Are 20x4.0" inner tubes OK for 20x4.25" tyres?

I need to replace the rear inner tube on my bike which has Innova 5189–10 tyres.

You'll probably be fine., its not a great deal of difference and if thats all you can find it gets you going.

 

Normally though, the more an innertube stretches, the quicker air can bleed through it. For example if its stretched a great deal the pores in the rubber are greatly expanded, and when the inner tube is for example on the other foot, a 4" with a 4.25 theres less stretching so the pores are smaller.

 

So for example in my 2.25 tyres, ill always use a 2.5 inner, and as a result i dont have to top it up so much.

Of course there are better quality tubes that lose air less than cheaper ones.

0.25 in 4 is a tiny mismatch. Smaller than the range of widths seen printed on non-fat bike tubes, so highly unlikely to be an issue.

Will the slimmer inner tube still remain centred on the wheel especially going over pothole or rough ground?

Will the slimmer inner tube still remain centred on the wheel especially going over pothole or rough ground?

 

Yes, because it will have expanded sufficiently to maintain contact over the whole inner tyre area. It's basically a balloon filling a space only slightly larger than itself.

 

I've routinely used slightly smaller inner tubes in preference to ones slightly too large, without any problems.

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