MTB to 'gravel' bike

figbat

OK, so I'm writing this as a sort of therapy, to get it out there and make it real rather than a perpetual daydream.

I have an old MTB currently surplus to requirements. It is a mid/late 90s Trek 830 with a cromoly frame and rigid forks. It has always struck me as being relatively lightweight compared to my much newer alloy hardtail. Anyway, with my graduation to a carbon 29er, the hardtail is now with the wife, leaving this old timer redundant.



Looking around it probably has a limited appeal as a 'retro' bike and doesn't appear to have any real value. I have a MTB and I have a road bike, but what I don't have is a drop-barred 'gravel' bike which got me thinking - what about making a project of the Trek?

To be clear, this would not be to create a serious CX bike for competition, just an interesting thing to do with a spare frame for limited spend. I realise I could buy something ready-made and better, but that's not the point - I fancy having something to twiddle with, some issues to overcome and a final thing to ride that I designed and built.

So what I'm thinking is:

- convert from 1 1/8" threaded to 1 1/8" threadless headset
- replace front fork with disc-tabbed version
- add stem and drop bars (compact drop, relatively wide)
- replace wheels with bigger ones on CX tyres (I fitted my road 700c wheel to the front and liked how it looked, but have to think about brakes)
- front mechanical disk (because hydraulic road levers are £££)
- rear mini-v brake (replacing existing canti, mini-v to match road lever cable pull)
- replace 3x7 with 1x10/11
- fit road levers (something like SRAM Rival 1)

The main challenge to overcome is rear brakes: bigger wheels mean the current brake posts are in the wrong place. There are adaptors that will move the post by around 16mm - this means going to a 700c/29" wheel will probably put the rims out of reach of the brakes (even when adapted), so am thinking about 650b/27.5" rims.



I would prefer to do this as clean as possible, so disk-brake adaptor plates, caliper-to-v-brake adaptors and Travel Agents are initially not on the table, hence the current brake selection. I originally thought about mini-v on the front too, but a replacement fork is relatively easy and cheap and the front is where the biggest braking is, so a disk up-front would be nice. I also like the idea of it being a bit quirky and fit-for-purpose.

Of course the next challenge is a wheelset that is disk and rim compatible (or having wheels that ostensibly 'match' but are rim and the back and disk up-front).

All of this is happening on a budget, and not a big one. I'm looking for second hand options, sales etc. The biggest cost looks like the wheels and crank.

It has a 135mm rear wheel fit, English thread BB - all pretty normal 90s stuff.

I have no definite plans for usage; there are some routes around me that would be good for it (interlinked roads and gravel tracks) and it would be a good commuter as there are some good routes I can't use on the road bike because of a short stretch off-road, but too much road to suit the 29er. And as I said, this is as much about being a thing to do and learn about than being a practical or cost-effective route to a bike.

So, now I've put it out there.... any thoughts? Anything I've missed? By all means come back with "not worth it", "don't bother", "it'll be rubbish" but don't be offended if I push on with it anyway. But don't expect this to move fast, I'm guessing I'll deliberate and procrastinate a lot and it may end up as another "For sale: project bike, not completed". As far as possible I want to make all change reversible, just in case the market for scruffy 90s Trek 830s suddenly sky-rockets.

trek_dan

Personally I'd stick with cantis, 26" and flat bars. Put some less knobbly tyres on it and upgrade to a 1x9/10 drivetrain.

figbat

So, after a little procrastination (turns out it is nearly 18 months’ worth) and a lot of watching items on eBay/Facebook Marketplace/BikeRadar/etc today I went outside with a bare frame and bunch of parts I had gathered and made a start. Now, it looks like this:



So far:

Old threaded headset punched out and replaced with a threadless FSA one I had lying about.
Fork with disc tabs kindly donated by a friend.
Oval Concepts stem I had lying about
Deda RHM 01 420mm handlebars from this very forum
Alloy seatpost salvaged from the old bike
Charge Spoon saddle from here too
Maddox RD 2.0 622x19c wheels off of eBay
Schwalbe CX Pro 30mm tyres from local Facebook selling group.

To do:
Fit brakes - I have a pair of TRP Spyres with rotors, need an IS to post adaptor for the front and an A2Z adaptor for the rear, plus some compressionless cabling
Find some Shimano 10 speed shifters - watching and bidding on eBay but no luck so far. Am planning on running 1x10 so left lever shifting will be redundant, but still hopefully act as a folding lever to avoid bending/snapping in a fall
Fit derailleur - I have one to try
Find a 10-speed cassette and chain
Cut the steerer down and fit spacers
Either drill out the rivets on the existing cranks and fit an appropriate ring, or find a cheap square taper crankset
Find some pedals, probably SPD.
Wrap some bar tape (was going to go with red).

It’s never going to be a winner at anything, but as a project to keep me amused it has been successful so far and I’m quite pleased with how it has turned out to this point.

cooldad

My SS attempt. Looks ok but a bit sh1t to ride. A bit twitchy.

penguin_of_death

If you are trying to save some money consider skipping the sti levers and going with separate brakes and a single bar-end shifter

figbat

Penguin of Death wrote:

If you are trying to save some money consider skipping the sti levers and going with separate brakes and a single bar-end shifter

I did think about this but have zero experience of bar-end shifters, and used Tiagra STIs are not too costly on eBay, if I can get some.

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.

veronese68

Good stuff. Must admit I’d stick some flared bars on it. No idea what they’re like to ride but they’d suit the whole frankenbike vibe.

figbat

That was in my original plan, but these ones came up at a good price so I grabbed them. Maybe v1.1 will get an update, once I have proof that I can pull together a bunch of disparate parts and make a working machine.

javanman123

phewww that is a pretty bike my friend. I have also been considering converting my old mtb laying around to something that is more suitable for local gravel rides.

figbat

No more progress in terms of build, but I now have some 4600 shifters, an 11-36 10 speed cassette and chain, full cable set (in yellow 8) ) and bar tape (red). When I get the time I now have almost everything I need to finish it. The only thing I am missing is an IS-to-post adaptor to fit the rear caliper to the A2Z adaptor, but I am not getting one until I have fitted the A2Z and offered up the caliper to see what is needed. Oh, I’ll also think about stuff like bottle cages and mudflaps (although I like how it looks without).

Over the winter the MTB group I ride with tends to stick to drier trails as the regular ones get pretty boggy. I’m hoping I might get out with them on this and see how it compares.

figbat

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!

figbat

OK, so I sorted the chain link issue (I was being a numpty) and took it for a brief ride round the block. Too soon to say anything other than it goes, rolls and stops, but that’s a start. The gears need setting up and I may need a chain guide to prevent dropping the chain on the smallest gear.

figbat

Another quickie: I have test-fitted the rear caliper which, with the use of shims and washers, can be made to align with and grab the disc - I'm using unsuitable bolts at the moment though so new, correct-length ones are inbound.

I have tried to dial in the gears - I am close but it isn't perfect. It's likely because I am mix'n'matching various components (XT 9-speed derallieur, Tiagra 4600 10s shifter, Shimano 11-36T 10s cassette). The mech swings from one side to the other OK in 10 increments but there is one shift around the 3-2 gears that tends to jump two when moving to the larger gear. If I dial this out I run into mech alignment issues elsewhere. I have got it just about there, so that when under light load the shifts do largely what I expect but it isn't perfectly clean. I may never be able to get it right or it might increment towards the optimum as I ride it, as the cable beds in and I fiddle with the inline adjuster on the fly.

Happy to report that I managed to ride down the road, down a short hill, stop at the bottom and then easily ride it back up again. I think it is geared for climbing more than descending (34T chainring), but that''s OK with me as I rarely spin out on any of my bikes but do sometimes wish for a better climbing ratio.

Just need to final-fit the rear caliper, cable it up and tape the bars.

figbat

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.

figbat

Update.

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.