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Long travel forks.
NB: Originally posted elsewhere on the Global Riders Network and appears via syndication.
Just from looking around it seems that most bikes have roughly the same suspension either end of the bike. Yet when you look at bikes like the M3 and V10 they have 10" on the back and only 8" on the front. I understand that there isn't actually 10" of stroke on the back and that its a function of the frame movement but is it not possible to have a 10" travel fork? I'm sure some of those mtx bikes must be 10" forks on them right?
Just a thought. I got this book on the science and engineering of bikes for xmas and I've only just started it so its got me thinking about bike design etc. Does anyone know anyone who works in bike design?
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I'm no scientist, but on long travel frames like those you mention, a lot of that 10" is taken up when, if your suspension is set up for downhill or freeride, you just sit on the bike. Usually around 35%-40% of the total travel. This gives the bike the ability to 'eat up' small bumps. 35% of 10" is 3.5", so just by sitting on the bike you are down to 6.5". Then with say, 30% sag on an 8" travel fork, which is 2.4", You then have 5.6" travel up the front. So the amount of travel is fairly similar.
With personal set up, the rider may use more or less sag at either end to achieve a more balanced feel, so it feels just right.
Oh course you can have a 10" travel fork, super monsters are 12", but why would you want one?
frames are designed with certain length travel forks in mind. The bikes you mentioned have angles designed for 8" travel forks. raising the front end too much stuffs the whole geometry.
It's easier to put more travel in the rear of the bike while keeping a sensible BB hight. If you lift the front you need to lift the lot to keep the steering angles.
Also as MB points out, big travel bikes run a lot of sag. Anywhere between 30-50% is normal for a DH rig
i was just plain old curious.
So theoretically you could have a frame designed to accommodate a 10" fork. I guessed that they were possible just not practical. 10"+ on the front im assuming would leave the realms of DH and enter the league of a pure drop off hucking bike right?
So when Santacruz was making the V-10 a 10" travel bike, why would they have decided to angle their frame to only take an 8" fork? Do we use more of our rear travel? I know I bottom out my front a lot more than the rear.
I really need to get stuck into this book and find out the effect of altering all these components of the geometry. Santacruz actually has some really cool tech articles on their website with regard to suspension in "Joe's corner". Stuff that makes a lot of sense but I just never thought of. Especially the bit about the effect of "wheel rate".
Its really good learning about something you actually give a toss about rather than something some teacher thinks you should know.
They only go for a 8" fork to keep the front end at a sensible hight.
You can have lots of rear end travel with out lifting the bike too much (especially when you factor in sag). But you can't do that with a fork. If you want lots of travel in the fork it' needs to be a longer fork. Take a look at any of the big Canfield bikes like the "Big Fat fatty fat"
or any of Josh Benders bikes such as the Karple
Huge fork rake = slow turning (not good for tight sniggle track)and High BB = higher center of gravity. Might be OK for throwing yourself of cliffs but then again Tyler "Super T" Klassen did most of Josh's big drops at the so called Benderland on an off the shelf 7" travel yeti... in one afternoon. So you then have a big heavy bike that has no handling that can't do anything a standard bike can't. Not much point is there really?
As for suspension physics... You can pretty much disregard anything you read on a manufacturers website.
While the VVP designed by Overland and refined by Santa Cruz and Intense, along with the DW link used by IronHorse, do have some sound theory behind them, most stuff you read on the manufactures site is pure marketing drivel dreamed up by advertising types not enginmaneers.
For a good read with some sound physics which cuts through the marketing BS try this paper
http://www.mundobiker.es/content/view/239/105/1/0/
yeah i know most marketing is BS but the santacruz one is... well less bs than others. they at lease use science to explain it rather than some sort of jargon buzzword. where did you get all this knowledge by the way?
so would it be too bizare to suggest a bike with a front fork linkage rather than pure travel? i know its probly stupid but i'm just throwing ideas about for shits and giggles really.
are there other chapters worth reading in that article? it says thats chapter 5.
linkage? that reminds me of the ol pro-flex linkage elastomer system in the 90's haha that was funny, everyone wanted one of them when they came out, shame they ended up being pieces of crap lol...
plus most new suspension technology seems to have alot of counter measures that work well for anti-bottoming out if u really hit it hard.. i dont know, i know big is better for bling with travel!, but you have to decide as flynny says where the geometry is affected and over-all feel is affected too much to warrant the extra inch or 2 your prob never gonna need anyway.. i think 7,8,9 inches is more than adequate! and too much and its prob like riding a bloody chopper! look at a fox 40 or 888 or boxxer, even a new totem in the single..these have loadsa travel and ill be buggered if ur gonna ever need more than that!
on travel, my only thing is i think the big boys of "freeride" i/e: jumping off cliffs! (steve romanuik, cam mcaul, tyler whatits, mike mcthingy, wade simmons, that guy that jumped the tour de france etc etc and the like) all do massive stuff and major high speed stuff on bikes with far less than 10" up front, i dont thik you really need it is all, there is a point where if you bottom out at a huge drop, the impact has already been pretty much obsorbed by the travel already..unless u land wrong
have been done, and still get done
Lawwill
Grivin 
Are just two examples.
They have some advantages in that they tend to resist pedal bob a lot better and the wheel path, back then up, can eat big square hits a lot smoother.
But they have the share of issues.
1 The back then up wheel path mean the fork tends to lock out like a rigid on flat landings and in corners.
2 With so many moving part exposed to the elements more maintenance, and harder to to achieve stiff wheel tracking
3 The back then up travel also changes the wheel base far more dramatically then a conventional telescopically fork
4 Hard to do big travel with
As for other chapters... I've never been able to find them.
So compared with my reign x1 which has 6.7 inches of travel, if i were to ride an m3 or v10 would it be more the head angle and bb height that i would notice? The back i guess has significantly more travel at 10" but the front only 1.3 inches more. A demo has 8" on the back so that would only be an extra 1.3" as well.
as for the link i played around with the url and came up with the other 4 chapters.
Index
http://www.mundobiker.es/content/view/234/104/1/0/
Chapter 1
http://www.mundobiker.es/content/view/235/104/1/0/
Chapter 2
http://www.mundobiker.es/content/view/236/104/1/0/
Chapter 3
http://www.mundobiker.es/content/view/237/104/1/0/
Chapter 4
http://www.mundobiker.es/content/view/238/104/1/0/
Chapter 5
http://www.mundobiker.es/content/view/239/104/1/0/
thats the one that crappy girvin on the right, lol i remember all my mates dramas with those things, elastomers seizing up, drying out, cracking, linkage wearing and then he snapped the bloody things racing dh at majura and ended up with a nasty injury! avoid them like their cancer haha. reminds me of my ol rst's with the mighty 1.5" travel where the stantions actually popped through the crown if they took too big a hit..they sure have come along way! bit off topic anyway but the memories came flooding back sorry
those other ones on the left looked damn heavy!
just curious bbetty, why the concern for the extra travel fork? u thinking of upgrading from the reign?
i could be wrong too but was thinking maybe the rear cops a bit more weight and force when landing than the front end? i know on bigger hit stuff your weight is usually more over the rear than anywhere.. i know the fork cops it too, but perhaps this contributes to the higher emphasis on travel for the rear than the front? just a guess i dont know...
well if i ever had the spare dosh lying around i would definitely be very tempted but i am genuinely interested in bike designs etc at the moment. you do see a lot of demos and v10s kickin around on farkin for 3-4k but its a lot of money to pay for something thats most likely been flogged.
yeah i understand what your saying about the different use of travel from front and back, it makes sense. also, i guess those linkage forks never got to iron out the creases that rear linkage suspension systems did. the book im reading actually has a history of how the bike came to be and it has diagrams of all its wacky ancestors most of which look pretty dangerous.
anyway, i'm off today to try and pedal a freeride bike round a 200km xc course, a DH bike should be the last thing on my mind.
That's a real long XC course, are you gonna ride it all
John