I am looking to build up a 29HT this winter. The frame I am looking at has a Fox F80 with a 51 degree offset. I would like to put a Marzochi Fork with a 44 degree offset. Is this too big a difference for the frame geometry? (Gary Fisher Paragon, G2 geometry )

Firstly, forks do not affect the angle of the steering - the offset is generally given in millimeters (mm) and is the distance ahead of the steering axis the fork puts the wheel - it is usually called 'rake.' Rake affects the "trail" of a bike, which is the derived measurement that determines a bike's tendancy to want to keep going straight.

Secondly, the G2 geometry is designed specifically around the 44mm rake forks, IIRC. The forks were designed specifically for the G2 geometry which has a more slack head tube angle than most bikes, as more rake tends to make a bike have quicker or tighter turning.

Using a fork with less rake will make the bike more stable and it will turn less tightly or quickly. I suspect going from 51 to 44 mm will make the bike a little sluggish, but certainly still ok to ride.

Also beware that the fork with less rake might give you problems with toe-overlap with the front wheel, and that can be a problem... If it is a very small frame this is more likely than if it is a big frame.

Someone with more experience with the G2 bike might have a more definitive answer.

Don't forget the fork length. I know little about suspension forks, but the same priciples apply. If the fork is longer or shorter, it will alter the head tube angle and further change the trail.

Apparently it's common for a 29er to have a lot of trail compared to a road bike. Those trail numbers are really large compared to values in the 54-68mm range found on road bikes.

https://www.fisherbikes.com/bike/model/paragon

Thanks for the info. The frame I am considering is an XL 21" so hopefully toe overlap won't be an issue. I will check the specs on the overall fork length. The fork I want to install has 100mm of travel, the Fox only has 80.

If I understand the G2, it's designed to take advantage of the newer offset forks, it's part of the secret sauce. Might make sense to have this thread moved the the Mountain Bike Forum, someone there will know.

I think the forks specced on Genesis2 bikes are made specifically for G2 geometry, i.e. Gary Fisher G2 bikes.