A bit of a stretch

There's a problem with 17-inch rims waiting to snag some off-roaders. This size is increasingly popular as an OEM rim, to the extent that it's almost the new 16! Some versions of the Hilux are the latest converts. Supporting this trend, good mud tyres are widely available in 17-inch size, although the selection of 15- and 16-inchers is still larger. But there's a problem for those, like myself, who would like to run tubes in their 17-inch tyres – there's no 17-inch tube on the market! Some tyre shops fit 16- or 16.5-inch tubes and report no problems. The smaller tubes have to be stretched, of course, but not by much. This should not be a problem for a good quality tube, the proponents say. However, Bill Prebble, who heads development and field engineering at Goodyear & Dunlop Tyres in Wellington is aghast. "I have a strong dislike of anything that is not engineered for the job, especially in a safety-critical component such as tyres," he told 4wdNewz. "Tubes are great for off-road, but if something happens at highway speed then the circumstances may cause grief. My main concern is stretching tubes. The potential of butyl tearing increases with stretch, which is why deflation of tubes is so rapid – a small cut or hole rapidly turns into a tear when the tube is stretched. I would not recommend either 16-inch or 16.5-inch tubes in 17-inch tyres." 

I have great sympathy for Bill Prebble's point of view and because I run one set of tyres for everything, will not again be tempted by running tubes until and if a 17-inch tube becomes available. However, for off roading where things happen at slow speeds, I can see that stretching a smaller tube might be okay. The proper way around it is to swap the 17s for 16s, but that's expensive.