Matching Tube Size to the Tyre Size
Stopaflat tubes are "Size Specific" to a tyre and extra care should always be taken when matching the Stopaflat tube to a tyre. External nominal tyre width size markings are clearly embossed on the outside wall of a tyre, however there can be variations in the internal tyre actual width size, this is due to various different design/internal structure, and tyre wall thickness between tyre types and tyres manufacturers. Occasionally it may be necessary to fit a larger or smaller Stopaflat tube than indicated by the tyre size to correct this. A simple test is to insert the Stopaflat tube into the tyre, pinch the beads together and measure from bead to bead. This should be around 20mm of the internal width of the rim.
Very important note applies to all sizes!
The Stopaflat tubes must be placed in the tyre tightly (there should be no internal gaps and no movement between the tyre and the Stopaflat tube at all). Tight/ interference fit is a necessary, essential condition for the Stopaflat tube product to function correctly.
If tight fit between the tyre and the Stopaflat tube is not achieved, DO NOT attempt to test ride because it will not work...! the internal friction generated by the "loose fit" will result in very high rolling resistance and will permanently damage the Stopaflat tube!
If a space/gap is formed between the tyre and the Stopaflat tube (even with matching sizes tyre/tube). You can either exchange the Stopaflat tube with a bigger size, or if the gap is small, you may use the old (pneumatic/inflatable) inner tube as a "SPACER", to "fill the gap" and achieve the required tight/ interference fit, See filling gap method as below:
Cut-out the valve stem on the old inner tube, and pack that inner tube into the inside of the tire... BEFORE inserting the puncture-proof tube unit. Leaving the old, airless inner tube inside (between the tyre and the Stopaflat) to fill-up the space and achieve a tight fit.
The tyre is too tight and we cannot get the tyre fitted over the Stopaflat tube.
Solution 1: Over-inflate the tyre with the standard pneumatic tube for a day or two before trying to install the Stopaflat. That will stretch the tyre a little and make installation a bit easier.
Solution 2: Soften the Stopaflat inner tube in hot boiled water (NOT BOILING WATER) for not more than 1 minute. Install it right away after taking it out of the water.
The tyre is too loose and there is a gap in between the Stopaflat tube and the tyre.
Solution: Cut-out the valve stem on the old inner tube, and pack that inner tube into the inside of the tire... BEFORE inserting the puncture-proof tube unit. Leaving the old, airless inner tube inside therefore filled-up some of the extra space remaining inside