xt m770 e type

[Bill C]

Hi all
building up the new xTc, would like to be able to switch easily between 44x32x22 xtr and 48x36x22 xt cranksets (cassettes and chain will be changed at same time, to tailor gearing) with out trashing the paint on the seat tube
I have seen the m770 e type, the spec says covers from 44t to 48t and mounts to the bb, are they any good? as it just sounds to easy to buy one fit it and sorted,
are the e types compatible with xt bb's or do i need the longer threaded saint bb80, i have one but it's gold are there any suitable in silver if the xt bb won't work, spose i could polish the gold off 

[Bill C]

sorry that's twice i started a topic only find out the answer myself after posting  should look harder before asking dumb questions
the ebay listing i was looking at claimed the e type was for 44&&48 rings seems after downloading the pdf it's for 44, unless anyone's used one on a 48T?

still interested if there is a braze on clamp like the M part one that offers 4 tooth adjustment?

[jags]

Worry not Bill i've been asking dumb Q this ten years.

[Danneaux]

still interested if there is a braze on clamp like the M part one that offers 4 tooth adjustment?

<nods> Yes, Bill, there is and I saw it in my online perusings last week. Unfortunately, I cleared my browser cache as I do weekly and so I've got to depend on my noggin to remember where I saw it, hence my delay in responding.

I'll be back with an answer if i can just find it!

All the best,

Dan.

[Bill C]

nice one Dan if you can find it !
when i changed my inner ring from 26 to 22 i remember reading somewhere  to use an allen key between the bottom of the chain and the front mech on the 26 granny ring and the 11t to see if it had enough clearance for the 22 ring, can't remember for sure but think it was 5mm allen key for each 2 teeth ? that ring any bells?
one of those bit's of info i wish had sunk in 
if it's right i'll need something with a bit over 10mm adjustment slot, but i'm not sure of the allen key rule,

atb Bill

[Bill C]

bit of googling and chainring diameters

28T = 116mm
32T = 132mm
34T = 141mm
36T = 149mm
38T = 157mm
44T = 182mm
48T = 199mm

so 2 teeth is between 8 and 9 mm half that and the 5mm allen key gives you a little bit of leeway 
looking for one with just over 10mm slot by the looks of it

things are looking up 

edit
bit rude ought to give credit to the bod who posted the ring diameters http://www.rotorburn.com/forums/showthread.php?75799-How-to-work-out-diameter-of-chainring-from-the-number-of-teeth&s=ff1f6251f999a14a916908ccb484e32a&p=863837&viewfull=1#post863837

[Danneaux]

Beat me to it, Bill. In 1979, I got tired of trying to guess cog diameters by sight and made a little gauge to do the job. My measurements square with yours from the posted link. As I recall, mine were about 8.6mm in diameter between even or odd numbers, so about half that for 1 1-tooth difference, and then half of that again for the radius.

Still looking for the long-slot braze-on front derailleur clamp. I think it was a European distributor of Asian-made components...BBB, XLC, Marwi, or Origin-8. It wasn't Quality Bike Products' Problem Solvers line, but something similar. I'll keep looking.

Best,

Dan.

[Bill C]

Hi Dan
after many hours of getting nowhere i found
"Description of Problem Solvers Clamp for braze-on Front Derailleurs - silver
This adapter clamp on to the seat tube so you can use your braze-on derailleur on a conventional frame. Available in three common seat tube sizes with 20mm of vertical adjustability. Available in different diameters."

now for a front mech 

Shimano XT M771 Direct Mount 9sp Front Mech says 44t in the blurb but the cage shape looks identical to Shimano XT M771 Conventional 9sp Front Mech which is 44 or 48

mech is £20 at crc, clamp now i know what to look for shouldn't be expensive, what do you reckon? as i can't at the mo find the pdf  for the direct mount mech

edit
looking at the pics the direct mount mech looks different than the fitting on the braze on clamp,
starts getting a bit iffy if you want non standard drivetrain 
i know nothing about road mechs so clueless on that front

[mickeg]

Or a quick calculation for an approximation.  A link is a half inch.  So, for example a 44 tooth ring has a circumference of 22 inches.  That is 558.8mm.  Diameter is circumference divided by pi, which is 177.9mm.  Cut that in half for radius, which is 88.9mm.

Your table is slightly different, perhaps the tooth length on the chainring is greater than the center of the chain pins by a few mm.

[jags]

good man mick you bet me to it.

[David Simpson]

Your table is slightly different, perhaps the tooth length on the chainring is greater than the center of the chain pins by a few mm.

Where is the circumference of a chainring measured? At the outer tip of the teeth, or at the point where the center of the chain pins pass? The calculations done by mickeg are for the circle created by the chain pins, not the circle of the tips of the teeth.

- Dave

[Danneaux]

Where is the circumference of a chainring measured? At the outer tip of the teeth...?

Yes. I always measured mine at the outer tips of the teeth because that is what the derailleur cage has to clear.

And also yes...the actual height of these teeth varies by maker and by intended use. That's why it seems to vary between 8mm and 9mm between even numbered teeth or odd numbered teeth. I settled on 8.6mm for my little gauge. Thorn specify longer teeth on their chainrings intended for use with Rohloff drivetrains than are sported by a number of chainrings intended for derailleur use.

Best,

Dan.