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Thread: 69er, or 67er or 79er...

  1. #1
    MoJo Cardinal RidingAgain's Avatar
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    69er, or 67er or 79er...

    So I bought a '07 Cannondale Prophet for its longish top tube, ability to convert the wheel size, and the Lefty fork... With the intention of building a 67er, or 69er or 79er.

    Some background... I'm 6'4", now 260lbs with gear, and have always felt that the bikes I've owned never had a long enough top tube length to build myself a comfortable set up. I've been riding on and off since '95, owning first a Coloi HT, then a Scott Racing HT (great steel bike and what I race on in the Clydesdale group back when I was in the 190s weightwise), then a Yeti 575, and now this Prophet. So I'm speaking with some riding experience.

    When I had the Yeti I used a 140mm stem and a Thomson setback seatpost with a Specialized Body Geometry seat (long with long rails) pushed as far back as was safe, and still felt like I wanted another inch in horizontal length. And the same goes for the Prophet I now have.

    So when I was thinking of getting back into riding (laid off for the last five years) I researched what was going on in the MTB world with bike design and found that it was heading in the direction that I always thought was the kind of design that would suit me... Slacker head angle, wider handlebars, longer top tubes (although that seems to have changed again), and some offering short chainstays (which I loved on my Scott HD). But shoot... The prices... Way above my budget. Which is why I started looking at old bikes and settled on the Cannondale Prophet.

    Riding style... Can go, and will go fast on flowy singletrack, weight works well going downhill. Not jumping/dropping off though never learned to in my younger days (South Florida doesn't have much in the way of hills) and didn't need to as race courses weren't really set up with jumps back then. Also love twisty singletrack. Not a lover of rocky sections that you need to slow down to almost a stop for; heavy weight will do that to you. I can pretty much ride most Walnut Creek trails, but think that the Root Crossing is not for me. And there is a shrot section with a roughish downhill that then sort of twists around into a somewhat double rocky uphill section that I get stuck on if I don't carry enough speed into the uphills.

    I mountain bike because I enjoy being outdoors, and enjoy the challenge of dexterity and concentration necessary, but I'm not interested in pushing myself far beyond a certain comfort point... Those days are behind me. And I also often ride with my wife, who is a conservative rider.

    Okay... So hopefully persons reading the above will know what my goal is regarding what I want out of my bike.

    Now to my thoughts on the bike and what I'd like advice on...

    My original though for the Prophet conversion was 27.5" front and back for two reason, better roll over and higher bottom bracket height. But then I started reading about the problems the Prophet has with fitting larger 27.5" tires on the back and came across folks using different sizes of wheels on their bikes. Something that may just work out even better for me by pushing the front end higher and slightly changing the angles of the bike to a slacker set up.

    With this new view in mind I'm thinking that a 29" up front will give me the most roll over, partnered with a large profile 26" or a smaller 27.5" tire/rim in the back to help not make the angles too slack. And also keep in mind that the Prophet has two rear suspension settings capability that can also be used to change set up angles. And the Lefty can handle this, so no new fork needed. The 29" in the front may also help the way I sit on the bike, which may help with that old niggling feeling that I'm a bit too far forward.

    Drivetrain I'm thinking will be 2:10/11; although if I go with a 1:10/11 set up it means the front derailleur is not necessary, and this will negate the major problem of a larger 27.5" tire rubbing against the front derailleur.

    And I'll use 720-40 handlebars, with a stem length that can be figured out after everything's been built out.

    That's about it... Sorry for the long post, just wanted to give a good a description as possible so that anyone giving feedback/advice has a good idea of what I'm hoping to achieve.

    Thanks for your help folks.

  2. #2
    prodigal son of Austin Teamsloan's Avatar
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    I'm sure there will be other more knowledgable replies, but here's my two cents...

    At your weight, I would consider sticking with a 26'er in the back with a higher volume tire on wider rims. The smaller wheel will be stronger as the shorter spoke length creates a wider angle. Boost hub spacing addresses this in larger wheels, but you can't do that with your current bike. Also, a higher volume tire will allow you to run a little lower PSI and help absorb more trail chatter.

    I'm not sure about the rest of the bike fit and how it would be affected by either a 29'er or 27.5 up front. At your size, I just think smaller wheels will be more durable unless you can move up to a newer bike with boost spacing front and back.
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    MoJo Bishop Dr. D's Avatar
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    I had a Prophet with 27.5 wheels, I fit 2.3" Hans Dampfs on the rear with no problem...as long as you kept the rear in XC mode (or whatever it was called). It was a tight fit but it fit non the less. Going with a 29" wheel up front would be cool, and slack it out a little more, which in my opinion the prophet needed (especially since you wont be able to put the rear in FR mode). Ditch the front derailleur, not needed with today's 1X10/11/12 and a narrow wide chainring. Stem length was always my issue with the lefty fork, could only fit a 90mm stem, any shorter and the handlebar would hit the top of the fork (strut).
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    MoJo Mother Superior characterzero's Avatar
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    Quote Originally Posted by RidingAgain View Post
    Some background... I'm 6'4", ...
    And I'll use 720-40 handlebars
    You should really try some 780-800mm bars...

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    MoJo Mother Superior notyal's Avatar
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    Quote Originally Posted by Dr. D View Post
    I had a Prophet with 27.5 wheels, I fit 2.3" Hans Dampfs on the rear with no problem...as long as you kept the rear in XC mode (or whatever it was called). It was a tight fit but it fit non the less. Going with a 29" wheel up front would be cool, and slack it out a little more, which in my opinion the prophet needed (especially since you wont be able to put the rear in FR mode). Ditch the front derailleur, not needed with today's 1X10/11/12 and a narrow wide chainring. Stem length was always my issue with the lefty fork, could only fit a 90mm stem, any shorter and the handlebar would hit the top of the fork (strut).
    This is probably the best reply you could hope to get. I'd be a little concerned about taking a bike designed around 26" wheels and turning into a 79er. That is going to raise the bottom bracket quite a bit. It may be fine, it may handle like this:

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    Live Medium Bamwa's Avatar
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    I put a 29er wheel and fork on a 26er once. Steering was "flopping over". Lasted a day.
    Grab life by the timbales.

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    My 26er frame has 29er rims and 700cc tires. Gravelgrinder. But, handled Cracass quite well the other day. Twas fun.

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    Last edited by Shinerider; 06-12-2017 at 09:49 AM.
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  8. #8
    MoJo Cardinal RidingAgain's Avatar
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    Quote Originally Posted by Bamwa View Post
    I put a 29er wheel and fork on a 26er once. Steering was "flopping over". Lasted a day.
    That's been discussed on serveral MTBR threads, and it seems that there's a fix for it... Lower head tube angle (change spacer height in Lefty, decrease air pressure) and put a little more body forward (longer stem, no setback seatpost). At least, that what folks say regarding the Prophet conversion.

    Here's a thread on it that has some useful info...

    Cannondale Prophet to a 69er?- Mtbr.com
    Last edited by RidingAgain; 06-14-2017 at 02:24 PM.

  9. #9
    MoJo Cardinal RidingAgain's Avatar
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    Quote Originally Posted by Teamsloan View Post
    I'm sure there will be other more knowledgable replies, but here's my two cents...

    At your weight, I would consider sticking with a 26'er in the back with a higher volume tire on wider rims. The smaller wheel will be stronger as the shorter spoke length creates a wider angle. Boost hub spacing addresses this in larger wheels, but you can't do that with your current bike. Also, a higher volume tire will allow you to run a little lower PSI and help absorb more trail chatter.

    I'm not sure about the rest of the bike fit and how it would be affected by either a 29'er or 27.5 up front. At your size, I just think smaller wheels will be more durable unless you can move up to a newer bike with boost spacing front and back.
    Good call on the smaller wheel size/higher volume on the back. Thanks.

    The thing is, with the Prophet I can try using both the 26" and the 27.5" and see what works for me best. The only change is the removal of the front derailleur, which some say doesn't have to go if narrower 27.5" tires are used.

    It's going to be a trial and error project... But fortunately, because of the price I paid for the Prophet I can afford to test a few different options without breaking the bank. And hopefully come out with a ride that works well for me.

  10. #10
    MoJo Mother Superior notyal's Avatar
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    Quote Originally Posted by RidingAgain View Post
    The thing is, with the Prophet I can try using both the 26" and the 27.5" and see what works for me best. The only change is the removal of the front derailleur, which some say doesn't have to go if narrower 27.5" tires are used.
    What the fuck is a front derailleur?

    Seriously, regardless of tire clearance issues, a 1x system with wide range cassette will change your life.
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  11. #11
    prodigal son of Austin Teamsloan's Avatar
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    ^ yup. Go 1x.
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  12. #12
    MoJo Cardinal RidingAgain's Avatar
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    Quote Originally Posted by notyal View Post
    What the fuck is a front derailleur?

    Seriously, regardless of tire clearance issues, a 1x system with wide range cassette will change your life.
    Something that you got when you bought a component set that included V-brakes.

    But I hear you...

    Over the past few rides I've been taking stock of just how I use my gears riding on SW Austin trails... No hills, but for what there is, I don't come out of my middle chainring and pretty much high -mid on the cassette — and yesterday evening I did just over ten miles in an hour ten minutes; my route being from around Cycle Werks area to the trail head under Mopac and Convict Rd., then up to Taco Bueneo/Slaughter Lane and back, with some runs into trails east and west of Mopac (I'm still getting familiar with the trail network). And that with a 32 middle ring. And I pretty much do the the same for Walnut creek, although I'm more in the middle - low on the cassette where the trail climbs or has twisty sections.

    So for here in Austin I'm thinking a single ring up front would work given what trails I like riding. But options are good to have.

    I'll be going with an oval chainring in the front, which reviews say will give a working range of three round rings (32 = 30-34, 34 = 32-36) and have been trying to decide on which to get. I'm thinking the 32 might be best, seeing that I'm not really looking for speed.

    My leaning to the 2/10(11) set up was thinking about any trips I might take to places where there's more climbing (e.g. New Mexico). which I'd like to do soon.
    Last edited by RidingAgain; 06-14-2017 at 02:23 PM.

  13. #13
    MoJo Bishop Dr. D's Avatar
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    I've ridden all over the country on a 1x10 with a 32T chainring and a 42T on the cassette. If I ever needed more gearing, which I cant remember but I'm sure I did, it was usually faster to walk the bike anyway. I'm 210 lbs of tacos and beer, you may fair better.

  14. #14
    MoJo Cardinal RidingAgain's Avatar
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    Okay, just got myself an inexpensive 29er wheel so that I can start the conversion process with my Cannondale Prophet w/Lefty Max...

    It's a 32-hole Bontrager AT650. Not great reviews on it, but I don't do jumps or fly low downhill. I ride XC trail, with rocks. Not slow, but not so fast either. Also, I'm not sure if I want a 29 or 27.5 front, so this is just to give it a try and see how I feel.

    I have an extra 26" wheel that has a Cannondale 32-hole front hub on it that I will use on the AT650 rim if I can...

    Couple things to consider...

    1)... Lefty hub is not as wide as the hub on the Bontrager rim.
    2)... Lefty hub flange diameter is not as wide as the hub flange on the Bontrager rim (about 3-4mm less).
    3)... Spokes on both rims seem to be straightpull and the same gauge, just different lengths (obviously).
    4)... The Mavic 26" rim is not a wide (external rim width) as the Bontrager rim, around 21mm vs 24mm.

    So first question is... Will the Cannondale Lefty hub that I currently have work with the Bontrager rim.

    Second question... The Bontrager rim was ridden on very little before being swapped out for a more expensive rim and the spokes look perfectly fine (almost new); so given that the flange of the Cannondale hub is slightly smaller than the hub of the Bontrager, could these spokes have enough threaded area to accomodate the 1.5mm-2mm difference between the two flange sizes, or will I need new spokes?

    I've never built a wheel, so all this is new to me.

    Thanks for the help.
    Last edited by RidingAgain; 07-01-2017 at 02:40 PM.

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    MoJo Cardinal RidingAgain's Avatar
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    Also... The Lefty Max that I have ('06/'07 model) has 140mm travel. From what I've read online (Craig Mendon, in particular, a Lefty expert) This needs to be reduced to 110mm travel to use with a 29er wheel... Which can be easily done with the proper spacer. Some are using 120mm, which Mendon says he's seen done without a problem as long as you're not using a big tyre.

    I have two Lefty Max shocks, one on my bike and an extra one that needs to be serviced (slight oil leak) and converted to TPC. I'd like to use this one for the 29er conversion. Is there anyone here in Austin that can do both the service/TPC conversion and the spacer work?

    I can send it to Mendon, but if I can save on the shipping and get it done here that would help with my budget.
    Last edited by RidingAgain; 07-01-2017 at 02:50 PM.

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    MoJo Mother Superior notyal's Avatar
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    Just buy a new bike and thank me later.
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    Ayatollah of Rock and Rollah mack_turtle's Avatar
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    based on how you recieved my critique of your very unconventional bike setup (saddle pointed nose-down, gigantic stem + wide bars, ridiculous handlebar drop), I get the impression that you're going to spend a lot money and time making a Frankenbike regardless of the well-meaning advice you get here. It might turn out well but it's most likely going to be a drag to build and you'll spend more time fiddling with it than riding it. you could be riding instead of rebuilding your bike in weird arrangements, or just buy a bike that fits your proportions, skills, suits the local terrain. from personal experience, I have seen too many people waste their time with Frankenbike projects that don't work out, so I wash my hands of any of this.

    this is coming from a bicycle over-analyzer who makes frame geometry spreadsheets and swaps frames every few months.
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  18. #18
    MoJo Cardinal RidingAgain's Avatar
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    Quote Originally Posted by notyal View Post
    Just buy a new bike and thank me later.
    I'm having a ton of fun on the bike I have, and I'm confident it will only get better. But thanks for the advice.
    Last edited by RidingAgain; 07-03-2017 at 12:32 AM.

  19. #19
    MoJo Cardinal RidingAgain's Avatar
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    Quote Originally Posted by mack_turtle View Post
    based on how you recieved my critique of your very unconventional bike setup (saddle pointed nose-down, gigantic stem + wide bars, ridiculous handlebar drop), I get the impression that you're going to spend a lot money and time making a Frankenbike regardless of the well-meaning advice you get here.
    I read what people write, and I appreciate it. But it doesn't mean that I agree with it.

    As for spending a lot of money on my bike... Let that be my concern, not yours.

    Quote Originally Posted by mack_turtle View Post
    It might turn out well but it's most likely going to be a drag to build and you'll spend more time fiddling with it than riding it.
    Perhaps... Or perhaps not.

    Again, let me worry about that.

    Quote Originally Posted by mack_turtle View Post
    you could be riding instead of rebuilding your bike in weird arrangements, or just buy a bike that fits your proportions, skills, suits the local terrain.
    But I am riding... Quite a lot actually.

    And lots of people ride bikes that are a little too small or a little too big for their proportions, which is why there's such a vibrant parts and accessories market.

    There's nothing "weird" about my bike "arrangements", mack_turtle... What I'm going to do to my Cannondale Prophet is something that other owners of the same bike have been doing for almost ten years. And been very happy with it too.

    Quote Originally Posted by mack_turtle View Post
    from personal experience, I have seen too many people waste their time with Frankenbike projects that don't work out, so I wash my hands of any of this... this is coming from a bicycle over-analyzer who makes frame geometry spreadsheets and swaps frames every few months.
    Okay. I understand. But thanks for what advice you have given.

  20. #20
    Ayatollah of Rock and Rollah mack_turtle's Avatar
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    it sounds like you're trying to do something that has been done with success, so there's hope. I think Voodoo is the wrong venue for this though. there are not enough people on this forum with extensive Cannondale-modding experience. I would check the Cannondale forum on MTBR.com for better advice from a broader range of people who have probably done just this.
    Last edited by mack_turtle; 07-03-2017 at 12:26 PM.
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