Re: Full sus 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

CROSS POST REF: http://www.retrobike.co.uk/forum/viewto ... highlight=

The Northern Monkey

1 question back though..... why?

nicklouse

1 some do some dont it depends on the design and the ride feel wanted.
2 just the same way many fork only have a spring in one side.
3 it depends on the bike. the steeper the the decent the slacker the geo needed. Also the frame needs to be strong enough to take the added forces.

Zziplex

You could have gone out for a ride in the same amount of time it took to construct that you 'effin lunatic.

Anonymous

well well well. I am fascinated. I shall be reading this very thoroughly

(don't worry, Nick, I shall stay out, I shall just be reading, I think)

The Northern Monkey

yeehaamcgee wrote:

well well well. I am fascinated. I shall be reading this very thoroughly

(don't worry, Nick, I shall stay out, I shall just be reading, I think)

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bails87

The fork thing......

Think about it, the lower is one piece, the upper is effectively one piece. It doesn't matter if there's only a spring in one side because the left side always has to do what the right side is doing, because they're joined together. It's like saying

why is there only a cable attached to the roof of the lift, shouldn't there be a cable on the floor to make sure that it moves up and down too?

But the floor and 'roof' are joined together, so when the cable pulls the top of the lift upwards, the floor comes with it. Same with the forks, when one side moves, the other moves too, you can't just move one side of the forks.

srands

KONA's email reply to me nicely sums it up:

"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!"

supersonic

The Kona reply does not apply to all scenarios as is plainly evident: longer forks are to be avoided is pure nonsense. Unless you are putting them on old Claud Butlers.

Context please.

Also the rear wheel path can completely avoid any seat tube interference. Depends on the design.

Kona's reply is extrememly generalistic.

Shaggy_Dog

Applying theory to mountain bike design is all well and good if you are an experienced bike designer, but as for picking a bike, sometimes the numbers don't add up. Some bikes sound like they'll be awful, but ride great. Some brands copy other classic designs inch for inch and still manage to mess it up. It's all in the RIDE, try not to think about theory and figures too much.