Planet X Jack Flash 26er – how versatile?

Looking at the geo charts the new version of the Jack Flash (26 inch wheel version) looks like it could be quite versatile as a general trail hack. Any owners got any views? How do you use yours?

Thinking of building up with rigid fork 27.5 front wheel, 26 rear, 10 speed, etc. Big winter BMX type of thing.

i had one of the original batch. still pissed off that it got stolen.

I can’t find a geo chart for the 26er on the website, but just eyeballing it, mulleting it looks like a recipe for a silly high BB and a very slack seattube.

Big winter BMX type of thing.

That’s exactly how I ran mine.
It was the most smile inducing bike I’ve ridden, just really good fun to ride.
The advise I’d give is not to go too heavy on weight and not too slack on angles, it worked best for me when it was as light as reasonably possible and keeping it’s steep angles. When I added a big, heavy fork it lost it’s pop a little.

mulleting it looks like a recipe for a silly high BB and a very slack seattube.

Scroll right down the page for the geo tab. A to C fork is 453mm, so 100mm travel fork. Should be easy enough to keep the angles roughly the same with a 405mm 27.5 rigid fork.

Thanks, lunge. I do want to keep it quite light rather than a burly jump bike, so that sounds good.

Should be easy enough to keep the angles roughly the same with a 405mm 27.5 rigid fork.

Interesting, I didn’t realise you could get 27.5″ forks with such a short axle-crown length. I thought the axle-crown on my old Superstar carbon 26″ rigid fork was about that (or maybe even 420mm), but I might be wrong.

Aye, On One Bootzipper fork in 27.5 size is 405mm A to C. 25mm difference in 26 to 27.5, 20mm or so for 100mm fork sag and we’re about even.

It’s similar to an old Trailstar so a 100-110mm fork or rigid equivalent will be fine. IIRC 435mm should fit, mines an LT designed for 130mm travel and I have a 465mm fork sitting. Revelation or Pike 426’s with U Turn are brilliant and the Revs are light enough to keep it fun. I think the Pikes have shorter travel (80 – 115mm) so may be more suited to the Flash.

I bought one of the raw disc-only frames last year to stick my old 26″ stuff onto. Used purely as a pump/FAB (f**kabout) bike and it’s great at that, but no way would I consider taking it onto the MTB trails I ride – just so stiff and short compared to the bikes I now ride.

looks like a good fun winter option

does anyone know the seatpost diameter? (just thinking what have i got in the spares bin!)

The original one was 27.2mm I think, not sure if that’s changed.

thanks, think you are right

no way would I consider taking it onto the MTB trails I ride – just so stiff and short compared to the bikes I now ride.

I did the Naughty on my Trailstar LT, they’re bloody fun on a good fast red as well, the old geometry lends itself to it.

Exactly. I want it to be significantly different to my other bikes, otherwise what’s the point in building something up if it’s similar to what you normally ride? It’ll be great for the FoD man made trails, I reckon. Verderers is just a big BMX track anyway, especially the final descent section.

‘just so stiff and short compared to the bikes I now ride.’

430 reach so its long for a jump bike. decent for a mess about. its a 27.2 seat tube which limits dropper option – bizarrely the seat tube is tapered to be smaller at the clamp which is bonkers.

my daughter loves hers. I quite like it on teh jumps too.

“430 reach so its long for a jump bike. decent for a mess about. its a 27.2 seat tube which limits dropper option – bizarrely the seat tube is tapered to be smaller at the clamp which is bonkers.”

You have to remember the 26″ version was designed pre-dropper posts and I believe they wanted to make an accurate reproduction. With no droppers, 27.2 and a QR was as good as it got.
It was also never a pure jump bike, more of an all round messing bike. Certain, mine was used for trials, trails, street, 4x and pretty much anything that wasn’t long rides. It had a habit of eating back wheels but that was definitely more my technique than the bikes fault…

Well, I ordered it. £50 for a frame is a bargain.

I checked the axle-crown on my Superstar rigid carbon forks this morning and it is a whopping 445mm.

They make the handling of the 1999 Orange Evo 2 they are on rather ‘interesting’ (fine for commuting as that’s all I use it for, but the BB is sky high), hence my initial scepticism.

£50 is a bargain, but either I’m being stupid af, or 26″ tapered forks are mad expensive and tapered headsets for straight steerers don’t exist? Kinda defeats the object of a scrap bin build if I’m having to shell out loads for forks…

No problem, just buy something like one of these: https://www.chainreactioncycles.com/hope-tapered-1-5-headset-reducer-crown/rp-prod71609

https://www.chainreactioncycles.com/nukeproof-reducer-crown-race-1-5-to-1-1-8-/rp-prod92344

Fab, thanks!

Same as a11y above, I got one of the raw frames and built it up into a single speed dirt jumper (with two brakes) to mess about on. I did take it for one short trip around the forest to chase after littleginge but it was pretty brutal and my old bones didn’t thank me for it.

The measurements I got for the main bits to fit to the frame when I got mine were:

Seatpost: 27.2 mm
Set Clamp: 31.8 mm
Bottom Bracket: 68 mm BSA
Headset: ZS44/ZS56

@misteralz, I managed to pick up a budget headset that let me use my old straight forks in the frame from ZTTO.

https://www.ebay.co.uk/itm/393465476579

Top tip – cut a slot through that reducer before you fit it, mine was bloody tight to fit.

Looks like a great frame, I’m hovering over the ‘buy’ button on one at the moment to transfer some of my 26″ GT aggressor bits to.

Would a 140mm fork be too much?

Considering they changed the steer tube to taped it seem odd no to alter the seattube as well.

Considering they changed the steer tube to taped it seem odd no to alter the seattube as well.

27.2mm seatposts still widely available. Straight steerer forks not so much – a frame that’s limited to using straight steerer forks in this day and age is severely limiting. And if you do have a straight steerer fork you want to use, crown races are available for various headsets to run a large bearing on a straight steerer fork, so easily accommodated.

Would a 140mm fork be too much?

Probably. It was designed for 100mm, so I guess 140 would raise the BB too much to still feel nice and nimble.

Would a 140mm fork be too much?

Yes, it’s at its best when it’s a little steep and twitchy. I put a 140mm fork on mine and it really spoiled the ride.

Cheers.

I’ll probably pop the 140mm on while I’m looking out for a 100mm. Although PX have sent me a frame that bears only passing resemblance to the one pictured so I’ll probably be waiting weeks to get the right one now…

What about a slackerizer or angleset headset? could add a 27.5 fork (or a 130mm 26er) and slacken the head angle by 2 degrees? Superstar, Works, and some guy on Pink Bike all offer. Anyone tried it?

What about a slackerizer or angleset headset? could add a 27.5 fork (or a 130mm 26er) and slacken the head angle by 2 degrees? Superstar, Works, and some guy on Pink Bike all offer. Anyone tried it?

As I’ve said a few times, trying to make it slacker and putting bigger forks on it made it a worse bike. It works best with steep angles and a bit twitchy.

Hi. New to this forum. I too bought the Jack Flash frame to use up old parts/bring over bits from a ex-full sus 26″ which was no longer being used/had been replaced/would cost too much to service. This is my effort:

It rides and fits my 5’8″ frame quite well, although a bit heavier that what I have become used to. I’ve done some maths and think it should be possible to put a 27.5″ wheel on the rear (with then a view to put a 27.5″ suspension fork and tyre on the front). Any thoughts?

@coffeebiker1.

I’ve done some maths and think it should be possible to put a 27.5″ wheel on the rear (with then a view to put a 27.5″ suspension fork and tyre on the front). Any thoughts?

I’m intrigued why you’d want bigger wheels, I can’t see how they’ve make the bike better. I also be interested in your calculations as the clearance wasn’t huge for 26” tyres.
It’s best when it’s built for playing around. So short travel forks, strong wheels, low saddle, steep angles.

@lunge Basically just want to see if it’s possible. I live near a bike park with short trails and a jump park so no need for enduro/XC/full sus, but wonder if this would make a reasonable 27.5″ trail/jump park cross over. As it is, it had no problems with a local 15km off road route.

JF2022 by

For what it’s worth, a 27.5″ rear wheel with a 2.1″ tyre fits with at least a cm of clearance….