Part of the issue with mtbs is that they have to cope with a huge variety of situations that motorbike don't. On a (road) motorbike you need to soak up small to medium sized bumps and not dive too much. On an MTB there's a lot more to contend with. Small bumps are not so important but then you've got steep technical rocky bits, big dropoffs, air time, bobbing away climbing, sprinting out of the saddle.
I've never ridden a linkage fork, so I can't really comment on how they ride!
For several reasons, and none of them to do with fashion:
- why overly complicate a design? We already have bearings at the rear, why double up the amount of maintenance and replacement costs?
- more difficult to clean.
- more parts involved means higher manufacturing costs and therefore higher prices.
- weight is an issue unless you use expensive, high-end materials resulting in higher costs, and ultimately, higher prices.
- more places to collect mud, hence higher weight due to the amount of mud collected out on the trail and higher maintenance.
Oh, and they look butt ugly.
^^ all of these reasons sound like some of the rear suspension designs many of us have. That's not the main reasons. The bike ind invested in telescopic forks and the bow wave of marketing succeeded.
I had a PRST-1 for a couple of years followed by a PRST-4. I made the mistake of fitting flat bars to the PRST-1 which made it more prone to throw you over the bars. After riding Jon Whyte's own PRST-4 I set mine up differently with the front shock very soft and as much weight as possible over the back wheel. I still regret getting rid of that bike, the best fast XC bike I ever had.
Molgrips - and a linkage fork can be built to improve performance in any situation. Separating steering from suspension leads to a stronger more responsive fork, removing the stiction from sliders improves performance, separating braking and bump loads means yo can tune a it to work better and finally you could use existing rear suspension units so all that dfevelopment of fancy damping can be used.
Mikey - need not be more expensive or heavier - remeber simpler load paths so less strength needed and its easier to use of the shelf bearings than manufacture stanchions and sliders to a high degree of accuracy.
Its also cheaper and easier to replace a bearing than a stanchion and bushes
^^ all of these reasons sound like some of the rear suspension designs many of us have.
Exactly, so why double-up the problem?
Its also cheaper and easier to replace a bearing than a stanchion and bushes
Yes, but don't forget you still have a shock unit to service, as well as all the pivots.
Molgrips - and a linkage fork can be built to improve performance in any situation
Yeah yeah we've done this before 🙂 I like the theory of linkage forks but I'm not so confident that I would back them in ANY situation without really having ridden them 🙂 However I still think the requirements for road motorbikes are different to mtbs
"there is a greater body of knowledge on how to make a telescopic fork work"
Yeh, because they all last so long without wearing out, they need so little maintenence and spares for replacing worn parts are so cheap/easily sourced
A few bearings, a couple of shock bushings and air sleeve maintenence (granted not cheap if you add it all up*) must be cheaper than if your fork bushes and stantions go. Requiring a £200+ set of uppers and now rockshox (for one) have made the lowers with non-replacable bushes, you need a complete set of lowers on top. If someone else is servicing it you're talking £400-500?
"maintenance and replacement costs?"
*Shock service sent away around £80ish (or less for less complex damped shocks) plus ~£40 for a shock shaft if needed? Plus a few bearings, cheaper than worn out forks as above?
"more difficult to clean"
But what NEEDs cleaning? Shock seals/shaft, a telescopic fork (okay not a lefty) has twice as many and many part of them are half hidden away behind the arch. Bearings should be sealed, plus once replaced are new again?
"Exactly, so why double-up the problem?"
Make it simpler still, put a rigid fork up front ..
Conventional sliding forks operate at a 1:1 ratio. Most linkage designs are at a higher ratio. Just like rear suspension, the lower the ratio, the more tunable it is.
In either issue 1 or 2 of http://www.switchbackmb.com they interviewed suspension pioneer Mert Lawill. He says that he's bringing back the Leader fork design...
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this is a hossack supermono i saw in the paddock once. Everything is made out of steel, and to quote the owner
"The front and rear 'forks' weigh 2.5kg each (about a quarter of the weight of a pair of forks and half the weight of an aluminum swingarm). This reduces the amount of unsprung mass and allows the sprung mass to be close to the centre of the bike. This allows improved suspension control, which becomes more of an issue with lighter bikes."
🙁 feels bad about making ade feel like i am trolling.
I am pretty sure i read a review mentioning diving back in the day and the people I've talked to who rode them have mentioned it. I do accept that i never rode one and as such my thoughts can be ignored!
Sorry for any offense ade and im sure you do know a whole world more than me on the subject. Would love to hear more about the design process and if there is some anti-dive going on in it.
Good answer Ade 🙂
the way I see it is simple. Linkage forks are technically better, but don't look "normal" therefore are shunned by the public.
<tries to think of smutty analogy, but fails>
From what I recall of the AMP forks I had years ago the only problem with them was they squeaked a fair bit.
Oh, and I broke them after a rather heavy landing 🙁
They were light, seemed to work pretty well and looked quite nice.
They're also the only bit of kit I've ever owned that people have shouted covetous thoughts about when they've seen them. That may not be a benefit.
Used to ride with someone who rode a prst-1. He loved it, especially since he didn't have to take the fork apart after every muddy ride, like on his last bike (some manitou things). The head angle didn't change when the suspension was compressed (apparently). He cracked the swing arm, mainframe and fork, he was a hard rider though.
I've got a PRST-1 languishing in the shed for commuter duties, IMO it was fine for XC, tracking beautifully over small bumps but when the pace was upped it would struggle and I went OTB more than once as the front plunged through it's travel.
I think that conventional tele's have had 70 odd years of R&D by a lot of manufactures and the linkage driven suspension has had hit and miss R&D over the same time. Perhaps if the same amount of money/time had been thrown at linkage systems they would not be seen as the quirky, sometimes flawed system that they can be.
Market forces/inertia have also influenced the direction/fashion of the motorbike/cycle industry.
However a 140mm travel DRCV shocked modern interpretation of a PRST would be very tempting.
In my experience of the PRST design (over 5000 miles) the weak point was the spherical bearing, on the PRST-1 I was changing them every couple of months until they brought out the rubber boot to cover it, but they never completely solved the problem. I never had the slightest problem with the other bearings.
agreed on the weak point being the spherical bearing - my PRST-4 lasted just six miles on it's original ! 😮
Turned out there was a machining fault on my lower wishbone; got a replacement wishbone couriered out the next day and it's been fine since (normal replacement schedule as I expected should I say) - That reminds me though - it's starting to exhibit the death rattle; I should get it booked in for a replacement...
BMW use them on motorcycles to great effect - both double and single wishbone systems. I had a BMW with the telelever set up. it was great and would work well on MTbs IMO
Ermmm no they don't, not for the "proper" off road 450 they had a few years back. Honestly if it was THAT much better it would be use at least in racing, where money is no object and weight matters more.
juan - Member
...if it was THAT much better it would be use at least in racing, where money is no object and weight matters more.
Not necessarily. Racing is a very conservative thing where incremental changes get made. Riders are accustomed to the feel of telescopics and having to adapt to a new system is highly risky. It's unlikely anyone is going to make the investment in a new system which has a high risk of being rejected because of the status quo. There's generations of riders who expect the front to dive when the brakes are applied hard and their riding reactions are built around that. Maybe someone stepping off a rigid bike may be the best candidate for a linkage system, but there's no top level pros racing on rigid forks.
We may see it happen in motorbike racing as the factories are all having to overcome problems with chatter in front wheels. Or more likely, even more expensive telescopic forks...
Are AMP the ones Philippe Perakis used to use back in the day?
I rode a PRST-1 for three years and I lost count of the number of "guaranteed for life" spherical bearings it consumed. In a straight line (up or down) the fork worked reasonably well but I always felt it had a tendency to "tuck in" on tight corners and throw me off.
