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Samb76 10-27-06 06:24 AM

New project - re-tuning a jestream P8
 
Hi,

I wondered if anyone had experience of replacing the rear shock and forks on the jetstream P8?
I have found the suspension lacking in suppleness to say the least, and a softer setup at both ends may result in better handling.
The frame seems really well made and seems worth re-fitting. Plus, I've just bought an impulse P24 to cannablise for the dual drive transmission.

The main problem seems to be the standard rear shock length of 125mm, and the aftermarket minimum shock size of 165mm. Thats going to change the head angle a bit! Maybe I can adjust the sag in the new shock to compensate.

For the front end, a different fork may yield better results and allow a disc brake / 100mm front hub. http://www.german-a.de/shop/

What do you think?

dannyg1 10-28-06 04:17 PM

The suspension on the Jet P8 isn't meant to be a plush ride, it's meant to offer the road feel of a suspensionless bike and take care of jolting shock absorbsion. The handling can be improved by mounting a stem to the handlepost and also lowering the bars (you'll most probably have to do this as custom work and you'll have to be very careful with how you implement the changes, as this stuff gets very dangerous, very quickly); Dahon offers an adjustable stem that does some of what you need, a Syntace accessory I believe,

The rear shock can be replaced with the Cane Creek AD5 that Dahon uses on the Jetstream XP and running that 'plushly' will be instructive as to the opening sentence of this reply. It does fit in a 'plug and play' way though.

Last, replacing the fork with one of the better German:A designs would be a great idea, except for the cost. The 20" models on the site start at around $1100 and go up from there. You'll have to ask them if they can make the Dahon propietary internally threaded steerer tube for you or if they'll need to take the one from your fork and place it on theirs.

I'll post pictures of some of these exact modifications, done to a 2005 Jet P8, soon.

DG1

Samb76 10-30-06 05:36 AM

Interesting -thanks for your comments.

I hadn't yet worked out that the steerer of the fork was unusual - this is useful information.
I already bought the syntace stem, but have not yet fitted it - currently I am using Bike Friday H-bars which are my favourites so far. Unfortunately its pretty much impossible to get spares for dahons here. I almost had to buy a new bike just to get some mudguards!

With regard to the geometry I will just have to try a standard shock to see if it works or not. My idea was that I could get enough float from the new set-up to take out small vibrations and possibly remote lock out.
What I did was buy a really cheap 165mm shock from ebay to fit and when it arrives I will see the effect on the steering. An extra 40mm at the back will change the head angle by one or two degrees and this should be okay as the jetstream feels quite relaxed in the steering. The main worry is the increase in the already high bottom bracket - at least I can pedal through tight corners!

If you have any pics of a modified jetstream, it would be great to see them.

Cheers, Sam

dannyg1 10-30-06 06:00 PM

5 Attachment(s)
Here's a bunch of quick photos of the upgrades I've done to my P8. The stem conversion required the purchase of a new handlepost, to begin. I then had to cut a shim to fit the upper neck of the stem so that it wouldn't rock side-to-side in the post, and would clamp down with sufficient force to prevent any pendulum action, above the stem clamp chuck.

The rear shock needed to have its shims filed to fit, side-to-side in the space provided by the rear triangles mount. The titanium bolts on the pivot hinge needed the axle to be rethreaded from 1.25 to 1.0.

The titanium bolt upgrade on the front fork is something i wish that I'd avoided as I may have ruined my fork doing it.Each bolt on the rear of the fork is held in place by a set screw, which MUST be removed before you attempt removing the key bolt. When you replace these bots you'll have to drill the new ones in situ, and then thread the titanium channel you've created. Titanium does not like to be threaded by high tensile steel taps and I shattered the one you see on the left side of the fork. Being HT steel, anything that'll cut through will wreek havoc on the aluminum and steel surrounding it. So, it sits, defying any attempt I've made at removal so far. Conidering how sharp the edges of the tap are, I'm thinking that it's only a metter of time before it bigins to wear through the axle itself and Dahon, for unexplained reasons, won't supply any parts for the fork itself. At some point in the nearer future, I'm going to have to buy another entire fork.

Wanna sell me yours?

DG1



Originally Posted by Samb76
Interesting -thanks for your comments.

I hadn't yet worked out that the steerer of the fork was unusual - this is useful information.
I already bought the syntace stem, but have not yet fitted it - currently I am using Bike Friday H-bars which are my favourites so far. Unfortunately its pretty much impossible to get spares for dahons here. I almost had to buy a new bike just to get some mudguards!

With regard to the geometry I will just have to try a standard shock to see if it works or not. My idea was that I could get enough float from the new set-up to take out small vibrations and possibly remote lock out.
What I did was buy a really cheap 165mm shock from ebay to fit and when it arrives I will see the effect on the steering. An extra 40mm at the back will change the head angle by one or two degrees and this should be okay as the jetstream feels quite relaxed in the steering. The main worry is the increase in the already high bottom bracket - at least I can pedal through tight corners!

If you have any pics of a modified jetstream, it would be great to see them.

Cheers, Sam


dannyg1 10-30-06 06:33 PM

http://i121.photobucket.com/albums/o...10_06small.jpg

dannyg1 10-30-06 06:34 PM

http://i121.photobucket.com/albums/o...shock10_06.jpg

dannyg1 10-30-06 06:35 PM

http://i121.photobucket.com/albums/o...ockupgrade.jpg

http://i121.photobucket.com/albums/o...8seatclamp.jpg

dannyg1 10-30-06 06:38 PM

http://i121.photobucket.com/albums/o...temsmaller.jpg

Samb76 10-31-06 07:16 AM

Thanks Dannyg1,

The pictures are very interesting. I can see that this is not a cheap project!
I presume the wheels are from a Helios XL - are they worth the extra expense? Do you have an idea of the new weight of the bike? I guess that you have saved a couple of kilos.

Actually the fork bolts on my fork have rounded at my first attempt at adjustment - I can see that their replacement is not going to be simple.
I'll see what the options are to transfer the steerer to a new fork.

The new rear shock arrived today. I'll fit it tonight and write my impressions after the journey to work.

dannyg1 10-31-06 11:21 AM

The Rolf wheels are, to me, a required upgrade and are worth the cost. These particular wheels are from and older Helios SL (2003/2004) or from a Helios XX, as they sport the DT Swiss/Hugi rear hub which I find much smoother rolling, but a good bit heavier, than the current American Classic hubbed version.

Here's a link to a thread that you probably need to read; I'm sure you'll find it veryinteresting anyway:

http://www.dahon.com/forum/index.php?showtopic=2953&hl=

DG1

Leisesturm 10-31-06 01:13 PM

I urge Samb to read Danny's comments again. I think he is dead on when he mentions that bicycle unlike automobile suspension cannot hope to delive the same level of comfort. The car or motorcycle engine has horsepower to spare compressing and uncompressing shock absorbers, human powerplants do not. Next, safety. Motorcycles publish rake and trail figures measured to tenths of an inch. A change of 1 degree in head tube angle is 'news'. Racing motorcycles continually skirt the boundary region of sporty handling/dangerously unstable design. Folding bikes are built with minimal trail and are not unlike helicopters in their performance envelope i.e. doable but you better stay on your p's and q's. A longer shock will quicken already dangerously quick steering and cannot be an advisable modification. With enough looking around a proper length shock can be found, after all the OEM found one.

H

Samb76 11-01-06 05:52 AM

2 Attachment(s)
Hi,

I fitted the new shock last night.
It is a cheap item with no damping whatsoever, but a softer spring and a wide range of preload adjustment that actually changes the length of the shock.
I was able to run the shock between 125mm (standard for the jetstream) and 165mm (smallest common aftermarket size).
On my ride to work this morning I was able to keep adjusting the length of the shock and experiment with how the bike handled.

Steering: I found that the quickness or responsiveness of the steering felt relatively unchanged by the shock length - largely I suspect because of the increased weight on the bars. Corners felt the same and so did hands free riding.

Weight distribution: With the shock at its longest the bottom bracket height increases and the front section of the bike 'leans forward' compared to standard. I found that this was the biggest perceived difference. Actually I like this change because the increased weight on the fork forces it into working. Also the seatpost angle is increased and I felt that this pedalling position was more efficient on hills. However slightly more weight was felt on the bars in this position. I always felt that the effective toptube of the jestream is too short and the change of riding position seemed to increase this feeling.

Effect of the new shock: Because there is no damping on this shock its difficult to predict how a more expensive shock will work. Certainly the increased weight on the front end brought the best out of the fork. The softer spring of the new shock improved ride quality on uneven surfaces a great deal - actually showing how bad the original shock is at this. However it is much easier now to unsettle the rear end if you pedal out of the saddle or throw your weight around. How much damping will help I don't know, but suspension is always a bit of a compromise.

Will I fit a 165mm shock? At the moment I'm not sure......certainly the handling is not dangerously changed. I am a little concerned by the height of the bottom bracket which was very high in the first place. I think I would try to get a shock with as much float and sag as possible and try to reach a compromise. I understand the limitations of bicycle suspension - I have been riding Moultons, Bromptons and birdys for a few years now. Actually they do a better job of suspension than the jetstream and I would like to move my bike in that direction. However it could be possible to produce a better solution given the flexibility of the Dahon's design......

Also I would like to address the problem of lengthening the stem!

The two photos show the effect of a relatively long and short shock on the bike.

Cheers, Sam

dannyg1 11-01-06 08:13 AM

I also own a Birdy and it's interesting that we disagree which of the two bikes is better at shock absorbtion. In my experience, the Birdy, while offering a mildly smooth ride, has a problem with what I call 'suspension reverb'; once a note is struck, it just keeps on bouncing, and bouncing. The Dahon, when it's set to a more rigid rear shock pressure, feels more like a hardtail in that it still transmits much of the road chatter that communicates your current state of tire contact, but takes the major shocks in stride. The Birdy rides more like an American car, the Dahon more like a sportscar. The Birdy is easier on my hands but the tradeoff less at-speed control after you've hit a bump.

When my Jet P8's rear shock gets low on air, I notice a very slight lateral movement/play that I find extremely disconcerting, especially if I stand on the pedals of the bike (powering up a hill, fjording an obstacle, bracing for a large shock downhill and at speed). The Birdy doesn't suffer from this as much but I find that I barely ever stand on the Birdy as it freaks me a bit too much when I do, to feel comfortable trying it again. Smaller wheel thing I suppose.

There is one thing that I've realised more clearly from this conversation: The Dahon Jet P8 could be improved by offering more lateral stiffness at the shock absorber joints. If that were done well, an adjustable progressively damped oil shock would serve both our purposes well. The Birdy would also be much improved by oil filled shocks, as the Japanese modification crowd has been trying to do successfully for the last couple of years, without much luck, but they'ld have to be tiny.

Another thing I'm finding is that I care alot less about how light the bike is as I focus my attention on how well it works.

DG1

timmhaan 11-01-06 11:57 AM

your bike is looking really good! very agressive and fast looking.

carloschan 11-01-06 01:38 PM

Hi Sam, Danny, I just bought a Dahon Jetstream P8 and am delighted with it. I see you guys are way ahead on modifying the bike and am very gratefull for all the information you have shared. I'm venturing to ask you some basic questions:-
1. The P8 came fitted with 1.5" Schwalbe Marathon Racer tyres (max.85psi). I'm toying with the idea of changing them for lighter, narrower tires like the Stelvio 120 psi to get a faster road ride. Any advice?
2. I use SPD's on my road and MTB bikes and really miss the sense of safety and the all round workout for my legs. Are there any folding SPD's or equivalent on the market. Which do you recommend?

dannyg1 11-01-06 06:59 PM


Originally Posted by timmhaan
your bike is looking really good! very agressive and fast looking.

If you're speaking of my P8, thanks very much. It's still a work in progress but it's pretty close to done.

DG1

dannyg1 11-01-06 07:07 PM

I'd try a Stelvio on the front, just to see first. Besides being expensive, they're a far more fragile tire and many people don't like them for that. So long as you avoid road obstacles with keen attention, they work fine and will last four months or so. I'd say that your first will probably only last you two months or so. I realise that that's not much time for expensive tires but you should know what you're buying. I ride mine around 14 miles a day.

Continental also makes a light tire in the 406 size and you may want to try that, but the reality is I've found these to be vaporware.

SPD's that have removable axles are available through ThorUSA.com from MKS. I don't have alot of trouble with my pedals protruding because they're pretty small. Smallest will be Bebop or Speedplay pedals, should you not want the MKS removables.

DG1


Originally Posted by carloschan
Hi Sam, Danny, I just bought a Dahon Jetstream P8 and am delighted with it. I see you guys are way ahead on modifying the bike and am very gratefull for all the information you have shared. I'm venturing to ask you some basic questions:-
1. The P8 came fitted with 1.5" Schwalbe Marathon Racer tyres (max.85psi). I'm toying with the idea of changing them for lighter, narrower tires like the Stelvio 120 psi to get a faster road ride. Any advice?
2. I use SPD's on my road and MTB bikes and really miss the sense of safety and the all round workout for my legs. Are there any folding SPD's or equivalent on the market. Which do you recommend?


dannyg1 11-01-06 07:10 PM

Not cheap at all. I'd say that I saved around 4.5 - 5 lbs. Probably right in the 18.5 lb range at the moment. If you remove the set screws, you should have alot of trouble getting the screws out, even stripped. You'll find they're aluminum though and installing titanium there is actually a good 1.5 oz. heavier. It looks quite nice though....

DG1


Originally Posted by Samb76
Thanks Dannyg1,

The pictures are very interesting. I can see that this is not a cheap project!
I presume the wheels are from a Helios XL - are they worth the extra expense? Do you have an idea of the new weight of the bike? I guess that you have saved a couple of kilos.

Actually the fork bolts on my fork have rounded at my first attempt at adjustment - I can see that their replacement is not going to be simple.
I'll see what the options are to transfer the steerer to a new fork.

The new rear shock arrived today. I'll fit it tonight and write my impressions after the journey to work.


jur 11-01-06 08:55 PM

What is the travel on the fork shock?

Which is the better option: The shock or the pantour hub?

dannyg1 11-02-06 03:19 AM


Originally Posted by jur
What is the travel on the fork shock?

Which is the better option: The shock or the pantour hub?

There's no contest between the two. The fork is a ridiculously better approach. The Pantour is an interesting option but has a tendency to stick to a side after a hard turn and your brake shoe will end up catching the underside of the rim just once, and you'll not like the loss of your front brake I'll bet. I'd love it if the Pantour were better, because it's so much lighter, but the negatives, and its lack of any real suspension travel make it an unworkable choice for me.

DG1

Samb76 11-02-06 06:02 AM


Originally Posted by dannyg1
When my Jet P8's rear shock gets low on air, I notice a very slight lateral movement/play that I find extremely disconcerting, especially if I stand on the pedals of the bike (powering up a hill, fjording an obstacle, bracing for a large shock downhill and at speed). The Birdy doesn't suffer from this as much but I find that I barely ever stand on the Birdy as it freaks me a bit too much when I do, to feel comfortable trying it again. Smaller wheel thing I suppose.

There is one thing that I've realised more clearly from this conversation: The Dahon Jet P8 could be improved by offering more lateral stiffness at the shock absorber joints. If that were done well, an adjustable progressively damped oil shock would serve both our purposes well.
DG1

Yes, I noticed the lateral play last night - there is quite a lot. It is probably a function of the rear shock and its crap bushes.
I also started noticing the amount of play in the front fork :(

With regard to the front end, I've managed to find a seller for a syntace low-profile type bar from a speed pro which should be interesting to try out.


Originally Posted by carloschan
1. The P8 came fitted with 1.5" Schwalbe Marathon Racer tyres (max.85psi). I'm toying with the idea of changing them for lighter, narrower tires like the Stelvio 120 psi to get a faster road ride. Any advice?

My bike originally came with standard Stelvios. I didn't like them. Actually the Marathon Slick was found to have better rolling resistance in real world conditions (tested by Mike Burrows) than the standard stelvio which is pretty bad for some reason. However the special 'stelvio light' (with the orange sides) is much, much better although I found the puncture resistance disappointing.
I currently run Vredstein S-licks which I really like and are a good compromise between speed and durability/ shock absorption at 1.35" wide and a really supple sidewall.
If I were you, I'd keep the Marathons.

Fear&Trembling 11-02-06 07:43 AM


Continental also makes a light tire in the 406 size and you may want to try that, but the reality is I've found these to be vaporware.
Try the Conti Contact Sport (not the GP) - it is heavy but very durable and resists puntures very well.


Which is the better option: The shock or the pantour hub?
Well there are a number of factors to take into account - but my experience of the Pantour has not ben favourable (however, I accept most of the responsibility for this - poor research before buying). Others seem to find the 12mm movement good at diminishing trail buzz, but it doesn't do much for bad road conditions. However, I think with some more tweaking they could have an excellent product on their hands. The Q fork appears much more compliant, with more suspension movement, but not sure how it copes with heavier riders...

The

P8 came fitted with 1.5" Schwalbe Marathon Racer tyres (max.85psi). I'm toying with the idea of changing them for lighter, narrower tires like the Stelvio 120 psi to get a faster road ride. Any advice?
Primo Comet Kevlar, Marthon Slick, Scorcher or the S-lick are all good alternatives.

@Dannyg1 - Nice set-up. The stem looks like more of a bodge than mine - well done! Very nice Pulsion cranks and Paul brakes by the way.

The bottom bracket does look high (the BB height appears higher than on a Birdy) and you are right over the crank juding by how far forward you are on the saddle rails. Have you done this to aid the suspension movement, or do you prefer this riding position?

LittlePixel 11-02-06 09:08 AM

Your P8 is crying out for a blackbird-stealth matt black makeover. It's so knobbly with all the little bits of detail... :)

dannyg1 11-02-06 04:26 PM

Interesting note on the tires. I'll keep that in mind on my next go round with them.

On the fork, when you describe play in the front, I'm worried. The bike as it is, is rock solid, so long as I keep the pressure in the rear shock high. The play I'm speaking of is a tendency of the rear end of the bike to tweak laterally under heavy pedalling force when the shocks air pressure is low. Also, If the shock doesn't have enough air in it, it'll dive a bit as well, under heavy pedal force. The fix would be to either widen the mounts the shock sits within - top and bottom -, mount braces on either side of the shock and/or stiffen the shock body itself, mechanically, so that it cannot flex.

If you're having problems with rear end stiffness with the standard spring shock mounted, check that your mounting bolts are good and tight and that the mount (both the frame holes and those on the shock itself) is unworn on both top and bottom.

On the front, any play you're feeling is probably due to headset adjustment problems as the fork is designed in a way that just doesn't flex. The internal headset is unforgiving of poor adjustment and I urge you to either fix this yourself quickly, or get someone to do it really soon.There's a large hex bolt you'll see in the middle of the H'post assembly (once you open the post and look down. It's stainless steel and big), tighten that really tight and then tighten the collar bolt (also pretty large) on the posts mount ring (which attachs the collar to where that monster bolt is) a bit more. That should cure any residual play in the headset. If not, you'll probably want to diagnose what's wrong. It'll be good for you to see how it's put together anyway.

DG1




Originally Posted by Samb76
Yes, I noticed the lateral play last night - there is quite a lot. It is probably a function of the rear shock and its crap bushes.
I also started noticing the amount of play in the front fork :(



My bike originally came with standard Stelvios. I didn't like them. Actually the Marathon Slick was found to have better rolling resistance in real world conditions (tested by Mike Burrows) than the standard stelvio which is pretty bad for some reason. However the special 'stelvio light' (with the orange sides) is much, much better although I found the puncture resistance disappointing.
I currently run Vredstein S-licks which I really like and are a good compromise between speed and durability/ shock absorption at 1.35" wide and a really supple sidewall.
If I were you, I'd keep the Marathons.


dannyg1 11-02-06 04:44 PM


Originally Posted by Fear&Trembling
Well there are a number of factors to take into account - but my experience of the Pantour...snip... However, I think with some more tweaking they could have an excellent product on their hands. The Q fork appears much more compliant, with more suspension movement, but not sure how it copes with heavier riders...

@Dannyg1 - Nice set-up. The stem looks like more of a bodge than mine - well done! Very nice Pulsion cranks and Paul brakes by the way.

The bottom bracket does look high (the BB height appears higher than on a Birdy) and you are right over the crank juding by how far forward you are on the saddle rails. Have you done this to aid the suspension movement, or do you prefer this riding position?

On the Pantour, I really didn't give it much of chance to prove itself and so can't dismiss it without some apology. The front braking thing ended my experimenting with it because I just didn't think it was worth toying with adjustments that might do me in first. I'd bet that my Q fork would work better under a heavier rider (I weigh around 155lbs), but cant really answer that either.

What's a bodge? Thanks for the compliments though, however inimitably British. I've been playing with the riding position since I bought my Jetstream XP 2 years ago, which has slowly morphed into this bike I've posted photos of. I find that if I put the seat back and move the bars back as well, I feel as though I'm riding a chopper motorcycle and after long rides my knees hurt a bit. I get a smoother spin over the bottom bracket, as I have it now, and no knee pain. When these cranks bite the dust, I'm going to try 165mm's, these are 172.5's, to improve the spinning qualities farther. As it is now, I've just bought a stem that's a 110mm track stem and has a much steeper drop. I'll need to machine another collar for it before I can mount it though (the current on has become one with the titanium stem it's mounted to because I used no lubricant when I mounted it) and so, it might be awhile before I get around to it

DG1


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