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Phatmike

Single-sided front fork - hub mounting suggestions etc

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Hey guys,

We've got split opinions in the office today. After quite a lot of work on the front hub for the Chopstick we have got the weight down pretty far.  The (disk) hub is now about as light as the lightest non-disk hubs, which we've been able to achieve by a lot of FEA, a nifty bit of problem solving to allow the flanges to be kept small (whilst still offering equal dish and spoke lengths both sides), and the fact the axle weight is in the fork itself: About 80g including all the mounting hardware.

At the moment we're looking to build a 450g fork, suitable for 24" and 26", with a +20mm post-mount adapter. Our data is showing that we can go significantly lighter than that though, so we'll be doing some real-world testing and testing in the lab too, whilst tooling for a 20" model. 

The issue at hand is about removing the wheel. As it is, you'd need to un-bolt the caliper to slide the wheel off the axle. We have a QR design to allow the wheel to slide off whilst keeping the rotor in place - it'll add about 20g to the total weight. My vote is to have that feature and accept the pretty minor weight penalty for convenience, but there is the argument that some would prefer to save every gram they can and/or wouldn't take the front wheel off enough to warrant it.

What do you reckon?

 

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on one hand in theory you would rarely need to take the wheel off as you could even change a tube or Tyre with it on but the other hand setting calipers up just right is a bit of a ball ache for anyone who needs to take there wheel off to get there bike in the car may not fancy re setting there brake up time i would say that eliminating that hassle is worth 20g 

i am not the in the target consumer group here though to be honest

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Assuming there'd be threaded inserts bonded into the fork leg my guess would be that the fewer times people need to fiddle with the caliper bolts the better. Not everyone understands mechanical sympathy!!

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19 minutes ago, monkeyseemonkeydo said:

Not everyone Depressingly few people understands mechanical sympathy!!

I think you need to decide what your primary goal is here, Mike.

Are you looking to build the lightest parts possible (which some of your statements seem to suggest) or simply the best performing parts that also happen to be very light?If the former, people can deal with a little extra effort to remove a wheel. If the latter, ease of use plays a factor so the QR seems to win (Y)

See also: I miss your face

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Add the weight.

My [debatable] reasoning:
The overlap of people looking to save every gram possible and front-disc users is almost non-existent overall, and even smaller when discussing not-20" riders.
If weight's their priority, they'd also be better served not using a disc anyway. If you're looking at ~450g + disc brake, that's already a good bit more than ~500g (existing carbon forks) + rim brake. If you were down in the region of a 350g fork + disk brake it might be worth trying to compete, but discs are so much heavier than rim brakes there's almost no point trying.

Adding 20g will have almost no impact on the people who would consider buying this product, but having to set a brake back up every time you want to get in the car would.
(If I was in the market for a product like this, finding out I had to do that would instantly make me decide against it.)
 

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Why not have a look at what cannondale have done with their latest iteration of lefty?  The caliper is mounted on a sub-bracket that has a quick release on it, undo QR, caliper falls off and is relocated on pegs.

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Why not make 2 versions of the fork? Also, if it's an IS disc tab you wouldn't have to set it up every time, you just unbolt the adapter instead of the caliper (assuming post mount caliper obviously). I'd opt for the non skewer fork, but i don't need to remove a wheel for travel.

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1 hour ago, Swoofty said:

Why not make 2 versions of the fork? Also, if it's an IS disc tab you wouldn't have to set it up every time, you just unbolt the adapter instead of the caliper (assuming post mount caliper obviously). I'd opt for the non skewer fork, but i don't need to remove a wheel for travel.

Tooling costs. It's post mount. Skewer/wheel attachment is not being discussed. 

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Ah yes, i meant quick release, not skewer. And yeah resetting a post mount would be no fun.

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Thanks guys, I think Flipp's hit the nail on the head - 

On 15/01/2019 at 1:33 AM, Luke Rainbird said:

I think you need to decide what your primary goal is here, Mike.

We just want to make parts that keep up with the fun of riding. Trials has always been as much about the bike to me as the riding itself. :) I agree that such a low weight penalty (we're working on it  at the moment, and it's looking at less than a 10g increase), is really small compared to the hassle and potential wear on the forks (yes molded in threaded inserts) of removing the caliper each time. 

Yes the forks + disk combo will be slightly heavier than a rim brake with CF forks, but not by much, and even then only eclipsed by the lightest of competition setups. I couldn't stand to run a front rim brake though, it's frustrating when I'm with guys that have to stop and walk their bike when going down a hill, or just make a shit ton of noise, plus I much prefer the modulated feel of the disk on the front. As it stands though, there are quite a few improvements coming in the not-too-distant that will see the total fork + brake weight come well  below the current CF fork + rim brake setup, that could interest the comp guys more too.

On 15/01/2019 at 10:38 AM, forteh said:

Why not have a look at what cannondale have done with their latest iteration of lefty?  The caliper is mounted on a sub-bracket that has a quick release on it, undo QR, caliper falls off and is relocated on pegs.

I do like the Ocho fork, for lots of reasons! That mounting hardware looks smart, very bulky and heavy compared to what we have in mind with the hub though.

 

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I'm with Flipp about the type of rider likely to buy light stuff.  Weight is part of it, but a large part of the reason comp riders run a front rim brake is due to the feel/performance of a rim brake vs. a disc brake.  That's why the top 20" riders are almost all running rear disc/front rim now too.  

At what stage are you planning on making a prototype of it, by the way?  It seems a bit risky to just rely on FEA to make it as light as you think you can get away with before actually using them for real.  If you haven't modelled it perfectly and have worked out a way to put all the random directions and degrees of force through it that you would do through riding (e.g. when you're doing a hook on an awkward shaped obstacle, you've got all kinds of unpleasant twisting/bending/grossness going on), you won't have as much margin for error?  Similarly, when carbon forks first came out there were riders complaining about how flexible they were.  If you're going that far down the road of making them super light without being able to feel what they're actually like on a bike again it seems like you might encounter problems when you try them for real - not just in them not being great forks, but also in having spent more time and effort on the design that you'll then have to go back and undo.  

I'm not by any means saying that the current carbon fork designs are optimised, and they could no doubt be lighter/better, so I know that expectations of your forks vs. those forks  based on weight alone won't necessarily be accurate (i.e. you saying that yours will be way lighter doesn't necessarily mean they'll have the problems associated with being too light).  It just seems from the outside looking in that starting off with a slightly heavier product that you can then refine and optimise after gauging the feel and performance of it would be better than cutting things too fine.

 

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23 minutes ago, Mark W said:

It seems a bit risky to just rely on FEA to make it as light as you think you can get away with before actually using them for real.  If you haven't modelled it perfectly and have worked out a way to put all the random directions and degrees of force through it that you would do through riding (e.g. when you're doing a hook on an awkward shaped obstacle, you've got all kinds of unpleasant twisting/bending/grossness going on)

That would be my fear too. Loading conditions for 'normal' bike conditions is pretty straightforward and I would guess (ignoring the complexities of modelling layup) FEA is reasonably reliable. You try and model what a fork is seeing when you've got a rider's weight hanging off of the thing while hooked over a cambered rock or whatever and it's just nasty. 

As mentioned, I think the way comps have moved on there is a huge reliance on front wheel moves and for that it seems the riders like the instant bite/lock that a rim brake gives rather than the often slightly mushier feel that a disc provides and so I would guess that market is not worth chasing too hard...

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Just as a side point, and unless I’m missing something - I wouldn’t touch the calliper mount if I were removing that wheel. I would take off the disc... only a few more bolts but leaves alignment perfect.

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On 16/01/2019 at 10:38 PM, monkeyseemonkeydo said:

That would be my fear too. Loading conditions for 'normal' bike conditions is pretty straightforward and I would guess (ignoring the complexities of modelling layup) FEA is reasonably reliable. You try and model what a fork is seeing when you've got a rider's weight hanging off of the thing while hooked over a cambered rock or whatever and it's just nasty. 

 

On 16/01/2019 at 10:08 PM, Mark W said:

It just seems from the outside looking in that starting off with a slightly heavier product that you can then refine and optimise after gauging the feel and performance of it would be better than cutting things too fine.

 

Yeah, just wanna let you guys know that we're all on the same page there. We've been as thorough as we can, looking at the worst case for/aft bending, twisting, side loading cases, even combining them together for a high-speed fat guy doing a 180 downgap to hook kinda thing. We're gonna find out for real when it's built - being currently conservatively overengineered for strength and stiffness, and then peel back the wall thickness of the carbon following the physical testing.

 

On 17/01/2019 at 5:34 AM, manuel said:

Just as a side point, and unless I’m missing something - I wouldn’t touch the calliper mount if I were removing that wheel. I would take off the disc... only a few more bolts but leaves alignment perfect.

Have gone with the QR-in-the-hub idea. We've saved weight elsewhere, and so the total hub weight still sits in at 80g. :) Parts (1), (2) and (3) are bonded together. Part 4 houses the LH bearing and rotor and stays on the axle, separating from (1)(2)(3) when removing the wheel.

HubPic.png

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2 hours ago, Phatmike said:

Part 4 houses the LH bearing and rotor and stays on the axle, separating from (1)(2)(3) when removing the wheel.

1

I like this concept, nice one team. If the hassle of removing the wheel comes from the disc/caliper, then simply remove the need for this to happen altogether for general wheel removal. Kudos (Y)

Not 100% sure how you've achieved it, but assuming some kind of splined interface between parts (as there appears to be at the outer face of the disc tabs, but may well be internal too and not displayed) than that should also create a floating rotor which will help compensate for some misalignment and even a smidge of flex in the system too.

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Full disclosure; we didn't invent that! Thanks Alchemist. The spline comes from the material around the rotor bolt holes and good tolerances. It's all designed to be well fitting and accurate. 

James, our engineer did the FEA and came up with the slotted hole idea to allow the spokes in with the smaller & lighter flanges. :)

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Not sure about the floating rotor side of things Luke mentioned- the assembly will be clamped together with the axle to preload bearings and keep things tight so don't think that can be possible. With that being the case I like the idea of the slightly tapered fit of the Alchemist design to self centre and locate tather than the parallel sides that have more potential to be come a bit sloppy.

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Ah yes, quite right Dave. Would be possible to modify the design to allow float but would add weight and complexity (and cost!)

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In using it, I would be scared of the disc mount container cracking/snapping off.
Presumably it's aluminium?

I know modelling is more effective than instinctive worry, but that looks a mighty thin wall for the forces involved in front-gaps etc.
(26" tyres OD leverage over... 70mm diameter stopping?)

Edit: Just remembered cranks... They have more meat around them, but I guess if that can mange this could too if you do it right.

Also, to be easy enough to separate that it would just slide out, wouldn't that have the smallest amount of play and feel the same as pad-rock?
Or are you envisaging it being a tight fit that requires a tool to separate the two parts?

Edited by aener

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If you put a taper on there then you may need a self extracting crank bolt on the end of the axle to draw the hub off, shouldn't be too much hassle to achieve :)

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