[Shilun]

I want to swap over a knobbly 406 x 1.75 and a slick 406 x 1.5. Thus, the 1.75 will end up on a wheel originally hoding the 1.5, and vice versa. Are there likely to be any problems?

Thanks

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[spunkyruss]

It depends upon the rim widths and frame/component clearance.

It's a bad idea to use a tire that is skinnier than your rim.

Normally there are no wheel/tire issues with running wider tires, however you might find that a wider tire rubs against the frame or fender, etc.

Tires need to be drastically wider than rims before improper bead-seating issues arise.

[maunakea]

...

It's a bad idea to use a tire that is skinnier than your rim.
...



More accurately, it's a bad idea to use a tire whose stated diameter is less than 1.5 times the width of the rim channel. On a 19 mm rim channel on an ISO 406 rim, you should run at least a 1.5 x 19 mm = 28 mm diameter tire (406 x ~1.125" is not the same as a 406 x 1-1/8"). I use 406 x 1.35"... = 406 x ~35.

[JonathanG]

Sheldon Brown has a chart showing tire-rim witdth compatibility here. (http://sheldonbrown.com/tire-sizing.html#width)
Jonathan

[spambait11]

maunakea:

What is the difference between a 406x1.125 vs. 406x1 1/8? Calhoun lists the Conti Grand Prixs (http://www.calhouncycle.com/productcart/pc/viewPrd.asp?idcategory=115&idproduct=76) and Sport Contacts (http://www.calhouncycle.com/productcart/pc/viewPrd.asp?idcategory=115&idproduct=72) as 406x1.125" though Stelvios (http://www.calhouncycle.com/productcart/pc/viewPrd.asp?idcategory=115&idproduct=461) are listed as 406x1 1/8. But I assumed this was just a writing quirk and not an actual size difference.

[maunakea]

sb11 I tried the 406 x 1-1/8 Stelvios on my stock DT FS rims (marked Dino 20 x 1.5/1.75). To get the Stelvios on, I had to use 200 psi to seat the rim, then deflate to 120 psi. The 20 x 1-1/8 seems to have a smaller lumen diameter than the decimal fraction tires for ISO 406. I checked with a few bike techs I trust before trying the 200 psi trick. I decided that if I flatted on the road, I would never be able to reseat the bead, so I exchanged the Stelvios (thank you, Calhoun Cycle) for Primo Kevlar Comets, 406 x 1.35. I can't tell the difference between the two, but I like being able to remount the tire when on the road (:) ) and the Kevlar. (Haven't flatted yet, but it's a matter of time. I have to ride on some disgusting shoulders.)

[LittlePixel]

maunakea: interested in your high pressure seating methods. Can you say a bit more about it as I often have trouble getting my Conti Grand Prix's seated evenly onto a 1.5" rim without a small bulge. Any details you can offer? And how do you get to 200. That must be some track pump!

[maunakea]

LittlePixelI have a monster air compressor. You may want to try the 406x1.35 tire size or change to fractional rims. I can't detect any difference between 406x1.35 and the smaller size, but gain Kevlar and easier mounting in the deal.

[spambait11]

Thanks for the explanation, maunakea. Interesting info for sure.

[maunakea]

Although shock pumps don't pump alot of air per stroke, they do go to 300 - 400 psi, and are fairly inexpensive (USD 30). You would have to adapt from the shock pump fitting to a tire valve, if that is possible.