Inner tubes might seem straightforward - just a rubber doughnut that holds air - but fitting the wrong tube or making a simple mistake during installation causes more punctures and slow leaks than many people realise. For workshops, dealers, and anyone fitting tyres on grounds maintenance or agricultural equipment, understanding inner tubes properly saves time, money, and frustration.
This guide covers how to read tube sizes, the different valve types and when to use each, and the common fitting mistakes that lead to problems down the line.
How Inner Tube Sizing Works
Inner tube sizes correspond to the tyres they fit inside. The size is printed on the tube packaging and usually on the tube itself, and it follows the same format as the tyre size.
For example, a tube marked 16x6.50-8 fits a tyre of the same size:
- 16 - overall tyre diameter in inches
- 6.50 - tyre width in inches
- 8 - rim diameter in inches
Some tubes are marked with a size range rather than a single size - for example, 16x6.50/7.50-8 - indicating the tube can stretch to fit tyres within that width range. This flexibility is useful but has limits; always stay within the stated range.
Metric tube sizes work the same way. A tube marked 185/60R12 fits a tyre of 185mm width, 60% aspect ratio, on a 12-inch rim. The key dimension for tube fitment is the rim diameter - this must match exactly.
Understanding Valve Types
The valve is the tube's weak point if not chosen correctly. Different rim designs and applications require different valve types, and fitting the wrong valve causes problems ranging from difficult inflation to air leaks and valve damage.
Straight Valves
Straight valves point directly outward from the tube. They are the most common type and suit most applications where there is adequate clearance around the valve hole.
- TR13: The standard straight rubber valve used on most small to medium tubes. Snap-in fitment to the rim hole. Common on wheelbarrows, mowers, trailers, and light equipment.
- TR15: Similar to TR13 but with a longer stem. Used where extra length is needed to clear deeper rim wells or hub caps.
- TR4 / Metal valves: Heavy-duty straight valves with a metal stem and rubber base. Used on larger agricultural and industrial tubes where durability is critical.
Bent Valves
Bent valves angle away from the tube, making inflation easier on rims where a straight valve would be hard to access.
- TR87: A 90-degree bent rubber valve. Common on small-diameter rims where a straight valve would point into the hub or be blocked by other components.
- TR218A: A heavy-duty metal bent valve used on agricultural and earthmover tubes. The metal construction handles higher pressures and rougher treatment.
When replacing a tube, always match the valve type to what was originally fitted - the rim was designed for that configuration. If you are unsure, measure the valve hole diameter and consider clearances around it.
Choosing the Right Tube for the Application
Beyond size and valve type, consider the application when selecting tubes:
- Standard tubes: Suitable for most applications. Made from butyl rubber, which holds air well and resists ageing.
- Heavy-duty tubes: Thicker rubber for applications with higher puncture risk or heavier loads. Worth the small extra cost for equipment that works in demanding conditions.
The Redwing inner tube range covers the common sizes for grounds maintenance, agricultural, and trailer applications, with both standard and heavy-duty options available.
Common Fitting Mistakes
Most tube failures are caused by fitting errors, not manufacturing defects. Avoid these common mistakes:
Pinching the Tube
The most common cause of instant punctures. When levering the tyre bead back onto the rim, the tube can get caught between the bead and rim edge. The pinch creates a distinctive snake-bite puncture - two small holes close together. To avoid this, partially inflate the tube before fitting so it holds its shape, and push the valve inward to ensure the tube is seated in the rim well before levering the final section of bead over.
Wrong Size Tube
An undersized tube stretches too thin, making it more puncture-prone and more likely to fail at the valve stem. An oversized tube bunches and folds inside the tyre, creating friction points that wear through over time. Always match the tube to the tyre size or stay within the stated range.
Wrong Valve Type
Fitting a straight valve where a bent valve is needed makes inflation awkward and can stress the valve stem if the pump head is forced on at an angle. Worse, the wrong valve length can leave the stem recessed in the rim or protruding so far it catches on other components.
Debris Inside the Tyre
Before fitting a new tube, always inspect the inside of the tyre and remove any debris, thorns, or wire that caused the previous puncture. Run your fingers carefully around the inside of the tread area. A thorn left in place will puncture the new tube within minutes.
Overinflation
Overinflating stretches the tube excessively and increases the risk of a blowout, particularly in hot weather when air expands. Always inflate to the tyre manufacturer's recommended pressure, not beyond.
Storing Inner Tubes
Tubes degrade over time, especially if stored poorly. Best practices:
- Keep tubes in their packaging: The packaging protects against light, dust, and accidental damage.
- Store away from sunlight and heat: UV and heat accelerate rubber degradation.
- Avoid contact with oils and solvents: These attack rubber and weaken the tube.
- Do not hang tubes on hooks for long periods: This can create stress points. Lay flat or store in boxes.
Tubes stored properly will last years. Tubes left on a sunny workshop shelf may degrade within months.
When to Replace Rather Than Repair
Tubes can be patched, but not indefinitely. Replace a tube when:
- Multiple patches are present: More than two or three patches weaken the tube structure.
- The valve is damaged: Cracks at the valve base or a bent stem cannot be reliably repaired.
- The rubber has hardened or cracked: Age-related degradation means patches will not adhere properly.
- The puncture is near the valve: Repairs close to the valve rarely hold due to the stress in that area.
Tubes are inexpensive compared to downtime. When in doubt, fit a new tube.
Find the Right Inner Tubes
Redstone stocks a comprehensive range of inner tubes for grounds maintenance, agricultural, and trailer applications, including all common valve types. Need help matching a tube to your tyre? Call us on 01243 558959 with the tyre size and we will find the right fit. Next-day delivery is available on stocked items.