Upside down forks

Why not? I know there are a couple out there but they don’t seem to have become the standard as they are in MX.

They generally have too much flex unless they are seriously over-built, in which case they become too heavy.

The last Manitou Dorados were supposed to be really good but were extraordinarily expensive.

because they are flexy blah blah blah!!
Own 3 pairs of Mavericks sc32 and love them easy to service and basically look after them selves

They flex a lot as you lose the brace between the ‘lowers’.

If you look at motorbikes, bigger bikes tend to have upside down forks as the weight is less of an issue, smaller classes tend to use conventional forks to save weight. Also more a fassion thing, MTB’ers are a lot more geeky about weight, on a motorbike weighing 120kg+ a couple of kg’s beefing the fork up is easily un-noticed.

They always were (are) largely a fashion statement on motorbikes. On motocross bikes they started using them in the early 80s, then stopped, then started again. Same thing happened on road bikes.

I’d guess that a large part of the reason USD aren’t common on MTB yet is purely fashion. I’m sure they’ll come.

Upside down forks can be stiffer for a given weight, that is why they are used on motorcycles. Think about it, the thicker part of the fork up near the crown is going to be stiffer.

This doesn’t work so well for MTBs because the axles are too thin/flexy to keep the lowers in alignment without using a fork brace. Look at the front hub on a motorcycle, the axle is a large diameter tube clamped into each fork leg. Effective but not very quick release. Aren’t downhill MTB forks like this? If not I’m sure they will be one day.

Lefty’s an upside down design. It started life as a conventional upside down fork called the moto that Cannondale engineers massively overbuilt for DH racing, They quickly realised that it was stiff enough to remove one side, lo and behold the lefty was born.

I’m around 17st (bit more at the moment) and its the only fork I ride with due to the stiffness!

They probably got a later start than they should have in MTB design history as disc brakes (and bolt through axles) had to become the accepted standard before UD forks could really start getting anywhere. Proprietary parts generally scare the bike buying public away, for better of worse.

It’s a shame the flex issue remains as it does, with UD forks necessitating the removal of the bridge. Otherwise, upside down forks make more sense to me in muddy situations where gravity helps protect the seals as well as keeping them lubricated. Less unsprung weight too.

Perhaps UD forks put the stanchions in a bit more danger, and perhaps raise the COG a bit, too. To what extend either of those are measurable issues is debatable, I’m sure. In my limited experience (and none of that is recent experience, I admit), unacceptable levels of flex were the issue.

The Lefty is UD of course, and apparently as flex free as any fork.

on a motorbike weighing 120kg+ a couple of kg’s beefing the fork up is easily un-noticed.

If those couple of kilos are on the lower leg it would have a significant impact on the suspension. Less unsprung weight, another plus of the upside down design.

Think about it, the thicker part of the fork up near the crown is going to be stiffer.

And the thinner bit near the wheels is going to be flexier.

The problem is on a tripple clamp/dual crown fork this bits already stiff, so make sese to use to beef up the flexy ‘inner’ part of the fork.

Leaving the stiff cast section at the other end.

Aren’t downhill MTB forks like this? If not I’m sure they will be one day.

Welcome to the 1990’s, yep, and most ‘trail’ forks are bolt through now as well. The problem is that you can still make this in addition to the 3 existing braces on a conventional downhill fork (the twin crowns and the lowers brace) making 4 connections, which will be stiffer than 3 comparable connections on upside down forks.

The Lefty is UD of course, and apparently as flex free as any fork.

The lefty runs on needle bearings which prevent it twisting, the bushings on a conventional fork allow the two sides to twist independandtly. A manufacturing nightmare to make that though I’d imagine! It’s a PITA to rebuild 1 lefty, let alone grow 3 more arms to build 2 legs at a time!

If those couple of kilos are on the lower leg it would have a significant impact on the suspension. Less unsprung weight, another plus of the upside down design.

You’re assuming that the ‘lower’ legs on a USD fork are lighter. They’re aluminium, whereas the cast section is usualy magnesium which is considerably lower density. Couple that with the nececity to overbuild USD forks and the difference is minimal.

You’d need a larger axle to offset the losses in stiffness, which makes getting a hub to fit a pain.

I remember Marzocchi announcing the Reverse Advanced Composite ‘RAC’ USD fork in the late 90s, it was going to be a 1kg 80mm travel XC super-fork with swoopy carbon legs. Never happened though, think a massively heavier and stupidly expensive version appeared fleetingly.

the ‘zocchi RAC was a a lvely looking thing.

Recently aquired a pair of SC32s. really plush, looking forward to servicing them 🙂
They do twist if you hold the front wheel and yank the bars, but Maverick say that’s not an on-trail issue. But if I pull the front brake hard, the wheel does pull to the left. I can probably only see it due to the big g@y mudguard mounted to the crown so I’ve a point of reference. Not an issue when riding.

what is an issue is that some scrote nicked the bling air-valve cap when the bike was on my car-rack, I think at Wetherby services. Anyone got a spare?

It started life as a conventional upside down fork called the moto that Cannondale engineers massively overbuilt for DH racing, They quickly realised that it was stiff enough to remove one side, lo and behold the lefty was born.

is this true? I’ve heard it before, didn’t know if it was a rumour. If it is it could be seen as quite a damning point on the viability of UD forks really.

It’s a PITA to rebuild 1 lefty, let alone grow 3 more arms to build 2 legs at a time!

To be a little bit pinickity, with a UD fork can’t you still build each leg one at a time? They’re only linked once the axle is in aren’t they?

I find my sc32’s to be just like a slightly nicer MX Comp. That’s no bad thing in my world. I’m 17 stone, so it should be flexy, but I ride like a Jessie, so it’s not.

If those couple of kilos are on the lower leg it would have a significant impact on the suspension. Less unsprung weight, another plus of the upside down design.

That’s the main reason they are used on motorbikes.

It started life as a conventional upside down fork called the moto that Cannondale engineers massively overbuilt for DH racing, They quickly realised that it was stiff enough to remove one side, lo and behold the lefty was born.
is this true? I’ve heard it before, didn’t know if it was a rumour. If it is it could be seen as quite a damning point on the viability of UD forks really.

no

the original moto was a conventional UD fork, circular legs, and glide bushings, and weighed a ton.

Then came the twin legged, right-side up moto forks, with needle bearings like the headshok, but they really did weigh a ton
(and I believe there was a UD needle moto in there briefly but not sure if they ever made it to non-team use)

The lefty was actually born from the desire to create a longer travel version of the headshok, (running octagonal peg in octagonal hole with 4 sets of needle bearings) without the weight of the needle moto , but there not being enough room in the headtube to house the amount of gubbins for the the travel.

They then realised they could shift the telescope sideways, with an upside down design, make the axle bigger and maintain stiffness while reducing the weight… hence the lefty.

*As told to me by Cannondale mechanic some time circa 2000

If those couple of kilos are on the lower leg it would have a significant impact on the suspension. Less unsprung weight, another plus of the upside down design.

That’s the main reason they are used on motorbikes.

Surely not though – considering unsprung weight = tyre + wheel + brake rotors + calipers + lowers + oil + 1/2 damping cart, surely any difference in lower weight is completely irrelevant?

For me the main advantage is lubrication – the oil is sat on the seals all the time. Dirt also doesn’t sit around the seals like they do on regular forks.

I was speaking to one of the guys at TFtuned a few months ago – apparently he had never seen a marzocchi shiver with worn bushings. Given that they’ve been around over 10 years now, that’s fairly impressive.

I’ve got 4 bikes with SC32’s plus an unused set in a box for spares. They work, they’re easy to work on and setup, I’m happy.
ir_bandito, you may be able to get a spare from Craig, see the bottom of this thread.http://www.singletrackworld.com/forum/topic/maverick-owners-couple-of-questions

The lefty is based on (half) the needle-bearing forks Cannondale had made previously.

Seems odd to me to say that it “evolved” from a headshock!

cheers Dibbs.
I was going to try Sideways first, but if no joy, wil try Simpson. John Atkins are also s Mav service centre too.

cynic-al, think we’re both actually saying the same thing, I’m just clarifying that the move to external from headtube setup was the beginning, the one leg bit was the attempt at weight saving from the beast that was the needle moto.

the orginal UD moto was not needle bearing

this one:
http://www.retrobike.co.uk/forum/files/moto2_443.jpg

where as the later (look like right way up, ie: have a lower leg and brace but actually UD):

this one:
http://www.bobbrowncycles.com/images/moto/moto_internals.jpg

came *after* the headshok

The headshok was developed before the needle bearing moto so seems perfectly reasonable to say that the lefty (and needle moto) was an evolution of the headshok…

headshok good => more travel required => wont fit in headtube => move external => needle moto => weighs a ton => one leg? => lefty

Surely not though – considering unsprung weight = tyre + wheel + brake rotors + calipers + lowers + oil + 1/2 damping cart, surely any difference in lower weight is completely irrelevant?

The fork lowers and the lower part of the stauntion they slide on are all part of the unsprung weight of a conventional fork. Upside down forks effectively move the lowers to the top of the fork above the spring, therefore reducing unsprung weight.

headshok good => more travel required => wont fit in headtube => move external => needle moto => weighs a ton => one leg? => lefty

The Headshok has the same A-C as a 100mm lefty (give of take a couple of mm). It wasn’t that the internals wouldn’t allow it, it’s more that the crown depth of the conventional unicrown fork of the headshok was too tall to make for a bike that would allow 100mm travel and not mean that inverted stems became the norm even on XL bikes. It wasn’t even the ‘lefty’ part of it that allowed this either, it was the twin crown that meant the lower crown could take up much less room than that of a unicrown headshok.

I love my Shiver DCs, ok they weigh nearly 9lb but I dont care it’s DH bike and I’m not exactly light, they’re bulletproof, easy to service and stiff where it counts, a little side to side deflection is not such a bad thing.

And in other news – Fox USD proto

additionally, Cannondale found that, of the time, sticking a dual crown fork on an XC bike was a no no as they just weighed far too much (ok, apart from that 3 lb prototype Sunn ObSyss UD carbon fork that was attached to a nice Exact Ti back in the late 90’s…) and it just so happened that the headshok design could allow the single sided fork. That axle though, I think that made more people nervous as it’s ‘only held on the one side’ 😉

I think thats what he was meaning by wouldn’t fit, you’d have to make the headtube taller to accommodate the extra travel and require a stem with massive drop.

getting back on topic though…

I had some shiver single crowns for a while a few years back and I did find them noticeably flexier than the Z1s they replaced.

just found the video with a shot of the original needle bearing DH fork that they lopped a leg off of.

http://www.pinkbike.com/news/cannondale-lefty-sea-otter-2010.html

Does anyone know if that needle bearing UD fork made production or if it was just team only?

from back in the day:

Suspenders Suspension Fork -inc cable actuated hydraulic disc brake

2 sets of Mav SC32 forks here too, make a great 29er conversion

Argh – the hamsters ate my post! Try again;

I have a set of the X-Fusion DH/Bionicon Special Agent hybrid upside down fork, stuck to the front of my Ironwood. They get around the stiffness issue by running a massive hexagonal axle that mates to the bottom of the sliders, with the fork rods extending right through the axle into massive nuts on the lower side. The diameter of this axle means the BCD on the disc rotor is huge, so you have to use Rohloff intended rotors, as well as a custom hub. And to remove the wheel, you need to use something like a 5mm allen key sideways through the holes in the nut to turn them. They then call it a ‘quick axle mounting system’ or something laughable!

Stiff? Not really. Not as stiff in my experience as Boxxers. Plush? Yep. Heavy. Oh yeah.

I’m in two minds on the Maverick fork flex issue.
I’ve owned a set of DUC32 for 6 years now and initially I found the flex a bit annoying. Tufty grass would seem to drag the wheel sideways and for a while I found the take off from jumps to be a little less confidence inspiring.

But I have to say, these days I don’t notice either problem and I’ve got other bikes with other suspension designs, so you’d think I’d still notice.

If I was significantly less fast than the people I ride with, or I fell off more often, then maybe I’d blame the forks, but neither of those things is true. They flex a lot less than other forks in the fore/aft plane, so maybe that helps even things up.

Anyway – I think they have great potential. It’s a shame that Paul Turner didn’t stay on to develop them further. I’d like to see more USD designs. Those new Fox ones look interesting.

I’m sure fashion has a lot to do with it. Everyone I ride with looks down their noses at mine 🙂

To be a little bit pinickity, with a UD fork can’t you still build each leg one at a time? They’re only linked once the axle is in aren’t they?

Good point!

Still there must be a reason no one uses them? Tollerances? A batch of SIDs was in circulation with bent lowers, which probably causes stiction and quicker wear, but still worked, given the fiddlyness of trying to line up 4 bearing races in a headshock I imagine they’d be prone to binding if the 2 legs arent perfect?

I’m in two minds on the Maverick fork flex issue.
I’ve owned a set of DUC32 for 6 years now and initially I found the flex a bit annoying. Tufty grass would seem to drag the wheel sideways and for a while I found the take off from jumps to be a little less confidence inspiring.

It’s all in the mind, the fact that Maverick forks are more easily twisted than a conventional fork is neither here nor there, you never really experience any twisting forces on a fork in use.

They flex a lot less than other forks in the fore/aft plane, so maybe that helps even things up.

This is one of the major advantages of the upside down design. For any doubters, just try riding a Maverick DUC or even an SC and you’ll see what I mean. The fore/aft flex is far less than with a conventional fork.

The biggest disadvantage with the upside down fork is that in order to eliminate enough of the twisting they can experience (despite it not really mattering, people are sceptical though), you need an axle much bigger than the current 20mm standard to make the connection between the lowers stiff enough. Mavericks 24mm axle is as big as you can go with a conventional 6 bolt rotor, and it requires a proprietary hub. It is twice as stiff as a 20mm axle though. Bump that up to 30mm with a proprietary hub and rotor and the stifness would be easily there with a conventional fork in terms of twisting. But this is the problem, you’d need a load of new standards (costs money to develop, make and store) and it puts the public off. I for one get annoyed with every new headset standard for the sake of it, and got annoyed by Fox/Shimano developing the 15mm front axle (why? 20mm is fine for RWU forks!). It’s not worth the time/effort/expense for the big fork manufacturers to bother doing in bulk, when a conventional fork works well enough to all intents and purposes. Yet…

Give it another 10 years or so and I predict we’ll see more USD forks in the mainstream, they took a long time to properly take off on motorbikes afterall, but they’re now standard except for on real cheap bikes.

you never really experience any twisting forces on a fork in use.

I’m not so sure – but with no real knowledge to back it up. What about hitting edges which aren’t perpendicular to the line of travel? Would they not work to push the wheel sideways, and therefore twist the fork?

I can understand the argument that “you never really experience any twisting forces on a fork in use.” as when you do the ‘between the knees’ test, everyone puts loads more force into the bars than you ever do on the trail – steering force is actually pretty tame.

But what I really need to do is to borrow a current bike and compare. I haven’t ridden anyone else’s bikes for a while now (probably 4 years) due to not wanting to get tempted (no money).

Alexsimon, if you borrow a bike with a maverick, see if you can get some from someon same weight as you: they are very fiddle-with-able and have different negative spring and damping oil weights for different size folk, just chainging air pressure will not make it feel as good as it could be for you if it was set up for someone significantly heavier or lighter than you.

SC32’s often come up pretty cheap on classifieds. Mrs j has one and she loves them.

A firm I used to work at bitd created one of the first upside down forks just after rockshox were making an appearance and they had an alloy disc brake rotor on em they were plenty stiff enough in fact I think I still have the crown and uppers somewhere

Bugger didn’t see that someone had posted the mc man above.