Why not linkage forks? « Singletrack Forum

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Why not linkage forks?

66 posts & 42 voices | Started 3 months ago by hisdog | Latest reply from DWH

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hisdog - Member

Someone on another thread mentioned the Whyte PRST-1, which was famous for its linkage forks. They always got great reviews, even though opinions on their looks was, erm, divided. Personally I think it looked great.

Now, the advantages of a linkage fork are that you can fine tune the travel path of the wheel (I seem to remember that the Whyte went backwards then up) and that they can be made stiffer than a 'normal' fork. Plus, surely, with a bot of thought they could be made to look a bit more aesthetically pleasing than the Whyte's. I would hav thought that you might also be able to isolate braking forces like on the USE ones of a while ago.

So why aren't there any around?

Posted 3 months ago #
IA - Member

So why aren't there any around?

Cos you didn't look for any?

http://www.german-a.de/en/kilo.html

I often wish to
" feel the supremacy and the light weight of their suspension fork on every single ride,"

;-P

Posted 3 months ago #
LoCo - Member

http://books.google.co.uk/books/about/Motorcycle_tuning.html?id=l2Zizg8I8p8C&redir_esc=y

and look at the bibliography in the back too.

Generally people don't like the feel or lack of from them although they can work quite well for given uses.

It would take a very long time to answer this fully

Posted 3 months ago #
pushbikerider - Member

When the travel goes over about 2" the axle path starts getting a bit weird and unpredictable. That's probably why the ones you can get these days (like the German A forks) are lightweight short travel jobs.

Plus you have the fun of dealing with lots of little fiddly bearings and the simplicity of two tubes sliding inside each other starts to look more appealing

Posted 3 months ago #
TandemJeremy - Member

IMO the conservatism of the consumer and probably most importantly thay cannot go on conventional frames ( apart from leading link which misses someof the advantages)

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

Posted 3 months ago #
Kuco - Member

Amp use to do some years ago.

Posted 3 months ago #
redfordrider - Member

I quite like the look of these http://www.german-a.de/en/kilo.html I guess that people are too concerned about how their bikes look than how they ride.

Posted 3 months ago #
TandemJeremy - Member

Pushbikerider - not necessarily - using double wishbone you can tailor the fork to have any path you want. My BMW had 7" of travel.

Posted 3 months ago #
hisdog - Member

Plus you have the fun of dealing with lots of little bearing

But you have that at the back of full sussers anyway and everyone seems to get on with it quite happily.

Posted 3 months ago #
porter_jamie - Member

IMO the conservatism of the consumer and probably most importantly thay cannot go on conventional frames ( apart from leading link which misses someof the advantages)

i agree 100% - bmw have been the bravest with the recent hossack and latterly the telelever front end, but largely everyone else has stuck with forks.

i would love to see something like a hossack system on a mtb. a friend of mine raced a hossack supermono and he claimed it provided huge confidence in the front end, especially on the brakes. i am imagining a 6" travel bike with a ccdb

Posted 3 months ago #
epicyclo - Member

Fashion to some extent.

Plus there is a greater body of knowledge on how to make a telescopic fork work nicely.

There's nothing wrong with the idea of a linkage fork, but many of the early linkage forks were poorly made with inadequate bearings (but so were the telescopics). However the suspension unit can be replaced with something more modern to improve them.

For the modern market the amount of travel would need to be greater so the linkage designs would have to be beefed up. Although you don't need as much travel on a linkage fork if you have it set to anti-dive, you still have to satisfy the market about having so many inches of travel.

Don't know if Parafork are still going, but their fork looks ok.

Posted 3 months ago #
GlitterGary - Member

I've got a set of the amp ones- they are steel, light as, and work pretty well for xc.

Posted 3 months ago #
LoCo - Member

If they worked better than telscopic forks, they'd be used in racing.

There is the agument that when motorcycle production was big, just after the war, when they had alot of machines for producing tubing (gun barrels) the most effective and cheapest way to produce the forks was make telescopic ones using the skills and machinery from the war effort, development went down this path and has stayed like that.

I don't necessarily agree with either of these statements mind you

Posted 3 months ago #
toys19 - Member

teej has it I reckon, too hard to get a foothold in the market place, and forks work pretty good..

Posted 3 months ago #
wool - Member

I had a pair of AMP forks on a Merlin ti XLM they were not to good I remember reading the instuctions and thinking this is so wrong " if you get a squeaking sound from the bushes just spray your bidon over them'' !!!!! Thats after nearly 20 years and I still can't get that out of my head. I sold them on soon after getting them.

Posted 3 months ago #
titusrider - Member

everyone who ive ever heard about the PRST-1 from said the fork dived deeper and faster than..... (insert poor taste joke here) and was therefore a complete nightmare to stop yourself going over the bars.

Posted 3 months ago #
tazzymtb - Member

Posted 3 months ago #
wwaswas - Member

they do look good on some bikes;

just mainly not bicycles.

Posted 3 months ago #
porter_jamie - Member

http://www.hossack-design.co.uk/

worth a read

Posted 3 months ago #
TandemJeremy - Member

The forks epicyclo posted above are compromised to allow them to fit on conventional frames - the BMW / Hossack system the wishbones and shock do not turn with the steering

Posted 3 months ago #
thisisnotaspoon - Member

Where do USE SUB forks com in? Kind of halfway between a leading link and telelever setup.

I always thought the problem was no one knows what the 'ideal' front axle path would be, do you go back then up to absorb impacts (which telescopic forks do quite well) but gives you sharper steering as the suspension compresses, or do you go verticaly upwards, giving a nice constant wheelbase as the axle path matches the rear better, but doesnt absorb impacts so well?

What I dont get is why fork stanchions are always parralel tot he steerer tube, surely they're missing a trick to slow the steering down a bit by making them more vertical so for the same static rake/trail figures the steering would slow down as the suspension compresses.

Posted 3 months ago #
epicyclo - Member

It is much easier to come up with a bad design for a linkage fork.

I would prefer something like the Vincent Girdraulic to a tele.

Posted 3 months ago #
pushbikerider - Member

TJ - you're right; you can get a much better axle path with a frame designed around the forks and longer links, I was thinking more about the self contained design needed to retro-fit to a conventional frame.

That Para fork does look rather good mind, unfortunately I was involved with making these instead

Posted 3 months ago #
epicyclo - Member

thisisnotaspoon - Member
...What I dont get is why fork stanchions are always parralel tot he steerer tube, surely they're missing a trick to slow the steering down a bit by making them more vertical so for the same static rake/trail...

The more vertical the fork tube is the more likely it is to stick. There's a sweet spot of headangle for teles - too much slack and they bind, too little and they bind. Fortunately the sweet spot has a reasonable range. Also with larger diameter tubes being used now, it is less of a problem. The shorter the fork the lesser the problem.

Posted 3 months ago #
leggyblonde - Member

Suntour FTW!

Posted 3 months ago #
wwaswas - Member

there must be, oh, several whole milimetres of travel on those suntours.

Posted 3 months ago #
TandemJeremy - Member

I think the telelever single wishbone type have potential for mountain bikes. Simple system, not too many bearings needed, direct mount handlebars, natural antidive while allowing bump absorption so yo can have soft springing without it plunging under breaking

Posted 3 months ago #
thepodge - Member

I my mate had some Girvin Vectors when I had RS Mag 20s and his were far more reliable than mine. I'd still love a set of linkage forks but then I'd also love a belt drive IHG full suss as I'm odd like that.

One of the issues with linkage forks has nothing to do with the suspension, they'll only fit a certain maximum headtube length so they end up being made long to accommodate all sizes and can as such look a bit odd

Posted 3 months ago #
stevehine - Member

The limiting factor on the Whyte (and you can see it on mine (apologies for posting the picture on a 2nd thread) is that the top linkage swings up towards the handle bars; limiting the maximum travel available by the height of the front end. It feels a little high with the travel available as it is; if you were to up it to 140 or more than it would get ridiculous.

I know Ade Ward (who was involved in the design and sometimes pops up on here) uses a 24" front wheel to help drop the front end down; though this steepens the head angle slightly. I've just swapped to some fleegles to help lower the bars without compromising the head angle change - it's a little steep by todays standards

Posted 3 months ago #
stevehine - Member

Oh; and fwiw @titusrider - I've never had an issue with that problem; but then I've only had air cans on the front of my PRST1 / 4's - It may well be a spring thing.

Posted 3 months ago #
choron - Member

My thoughts are that the weight and complexity to benefit ratio isn't quite there for push-bikes, and might not be there for motos either.

It's often a more effective solution to put your time and effort into making an already relatively mature technology fit the application better (linear push-rod dampers in telescopic forks), rather than scrapping the whole system and generating entirely new sets of problems (stiffness, damping characteristics, unsprung weight etc) for a possibly marginal gain (better wheel path).

In a way, this is analogous to the single pivot vs multi-link question: by putting design effort into damper technology, stiffness and weight, single pivot bikes remain competitive despite their 'obvious' flaws. Linkage forks are the same but more-so IMO.

Posted 3 months ago #
pete68 - Member

I also had Girvin Vector forks many years ago on a Proflex.By far the worst forks i've ever had.I swapped them for some RS Judys and even they were massively better.

Posted 3 months ago #
Macavity - Member

http://singletrackworld.com/forum/topic/what-was-wrong-with-leading-link-forks-whyte-use-sub-girvins

Posted 3 months ago #
TandemJeremy - Member

the whyte is also compromised by the short top wishbone and the top wishbone being used for steering - compare to the BMW double wishbone system which has a separate steering linkage. the shock would also effectivly have a falling rate leverage ration from the angle its mounted at - presumably for a reason tho

Posted 3 months ago #
b r - Member

I got into the whole 'telescopic forks are a compromise' story back in the 80's when I had a Feet Forward M/C, like these:

http://www.bikeweb.com/node/458

And I've ridden most of the old crop of various methods, but tbh none of them were as good as the mass-produced forks available on bikes at the time. I don't doubt that with some decent engineering they could be (as good?), but even those tried didn't sell particularly well (BMW excepted):

http://en.wikipedia.org/wiki/Yamaha_GTS1000

And tele-forks just work

Posted 3 months ago #

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