I have a 2003 Kona Cinder Cone, which I'm gradually upgrading. Current target is a new pair of forks, to replace the rather pants 80mm Marzocchi EXR airs that it came with. I'm mulling over a pair of MX Pro ETAs, or possibly Marathon SL Coils - there seem to be some fairly good deals going on these at the moment, presumably because M. are about to release the 2005 forks.

Problem: The MX Pros only seem to come in 105 or 120mm travel, and the Marathons are hard to find cheaply in 85mm. So I might be looking at increasing the fork travel from 80 to 105 mm.

Question: Is this likely to either (a) screw up the handling, or (b) damage the frame. If so (or even if not), has anyone got a recommendation for a good mid-range (c.£300) fork, about 80mm travel, not too flexy ?

They'll be for general 'aggressive XC' use - I need them to take a reasonable beating, but I'm not going to be racing, or hucking off cliffs with them (at least, not more than once ;-)

TIA

Chris

Normally the extra 20mm won't matter much, though anything more than that will.
Where the problems start is when the manufacturer has already added that extra (ie bike was originally designed for 65mm, but shipped with 80mm cos its still fine)
But your Kona will be fine at 100mm. If the steering gets a little slow fit a shorter stem.

Interesting point - My S-Works is built to take an 80mm fork (normally the Fox F80x). I slapped on my Duke XCs which have an adjustable travel of 63 - 108mm. I normally use it at between 75 - 80mm as at this point the bike is responsive and nippy, but retains sufficient "boinginess" to be useful. On Saturday I cranked the travel up to 108mm as an experiment and it completely changed the ride - the bike steered like a dog and climbed like an asthmatic gerbil. Horrible.

The moral of the story? A 28mm change in geometry DOES matter!

Hmm.

I personally found that putting 120mm Shiver SCs on a Kona Cinder Cone didn't make the ride worse at all, despite the fact that it came with 63mm Indys. Shivers do have a ridiculously low stack height though. Also I'm used to riding a bike with a 64° head angle...

Go for it I reckon, 100mm will be fine, especially on one of the newer frames. Is it steel or alu? I'm getting all misty-eyed now.... *sniff*

The thing is Steve I reckon your S-Works is really optimised for either SID's (65mm) or F80's so its going to be really 65mm with 80 as an option. Hence 108 is too much.

But also your Dukes aren't really 108mm travel forks. They are rely heavily on overlap to keep them stiff at around 80-90mm travel, and at 108mm they get rather flexy, which won't help.

But Rich has a good point. Not all 100mm are equal.

but if you had a 100mm fork and you ran it with the recommended sag of 20 to 30% that = 70 mm travel????
am i missing something??
does that mean an 80mm travel fork is only running at 50mm travel???

i run 130mm z1's on my hummer and it rocks!

or maybe the industry is conning us.
"can i have some 120mm travel forks please?"
"certainly sir, but they only have 85mm of travel sir. there you go sir"

A-ha! Good points Doc...

The whole travel thing is a wee bit of a red herring, really. What counts is the overall length of the fork when you're riding along. For a given travel some forks are shorter than others, so manufacturers either have to come up with some sort of average or design the frame specifically for a particular fork.

Anyway, I'm going to kind of go against the general flow here and suggest sticking to shorter-travel forks on the Kona in question, but possibly only because I'm liking proper old-school fast-handling bikes at the moment ;-)

i been talking about this with a few people, and they reckon that if you had a 100mm travel fork on a frame designed for 80mm, with the sag taken into consideration, that you would in fact have 80mm of travel. therefore the correct amount of travel that the frame was designed for....

Except that the frame would be designed for a sagged 80mm fork. And a 100mm fork with 25% sag is still 15mm longer than an 80mm fork with 25% sag, all else being equal. You could run the 100mm fork with 40mm of sag but it's liable to get a wee bit mushy ;-)

so am i right in thinking that a frame designed for a 100mm fork has the sag allowed into the equation. so tis designed for only 75mm travel, rather than the 100mm travel its labelled as?

I'd agree with Mike in this instance. I had a 2001 Cindercone & switched from 80mm forks to 100mm & it was horrible - front end wagged all over the place on climbs & it was very slow in twisty singletrack - fast downhill though.

63mm SIDS are where it's at

"so am i right in thinking that a frame designed for a 100mm fork has the sag allowed into the equation. so tis designed for only 75mm travel, rather than the 100mm travel its labelled as?"

No, it's designed for a sagged 100mm fork. Which is not the same as a 75mm fork. Because "travel" is how far it's able to move in total. Generally frames are designed for a ride height rather than a travel. If you're going from an above-averagely long 80mm fork to an unusually short 100mm one then the difference becomes fairly minor.

My elderly Kona's running an 80mm SID, but I've never seen more than 70mm out of it. Nice and quick. I'm also riding an old Mountain Cycle Moho that's perfectly acceptable with 100mm of travel with a 75mm travel fork in it. That's even quicker ;-)

cheers mike