how can I improve my bike? It has some problems:-?

[vyom]

1)It starts vibrating above the speed of 45 kph
2)It's top speed is limited to 70 kph

 

[phoniamyronia]

take it to the bike shop if it still gives problem then it is time to shop around for a new bike.

 

[PaulH]

see above

 

[RP]

Do your MAINTENANCE. =^ )