capturing fps drops with lower resolution opencv

Question

I have a USB camera that is able to record 60 fps. I am using openCV with simple python code on Windows to capture some videos however it is not going all smoothly!

My main problem is that, if I set the [width, height] properties to the maximum the camera accepts it is able to record 60 fps just fine otherwise (i.e. any lower resolution) the recording/streaming will drop to 30 fps max (the recording will be so funny that is either sped up or slowed down to match the specified recording fps; i.e. if the resolution specified 320X240 and recording fps set to 60 and for 10 seconds the resultant video will be squashed to 5 seconds so basically sped up 2x!!)

I don't understand why exactly that happens? any ideas?

here is a snippet of the code:

import cv2
import os
import time

def readVideo(Did):
    cap = cv2.VideoCapture(Did)
    # cap.set(cv2.CAP_PROP_FPS, 60) # no matter if you specify or not it selects what suits!!
    cap.set(cv2.CAP_PROP_FRAME_WIDTH, 320) # 640 is maximum
    cap.set(cv2.CAP_PROP_FRAME_HEIGHT, 240) # 480 is maximum
    ret,frame = cap.read()

    fourcc = cv2.VideoWriter_fourcc(*'XVID')
    out = cv2.VideoWriter('./output.avi', fourcc, 60.0, (320,240)) # (width,height) must match what is stated above in CAP!
    while ret:
        ret,frame = cap.read()
        elapsed = time.time() - start
        count = count + 1 # frame numbers
        cv2.putText(frame,str(cfpsBacked), (25,15),font,fontScale,fontColor,lineType)
        out.write(frame)
        cv2.imshow('camera',frame)
        if elapsed - tick >= 1:
            print("Actual count:{}",count)
            tick += 1
            cfpsBacked = count
            count = 0
        if tick - 10 == 0: # just records 10 seconds
            break

        if cv2.waitKey(10) & 0xFF == ord('q'):
            break
    out.release()
    cap.release()
    cv2.destroyAllWindows()  # destroy all the opened windows