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2.40 Tubeless on my Cobia?

Original Post
Chris WJ · · Unknown Hometown · Joined Sep 2016 · Points: 0

It's time for new skins on my Trek Cobia (29er) and I want to upgrade.  I have stock Bontrager AT-850 wheels which I plan to make tubeless with Stan's yellow tape, valves, etc.  I'd like to go with Maxxis Ardent 2.40's.  I haven't found a good source of info on what rim sizes will accomodate what tire sizes.  Has anyone done this on the AT-850's, or like to comment on if it will work?  The next size down is a 2.25, and it has tubed 2.10's on it stock.

Thanks guys!

Zachary Wagner · · Manchester, NH · Joined Jul 2016 · Points: 403

Hey man,

I realize your post is a little old, so you've probably already got it handled, but I thought I'd jump in just in case.  After a quick run of some forums in various places, it looks like plenty of people have converted those 850's to tubeless without an issue (or with minimal issues).  Sometimes you can have issues with certain tires on rims that aren't specifically tubeless ready, which is why manufacturers really don't recommend doing it, as tires *could* potentially blow off the rim in a corner because the rims aren't meant to hold onto a tubeless tire.  But most of the time in these cases it works fine.  The tire size won't really matter.  You can do 2.4's just fine I would think if your bike will fit them.  The rims probably have a skinnier inner rim width so tire shape won't be ideal, but it should still be no problem.

Anyway, I'm curious to see how it goes for you, so let me know if you get a chance.  

Brian Smith · · Boulder, CO · Joined Dec 2014 · Points: 5,541

Zachary pretty much covered it. 

Only thing I'd add is that you should check out your rear triangle and fork clearance (i.e. how much wiggle room does your current tire have?). Remember, you want any tire you mount to fit with some margin for mud and/or wheel flex/wobble. 

Keith Merson · · Unknown Hometown · Joined Jun 2016 · Points: 0
Chris WJ wrote:

I haven't found a good source of info on what rim sizes will accomodate what tire sizes.

This is complicated because you can fit a relatively wide range of tires on a given rim, but it becomes a question of performance. If a wide tire is mounted on a narrow rim, the sidewalls have to extend out at a pretty good angle (profile resembles a light bulb). That can be problematic. But the same tire on a wider rim allows the sidewalls to be flatter, which is generally preferable. For example, on my 29er singlespeed the rims are called 25 mm but really only have 23 mm internal width. Putting 2.4s on those rims would probably not work but I can run 2.2s without a problem. You should be able to ID the rims and then the manufacturer's website should tell you the rim width. What you really want to know when it comes to fitting tires is the internal rim width, so if the rim manufacturer's website doesn't specify whether the width is internal or external, I'd send them an email. Once you know the internal width of the rims, you should be able to find plenty of tires that fit.

Guideline #1: Don't be a jerk.

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