effect on the power at very low rpm. If you use a good aftermarket CDI you might be able to find a good balance of both. I wonder if the four stroking you're talking about is actually backfiring from overly advanced spark timing at high rpm...

 

[FurryOnTheInside]

Some of what your saying here makes no sence,you say that your doing 40 mph but then you state that your doing 60-70 kph on flats? 70kph is 43mph and on your setup requires 10,200 rpm then you say it 4strokes above 50 kph wich is only 7,000 rpm so explain to us how you manage to make 3,200 rpm after it starts 4 stroking and shaking?I think you better double check your claims,it's not that it cant be done but what you describe and claim dont add up.

I agree there's something not sounding right here. Perhaps the speedo is not correctly calibrated or not functioning correctly.

P.C. You will need to do a rollout measurement to find the actual distance the bike moves forward with each wheel rotation when the tyre is compressed by the weight of the bike and rider.
A tachometer is a great way to see what the engine is doing because there's no calibration necessary and you will see when the RPM climbs quickly and when it starts to climb slower.