Hobbyist 29er Questions and Hopefully Lessons Learned.

[JLP]

So it's the rainy season in Seattle, and I find myself dreaming up projects. I've pretty much built myself all the iterations of road bikes I can think of. I get a kick out of riding bikes I've built myself, so I thought I'd build a frame to replace a Specialized 29er I have and move the parts to the new bike. I'm a lifelong road cyclist, but I only mess around a little on mountain bikes, so I'm much more of a newbie on my preferences here. Would you entertain me with some thoughts on some proposed geometry? After that, suspect I may follow up with thoughts on tubing to make all the clearances work.

For background, I have two 29ers that I think fit me just fine and work well for what I do. They are a medium Salsa El Mariachi and a 18" Specialized Stumpjumper Marathon aluminum. I ride them with a 76cm height from saddle to crank and 9-10 cm stems. 175mm cranks. I don't ride anything epic. I'm 51 and like longer distance on anything from gravel to mild single track. I'm 5' 10" and 165-170. On a road bike built for distance I ride a bit upright with about a 58 ctc seat tube and a 57 top with an 11 or so stem depending...

I'm proposing to make something tried and true. Looking at geometry charts for the bikes I have and other popular bikes, does this look reasonable with the Fox 80mm 32 29er fork from the Specialized?

Seat Tube ctc 435
Top Tube (effective) 600
Chainstay 440
BB Drop 65
Seat tube angle* 73
Head tube angle* 71
Head tube 100
Fork ATC 481
Fork Offset 44

*with 20% sag in fork

Thanks for everything. I very much enjoy the advice here. Joe

[afwalker]

Lots of nice fork options take a tapered head tube. Consider one like this, 1.5 by 1.125 TAPERED HEADTUBE 44mm x 34mm I.D. :: 1.5/1.125 Headtubes :: HEAD TUBES :: TUBES STEEL :: Nova Cycles Supply Inc.
Then you can use the Cane creek angleset and adjust the head tube angle. Now you can tighten it up and make it quick, or relax it if you like. Ever consider the 29r+ tires?
You can probably get the bike to do both, and if you do slider dropouts, now it can be super adjustable.
andy

[JLP]

Andy, thank you for your reply.

The fork I was going to move over is 1.125 not tapered. If I understand you correctly, you would suggest I not do that and go tapered even though I already have the fork from the donor.

I like the idea of using the angle headset and sliding dropouts so I can experiment to see what I feel.

I would very much like to be able to try 29r+ tires for fun, but I was assuming, perhaps with no information, that getting everything to clear might get too tricky. Should I be able to clear these tires with readily available stays? I can dimple stays, but I can't bend them. I don't want to reach too far - this will only be my 9th full frame and my first non-lugged.

Do the other angles and dimensions look in the ballpark to you?

Thanks again. Joe

[afwalker]

The ability to change the head tube angle is very nice to dial in the handling depending on the type of riding and tires you're using. They make it for 44/44 head tubes as well if you don't plan on ever using a tapered fork. Without doing some bending, getting the stays to fit 29r+ 3" tires will be a bit hard, unless you do a boost bike:) 83mm bottom bracket, 148mm dropouts. But that is getting away from your original plan, and depending on the riding you do, the bike you really want. If you can alter head tube angle and effective chain stay length, really the wheelbase longer or shorter, the angles are less critical for a great ride. Those numbers look fine.
andy

[JLP]

A little update. The frame is complete except for finish work. It was quite the learning experience. I'll be happy to ride it. I went with geometry similar to what I listed above. Here's a list of things that were tricky or surprising as a hobbyist on my 9th frame. First mountain bike and first fillet brazed frame.

- I almost didn't leave enough length on the head tube for the wide Fox fork to turn without hitting the downtube.
- I ruined a set of seat stays. I had purchased a set with a slight s bend, and I was going to miter them to the seat tube sleeve without a cap. A surprisingly tricky miter, for some reason. This would have put them too close to the tire, and I buggered them while trying to add some curve. It was easy to put a single bend in some other straight stays I had, but I ended up capping them and tacking them to the side of the seat tube like I do in road bikes. I think it would have looked better without a cap. This led to the biggest screwup on the frame. I've only used straight seat stays before, and I worry about getting the caps on both sides aligned close enough. Well I did that, but I didn't worry enough about the curve, and forgot that I didn't get the caps at exactly the same place on both stays, so now I have crooked stays. The wheel is in the right place, but the stays are off. Oh well. It's a bike for me, and I decided to keep it rather than take things apart. Not sure if that was the right choice.
- I was happy with some of the fillets -- others I made quite the mess. I found that unlike silver if I had too much flux (the Cycle Designs stuff) I have a hard time seeing through orange blobs of flux. I did better with less flux.
- I confused the heck out of myself when tacking the frame because without lugs, I didn't have anything in place to hold the other side of the tubes and my nice tight fit wasn't even close when I moved to the other side of the bike. DUH!!! Fixed it and moved on.
- Fitting a 2.5" tire, chainrings, and a front derailleur is tricky.
- I put a bridge between the stays on the brake side, but I think I didn't need to do that with the Paragon dropouts, so I feel silly about that.
- My extra Thompson 30.6 seat post that just barely fit in the tube before brazing is probably going to be too tight for comfort since I don't think I should go too heavy on reaming. I've found an inexpensive 30.4 that I'll try or I may just use the shim to 27.2 that came with the nova set.

Anyway, a pretty steep learning curve, for sure. I'm looking forward to completing the swap from the generic donor cycle.

Joe


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