Since you did not mention which Meniscus you tore, or what kind of tear you've sustained- I'm going to assume that you tore your Medial meniscus(inner aspect of the tibial plateau. I cannot guess the "type" of tear, however.
Lets start with a very basic anatomy of the cartilage you have injured. In my own words....
The Anterior Cruciate Ligament, located in the center of the knee joint, connects the femur to the tibia and is attached to the femural condyle and tibial plateau.
The ACL is one of the 4 ligaments that provides stabilization to the knee and prevents Anterior movement of the Tibia as well as preventing inproper roatation.
A completely torn ACL is usually repaired using an AutoGraph(a graph taken from elsewhere on the patient, ie a bone-tendon-bone graft taken from the patella tendon) or utilizing an Allograph, which is harvested from a human cadaver(usually utilizing the Achillies heal tendon.
There are other methods, however, the 2 mentioned are the most common.
Recovering from an ACL reconstruction surgery. Listen to your Doctors orders. Try not to extend the surgery leg while under resistance(like doing a leg extension in the gym) for 9-15months. Refrain from "cutting" or "twisting" motions(like soccer or football).
Do your best to keep your leg stable and carry out the physical therapists excersize instructions for 9-15months before deviating from his routine.
The Meniscus. The Meniscus is a C shaped "pad" of tissue. There are 2, the Lateral Meniscus(outer aspect of the leg) and the Medial Meniscus(inner aspect of the leg). Both serve as a "shock absorber" for the knee joint. More importantly, the meniscal tissue keeps the knee aligned and prevents "twisting" of the knee. The femural condyle(the end of the femur), is, more lack of a better explanation, seated in the meniscus. Thus, the meniscus prevent oscilation of the tibia(bottom leg bone twisting different direction than the top leg bone.
Torn Meniscus. The meniscus can suffer various "types" of tears. Some can be sutured, others require the Surgeon to cut the portion of the torn cartilage out. Why ? If the maniscus is torn, it can fold up, or flap- thus, interupting the mechanics of the knee which may cause the knee to buckle and injured vital ligaments.
If the meniscus is sutured, a diet rich in essential vitamins, proteins and time will allow the meniscus(which lacks a crucial blood supply) to heal properly.
If the meniscal tear needs be removed(Menisectomy) be it partial, sub-total or total, the patient should excersize extreme caution for the rest of their live. The more of the Meniscal cartilage that is removed, the more serious the long term side effects.
Lacking a substantial portion of the meniscus will allow the femural condyle to directly contact the tibial platuea. This is referred to as "bone on bone" contact. Also, the prevention of "twisting" will now be limited and a future injury is likely, should the patient not protect this knee.
Over time, the articular cartilage of the bone ends will begin to break down causing arthritis.
Summary. The injury you have sustained, I have sustained twice. I have had 2 ACL reconstruction surgeries, both with meniscal tears. A derotational brace is VERY important. Don Joy and CTI are the most commonly perscribed devices, however, you may not be perscribed a brace and they are expensive. Asterisk makes a pretty nice brace and I own 2 of them, along with my Don Joy.
Take it easy for a year. Keep your weight in check, eat healthy and take pleanty of vitamins. Glucosamine, Chondroitin & Msm will speed the recovery of the damaged cartilage within your knee. Go buy extra strenght G,C,M and take it daily.
Make sure that you stretch your leg after each workout, ALL MUSCLES. Get an understanding of the Anatomy and function(s) of the knee, this will help you cater to it.
Best of luck. Stay off that bike until your Doctor feels you are ready, trust me, not only am I in the Medical Profession, but I have seen many injuries and sustained many of my own....
Later.
Semper Fi