Wednesday, March 28, 2007
HyMDT Cruzbike Folder (Update#2)
I learned a great deal during my experimentation period with the hybridization of the Downtube and the Kona MTB. I like the idea of a 20 inch wheel in the back and if a frame with a disk brake mount is used there is not a compatibility problem. I am looking at a small chrome-moly diamond frame. I didn't get a chance to experiment with a seat post suspension, but the lack of a rear suspension is not really an issue for a paved or gravel road machine. With a weight distribution of 50/50 the front suspension takes more of the load than a conventional hard tail, and it is possible to put some weight on the arms when riding on rough surfaces as well as shifting more weight to your butt by leaning forward a bit, transferring even move weight to the front suspension. A hard tail is a hard tail whether you have the pedals in front of you or below you the way it seemed to me although I didn't try steps I jumped curbs without much problem.
For the record I have rebuilt the Downtube after replaceomg the original NECO Bottom Bracket. I replaced the BB bracket with a Shimano UN54 - 107mm sealed unit which is the same as UN52 as far as I could tell. It is a nice fit for chainline etc. with the Bulletproof 110mm BCD double. I am using just the inside ring (34T) but there is room for a chainring on the outside. 110mm BCD chainrings are available in just about any size you may want. The Bulletproof cranks are not the lightest but they make a nice running system with the SA8 rear hub.
There are several things about the NECO BB that I really don't care for.
1) the splines are shallow and slightly oversized thus hard on removal tools, and the threads were dry so removing the BB to grease the exterior threads is something that must be done when the bicycle is new, otherwise the frame may be damaged when it must be removed with extreme force because the bearing are shot.
2) the lock ring, the same thing used on a cup and cone set up, is necessary to set the bearings but is there a cone is on the sealed end? Maybe, but I couldn't tell by looking, the thing is sealed, kinda. (added 30Mar07) Well I did figure out how this thing works, I took out the seal gave the axle a sharp rap with a hammer while the drive side was still n the frame and the adjustable cup was removed. It came out quite easily.
The bearing has a retainer which could be removed and replaced with all ball bearings. The BB could be serviced without removing the right side. In fact, that is the way it should be done. I will have to say that after I figured it out this is a better deal than I thought a couple of days ago. The things you discover by playing.
It is all guess work where it should be set such is the case with the cup and cone but .... Like I said long ago--replace the BB with a sealed unit. Basically do it when the new bike is being checked over by the LBS and forget it for years. Even a moderately priced Sealed BB will last a long time. I guess I still stand by this advice, but if you do you own work the original BB is okay.
Stem
I also replaced the stem with a 7 degree 130mm stem to fit me and reduce the globby looking adjustable unit that is fine if several people are using the bicycle but that is not the case here. Besides I still have the adjustable unit in the parts cache.
I took the cassette head set assembly that I had installed for the Manitou fork off the Downtube and reinstalled the stock head bearing assembly.
I am going to put a moisture seal in place now as the stock head set assembly does not even have a gasket to protect the bearings.
I will detail that in a day or two. It can be done for pennies and it keeps the bearing clean and dry--remember it is the dust and grit that destroys the effectiveness of the grease and wears out the bearings. Prevention is the best maintenance.
For the record I have rebuilt the Downtube after replaceomg the original NECO Bottom Bracket. I replaced the BB bracket with a Shimano UN54 - 107mm sealed unit which is the same as UN52 as far as I could tell. It is a nice fit for chainline etc. with the Bulletproof 110mm BCD double. I am using just the inside ring (34T) but there is room for a chainring on the outside. 110mm BCD chainrings are available in just about any size you may want. The Bulletproof cranks are not the lightest but they make a nice running system with the SA8 rear hub.
There are several things about the NECO BB that I really don't care for.
1) the splines are shallow and slightly oversized thus hard on removal tools, and the threads were dry so removing the BB to grease the exterior threads is something that must be done when the bicycle is new, otherwise the frame may be damaged when it must be removed with extreme force because the bearing are shot.
2) the lock ring, the same thing used on a cup and cone set up, is necessary to set the bearings but is there a cone is on the sealed end? Maybe, but I couldn't tell by looking, the thing is sealed, kinda. (added 30Mar07) Well I did figure out how this thing works, I took out the seal gave the axle a sharp rap with a hammer while the drive side was still n the frame and the adjustable cup was removed. It came out quite easily.
The bearing has a retainer which could be removed and replaced with all ball bearings. The BB could be serviced without removing the right side. In fact, that is the way it should be done. I will have to say that after I figured it out this is a better deal than I thought a couple of days ago. The things you discover by playing.
It is all guess work where it should be set such is the case with the cup and cone but .... Like I said long ago--replace the BB with a sealed unit. Basically do it when the new bike is being checked over by the LBS and forget it for years. Even a moderately priced Sealed BB will last a long time. I guess I still stand by this advice, but if you do you own work the original BB is okay.
Stem
I also replaced the stem with a 7 degree 130mm stem to fit me and reduce the globby looking adjustable unit that is fine if several people are using the bicycle but that is not the case here. Besides I still have the adjustable unit in the parts cache.
I took the cassette head set assembly that I had installed for the Manitou fork off the Downtube and reinstalled the stock head bearing assembly.
I am going to put a moisture seal in place now as the stock head set assembly does not even have a gasket to protect the bearings.
I will detail that in a day or two. It can be done for pennies and it keeps the bearing clean and dry--remember it is the dust and grit that destroys the effectiveness of the grease and wears out the bearings. Prevention is the best maintenance.
Labels: BB, chainrings, Cruzbike, maintenance
Friday, March 23, 2007
Just for the record - HyMDT Cruz stats
More Specs
The trail measurement is 125mm. and the seat pan has been move on the mounting bracket one set of holes and it comes close to John Tolhurst's suggestion, "The seat pan should point to a spot about a foot above the crank."
Post # 1569 to the Yahoo Group
Establishing the seat-handlebar config correctly
FWD
I have the FWD operating nicely although I have not connected the dérailleur so I can shift yet, just clamped into a single gear.
Preliminary Test Ride
The ride skills are improving rapidly spinning in low gears. I have adjusted the handlebars to meet knee clearance [It feels like the stem choice should raise the bars about 40-50mm and move them forward about 25). I will say as it is feels pretty comfortable when I relax and sit back like I'm in my recliner.
Seat position
I am a bit confused about the suggestion for seat placement. It says, "Position the lower part of the the arc to be 8" in front of the seat post tube."
Well here is what I did. I matched up one set of holes on the seat support bracket with the water bottle mounting taps in front of the Downtube Folding bracket--the folding bracket is still operable with this placement. I chose the bracket holes so that it fit as far back as possible. Then I mounted the seat pan so that the back of the pan is 18 3/4 inches forward of the rear axle vertical bisector and 27.5 inches from the ground. The wheel base is 43 1/2 inches, the crank axle is 10 in forward of the front axle vertical bisector and 28 inches from the ground.
Weight distribution
I weighed (bathroom scale) the front and back with rider in pedaling position to get a figure for weight distribution, rear = 128# front=102#. I knew the short rear chain stays for the 20" would have the effect of needing to move the seat forward to have the same moment, but I just guessed where to place it and took advantage of the water bottle tap holes.
The general information speaks to a nearly 50/50 weight distribution and what I have puts the center of weight about over the orginal BB. The long trail induced by the change of head angle from 72 to 65 from the 3" wheel radius increase has some effect on quickness of response but I haven't ridden enough to know if it is a substantive issue.
I do like the way a 26" wheel rolls through gutters and feels on roughed surfaces. I still have the original rear wheel in place but I don't expect the change to the front wheel will produce any discernable change.
Seat Back Mount
The seat back is at about 38 degrees as it sits (sic) and I intend to bend some rod into a seat mount that adapts to a horizontal precision seat post. It will have some milder suspension effect and fore/aft adjustment as well as seat back angle from the vertical seat post adjustment, but
that will not be undertaken until the seat placement is optimized. I could easily cut a piece of wood and drill holes to make fore/aft adjustment seasier (the old backwards seat is as far back as it will go :D) if you people think it is a critical issue it getting things optimized for handling and maneuverability .
So what do you think? I can make some additional measurements and pics too if that is needed.
Thanks for your help.
Post #1570 in response:
I think you've got everything in the range of values where the
design becomes pretty insensitive to small changes. The thing that
will most influence the operation of the bike at this stage is
riding experience.
What I didn't do, and should have, was to get the bike in about the
stage of completion that you have, get the ancillaries hooked up and
fettled (i.e., derailleurs and seat post), and then put a minimum of
about 100 miles on it. This will give you enough time to decide what
is most comfortable for the long-term, and what parts of the riding
dynamic you want to tweek, and why.
Tom Traylor uses fairly large trail dimensions on his bikes with
good results. The design is pretty insensitive to large trail
because the influence of the weight of your legs, combined with the
dampinig effect provided by your leg muscles, is a much larger
signal than the traditional inputs that result in "wheel flop" on a
conventional recumbent. Small trail can make the bike nervous at
high speed, just like a conventional bike, though you need to be
almost at zero or negative to encounter it.
All in all I think you're in good shape. It's an interesting and
versatile application of the kit.
Have fun,
Doug
"Doug Burton" <hardtailcruzer@...>
The trail measurement is 125mm. and the seat pan has been move on the mounting bracket one set of holes and it comes close to John Tolhurst's suggestion, "The seat pan should point to a spot about a foot above the crank."
Post # 1569 to the Yahoo Group
Establishing the seat-handlebar config correctly
FWD
I have the FWD operating nicely although I have not connected the dérailleur so I can shift yet, just clamped into a single gear.
Preliminary Test Ride
The ride skills are improving rapidly spinning in low gears. I have adjusted the handlebars to meet knee clearance [It feels like the stem choice should raise the bars about 40-50mm and move them forward about 25). I will say as it is feels pretty comfortable when I relax and sit back like I'm in my recliner.
Seat position
I am a bit confused about the suggestion for seat placement. It says, "Position the lower part of the the arc to be 8" in front of the seat post tube."
Well here is what I did. I matched up one set of holes on the seat support bracket with the water bottle mounting taps in front of the Downtube Folding bracket--the folding bracket is still operable with this placement. I chose the bracket holes so that it fit as far back as possible. Then I mounted the seat pan so that the back of the pan is 18 3/4 inches forward of the rear axle vertical bisector and 27.5 inches from the ground. The wheel base is 43 1/2 inches, the crank axle is 10 in forward of the front axle vertical bisector and 28 inches from the ground.
Weight distribution
I weighed (bathroom scale) the front and back with rider in pedaling position to get a figure for weight distribution, rear = 128# front=102#. I knew the short rear chain stays for the 20" would have the effect of needing to move the seat forward to have the same moment, but I just guessed where to place it and took advantage of the water bottle tap holes.
The general information speaks to a nearly 50/50 weight distribution and what I have puts the center of weight about over the orginal BB. The long trail induced by the change of head angle from 72 to 65 from the 3" wheel radius increase has some effect on quickness of response but I haven't ridden enough to know if it is a substantive issue.
I do like the way a 26" wheel rolls through gutters and feels on roughed surfaces. I still have the original rear wheel in place but I don't expect the change to the front wheel will produce any discernable change.
Seat Back Mount
The seat back is at about 38 degrees as it sits (sic) and I intend to bend some rod into a seat mount that adapts to a horizontal precision seat post. It will have some milder suspension effect and fore/aft adjustment as well as seat back angle from the vertical seat post adjustment, but
that will not be undertaken until the seat placement is optimized. I could easily cut a piece of wood and drill holes to make fore/aft adjustment seasier (the old backwards seat is as far back as it will go :D) if you people think it is a critical issue it getting things optimized for handling and maneuverability .
So what do you think? I can make some additional measurements and pics too if that is needed.
Thanks for your help.
Post #1570 in response:
Re: Establishing the seat-handlebar config correctly
I think you've got everything in the range of values where the
design becomes pretty insensitive to small changes. The thing that
will most influence the operation of the bike at this stage is
riding experience.
What I didn't do, and should have, was to get the bike in about the
stage of completion that you have, get the ancillaries hooked up and
fettled (i.e., derailleurs and seat post), and then put a minimum of
about 100 miles on it. This will give you enough time to decide what
is most comfortable for the long-term, and what parts of the riding
dynamic you want to tweek, and why.
Tom Traylor uses fairly large trail dimensions on his bikes with
good results. The design is pretty insensitive to large trail
because the influence of the weight of your legs, combined with the
dampinig effect provided by your leg muscles, is a much larger
signal than the traditional inputs that result in "wheel flop" on a
conventional recumbent. Small trail can make the bike nervous at
high speed, just like a conventional bike, though you need to be
almost at zero or negative to encounter it.
All in all I think you're in good shape. It's an interesting and
versatile application of the kit.
Have fun,
Doug
"Doug Burton" <hardtailcruzer@...>
Labels: Cruzbike, Downtube, specifications
Tuesday, March 20, 2007
HyMDT Cruzbike Folder (Update)
I went out to the hardware store and bought a automotive stud bolt (threads on each end) of the same diameter & 62mm in length cut a length of tubing for a spacer to hold the brass bushings in place on the Pivot Clamp, used 2 jam nuts on the outside ends. Very nice looking and works great. Maybe the dowel pin wasn't so essential after all.
In fact, I kind of like the idea of a solid shaft at this joint--even if the nuts loosen the shaft will stay in place but I am not so sure of the other system. I do know the threaded joint is inside and not easily seen, I don't like that.
I assembled things and got around the block a couple times this afternoon on a test ride. It's a bit strange to begin, but I am sure that has been said before. How the heck do I know how it handles, I don't have any basis for comparison? Actually it felt pretty good despite the 35mph winds.
I have some tweaking to do before I am finished and ready for the road, but it looks like I'll be ready before the weather is pleasant. I am sure riding skill will improve quickly, but I am not ready for a video quite yet.
.............................< = >............................................
Labels: Cruzbike, Downtube, fun
Friday, March 16, 2007
HyMDT Cruzbike Folder
Click to enlarge pics for greater detail,
on the
Hybrid Mountain Downtube Cruzbike Folder
<<<<.................................................................................................................>>>>
Strange things happen when bicycles get close to each other in MPV (muscle powered vehicles) Husbandry Workshop Laboratory!
The old Kona Kilauea MTB has been with me for 12 years/30K+ miles, including a frame and fork replacement, and is not going to give up first stall in the stable to some new filly without having a piece of the outcome.
The Cruzbike conversion still needs some work to get the custom look and feel, not to mention parts compatibility (I never had a bike that didn't need a stem change), but I am pumped and can hardly wait to get the new MPV config on the road for a test ride. Why should the bicycles have all the fun?
Later:
By Pickup Tools time this afternoon, the cassette headset assembly had been transferred from the MTB to the folder frame and the Downtube fork stripped of the original bearing races, etc. so that exchanging the forks requires no headset bearing adjustments. The front brake cable works for both forks--one is threadless the other threaded.
There was one essential piece (dowel pin) missing from the conversion kit, when that arrives a test ride is not far away. I don't like the seat back mount but that will be fixed with a couple hardware parts from the bigger hammer hardware store.
Stay tuned for a report on the test ride.
Labels: Cruzbike, Downtube, hybrid
