Originally Posted by Barrettscv (Post 11852129)

Hi Dave,

Thank you for the detailed reply. And yes, the chainstays are very important to creating a rigid structure. I agree that the chainstays are also more important than the seattube or down tube in providing a stable support for the crankset and rear wheel. However, even if the downtube is in tension, the lateral rigidity of the downtube is critical to a rigid housing for the crankset. A BB without a rigid downtube would rock uncontrollably.

I certainly think that steel can be as very rigid in the hands of a skilled builder. However titanium can be rigid, I have no doubts about that.

I'll take a hard look at steel for my next bike. If the frame is truly stiff and meets my needs, I'll go with steel.

Michael

Originally Posted by Dave Kirk (Post 11852198)

Originally Posted by Barrettscv (Post 11852246)

Boy that is wierd. I wish my cadence was that smooth. Thanks again!

Originally Posted by PanTerra (Post 11861233)

I am 6'4" 265 and ride a 62cm Serotta CSi and doesn't flex hardly at all. Ti at this large of a frame is a little wippy, more so in non-custom stock frames. I tested a Seven Ti and it was stiff but a bit springy, especially when I really got down on it and hammered - although, felt pretty interesting. I haven't tried a Legend Ti. Dave, I have always wondered how a Terraplane would feel at this big of a frame.

Originally Posted by Dave Kirk (Post 11861453)

I don't know if I feel 100% comfortable talking about my work here. I'm proud of my work and don't get me wrong I like to talk about it but it feels a bit like the etiquette might be off. I don't know this place well enough to know if it's cool to talk about my own work here or not. If nothing else you should feel free to write or call me directly and i'll tell you whatever you want to know.

Until then what is the accepted etiquette here?

dave

Originally Posted by Dave Kirk (Post 11861453)

Until then what is the accepted etiquette here?

dave

Originally Posted by PanTerra (Post 11861233)

I am 6'4" 265 and ride a 62cm ............ Dave, I have always wondered how a Terraplane would feel at this big of a frame.

Originally Posted by Dave Kirk (Post 11863057)

First off I thank you all for the warm welcome. I find it to be near impossible to stay on the proper side of vague and wavering line when it comes to talking about my own work and not being self promoting..... and what feels to me like 'just informing' others about my work can come off as a sales pitch to those reading. So with all that said -

PanTerra - you and I are about the same height but I am so skinny (185lbs) I don't have a shadow so I have a lot of experience with making bikes in this size range. When it comes to the Terraplane stays there is a lot of customization for the size and weight of the rider that isn't obvious when looking at the bike. Here's how the Terraplane stays are customized -

* first factor is seat tube length. The longer the seat tube the longer the seat stays and the lower the spring rate becomes. A longer spring, all else being equal, is softer than a shorter spring. The other thing seat tube length affects is the angle that the seat stays take from the dropouts to the seat tube. This is very important. Tall bikes have very upright s-stays which gives a near 1:1 ratio of the stay compressing and the wheel moving. On very small bikes the s-stays are laid down at a much lower angle and the ratio of stay compression to wheel movement changes. So a little compression of the stays makes a good bit of wheel movement. So........... a big light rider will have a different bend than a big heavy rider and a small rider will have a different bend than those two and so on...........

* rider weight. A heavier rider will get less bend (both in radius and duration) than a lighter rider. The aim to to have everyone have the same ride regardless of size/weight.

* rider weight part B. A heavier rider will often (depends os frame size) have a s-stay with a heavier wall thickness to make the stay stiffer.

* how/where the bike will be used. If the bike is to be used on butter smooth roads without large hills (making for fast descents) then there is less need and advantage is having the rear wheel move. But if the rider's roads are not good (chip seal, back country farm roads, steep hills with fast corners) then there will be more to gain by having the stays a bit softer to give more wheel movement.

In the end I rarely do the same stay bend twice. The aim is to give each rider the same experience regardless of their size and weight. I love the way they ride and think that folks that have them will say the same thing. There are of course nay-sayers and skeptics that say that the Terraplane stays can't do anything (I've even had someone say they can only make the rear end of the bike stiffer!) but in every case I've seen those people have never ridden one. If you come to Bozeman you can ride my bike around and see what you think. It wouldn't be the same thing I would build for you but you would get an idea of the ride. It's a sincere offer.

Thanks for reading.

Dave

Originally Posted by PaMTBRider (Post 11886552)

Thanks for sharing your thoughts Dave. I plan on purchasing a custom frame within the next few months. I am 6'3" 180lbs so we have a very similar build. I was sold on Ti and really wasn't considering steel but your comments have me re-evaluating that decision. My wife has a steel coupled Spectrum and a Ti Spectrum. They have identical geometries but she prefers the ride of the Ti bike. Of course she weighs quite a bit less than I do. I think I will take your advice and talk to Tom about steel vs Ti and see which he recommends for me. Thanks again.

Originally Posted by Dave Kirk (Post 11845473)

I tend to agree with your friend's assessment of Ti and steel. I think Ti is an ideal material for smaller and lighter riders and that bigger riders may find it lacking. It's true what was said above that Ti bikes can be made stiffer using larger tubes - but not entirely true.

Most of the tubes on a bike have no practical limit to the diameter of the tube that can be used so it's easy to design and build the frame with large main tubes - but the issue boils down to chainstays. Because we need to squeeze the chainstays into a small space left between the chainrings and the tire the size of the chainstays is limited to about 7/8" in most cases. This is what is used on most steel bikes and getting anything larger in their is near impossible without some serious stiffness stealing dents to give clearance. So when you combine this with the fact that Ti is much more flexible than steel you end up with the rear end of the Ti bike being much softer than the rear end of a steel bike.

Some will counter by saying that you can use ovalized Ti chainstays to get more material in there to make it stiffer - but it has little effect. If you make the Ti stays 20 mm wide and say 30 mm tall (a big assed stay!) it will not be as laterally stiff as a round 22.2 mm steel stay. This is for two reasons. First is the obvious that Ti flexes much more than steel does. The second reason is that the oval stay is still not as large in diameter horizontally that the steel stay is. Any oval tube has the bending stiffness roughly equivalent to a round stay of the same diameter. So an oval Ti c-stay will behave in lateral flex about the same as a round Ti tube whose diameter is the same as the minor diameter of the oval. ........... I don't think I said that well. How about this? - a tall oval Ti c-stay that is 20 mm wide will flex about the same as a round Ti c-stay that is 20 mm in diameter.

So you end up with a oval Ti stay that is stiff vertically and about the same laterally as a round Ti stay. There is very little to be gained here with diameter as long as the chainrings and tire are competing for space. But when you look at a steel stay you have the same amount of room so can fit the same diameter c-stay in there and because it's steel it will be MUCH stiffer.

You will also see folks argue that if you put a big down tube in the bike that it will be stiff. It doesn't really work that way IMO. There are only two tubes that can and do transfer the power from the BB to the rear wheel and those are the chainstays. You can remove the down tube and make a bike that transfers power very well - i.e. the "Slingshot" bikes what have a cable instead of a down tube. The Slingshots had very stiff BB's because the chainstays were designed to do the job. Since the chainstays do the work of getting the power from the BB to the rear wheel they are the tubes that will make or break the power transfer of the bike. The chainstays see a combination of three loads - compression end to end, torsion, and bending. The compression loads are small and can for the most part be set aside while the other two are very dependent on diameter. And since the diameter that can be used is limited by the space to put the tube in then you really need to have a stiff material to get the job done and Ti just isn't stiff enough if you are a big guy.

This is the reason I think Ti isn't great for big guys and that other materials like carbon or steel can be better. IMO big guys would be best off getting a steel or carbon bike designed with a big guy in mind and leave Ti to smaller and lighter riders.

Thanks for reading all the above - I got wordy.

Dave

Originally Posted by Barrettscv (Post 11850027)

I have several steel bikes in Reynolds 531 and Tange Prestige and a made-by-Lynskey Ti bike.

Hands down, The Lynskey bike is stiffer by a large margin. I'm 210+ lbs.


Michael

Originally Posted by Barrettscv (Post 11850027)

I have several steel bikes in Reynolds 531 and Tange Prestige and a made-by-Lynskey Ti bike.

Hands down, The Lynskey bike is stiffer by a large margin. I'm 210+ lbs.


Michael

Originally Posted by Dave Kirk (Post 11845473)

I tend to agree with your friend's assessment of Ti and steel. I think Ti is an ideal material for smaller and lighter riders and that bigger riders may find it lacking. It's true what was said above that Ti bikes can be made stiffer using larger tubes - but not entirely true.

Most of the tubes on a bike have no practical limit to the diameter of the tube that can be used so it's easy to design and build the frame with large main tubes - but the issue boils down to chainstays. Because we need to squeeze the chainstays into a small space left between the chainrings and the tire the size of the chainstays is limited to about 7/8" in most cases. This is what is used on most steel bikes and getting anything larger in their is near impossible without some serious stiffness stealing dents to give clearance. So when you combine this with the fact that Ti is much more flexible than steel you end up with the rear end of the Ti bike being much softer than the rear end of a steel bike.

Some will counter by saying that you can use ovalized Ti chainstays to get more material in there to make it stiffer - but it has little effect. If you make the Ti stays 20 mm wide and say 30 mm tall (a big assed stay!) it will not be as laterally stiff as a round 22.2 mm steel stay. This is for two reasons. First is the obvious that Ti flexes much more than steel does. The second reason is that the oval stay is still not as large in diameter horizontally that the steel stay is. Any oval tube has the bending stiffness roughly equivalent to a round stay of the same diameter. So an oval Ti c-stay will behave in lateral flex about the same as a round Ti tube whose diameter is the same as the minor diameter of the oval. ........... I don't think I said that well. How about this? - a tall oval Ti c-stay that is 20 mm wide will flex about the same as a round Ti c-stay that is 20 mm in diameter.

So you end up with a oval Ti stay that is stiff vertically and about the same laterally as a round Ti stay. There is very little to be gained here with diameter as long as the chainrings and tire are competing for space. But when you look at a steel stay you have the same amount of room so can fit the same diameter c-stay in there and because it's steel it will be MUCH stiffer.

You will also see folks argue that if you put a big down tube in the bike that it will be stiff. It doesn't really work that way IMO. There are only two tubes that can and do transfer the power from the BB to the rear wheel and those are the chainstays. You can remove the down tube and make a bike that transfers power very well - i.e. the "Slingshot" bikes what have a cable instead of a down tube. The Slingshots had very stiff BB's because the chainstays were designed to do the job. Since the chainstays do the work of getting the power from the BB to the rear wheel they are the tubes that will make or break the power transfer of the bike. The chainstays see a combination of three loads - compression end to end, torsion, and bending. The compression loads are small and can for the most part be set aside while the other two are very dependent on diameter. And since the diameter that can be used is limited by the space to put the tube in then you really need to have a stiff material to get the job done and Ti just isn't stiff enough if you are a big guy.

This is the reason I think Ti isn't great for big guys and that other materials like carbon or steel can be better. IMO big guys would be best off getting a steel or carbon bike designed with a big guy in mind and leave Ti to smaller and lighter riders.

Thanks for reading all the above - I got wordy.

Dave