In this case, "if you have to ask..." Why take a chance, at any speed? Think about how long it might take you to get back on the road if you go down from lack of traction or flatting on the way down? Keep this to carry a spare if you like.
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FB4K - Every October we wrench on donated bikes. Every December, a few thousand kids get bikes for Christmas. For many, it is their first bike, ever. Every bike, new and used, was donated, built, cleaned and repaired. Check us out on FaceBook: FB4K.
Disclaimer: 99% of what I know about cycling I learned on BF. That would make, ummm, 1% experience. And a lot of posts.