I bought a new hybrid bike (Saracen urban X2) and after two days, the rim of rear wheels got trouble. The shape of the wheel slightly changed from circle to earth like shape. A very little but I can see the bump. I ride with the bike only on road not that bad condition. (Some part of the road is not very smooth but cannot say rough road). Now my question is how this can happen? Is my weight (220 pounds) too heavy for riding this bike? I am not an expert about bicycles. Please help.
220 pounds (100kg) is not that heavy.
At £459 or about US$600 retail, the Saracen is also not an inexpensive bike. It should be more than able to handle your weight unless you're doing very aggressive biking (such as hopping on and off curbs or doing wild jumps without the proper technique). Riding on rough roads is well within the design parameters of this "hybrid" bike.
If your wheels are deforming**, it is likely either a manufacturing defect in the rim or your spokes were not properly adjusted/checked by the dealer. As @Orb notes, you should have also gotten a request from the dealer to come in after the first week to tighten things up as part of the new bike service. I would immediately go back and demand that it be fixed or replaced. I would myself insist on new wheels and insist that the spoke tension and hubs be properly checked before they are reinstalled.
** Note that I'm assuming your wheel (the metal bits) are deforming. Your description is vague. If your tire (the rubber bits) is bulging, then that could be caused by a local weakness in the tire wall. In either case, take it back to the shop to get it replaced.
The UK has good retail trade laws so you should be well within your rights to demand resolution.
ps. I do hope you bought it from a local bike shop rather than online. It's much harder to yell at people online, I've found.
Its not unusual for wheels to go out of true within the first few miles or so of riding a new bike.. Especially if they're not built up strongly by a trained wheel builder... Most cheap to mid range bikes have wheels that are assembled by machine these days and the machines build them quite loose in a lot of cases.. Then when you put weight and lateral loads on the wheels during riding, they flex and end up out of true.
The bike should be checked after a while by the place you bought It from, a sort of first service (normally free) And as well as checking the bike over.. They should also re-true the wheels for you and tension all the spokes again properly. This takes out the initial slack & flex in the wheels meaning that the wheel will stay straighter for far longer in future.