need advice on modifying drivetrain

[David Kelling]

my wife bought a cannondale r800 2 years ago. it has a truvativ isis
splined bb with truvative elita triple crank 52/42/30 and 12-25 9spd
cassette. she'd like an all around lower gear range. she rarely uses
the 52 and spends most of her riding in the 30.

i switched out the 42/30 in the crank to a 39/26 which is better, but
i'd like to go farther and put a mtb drivetrain on the bike with a
42/32/22 on front and a 11-34 cassette on back. based on the gears she
uses most, she'd sit right in the middle of a mtb drivetrain and this
seems ideal for her riding style (but she loves a road bike, doesn't
want a mtn bike).

if you can suggest or point to a reference on the web where i can get
specs for what i need, that'd be great. my questions are:

given a certain brand of crank, how do i determine what length of
spindle i need for the bottom bracket? as best i can tell it has a
68x118 now. can i put an mtb crank on as-is or do i need a different
length bb and how do i determine what length i need based on the crank
i get?

will the 105 triple road front derailleur be ok with a mtb crank?
assuming the space between rings in the crank is the same for triple
road and triple mtb, it seems i would only need to move the front
derailleur down the seat tube a little bit to accomodate the smaller
crank. true?

i think i'm ok with figuring out proper chain length and figuring out
if the rear derailleur will be ok, but i'm stumped on what to order
for a bb and crank. yeah, sure, i could pay the local bike shop to do
it all but i like to learn, like to fix my own bikes, and don't have
lots of cash so try to find deals online on parts.

thanks for your suggestions and advice!

 

[Paul Kopit]

On 25 Nov 2004 08:14:26 -0800, [email protected] (David Kelling)
wrote:

>i switched out the 42/30 in the crank to a 39/26 which is better, but
>i'd like to go farther and put a mtb drivetrain on the bike with a
>42/32/22 on front and a 11-34 cassette on back. based on the gears she

The selection of the front derailleur may be tricky. The MTB front
changer may be so low that its inner movement is restricted by the
right chain stay. The cage will stop when hitting the stay.

I think that something like a Sugino XD triple comes standard with
46/36/24, which would be close to what you are looking for.

 

[Booker C. Bense]

-----BEGIN PGP SIGNED MESSAGE-----

In article <[email protected]>,
David Kelling <[email protected]> wrote:
>my wife bought a cannondale r800 2 years ago. it has a truvativ isis
>splined bb with truvative elita triple crank 52/42/30 and 12-25 9spd
>cassette. she'd like an all around lower gear range. she rarely uses
>the 52 and spends most of her riding in the 30.
>
>i switched out the 42/30 in the crank to a 39/26 which is better, but
>i'd like to go farther and put a mtb drivetrain on the bike with a
>42/32/22 on front and a 11-34 cassette on back. based on the gears she
>uses most, she'd sit right in the middle of a mtb drivetrain and this
>seems ideal for her riding style (but she loves a road bike, doesn't
>want a mtn bike).
>
>if you can suggest or point to a reference on the web where i can get
>specs for what i need, that'd be great.

_ Sheldon Brown's website

http://sheldonbrown.com/harris/new.html

> my questions are:
>
>given a certain brand of crank, how do i determine what length of
>spindle i need for the bottom bracket?

_ The best way is to have the manufacturer of the crank tell you,
this information almost always comes with the little data sheet
that comes with the parts. If you don't have that, there is
a database on Sheldon's site. Look for the article on chainline
to start with.


> as best i can tell it has a
>68x118 now. can i put an mtb crank on as-is or do i need a different
>length bb and how do i determine what length i need based on the crank
>i get?

_ 118 will work with many MTB triples, but you need to double
check.

>
>will the 105 triple road front derailleur be ok with a mtb
>crank?

_ Maybe, Rivendell uses that derailler with Sugino 48/36/26
chainrings, but they don't use indexed shifting.

>assuming the space between rings in the crank is the same for triple
>road and triple mtb, it seems i would only need to move the front
>derailleur down the seat tube a little bit to accomodate the smaller
>crank. true?

_ You'll get the best shifting when the curvature of the
derailler matches that of the largest chainring. I'm not sure how well
a 105 road derailler built to match a 53 or 52 chainring will
work with a 42 or 44. This all gets very complicated with indexed
shifting as MTB and road front deraillers need the index to pull
different amounts of cable. You can make it all work, but it gets
pricey.

>
>i think i'm ok with figuring out proper chain length and figuring out
>if the rear derailleur will be ok, but i'm stumped on what to order
>for a bb and crank.

_ If you want to go much larger than 30 on the back you'll need
a MTB rear derailler.

> yeah, sure, i could pay the local bike shop to do
>it all but i like to learn, like to fix my own bikes, and don't have
>lots of cash so try to find deals online on parts.
>
>thanks for your suggestions and advice!

_ I think the cheapest solution might be to start with the rear
cluster first and replacing one of the chainrings. Replace the
52 with a 48 or 50 and either get a custom cluster from Harris
Cyclery or by a couple of HG50 or HG70 cassettes and make up your
own. Something like the first couple listed might be good.

http://sheldonbrown.com/harris/k7.html

_ The century special would work well, but it's very pricey.
My favorite is to start with the Ultegra 9 speed 14-25 and
replace the 23,25 with a 24 and 28.

_ Booker C. Bense

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[Russell Seaton]

[email protected] (David Kelling) wrote in message news:<[email protected]>...
> my wife bought a cannondale r800 2 years ago. it has a truvativ isis
> splined bb with truvative elita triple crank 52/42/30 and 12-25 9spd
> cassette. she'd like an all around lower gear range. she rarely uses
> the 52 and spends most of her riding in the 30.
>
> i switched out the 42/30 in the crank to a 39/26 which is better, but
> i'd like to go farther and put a mtb drivetrain on the bike with a
> 42/32/22 on front and a 11-34 cassette on back. based on the gears she
> uses most, she'd sit right in the middle of a mtb drivetrain and this
> seems ideal for her riding style (but she loves a road bike, doesn't
> want a mtn bike).
>
> if you can suggest or point to a reference on the web where i can get
> specs for what i need, that'd be great. my questions are:
>
> given a certain brand of crank, how do i determine what length of
> spindle i need for the bottom bracket? as best i can tell it has a
> 68x118 now. can i put an mtb crank on as-is or do i need a different
> length bb and how do i determine what length i need based on the crank
> i get?
>
> will the 105 triple road front derailleur be ok with a mtb crank?
> assuming the space between rings in the crank is the same for triple
> road and triple mtb, it seems i would only need to move the front
> derailleur down the seat tube a little bit to accomodate the smaller
> crank. true?
>
> i think i'm ok with figuring out proper chain length and figuring out
> if the rear derailleur will be ok, but i'm stumped on what to order
> for a bb and crank. yeah, sure, i could pay the local bike shop to do
> it all but i like to learn, like to fix my own bikes, and don't have
> lots of cash so try to find deals online on parts.
>
> thanks for your suggestions and advice!

Here is my suggestion. Take off the 52 chainring and put on the
original 42 chainring in the outer position. Free since you kept the
chainring you took off. Keep the replacement 39 in the middle
position. Consider buying a 24 chainring for the inner. But you can
wait until you find one at Nashbar for $2 since you already have a 26.
Buy a 12-34 or 11-34 cassette and put it on. About $40 on sale from
Nashbar or Performance. Hopefully the triple 105 rear derailleur will
clear the 34 cog. Its cage should be long enough to take up the slack
since you will only have a 16 difference in front (42-26) and 23
difference in back (34-11). You may not have to replace the chain
since it was installed to work with a 52x25 it may also work with
42x34. But chains are $10 on sale so get one anyway. Total cost $50
if you spurge for the chain.

Send your wife out to ride to see if the new gearing is good. I
suspect it will be just fine and she will use the 39 and 42 chainrings
for the vast majority of riding. And the 26 for hilly riding.

 

[Sheldon Brown]

Quoth David Kelling:

> my wife bought a cannondale r800 2 years ago. it has a truvativ isis
> splined bb with truvative elita triple crank 52/42/30 and 12-25 9spd
> cassette. she'd like an all around lower gear range. she rarely uses
> the 52 and spends most of her riding in the 30.
>
> i switched out the 42/30 in the crank to a 39/26 which is better, but
> i'd like to go farther and put a mtb drivetrain on the bike with a
> 42/32/22 on front and a 11-34 cassette on back. based on the gears she
> uses most, she'd sit right in the middle of a mtb drivetrain and this
> seems ideal for her riding style (but she loves a road bike, doesn't
> want a mtn bike).
>
> given a certain brand of crank, how do i determine what length of
> spindle i need for the bottom bracket? as best i can tell it has a
> 68x118 now. can i put an mtb crank on as-is or do i need a different
> length bb and how do i determine what length i need based on the crank
> i get?

The "68" has to do with how it fits the frame. The 118 has to do with
how it fits the crank. You normally would go with the length
recommended by the manufacturer for that specific crank model. If a
range of lengths is recommeded, use the shortest for a road bike.

See: http://sheldonbrown.com/bbsize...but-I would advise _against_
replacing the crank.

In addition to the considerable expense involved, it can turn into a can
of worms trying to get road shifters to work with "microdrive" mtb
cranks like that.

See: http://sheldonbrown.com/derailer-adjustment
>
> will the 105 triple road front derailleur be ok with a mtb crank?

No, it will work very poorly.

> assuming the space between rings in the crank is the same for triple
> road and triple mtb, it seems i would only need to move the front
> derailleur down the seat tube a little bit to accomodate the smaller
> crank. true?

The cage is designed to match the contour of a 52 tooth big ring, it
will work poorly with a 42.
>
> i think i'm ok with figuring out proper chain length and figuring out
> if the rear derailleur will be ok, but i'm stumped on what to order
> for a bb and crank. yeah, sure, i could pay the local bike shop to do
> it all but i like to learn, like to fix my own bikes, and don't have
> lots of cash so try to find deals online on parts.

My advice would be to go with one of my Cyclotouriste 14 cassettes
(14-34) and leave the cranks alone. You will also need a new rear
derailer, but derailers are cheap. There are no indexing issues in the
rear, as long as she sticks with a Shimano derailer.

See: http://harriscyclery.com/9

and: http://harriscyclery.com/derailers

Sheldon "Keep The Crank" Brown
+-----------------------------------------------------------------+
| Love seems the swiftest, but it is the slowest of all growths. |
| No man or woman really knows what perfect love is until they |
| have been married a quarter of a century. --Mark Twain |
+-----------------------------------------------------------------+
(I'll find out if this is true tomorrow. So far it seems to be!)

Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

 

[dvt]

Russell Seaton wrote:
> Buy a 12-34 or 11-34 cassette and put it on.
> Hopefully the triple 105 rear derailleur will
> clear the 34 cog.

It probably won't. Shimano road rear derailers are usually rated for 27t
max cog, but I'm not the only one that has stretched that to 28t. I've
heard that a 30t cog is a hit-or-miss proposition, so I'm pretty sure a
32t or 34t cog won't work with the 105 derailer.

--
Dave
dvt at psu dot edu

 

[dvt]

David Kelling wrote:

> my wife bought a cannondale r800 2 years ago. it has a truvativ isis
> splined bb with truvative elita triple crank 52/42/30 and 12-25 9spd
> cassette. she'd like an all around lower gear range. she rarely uses
> the 52 and spends most of her riding in the 30.
>
> i switched out the 42/30 in the crank to a 39/26 which is better...

Sounds like you made one logical step by changing out the chainrings.

You say she used the 30 x 13-25 most often, assuming she doesn't
cross-chain into the 30 x 12 combination. She now has a 39t cog in the
middle, so the corresponding cog set to get similar gears is 17-33.
Sheldon's suggestion of a 14-34 cog set and a new rear derailler will
give her nearly the same ratios with the 39t ring as she had with the
30t ring, which seems like a good idea.

If you want to use the existing rear derailler, you could try a
different cog set. A 12-27 or 11-28 would work with your rear derailler,
and she'd get a slightly taller set of gears with the 39t that she had
with the 30t. The low gears would still be available with the 26t chainring.

If she spent a lot of time in the 30x23 and 30x25, I'd go with the 14-34
and a new derailler. If she spent most of her time in the 30x13 to 30x21
range, I'd go with a 12-27 and use the existing derailer.

> i'd like to go farther and put a mtb drivetrain on the bike with a
> 42/32/22 on front and a 11-34 cassette on back.

A 22x34 is a *really* low gear. If she wants such a low gear, then you
should get the monster cassette. I'll bet that once she tries the 26x34
(4.9 mph @ 80 rpm), she won't be asking for lower gears. She might not
even want a gear lower than 26x27 (6.1 mph @ 80 rpm). It gets pretty
tough to balance a bike at such slow speeds, so it would be easier to walk.

(speed @ rpm calculations assume 28-622 [700x28] wheels)

--
Dave
dvt at psu dot edu

 

[Booker C. Bense]

-----BEGIN PGP SIGNED MESSAGE-----

In article <[email protected]>, dvt <[email protected]> wrote:
>Russell Seaton wrote:
>> Buy a 12-34 or 11-34 cassette and put it on.
> > Hopefully the triple 105 rear derailleur will
>> clear the 34 cog.
>
>It probably won't. Shimano road rear derailers are usually rated for 27t
>max cog, but I'm not the only one that has stretched that to 28t. I've
>heard that a 30t cog is a hit-or-miss proposition, so I'm pretty sure a
>32t or 34t cog won't work with the 105 derailer.
>

_ I've used a 30t rear cog with both a Ultegra and Tiagra Triple
rear derailler, but not with indexed shifting. You have to tweak
the B adjustment pretty far out[1], but it worked fine.

_ Booker C. Bense

[1]- This might be a problem since it depends on exactly how the
rear dropouts are configured. You can always get a longer screw.


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[David Kelling]

thank you all SO VERY MUCH for your input!
i've got things to consider and then things to try!
again, thanks so much.

i ride in the winter, but she doesn't, so it'll be some time until i
post what i did as i've got some flexibility. but i will ost for
future use.

thanks again!

[email protected] (David Kelling) wrote in message news:<[email protected]>...
> my wife bought a cannondale r800 2 years ago. it has a truvativ isis
> splined bb with truvative elita triple crank 52/42/30 and 12-25 9spd
> cassette. she'd like an all around lower gear range. she rarely uses
> the 52 and spends most of her riding in the 30.

....

 

[Dan Burkhart]

Quoth David Kelling:

> my wife bought a cannondale r800 2 years ago. it has a truvativ isis
> splined bb with truvative elita triple crank 52/42/30 and 12-25 9spd
> cassette. she'd like an all around lower gear range. she rarely uses
> the 52 and spends most of her riding in the 30.
>
> i switched out the 42/30 in the crank to a 39/26 which is better, but
> i'd like to go farther and put a mtb drivetrain on the bike with a
> 42/32/22 on front and a 11-34 cassette on back. based on the gears she
> uses most, she'd sit right in the middle of a mtb drivetrain and this
> seems ideal for her riding style (but she loves a road bike, doesn't
> want a mtn bike).
>
> given a certain brand of crank, how do i determine what length of
> spindle i need for the bottom bracket? as best i can tell it has a
> 68x118 now. can i put an mtb crank on as-is or do i need a different
> length bb and how do i determine what length i need based on the crank
> i get?

The "68" has to do with how it fits the frame. The 118 has to do with
how it fits the crank. You normally would go with the length
recommended by the manufacturer for that specific crank model. If a
range of lengths is recommeded, use the shortest for a road bike.

See: http://sheldonbrown.com/bbsize...but-I would advise _against_
replacing the crank.

In addition to the considerable expense involved, it can turn into a can
of worms trying to get road shifters to work with "microdrive" mtb
cranks like that.

See: http://sheldonbrown.com/derailer-adjustment
>
> will the 105 triple road front derailleur be ok with a mtb crank?

No, it will work very poorly.

> assuming the space between rings in the crank is the same for triple
> road and triple mtb, it seems i would only need to move the front
> derailleur down the seat tube a little bit to accomodate the smaller
> crank. true?

The cage is designed to match the contour of a 52 tooth big ring, it
will work poorly with a 42.
>
> i think i'm ok with figuring out proper chain length and figuring out
> if the rear derailleur will be ok, but i'm stumped on what to order
> for a bb and crank. yeah, sure, i could pay the local bike shop to do
> it all but i like to learn, like to fix my own bikes, and don't have
> lots of cash so try to find deals online on parts.

My advice would be to go with one of my Cyclotouriste 14 cassettes
(14-34) and leave the cranks alone. You will also need a new rear
derailer, but derailers are cheap. There are no indexing issues in the
rear, as long as she sticks with a Shimano derailer.

See: http://harriscyclery.com/9

and: http://harriscyclery.com/derailers

Sheldon "Keep The Crank" Brown
+-----------------------------------------------------------------+
| Love seems the swiftest, but it is the slowest of all growths. |
| No man or woman really knows what perfect love is until they |
| have been married a quarter of a century. --Mark Twain |
+-----------------------------------------------------------------+
(I'll find out if this is true tomorrow. So far it seems to be!)

Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

Sheldon
Congrats on your impending 25th. I fell a couple of years short of it the first time around. Hopefully I'll live long enough to achieve it on the second try.
Dan