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Thread: ECDM Geometry

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    ECDM Geometry

    Has any one felt the need to slacken the fork rake on an ECDM using an Angleset? The 70.4 degrees quoted by Ventana seems a bit steep to me with my limited tandem experience.

    Our new ECDM feels a bit too light and sensitive on the steering for my liking. We test rode one fitted with a Fox Float 36 and that one was just right. Ours is fitted with the new Pike. 90mm stem. Tapered head.

    I've emailed Ventana for advice.

    I just want to load it a bit without going so far that it becomes floppy during low speed manoeuvring.

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    ECDM Geometry

    Old thread....

    Did you ever come up with anything to give you a better feel? How long is the pike? Or I guess I should ask if the AtoC is much greater than the frame was designed for?

    I've got an '06 ECDM (26" wheels) and my fork is taller than recommended, and the steering is like you describe. I think I'm going to space the fork down another 1/2" and see if it improves it. I'm currently on a Fox 40 at either 5 or 5.5"travel. I can only space it down so far before I will have to shorten the springs....

    I dragged the old KHS tandem out of the garage the other day and I really like the way that bike steers and handles better than the ECDM. But it has a fork that is (close to) the recommended A to C.
    --Reamer

    SC Tallboy LTc
    Ventana ECDM 26
    ventana el Ciclon
    Litespeed Classic
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    Quote Originally Posted by reamer41 View Post
    Old thread....

    Did you ever come up with anything to give you a better feel? How long is the pike? Or I guess I should ask if the AtoC is much greater than the frame was designed for?

    I've got an '06 ECDM (26" wheels) and my fork is taller than recommended, and the steering is like you describe. I think I'm going to space the fork down another 1/2" and see if it improves it. I'm currently on a Fox 40 at either 5 or 5.5"travel. I can only space it down so far before I will have to shorten the springs....

    I dragged the old KHS tandem out of the garage the other day and I really like the way that bike steers and handles better than the ECDM. But it has a fork that is (close to) the recommended A to C.
    A great example of how two similar machines, used in defferent locations prefer different setups.

    We also have an 06, with 26" wheels. Also run a Fox 40, and have no concerns with handling. Our 40 has had the traveled decreased and runs a firmer spring.

    If I had one complaint about the 40, it is the style of triple clamps and offset axle limit the left and right steering lock angle. Most times a non issue, but there are a few local sections we seldom ride clean since I can not turn the front wheel enough to get the tandem around the corner.

    PK
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    ECDM Geometry

    Paul, how much have you decreased the travel? Or should I ask, how much travel are you running? My comments regarding handling really only pertain to slow speed riding and maneuvering.

    I totally agree about the steering lock. I've ridden some tight turn with the fork bumpers on the frame the whole way around. It's a little unnerving! And there are those tight spots which are unridable due to the limited steering lock.
    --Reamer

    SC Tallboy LTc
    Ventana ECDM 26
    ventana el Ciclon
    Litespeed Classic
    Seven Ti Axion Tandem
    1989 Stumpjumper

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    Quote Originally Posted by reamer41 View Post
    Paul, how much have you decreased the travel? Or should I ask, how much travel are you running? My comments regarding handling really only pertain to slow speed riding and maneuvering.

    I totally agree about the steering lock. I've ridden some tight turn with the fork bumpers on the frame the whole way around. It's a little unnerving! And there are those tight spots which are unridable due to the limited steering lock.
    As for the travel, can I reply in a few days when I get home?

    Yes slower speeds are always a bit more challenging but not too bad, except for dealing with super tight turns.

    Before going to a change on the front, have you checked the rear sag? Running the RP23, make certain you have a small air can or reduced air volume. For rear sag, run 1/8" with the stoker alone on the bike.

    With the smaller air volume, the bike will not wallow and holds the rear end higher up. Not sure what setup your bike came with, it may already have a smaller air can.

    This would be an easy bike to sort out if you were local.

    PK
    Reps! We don't need no stickin' reps!

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    Quote Originally Posted by reamer41 View Post
    Old thread....

    Did you ever come up with anything to give you a better feel? How long is the pike? Or I guess I should ask if the AtoC is much greater than the frame was designed for?
    We had the Pike reduced to 140mm from 150mm travel.

    Ventana suggested to steepen the head angle by 0.5 degrees(as opposed to slackening it) as the frame is designed around a 100mm fork, but can go to 120mm. I could only get a 1 degree AngleSet at the time and this was fitted to steepen the head angle, I was assured by the shop that I wouldn't notice the difference.

    The steering weight improved enough for me to go back to a 60mm stem from the 90mm I fitted, as was intended for the top tube length specified in the build.

    The problem now is that it's very difficult to steer on a camber or in a depression/rain gully as the steering is always trying to kick you down the slope to the bottom and makes it very hard to change your preferred line to get out of the low point. It's come to the point where I have to slow down to get the bike back under control, bouncing from one side to the other. On a slow cambered corner the front feels like it wants to "tuck-under".

    It's due into the workshop tomorrow to have the AngleSet swung through 180 degrees to slacken the angle by 1 degree from original. Everything I've read on various forums suggests this will work, and it was my original thought to do this. The steering will be slower than before, but I don't mind that if it fixes the extreme twitchyness. I'm not convinced that you need the same steering speed as a solo bike, as you can't really flick it round the trees in the same way.

    The suspension company I use has also suggested running less sag on the rear to prop it up more.
    Welcome to Sussed Out Suspension UK - The Eastern regions most dedicated mountain bike (MTB) suspension centre! Based in Essex/Suffolk not far from Thetford Forest in Norfolk! UK Mondraker & GT bikes dealer! Fox, Rockshox, Cannondale, Cane Creek, Mag

    I will report back in a few weeks time when we've had the chance to try it.

    John

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    ECDM Geometry

    Very interesting, John! Thanks for posting that. I'm interested to hear what the change to slacker steering yields in feel.

    --Charlie
    --Reamer

    SC Tallboy LTc
    Ventana ECDM 26
    ventana el Ciclon
    Litespeed Classic
    Seven Ti Axion Tandem
    1989 Stumpjumper

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    Quote Originally Posted by switchbacktrog View Post
    We had the Pike reduced to 140mm from 150mm travel.

    Ventana suggested to steepen the head angle by 0.5 degrees(as opposed to slackening it) as the frame is designed around a 100mm fork, but can go to 120mm. I could only get a 1 degree AngleSet at the time and this was fitted to steepen the head angle, I was assured by the shop that I wouldn't notice the difference.

    The steering weight improved enough for me to go back to a 60mm stem from the 90mm I fitted, as was intended for the top tube length specified in the build.

    The problem now is that it's very difficult to steer on a camber or in a depression/rain gully as the steering is always trying to kick you down the slope to the bottom and makes it very hard to change your preferred line to get out of the low point. It's come to the point where I have to slow down to get the bike back under control, bouncing from one side to the other. On a slow cambered corner the front feels like it wants to "tuck-under".

    It's due into the workshop tomorrow to have the AngleSet swung through 180 degrees to slacken the angle by 1 degree from original. Everything I've read on various forums suggests this will work, and it was my original thought to do this. The steering will be slower than before, but I don't mind that if it fixes the extreme twitchyness. I'm not convinced that you need the same steering speed as a solo bike, as you can't really flick it round the trees in the same way.

    The suspension company I use has also suggested running less sag on the rear to prop it up more.
    Welcome to Sussed Out Suspension UK - The Eastern regions most dedicated mountain bike (MTB) suspension centre! Based in Essex/Suffolk not far from Thetford Forest in Norfolk! UK Mondraker & GT bikes dealer! Fox, Rockshox, Cannondale, Cane Creek, Mag

    I will report back in a few weeks time when we've had the chance to try it.

    John
    I would agree with less rear sag or a small air can to reduce mid stroke wallow. If you already run a small can, you may be able to lessen the volume more if you notice the rising rate is not enough.

    As for the front, twitchy is a good description. Consider though that compared to a MX race bike, the bicycle has little ability to change fork offset. Front end geometry is not solely about headtube angle. It is a combination of headtube angle, offset of the axle in regards to the steering axis centerline and wheel diameter.

    So even though you could run two forks, both 100mm as an example, one fork may have a different offset than the other, which will result in a different trail dimension. This change can improve or make worse cornering on account of how the tread on the tire side knobs bites the dirt. Head angles too steep will tend to run more on the tires center, whereas slack angles will also run on the tire sideknobs. The difference is in how everything works together to put weight on the front tire.

    With MX bikes, we are able to buy different triple clamp offsets. 2mm is a noticeable change.

    Slack headtubes tend create a feeling of wheel flop, while steep angles become twitchy.

    The comment about tandems differing from a single I would agree with 100%. Kind of the same, but a lot different.

    Fun technical topic...

    PK
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    ECDM Geometry

    Ha!
    Pulled off a tight, descending, loose, washed out, switchback today! It was a bit sketchy, and Joyce was a bit 'concerned' but we rode through it. It wouldn't have been terribly fun to have had to bail in that spot.... Steering was not on the locks the whole time and the front end felt a bit vague at the bars.

    Is that slow-speed looseness what you're trying to firm up, John?

    When I had a Marz Jr. T at 170mm (had been told it was shortened but hadn't been) it felt like the front tire contact patch was perched on an ice cube (as far as feel, not traction). Shortening the travel helped. Never really liked the Jr T, though.

    Also, for the record.... I do have the small air can on the rear Fox. And I have the rockers that give a 2.5:1 ratio yielding 5" rear travel. Those rockers did raise the back end a bit. When I lived in Phoenix, AZ it was very rough and rocky going and the extra travel was a nice thing (but may have overwhelmed the Fox @285psi). Now living in Prescott 4" would be fine, but don't want to lower the back (without lowering the front).
    --Reamer

    SC Tallboy LTc
    Ventana ECDM 26
    ventana el Ciclon
    Litespeed Classic
    Seven Ti Axion Tandem
    1989 Stumpjumper

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    Quote Originally Posted by reamer41 View Post
    Ha!
    Pulled off a tight, descending, loose, washed out, switchback today! It was a bit sketchy, and Joyce was a bit 'concerned' but we rode through it. It wouldn't have been terribly fun to have had to bail in that spot.... Steering was not on the locks the whole time and the front end felt a bit vague at the bars.

    Is that slow-speed looseness what you're trying to firm up, John?

    When I had a Marz Jr. T at 170mm (had been told it was shortened but hadn't been) it felt like the front tire contact patch was perched on an ice cube (as far as feel, not traction). Shortening the travel helped. Never really liked the Jr T, though.

    Also, for the record.... I do have the small air can on the rear Fox. And I have the rockers that give a 2.5:1 ratio yielding 5" rear travel. Those rockers did raise the back end a bit. When I lived in Phoenix, AZ it was very rough and rocky going and the extra travel was a nice thing (but may have overwhelmed the Fox @285psi). Now living in Prescott 4" would be fine, but don't want to lower the back (without lowering the front).
    Consider also for the rear, the shock length we run comes in two travel variations. Stock is 2.0 and Fox also offers a 2.25. Never fitted a 2.25. If someone tries it, cycle the entire suspension movement before riding it to ensure no interference of the shock to the frame or links.

    PK
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    Hmmm... I have a 2.25' shock from a Ventana El Ciclion. I'll take a look at that with the 4" and 5" rockers on the ECDM and see how it looks. I don't recall if the eye-to-eye length is the same or ' longer than the stock unit on the dcdm. Totally understand about cycling suspension with new rocker and/or shock!

    I don't need more rear travel, just better travel.
    --Reamer

    SC Tallboy LTc
    Ventana ECDM 26
    ventana el Ciclon
    Litespeed Classic
    Seven Ti Axion Tandem
    1989 Stumpjumper

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    Quote Originally Posted by reamer41 View Post
    Ha!


    Is that slow-speed looseness what you're trying to firm up, John?

    Also, for the record.... I do have the small air can on the rear Fox.
    Compared to JD Tandems' demo bike with a Fox 36 @120mm, I thought ours was too "light" on the steering effort, but put this down to the fork length(150mm at the time) and the shorter stem. I tried a longer stem as a trial(90mm) and it did increase the effort but obviously increased the reach too much. So replaced it with the short one, decreased the fork travel to 140mm and fitted the AngleSet.

    Since then, I've put shorter stems on my solo bikes as well. This lighter feel took some getting used to but now it feels fine, so perhaps the tandem set-up wasn't too far wrong in the first place, and it was just me that was the problem .

    Anyway.................The AngleSet has now been rotated by 180 degrees to give a 1 degree slacker head angle to standard. Trials on the road seem OK, with the steering effort pretty much the same as before, with no apparent adverse affects, even when doing slow speed manoeuvres .

    I won't get the chance to take it on the trails until next weekend, but hopefully the "twitchyness" and side-slope deflections will have gone as well.

    As for the air can size....................It's one of these as supplied from Ventana. No idea what the air can size is. We run it at the standard 25/30% sag and with the "trail adjust" at setting 3 (firm). It does still "blow through" on occasions so perhaps we need to add a bit more air.

    ECDM Geometry-15781193182_d89c3e9994_z.jpg

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    ECDM Geometry

    Quote Originally Posted by PMK View Post
    Consider also for the rear, the shock length we run comes in two travel variations. Stock is 2.0 and Fox also offers a 2.25. Never fitted a 2.25. If someone tries it, cycle the entire suspension movement before riding it to ensure no interference of the shock to the frame or links.

    PK
    I measured the 2.25" shock I have. The uncompressed eye-to-eye length is the same as the stock 2" shock. So the longer travel shock wouldn't be a benefit as far as rear ride height, just allow stroking further on a big hit -- as near as I can tell.

    Any other thoughts Paul? Am I missing something there?
    --Reamer

    SC Tallboy LTc
    Ventana ECDM 26
    ventana el Ciclon
    Litespeed Classic
    Seven Ti Axion Tandem
    1989 Stumpjumper

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    ECDM Geometry

    Quote Originally Posted by switchbacktrog View Post
    .

    As for the air can size....................It's one of these as supplied from Ventana. No idea what the air can size is. We run it at the standard 25/30% sag and with the "trail adjust" at setting 3 (firm). It does still "blow through" on occasions so perhaps we need to add a bit more air.

    Click image for larger version. 

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    That's the small air canister.
    --Reamer

    SC Tallboy LTc
    Ventana ECDM 26
    ventana el Ciclon
    Litespeed Classic
    Seven Ti Axion Tandem
    1989 Stumpjumper

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    Quote Originally Posted by reamer41 View Post
    I measured the 2.25" shock I have. The uncompressed eye-to-eye length is the same as the stock 2" shock. So the longer travel shock wouldn't be a benefit as far as rear ride height, just allow stroking further on a big hit -- as near as I can tell.

    Any other thoughts Paul? Am I missing something there?
    Not missing anything. I offered the suggestion simply to set middle ground for you. Assuming there is no clearance issues with the 2.25 shock, you could have more travel than a stock rocker ECDM but less than a long travel rocker ECDM. Changing the leverage ratio will help hold the rear end up, keeping the steering angle more vertical, and minimize wallow or blowing through the travel.

    You made an excellent comment also.

    I don't need more rear travel, just better travel.

    One thing I don't know, is do you have a set of 4" rockers?

    I'm suggesting things (2.25 shock) to keep the stoker content with 4.5" rear travel so slightly less than now, but helping to hold the rear end up from a better leverage ratio.

    Our friends with a newer ECDM 29 had weird handling like you guys are describing. For him to dial in the how the front end cornered, tracked, gain low speed agility and minimize front wheel flop, he gave up rear travel and runs very little rear preload (more air pressure).

    Let me get home and pull out our ECDM. I will take a couple of measurements and post back. As a rough recollection...

    Fork is 150 (6") mm travel, front sag with both riders on is around 1.5" or 25%.

    Rear is set for 1/8" (shock stroke) with stoker only and may drop to 1/4" with both riders, so about 12-15%.

    This is two riders ready to ride with all gear.

    But I will double check this weekend.

    Consider also, with me running a DHX 5.0 air rear shock, by design of the shock it has adjustable bottoming control in addition to propedal. So this also offers me adjustability to prevent wallow on midstroke and helps change the true rising rate of the entire rear suspension without a change in leverage ratio.

    PK
    Reps! We don't need no stickin' reps!

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    ECDM Geometry

    Thanks for your comments, Paul.

    I do have the 4" rockers. I will dig them out. I'll also see if there's clearance to run that 2.25" shock. If nothing else it's seen less and easier use than the current shock on the ECDM.
    --Reamer

    SC Tallboy LTc
    Ventana ECDM 26
    ventana el Ciclon
    Litespeed Classic
    Seven Ti Axion Tandem
    1989 Stumpjumper

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    FWIW, our 40 is 145mm or about 5 3/4" front travel.

    PK
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    I will try and scan some pages that will explain much of this and post them here.

    Good handling and / or good suspension is a best compromise of many parameters and settings.

    So often steering angle is stated as the culprit, but really it all sorts of things. Rear sag, rear spring rate, and overall rear suspension action is a definite factor to proper front end performance and handling.

    FWIW, it is more difficult to get good suspension on a bicycle than on a motorcycle. Much has to do with the rider being the larger mass on the bike, and without a throttle, it can be tough to get good suspension action.

    PK
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    ECDM Geometry

    Quote Originally Posted by PMK View Post
    FWIW, our 40 is 145mm or about 5 3/4" front travel.

    PK
    Mine is pretty much the same. (I don't remember exactly how close the wipers come the the bottom triple clamp when bottomed -- close, though.)

    Next time I have the fork opened up I will add another 1/2" spacer. Might have to shorten the springs, though. (Which are the heaviest Fox offers. I weigh 210, and stoker about 160.)
    --Reamer

    SC Tallboy LTc
    Ventana ECDM 26
    ventana el Ciclon
    Litespeed Classic
    Seven Ti Axion Tandem
    1989 Stumpjumper

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    Quote Originally Posted by reamer41 View Post
    Mine is pretty much the same. (I don't remember exactly how close the wipers come the the bottom triple clamp when bottomed -- close, though.)

    Next time I have the fork opened up I will add another 1/2" spacer. Might have to shorten the springs, though. (Which are the heaviest Fox offers. I weigh 210, and stoker about 160.)
    Team wise, about the same. Firm the rear before dealing with the front.

    PK
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