Re: Bike Mechanics Impart Their Wisdom On Vorb

Postby great uncle bulgaria on Thu 31/Jan/13 4:44pm

Simonius_Titius wrote:
great uncle bulgaria wrote:Hey. How do you calculate clamp stem offset exactly? Ta

How's this?
http://www.brightspoke.com/t/bike-stem-calculator.html

thanks
I knew i'd written it wrong but was in a hurry and failed to proof read myself
what i actually meant to write was clampseatpost offset . . .?
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Re: Bike Mechanics Impart Their Wisdom On Vorb

Postby Simonius_Titius on Fri 1/Feb/13 1:23am

I'm still confused.

Post insertion depth? 2.5x the post diameter is a common US and UK standard.
Dunno about new-fangled frames though, I'd guess some of them could do with more insertion.
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Re: Bike Mechanics Impart Their Wisdom On Vorb

Postby Velocipedestrian on Fri 1/Feb/13 10:42am

Enough for the bottom of the post to clear the bottom weld of the seat-tube / top-tube join is usually good.
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Re: Bike Mechanics Impart Their Wisdom On Vorb

Postby .I. on Fri 1/Feb/13 10:47am

great uncle bulgaria wrote:
Simonius_Titius wrote:
great uncle bulgaria wrote:Hey. How do you calculate clamp stem offset exactly? Ta

How's this?
http://www.brightspoke.com/t/bike-stem-calculator.html

thanks
I knew i'd written it wrong but was in a hurry and failed to proof read myself
what i actually meant to write was clampseatpost offset . . .?

is this what you are after
"Offset is the distance between the centerline of the seatpost tube, and the centerline of the clamp area"
.I.
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Re: Bike Mechanics Impart Their Wisdom On Vorb

Postby tcr on Sat 2/Feb/13 9:06am

Oli wrote:Glenn is the MAN. :thumbsup:


Cool, thanks. Glenn Muirhead?
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Re: Bike Mechanics Impart Their Wisdom On Vorb

Postby Oli on Sat 2/Feb/13 1:30pm

tcr wrote:
Oli wrote:Glenn is the MAN. :thumbsup:


Cool, thanks. Glenn Muirhead?
Yes indeed.
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Re: Bike Mechanics Impart Their Wisdom On Vorb

Postby thelivo on Sat 2/Feb/13 6:42pm

tcr wrote:
Oli wrote:Glenn is the MAN. :thumbsup:


Cool, thanks. Glenn Muirhead?


+1 - Never come across anyone better.
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Re: Bike Mechanics Impart Their Wisdom On Vorb

Postby AdamMTB on Thu 7/Feb/13 12:31pm

I have a XTR M985 crank set which runs the 40/28 rings. The big ring is warn and I want to replace it but would like to go to a 42. Can anyone see any issue marrying the 42 with the 28?
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Re: Bike Mechanics Impart Their Wisdom On Vorb

Postby wachtourak on Thu 7/Feb/13 1:11pm

22-36 SLX cranksets exist, so a 14T jump shouldn't be out of the question? :eh:
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Re: Bike Mechanics Impart Their Wisdom On Vorb

Postby BrokenKonaRider on Thu 7/Feb/13 1:31pm

Bigger issue might be matching a new chainring with a substantially older chain?
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Re: Bike Mechanics Impart Their Wisdom On Vorb

Postby Percy Pig on Fri 8/Feb/13 1:56pm

I say o wisdomous bike mechanicey peeps, can you replace an old style open bearing BB with the nutted axle, with a new style BB square taper unit?
And if so does the axle length need to be the same? :blink:
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Re: Bike Mechanics Impart Their Wisdom On Vorb

Postby Velocipedestrian on Fri 8/Feb/13 2:04pm

I'll give that a yes, and yes.
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Re: Bike Mechanics Impart Their Wisdom On Vorb

Postby Simonius_Titius on Fri 8/Feb/13 2:49pm

Percy Pig wrote:... can you replace an old style open bearing BB with the nutted axle, with a new style BB square taper unit?
And if so does the axle length need to be the same? :blink:


Check the frame BB shell width first. 68/70/73mm.

Check whether the old axle is symmetrical. (All modern cartridge BBs from 110mm up are roughly symmetrical).
Older BBs often had an extra 1-7mm on the RHS.
To get the chainline right consider:
- The correct discrete axle (look for a stamped code e.g. 3P, then try Burkes)
- A spacer on the RHS
- A left crank with a different offset. Measure the offset from the base of the taper to the pedal interface.
- Tolerating an uneven pedal offset. Chainline is more critical.
Last edited by Simonius_Titius on Mon 11/Feb/13 3:07pm, edited 1 time in total.
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Re: Bike Mechanics Impart Their Wisdom On Vorb

Postby Percy Pig on Fri 8/Feb/13 3:12pm

Roger roger! :thumbsup:
Cheers for that. :cool:
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Re: Bike Mechanics Impart Their Wisdom On Vorb

Postby cep32 on Mon 11/Feb/13 2:10pm

Is it best practice to grease the axle on a crankset before installing in the bottom bracket? It just seems a little strange as don't I want the crank axle to grip the inside of the bearing (plastic dust cover in an shimano press-fit BB) so the bearings are doing all of the work and there is no movement between the crank axle and inside of bearing?

The reason I ask is that I removed it today and found that the crack axle is very shiny where the dust cap contacts it which would imply some movement. The bearings are running pretty free but I have opened them up anyway and cleaned all of the grease out (was still nice and blue) to free it up more.

Is it worth running a lighter grease and if so any recommendations?

Cheers,
Chris
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