Using a 51mm offset fork in a 098 frame (46mm offset)

[Maxeld]

Hi guys
I have bough a 098 frame (still waiting to arrive).
I would like to go for a Pike RCT3 fork with 46 mm offset (in the frame's description and frames diagrams there is a 46mm offset in the fork) but I can't find that fork in 46mm offset. I can only find 51mm offset forks.
Does the 51mm offset fork compromises the frame's safety or does it add some risk to the frame?
I have read the differences between a 51mm fork vs 46 mm fork and I know the effect the 5mm difference over the bike's trail and bike's handling, but I don't know if it is safe to mount a 51mm offset fork in a frame apparently designed for a 46 mm offset fork.

[JohnnyNT]

It is perfectly safe It will change the geometry marginally (probably a little more stable ride) but that should be all.

[xcbarny]

What is the Head angle on the 098 frame?

G2 (51mm offset) was designed to quicken up the steering on slacker angled 29ers. Gary Fisher introduced it, and it allowed them to make smaller sized 29er frames.

The slacker Head tube angle, gives more clearance from the riders toes to the front wheel, which is an issue on smaller frames. The increased 5mm of offset (46 to 51mm) also improves this, but more importantly, it reduces the trail, which speeds up the steering, which counters the effect that the slacker head tube angle has of slowing the steering down.

If the HTA on the 098 is 70 or steeper, then it will probably make the front end too twitchy. However if it is less than 70, then it should be ok, depending on your trails and how you like your bike to handle ( I love twitchy on a 29er in fast singletrack). From memory, Gary fishers had a HTA of 69.3, so this is what the 51mm offset was designed for.

[cmh]

What is the Head angle on the 098 frame?

According to this, it's 70 degrees:



That should result in pretty lively steering, which I really like, don't know if Maxeld agrees. When the valving got screwy on my wife's 46mm offset fork, I swapped on the G2 (51mm offset) fork from my Rumblefish, and she really liked the quicker handling, but she's on a Scott Scale which has a 69.5 degree head tube angle.

[xcbarny]

I've never ridden one, but from the geometry numbers, I always thought the Scale should come with a G2 fork.

Seems like more and more 29ers now are coming with the G2 offset (Ibis ripley, Lapierre XR are 2 that I know of). I'm not sure if Gary Fisher / Trek had a patent on this, or if its only now that other manufacturers are catching on?

[SportingGoods]

I must be REALLY missing something here 

The 51 mm offset is, to me, the equivalent of a slacker head tube angle. So, it does stabilize the bike at high speed but does not make the steering more lively (it's actually the opposite). You end up with a longer bike, slacker head tube feeling. Better for downhill. Not for a lively uphill control.

[xcbarny]

It can be a bit hard to get your head around it. Basically its all to do with trail. A bigger trail number will result in a more stable feeling, and a smaller trail number will result in twitchy steering.

Slackening the head tube increases the trail - so makes the bike steer slower / more stable.
Increasing the fork offset, actually decreases the trail, so results in a slightly more twitchy feel.

There's some info here about how the head angle, wheel size and fork offset / rake affects the trail:
https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry

[RS VR6]

What is the Head angle on the 098 frame?

According to this, it's 70 degrees:



That should result in pretty lively steering, which I really like, don't know if Maxeld agrees. When the valving got screwy on my wife's 46mm offset fork, I swapped on the G2 (51mm offset) fork from my Rumblefish, and she really liked the quicker handling, but she's on a Scott Scale which has a 69.5 degree head tube angle.

That frame looks like an Enduro (at least the front half). The Enduro has a 67.5 HTA with a 160mm fork and 46mm offset. "Trail" is 99mm.

I wonder what fork's axle to crown measurement they used on the 098.

[SportingGoods]

It can be a bit hard to get your head around it. Basically its all to do with trail. A bigger trail number will result in a more stable feeling, and a smaller trail number will result in twitchy steering.

Slackening the head tube increases the trail - so makes the bike steer slower / more stable.
Increasing the fork offset, actually decreases the trail, so results in a slightly more twitchy feel.

There's some info here about how the head angle, wheel size and fork offset / rake affects the trail:
https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry

I think that's precisely where I don't agree. True that the "trail" decreases but the key parameter here is that the wheelbase will be longer, ending up with more stability at high speed.
What they mean with a short "trail" causing lively steering is that it will feel more "direct", but you still benefit from the added stability of longer wheelbase.

Now I think about it, it is a win-win: both on high speed stability and steering feel. We should go for larger offset!

[Maxeld]

Thanks to all of you guys for your kind answers and suggestions. I decided to order the 51mm offset fork. Once delivered, I'll mount it and I'll tell you my feelings on the bike.