bcd and gearing questions, need info please

[guybe]

Just 2 questions to ask for advice and info as I am stuck! :roll:

Q1, if you are running 8 speed either gripshifts or thumbshifts, can that work on 9 speed rear mech?

Q2, 'bcd' there is only 2 sizes for five bolts chainrings? (standard and compact?) as I am changing the cranks from Coda to Middleburn, which seem to have bigger gaps between bolt holes than Coda.

If I have to buy new chainrings, what best 'make' for the middle range of chainrings as I dont want to bust my wallet too much! :?

thanks for reading, hope to hear from the experts

 

[shovelon]

Maybe I can answer Q1.

And 8 speed shifter will work on 9 speed cogset, but only on 6 of the cogs. The gaps between 9 speed cogs are 1.5 mm, as 8 speed gaps between cogs are 2 mm. You would be better suited to find an 8 speed cogset. An 8 speed chain is a tad wider and thus stronger too. I have less greif with 8 speed drivetrains.

 

[pete_mcc]

Just 2 questions to ask for advice and info as I am stuck! :roll:

Q1, if you are running 8 speed either gripshifts or thumbshifts, can that work on 9 speed rear mech?

Do you mean using a new 9spd rear mech or using a rear mech on a 9sd block. If you're just using a new mech then you'll be fine, if you're using them on a 9spd block then no, don't bother!!

Q2, 'bcd' there is only 2 sizes for five bolts chainrings? (standard and compact?) as I am changing the cranks from Coda to Middleburn, which seem to have bigger gaps between bolt holes than Coda.
If I have to buy new chainrings, what best 'make' for the middle range of chainrings as I dont want to bust my wallet too much! :?

Get middleburn, Race Face or TA- great chainrings and last a decent while. Go to CRC as they always have deals on! Sounds like you need 110bcd rather than 94 (assuming your coda's are 5 arm cranks)

 

[guybe]

Thanks shovelon and pete_mcc

It's 8 speed shifter on 8 speed cassette using 9 speed rear mech, that what I was meaning.

On bcd, do you measure from the centres of between bolt holes which it will give you correct measurements?

cheers

 

[elite504]

If its just the 9 sp mech, and the rest is 8sp, you should be ok. Good rule of thumb (yes, I know there are exceptions) is match the shifter to the block. cassette.

Bolt circles. Nope its the dianeter of an imaginative circle that all the bolts would project onto , 94 and 110 are the common MTB sizes, for tiples,

but to answer the question fully, 130mm for road, 135mm for campag road, 144 for track and 70'd campag double, and tiny stuff for 1930's-50's stuff.

 

[guybe]

Thanks I am getting there! last question:-

Using 8 speed cassette and gripshifts with 9 speed rear mech, it's ok to use front mech 9 speed?

I am looking to buy SRAM stuff, they all come different code number, like 7.0, 5.0, etc, it doesnt have to be be the same code number to make it work?

Cheers for your help

 

[Old Ned]

For BCD have a look on the reliable 'cyclists friend' Sheldon Brown website -

http://www.sheldonbrown.com/gloss_bo-z.html#bcd

All will be explained.

 

[guybe]

Hello again

It's possible to put 44T outer chaingring on ATB pattern (standard drive) cranks of 110mm BCD?

I just looked CRC and it seem 46T is the only one for ATB cranks.

I am stuck!

 

[DM]

Hello again

It's possible to put 44T outer chaingring on ATB pattern (standard drive) cranks of 110mm BCD?

I just looked CRC and it seem 46T is the only one for ATB cranks.

I am stuck!

I don't quite understand the question.
If the BCD of your crank arms and your chainring are the same the ring will fit... whether anyone makes a ring with the exact number of teeth you want is a different matter.

Middleburn do them in loads of sizes for 110BCD, with 2-tooth increments.

Also, the "NEW" [cough] road "compact" double chainsets use 110BCD rings, as do lots of old BMX cranks. So there are lots of teeth-sizes out there and availability should remain good for a long time yet.

If all else fails, try the CNC wizards at Highpath Engineering.
If their stuff is good enough for Boardman it should be OK for the rest of us.

They'll machine you any size (or shape - think elipses!) ring in any BCD you need.

 

[guybe]

Thansk DM,

I am going to use SRAM front mech along with my SRAM gripshifts and want to use Middleburn cranks, the front mech I wish to buy is only do max 44 tooth, on CRC website, I looked for Middleburn chainrings aswell other makes, it seem only have 46 tooth outer chainring, cannot find any 44 tooth for ATB pattern (standard drive) 110mm BCD cranks, so I am a little stuck, I will be collecting my Cannondale frame next week from the sprayers and want it up and ready to use asap while the weather is good atm.