(ORBO) BACK40 by LTJ, design by OJ. (ROLLING! But withdrawing from the build-off.)
- Thread starter LukeTheJoker
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If you are at 65 degrees on ST, I would stick more to the 69-70 degree HT angle. 72 might be a little steep.
That's gonna be some unconventional trailbike geometry, regardless..... Can't wait to see this one finished.
Yeah, I am pushing the conventional ideas a little!
When OddJob suggested the super short chain stays I started looking at MTB geometry and that lead me to looking at the new 'forward geometry' concepts, which lead me to a few other ideas like how my old BMX was set up, I was always pretty tall so riding a 20" BMX to school required a long swan neck set post and some tall bars, the S bend seat post moved the seat back to about the same angle I have made this bike, but I still want it fairly steep in the front end to make it turn quick and keep the wheelbase really short.
Does that make sense or am I just kidding myself that this might work?
Luke.
The monocog is closer to the XC side of things geometry-wise. If you are gearing this more towards a DJ or Klunker, I would recommend going slacker for more stability at speed. 69-70 sounds good. It all depends on what your goals are.
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Sent from my SPH-M830 using Tapatalk
In my experience, most bikes that are straight are rideable, and once you ride a bike a few times, you generally get accustomed to the geometry. A short wheelbase is good, but in reality, too much of a good thing isn't necessarily all that awesome. But, I'm not the kind of geometry-wizard who can just look at your drawings and just "know" that you'd be better off with a longer wheelbase or a slacker headtube, y'know?
Speaking more from my guts than experience, i think your plan does make sense, and i think your bike will "work" just fine.... but it may not work out exactly how you're planning it.
(FWIW, i'm planning on going with a 71d HTA, a 73d STA, and shooting for maybe a 42" WB with CSs around 16.5" long...
You know. all this talk of bike frame geometry, and my ignorance on the subject, makes me wonder - is that why some bikes are my favorites and some I just hate to ride? Don't do much off road so I'd be confined to road and cruiser bikes.
One bike I hated to ride was this Murray mountain bike.
The few times I rode the thing I was in pain.
One bike I hated to ride was this Murray mountain bike.
The few times I rode the thing I was in pain.
Yeah, geometry is a huge factor, but so is stiffness, weight, and other variables (eg, componentry)... all of these things can make or break a rider's experience with a bike, and some are easily remedied. Others are not.
That being said, we do all have our preferences. What is a dud for you might be awesome for me, or vice versa. I'm a heavy rider (neighborhood of 250lbs), so a lot of bikes that smaller folks think are stiff to the point of harshness, I tend to like those. Conversely, some bikes that I think are a bit whippy/flexy, smaller riders might think those are just comfy....
That being said, we do all have our preferences. What is a dud for you might be awesome for me, or vice versa. I'm a heavy rider (neighborhood of 250lbs), so a lot of bikes that smaller folks think are stiff to the point of harshness, I tend to like those. Conversely, some bikes that I think are a bit whippy/flexy, smaller riders might think those are just comfy....
You know. all this talk of bike frame geometry, and my ignorance on the subject, makes me wonder - is that why some bikes are my favorites and some I just hate to ride? Don't do much off road so I'd be confined to road and cruiser bikes.
One bike I hated to ride was this Murray mountain bike.
The few times I rode the thing I was in pain.
Actually, My brother gave me the Murray, He wanted it back when I told him I was gonna part it - and he happily rides it today.
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You know. all this talk of bike frame geometry, and my ignorance on the subject, makes me wonder - is that why some bikes are my favorites and some I just hate to ride? Don't do much off road so I'd be confined to road and cruiser bikes.
One bike I hated to ride was this Murray mountain bike.
The few times I rode the thing I was in pain.
I found that a bigger comfort factor than I ever realized is wheel weight. I wonder why it took me so long to realize this? I rode bikes in the summer and loved them, then put homemade studded tires on them with super heavy duty tubes that weigh more than a tire plus a split inner tube tire liner glued into the inside of the tire with contact cement. Just putting on these tires made the bike into a "medicine bike" and the comfort went down as all the added effort was transfered to my butt, legs and back. A 10 mile ride feels like 20 and even gradual slopes become challenging. This is with greatly reduced gearing. I thought it was pushing the snow that made it hard but now I realize it is the rolling resistance as it is just as hard on dry pavement. I recently rode a $4000+ carbon fat bike with carbon wheels. I spun the wheels and they rolled forever. Then I spun the 14 other fat bike tires on our ride and none of them came even close. These were also very expensive fat bikes. The 26 pound carbon fat bike on packed snow felt like I was riding a road bike. I think weight is the biggest factor in comfort, especially wheels. I have made clunkers out of Huffy's, Columbia's, Schwinn's, and CWCs. Non of them had MTN bike geometry but they ride single track well when I put alloy wheels and light tires on them. They still weighed 35 to 40 pounds but ride well. I rode the Schwinn on single track with full fenders, steel rims and a chain guard and then stripped it and put on alloys and there was a big difference. But, the surprising revelation for me was how bad things get when you increase wheel weight. Too bad carbon rims are so stiff, but they were OK with 4.8 inch tires on the carbon fatty. I would love to put carbon rims on a klunker but without suspension my fillings would fall out. If you put a bunch of money into the Murray, wheels, gearing, seat, stem and brakes you would like it, providing the cockpit can be made to fit you. If it's too big a frame forget it. If it's a little small you can usually make it fit better. It will still be heavy. I wouldn't bother putting money into the Murray, but this is basically what I do with old cruisers and they are a joy to ride on trails. All it takes is money. On the other hand, these other bikes don't hold a candle to my Specialized MTB with the correct geometry and full suspension. I never feel like I had a workout after our usual 12 mile single track rides with this bike. My heart never feels like it will explode and I don't feel beat up. It's like riding a couch. I do miss the beat up feeling and feel cheated after riding the Specialized.
Great progress Luke. Looks like another cool build. Love all the tech talk in this thread too.
My 2 cents on the head tube angle. I notice with a steep head tube it makes it more difficult to cruise slowly. You end up steering back and forth a lot but it def makes it more responsive.
My 2 cents on the head tube angle. I notice with a steep head tube it makes it more difficult to cruise slowly. You end up steering back and forth a lot but it def makes it more responsive.
That is my basic understanding too, also a slacker headtube is better for higher speeds and cruising, but I really want this to turn quick...Anyway, overdid things yesterday working on a different bike so was going to do nothing today, but that gets boring quick, so decided to hand bend the seat stay/top tube bars. I basically just lay the tube on some soft grass, stand on the tube and pull up a little on the ends, working my way along the tube then test it against the drawing, anywhere needs more bend just stand there and pull on each end, taking the bend out is easier, so I usually go a little over and work my way back to where it needs to be.
First one done:
Second one done:
Good result for an off day!
This is also my first post direct uploading pics, I have been a Pro Member since that option started but just kept using Flickr as it was easier, but for the sake of the forum and making sure pics stay in place and don't get lost, figured it was about time to do it properly.
Shame my cameras lowest setting is still double the required size... I ended up uploading to Flickr from my phone and downloading it smaller from there to my computer. I'm sure I will get used to it!
Luke.
That geometry is exactly what I am trying to avoid, I have trouble getting comfortable on any MTB usually, I am hoping a longer top tube, taller bars and cranks further forward will get me a bit more comfortable, relying on the short wheelbase to keep it nimble...One bike I hated to ride was this Murray mountain bike.
The few times I rode the thing I was in pain.
One way to find out!
Thinking now that I might leave the current 72 degree headtube in place for the first couple of rides, using a standard fork, that way I can find out if it will work before welding in the 1 1/8th replacement, if it is too twitchy I can take a couple of degrees out. Good idea?
Luke.
I agree, ride it for a few miles. See if your shoulders or back feel fatigue, make sure the angle and stance don't make your hands go to sleep during some complex riding as well. If its comfy, all good, else change it up ;-)
Building... riding...
Building... riding...
Amazing... you described my experience riding the Murray esp. the back ache and the numb hands!
Did a quick computer mock-up, should look good!
The new brake pads arrived today for my second hand Tektro Aquila callipers, I went for the sintered copper alloy ones even though they will never get enough use the way I ride for fade with standard resin pads to be an issue...
Pretty sure I have everything for the build now, my last item came in today for the wheel builds, so I just need to pick it up and that should be it!
Luke.
The new brake pads arrived today for my second hand Tektro Aquila callipers, I went for the sintered copper alloy ones even though they will never get enough use the way I ride for fade with standard resin pads to be an issue...
Pretty sure I have everything for the build now, my last item came in today for the wheel builds, so I just need to pick it up and that should be it!
Luke.
Did a quick computer mock-up, should look good!
View attachment 14931
The new brake pads arrived today for my second hand Tektro Aquila callipers, I went for the sintered copper alloy ones even though they will never get enough use the way I ride for fade with standard resin pads to be an issue...
View attachment 14933
Pretty sure I have everything for the build now, my last item came in today for the wheel builds, so I just need to pick it up and that should be it!
Luke.
That looks sharp!! I like it a lot.
Building... riding...
Darn you, Luke! Darn you, Odd Job! I thought I had a brilliant plan for a vintage straightbar frame that I'd klunkify, but your project is so much more sophisticated and well planned, I think I'll just give up.
Don't do that! I can't compete with a vintage bike, it would not surprise me if you did better in voting than I will!
No vintage frames available here, that is why I am building my own...
Very little progress today, but I did paint the hubs ready to build the wheels.
Luke.
Hubs came out awesome! I masked the Hazard label on the rear hub, love it!
Decided to black out the polished sidewalls on the rims too, running disc brakes, so wont need them, makes for a tougher look I think!
Picked up the last item needed to lace up the wheels, 25 lengths of 2mm yellow heatshrink tubing:
Why? Maybe you should ask @OneHorsePower, he gave me the idea from one of his posts a few years back...
Looking forward to getting these done!
Luke.
Decided to black out the polished sidewalls on the rims too, running disc brakes, so wont need them, makes for a tougher look I think!
Picked up the last item needed to lace up the wheels, 25 lengths of 2mm yellow heatshrink tubing:
Why? Maybe you should ask @OneHorsePower, he gave me the idea from one of his posts a few years back...
Looking forward to getting these done!
Luke.
