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Tom K/Spectrum View on Compact Frames(6 posts)

Tom K/Spectrum View on Compact FramesFez
Jan 23, 2004 8:04 AM

In a nutshell, I believe he said the biggest difference he could observe was in STANDING climbs or accelerations, where he said the rocking back & forth appeared to be reduced. He said he could notice a huge difference.

Assuming all that is true, do you think it translated to faster speeds? Or was it just a "feeling?" He said the compact design was not appreciably stiffer or lighter. Since the weight was not an issue in this case, the only difference I can ascertain is the location of the weight due to the sloping design.

Anyone want to comment on this alleged reduced inertia or the bike as it rocks back and forth?

Here's a copy of the relevant paragraph:

In designing the our first compact prototype back in mid '98, we wanted to discover what if any the real world differences there would be between traditional and compact frame designs. Our first compact frame (still my favorite frame) was an exact replica of my then current titanium frame in materials and geometry save for the sloping top tube. I designed it with a severe (17 degree) slope to ensure that any differences would be as obvious as possible. We had assumed that the new frame would be somewhat stiffer and lighter. It was lighter (about 4 ounces) but it was not appreciatively stiffer. Although we were able to measure a slight increase in stiffness, it was too slight to feel. The big change came when I stood to accelerate or climb. As I stood up, the bike appeared to loose three pounds. The inertia of the bike as I rocked it back and fourth was reduced so much that I felt as though I was on a twelve-pound bike. Interestingly, when seated, a compact frame feels exactly like a traditional design. The compact design has no effect on handling beyond the increases responsiveness during climbing and accelerating.
Before you chisel 'compact design reduces rocking' in stone...LactateIntolerant
Jan 23, 2004 8:27 AM
...reread what he wrote. He contends the inertia of the bike was reduced, which makes sense considering the lower center of gravity.
I did mention the lower center of gravity...Fez
Jan 23, 2004 8:53 AM
In fact, that was the only difference I could ascertain in his example. My question was whether:

a) One could feel the difference (Tom K said YES)
b) If this translated to faster speeds, since the weight and stiffness were NOT a factor in this comparison.

c) And this advantage is only evident during STANDING, when the bike rocks side to side?
Similar to...Ray Sachs
Jan 23, 2004 10:01 AM
...if you ever move from a really heavy saddle to a really light saddle, the place you feel it is rocking the bike while out of the saddle. I have a bike that I ride with a Brooks sometimes and with an Aliante other times. The difference in weight isn't really noticeable to me when seated, even on major climbs, but when you rock the bike, you can sure feel it. I guess moving the weight of the top tube down lower can have this same effect to a degree. I used to have a Bike Friday, which has no top tube per se, and it always took me a while to even feel comfortable out of the saddle on this bike when I hadn't ridden it in a while.

Similar to...andre71144
Jan 23, 2004 7:04 PM
just curious would the longer seat post have a pendulem(sp)effect and tend to raise the center of gravity or may be this is not even an issue
Similar to...ramboorider
Jan 24, 2004 4:50 AM
I doubt there's much difference in weight between more seat tube or more seat-post (you gotta have one or the other to get the seat to the same place). So I think the primary difference would be the location of the top tube. Or, in my case, the weight of the saddle.