does suspension need an update?

loves2spooge

i've just started riding suspension again after about 6 years of rigid or bmx (finally decided it was time to grow up...) and have found the change pretty hard going (currently running 130mm forks). I think this may be because of the change in headtube angle, and consequently the trail on the fork (been reading up to try and find out what problem might be) through the compression of the fork (particularly unnerving in fast corners where the change in suspension geometry feels quite noticeable. Does anyone think a system like bmw's telelever (would put up a pic, but new to forum and not sure how) if put on a hardtail bike and adjusted to keep work with a pivoted headtube in order to keep the fork at the same angle relative to the ground might be a good thing? this would mean that your bike could have a 72 or whatever you felt appropriate head angle all the way through it's travel, rather than varying between say 68 and 75 ish for a 130mm travel fork? would avouding this change in geometry through compression be a good thing?
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supersonic

they already exist, but rare. Is your fork set up correctly?

loves2spooge

hi supersonic, think set up is ok, roughly .25-.3 of total travel is sag, never fiddled with damping, but seems reasonable, not over bouncy, but returns fast enough from hits. think i just notice the change in geo. as i'm used to totally static geometry, to me it seems there is an opportunity to make a bike with that surefooted and consistant steering while still giving comfort and grip of suspension.

I was more interested to hear what people think of the potential of these goemetry correction type systems is? they mostly seem to occur on ful suspension bikes, eg. the bmw, and lesser extent whyte, but on full sus the front and rear ends will normally vary in height by comparable amounts on any compression, so usually the head-angle stays pretty constant. would this consistancy be good on a mountain bike (if you could get round the extra weight, and somehow get away from using spherical bearings and all the problems they cause...

opinions?

supersonic

It is an interesting idea, but wheter it will catch on is another matter as will involve a frame redesign for a true telelever. If it does, will then be simple personal preferance. The axle path seems to be more vertical which will reduce small bump compliance.

There is a fork that reduces brake dive called the USE sub which uses the disc brake force to counter dive from weight transfer, rather than add to it using a linkage. Low speed compression damping can prevent excess dive too.

loves2spooge

yeah, i've seen the use system, it's advantages are primarily under braking though aren't they (at least as far as i can see). yep axle path does end up almost perfectly vertical, so yes in theory you get worse small bump performance, but then if you could design the system to take the load off the fork bushings like a rear system, or the whyte prst forks, then the reduction in stiction might be enough to compensate for the small bump performance. alternatively there may be a compromise of halving the haedtube angle change and keeping the axle path moving back over bumps which might result in a better compromise of handling characteristics...

thoughts?

supersonic

It seems to be a trade off of ideals, much like rear suspension! I bet some riders will love it, others who are used to countering dive with weight shifts may find it harder to accomodate. On very long travel forks I can certainly see benfits for some.

Anonymous

Hmm, I'm not sure if it would catch on. Motorcycles seem to have standardized on telescopic forks (for the most part) for a long long time, and the speed of the MotoGP or WSB riders suggests that maybe varying head angle under compression or especially braking, is not much of a problem.

Personally, I learnt years ago to make use of the steeper head angle when leaning over the front, or when braking.
For example, given enough traction, a quick jab on the front brake will make the bike 'snap' inwards, almost like lift-off oversteer, or a stab of left-foot brake in a front wheel drive car.
Alternatively, throwing weight forwards, or throwing the front down using your arms, can have a similar result.
I use both of these techniques almost subconsciously now when I'm cornering, and find out that the corner is tightening, or was tighter than I first thought.

loves2spooge

thanks for the comments guys. Well like any different ideas i'm sure it won't be to everyone's taste, but it might be interesting to have that choice. RE: motorcycles standardising on telescopic-no argument, however the conditions are rather different, as both the front and rear wheels tended to be leaded evenly and almost all bikes have full sus, therefore with equal compression on front and rear you have no need to correct head angle, and the bike move down, rather than pitching - that's why i was specifically thinking of the system for a hardtail, as currently all these long forks people are starting to like seem to be begging for something like this to tame their handling characteristics. although maybe i'm just picky... i feel there should be a better way, and just find it interesting thinking what that might be.... afterall if someone told you 15 years ago 90% of xc bike would have disc brakes in 15 year time you'd have thought they were crazy right? is there a possibility for a big geometry shake-up?

nicklouse

there are lots available in Germany.

google Parafork and German Answer

Anonymous

loves2spooge wrote:

RE: motorcycles standardising on telescopic-no argument, however the conditions are rather different, as both the front and rear wheels tended to be leaded evenly and almost all bikes have full sus, therefore with equal compression on front and rear you have no need to correct head angle, and the bike move down, rather than pitching

But with the weight of a motorcycle, the effects of brake dive are enormously noticeable.
I'd say it's enough of a problem that most bikers wouldn't dream of touching their front brakes whilst cornering.

loves2spooge

thanks nicklouse, i've seen a few simillar designs before, however all seem to be anti-dive forks, while using a self-adjusting head-angle system like the telelink would reduce dive i am more interested in people's thoughts on general trail handling, say if you shift weight around, or hit bumps in corners, go round them fast, or any combination. it's possible for geometry to change quite a lot due to these factors, particularly on longer travel bikes. how do you think general handling could be effected by this constant steering geometry, do you think that differences would be noticeable, or would the occasions where it would be beneficial be so rare as to make the system useless?

nicklouse

loves2spooge
are you looking at HT use or Fully use?

TBH i would not be looking to a constant head angle on either set ups. As the ability to play with tha angle in use has a lot of benefits.

a constant head angle would have very limited benefits to any use that i can currently think of. But it is early in the morning.

Anonymous

Theoretically, having a standard telescopic fork, hitting a bump should not change the head angle, just bring the front wheel closer to the bike, if you see what I'm getting at.

loves2spooge

hi nicklouse, just looking at hardtail use, as otherwise the rear suspension is likely to keep angles fairly constant except under braking.

Maybe i'm just not using my variable head-angle properly, i just find corners particularly in tight singletrack etc that i used to rail on rigid i now end up steering wide as my balance goes off under suspension compression as i'm never totally sure how the bike will steer as it's feels pretty different depending on speed, and i often have to often slow down to get out of potentially sticky situations. essentially i think when i've adapted to the bike it'll be fine most of the time, but then isn't there the potential to make a system so that steering will be more natural without having to compensate for occasionally odd bike movements and changes in steering characteristics. for my mind it's a little unpredictable, and i'd have thought consistancy would be key, but i'm very willing to be told otherwise.

loves2spooge

i see what you're saying yehaamcgee, as it seems the angle will stay the say in these circumstances, this is one issue where the real-world will tell all. To my mind when say just the fork goes up over a bump, then the bike's wheelbase (between the two axles) is momentarily tipped back slightly, while the rider and frame stay in the same position, thereby still resulting in a steepening of the head angle, afterall, both wheels are still touching the ground. it seems to me to be logical to measure the goemetry relative to where the two axles are as effectively the horizontal, then calculate H.A. from there.

afterall when you ride up a hill would front wheel is higher than the rear, but it has no effect on the trail of the fork, and head angle will feel the same, as the geometry does not change.

- seems to be turning into quite an interesting discussion - keep the opinions/questions coming!

Anonymous

loves2spooge wrote:

To my mind when say just the fork goes up over a bump, then the bike's wheelbase (between the two axles) is momentarily tipped back slightly,

ah, yes, of course!
however, I can't get my head round the fact that having a constant head angle would probably be worse in that situation? hmm.
I'm trying to visualise it, and the effect it would have on handling if the angle of your forks (castor?) were to change for every bump.

as for the way long travel forks behave round rough corners (the 55s are 160mm) I do notice the handling being a bit odd at low speeds, such as when you're slow enough to feel every individual bump.
But, at higher speeds, it deosn't seem such a prevalent effect, and the bike seems to float more effectively.

supersonic

Its all about predictability. If we can make the gaps smaller, then we are more accurate ;-)

This is what a lever system tries to achieve. However for many accuracy is what about we already know and can predict, and make use of.

"afterall if someone told you 15 years ago 90% of xc bike would have disc brakes in 15 year time you'd have thought they were crazy right?"

I still think for many riders discs are overkill! Not saying there are not advantages, but to take things in context. And for many riders, budget dictates what we have on our bikes. to me it is always fork first, wheels and tyres, frame (and geometry, but I take that as given to start), brakes, and drivetrain last. Other bits are more about longevity and weight than pure performance.

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loves2spooge

i can see what you're saying meeyaahmcgee, i was thinking that the handling should stay far more constant than with traditional systems, as when the wheelbase angle changes the fork will always be at the same angle relative to the effective grounding of the bike, therefore the trail - the distange between the imaginary contact area of the headtube with the ground, and the front wheel's actual contact area with the ground, will always be the same. I feel this SHOULD give more consistant handling, but no-one really seems to have effectively done this before, so i don't know if it would just feel weird? i have to agree that part of me thinks it would be weird having the fork go over a bump, as it looks like the fork would change angle when normally the angle would look like it was staying the same, however if you consider steering when the fork was compressed on a normal set up over our imaginary bump, then the fork is compressed, both wheels are in contact with the ground, therefore the head angle will be steeper than if the fork was uncompressed. i don't think the angle the bike is at matters, it seems to be all about the headtube angle relative to the imaginary line between the two wheel centres.

supersonic, i totally agree with you about discs, silly expensive, do actually run them myself, but only off ebay if i can get them for £30 or so, and i still find it hard to justify these longer travel forks for the kind of riding i see most people using them for, but it's mostly about feel, i love the solid feel of discs, and the knowledge i'm not just bending my frame every time i squeeze them...

what do you mean about a lever system? do you just mean suspension as it is with telescopic forks on an unpivoted headtube?