Bicycle Mechanics - has the LBS sold me the wrong tires?

On looking at Sheldon Brown´s tyre width calculator (http://www.sheldonbrown.com/tire-sizing.html) it appears that the correct width tyre for my Mavic 559 x 17 rims is a tyre with a width of between 25 and 37 mm. I took my bike in and asked my LBS for some light weight MTB tyres and they gave me some 54-559 Schwalbe Black Jack light folding tyres. Obviously the width of these tyres (54mm) is much much higher than recommended by Sheldon. These tyres should be on super wide rims (like Snowcats) according to Sheldons table

So what has happened? have they sold me the wrong tyres? should I go back there and kick their asses?

Have you tried them on?

Yes they have been on the bike for a while and they don´t fall off- but if they are in fact the right size how can Sheldon be so wrong?? :(

Yes they have been on the bike for a while and they don´t fall off- but if they are in fact the right size how can Sheldon be so wrong?? :(

I can't read Sheldon's mind, but you are probably in that gray area between "recommended" and "will it work".

I am not an expert, but I suspect with a tire that wide you are probably limited on the air pressure by the tire manufacturer. I would be extremely cautious about tire pressure... Too much and you could blow the tire off of the rim due to the increased angle between the sidewall and the rim. Too little, and I would fear instability, pinch flats or both.

I have usually been running them at the max, i.e. 65 psi

Assuming this is a mountain bike rim, I cannot imagine it being limited to a 37mm tire width. That's less than 1.5"

check out this link (http://www.speedgoat.com/product.asp?part=82090&cat=260&brand=155)

Assuming this is a mountain bike rim, I cannot imagine it being limited to a 37mm tire width. That's less than 1.5"

maybe I just don´t understand Sheldon´s table then- I agree it doesn´t sound right for an MTB rim

the Cannondale Bad Boy has the same rim as I have (Mavix x223 disc) and comes with a 54-559 tyre (26 x 2.10)

http://www.epinions.com/bicycles_2003_Cannondale_Bad_Boy_1FG_HeadShok/display_~full_specs

maybe I just don´t understand Sheldon´s table then- I agree it doesn´t sound right for an MTB rim



Actually I think it is just a conflict between Sheldon's(and others I'm sure) and the manufacturer's opinions. I cite this paragragh from Sheldon's page you linked to:

If you use a very wide tire on a narrow rim, you risk sidewall or rim failure. This combination causes very sloppy handling at low speeds. Unfortunately, current mountain-bike fashion pushes the edge of this. In the interest of weight saving, most current mountain bikes have excessively narrow rims. Such narrow rims work very poorly with wide tires, unless the tires are overinflated...but that defeats the purpose of wide tires, and puts undue stress on the rim sidewalls.

My narrow-ass aero rims are happy with anything from a 700x20 to a 700x52, so I wouldn't worry too much about it.

You're not one of the people posting about all the flats you're getting, and you haven't rolled the thing, so you're fine. Sheldon, like anyone, has his biases. Just because he made a table or a calculator doesn't mean it's an incontrovertible truth.

I do get a lot of flats but not pinch flats as the light Black Jack folding tyres are not puncture resistant at all. They look quite tough and knobbly but they flat on average about once every couple of weeks when I commute on them.