Gravel bike from old MTB


Well-Known Member
Below is a combined summary of a series of posts I made on another forum over the course of this project. I’ll post it in order as if it were happening now, but obviously you'll get the finale straight away.

My project.

Over time we have accumulated a number of bikes in our household. One of them was an old Trek 830 (circa 1997) which was picked up many years ago for around £20 for my wife to ride. Over time I moved up from a 26er alloy hardtail to a 29er c/fibre hardtail, so my wife got my 26er, making the Trek redundant. It has sat in the shed for years and moved house twice but never been ridden. So it is now my little project.

It's not worth much as a retro/vintage MTB, isn't especially rare or desirable but is a nicely-made cromoly steel frame in slightly scruffy but sound condition. Over the last few months I have been scrounging, finding and where necessary buying parts to turn it into a mongrel bike. I am aiming for a CX/gravel type of thing with drop bars.

Here is how it started:

And after this weekend, here's how it now stands:

First I stripped the frame of all components (except the bottom bracket, which is a very solid square taper running smooth and free, so I left it alone).

Then I punched out the threaded headset and pressed a 1 1/8" threadless headset into it - this was to open up options for a replacement fork; I had the headset already.

A friend I ride with donated a fork he happened to have lying about, which had disc brake tabs on; it'll need the steerer cutting down as you can see.

I had a spare stem and picked up some cheap 'bars from a cycling forum.

The alloy seatpost is from the original bike, topped with a Charge Spoon saddle also picked up from the cycling forum.

The wheels are 622x19c disc wheels, picked up from eBay - the biggest unknown I faced was whether I could fit 700c wheels with chunkyish tyres into the frame - they fit with room to spare. The Schwalbe CX Pro 30mm tyres came from a local selling group on Facebook.

That is how the rolling chassis now sits. Next I have to:

Fit the brakes - I have some TRP Spyre mechanical disc calipers from eBay but still no levers; I am after a 10-speed Shimano STI set and still looking. I'll also need an IS-to-post mount adaptor on the front and an A2Z disc brake adaptor for the rear (this is one thing I am uncertain on whether it'll work). I'll also need some compressionless cable housing.

I need a crankset - the one that came off it is three-ring but the rings are riveted onto the spider and the BCD doesn't match any common standards so I'm hunting for a cheap, square taper crankset for a single ring set-up.

I need a 10-speed cassette and chain. I have a derailleur to try out.

I need to set the stack height and cut the steerer tube.

I need to wrap the bars (I'm looking at red).

And then it is just finishing touches.

I know it won't win anything. I also know it'll end up being worth less than the parts I bought for it and may not even ride very well, but that isn't the point. It will be my bike, that I designed, with solutions to challenges unique to this bike. It is something to keep my mind and hands busy and so far has served that purpose well.

I'm in no rush - it has been over a year to get to this point (that is over a year of waiting, bidding, finding, researching and gathering and about 2 hours building this weekend). It may take another year to find the parts I want for the money I want to spend (ie very little). However, so far I am pretty pleased with how it is turning out.
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Well-Known Member
Some small updates today:

- fitted a disc to the rear wheel; it clears the chain stay by a few mm, so all good there
- offered up the A2Z disc caliper adaptor; looks like it’ll work with a small amount of fettling
- fitted a road 10-speed cassette I had lying about, just until I can get a wider range one
- fitted some new crank arms with a narrow-wide 34t chain ring
- fitted the pedals off of the old MTB, just for somewhere to put my feet until I can get some SPDs
- fitted a XT derailleur
- added some spacers to the steerer; stack height feels good so I can cut the steerer I think
- offered up the front brake caliper; seems to line up ok with the disc.

To do:

- fit the front caliper; I thought I didn’t have any M5 bolts to fit them but it turns out the bolts from the old canti bosses fit perfectly, which I only realised after I had downed tools for the day
- fettle and fit the A2Z; it’ll need a little bit of trimming with a Dremel grinding tool to sit flush against the dropout
- acquire another IS to post adaptor to fit the rear caliper to the A2Z
- acquire and fit a cassette (looking for 11-36 ideally) and chain
- acquire and fit some shifters/levers and compressionless cabling
- wrap the bars.

With the cranks and pedals fitted I took it for a brief freewheel up and down the drive and across the road. In the very limited ‘ride’ it felt pretty goodn it rolled, balanced, steered and generally behaved like a bicycle should. I’ve never built a bike before, so can’t wait to actually ride it.




Well-Known Member
I have nearly everything to finish it now, just need time to get it together. I have some Tiagra 4600 levers, a 11-36t 10-speed cassette and chain, a cable set (in yellow :biggrin:) and some red bar tape. I have to build it outside so need light and weather (and free time) to get on with it.
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Well-Known Member
Bit more progress today, a couple of the bigger jobs done:

- modified and fitted the A2Z brake disc adaptor. It needed some metal shaving off to fit the dropout and frame neatly, but it’s on now and seems solid (no caliper mounted yet though)
- cut the steerer and mounted the fork properly
- mounted the front caliper
- mounted the brake levers/shifters
- cabled up the front brake, now fully working
- ran cables for the rear brake and derailleur
- fitted the wider range cassette.

To do:

- fit a chain, cable up the derailleur and index the gears; the chain I have did not accept the KMC quick link I had, so will need another option
- mount the rear caliper (still need an IS to post adaptor) and attach cable
- put the bar tape on
- test ride!



Well-Known Member
Finally - done! Mostly.


The indexing is still not right - I’m looking out for a Tiagra 4600 long cage rear mech - but I took it for a ride with the kids and other than the occasional skipped gear everything else worked as it should. I need to shake it down fully before I will trust it on a longer/faster/harder ride, but I’m pretty pleased with the outcome.


Well-Known Member

When I first conceived the project I was aiming to pass some time, have a project and hopefully build something that worked. There was a chance it would fall apart like a clown bike, or be a fatally flawed design, or just be ugly.

Having finished it and ridden it it is fast becoming my favourite bike. It’s not a beauty, but I still love looking at it. It’s not a lightweight, but I keep reaching for it when given the choice of a carbon fibre hardtail 29er, an alloy Synapse or a carbon fibre Fuji road bike. I have ridden it over a range of surfaces, from road to singletrack. I have climbed my worst local climbs and descended the best descents. It is not that much slower than a road bike on the road, despite the weight and 43mm tyres and handles some pretty rough off-road. So far nothing has fallen off or gone wrong and it rides really nicely. I’ve had one small off which it shrugged off with nothing more than marked bar tape.

When on the 29er I feel out of place any time I have to link up on the road. On the road bikes there’s little choice but to stay on-road. On the FrankenTrek it feels good everywhere and means I can link up road and track to make new routes. I made a bike and I like it.



Über Member
I really like that, great project and really nicely done. How is the gearing for the road? That’s a very small front chain ring.
great job , I like that ….a lot:okay:

the snail

The indexing is still not right - I’m looking out for a Tiagra 4600 long cage rear mech
looks like you've already got the medium cage rd on there. If that isn't enough, I think you could try a derailleur hanger extension, or If you want an actual long-cage rd, a 9 speed mtb derailleur should work? Also worth making sure the b-screw adjustment is good. Nice job though - those old mtbs are certainly versatile bikes.


Well-Known Member
I think I have worked out that the mech hanger is slightly bent making the derailleur toe-in a little. Unfortunately it is part of the frame so I plan to gently try and persuade it back into line. 😬
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