Re: FULL SUSPENSION FRAME DESIGN? FRONT SUS: EVEN TRAVEL?

[srands]

Hello, obviously front & full suspension has been around for many many years now, but I realise my following questions aren't debated often by keen cyclists, shops, MTB mags/websites, so I have 3 questions about suspension:

Full suspension bikes QUESTION:

Q1. In the main (To generalise, amongst the mass of many differing models!) do FULL SUSPENSION MTB's have LONGER chainstays, then there HARDTAIL counterparts?
EG:
FULL SUS: GHOST AMR LECTOR

& HARDTAIL: GHOST HTX LECTOR 9000?

FULL SUSPENSION CHAINSTAYS LONGER THEN HARDTAIL, DIFFERENCE: 10mm=1cm



Or either ODD FRAME DESIGNS TO PREVENT THE REAR TRIANGE/ WHEEL&TYRE FROM TOUCHING THE FRONT TRIANGLE (SEAT TUBE)?

Thoughts on these matters:
The reason for my question is when closely examining how far away rear wheel tyres are from the SEAT TUBE, theorising how much SUSPENSION TRAVEL the bike would have, IF the rear triangle could pivot. At most depending on the bike and size, the predicted suspension travel seems to be about 10cm to 15cm, approximately, if the angle/legth of the SEAT TUBE remained the same.

After comparing alot, I have arranged these into a few categories amonst full suspension frames:
(A) CURVED/GREATED ANGLED SEAT TUBE (Like: SCOTT GENIUS LT40)

(B) PART OF SEAT TUBE MISSING (Like: SAN ANDREAS)

(C) CONVENTIONAL LOOKING FULL SUS (Like: GHOST AMR LECTOR 7700)
& presumably less travel suspension then the two categories above (A&B).

Front suspension QUESTION:
Q2. In the main (To generalise of all mass produced front suspension forks) is the SOFTNESS/HARDNESS of a fork, only controlled on one side of a suspension fork?
So does travel just happen to level out EVENLY on both fork upper legs, when under pressure?

It's unlikely that any forks have an the adjuster has a linkage cable/bar, through the fork crown, to the opposite fork upper leg, more likely some forks have adjusters on both upper legs. Most quality suspension forks I've had only had an adjuster on one leg of the suspension fork, and these worked EVENLY on both sides, despite being adjusted on just one side.

Thoughts on these matters:
I realise the length of travel a suspension fork can have, is limited by the distance between: The top of the front tyre (Or fork brake) & The suspension fork steerer crown (Something like 10cm).

Hence I realise to increase travel, the simple option is to increase the length of the legs of the forks.

So fitting a longer fork, will give the bike a higher front end, and a slacker head/seat tube angle (But ironically the head/seat tube will appear steeper because the head/seat tube is LESS vertical, obviously head and seat aren't perfectly parallel, mean they are not the same angle as each other, on most bikes). So the bike will be more rideable over steeper terrain.

However in theory the greater the length of the fork legs (Upper & Lower), the greater the leverage of the legs being pulled from the crown, but isn't TRIPLE CLAMPS a gimmick? Or only really needed by WORLD DH CHAMPS (Or serious hobby riders)? Can't say I've had any problems with rigidity/wandering suspension forks, or legs ever working loose.

Q3. Fitting a longer fork will change the geometry of the bike that the forks are fitted to. What is deemed as too slack head/seat tube angle (EG 45 degrees), as adversely affecting the geometry of the bike?
Obviously bikes have different geometry, and a typical length fork will be used in the design (Compuer Aided Design) of bike frames, and since some full suspension frames are a very elabourate design, and the head/seat tube angles only become obvious from manufacturers geometry statistics, also since full suspension frames aren't the conventional two triangles, hence tube lengths maybe invisible line calculations (CAD), etc.

Thoughts on these matters:
For example for riders a too slack head tube would be ineffective steering, that would also make ineffective use of the front suspension (Which is more likely the damage the suspension fork crown because of the increased torque load on the fork crown), because the head tube would be at too much of an angle, this prevents direct pressure from being excerted to compress the fork (Hence impacts act like leverage instead). Hence riders don't want to ride the modern day equivalent of the Penny Farthing (Ironically enough, on these historic bikes despite the huge front wheel, the head tube was near vertical, hence the riding position, was very high in the old days, elevated you might say, those Crazy Victorians!).

Cheers on your thoughts, on this one!

Stephan

MTB routes in/near Hull, Humberside

www.srands.co.uk

 

[T'boo Ted]

wow what a bonkers topic! I'll try to answer with my limited knowledge (disclaimer, what I say is not fact, and may indeed be wrong)

new bikes the rear wheel doesn't usually travel in an arc, but is designed to travel more upwards, well modern stuff. old short travel stuff didn't matter about hitting seat tube
you have a damper in 1 leg of fork and the spring in the other, they work independently, but the stiffness of the fork bracing make them work in unison.
a frame designed for a certain amount of travel will always slacken out from a longer fork, so they design a frame around a longer travel fork and adjust the angles.
using a triple crown will keep the fork rigidity when using much longer travel forks and being used in more extreme terrain...
having a slack head angle helps when going DH, as you are pointing DH.

And what the hell does this have to do with retro bikes?

 

[srands]

FRAME/FORK LIMITATIONS

What has it got to do with old bikes?

Well every year, there is hype and anticipation of what the industry will surprise us with next year: i.e.
~ Front Suspension, with even longer travel
~ Full Suspension, with even longer travel

But my point is the LENGTH OF TRAVEL is limited by the:
~ LENGTH OF THE FORK
~ FRAME SIZE (CHAINSTAY LENGTH & OBSTRUCTION of SEAT TUBE in relation to REAR WHEEL)

Hence without resorting to silly riding positions, I guess 10cm to 15cm is about the most suspension we are going to see, unless we talking 22" + MTB's or something.

But MTB's and their components have progressed vastly since the first incarnations I remember seeing, components are far smoother shifting and longer lasting, and the rear suspension has come along way, far better since, for example, Pro-Flex rear suss with about 1cm of travel, but that was 20 years ago! And my mates who had them, loved them to bits, I'm not sure which of my mates didn't have a 752, or something like that instead. Well my mates who rode well, all rode them.

OK!

Cheers

Stephan Rands

MTB routes in/near Hull, Humberside

www.srands.co.uk

 

[T'boo Ted]

well yeah a fork can't have more travel than its own length, thats a given, i'd say the frame travel is more a function of the suspension design that frame size, the frame will come into the equation eventually...
but there are already forks with over 20cm of travel and frames with over 25cm, both have been around for a little while. I'd say you could get a little more, but how much do you really need on a mountain bike?


Still, I think maybe you have the wrong section...talking about the merits of old proflexs is more in line than how much suspension can we achieve...

 

[FluffyChicken]

I know nothing about the rear suspension, but I do know where a nice proflex is you maybe could have a play on, though. I think it's to big though.

Anyway front.

The suspension and damping setups.
It depends on the design, you can either have identical in both legs, like the old RockShox MAGs and PACE forks or the turn of the 00's Bomber forks.

Some like the JUDY employed springs/MCU's in both legs but only damped in one leg.

To make things lighter and simpler they did start to spring in one leg and damp in the other leg, while this increases the twisting forces due to the asynchronous nature (ones pushing while the other is dragging sort of thing). Everything needed to be bolted together better, the legs got stiffer, the crowns became stiffer and most importantly the brace and HUB binding/setup became much stiffer to keep the legs acting as one.

When taking angles into consideration you need to take account the length of the bike, a longer bike (wheelbase) will not be altered so much compared to a short wheelbase bike and you need to account for sag in the forks under actual use not just it's axle to crown length. A longer travel fork would usually be used with a greater sag setting.

The biggest problem designers have had (other than new EU tests or whatever they are) are stopping the long forks snapping the frame with the increased leverage of a long thing.

To negate the slacker angle you can use a shorter stem to get the 'quickness' of steering back. Kona used this principle for quite some time. Though it does alter the reach and many other things

http://bikegeo.muha.cc/ is a good simple site to use

 

[Bullpup]

Interesting topic - even if I am not sure I understand it all. It does seem to me that there appears to be a largely unexplored area of the effect of rising rate springs.

 

[mikesnowdon]

Can I just say all of the bikes in the first post are ugly as s**t!
:shock:

But then most modern bikes are :roll:

EDIT: The sannys ok i suppose

 

[andrewl]

I'll briefly reply to your many questions...

Q1: Yes and No; there are suspension frames which have shorter effective stays than their hardtail counter parts but yes as the travel goes up a longer stay gives better characteristics for the intended purpoises

Interrupted seat tubes are primarily a function of suspension movement and not wheel clearance

Q2: because mountain bikers like things lighter, spring media and damping are placed in different sides. Some forks have duplicate damping/springs both sides (notably original Z1) but they will be heavier. Even though the side may have different functions, the two sides are mechanically linked but a one piece lower (or bolted arch) and at the hub.

As for DUAL CROWN forks, well simple engineering will tell you for a longer travel fork they are not a gimmick. Hint look at the steerer on a long travel single crown and compare that to a dual crown and google bent steerers.

Also a triple clamp simply means there are three clamps and a triple clamp can the used on single and dual crown forks. The Marzocchi DH3 is an example of a single crown triple clamp ie two clamps for the stanchions and one for the steerer.

Q3: Depends on the intended purpose of the frame and the rider, a dual slalom frame will by design have a slacker head angle.

 

[srands]

KONA's email reply

And here is the email reply from KONA after asking them as well:

"Suspension bike have longer stays. The less traditional styles like interrupted seat tube become more common as the travel increases and it is difficult to package the mechanism while keeping the rider in a reasonable pedaling position.

Damping control is often only located in one leg of a fork. The first suspension forks had both sides under control but it was found you could get the fork to work fine with only one side and save weight so that’s the current style of forks. Most will still run preload on both sides.

Long forks are to be avoided. The slack angle means the rider’s weight is back and the front tire is un-weighted. This means it looses traction or washes out on descents or wanders and wheelies on climbs. Also the fork gets more energy put into bending it instead of compressing it so the damping control can be compromised. The right angle to keep the head tube is more of a soft science than a hard and fast rule. It depends on the type of bike and the rider.

Happy Trails!"

 

[The Ken]

That's pretty good that they took the time to reply.