Dahon Jetstream conversion

[cwah]

this one does seem even simpler:
http://www.aliexpress.com/item/Mountain-bike-stem-lengthen-riser-increased-device-elevator-riser-elevator-20/1540934804.html

but may not make my bike very appealing. But thinking about it.. It would be perfect for folding ability.

And construction does seem robust.

Is the 28.6mm compatible? If so, I'm going to get it.

Thank you

 

[selrahc1992]

this one does seem even simpler:
http://www.aliexpress.com/item/Mountain-bike-stem-lengthen-riser-increased-device-elevator-riser-elevator-20/1540934804.html

but may not make my bike very appealing. But thinking about it.. It would be perfect for folding ability.

And construction does seem robust.

Is the 28.6mm compatible? If so, I'm going to get it.

Thank you

the aliexpress one is certainly highly original, but do you trust that hinge to take all the torsion of throwing ones weight forward against it while braking on a steep descent? I have a friend who has a kalkhoff tasman with what seems to me the perfect low key folding handlebar, will check name next time I see her

 

[Urbanbiker]

Hi, I am new to the forum. @cwah like the SR Suntour suspension fork. I want to do the same, would you be kind enough to guide me what bits(Crown etc) I need to convert the current headset to adapt this suspension fork? Regards.

 

[cwah]

Hey yes I installed it but haven't tested... as I had 1 battery stolen and 1 motor non working... I'm not able to do the test on my bike yet.... I'll do a post as soon as I have either a new battery or the motor repaired...

 

[cwah]

Finally how it looks now:

It doesn't ride too bad, however it isn't as stable as my 26" mountain bike at 25mph... Hopefully the way I created my battery pack allow me to swap it between bikes

I wonder if it's normal? Ideally I'd like to only get a folding bike. It's more compact, saves space and has more torque....

Or maybe I should stick to the bigger bike? Or maybe change my 26" bike with 20" wheel?

 

[trex]

I'd lace a DD motor to a 24" rear wide rim for your 26" bike.
how fast can you ride with the Dahon?

 

[cwah]

it goes up to 30mph.. but lack stability at that speed.

Torque is much better than on my 26" wheel that's why I'm considering changing my bigger bike to 20" wheel? 24" may not make much difference.

Why is it lacking stability? I don't understand

 

[trex]

...
Why is it lacking stability? I don't understand

the moment of inertia of the wheels is proportional to the square of wheel's diameter.
I reckon 24" is about best compromise for 25mph-30mph.

 

[cwah]

Why motorbike have small wheel then? they go superfast but their wheel are not massive at all!!

There must be something else in factor??

 

[Deleted member 4366]

The lack of stability is probably due to the different geometry of the new fork. As an experiment, you could try it with the forks on backwards. You only need to loosen and rotate the stem.

 

[cwah]

but the fork is as high as the previous one so it should be ok? I can try moving the fork backward but i don't think it will make much difference

How do I make sure geometry is right?

 

[Deleted member 4366]

Have a read of this:
http://calfeedesign.com/tech-papers/geometry-of-bike-handling/

Your steering axis hadn't changed, except that if your steering head is a different height ftom the ground, it can make a small difference. The thing that has changed is the off-set (rake), which then affects the trail. The bigger the trail, the more high-speed stability you have at the expense of nimbleness for low-speed turns..

It's very difficult to measure these things. The only thing I can suggest is to find a photo of a standard Jetstream taken from the side, then take a similar photo of yours and adjust the size until you can lay one photo on top of the other so that frames are directly on top of each other? You should then be able to see any difference in the wheel position.

The other thing that affects stability is the adjustment of the steering head bearings - too tight or too loose. If you hold the front brake on and push the bike forwards and backwards, and you can feel anybmovement in the steering head, they're too loose. If you lift yhe wheel and the bars can't flop ftom side to side, they're too tight.

 

[cwah]

is the conclusion to get a higher rear shock to compensate the trail angle?

 

[cwah]

My spring keeps bottoming up when I go on small bumps:

http://www.tesco.com/direct/sr-suntour-xct-jr-20inch-suspension-fork-255mm-ahead-black/131-8410.prd?skuId=131-8410&pageLevel=sku
It does feel that the spring isn't strong enough? I keep turning the preload on either side and I can't see much difference. Have I missed something?