I’ve just got a set of 2018 Rockshox Revelations to go on my Trek Stache. They’re 150mm travel, 29″ versions that I’m running with 29×3 tyres.

150mm travel is too much for the thing anyway (although last night’s ride suggests otherwise, it’s a bit of a hooligan now) but the problem I have is that the axle to crown of the Revs at 150mm is almost the same as the Manitou Magnums they are replacing. The Revs are 562mm and the Magnums 550mm.

The Magnums have 110mm travel BUT the stanchions are actually for 120mm travel (there is an internal spacer limiting the travel).

In terms of stress on the headtube, is it the travel or the a2c that are worse? I’ve bought an air shaft to reduce the travel to 130mm but this will steepen the head angle, so I was looking into getting a 25mm crown race to make up the slack. Will all of this rip my headtube off? Should I put them at 130mm and not add the big crown race?

I know people are running these bikes with 140mm travel but using 650b+ wheels if that makes a difference.

In terms of stress on the headtube, is it the travel or the a2c that are worse?

The main factor in stress on the headtube is how you ride the bike, followed by your own weight. If you are smashing through rock gardens and doing big drops onto a flat landing, you will stress the frame much more than if you ride gentle XC stuff. If you weigh 350 pounds, you’ll break gear without trying. If you weigh 120 pounds, you will need to try much harder to break it.

A 20mm increase in AC is less than 5% increase in leverage on the headtube. That’s the difference between riding with a bag full of gear or not carrying a bag.

150mm fork should sag 45mm

110mm fork should sag 33mm.

So that’s 12mm ride height difference.

So it’s all the same when you are on the bike.

You sure that doesn’t come to 28mm?

Edit: read it all now, a to c is the same on both etc

Neither directly affects stress on the HT Luke (as I think Brant once confirmed), mfrs limit fork length as longer fork = hooligan rider.

Max stress through the fork will come when it’s compressed, ye see!

Mfrs recommendation will be based around what geometry it was designed for.

And it should have been fatigue tested at that length. Full extended. Usually with a big solid bar instead of a fork.

You can submit frames for test with an actual suspension fork which will also be locked out. Which is a bit gentler on frames than a bloody big steel bar

That said it’s good to give things a right bashing to make sure they don’t fall apart.

Does the 29*3.0 actually fit in the fork? It doesn’t hit the fork crown at full compression does it?

Horatio- no, it doesn’t hit the crown. Clearance is good there, and around the arch (with a year old, well stretched Chupacabra tyre on Mulefut 50mm rims).

150mm fork should sag 45mm

110mm fork should sag 33mm.

So that’s 12mm ride height difference.

So it’s all the same when you are on the bike.

bollox