Determining your car’s maximum towing capacity before you begin towing a bike rack is vital. Exceeding the manufacturer’s indicated capacity may lead to an unsafe driving situation, and may damage different parts of your vehicle like the engine, brakes, transmission, wheel bearings, and rear axle. Also, it will void the manufacturer’s warranty. 

For first time buyers of a tow vehicle, keep in mind that AWD and 4WD vehicles generally have a lower towing capacity as compared to 2WD vehicles. Crew cab and pickup trucks with extra-cab also have a lower towing capacity as compared to standard cab designs. It is a must that you research towing capacities thoroughly before purchasing. It is best to buy a tow vehicle with a higher towing capability than what you need. 

Read your vehicle’s user’s manual
The best way to determine your vehicle’s towing capacity is to check your vehicle’s owner manual. Check your certification plate on the driver’s door sill and then compare the data there on what is written in the manual. The user’s manual has detailed instructions and limitations, together with the tips for safe towing. 

If you do not have a copy of the manual, you can check online. Most vehicle manufacturers allow you to download a copy for free from the Internet.

Look for your vehicle’s compliance certification label
After reading your vehicle’s manual, double-check the compliance certification label. If you are not sure where to look for it, it is a sticker found on the driver’s door sill. This label will have various fields, with acronyms like GAW, GCWR, GVR, and others. Let’s define the following acronyms:

Gross Axle Weight (GAW)
The Gross Axle Weight (GAW) are the weights placed on your vehicle’s rear and front wheels. These numbers are different to account for engine weight and other factors. 

Gross Vehicle Weight Rating (GVWR)
The Gross Vehicle Weight Rating is the actual safe weight of your car. If in case you exceeded the number, the car’s brakes, transmission, engine, and others will be forced to work beyond its capabilities.  

Gross Combination Weight Rating (GCWR)
The Gross Combination Weight Rating (GCWR) is the safe weight of your combined trailer and vehicle. The weight includes all luggage, people, and other materials. If in case the combined towing setup exceeds the specified weight, the transmission, brakes, engine, and others will be forced to work beyond their limits. 

Gross Vehicle Weight (GVW)
The Gross Vehicle Weight is the car's standard curb weight, plus an added weight for the standard weight of the gas, passengers, and luggage as given by the manufacturer. The weight of your vehicle will depend on the weight of the luggage, passengers, and volume of gasoline. So, it means that GVW is only an approximation.

Gross Combination Weight (GCW)
The Gross Combination Weight is the actual weight of your vehicle, including the total weight of the trailer. It should be not higher than your car’s GCWR.

Gross Axle Weight Rating (GAWR)
The Gross Axle Weight Rating (GAWR) is the safe weight that you can add on your rear or front wheels. Front and rear axles have their specific GAWR. These two numbers take into account trailer tongue weight, engine weight, passengers, and luggage. If in case you exceed this weight rating on the rear or front tires, you can damage your vehicle. 

Defining other terms vital in determining towing capacity 
You should understand the meaning of the following terms in determining the towing capacity:

Tongue Weight
It is the amount of your trailer’s weight that can be transferred to your tow vehicle through the gooseneck and trailer’s tongue. You can use a scale on measuring the tongue weight. 

Payload Capacity
It is the total weight capacity of your trailer. To calculate the maximum payload capacity, subtract the trailer weight from the Gross Vehicle Weight Rating. 

Trailer Weight 
It is the empty weight of your trailer. You can check this by weighing your trailer at a truck stop or on other locations using a certified scale. 

Checking Trailer Weight
You also need to learn your trailer’s weight. Your trailer has a VIN or Vehicle Identification Number plate. The VIN plate has the trailer’s serial number, the unloaded GVW and the GAWR for each axle on the trailer and a maximum GVWR for the trailer. 

In case you cannot find your vehicle's VIN plate or if it is difficult to determine the total weight, you will be adding to the GVW of the trailer. The best way to do is to load your trailer and take it to a certified scale. The scales are available at commercial truck stops, state highway weigh stations, and refuse transfer stations. The advantage of using this method is that you can determine the actual weight of your loaded trailer. 

Checking Tongue Weight
You also need to consider your trailer’s tongue weight. Try carrying 10% of the total trailer weight on the tongue. Receivers and other hitches presume that the tongue weight is about 10%, if you stick to this ratio, you can improve your towing experience

With the use of a specialized scale, you can check your trailer’s tongue weight. If you don’t need to measure your trailer’s tongue weight often, you can call your trailer dealer and ask if they have a tongue scale that you can use. 

You can change your trailer’s tongue weight by changing the way you load the trailer. If you add more weight in front of the axle, you will add more tongue weight. If you add more weight at the back of the shaft, you can generate negative tongue weight. 

Your combined tow rig will droop at the coupler, and you will notice that your tow vehicle needs to pull the load harder. If you do not have sufficient tongue weight, the trailer will shift. If in case your tongue weight is negative, your back tire traction is reduced, which is dangerous. You have to strive for a 10% tongue weight to achieve better results. 

Buying a bike rack 
One of the vital questions in buying a bike rack is what type of rack you should choose. It is best to select a trunk or hitch rack. A certain kind of frame tends to be more economical and have less easy-to-lose parts than a full system that integrates other equipment. Check out green4u for more info on how to select the best bike racks for cars.

It is essential to know how much weight you can add to your carrier. After determining your vehicle’s TWC, you can subtract the weight of the carrier and frame so you will know how much weight you can safely carry. For instance, you need to use a hitch bike rack, and the GTWR of your vehicle is 1500 lbs., then your tongue capacity is 150 lbs. If your bike rack weighs around 40 lbs., you can carry bikes that weigh 110 lbs.