[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.
[img] [/img]

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.

that's simply amazing.
Could you run the timing chain on a pair of granny rings, and shift your 2 main rings out?

neil - Googled Thorn Tandem but so far can't find a pic. of their set-up. I should mention that initially I did get some chain conflict / interference between the timing chain and rear drive chain when on the smallest cassette cogs. I cured this by grinding the mounting points of the rear timing chainring so that it sits a few mm closer to the crank arm.

My partner actually has more torque than me, she does 50 lengths breastroke several times a week at the local pool.

ir_bandito - the problem with that is we definately need the granny on our final-drive for the hills around here. I even converted our nine speed cassette to compensate for the gearing change caused by using 29er wheels. - i.e use a worn (for the purpose of re-cycling) 11-34t cassette where the chain slips on the two smaller cogs - place a single 36t cog on the freewheel - spacer ring - now place on the main xt or xtr cassette body - throw away the two smaller worn 11t & 13t cogs and now place a new 13t 'end' cog and slightly oversised lock ring. You now have a 13-36t cassette which gives you near enough the same ratio as the 11-34t on a 26er wheel. (O.K perhaps all unecessary if you went for a 10-speed 36t setup; but that wasn't in my pre-existing parts bin!).

Stoker leads by two teeth, pulling the captain through (a little). Avoid 90 degrees, I've used it on my kiddyback fine where there is a BIG difference in power), but off road, you will want to keep the pedals horizontal at times. Both sets of pedals 😉

Practice standing for the professional look, call bumps too.

Single-sided drive is a an obvious solution for a 2x10 mtb. Avoids the need for three left hand threaded cranks. In fact now we have such wide ranges at the back, it could become more common on the road too.

Some good tips - thanks.

Mad. As. A. Hatter. Bravo!

Now you've got me itching to build up an MTB tandem... enjoyed your pics... now any chance of some videos like this one? 😉

Good video. And for those wanting a shorter wheelbase tandem check this out (if I can work out how to post up a Video link).

No that didn't work - if anyone can tell me what I did wrong I would be interested to know meanwhile just paste this into a new browser and you will get there:- www.youtube.com/watch?v=5unMlXg6WL4

Heh, back-to-back tandems... wouldn't want to go off-road on one!

Video... needs the [i]http://[/i] bit?

Test:

O.K - that's the one! without posting it again just to do a test would that show in "Preview" prior to actually posting?

Fantastic!

Running timing chain on drive side is also "supposed" to make the rear bb last longer - tension from timing chain cancels out some of the tension from the rear drive chain. Must admit we used to regularly kill our Cannondale rear bb (regular lh timing chain setup). And can also second the comment that timing chain clearance can be an issue sometimes (we chainsawed a few wooden bridge drop-offs).

Tandem sold now - we both had different lead legs when descending (pedals level) so never really felt 100% comfortable - eventually held a truce where whoever was steering got to have their chosen lead leg 🙂

That is AWESOME! My lad can't ride a bike due to his cerebral palsy but we just about get by on a tandem. I need to learn to do man stuff like weldying....

[quote=[url= http://singletrackworld.com/forum/topic/interested-to-see-26er-tandem-hadtail-conversion-to-mtb-29er-full-sus-tandem/page/2#post-4295863 ]nail[/url]]without posting it again just to do a test would that show in "Preview" prior to actually posting?

Nope, doesn't show in preview... the forum software here is a bit daft like that.

Actually, I do have a question about using a Fox 26er fork... any issues with the fork offset being, well... wrong!

jonstanley - Presumably your referring to 29er forks that are built with more offset compared to 26er forks? Well if it's about foot clearance issue then I have had no problems; if it's a handling issue .... well who knows!!?? I havn't had a lot of experience of other Tandems and well it's absolutely nothing like riding a solo bike ... even the Stoker on the rear trying to steer (by habit) can be detected on the front. I will, however be chucking some 26" wheels on and also giving it a go as a 26er. But I can say that on my 29er solo bike which is a '06 Marin Wolf Ridge with a minor conversion at the rear linkage in order to take a 29er rear wheel I have converted my Fox Talas 150 RLC's 26er's to 29er simply by sliding on a set of 32 niner fork legs (with bushings in the correct position). I normally ride a size large but I did this to a Medium which gives me the same standover height with 29er wheels ...... well the end result is that I have no problems with handling and it is usually the bike I grab more often especially in bad weather as it offers so much more grip with 29er wheels.

slowrider - Member
That is AWESOME! My lad can't ride a bike due to his cerebral palsy but we just about get by on a tandem.

That's how we first discovered the mountain tandem. We were at CYB on a NATS weekend trip back in about 1996, I was riding, Sandy wasn't a rider then and was passing the time in the cafe. I came back down the final descent into the car park and could hear my wife screaming with laughter from about half a mile away! As I came out into the car park she went flying past on the back of a red cannondale tandem with moto triple clamps on the front.
Turns out it was 2 brothers, one of whom had CP, and this was how he got his biking kicks, stoking for his brother. With Sandy's ME, turns out it was a perfect solution for us too.

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

Yep, captains chainset is my old Raceface Evolve just fitted wrong way round. Strip the pedals, take the axles out, swap them round, rebuild.
Rear is on a square taper BB, though I guess ISIS or Octalink would work too, so you can fit 2 driveside cranks. I had a spare set of the same pedals, so could put a RH axle in the LH pedal. Threadlock everything and touch wood I've not had a problem with anything trying to undo itself.

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.

Rob

I wish you many miles happy thrashing

So then going back to this altering the timing between captain and stoker.
Do you not find that when you do this that neither of you can get the cranks flat while stood up and rolling?

That drives me nuts.

Strip the pedals, take the axles out, swap them round, rebuild.

[quote=[url= http://singletrackworld.com/forum/topic/interested-to-see-26er-tandem-hadtail-conversion-to-mtb-29er-full-sus-tandem/page/2#post-4296458 ]nail[/url]]Presumably your referring to 29er forks that are built with more offset compared to 26er forks? Well if it's about foot clearance issue then I have had no problems; if it's a handling issue .... well who knows!!??

Yeah... fork offset. I do know that with Santana, their road tandems have more fork offset compared to "regular" road tandems... they do it this way as apparently more fork offset lessens stoker induced steering, in addition to making the steering less sluggish. Hmmm.

they do it this way as apparently more fork offset lessens stoker induced steering

So then going back to this altering the timing between captain and stoker.
Do you not find that when you do this that neither of you can get the cranks flat while stood up and rolling?

Perhaps it would be interesting to try different sized timing rings between the front & rear?

I think you'd just end up having really bad pedal strike problems and fighting each other with which way you wanted to lean the bike while pedaling.

Just for the hell of it here's us at Brechfa on our tandem.

What's a tandem like on tight trails?

FB jnr has cerebral palsy and currently rides a trike. The back 2 wheels can be detached from the front and attached to my bike with a tag along style adaptor. The width of the rear 2 wheels preclude any narrow trails such as at the SE mtb mecca that is Bedgebury.

He gets upset that we are restricted to the family trail and wants to do the singletrack when my mate & his son branch off and do some sections of that.

Having seen this thread, I wonder if a tandem might be an option but wonder about it's steering through narrow trails?

- Rob, sorry I'm missing that one? why don't the pedals just stay with their relative cranks with lots of thread lock?

Conventional tandem chainsets have THREE left-hand threaded cranks - only the stoker drive side is a normal crank. All the others are on the "wrong" side to prevent the [url= http://en.wikipedia.org/wiki/Precession_(mechanical) ]pedals loosening[/url] under normal use. Some tandems, such as yours, use a single drive side. This means you can use conventional cranks, but may run into problems with chain overlap. SJS have always gone with this solution and used an outer chainring timing chain. My Dawes tandems use alternate drive.

As for timing offset. There is a lot of debate - see [url= http://www.thetandemlink.com/hobbes.html ]tandem@hobbes[/url] for further (endless) details. But I found that with a weaker stoker, just a couple of teeth detent was helpful for us. With the kids on the back, 90 degrees was better - this isn't off road, mind. You could try 180 degrees out of phase, just for fun. The [url= http://www.davincitandems.com/dv2.html ]Da Vinci[/url] system allows the stoker to freewheel, essentially giving arbitraty phasing.

tandemspeedstu - That's brilliant, what tandem is it you ride?

Having seen this thread, I wonder if a tandem might be an option but wonder about it's steering through narrow trails?

We've taken ours to Brechfa, Afan and Nant y Arian. Just to give you an idea if you've ridden any of them.

[url= http://farm3.staticflickr.com/2547/3849013327_18b80671f4.jp g" target="_blank">http://farm3.staticflickr.com/2547/3849013327_18b80671f4.jp g"/> [/img][/url]
[url= http://www.flickr.com/photos/sheldona/3849013327/ ]Mincy[/url] by [url= http://www.flickr.com/people/sheldona/ ]sheldonattwood[/url], on Flickr

It's one of JD Cycles home brand frames with Lyric and Hope Moto's on.

[url= http://farm7.staticflickr.com/6208/6039241084_f4c14df794.jp g" target="_blank">http://farm7.staticflickr.com/6208/6039241084_f4c14df794.jp g"/> [/img][/url]
[url= http://www.flickr.com/photos/stu-b/6039241084/ ]110813_132922[/url] by [url= http://www.flickr.com/people/stu-b/ ]singlespeedstu[/url], on Flickr

FB-ATB - I have ridden Bedgebury three or four times on a nornal bike; from memory, apart perhaps from a couple of small sections I rekon we could do it on the tandem with relative ease; but that as I say is only from memory (but I wouldn't attempt the black section).

We've done some pretty tight trails near us, it takes some work but they're doable. No video footage sadly. For instance, we've ridden this hairpin - the zig zag bit in the middle, going from right to left downhill.

https://maps.google.co.uk/maps?q=mellor&hl=en&ll=53.383527,-2.029542&spn=0.005177,0.009645&sll=52.8382,-2.327815&sspn=10.7466,19.753418&t=h&hnear=Mellor,+United+Kingdom&z=17

Going down that, the rear wheel stayed still while the front end wnt all the way round the outside.

If you're close to us (Marple) then you;d be welcome to give the tandem a go

I've ridden at Afan, but a while ago pre kids, so the memory is a bit hazy!

I'll have to pay more attention next time I'm at Bedgebury to possible sections we could divert from the family trail to.

Got a while to go yet as FB jr has only just had his 6th birthday and has to improve his balance before he can sit on a saddle without any side supports that his trike currently has!

Neil

why don't the pedals just stay with their relative cranks with lots of thread lock?

singlespeedstu - Member
So then going back to this altering the timing between captain and stoker.
Do you not find that when you do this that neither of you can get the cranks flat while stood up and rolling?

just 1 or 2 teeth we don't really notice when level pedals, but Sandy will often shout that she wants to change lead foot.

nbt
thanks for the offer, we're darn sarf and jnr needs a bit more growing to do before we can take you up on that! And possibly Mum will need some convincing as he tipped his trike over at buckmore park kart track under my supervision.

I had to learn to ride the opposite foot forward to accomadate the stoker. 😆

[quote=tandemwarriors ]
just 1 or 2 teeth we don't really notice when level pedals, but Sandy will often shout that she wants to change lead foot.

We have this issue as we have opposite lead feet: I'm driving, so my lead foot is forward, if I try to go the other way then we're more likely to crash. We also struggle a bit on corners as I quite often drop the outside pedal whereas Mrs NBT will just coast round pedals level most of the time. Had one incident last week where we got to the bottom and she said "I normally take a different line over to the right"

"I know," I said, "I could feel you leaning that way to get me over there!"

We also struggle a bit on corners as I quite often drop the outside pedal whereas Mrs NBT will just coast round pedals level most of the time

Had one incident last week where we got to the bottom and she said "I normally take a different line over to the right"

"I know," I said, "I could feel you leaning that way to get me over there!"

FB-ATB - Member
What's a tandem like on tight trails?

that question that non-tandemers always ask - "but you can't steer at the back". Oh yes they bloody well can!!!!

I was quite shocked by how much influence the stoker had on steering the first time we had a go on a test tandem.

[quote=[url= http://singletrackworld.com/forum/topic/interested-to-see-26er-tandem-hadtail-conversion-to-mtb-29er-full-sus-tandem/page/2#post-4297038 ]nail[/url]]hmmm interesting do you think it would also reduce the possibility of that dreaded tandem steering wobble at low speed?

...

I havn't tried altering the timing yet so I personally can't comment but my partner is used to riding a slower cadience than me and she is always suggesting I change gear.

For regular road half-bik, err, solo bikes... fork offset is 40~45mm. Co-Motion has 50mm on their tandems and Santana are "the benchmark" at 55mm. Long version of handling differences over at Tandem Geek's blog: http://tandemgeek.wordpress.com/2011/05/15/2011-santana-beyond-review-beyond-sublime/

So anyway, back to MTB tandems. If memory serves, a 26er Fox 36 uses 39mm offset? With 29er wheels, that's a fair bit less trail. "Old skool" 29er forks have 44mm and current 29er forks have 51mm. The £££ Manitou Dorado is 50.something mm... and the new Cannondale Lefty "as strong as a DH double crown" Supermax is 53mm (saw it listed with 60mm offset as well?!). Not knowing if you're a bottomless pit of money, I guess it would be interesting to see how a Fox 34 29er fork with that extra 12mm offset makes much/any difference?

As for peddling cadence... might be worth a shot at trying out proportional crank lengths? Longer (175~180mm) cranks for the captain, so can't spin as fast... and shorter ones (<170mm) for the stoker, making it easier for them to spin?

[quote=[url= http://singletrackworld.com/forum/topic/interested-to-see-26er-tandem-hadtail-conversion-to-mtb-29er-full-sus-tandem/page/3#post-4297432 ]tandemwarriors[/url]]Yep, which answers that question that non-tandemers always ask - "but you can't steer at the back". Oh yes they bloody well can!!!!

Indeed, even when the stoker at the back is just over 5ft and a lithe 105 lbs "ready to ride"! Am tempted one day to get them to captain instead, if it weren't for the bike-fit issues...

[shameless plug]
if anyones interested in doing the fox fork 26 to 29 bodge I'm selling some brand new Fox f29 lower legs that have new seals and bushings fitted..
[shameless plug ends]
top thread as well 😀