Difference is in the radio frequency used.
Either should be fine, but it depends on the regulations in your country and local area.
Tell me your country, nearest city, distance to city centre, and approximate bearing. If it is one that I know, I'll be able to answer. Otherwise the most likely answer is to use 433 MHz.
For Australia, the regulations can be found at the ACMA web site. They specify maximum power, frequency, duration, and a few other things. See The Radiocommunications (Low Interference Potential Devices) Class Licence 2015 (the LIPD Class Licence).
Please, be careful. Read through the regulations, especially those that relate to the frequency you'll be using, and take precautions to avoid interfering with other users of that frequency.
The 433 MHz frequency is used for many many things. You will have outside interference affecting your design, and you have to make sure you don't cause interference. Best way to do that is (a) restrain power, (b) transmit very briefly, (c) have some way to prove the data you received from the handlebars is genuine, (d) repeat the transmissions until you get a valid acknowledgement from the other unit.
You may be required to lower the transmit power in software to stay within regulations. The distance you are transmitting; worst case from the handle bars through a human body to the back of a jersey, doesn't need any significant power.
There are places you cannot use 433 MHz, and the license goes into detail.
The 915 MHz frequency isn't available in Australia under LIPD. You might need a separate license to use that module.