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I've got an early-mid 2000's Trek touring frame, I think – got it about 6 years ago at a local bike co-op for my first (and only) ground-up build, and had it powder coated, and unfortunately I didn’t write down any info on it before that.

I moved from the flatland to the mountains a couple year ago and have done my best to make it a gravel-worthy bike:

here’s the current setup

However, on the century ride I did last summer that included 8,0000 feet of elevation, I realized how badly it is outmatched with the 11-28 cassette and 32mm tires. So now I'm looking at what it would take to get it more capable of 10 percent gravel climbs.

I'd ideally like to get 650b wheels to hopefully allow for 38-40mm tire, an 11-speed cassette, and disc brakes. I'm unsure whether the frame is compatible with IS mounted calipers. There are two threadless holes on the non-drive side that measure 51mm apart at the outer part of the holes:

two threadless holes that measure 51mm at their outer point

If this is not for an IS caliper mount, my next question would be: does anyone have a suggestion for 650b quick release wheels with a 135mm hub that can fit an 11-speed cassette?

If that's not a thing, then how about suggestions for a 650b quick release wheel with a 135mm hub that can fit an 11-speed cassette and is rim-brake compatible?

I am very attached to this frame, as it has carried me through every type of weather as a commuter, and mountain bike trails high in the mountains.

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  • Can you please tell us the model of rear derailleur ? Should be stamped somewhere on it.
    – Criggie
    Mar 3, 2022 at 0:44
  • It’s a Microshift r9 Mar 3, 2022 at 4:00
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    Great - microshift.com/models/rd-r43m says under "full specs" that it has a Max Cog of 30-34 so in theory your 28 is too small. It has a capacity of 39 links.
    – Criggie
    Mar 3, 2022 at 4:46
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    How much clearance do you have for bigger tyres without changing the wheels (brakes and frame/forks, recalling that front and rear tyres don't have to be the same)? I've run a variety on my rugged tourer and find that even going from 28mm to 32mm helps quite a bit on gravel, even with both being slicks. If you can get 35s in there you've got a huge choice. There are also a few 30mm tyres, but nothing actually ends up at its nominal size, and the difference between real and nominal width varies with manufacturer and range.
    – Chris H
    Mar 3, 2022 at 8:58
  • @ChrisH and Michael:I have 32mm tires on there now, and run at 45psi they’re actually only 30mm. Width wise I could maybe squeeze in a 35, but my issue is top clearance where the seat stays split. In wet conditions, mud gets caked there and the tire rubs quite badly, which is what prompted my thought to try 650b wheels. The 32’s do well in the foothills, but I was hoping to do some bike packing, and they just can’t handle the really steep loose gravel. If I could fit a 35mm and get a cassette with a 36t ring, I’d probably be able to swing it 🤔 Mar 4, 2022 at 2:51

4 Answers 4

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Nope. This frame does not have disc-brake mounts. IS mounts would be up the seatstay from the dropout, on a little flange. Those look like fender/rack mounts.

You will not be able to put disc brakes on this bike without the assistance of a torch. It's not economically viable. This means you will not be able to put a different wheel size on it.

You're stuck using sidepull brakes, which really limits your tire size, although the frame probably limits the tire size too.

I totally get being attached to this bike, but I recommend making it the best version of itself, rather than trying to make it something it's not well adapted to.

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As Adam says, you're out of luck with disk brakes here. To get all your wish-list items, you're looking at another bike.

There are adapters for disk calipers, but they don't reinforce the frame and you risk bending the forks especially. Not recommended.

You might be able to get a front disk brake by changing out the fork, but this is getting rapidly more expensive - fork, wheel, rotor, caliper all add up.


You don't require 11 speed either - to make the bike easier on your knees you simply require a better gear ratio for climbs without sacrificing a high gear for flat/fast riding.

Your cassette would be 11 tooth on the small end, and "as big as your derailleur can handle" on the low/large cog.

So you may be able to have a 32 / 34 / 36 tooth low gear, which gives 10% to 20% lower low gearing than a 28 tooth. The cassette needs to be the same number of speeds as the bike is now. Do this when you change cassette and chain anyway and its basically free.

You can put a smaller inner chainring on the front to lower gearing too, but the maximum difference between chainrings is supposed to be 13 tooth at most. Otherwise its hard to change accurately.

You might consider putting a triple chainset on the front, so there's a big, medium, and small chainring. I had a road bike with a 28 tooth small chainring (aka a grannie ring) and a 34 tooth low gear, resulting in a sub 1:1 gearing ratio. That let me climb a 30+% slope albeit slowly.


If you can swing it, get an additional bike. A 29" MTB in rigid or front-suspension, then fit drop bars may be a solution for you, depends a lot on what is available in your location.

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    More sprockets in the cassette doesn't make the hills any easier, it just makes finding a comfortable cadence easier, so there's really no harm in sticking with 9-speed, and at 9-speed (at least with Shimano, which I have) road and MTB parts are interchangeable so you could put a mountain RD and cassette on there (I've done both on my tourer, though not at the same time).
    – Chris H
    Mar 3, 2022 at 8:55
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    @ChrisH yeah this kind of thing sound just like you :) Also, that matching 9 speed parts are cheaper than 11 speed parts. N+1 (or 2 or 3) is quite a good solution, if cash and storage space permits.
    – Criggie
    Mar 3, 2022 at 9:35
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    @BighornBum a lower gear is unlikely to help with traction - it may even make it worse as you are able to apply more torque to the rear wheel.
    – Andy P
    Mar 3, 2022 at 10:40
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    Good point @AndyP. Traction would be better addressed with more suitable tyres even if wider isn't an option. But 28T seems a bit small for gravelly climbs depending on what's at the front, so changing the cassette might still have benefits
    – Chris H
    Mar 3, 2022 at 10:48
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    @BighornBum yes - there are several - Tanpan and Wolftooth come to mind. Check out bicycles.stackexchange.com/search?q=tanpan and bicycles.stackexchange.com/questions/72267/… for more info. Basically they're all a compromise, bigger toothcount low but worse chain/cassette engagement in high gears, plus added flex.
    – Criggie
    Mar 5, 2022 at 7:51
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Some Trek frames do not come ready for disc brakes but an adapter does exist.

I had a Trek Fuel (Full suspension Frame for XC) and the authorized dealer has proposed to upgrade the bike by adding the adapter. Your frame dropouts looks the same shape as mine.

I'll add a picture for reference, this is not my bike but shows the example. I've seen fellow riders with this adapter in other models of Trek MTB.

enter image description here

Edit: By the way, in order to find this picture i googled "trek frame disc brake adapter".

While re-visiting the search engine, I saw a picture of one adapter that does not require a second piece to fit post mount calipers:

enter image description here

In order to install Disc brakes on the front, the usual route is to swap the fork, using one that has been designed for disk brakes and thus, has the mounts. Forks for disk brakes may also have stronger "legs" and slightly different dropouts.

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    Interesting. Just to clarify, this is an adapter that still requires another adapter to fit a disc brake.
    – Adam Rice
    Mar 4, 2022 at 17:23
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    @AdamRice "Yo dawg I heard you like adapters...." separately, its interesting how this is the rear brake (being the less-useful one). Perhaps that pictured bike had a front fork with disk brake mounts.
    – Criggie
    Mar 4, 2022 at 21:22
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    That is interesting and does look to be the same. Overt confounded, but let’s face it, I’m almost purposefully trying to be confounded at this point. Haha. This gives me something to think about Mar 5, 2022 at 5:47
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    @BighornBum that feeling is called "learning" and its always fun. Sometimes expensive too. You could sink a lot of money into doing this change and still end up with a bike that isn't great, and possibly worse than it was. It may even cost you more in parts than buying a second bike. Spend some time exploring what is available locally to you, and have some spare cash to take advantage of any opportunity.
    – Criggie
    Mar 5, 2022 at 21:55
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    @AdamRice, indeed, it's an adapter on top of another. I have seen calipers that interface directly with I.S. mounts, but are quite rare. I do not rule out the possibility of an adapter that directly adds the post mount directly to the frame, but if It exists, I haven't seen it.
    – Jahaziel
    Mar 5, 2022 at 22:34
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In addition to the frame not having the correct mounts, be aware that frames are assembled in a different geometry as well as slightly different joins, thicknesses of metal, and other mechanical aspects.

This will not only make a road bike less efficient and likely uncomfortable as a gravel bike, but will also make it more likely to fail when put under the different stresses a gravel ride provides, particularly over time as they are repeated.

The biggest geometry difference is that a gravel bike is optimized for riding out of the seat as much as in the seat, with a fairly upright posture, while a road bike is primarily optimized for riding in the seat with a fairly low profile leaning posture. What this usually means practically is that when going downhill standing, the seat will be in the way, and your body will be much further forward, putting your center of mass forward, which increases the risk of Rubber Side Up condition. You can lower the seat, but the geometry is all wrong and that will make riding in the seat a cramped, uncomfortable experience.

Take a look at the following picture. Notice the following about the gravel bike on the right compared to the road bike on the left:

  1. Thicker tubes
  2. Seat tube angle slightly different (puts the pedals further front of the rider)
  3. Steering tube angle - steeper angle provides greater stability

Road bike on left, mountain bike on right

You can fix a lot of the other differences, such as adding shocks, bring the handlebars closer to the rider and higher, decreasing the chainring size and increasing the cassettes, but the frame itself is going to severely limit your success, and the cost of changing all these things just to end up with a poor gravel bike will easily equal the cost of an inexpensive gravel bike.

So buy a gravel bike and keep your loved road bike. They are two different vehicles for different situations, and there's no need to get rid of one just because you're starting to use the other riding style.

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    That's not what a lot of people would think of as a gravel bike, That's a hardtail MTB
    – Chris H
    Mar 4, 2022 at 15:11
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    Overall I would totally agree. They are purpose built. However, I may have snagged a dropper post from a friend and kind of just want this to keep getting out of hand. 😂 I find a lot of joy in simply trying to make this work. It may not be the overall “best” or most efficient choice, but it’s a fun challenge. Your point about durability is the main thing that does concern me, but I guess my hope is that if I’m able to get other components switched out that are more capable, it may help reduce some of the negative stresses on the frame. Mar 5, 2022 at 5:46
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    Don't fall victim to marketing copy BS. As far as the forces on a bike are concerned, there is virtually no difference between gravel and crappy pavement. People were riding road bikes on gravel since bicycles first came into existence. If road bikes can handle Paris–Roubaix, they'll do just fine on gravel, which they do. Gravel bikes today are basically just road bikes with a little extra tire clearance a little relaxed geometry, that's it. Mar 5, 2022 at 21:03
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    Road bikes are just like gravel bikes which are just 90's MTBs. Finally it's proven, road bikes are MTBs after all. Turtles all the way down.
    – Erlkoenig
    Mar 5, 2022 at 23:54
  • @whatsisname it does make sense, especially with growing up riding horrendous Midwestern roads...I did snap a seat down-tube once though. 😅 Mar 6, 2022 at 0:12

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