Dahon Jetstream conversion

[cwah]

Hello all,

I have changed the fork of my dahon jetstream to allow front disc brake and better suspension:

It doesn't look as nice as I hoped... so I have few questions:
- Would the frame hold the weight with the new geometry? It does look like a lot of weight will be managed by the middle of the frame and I fear it may break someday in the middle?
- Is it better to have 20" or 26" front wheel? The fork is for 20" wheel
- The bottom of the fork doesn't completely fit inside the frame (it ends wider), is that normal? And what can I do?


Thanks guys

 

[Deleted member 4366]

There's no extra weight on the frame. It's all on the wheel, which can easily take it. It looks awesome. Can we see some more photos from the side in the daylight?

 

[Deleted member 4366]

Just thnking about it, I think you've made a mistake. The steerer tube is designed to have the lower bearing at the bottom of the steerer tube where you have some spacers. Where you have it, the tube is slightly narrower, so there will be some play in the bearings, which might affect the steering. You should remve all the spacers from below the seering head and put them above it.

20" wheel would probably be best, but they're not easy to find with a disc hub, so if you can't find one, dismantle the hub from an unused 26" wheel (or buy a new hub) and build it onto a 20" BMX rim. It would look even more awesome if you had matching wider BMX rims front and rear providing that there's enough space for a wider BMX tyre in the back. That would give a lot more grip too.

 

[cwah]

In endless sphere they advise to completely change the fork as it is likely to lead to a catastrophic failure:
http://endless-sphere.com/forums/viewtopic.php?f=3&t=65560&p=985597#p985597

Shall I listen to them and find another fork?

 

[Deleted member 4366]

I thought you had put spacers under the steering head, but now I can see in the bigger ES photo that you have a tapered steerer. Although it's not right, I can't see any reason for it to fail. The lower bearing piece will sit tight on the taper, so you won't get the problem I mentioned before. The only thing that I can think of is that the front wheel is a long way from the steering head, which gives it more leverage under braking. The steering head is well braced by the box section frame, so the frame should be OK. I'm pretty sure that the forks will be strong enough too, so I reckon it should be OK. To be sure, you should check the welds that join the frame to the head tube from time to time for as long as you have the bike, because they might eventually crack. Once cracks start, doom will come soon after.

 

[Nealh]

I don't like to criticise but this just looks wrong. 1 1/8" head tube requires 1 1/8" steerer tube not tapered 1 1/2" - 1 1/8". Obviously Cwah has not done his home work and bought a fork with the wrong steerer tube, albeit that it is for a 26" wheel it would look a bit better if it sat on the crown race as it should. I also have my doubts as to whether the steering will handle that well as the tapered tube angle will not suit the lower bearing seat angle, all of the pressure on the lower bearing race will be on the outer edge instead of across the bearing race and I can see premature wear or malfunction being the issue. In my eyes it is a poor choice and a poor decision.

 

[cwah]

I don't like to criticise but this just looks wrong. 1 1/8" head tube requires 1 1/8" steerer tube not tapered 1 1/2" - 1 1/8". Obviously Cwah has not done his home work and bought a fork with the wrong steerer tube, albeit that it is for a 26" wheel it would look a bit better if it sat on the crown race as it should. I also have my doubts as to whether the steering will handle that well as the tapered tube angle will not suit the lower bearing seat angle, all of the pressure on the lower bearing race will be on the outer edge instead of across the bearing race and I can see premature wear or malfunction being the issue. In my eyes it is a poor choice and a poor decision.

I bought this one and it only mentioned 1 1/8" steerer tube in the description. it never mentioned 1/2" anywhere:
http://www.ribblecycles.co.uk/sp/mtb-bmx-bike/forks-mtb-rock-shox-xc-30-tapered-forks-canti-bosses/rockform305

 

[mfj197]

I bought this one and it only mentioned 1 1/8" steerer tube in the description. it never mentioned 1/2" anywhere:
http://www.ribblecycles.co.uk/sp/mtb-bmx-bike/forks-mtb-rock-shox-xc-30-tapered-forks-canti-bosses/rockform305

No it doesn't - but it does mention "tapered" in the title which refers to the steerer tube. You might be able to return it though as the listing is not clear.

Michael
Edit: The XC30 is available with straight steerer tube options as well. See here.

 

[cwah]

I don't think I can return it because I started to trim the top tube

I was thinking to sell it back in ebay... or somewhere else

Would this one work for SURE?
http://www.winstanleysbikes.co.uk/product/64926/RockShox_XC30_TK_Coil_2015_Forks_RS8627000

 

[cwah]

Or maybe I sell this dahon and get a proper 26" folding bike such as a montague?

 

[Nealh]

I bought this one and it only mentioned 1 1/8" steerer tube in the description. it never mentioned 1/2" anywhere:
http://www.ribblecycles.co.uk/sp/mtb-bmx-bike/forks-mtb-rock-shox-xc-30-tapered-forks-canti-bosses/rockform305

The title does clearly state tapered although the description says 1 1/8" steerer, though clicking and viewing a zoomed piccy it cleary shows they are 11/8" tapered.
After being patient I recently acquired Rockshok Recons with remote lockout on ebay.

 

[Nealh]

http://www.ebay.co.uk/itm/rock-shox-tora-289-forks-/251763966485?&_trksid=p2056016.l4276#ht_108wt_1190

These would fit Cwah steerer length 220mm any good only 20hrs to go at 99p & £9.99 p&p, might have to bid against the rest of the forum now its been posted here . Steerer tube will clean up ok with some 3 in 1 and fine wire wool and they are disc mount only.
p.s.
Just had a look again at the poor quality pic, description says v.g.c but chrome stantions look like they may have rust speckles on them, but on reflection I think its just the poor piccy that makes it look that way.

 

[Deleted member 4366]

Cwah, have you tried it yet? I think you just ride it for a bit to see how it goes. Despite what people say, I still can't see anything that would give a problem other than maybe the steering geometry, which would show itself as soon as you ride the bike. The steering head bearings are properly seated and loaded the way you have it, so they shouldn't break. The bottom bearing inner will be wedged on the taper just like it wedges on the normal taper at the botom of the steerer tube. There's a slight question of whether it's sitting straight without the edge of the fork crown to hold it square, but I think it would self-centralise if it were crooked.

 

[trex]

cwah, you've got to take that fork off.
It does not only look totally wrong on the bike but also looks dangerous.
Just think that the front brake is only as good as how the headset is fitted.
If the bottom crown race moves, the whole of the headset will slacken, the bearing will pop its balls and you'd be goner.

 

[Cyclezee]

Hi cwah,

To me this looks like an accident waiting to happen.

If it were me I would abandon this project, restore the Dahon to as near original condition as possible and get another bike.
Assuming it is a large wheel folder that you want/need a Montague, Dahon Cadenza or Espresso, Tern Joe would be good choices.

Whatever you decide, I hope you have good Christmas.

 

[Deleted member 4366]

If the bottom crown race moves, the whole of the headset will slacken, the bearing will pop its balls and you'd be goner.

How can it move? It's wedged on the taper.

 

[trex]

how can you trust a piece of steel 1.5mm thick with a hole 28mm wide not to rock when violently pushed from one side?

 

[Nealh]

Did you use a crown race Cwah ?

 

[cwah]

No I didn't use a crown race and I don't know what it is

What about this one instead of the tora?
http://www.winstanleysbikes.co.uk/product/64926/RockShox_XC30_TK_Coil_2015_Forks

The other fork doesn't seem so nice and do not have great review either

 

[Nealh]

No Crown race you will hit the deck.

http://www.wiggle.co.uk/ritchey-wcs-crown-race/
Crown race example some are universal and some bearing or makes will need a specific race.

The Crown race is a part of the head set for the steerer tube, it is a ring that sits on the lower end of the steerer tube some are split to make fitting easier. Once fitted ( the correct one for your head set should be on your origanl forks you removed) it seats against the lower bearing which has a 45 degree seat angle or some are 36 degrees, in turn this gives a free and easy steering action hence why you should are able to ride hands free.
With out one fitted the steering will be very torqy,stiff and unpredictable eventually leading to loss of direction and control, riding hands free will be virtually impossible and if you try it you will end up hitting the tarmac.

The RS Tora fork is the next level up from the popular entry level RS Dart so should be a bit better, reviews I find can be bias against some of the lower end components soley because of price.