Ti vs steel geometry

[PaMtbRider]

Does the frame material affect the design geometry of a bike? If a builder is designing a frame, will the same frame dimensions of a steel and a Ti bike ride and handle the same? I am assuming tube diameter, thickness, butting, would be selected for each material to provide the same amount of drivetrain rigidity, vertical compliance...

[michael white]

Hi,

as I recall, Tom Kellogg has written about this on his site. At least, I think it was him, and he would know.

To summarize what I recall, and also what I've experienced: Ti is not as stable (or usually as heavy) as steel, and that makes a ti bike, in general, a bit quicker (some say twitchy) handling. My 55 cm. Merlin has a 40 mm fork rake, which I presume is designed to counter that effect and steady the handling, and it works.

[swoop]

no. it affects feel. the material dictates how you use the material to get the bike to have a certain ride quality. but geo is geo.
atmo

[michael white]

I'm sort of disagreeing with Swoop. According to Tom Kellogg, and also to my experience, a steel bike and ti bike built to the same geometry will handle much differently; it's a complicated matter best left to experts like TK, but here is an example from the Spectrum site where TK discusses the difference between a ti and steel bike built with identical geo. (I would say the key is gauges and all the other dynamic characteristics of the tube, including material, not simply geo.)


"TITANIUM RESPONSIVENESS
By 1987 (the year I tested the first prototype Titanium frame) I had already built dozens of bikes for my own personal use. Given my training and racing style I had come to what I thought was my ideal frame design. My personal steel frames were built with a 55cm ctr. to top seat tube, a 58 top tube, 73-degree seat angle, 73.5-degree head angle, and a 7cm drop. In working with Merlin on that first Titanium prototype, it seemed logical that I simply build my ideal steel frame only this time in Titanium. I wanted to compare steel and Titanium with a minimum of confusing variables. At the time, I thought the Titanium prototype would ride similarly to my steel frame since the design of the two frames was identical. Boy was I in for a shock.

After only a few seconds on the Titanium bicycle I swore I must have completely redesigned the frame. It seemed to fit the same. I measured it and it had the same wheelbase. The clearances of my steel and the Titanium prototype were also the same. One thing was quite different though. The titanium bike felt considerably quicker handling. Handling responsiveness seemed to be instantaneous on the Ti prototype compared to my trusty steel frame. I still remember how alive that first ride was. In fact, all my rides on Spectrum Titanium bicycles feel as alive as the first.

I soon found out that the handling advances of a well-made Ti frame do not hold for all Ti frames. Only high quality Titanium frames built by knowledgeable and experienced masters are able to enable Titanium to feel so lively. Several factors can lead to a less than ideal titanium feel. For example, Titanium tubes tends to loose the "Ti advantage" when tubes are tapered or use thicker gauge tubing because of smaller diameters. The noticeable handling changes appear to be related to the resiliency of the entire structure. Put simply, Titanium is a very resilient material. If that resiliency isn't designed out of the frame, handling responsiveness is enhanced. The advantage is that a builder with the knowledge and experience can design an even more comfortable and stable Titanium frame while at the same time improving responsiveness."

[J.Greene]

Sounds like a very effective marketing piece. I'm sure it would not have been on the web if it wern't true.

JG


I soon found out that the handling advances of a well-made Ti frame do not hold for all Ti frames. Only high quality Titanium frames built by knowledgeable and experienced masters are able to enable Titanium to feel so lively. Several factors can lead to a less than ideal titanium feel. For example, Titanium tubes tends to loose the "Ti advantage" when tubes are tapered or use thicker gauge tubing because of smaller diameters. The noticeable handling changes appear to be related to the resiliency of the entire structure. Put simply, Titanium is a very resilient material. If that resiliency isn't designed out of the frame, handling responsiveness is enhanced. The advantage is that a builder with the knowledge and experience can design an even more comfortable and stable Titanium frame while at the same time improving responsiveness."

[swoop]

no. it affects feel. the material dictates how you use the material to get the bike to have a certain ride quality. but geo is geo.
atmo

i defer to tk in anything bike and moustache related. he's forgotten more than i will ever know. that being said... i stand by my lil statement. the return of energy one gets from ti does make for a more lively ride.
but i'll take the same geo please.

[michael white]

I doubt I'll get another ti bike because I'm happy with the one I have. But if I do, I'd probably not change geo much between steel and ti myself. Heck, typical geo is all such a narrow range anyway.

that said, I'm just pointing out, there are differences which have been discussed by experts, and I do think these differences are what the op was asking about.

best,
mw

[Ray]

Sounds like a very effective marketing piece. I'm sure it would not have been on the web if it wern't true.

JG
That would be my first reaction too and I still have to admit to a small amount of skepticism. But I own a couple of Spectra and have talked to TK about this a few times and he clearly believes it. And he never used this to try to sell me a ti bike rather than a steel one - he likes both. He used it to explain why he'd design a ti frame with a slightly slacker head tube (half a degree IIRC) to get the same handling characteristics as an otherwise identical steel frame. Whether I fully believe it or not, I've never ridden another bike that handles as well as my Spectrum, so TK certainly has never steered me wrong. With that advice or any other. So I give him the benefit of the doubt, as dubious as it sounds.

-Ray

[coylifut]

i had this discussion directly with tk and when my bike came back the geo was a little more relaxed than expected, but it rode more lively than anticipated. there's a chance ya'll might find me too trusting of builders. tk built a bike based how I should sit on a bike and Zank built one based on my cx position. C'mon, Tom built Danny Clarke's six-day bikes, what do I have to add?

[dawgie]

Based on my experiences, I think ti and steel frames with the same geometry and key components would handle nearly the same. I have two Eddy Merckx frames that are both the same size and century geometry, but one is steel (Corsa 01) and the other titanium (AX model). The both have the same wheels (Mavic Open Pros), saddles (Fizik), handlebars, pedals. The Corsa has Michelin ProRace 23s, and the AX has the same tires in 25s (although previously it had 23s). The Corsa has a steel chrome fork, the AX a Serotta F1 carbon with steel steerer tube.

Both bikes handle the same as far as cornering, general feel, stability. The Corsa is a little more comfortable in the rear when hitting things like potholes, presumably because the ti frame has much stouter chain stays. The AX seems a little smoother on the front end over rough pavement, presumably due to the carbon fork. These differences are minor, however.

The main difference I notice is that the ti frame is noisier. It makes little pinging noises on rough pavement similar to an aluminum frame, while the steel frame is mostly silent. The ti frame is a little lighter but that doesn't seem to help my climbing any. My fastest ride ever (average speed) was on the heavier steel frame over a moderately hilly route.

[coylifut]

My fastest ride ever (average speed) was on the heavier steel frame over a moderately hilly route.

it's cause it was built in Belgium and Eddy walked by and blessed it.

[PaMtbRider]

Thanks for the info. I should have thought to check Tom's site. He recently made a Ti Super for my wife and we are now considering S&S steel bikes. I am curious how her geometry will compare between the two bikes.

[swoop]

i would give TK my money and my measurements and let him do whatever he wanted. i woudn't say a thing other than thank you.

[Ken Robb]

when Serotta builds bikes with stock geos they are the same regardless of the materials chosen. I must be mistaken in thinking that my Legend rides well because it has those darn tapered tubes that I now know negate the titanium advantage.

[British]

Does this mean that the tubes that as an example Moots use (straight guage and straight line) are the ideal to get a great feeling and riding frame, and that all that involved shaping, butting and expense(!) of the Serotta Colorado Concept tubes results in no beneficial gain whatsoever? Err?

Am I being taken for a ride?