Excuse my ignorance here, but how come mountain bikes don't have USD forks ?
Seems pretty much all decent motorbikes come with them now, so why not mtb's
they do, WAKEY WAKEY!!
Unless you have a 20 mm axle they will be flexy or heavy ( to avoid flex) as they cannot have a fork brace / bridge.
Mainly fashion on motorcycles anyway - there are marginal benefits for racing - slightly less unsprung weight and increased rigidity in the upper tubes and longer overlap possible.
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Mainly fashion on motorcycles anyway
You do talk some shite sometimes.
Stiffer for a given weight, although I understand dearer to produce.
singlespeedstu - Member
> Mainly fashion on motorcycles anyway
You do talk some shite sometimes.
Aww - that's not very fair. It's [i]most[/i] of the time.
Give me a reason why they have them on many fairly ordinary bikes thats not fashion led. Most of the motorcycle world is fashion led these days.
Druidh in "funny twice in one week" shocker.
Jeremy.
Ride an MXer flat out round a GP track and then tell me that having a stiffer more direct fork is a fashion thing with only marginal benifits.
Try living in the real world with real experiences instead of just reading about it.
surely simple engineering (bending moments) says a USD fork is a better design. I'm sure us meer mortals would never tell the difference on a motorbike(I've owned both and sure as hell can't) but it has to be stronger for a given weight. Oh, and motorbikes don't use a brace/arch even on traditional forks.
mark, yes they do, its often aftermarket though to stiffen things up.
USD forks just arent as stiff as their conventional counterparts. Yes you can fit the thicker/stiffer parts at the frame end, but you loose a brace.
Very much a fassion thing on motorbikes, the USD forks on a touring bike have about as much in common with the ones on rossi's bike as custard.
n.b. dont confuse stiff enough with stiffer
USD = stiff enough
conventional forks = stiffer
A motorbike has a minimum weight limit for competition, so you may as well beef the forks up to get a marginal increace in performance rather than go for a conventional design with subtly different performance, but in a stiffer chassis.
Mountainbikes just strive to be as light as possible, so the lightest desing wins.
Take the dorrado, bloomin expensive and fancy materials, but the boxxer is infinately stiffer for a similar weight from plain old aluminium tubes and magnesium lowers.
motorbikes don't use a brace/arch even on traditional forks.
Of my most recent 6 m/cycles - 3 hondas, 2 suzukis, a bmw all with fork braces. Only the BMW was an aftermarket one.
That must explain why all modern production MXers come with an inverted fork then.Makes perfect sense to have a fork thats not as stiff as it could be when plowing into a flat out rutted whooped out corner. 🙄
😉
That must explain why all modern production MXers come with an inverted fork then.Makes perfect sense to have a fork thats not as stiff as it could be when plowing into a flat out rutted whooped out corner.
So you're saying that USD forks are stiffer than conventional ones?
My ZX-6R didn't have a brace, neither did my VRF. What bikes were yours?
SST - for race use they might have some advantages - reduced unsprung weight and better resistance to stiction and bending moments ( but worse for twisting)- especially at long travel. There will still be a fashion element tho in that everyone expects USD forks as thats what Rossi and Carmichael have.
For the majority of motorcycles tho its purely for fashion as I said. Hyosung 650 with USD?
Marky - have a look under the mudguard on RWU forked bikes. Every bike I have ever seen with a RWU fork has a solid connection between the top of the fork legs - either combined with the mudguard mountings or under the mudguard
Why is the Lefty USD, surely if this logic follows cannondale could have made it lighter the other way up?
Surely the limiting thing with MTB design is the 20mm axle (without making it out of steel which screws the weight).
under the mudguard on RWU forked bikes. Every bike I have ever seen with a RWU fork has a solid connection between the top of the fork legs
Not a VFR (NC-30)or ZX-6R (J1). I have removed the forks from both bikes personnally. Like USD forks they relied on the axle and pinch bolts.
So the mudguard did not bolt solidly onto the fork each side with a metal mounting bracket under the guard?
I'm pretty sure I've only owned one motorbike with USD forks, but it certainly had the most capable front suspension of them all:
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Mudguard was plastic, no metal. Surely commom sense says no flimsy thin guage sheet metal bracket hidden under a mudguard is going to add any strength to forks relative to a hulking great 30 or 40mm dia steel axle.
USD forks are mainly used to reduce unsprung mass which makes the suspension respond faster.
Every bike I've had with RWU forks has had some sort of brace near the mudguard mounts.
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i rememmber reading the US dirtbike mag shootout between desert bikes a few years back..ktm 640 vs honda XR650..they tested both stock and tuned bikes (engine and suspension)and the XR had the better suspension (conventional) but dirtbikes do have mostly usd forks...i remmember a few years ago when racing where they changed back and forth...
i do know personally coventional fork seals are easier to change...
i still think mtb fork prices are a massive rip off... 😮
snaps - americans can't make motorbikes, they make things out of cast iron and mild steel and rubber belts.
Yep, I rode a Buell once - horrible vibration, thought it was going to fall to bits, confirmed my vision of American bikes - give me a Jap bike any day!
surely RWU vs USD is mainly a cost thing, with RWU being cheaper to manufacture as there is no requirement to machine the outside of the lowers, where as on USD fork you need to. You also need additional parts to carry the caliper/axle on the end of the lower leg on USD and these need to be presicion machined and pressed onto lower legs. More parts, more steps in machining, more assembly = more cost.
Anyway....that's me for the evening....
Buell is about the only exception to the cast iron and mild steel comment (when they use rotax engines at any rate)
No it was a 97 White lightning with a Harley engine, bloody horrible! It vibrated so bad at tick over that the mirrors were useless & I thought it was going to knock itself into gear, the week after I rode it the exhaust fell off & the drive belt wore through the rear brake line covering the owner in fluid 🙄
I think you're probably right with the cost thing as the lowers of RWU forks are cast & fitted to budget bikes.
I had a pair of Simons USD forks fitted on one of my mx bikes in the early 80's- 83-84 I think. The guy who invented them worked for Fox, and had designed the Fox Air Shock.
The selling points then were: larger diameter hence stiffer tubes, better slider overlap, again for stiffness, and the elimination of the need for a leading axle fork- as fork travel started hitting the 12" mark the extension below the axle could actually ground in the right conditions.
TJ et al, MX bikes have no fork brace- the mudguard mounts onto the bottom triple clamp.
The best performing fork I ever ridden/owned was my Avalanche Dhf8, forget Fox40's they're crap, that Avy was awesome. USD design-only issue was when you crashed and 'dug' the bars in you needed to loosen the crowns and straighten the forks back up. Never any flex with its 20mm when riding.
http://www.avalanchedownhillracing.com/dhf8forka.html
RWD vs USD on motorbikes IS mostly fashion. Compare a GSXR600 SRAD with a GSXR750 SRAD, one has USD forks, one RWU. The RWUs (as long as they're the later model with the full adjustability) are ever so [i]slightly[/i] better than the USDs. But nobody ever rode an SRAD 600 and said "Oh, these forks are too noodly"- in fact mostly if you rode the 2 back to back the only front end difference you'd notice was the crap brakes on the 750 (also fashion led)
Everyone tells you that it's for unsprung weight, but which of the 2 had less unsprung weight? Clue, it's not the 750 😉
It's no different than radial calipers and master cylinders. Road bikes end up with what's best for race bikes, not what's best for road bikes. Any quality RWU or USD fork is stiff enough.
Anyway, getting a wee bit OT there. And yes, my motorbike does have USD forks, off of a GSXR750K4, and it was a purely fashion led decision 😉
I love my Mavericks, especially as they are so out of favour, and hence picked up a brand new set including the 24mm axle hub for under £200 last year..
The inverted design has a great benefit of gravity helping to keep the crap away from the seals instead of on it, they seem plenty stiff for and aft wise where it counts but if you hold the wheel between your knees and twist the bars yes they flex... In use you dont notice any, and any for and aft flex there is comes from the crown much more than the legs themself's, this would be the same whatever design of single crown fork.
I was racing when they became the norm in MX (we still called it Scrambling then), and they were touted at the time as stiffer, having the larger tube at the top where the leverage is greatest this makes sense, but the biggest benefit was that as travel had increased so much during the suspesnion revolution, RWU forks had such a huge overhang past the leading axle to acheive the enormous travel & this could and did catch on the inside of deep ruts. USD forks dont require the overhang.
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Both my pairs of maverick sc's are soooo flexy that i can't ride my bike in a straight line. NOT 😈
thisisnotaspoon - MemberA motorbike has a minimum weight limit for competition.
Not in my days of motocross and enduro riding they didn't, and AFAIK they don't now either.
Anyway, tinsy has hit the nail on the head - the big advantage of USD forks was that you could achieve long travel with sufficient slider/stanchion overlap without having the end of the sliders practically dragging on the ground.
RWD vs USD on motorbikes IS mostly fashion
That may be so. But, even you admit it's MOSTLY fashion, so there's no doubt there is some performance advantage, even if it's only a bit. And that's how technology progresses - Bit by bit, slowly. If it didn't, we'd all still be riding round on noodly things that needed an extra brace like those in the pic above. Can you get braces for modern bikes? Do they need them? I think not! 🙂
And what's wrong with fashion anyway? My Monster would have looked bloody stupid with RWU forks 🙂
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Mainly fashion on motorcycles anyway
TJ, as usual you're talking pure bull.
For the majority of motorcycles tho its purely for fashion as I said. Hyosung 650 with USD?
Fashion and Hyosung together in the same sentence? Why not?
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I remember back in the day (probably about 2000) Marzocchi announced a 1000g USD XC fork, the RAC, which IIRC (just to get another TLA in there) was 'Reversed Advanced (or Action) Composite.
Unfortunately they could never make it work properly, and the production version of the RAC was a short travel fork which ended up weighing quite a bit!
These:
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Hairchested as I said and others agree - its mainly fashion. Are you really trying to say that the hyosung has usd forks for a performance advantage? If they had spent the money on a better pair of RWU forks it would handle better.
I am struggling to see why USD are any more expensive to make than RWU, and I have worked in a production engineering enviroment for over 20 years, the cost as ever will be down to the numbers produced, materials used, & what you can make common parts with other derivatives etc, etc, the part count in either fork must be very similar.
I have had this moan about MTB forks before, the manufacturers make a travel adjustable fork so it suits lots more applications, this adds cost and complexity to the fork that we pay for, what in most cases we really need is a simpler fork with a lock down feature for climbing, but why produce that when the end user is still happy to pay for lots of tech he rarely if ever uses.
My mav's lock down its a great feature when your running forks that are at or over the upper limit of travel for your frame.
what in most cases we really need is a simpler fork with a lock down feature for climbing
Sounds just like the Maverick SC/DUC32
Supersport certaily has a weight limit, no idea about anyone else, in MX it would be unenforceable with all the mud!
[b]On the flexiness point:[/b]
OK the two owners of USD mountainbike forks up there ------------^ on the last page.......
Maverick - you can flex them between your knees, this is true for all USD forks, from shivers through to dorrados, they all flex horrfificaly.
Avalanche - if you crashed they had to be re set in the cowns as they had bent out of shape.
Take a set of fox f120's with 15mm axel and compare their stiffness against the maverick SC32's, if you find the fox is less stiff I'll eat my own trillby.
USD forks are flexier than their conventional counterparts for a given weight. On motorbikes weight is less of an issue, so they go with USD. On mountainbikes we rather have a stiff and light fork.
[b]on the weight point:[/b]
An MX bike has 60hp+ pushing it allong, adding 1lb to the fork uppers makes no noticable difference, and the lower stiction of USD forks is more of an advantage.
Take a DH bike, if you added 1lb of unnececary weight you'd never sell a single one! And if youve ever taken a set of forks appart, youd know the lowers are magnesium and weigh SFA anyway, it'd be hard to get much lighter with big aluminium tubes and machined dropouts.
Tinsey - with rwu forks the sliders can be left as cast except for a few areas for mountings - with USD forks more / all of the upper leg needs to be machined.
One last point.............
Motorbikes use (or did last time I checked) 1" steeres, becasue they aren't so bothered about the weight saving, they could use a solid bar in there if they liked. Mountainbikes are lighter therefore we almost addopted 1.25, then setteled on 1.125 and 1.5 steerers,
And....................
Look at the lower tiers of moto gp, the 125's.
Much more weight concious as they have 50bhp rather than 250bhp pushing them allong, conventional forks IIRC are still fairly common as they can be made stiff enough without throwing weight at them.
TINAS, your right of course I covered that in my first post, but in real terms and whilst riding that flex just doesnt manifest itself as an issue, the for and aft flex is probably a bit less than conventional forks, the worst area for flex on either type is the crown thats where all the load is, also covered in my first post.
Did you see the guy the other day with the bent steerer tube after a crash? thats where most of the flexxing is going on, hence the slow move to 1.5 and tapered steerers..
But they did add an extra 1lb into DH forks as they got longr and longer, thats what the dual crown is all about to stiffen the flexy area of the crown and steerer tube. Dual crown is loads heaver but hugely stiffer, even with the old skinny legged Boxxers, still loads stiffer up top where the leverage is. If that are dual crown USD fors they are even stiffer still as the large tubes at the top are stiffer.
TINAS, again your right about the tiddler classes still running conventional forks, but your forgetting its not just the power they have lots less of, its also the weight, it takes a lot less to stop a light weight than a big bike so you dont need that stiffness.
One of the big things, for me, is check out the amount of scratching around the axle of a normal fork - they regularly get beaten on rocks/trees, rested on the ground etc. Even with guards the only USD forks I saw on MTBs (couple of local riders brought them into the shop) had scratches all over their vital bits - that put me off to begin with, I'm not sure it's the best sport for them TBH, except maybe at race level. I think it's hard to draw a line under X is more stiff than Y, it depends totally on the materials, shapes and techniques used - sure one may tend towards more noodleyness but that doesn't mean it is impossible to design it out.
PErsonally I've always wanted a set of ~2000 Jnr Ts, seemed like the ideal compromise really.
Lever / wishbone forks would be better for MTBs imo - no vulnerable sliders, geometric effects for play with for dive. Separation of steering and braking forces, less unsprung weight. Hossack type I think
Halson baby
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TJ you would gain that back because the casting cost would be reduced, especially in the MTB design with an arch, its a lot mor complicated to cast the 2 loweres together than seperate.. pretty sure we could go on all day pointing out why one fork would be cheaper to produce but at the end of all that I stick by my comment the cost would be very similar as long as they have the same features for either.
TJ you on about Leading link forks? Like the USE sub for example?
Fair enough tinsey
I've ridden marzzochi shivers on a DH bike, even just riding down a set of steps the flex was disconcerting.
I've ridden shiver SC's again, though big rocks (stanage casueway and the beast) they felt horrible. On a par stiffness wise with my old manitou minutes which were utter pap.
Yes DH forks weigh more than conventional forks, but look at the marzocchi shivers and the original 888's, both made at the same time, both used a similar damper, the 888's were much stiffer, and much lighter, and the shiveres thankfully eventually dissapeared.
The original dorrado's were nicknamed flexarado, nuff said.
TJ, you mean like on the prst-4? With it's "J" axle action that everyone said felt like the wheel tucked under as you turned and it compressed. Obviusly could be tuned with different bone lengths, but it also had issues with shock getting covered in junk. Not sure if it was lighter, anyone got any figures?
I don't ever remember trying to ride my bike with the forks wedged between my knees so that 'stiffness' test is a nonsense!
Gheezz! What with my 29" wheels and my noodle forks I'm surprised I can ride at all 
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I don't ever remember trying to ride my bike with the forks wedged between anything so that 'stiffness' test is a nonsense!
Ever time the forks hit a rock not quite straight on thats exaclty what happens, they twist.
Every time you brake the fork twists
Every time you turn the bars, the fork twists
Every time you go round a corner, the fork twists.
If stiffness isn't apparent, why is there a trend towards bolt through lowers?
Look at it this way, if it was actualy any good, why does no one make them for the mass market (i.e. i'm excluding £3000 dorrados and foes forks).
Look at it this way, if it was actualy any good, why does no one make them for the mass market (i.e. i'm excluding £70000 ferraris and lamborghinis).
Just because they're not good for mass production doesn't mean they're inherently not good.
So.............my forks are rubbish? Mmmmmmm I still manage ok on them thanks.
One day they will be.. For now I will stick with my Mavericks USD mass produced twisty things..
When Fox make USD forks and one day they will, perhaps opinion will change.
To be honest its just a push bike, ride it and enjoy it.
Look at it this way, if it was actualy any good, why does no one make them for the mass market (i.e. i'm excluding £70000 ferraris and lamborghinis).
firstly, where can I get a new lambo for £70k? Dont drag it OT just to avoid the point.
Secondly, the fact no one outside a couple of niche manufacturers uses(even whyte abandoned maverick forks) has to prove something. If they were better, racers would demand them, consumers would demand them. Theyr not, and we dont.
People want stiff forks
People want light forks
People get conentional forks as it fourfills both those requirements better than USD designs.
By all means keep using them, but I dont bleieve for one moment they are better in any way than being more niche than the current generation of conventional designs.
If stiffness isn't apparent, why is there a trend towards bolt through lowers?
Because the marketeers have convinced everyone that they need it? 🙂 Either for stiffness (because everything previous was near unrideable because of the flex) or for safety (because all QRs come undone so YOU'LL DIE)
I just bought some 160mm Manipoo Sherman flicks (conventional) to build a budget alps bike, no doubt their will be lots of better forks for the job USD OR RWU, but none of that will be going through my head when I am caning Plenny run.
For now conventional forks fulfil all the requirments you want TINAS stick with them as thats where the R&D is right now for MTB, but one day it will change, it will take FOX to have a swipe before genral opinion is changed.
Surely with USD forks its all about the tube diameter. Increasing the tubing cross section will incresase the strength exponentially...MX bikes can use larger tubing so are much stiffer hence they can use USD forks. Look at the foes xtd f1 fork, it uses a 30mm axle and users have no problems with stiffness and dont weight too much either.
How about Leftys? Theyre USD and I have been led to believe they're stiff, light and work quite well. Sure, price has been a problem in the past but pretty much on par with the competition now, and and you can get adapters (Project 321) to fit pretty much any bike.
For me they seem like a pretty smart design that tackles most of the problems off both traditional fork types. Mind you, I havent ridden one, so they could be utterly horrible.
maped, work of the devil them forks, cant possibly work.. 🙂
Lefty are different because they run on flat surfaces with roller bearings - just like the headshok
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Alternative forks - I was meaning like the whyte - altho that is comprimised in lengths of the wishbones as it uses the top wishbone as the steering link.
The sub and the lefty both turn the suspension - a true alternative front end separates the steering from the suspension. - suspension componenets do not turn with the steering. Requires specific frames tho. Has real advantages in that you can tune resonse curves with the location of the wishbones and pivots and you can make them stiffer for the same weight.
A few motorcycles use them - BMWs mainly
singlewishbone / mcpherson strut / telelever
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Twin wishbone / duolever
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lefty's run on needle bearings which means yor taking more advantage of the stiffness of the tube, in theory you could build a very expensive fork with two legs using the same needle bearing system, but it'd be just that, expensive.
I just bought some 160mm Manipoo Sherman
I love those forks, are they the TPC+ versions?
TINAS, Yes they have TPC compression and rebound adjust... Were they expensive in their day?
Sure the execution in Lefty is different, but they are still uppy-downy things in front of the bike that make it easier not to crash. Cannondale propably has the design pretty well patented, but I'm still wondering why other manufacturers haven't tried anything like it. To me it seems like a pretty smart design altogether and gets rid off some problems both USD and RWU forks have, mainly the ones brought by having to use round stanchions. Sure, it propably wouldn't work in motorcycles due to the speed of the movement (the [s]roller[/s] needle bearings couldn't keep up?) but for bicycle use it seems like an ingenious idea to get rid of stiction brought by multiple seals and bushings and the vulnerability of the stanchions to dirt and rocks.
no, but they were infinately better than the SPV ones that folowed, TPC+ has made a reapearance in recent years, its like conventional foks, USD and SPV are fancier systems, but the simple ones always work better.
Just remember to change the oil in the damper and lowers, manitou always seemed to go off quicker with old oil than other brands, probably becasue they use smaller dampers/less oil to save weight.
And theres a lot of plastic in them so easy does it with the torque when serviceing.
I was just going to bolt them on and ride it!!! guess I could run to a service, I have oodles of fork oil. At £80 I am not expecting earth shattering performance.
thisisnotaspoon - Member
I've ridden marzzochi shivers on a DH bike, even just riding down a set of steps the flex was disconcerting.
Well, I've got Shivers on my Session 10 over the page, and yes if you do the (utterly pointless) twist your handlebar with the front wheel in between your knees test then they twist quite a bit, but on the Black and Double Black trails on the North Shore that I've ridden with them so far I've not noticed flax to be a significant issue. I only notice it a bit on tight rocky switchbacks and on the road if you turn quickly from one direction to another while leaning back. In both cases, the fork would be fairly well extended. Once it gets into it's travel then there are no issues to me.
I think Jedi still rocks a Shiver on his Demo 9, and seeing the riding he does, if flex was really that bad, he'd have died years ago!
Anyway, I only got it because I think they look great, and it was 200 bucks in mint condition...
firstly, where can I get a new lambo for £70k? Dont drag it OT just to avoid the point.
With respect, I wasn't dragging it off-topic at all, I was drawing a direct comparison. The way ferrari do things is better, lighter and more performance oriented than the way ford do things. But it costs more to do it properly that way. It doesn't mean they're flawed in any way, just that they're not mass-market and not the cheapest way to make lightweight stiff forks. I think you're confusing market potential with performance, that's all. Most manufacturers abandon maveric designs when they realise that either they're naff or they're too expensive to make properly. It doesnt make them a bad design, just not an accountants design.