100mm or 120mm fork???

Fanis

Hi
I want to change my old RST 100mm fork with a new one Marzocchi/Rock Shox but i don't know what is better to install 100mm or 120mm???I ask this because i like to do small jumps/little downhill.Will i have problem with my hardtail bike geometry???

BlackSpur

What bike is it going onto?

Fanis

BlackSpur wrote:

What bike is it going onto?

It's an XC mtb

z000m

Fanis wrote:

It's an XC mtb

good answer

Fanis

z000m wrote:

Fanis wrote:

It's an XC mtb

good answer

What brand do you mean???

supersonic

Make, model, year if you know it.

Symchicken

Just to mix things up a little, the question also applies to me. The forks are the next thing I want to upgrade. Any idea of the range I should be looking at, got a Specialized Hardrock Pro '08.

Sorry to butt in old bean.

supersonic

How much dosh to splosh? 100-150 cant go wrong with an RS Tora really.

Symchicken

got about £220 to blow and was looking at Marzocchi dirtjumper 2's. They're the same 100mm travel as whhat I have now, but would it be an idea to go for 120 - 130 so I can be a bit more aggressive, or would the frame be buggered? Can't find anything in the manual etc.

supersonic

Better check with specialized. The geometry should be ok upto 120 I would have thought, but its not a jump bike really, not sure spesh would like you doing that (check warranty!)

Symchicken

yeah thought so tbh, cheers for the tip on the RS tora's though. Found a nice set on chainreaction. Bonus.

Fanis

supersonic wrote:

Make, model, year if you know it.

Ideal Target 2006

dave_hill

Once again, the important issue here is not the fork travel, it's the axle-to-crown length you need to check.

For every 20mm increase or decrease in overall fork length, you change the head angle of your bike by 1 degree.

Measure the distance between the centre of the front axle and the top of the fork crown, just under the headset. Then check this against the same measurement on the forks that you intend to buy.

If the difference is more than 20mm then it will start to have an effect on how the bike handles. If the fork is too long you can set more sag to compensate but of course you will lose some travel.

supersonic

True, but most forks of 100mm travel are within 5mm of each other, and the flip side is that the head angle will be steeper at full travel.

dave_hill

supersonic wrote:

True, but most forks of 100mm travel are within 5mm of each other, and the flip side is that the head angle will be steeper at full travel.

Not so -

Lets take 3 100mm travel jump forks -

Rock Shox Argyle 302 - 491mm axle to crown
Society Xeno - 480mm
Manitou Gold Label - 455mm

Now in my book, the total difference between the 3 forks is 36mm which would add up to a 1,5 degree change in head angle - if our friend has a fork now which is 455mm long and he swaps it for one 491mm long, he will notice a difference in the way the bike handles. 1,5 degrees might not seem a lot but it is noticeable.

Yes, the head angle will steepen at full compression, but how many people do you know who ride everywhere with the forks fully compressed?

You can compensate for a slacker head angle by setting the fork up with more sag (so that it rides further into the travel under normal conditions), but that defeats the object.

supersonic

455, are you sure? The spiel I have says it 480mm. If it was 455 I am pretty sure the tyre would hit the crown at full travel!

dave_hill

S'wot it says on the website! :?

supersonic

I think its a mistake! But I was probably a bit off target saying it was 5mm, more like 10mm.

dave_hill

Just realised - they do an 80mm version of the Gold Label - that would make more sense, if the 100mm travel version is 20mm longer it would make it 475 overall...

bikeperson45

I was just getting new forks for my hardrock. I got the Toras theyre really plush, rebound is good and being able to adjust from 85mm to 130mm is great.