Custom Rob English MTB

I might just suck it up and go with offset?
I think a cuppa will help me decide. :]

Like this......;)

Although if the chainline of the alfine is in fact 42mm. you'll need to find another 5mm.
(now I really need to work. Fun interferring though)

I've decided you want a 83mm DH BB shell, and a 7,5mm offset 135mm rear (and forks).

• The tyre will hit the belt only if it is over say 102mm in width. Which wont be a problem for your spec.
  
• The beltline will be a perfectly straight DH 55mm.
  
• You wont need a special offset rim to achive 7.5mm of offset*.
  
• Its still 10mm less offset than your old pugs.
  
  

(*difficult to garantee this. But I'm pretty sure my front fat lefty wheel has at least this without specal rim drilling + lacing)

OK....after walking the dog and thinking things through, I think I'm settling on my earlier plan before thoughts of my Pugsley popped into my head. :]

I'm sticking with 135mm, non offset front and rear...73mm BB...clearance for the 3" x 29" Knard/Krampus tyre on the rear, Clearance for up to 4.7" fat bike tyres up front.

This will allow me to run regular 29er tyres front and rear, or 3" x 29er tyres front and rear...both with interchangeable wheels.
OR...any size 29er rear with any size fatbike tyre up front, but without the interchangeability.

This means I can still run an Alfine rear hub, with belt drive, and with my folding back end.

Job's a good un! :]

FWIW you're obviously right.

With the small chainline of the Alfine, and the width + fussiness of the belt, demanding over 7mm of offset. You're starting to need to use an offset rim drilling. Which isnt going to work for the 29er options.

I'd be pretty excited about a Knard (3" x 29") rear, Bud (4.8" x 26") front combo.

For info:

The Knard is 78mm wide on a 50mm surly rim. 39mm of clearance needed. Which will be bloody close to the belt on an Alfine.

The knard is 779mm tall on a 50mm surly rim.
The Bud is 762mm tall on a 82mm surly rim.

Realistically its probably enought to have a Knard wheelset, and a lightweight 29er XC style wheelset. But That Bud is a beast. I'm pretty gutted it'll never fit on my fat lefty.

This will be porn

For info:

The Knard is 78mm wide on a 50mm surly rim. 39mm of clearance needed. Which will be bloody close to the belt on an Alfine.

The knard is 779mm tall on a 50mm surly rim.
The Bud is 762mm tall on a 82mm surly rim.

Realistically its probably enought to have a Knard wheelset, and a lightweight 29er XC style wheelset. But That Bud is a beast. I'm pretty gutted it'll never fit on my fat lefty.

I'm pretty sure that the Belt cogs add a bit to the chainline over the standard alfine cog. I reckon It will just about work. If not, I'll have a shitload of mud clearance. :]

Close but well doable.

What fun! I shall enjoy watching somebody else getting massively stressed out working through all the small details of a custom build.

I've had a few custom MTB's before so I know what to expect. :]
Like the one I'd waited months for only to have the bike shop owner crush the top tube in the workstand on the day I went to collect it! :]

I think I used that bike shop.

Once.

tube in the workstand on the day I went to collect it! :]

How was this resolved?

It had to go straight back to the builder to be stripped, have the top tube taken out, a new one put in, then be resprayed again....and i had to wait another week. :[

I had to wait another week. :[

Plenty of time to dispose of the body then ;-)

OK...I've been chatting to Rob about this and the conclusion we arrived at is that while the Krampus 3" setup might be fun, the extra couple of pounds of weight probably isn't worth it for the extra .6 of an inch....and the hassle involved in trying to clear the belt.
This means I can go back to the original plan of regular twenty niner wheels, but with the option to run a fat front wheel.
This will mean a lighter bike, more compatibility without any silly offsets, shorter chainstays for better climbing etc.

As nice as it might be to have all the fun wheel options, this bike is meant to be covering distance mostly, so I'm being sensible.

Perhaps as soon as it's done I'll re-join the queue and ask Rob for a purpose built fat bike! :]

^ I'd definitely agree with the compatibility issue. Especially for the kind of ride that you're planning.

Versatility in design, is brilliant.

As is a pure and focused 'fit for purpose' design.

Somewhere in the middle is the sweetspot.

A Racing Ralph 2.4 is listed as 66mm wide on a surly rabbit hole rim. A full 12mm narrower, so loads more clearance. But would probably still run at seriously low PSI.
http://surlybikes.com/blog/post/your_rabbit_hole_looks_knardy

So you could still have the option of a 50mm 29er rim out back, and a fat 26er rim up front. Maybe as a fun SS wheelset. The amount of 2.5" 29er tyres on the market is pretty good these days, as is the number of 4" 26er tyres.

Another good reason not to try and go full fat is the Q-factor required to clear the fatties. Not really what you want when in long distance 29er mode.

Versatility in design, is brilliant.

As is a pure and focused 'fit for purpose' design.

Somewhere in the middle is the sweetspot.

A Racing Ralph 2.4 is listed as 66mm wide on a surly rabbit hole rim. A full 12mm narrower, so loads more clearance. But would probably still run at seriously low PSI.
http://surlybikes.com/blog/post/your_rabbit_hole_looks_knardy

So you could still have the option of a 50mm 29er rim out back, and a fat 26er rim up front. Maybe as a fun SS wheelset. The amount of 2.5" 29er tyres on the market is pretty good these days, as is the number of 4" 26er tyres.

Another good reason not to try and go full fat is the Q-factor required to clear the fatties. Not really what you want when in long distance 29er mode.

I'm thinking more around 2.3 to 2.4 tyres anyway so I can keep the stays fairly short. The amount of climbing in theTour divide is equivalent to seven times up mount everest, so the better the bike climbs, the happier I'll be. :]

I agree on the Q factor. It's totally possible on 1OOmm BB, but my knees are a bit shit these days, so might not appreciate too many miles on a 1OOmm BB. :]

I'm thinking more around 2.3 to 2.4 tyres anyway so I can keep the stays fairly short. The amount of climbing in theTour divide is equivalent to seven times up mount everest, so the better the bike climbs, the happier I'll be. :]

I agree on the Q factor. It's totally possible on 1OOmm BB, but my knees are a bit shit these days, so might not appreciate too many miles on a 1OOmm BB. :]

Well the ability to run a a rear Rabbit hole rim at the rear wont increase your chainstay length. Its the Knard tyres that do that.

The stort vs long stays for off-road climbing thing. Is a bit magnets for me.
How do they work?
Short for weight over contact patch and stiffness.
Long for stability, and less wheelie-ing.

I dunno.

Well from my experience. Longer stays are more stable on the downhills, but the problem on the climbs is that you have to move further back to keep the weight over the wheel, which then lightens the front again. Shorter stays make it easier to keep the front end down without spinning out at the back so easily.

I'm eagerly awaiting his next email now so that we can start discussing all the finer details. :]

So I've been chatting back n forth with Rob over the past few days, and giving him my measurements and preferences etc, and today I got the first proper drawing of the frame layout with measurements and angles...along with the full parts spec, which is a combination of my own preferences and his recommendations.
It's all getting very exciting now. :]

The final plan for the bike is basically, fully rigid twenty niner, with a folding frame, EBB, inboard disc mount, custom frame bag mountings, clearance for up to 2.4" tyre, rear hub gear, with a single speed front[rear] wheel as a backup, belt drive, fat front compatible forks with no steerer and removable, integrated mini front rack, and bottle/anything cage mounts, custom stem with built in fork steerer and removable integrated aero bars.

The plan is to 'hopefully' be able to fit the bike into a 26" x 26" S&S airline checkable case.

I've also finally weakened to the lure of tubeless with this bike. :]

The spec is roughly as follows....

Wheelset:
Rims: NoTubes ZTR Arch EX 29"
Rear hub: Shimano Alfine 8spd, black 32h
Adapter: Shimano center-lock to 6 bolt
Parts: Alfine small parts kit
Front hub: Chris King Rear Iso singlespeed, 32h
Spokes: Wheelsmith double butted, black
Nipples: Wheelsmith aluminium, black
Tires: Schwalbe Racing Ralph 29x2.4

Components:
Handlebar: Jones Loop bar, aluminium
Headset: Chris King NoThreadSet
Brakes: Avid BB7 mechanical disc, 160mm
Brake levers: Avid speed dial ultimate
Shifter: Shimano Alfine 8spd rapidfire
BB: Chris King
Crank: Middleburn RS8, 175mm, black
Carbon drive: Cog, Ring and belt, plus extra cog
Seatpost: Thomson setback, 410mm, black
Saddle: Fizik Gobi XM
Grips: Ergon GS1-L
Pedals: Time Atac carbon

So that's about where it stands so far. :]

Good job Rob's a clever bloke. That lot makes my head hurt :-)

He even understood my explanation for my custom aero bar idea...god knows how? :]

Thankfully even the belt drive has worked out well. I've been able to get the range I wanted from the hub gear, while having pretty much the exact gear i wanted for the spare rear/front wheel, AND the right chainstay length. :That could have ended up a massive headache too. :]

I think you'd better get Rob to build 2 of them, just in case.

He might even give you a discount for the 2nd ;-)

You wouldn't say that if you knew how much this was costing. :]

I think I'll be putting my name straight back on the list though anyway for another bike once this is done....more likely a road bike though. :]

all that and you're speccing it with mechanical disc brakes? I've not scrutinised the thread, but why mechanical?