[Closed] Tandem 26er Hardtail conversion to:- Mtb 29er Full Suspension Tandem Build

looks awesome!

cracking!! but somewhat scary forks!

are those gears normal? i thought the chain went on the other side?

It's a challenge to ride in these very wet and slippery conditions we have been off quite a few times - if you get in a muddy rut you really have to concentrate. Had to change those Maxxis Ardents straight away in favour of Specialised Prgatory Control's much better grip and less understeer in the mud. It really concentrates the mind on picking the best route.

Do you really need a fork bridge? Sure it keeps the fork outers straight especially on the brake side! .. and there are many inverted forks which don't have a bridge. It is stiffer than it was as standard.

Normally the Timing chain is on the left but I am using my parts bin so using some old xtr m960 crank sets - swopped the middle ring from a 32t to a 36t and that is fine for the conditions and hills around here - if we can't pedal that fast we just freewheel; so made the outer rings the timing chain - simple really

looks a long way off the ground !

The 29er wheels give it an extra 30mm and Ground Clearance is everything for Mtb Tandem - it's not possible to hop over logs and rocks etc. In fact you just plough into the obstacles and hope you go over .... unless I missing a trick or two. The 29ers roll better over the obstacles ... but easier to bend!

Looks ace! Are you bringing it to the tandem weekender?

http://singletrackworld.com/forum/topic/mtb-dales-tandem-weekend

And yes, when riding a tandem you can't unweight the bike and flick over stuff like on a solo, you're going *that* way and if you want to change direction you need to give the bike advance warning. proper fun 🙂

That is genius

I did read about the weekend and would really love to be there, but I'm on the South Coast so it's a very long way for us.

Will try to persuade Chipps to organise next year's a bit further south!

P.S In case anyone wonders what the extra holes are for in front of the lower shock mount I also designed it to take 200mm eye to eye shocks of which I have a number of spares surch as a DHX 5.0 etc. A longer shock just mounts up using a 8mm bolt.

Genius....

nbt - Well if it had been earlier in the year might have come up in our Camper and made a long week of it; but sadly it has been Sorned for the winter now.

I'm very impressed with this - top work!

That freaking awsum work.
Long live the people that aren't afraid to experiment with new stuff.

needs a dropper post 😉

that is Totes though!

That is both insane and awesome simultaneously!!

rOcKeTdOg - Member

needs a dropper post

Joking apart I recon a dropper post would be awsum on our tandem.
Mrs ssstu has longer legs than me and sits quite a bit higher on the bike.
Imagin putting some weights behind and higher than yourself and you'll get an idea of how it feels on a descent. 😯

I couldn't see her legs today ssstu ;0)

The first time we went down a steep incline my partner (Mrs Stoker) shouted "I havn't got a dropper post" - I said "don't be daft, we can't go over the handlebars your too heavy".

😯

Well she was sat down on the bench...

You should have stopped and told us how wrong our bikes were . 😉

That would've meant being seen with you in public. No thanks. There was only one wrong bike there that I could see, it was grabbing all the attention at the front. 😛

I was gonna wind down the window and shout some abuse, but as I had a cracking hangover I wanted to stay quiet

Oh - I tell you a funny one ..... When we get started I normally say '1-2-3 go' ..... yesterday I went 1-2-3 go - pedalled away only to hear "hang-on, I'm not even on the bike yet". I had gone off without her! I think I'm losing it!

Houns.
Was that your nan's car?

I had gone off without her!

Yes it was!

Yes it was!

😀

Not very often that I'm impressed by any homebrew engineering that I see on this forum, but genuinely massively impressed by this!

First thoughts were "The BB's will be a bit bloody high", but then of course realised that on a Tandem that's more of a positive than a negative. And of course, the ridiculous chainstay length of the 29er Giant Anthem Swingarm is neither here nor there on a tandem either.

The fact you're achieving 6" travel out of it also is cos Anthem's normally have a 165mm eye to eye shock with 38mm stroke to achieve 4". So you've got 50% more stroke, therefore 50% more travel.

Top job anyway! I badly want a go on that... 😀

They're some slack seat angles going on there

Extra 29" bodge crown looks a lot less worrying than some of the cutaway crown pics I've seen before. Didn't think they'd be room between it and the crown under bottom out

DS timing chain AND twin ring setup looks interesting too

Forks can "totally' bottom-out with no interference at the crown; I had thought the seat angles were right, but I'm no expert on those matters. I had initially been worried that the head angle was a bit steep but it appears to match with most tandems; however the talas forks slacken it off when in 130 & again in 160 settings.

Mboy - thanks. The hardest part was working out the geometry; a couple of mm fore or aft wth the main d-link pivot and the position of the upper rocker pivot are all critical. With the front mech at the optimum height (as low as pos.) there is only 2mm before the chain stay would hit the mech. The hardest aspect though is to get the"tracking" straight as no matter how well it is jigged the heat of welding changes everything so there is a certain amount of persuasion required to get it all right - even 1mm makes a huge difference especially due to the length of the wheelbase. The best check is to put the wheels on and roll it along a straight line and then see if the rear wheel is still dead on it.

Not sure how the chain stay length of a Sus. 29er can be any shorter? Unless it is like my 26er Marin Wolf Ridge which I converted to 29er which has a very short wheelbase for a full sus. 29er; that has 5.5" travel - previously it was 6" but lost half an inch due to the tyre rubbing the seat tube at full boottom-out; this is fully controlled by the bottom-out adjustment of a DHX 5.0 Shock. You can see all the pics here:- https://picasaweb.google.com/112598676564367425025/06MarinWolfRidge29erUsingA26erMediumFrame?authuser=0&authkey=Gv1sRgCJSO3KmAxv-RlQE&feat=directlink

Quite simply a fantastic creation - hats off to you for having the balls and skills to create such a bike

Incredibly impressive 😀

boltonjohn - thanks. The worrying part is investing the money in the parts and wondering if you can actually achieve the end goal. I bought the frame on eBay and the giant swing arm was a surplus clearance via Fulford Cycles who were incredibly helpful in also supplying me with all the bearings, d-link, Rocker Arm and mech hanger etc. - a bunch of great guys whom I fully recommend.

Not sure how the chain stay length of a Sus. 29er can be any shorter?

Quite easy with a 4 bar, take a look at the new Whyte M-109 for instance, a full 25mm shorter chainstays than on the Giant Anthem 29er.

Though on a tandem, short chainstays would be the least of your worries geometry wise!

Looking at the first pic again, those seat angles do indeed look a tad slack. You thought about running inline seatposts instead of layback?

I see what you mean - but achieved by giving it a direct pivot at the BB and moving away from their famed quad geometry.

With regard to the seat angles the problem is I am pretty long in the legs so I do need a bit of space up front. However I did compensate for this somewhat by setting-up the forward concentric BB so that it tensions the timing chain at a rear and downward setting i.e the center of the forward BB is well to the rear of the centerline of the seat tube.

Looks fantastic. You might like to try moving the timing of the front back two or three teeth so that the stoker leads. This tends to smooth out pedaling a little and the person on the back won't feel as though they are being dragged through the pedal stroke.

I have never seen a tandem do a wheelie, so good luck lifting that front wheel 😆

diaustin - An interesting tip; so you mean that the stoker would effectively be further down the power stroke? I think I have also read about setting the timing at 90deg - but I'm not sure about that? ... and I don't think that would work if you were both out of the saddle? Any other good tips are more than welcome - thanks.

Just WOW! 😯 There's some serious work gone into that! Amazing!

You might like to try moving the timing of the front back two or three teeth so that the stoker leads.

We've tried this and didn't like it at all.
Made it harder to pedal while stood up and also harder to avoid pedal strikes.

Superb, that's a brilliant piece of garden shed engineering!
By no means intended as a criticism, but considering how much effort you've put in, I'm guessing you've addressed the issues of not being able to heat treat the frame post welding and came up with a cunning solution?

The BB height looks great, but you'll loose a lot of clearance with the big timing rings - its the front chainring that we always used to bash, so we used to run a bashring. I've now changed to 22t timing rings to maximise clearance over steps & drops. I didn't use 'proper' tandem cranks, just normal ones with pedals rebuilt and lots of threadlock. Might be worth considering as a future mod.
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You might like to try moving the timing of the front back two or three teeth so that the stoker leads

Looking forward to seeing photo's of it in action 🙂

Rob

tandemwarriors - Well I have been repairing several broken Ali Mtb frames for years and never actually had any problems and I'm still thrashing them some of them and based on prior experience I don't expect any problems. The stress on the rear seat tube would have been the prime suspect but my re-inforcing gussets either side of the Rocker Pivot are well sturdy enough.

I am definately going to experiment with the timing chain sync as you describe.

I did think about your crank system but it wouldn't work with the chainsets I had as I guess you need them without a billet pipe axle i.e not with outer bb bearings as you need to attach a right hand chainset pedal to the left-hand rear.

Bear in mind though that I do have Talas 36 forks up front, which I can rise-up to 160 - that raises the front chainring very significantly; although unlike on a solo bike, whereby you de-weight the front, it is nesessary to stop and then de-weight the front in order for them to rise-up.

I love your tandem; it seems to me that a Ventana is undoubtably the frame to have. I wouldn't however been able to make that sort of investment before convincing my partner that stoking the back of a tandem could be a lot of fun!

Thorn tandems have all the drive train on the same side and they work very nicely. It also means there is a "clean" side of the bike (useful when you are lifting etc). We used the "3 teeth advanced" method on ours - helpful if the stoker is a less powerful rider as it forces them to begin the pedal stroke and prevents them from feeling like their feet are being dragged around by the captain's pedal stroke.