Kirk Frameworks

[monkeybanana86]

Yeah what a beaut!

[basilic]

really, I'd say if you are on the fence - just do it. Get your own custom from DK. Don't buy second hand, you'll always wonder if it was right for you. After a few years the cost of a frameset per mile is less than what you spend on tires.

[David Kirk]

By far the most challenging part of making a fillet bike pretty is the bottom bracket. You’ve got all the tubes meeting in a small place and much of the fillet is in a concave form. When you are making a top tube/head tube joint smile-worthy the shape is all convex and this makes it easy to file or sand or polish. The concave shape of the bottom bracket it a different animal and it means you are in effect sanding or polishing is a shallow dip or hole for long periods of time. You can’t just work a strip of emery cloth over the joint and call it a day.

This means that one needs to be very precise and tidy when laying the fillet in the first place so that there’s the least amount of work as possible in making it look just right. For the past 3 decades I’ve been working on this skill and the work is never really done and there’s always more to be learned and there are skills to be honed. It never ends and that’s a very good thing.

The pictured frame is an Onesto fillet and its 100% stainless with silver fillets so it will get zero paint work and it ready to ride and use as shown.

dave

[AR2266]

Originally Posted by David Kirk

By far the most challenging part of making a fillet bike pretty is the bottom bracket

Always insightful to read your thoughts penned down, Dave.

I'm not sure if you have commented before, but what are your thoughts on the T47 BB and if there is any merit in your opinion, over the BSA
Have you actually used it for any of the frames you built.

While we're at it, I was thinking about the different seatpost diameters of 27.2 and 30.6, when would you use the bigger diameter in your design, if at all.
It seems 27.2 gives a more compliant ride most of the time.

Also, for steerer tube diameters - do most of your current frames like the MRB now use 1 1/8 inch? when do you revert to 1 inch steerers?

[David Kirk]

Originally Posted by AR2266

Always insightful to read your thoughts penned down, Dave.

I'm not sure if you have commented before, but what are your thoughts on the T47 BB and if there is any merit in your opinion, over the BSA
Have you actually used it for any of the frames you built.

While we're at it, I was thinking about the different seatpost diameters of 27.2 and 30.6, when would you use the bigger diameter in your design, if at all.
It seems 27.2 gives a more compliant ride most of the time.

Also, for steerer tube diameters - do most of your current frames like the MRB now use 1 1/8 inch? when do you revert to 1 inch steerers?

Good questions.

I have not used a T47 BB. For the bikes that I make I can't find the advantage of going with a bigger and heavier shell.

Seat post diameter is of course a function of seat tube OD and ID. On lugged bikes with a normal OS tubeset the seat post is 27.2 mm. If the lugged frame is built with XL sized tubes then the seat post diameter has to increase to match the ID of the larger seat tube....which in most cases is a 30.6 if using a thin walled seat tube.

If the frames is fillet brazed it will most often use a 27.2 post because the ID of the 1 1/8" seat tube calls for it or because a seat tube sleeve brazed into a 1 1/4" seat tube will call for it.

A traditional OS tubed lugged frame will use a 1" steerer...while a XL tubed lugged frame will use a 1 1/8" steerer. This is driven in large part by the size of the head tube which in turn is dictated by the lug sizes.

Fillet frames could have either a 1" or 1 1/8" fork since there are no lugs to dictate the size. Small and light riders can save weight and get a smoother ride by using a 1" fork...while larger, heavier or more aggressive riders can use a 1 1/8" fork. It's a nice way to fine tune the ride.

I hope that all makes sense...I've been away at a 4 day snowboard event where I was teaching clinics and it feels like I've been living on coffee and cookies for the past week and sleep was in short supply!...so the above makes sense to me at the moment but that might be just me.

dave

[AR2266]

Originally Posted by David Kirk

If the lugged frame is built with XL sized tubes then the seat post diameter has to increase to match the ID of the larger seat tube....which in most cases is a 30.6 if using a thin walled seat tube.

A traditional OS tubed lugged frame will use a 1" steerer...while a XL tubed lugged frame will use a 1 1/8" steerer. This is driven in large part by the size of the head tube which in turn is dictated by the lug sizes.

Insightful as always, Dave. I hope you had a good weekend of rest.

So i have more questions for the lugged frames -

1. Could we not braze a shim/ internal sleeve to the XL seat tube to maintain the 27.2 seatpost dia.? - aesthetically, I am assuming the trade-off is is a rather noticeable gap between the seat lug and the 27.2 seatpost.

2. For a rider that does not necessarily need the XL tube set but would like a 1 1/8" steerer for some reason, how would you tune the frame so it is less harsh (I am assuming, it is not practical to mix and match XL and OS tubes as the lugs are the restriction)

Thanks for being patient with the clarifications.

[David Kirk]

Originally Posted by AR2266

Insightful as always, Dave. I hope you had a good weekend of rest.

So i have more questions for the lugged frames -

1. Could we not braze a shim/ internal sleeve to the XL seat tube to maintain the 27.2 seatpost dia.? - aesthetically, I am assuming the trade-off is is a rather noticeable gap between the seat lug and the 27.2 seatpost.

2. For a rider that does not necessarily need the XL tube set but would like a 1 1/8" steerer for some reason, how would you tune the frame so it is less harsh (I am assuming, it is not practical to mix and match XL and OS tubes as the lugs are the restriction)

Thanks for being patient with the clarifications.

Hello Again -

- one could sleeve the inside of the larger seat tube to downsize it to a 27.2 post but that's problematic in a few ways...one of which is the gap you speak of. Years ago I mocked this up to see if it was a good idea and I decided against it because it made the upper seat tube wall (seat tube, sleeve, and lug) very thick and I feared that it might wrap and clamp the seat post well. There's also the issue with a gap. In the end the larger seatpost acts just like the larger seat tube does and gives more stiffness and support of a heaver rider. If the rider benefits from the larger seat tube you can bet that they will also benefit from a larger post for the same reason.

- If the rider wants a 1 1/8" steerer and wants lugs they are going to get XL tubes. Could those XL tubes be tuned so that they soften the stiffer ride brought about by their size? To a small degree yes. But the larger tubes will be stiffer no matter what than the normal OS tubes. One can make the wall of the big tube thin enough to make it behave the same as a smaller tube.

- If the rider insists on a 1 1/8" steerer but they want OS tubes (as opposed to XL) to give a smoother ride that can be done but not with lugs....it will need to be built with fillets.


I hope that adds up for you. Let me know what you think.

dave

[Zartan_d1]

Amazing!

[AR2266]

Originally Posted by David Kirk

Let me know what you think.

Thanks Dave - you certainly cleared the silent questions I never asked.
I think my next bike from you will be one with fillet joints.

[slowpoke]

Originally Posted by David Kirk

Small and light riders can save weight and get a smoother ride by using a 1" fork...while larger, heavier or more aggressive riders can use a 1 1/8" fork. It's a nice way to fine tune the ride.

Hi Dave, what's your general threshold for when someone should be on a 1 1/8" fork versus just a 1"? Thanks

[David Kirk]

Originally Posted by slowpoke

Hi Dave, what's your general threshold for when someone should be on a 1 1/8" fork versus just a 1"? Thanks

That’s a tough question to give a succinct answer to…and I dislike saying “it depends”. But it boils down to “it depends” any way you cut it.

The most important thing to note is that the choice of 1” or 1 1/8” steerer is not based on strength or durability. Both will be more than strong enough as has proven over the past century of steel framebuilding. So it really comes down to two things -

- will the rider benefit from a stiffer fork?

- what size main tubes will serve the rider best and then what size steerer will work with the chosen head tube?


A small and light rider is often best served by the 1” steerer and I can pick one with a lighter wall thickness. This will save weight and give a smaller and lighter rider a smooth ride. If the rider is taller but still light the 1” will work well if I choose the proper wall thickness. The longer steerer will benefit from a bit more wall to keep it stiff enough.

If the rider is larger and heavier but wants a butter smooth century bike the smaller steerer can help with that. A larger and heavier rider that rides aggressively and/or rides dirt and gravel will most likely enjoy the larger 1 1/8” steerer more…and they probably have larger main tubes that will call for the larger steerer anyway so it all works out.

Hows that for a response? I went to a reading many years ago by of my favorite author Spaulding Gray and at the end of the reading he had the lights turned up and he took questions from the audience. He said we could ask him anything but that “I can’t promise answers, I can only promise responses”. I feel a bit like I’m channeling Gray in this response!


Dave

[lavi]

I'll say this regarding steerer size: it depends.

This is my JKS. It's a marvel. It was Dave's 2011 NAHBS bike that I picked up locally from an LBS (on consignment no less!).

It has a 1" steerer. I think the entire package is simply flawless. I'm 6'2", 195. I'm not a hammer, but I'm not a light/easy rider either. I ride this rig. I feel zero wiggle from the front end of the bike. I wouldn't have it any other way.

[carlucci1106]

Originally Posted by lavi

I'll say this regarding steerer size: it depends...

It has a 1" steerer. I think the entire package is simply flawless. I'm 6'2", 195. I'm not a hammer, but I'm not a light/easy rider either. I ride this rig. I feel zero wiggle from the front end of the bike. I wouldn't have it any other way.

Lavi,

This bike is simply gorgeous. Yeah, what I understand based on what I know about frame composition, is that a wandering or unnerving front end cannot be blamed on the steerer diameter alone.

It would seem to me that when DK describes torsional flex in his 3 flexes article, that if the seat tube and the head tube come too far out of plane during hard leans while descending, a rider could feel the bike is noodly and non- confidence inspiring. But the 1" fork steerer alone, given the rest of the frame/fork stiffness is designed properly for the rider, will only serve to damp small vibrations. It won't be at-risk of waggling all around. That's not the steer tube's job.

I have a CSi, don't feel any waggling, even with a 1" carbon steerer, and it's been on some monster descents in the Rockies.

[David Kirk]

Speaking of forks....here's an Onesto stainless fork that will be paired with a Onesto Fillet MRB once it's done. The fork is built to work with a mid reach rim brake and will fit a 35 mm tire at a minimum.

This one is built for a big tall guy and sports 1 1/8" steerer. Now onto the frame.....

dave

[AngryScientist]

Very nice Dave.

Is getting the inside of that window on the fork crown cleaned up as much of a tedious pain in the butt as I'm imagining it to be??