# Any issues running an 18-25mm tube in a 28mm tire?



## lacofdfireman

I bought me a new 2017 Giant TCR Advanced Disc bike that came setup with Giant Tubeless wheels and Giant Tires. Never ridden tubeless on the road so figured I'd give them a shot. They are 25mm tires and typically because of my size of 250+lbs I'd usually run a 28mm tire. Well less than 100 miles on the bike and the rear tire is shot. Cut in sidewall. Not saying this wouldn't have also happened min my Continental Gator skin Hard shells in a 28mm that I normally would use but after this experience I'm going back to the Gator Skins in a 28mm. 

So now the dumb question. I never really thought about it but I got to looking and all my spare tubes are 700c 18-25mm. Is that a big deal running these in a 700c 28mm tire? Or do I need to buy some bigger 700c 28-32mm tubes? What do ya think?

Photo of my flat 











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## Jay Strongbow

Not only is it not a big deal but it's preferable. It makes it slightly easier to mount and not that the amount weight matters but why not use the slightly lighter smaller tube.

I use tubes that are advertised as 19-23 with 33mm tires not problem at all.


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## Kerry Irons

lacofdfireman said:


> So now the dumb question. I never really thought about it but I got to looking and all my spare tubes are 700c 18-25mm. Is that a big deal running these in a 700c 28mm tire? Or do I need to buy some bigger 700c 28-32mm tubes? What do ya think?


Pump up a tube and see how much it expands. The amount it expands in filling the tire is nothing.


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## Lombard

It will work, but the tube will end up thinner. Call it a poor man's lightweight tube.


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## dcgriz

Running undersized tubes will work in a pinch but I dont see why making it a practice since there are better choices, at least if we are to believe the manufacturers who make them.


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## Lombard

dcgriz said:


> Running undersized tubes will work in a *pinch* but I dont see why making it a practice since there are better choices, at least if we are to believe the manufacturers who make them.



Was that pun intended?


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## dcgriz

Lombard said:


> Was that pun intended?


.......you give me too much credit.......:wink5:


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## Jay Strongbow

dcgriz said:


> Running undersized tubes will work in a pinch but I dont see why making it a practice since there are better choices, at least *if we are to believe the manufacturers who make them.*


We don't. But if you do I assume you use between 115 and 145 PSI because it's printed on the tires made by the same company?


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## Lombard

Jay Strongbow said:


> We don't. But if you do I assume you use between 115 and 145 PSI because it's printed on the tires made by the same company?




Most tires have a maximum pressure rating. Most people erroneously think this is the recommended pressure. Some do have a range. Here again, this is a recommended range, not a mandatory range.


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## Jay Strongbow

Lombard said:


> Most tires have a maximum pressure rating. Most people erroneously think this is the recommended pressure. Some do have a range. Here again, this is a recommended range, not a mandatory range.


Call it what you want but what it is is an arbitrary and stupid number for them to print on the side of the tires. Do you really think Vittoria employees ride around with 115 PSI because that's what they recommend as a psi floor? I doubt many of the non-obese ones do.


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## Lombard

Jay Strongbow said:


> Call it what you want but what it is is an arbitrary and stupid number for them to print on the side of the tires. Do you really think Vittoria employees ride around with 115 PSI because that's what they recommend as a psi floor?




Exactly my point. They're most like "lawyer PSI ratings".


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## bobf

Lombard said:


> Exactly my point. They're most like "lawyer PSI ratings".


I guess that explains the bizarre "iTire" pressure app on the Vittoria web site. Among other strange features, it ignores tire width.


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## Jay Strongbow

Lombard said:


> Exactly my point. They're most like "lawyer PSI ratings".


What incentive would a lawyer have to say 145psi especially given the rims would be an unknown to them? Just because someone said something on the internet doesn't make it true.


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## lacofdfireman

Thanks for all the insite. Learned more than what size tube to use today. I always assumed I could use a smaller tube due to expansion but just wasn't sure if it's preferred or not. Being a heavy weight and all. 


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## Roland44

Jay Strongbow said:


> What incentive would a lawyer have to say 145psi especially given the rims would be an unknown to them? Just because someone said something on the internet doesn't make it true.


Exactly, makes no sense to me...


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## dcgriz

Lombard said:


> Exactly my point. They're most like "lawyer PSI ratings".


That's precisely what they are. Commonly half of the tire blow-off pressure.


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## Lombard

Jay Strongbow said:


> What incentive would a lawyer have to say 145psi especially given the rims would be an unknown to them? Just because someone said something on the internet doesn't make it true.




What??? Oh com'on! Everything on the internet is true!  

Seriously, for the purpose of liability, I'm guessing they figure there is less of a chance of an accident *due to tire failure* by overinflating, than by underinflating. I'm just guessing, but I'm not a lawyer, so I really don't know.


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## Kerry Irons

Lombard said:


> Exactly my point. They're most like "lawyer PSI ratings".


No, they are marketing department PSI ratings. "Everyone knows" that higher pressure rated tires are better so the higher the number on the sidewall, the better the tire. It's just science.


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## Manning

counter point to the small tube in a big tire subject.....

In the everyday training wheels, I run the biggest tube that will fit in the tire without bunching. Why? thorn type punctures deflate much slower since the tube isn't streched, and thus the puncture hole doesn't open up like it does in a streched tube. Most of the time I don't know about a puncture until the next day. Same for pinch type punctures. Since the tube isn't streched as much, the tube is harder to pinch.


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## Blue CheeseHead

There are no issues. Install and ride it with confidence. Using tubes for 2.25-2.75" tires is common in 4" fat bike tires. When stranded I once used a 650 tube on a 700 wheel. It got me home. That added 10% stretch is insignificant. Blow up a tube with it not inside a tire. it will get quite large quite easily.


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## Lombard

Blue CheeseHead said:


> That added 10% stretch is insignificant. Blow up a tube with it not inside a tire. it will get quite large quite easily.



Yep. Reminds me of a leech after a full blood meal.


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## dcgriz

Butyl is designed to expand 1.5 times its non-inflated size. For sustained optimum use for performance (re: rolling resistance) and dependability (re: punctures, valve stem separation, etc) do the arithmetic; if you fall within this range you should be fine, if not change size.
Latex expands 7 times its original size so much more adaptable to a wider variety of sizes.


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## rm -rf

I've had an undersized tube split at the molding line. I don't know for sure that it's related to the stretching of the small tube, but now I'm more likely to use a tube that's rated for that size tire.


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## Kerry Irons

Manning said:


> counter point to the small tube in a big tire subject.....
> 
> In the everyday training wheels, I run the biggest tube that will fit in the tire without bunching. Why? thorn type punctures deflate much slower since the tube isn't streched, and thus the puncture hole doesn't open up like it does in a streched tube. Most of the time I don't know about a puncture until the next day. Same for pinch type punctures. Since the tube isn't streched as much, the tube is harder to pinch.


Not sure there is a cause and effect to your experience. Punctures are punctures and running larger tubes is not going to prevent a bit of glass or wire or a screw or construction staple penetrating the tube if it has been through the tire casing and tread. While your statement about pinches might be correct in theory (tube is a bit thinner) the impact of the tire bottoming out against the rim with the tube pinched in between is pretty high and the tube can be damaged whether it is stretched a bit more or not. Don't confuse correlation with causation.


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## Manning

Kerry Irons said:


> Not sure there is a cause and effect to your experience. Punctures are punctures and running larger tubes is not going to prevent a bit of glass or wire or a screw or construction staple penetrating the tube if it has been through the tire casing and tread. While your statement about pinches might be correct in theory (tube is a bit thinner) the impact of the tire bottoming out against the rim with the tube pinched in between is pretty high and the tube can be damaged whether it is stretched a bit more or not. Don't confuse correlation with causation.


I did not state there is no puncture. 

I attempted to state that when you get a puncture, the hole that is made by the puncture does not open up, therefore the air does not leak out nearly as quickly, and lots of times the ride can be finished with out repair. 

This is experience with riding mountain bikes in thorny areas before tubeless and sealant was popular. After I started running the larger tubes, I finished many rides with thorns in the tire. Also from riding bicycle trials where there are ample opportunities to smash the rear tire into objects. Even recently I mis-timed a hop, caught the top step of some stairs, and expected to walk home, but there was no pinch.


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## Jay Strongbow

Manning said:


> I did not state there is no puncture.
> 
> I attempted to state that when you get a puncture, the hole that is *made by the puncture does not open up, therefore the air does not leak out nearly as quickly*, and lots of times the ride can be finished with out repair.
> 
> This is experience with riding mountain bikes in thorny areas before tubeless and sealant was popular. After I started running the larger tubes, I finished many rides with thorns in the tire. Also from riding bicycle trials where there are ample opportunities to smash the rear tire into objects. Even recently *I mis-timed a hop, caught the top step of some stairs, and expected to walk home, but there was no pinch.*


Those things happen with tubes that are 'too small" also, and by the same taken you can most certainly pinch flat big tubes and they can flat very quick. Logically, yeah, thicker less stretched is an advantage but I'd guess you're really not helping as much as you seem to think. Then again you're not hurting anything either so whatever floats your boat.


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