"XT" tantan FM08 29er build

[GreyCactus]

The new bike still hasn't yet quite reached its 'final' state, so the upgrade-testride cycle continues.

The latest test ride went close to expectations.  Not a great ride, as the trails were still wet from rain from the days before, and not familiar with the new tyre etc.

Firstly, the longer fork and taller front tyre definitely made the bike feel noticeably taller.  I was surprised at the difference.  I think it was barely 6mm higher at the bottom bracket - though I did re-measure it, and it was closer to 445 than the earlier measurement of 443.  I didn't hit my cranks once, riding the same trails as the previous ride, including a lot techy climbing.  And I was noticeably worse at cornering too.  Perhaps the wet roots and rocks contributed though.  Not sure.  But this has confirmed my approach with this bike, to lower it below the frame's standard specced geo, with a 10mm shorter-than-spec fork and lowered rear end via a shortened shock.  I still plan to start with 2.5mm off the shock's stroke/length, which translates to a ~8mm lowered rear end (to about 142mm travel), but I could end up droping it further again.  My only reservation about going further is that the angles might be getting a bit slack - I don't think my trails or riding style would benefit from a HA much lower than 66.5.  I'm glad I went for a 140mm air shaft for my fork too, as a 150mm fork would've made the bike too tall (or too slack, if I dropped the rear end to bring it back down).

For the first time, I noticed the feeling of being a little further back, which will get worse when I lower the rear end.  However this was only on a super steep climb (Probably 15%grade), so I don't think it will be a problem.

I thought I put 75psi in the fork, but I think I was mistaken.  I might've put the recommended 85psi in, just in case it bottomed with the no volume tokens in it.  Got over halfway through the ride and noticed the fork barely used 110mm of the 140mm.  I dropped  it to 75psi for the rest of the ride, but didn't hit anything big, so it barely used any more travel. I'll leave it as is, and see how it goes on some bigger stuff.

With the rear shock on full volume, I went for low sag initially, and pre-ride settled on 160psi to get just under 25% sag.  Mid way through the ride, it had used only 44mm stroke (of 56mm, so about 80%), so I dropped it to 155psi.  Was still around 44mm at the end of the ride.  I'll drop it to 150psi after I shorten the shock.  As expected, the McLeod shock was awesome at erasing bumps, while at the same time not ever feeling wallowy.  I thought the not-high main pivot on this frame could result in a bit of Bob, but it is near non-existent.

With the wet trails, i was a bit hesitant to really put the new DHF tyre into any big leans, but in hindsight it barely slipped at all.  Perhaps the next (hopefully drier) ride will be better, and I have more trust in it.

The latest round of upgrades added more weight (mainly the tyre).  Bike is now 13.44kg, which is probably as heavy as it will ever get. It will lose a little weight when I go tubeless, and a slightly lighter stem.

The key is in the details! Thanks for your detailed quotes!

[sclyde2]

Well, it had been close to 3 months since my last update, and I certainly haven't been getting the ride time on the trail bike that I had hoped for.  I accumulated a few injuries in the last 4 months (knee injury flared up in September, got a weird glute strain in October), so have been prioritising the riding.  Unfortunately, trail riding is the lowest priority, with commuting to work (a necessity) and completing the xc race series (which I won) coming first. 

I did ride the FM08 in late October, and had a terrible ride:
- flatted the rear tyre in the first 10 minutes
- had some creaking in the rear shock mount
- had a stack - clipped a tree with the end of my handlebar (must've had my hand at a couple cm from the end), throwing my off the bike, but worse, giving me a thumb injury (still not 100%)

While I haven't ridden it since, I have made a few changes:
- greased the rear shock mount to avoid the creak.  Am considering putting a RWS roller bearing kit in there.
- put some spacers in the rear shock, to shorten the stroke and length by 2.5mm.  with the shock now at 197.5x53.5, the BB height is around 339mm, and I estimate the rear travel to be 140-141mm (if TanTan's leverage curves are accurate).
- went tubeless on the rear tyre.  Front still has a tube.
- got some new grips
- got a wcs trail stem (got a decent deal).  5mm shorter than the old stem (65 to 60mm), and a lot nicer, and lighter.  The steerer clamp height is a bit higher though, and it moved the bars up a bit.  Might look into a lower stack height top headset, to bring the bars down.

Weighs in at 13.22kg now.  Have a ride planned for Saturday.

[sclyde2]

Despite my thumb still being a bit tender, the ride today went extremely well.  pretty much the same track as last time: a loop with a mix of XC-ish twisty singletrack, combined with lots of rocks, a bit of techy climbing, lot of square-edged rock step-ups, a little techy downhill, some flowy downhill, but only a couple jumps, no big drops.

today was the coolest day in a while, and there was light rain when we arrived at the trail head.  this was actually perfect conditions, as it has been super dry and hot lately (dunno if you have heard about the weather and bushfires we have had in oz lately) so this actually improved the trail immensely, turning it all into hero dirt.  not enough rain to create any mud or puddles whatsoever, but there were a few moist rocks and roots to be wary of.

i checked the pressures at the start of the ride.  23 psi in the rear (tubeless) tyre, 22psi in the front (tubed) tyre.  just under 75psi (probably 73) in the fork, 130psi in the rear shock.  that 130 is a fair bit lower than what i had last time, but i thought i'd just leave it there, as i have been having problems using all the travel in past rides.  after taking 2 weeks off the bike over Xmas, and all the festive season drinking/eating, i reckon i am about 2kg heavier than i was a few months ago.  i went back to work on monday, so have put a few hours on the commuter bike this week, and the fitness is already coming back, so pedaling was no problem.

despite there being no big drops, i was pretty much using all the travel, bar the shock's internal bottom out bumper - i stopped a few times to check the o-ring (and reset it) and it was at 50-50.5mm (of 53.5) each time.  so the 130psi in the rear shock was too low.  post ride, i have increased the rear shock to 140psi.  i am guessing the square edged rocks on the techy climbs were using the travel.  i did not feel any harshness or bottoming.

i think i have found the final setup for the fork - at just under 75psi it was using 132-133mm travel (of 140mm).  post ride, i put a few psi into the fork to bring it to 75, to give a little more buffer against bottoming, for when i start hitting some bigger hits.  i think i will leave it there for a while, unless i get some frequent bottoming (in which case i would consider putting a volume-reducing token back in).

overall, the bike rode absolutely awesomely.  with that bit of grease in the rear shock mount, the bike is now blissfully silent.  the suspension (front and rear) disappeared beneath me, totally unnoticeable (the way it should be), and ironed out the bumps extremely well, both up, down, everywhere.  with the bike now at its slackest yet (probably 66.5 degree HA), it still went around the tighter XC-ish corners unbelievably well, had no downsides on the climbs, and only upsides on the faster/downhill stuff.  i simply couldn't fault it, nor could i imagine how it could be much better.  i think i will do a tiny bit more tinkering though:
- as mentioned before, drop the bars a few mm, via a lower stack height top headset
- might add another spacer in the rear shock - take out another 1.25mm of shock stroke & length, which would translate to 3mm less travel at the rear wheel (to about 138mm), and about a 2mm lower BB (to about 337mm).  with the way i had the shock today, with the too-low pressure, it must've been running excessive sag - yet i still very rarely hit pedals (and only minor scrapes when i did), even on a techy trail often navigating over and around rocks, and doing some sloppy pedal timing too.  as the steering is still not too slack, i think there is still scope to lower and slacken it a bit further, so i will try the experiment of putting in that extra 1.25mm spacer.
- maybe tilt the saddle nose down a tiny bit
- front tyre still yet to go tubeless

the only remaining gripe i have with this bike relates to my injured thumb: the shift effort is a bit high - not sure where the friction is, but even with an xtr shifter, i did get a sore thumb from pushing on that shift lever.

[sclyde2]

a couple more rides on the FM08, exact same trails (both times) as previous ride.

1st ride was with the same setup as previously (2 rear travel reduction spacers), but i increased the rear shock air pressure, to 140psi at the start of the ride.  without any major drops etc, it was getting about 49-50mm of stroke (of 53.5), so i increased it again to 150, and still seemed to get around 48-49mm.  despite a bit of techy climbing, lots of prime candidate rocks to hit pedals etc i simply was not getting any pedal strikes.  towards the end i was literally trying to hit pedals (pedaling around corners with rocks on the inside) and finally got a couple scrapes.  note that i use 170mm cranks on all my bikes, so this probably helps.  as the steering was still fine for the twisty stuff (i.e. not too slack), this was the final confirmation to make the decision to drop the rear end further, by adding another 1.25mm stroke reduction spacer (which also reduces the shock length).

after the 1st ride, i remeasured the BBH.  making sure the fork was fully extended (140mm), it was actually a bit higher than i previously measured, at around 341-342mm.  i then added the extra travel reduction spacer - now 3 spacers, which is 3x1.25=3.75mm, so the stroke is now 52.25 (56-3.75).  Based on the leverage curves (a bit over 3:1 near top out), i reckon the spacers reduce travel (and the rear end) by nearly 4mm for each spacer.  with 3 spacers, it would have around 138mm rear travel - if the leverage curves etc from the manufacturer are to be believed.  After putting in the extra spacer, BBH was again measured, now at 337-338mm.

further tweaks done to the bike at that time:
- went full tubeless.  i.e. converted the front tyre.  i dont think i've ever had a tyre seal so easily.  bike dropped a little weight, but less reduction than expected (i didn't realise i had a lightweight tube in it).  bike is now 13.16kg, which is pretty much right on 29 pounds.  that's the "final" weight, i reckon.
- found a lower stack height top headset cap and put that on.  maybe dropped the bars about 5mm.

the 2nd ride started with the rear shock at 150psi.  continuing with a similar less-disciplined approach to pedal timing as i have on previous rides, pedaling through the first few corners there was a noticeable increase in pedal scrapes.  so i tidied up my pedaling a bit, and it was far from a problem.  with bike slackened a bit further, i definitely felt more over the back wheel, and the bike was using a lot of travel (around 49mm of the 52mm).  halfway through the ride, i upped the rear shock to 160 (back to where i was months ago), and it was using only 44-45mm.  i reckon i will end up around 155psi.

confidence in front tyre has been increasing with each ride.  with it now tubeless, i have reduced to 20psi.  i seem to be much more comfortable putting it into some more extreme leans, such that i am starting to find the limits of the rear tyre's grip, with it letting go a few times, but not anything i couldnt catch.  maybe i'll have to move up from an XC tyre for the rear, or i could end up paying the price....

did a few pbs on some strava segments, including some fast downhill flowy/jumpy/bermy stuff, and some flatter twisty stuff.  i have ridden this trail quite a lot, so some of it was surprising, especially the flatter stuff, given i have done some fast runs on my XC bike through there.

i think i have settled on the final geometry, especially the rear travel / ride height.  for the first time, i did notice the steering a tiny bit "floppy" through some very slow speed series of corners through trees, so i think i've found the slackest i want to go with the steering (probably a touch over 66 degrees HA, with a 51mm offset fork).   i might need to drop the bars more (would need another stem,if i do), will see how it feels after the XC season starts and i start getting used to my XC bike again.  getting close to finalising spring rates on the the fork (75psi, uses about 120mm with no big drops) and rear shock (will try 155psi next time).  next step will be to confirm sag levels are good (and, if not, reduce air spring volume/s, and then re-do pressures again), and then do some experiments with different rebound settings. 

bike is turning out to be perfect for that trail.  i certainly appreciate how active the suspension is under power, as there a quite a few rock steppy stuff on the climbs on that trail.  a few more runs on it to confirm the bike is dialed there, then i think i need to try it out somewhere else.

[sclyde2]

during today's ride

[GreyCactus]

My lightcarbon 713 with 170mm Fox 36 and -2degree angleset.
Super fast on high speed sections