Do inner-tube widths need to match the tyre spec?

[halfer]

I've recently purchased a KTM Macina Action 29 (and, as is my custom, I'll write a review article in due course, for interest and edification - broadly it gets a thumbs up!). I took it for some light off-road recently and acquired slow punctures in both wheels, probably caused by thorns; I suspect one of my routes was a bit optimistic as to what the wheels could take!

So I popped to a bike shop to grab a self-sealing Bontrager inner tube, and have fitted it despite finding that the spec isn't an exact match. The wheels are marked as 29x2.25, and the inner tube is 29x1.75-2.125. Placed flat atop each other, the old and new tubes seemed to be an exact width match, but I guess 0.1" was always going to be a small difference. It seems to be holding circa 30psi fine, but it's not had any use yet.

Am I taking any safety risks by fitting this? I'm presently minded to make this bike my off-road bike, so it won't see as much commuting use as my other e-bike (where safety is more critical, in my view).

 

[Alan Quay]

I think the width quoted on the tube is about how thick the rubber is. If you have a thin tyre, you only need thin rubber, but with a wide tyre the tube will be stretched pretty thin by the time it's inflated to fill the gap.

I always go for the ones that go up to 2.5 , as I run 2.5 tyres.

That said, I'd be inclined to risk it and carry a spare tube.

 

[Deleted member 4366]

I wouldn't worry about it. I often use tubes that are wildly out on size

 

[KTM Bike Industries UK]

yeah... don't worry about it. Even the tyre brands can't agree on where they are measuring too and from to get the width of a tyre anyway.

A Schwable tyre for instance in a 2.25 is wider than a 2.5 in many other brands.

So just get something close, if you're worried about flatting go bigger, as the tube won't have to stretch so much to fit... if you're worried about weight get thinner and the tube will be a lighter.

 

[halfer]

Alright, thanks all - good to know!

 

[pn_day]

Just a word of caution - if you go for a tube that is much narrower than the tyre then the tube will be more likely to burst - it will be stretched beyond expected limits.
Having said that you can often get away with going one above or below with the size ranges without problems.

If punctures are a problem get some decent tyres - I've not had punctures in the last 2.5 years. Was using marathons before converting to ebike, now using marathon plus tours as the extra weight is not a problem for the ebike.

 

[halfer]

If punctures are a problem get some decent tyres - I've not had punctures in the last 2.5 years. Was using marathons before converting to ebike, now using marathon plus tours as the extra weight is not a problem for the ebike.

Yes, I have a Marathon plus on the back wheel of my Ave, replacing a Racing Ralph off-road tyre (pretty flimsy in my view). Marathons seem to be pretty much bullet-proof.

My new KTM Macina has Rocket Ron off-road tyres, and these seem to be the same - sacrificing puncture resistance in order to save weight. I'm opting for slimed tubes to improve their reliability to start with, and will swap the tyres if that doesn't fix it.

 

[kinega]

Had the same issue with punctures on my KTM, have got some Rocket Rob tyres & been OK so far.

 

[RobF]

The 2.125 on the tube does refer to the maximum recommended width of a tyre to fit.

As has been said, there is some wiggle room which you are well within.

You mention 'circa 30psi'.

Seems a bit low to me, even for a wide tyre.

The low pressure could account for your punctures.

I would suggest trying 50-60psi, maybe nearer 60 in the back and nearer 50 in the front.

 

[Alan Quay]

.....A Schwable tyre for instance in a 2.25 is wider than a 2.5 in many other brands......

I can vouch for that. My Schwalbe Fat Frank's (marked as 2.3) are a smidge wider than my DMR motors (marked as 2.5)

 

[oldtom]

You mention 'circa 30psi'.

Rob, I thought the OP was just testing his tube to see if it maintained pressure. I can't imagine anyone taking to the road with such low pressure in the tyres.

By and large, I find the maximum recommended pressure is usually about right and a few psi less isn't noticeable on an ebike. At lower pressures, I find the rolling resistance becomes quite pronounced and the risk of pinch punctures is increased. I ride my suspended bikes with the front fork screwed down pretty tight, almost like a rigid fork but with just enough give to take the edge off knobbly surfaces. On my fixed fork bikes, I run about 4-5 psi under the max recommended by the tyre maker, again just to take the harsh edge off the ride but allowing good roll.

I presume the OP doesn't ride at 30 psi but if he does, he's taking risks, not just of punctures!

Tom

 

[halfer]

Yes, 30 psi is mainly for testing. It is also a result of the gauge on my track pump not being as reliable on Presta valves as it is for Schrader - I connect it, and it seems to register a value before gradually reducing.

I had a tube blow up the other day whilst inflating it (it wasn't sitting in the tyre correctly) so I have another reason to be cautious.

But, yes, I'll only ride when they are rock solid. Not sure what pressure they're at, but I don't think it was the reason for the punctures. I think the brambles were the reason for that .

(If I can't get my pump to behave itself, I'll get a Schrader to Presta converter for my pressure gauge. I should think 50psi should do it, as Tom says - 5 psi under the stated maximum).

 

[oldtom]

If I can't get my pump to behave itself, I'll get a Schrader to Presta converter for my pressure gauge.

I know there was a discussion recently about track pumps and I have two. One is a cheapo thing I keep in my shed in Spain which does the job ok on Schraders. The other one is the Joe Blow from Topeak which works well on all valve types and is fairly accurate according to my separate gauge.

I can't remember how much I paid for the Topeak one, not long after they hit the market but experience tells me it was worth it. Perhaps there are others out there now for less money that are as good or better but if this one broke now, I'd be inclined to replace it with the same model.

Woods valves seem somewhat unfashionable these days in the UK although they are fairly common on mainland europe. I don't have a problem with them and bought some new inners so equipped just recently. Some change to Schraders to avoid the Woods valves as they normally fit in the same diameter rim drilling although I don't know why as the Woods type are readily available, certainly on the inter web thingy.

Running my Schwalbe MP+ rubber at 85 psi on my PC with no problems and no discomfort. 65 psi on all my other bikes.

Tom