speed rating de-rate when an inner tube is fitted

[Tmoose]

My question is if a tube derate guideline exists for when somebody puts a tube in a still unpunctured passenger car tire, perhaps because they are unwilling to fight with old rim bead leaks anymore.

Plenty of places say don't install a tube in a tubeless tire, generally in sections pertaining to acceptable flat repairs.

Of course a few motorcycles are still around (right in my garage) that use spoked wheels and thus need tubes, but I have not seen how the speed rating is affected ( definite derate I expect) when a tube is fitted.

Maybe not such a big deal when fitting with a V or H rated tire, but some low end passenger tires and lots of real winter tires start off at what? 85 mph?

thanks

Dan T

 

[CapriRacer]

Dan,

I started off writing my response from the passenger car tire perspective - taking your comment about motorcycle tires as an aside. Then I realized that maybe that was the source of your inquiry. So I have left what I wrote about passenger car tires below and want to point out I will talk about motorcycle tires following that section.

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Passenger Car Tires:

So let's start with the idea of using a tube in a tubeless tire. I see this as trying to band-aid a problem, rather than try to fix it. That means it is less than optimal and creates its own set of shortcomings. Personally, I'd really consider fixing the real problem before using a tube.

But assuming you are going to use a tube anyway: The overall tire gets thicker and in theory, reduces the speed capability of the tire. I don't think anyone has quantified this, so there aren't any guidelines.

Second, the valve hole for tubeless rims, generally aren't in the right location for a tube. There is going to be some strain on the tube to get the valve through the hole and that increases the risk of a failure.

And lastly, if the speed capability of a tire is a concern, you not only shouldn't be using a tube, ALL your tires and wheels should be in perfect working order - no repairs, no leaks, etc. In other words, if someone is considering doing something less than optimal, they had better be driving much slower than the speed rating of the tire.

OK, so now I need to talk about speed ratings. Typical passenger car tires are S speed rating (112 mph). Winter tires are usually Q speed rated (99 mph), except for high performance winter tires which are H or V rated (which we don't need to talk about).

I am of the opinion that anyone traveling faster than 70 mph needs H rated tires. Some of this is due to the affects aging has on speed ratings.

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Motorcycle Tires.

Because motorcycles are different than cars in the way they operate, the tires are also different. Some of the rules are different as well.

I can see using a tube in a tubeless tire if the original tire spec was a tubetype - and as I said for passenger car tires, if you are operating anywhere near the speed rating of the tire, you need to have nearly perfect tires and wheels - and a tube in a tubeless isn't one of those.

I also think there is very little overlap between tubeless and tubetype. Since this is not really within my area of expertise, you should take this as an educated guess after looking at a few charts.

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So there you have it.