Explaining Handling and Ride Differences

[Michael Katz]

I have both a Seven Axiom Ti and a Spectrum Ti Superlight that have remarkably similar geometries but which have very noticable and distinctive differences in handling characteristics.

The Axiom gives me the stability I wanted but feels like this is at the sacrifice of quick and responsive handling. I feel like this is due to the Seven being built with a higher center of gravity and slight understeering at the front end. I feel like I am sitting on top of the Seven and not immersed into the cockpit.

The Spectrum is a much more responsive handler yet is as stable as the Seven. With its 1" chainstays, it feels stiffer through the bb and drivetrain. It has an aggressive upper body position (Ifeel immersed in the cockpit) but yet is ergonomically more comfortable on long rides. It feels like a performance machine tuned to the ergonomics of my body.

The kicker is, here are the specs on the 2 bikes:
Seven -
TT length c-c =54.8, 2 degree slope
ST length c-c =52.5
HT length = 14.8
HT angle = 73
ST angle = 73
BB Drop - 7 cm
Chainstay - 41 cm
Stem - 11cm, +10 degree
Fork Rake - 45mm

Spectrum -
TT length c-c = 55.2, 3 degree slope
ST length c-t = 56 (54 c-c?)
HT length = 13.3
HT angle = 73
ST angle = 73
BB Drop = 7.5
Chainstay - 41.5 cm
Stem - 10 cm, +10 degree
Fork Rake - 45mm

At first blush, stats don't seem to explain handling differences but my Spectrum is the clear winner in the responsiveness department and is stable as hell during 50 mph descents! The forks on both are Wound Up. Any thoughts on why the distinctively different feel to the handling? I am looking for some informed lucid and objective comments on frame geometry, bike set up and handling. "Flamers" should go play elsewhere.

[dbrk]

As fer as I can figure, descending is the means test to greatness because a great descender is always at least a reasonable climber, sprinter, etc. At least that's how I see it because a bad descender is the worst sort of bike...but to get to your question. Chainstay length and bb drop are likely the key numbers since the angles are all the same and quite neutral. You didn't mention the chainstays, however...

dbrk

[Michael Katz]

dbrk, I checked the 2 stats you raised. Chainstay 41 cm on Seven and 41.5 on Spectrum. BB drop 7 cm on Seven and 7.5 on Spectrum. Now I'm really puzzled!

[csb]

[Jeff N.]

Whats the wheelbase on each? Jeff N.

[vaxn8r]

I'd be willing to bet the differences in handling are due to the welds. Spectrum's are prettiest right? So there you go.

[Michael Katz]

Wheelbase for the Spectrum is 98.4cm. Have to find out the Seven's.

[Climb01742]

this may not be germain but...how about saddle setback? same seatposts? i've discovered that on my bikes, using different seatposts tends to put my saddle in slightly different places. you have to really focus on a consistent saddle setback, irrespective of seatpost. i've found that even small differences greatly impact ride/handling feel. as i said, may not address your issues, but one more thing to consider.

[jpw]

Sometimes it's hard to take a thread seriously. Here there is a splicing together of the conscientious and the frivolous. Makes for funny reading.

[lanton]

I always wonder about the head tube angles. If a very small difference of say less than a half a degree can have a noticeable effect on steering responsiveness, and if custom builders often try to work with such small changes according to customers preferences. If most people are using a set selection of forks it seems like it might be the only place for a custom builder to have a little input in that area. It's really hard to try to make these measurements accurately yourself but it might be interesting to try to measure the trail.

[dbrk]

dbrk, I checked the 2 stats you raised. Chainstay 41 cm on Seven and 41.5 on Spectrum. BB drop 7 cm on Seven and 7.5 on Spectrum. Now I'm really puzzled!

I think you have answered your question: lower bb plus longer chainstay equals more stable ride.

Since road geometries are so close to dialed in by reason of tradition, trial and error, etc. (there being not that much to discuss, really), the rule of 2% applies. That's my term, I made it up. What I mean is that 98% of stuff being all the same, the last 2% accounts for actual, significant differences in the way a bike handles, rides, etc.

actually, it's the color that makes the real difference, as we all know,

dbrk

[Jeff N.]

The last Mer...I mean... Spectrum I saw had welds that looked sanded smooth. Is that how they're done routinely? Jeff N.

[Michael Katz]

dbrk, the numbers are the opposite of what I would expect. The Spectrum has the slightly lower BB and slightly longer chainstay but yet is a more responsive, quicker handling bike.

As suggested by Climb01742, I'm going to check seat post setback and relative saddle position to BB spindle but I think they are very close.

I'm beginning to think maybe it is the paint color or the smoothness of the welds or - perish the thought -"THE TUBES".

[Michael Katz]

Jeff N - Spectrums are smooth, Merlin's are not. Final finishing on Spectrum's raw frames is done by Tom Kellogg.

[dbrk]

The last Mer...I mean... Spectrum I saw had welds that looked sanded smooth. Is that how they're done routinely? Jeff N.

Yes, that is how they come from the welder. Spectrum does no further work on the welds. It has something to do with double passing or something, but it makes NOT ONE DIFFERENCE if a ti weld is single or double or whatever passed so long as it is not corrupted by oxygen, etc., the weld will hold up for centuries (years, not rides). I am trying to stop yet another thread about single vs. double pass welds, a matter that does not fall under the Last 2% Makes the Difference rule (I made it up, there is no "rule" but it makes sense).

As for Michael's conclusion, all I can say is that more relaxed and stable bikes actually handle more sprightly, better. We should be surprised?

dbrk

[Jeff N.]

But if you sand the welds smooth, doesn't that.....never mind. I'm not goin' there. Jeff N.

[Too Tall]

Everything I know about rating bicycle handling qualities are embraced in one and two word credos vis-a-vis the BMX and wideboy crowd.

[Matt Barkley]

From first glance it looked to me like the front end of M. Katz's Seven is higher (steerer-tube is a couple cm.s longer - positive degree stem longer and higher maybe on the Seven) he doesn't mention stack heights - but I would say there are a bunch of differences between these bikes and the front end makes a huge difference ESPECIALLY with the comments made about feeling immersed in the cockpit "aggresive upper body position" - vs. tall on the bike "sitting on top of the bike".

[lanton]

Handling and responsiveness must be very interconnected but I think of them as different characteristics. I think you can have a bike that handles well but is not very responsive and a bike that is very responsive but doesn't handle very well. I think of handling being more dependent on how well you're fit to your bike and how you distribute your weight, while responsiveness seems more dependent on ht angles and trail. I can see how longer chainstays and lower bb and even tubes might help handling and stability but it seems like responsiveness is something more likely to do with the front end geometry.

[vaxn8r]

Your stem's not long enough or low enough.

Seriously, what is the saddle-bar drop of the two bikes? Stack heights? Lowering your bar or lenghtening it makes your bike ride better (more responsive).

[csb]

[JackL]

Two comments:

(1) I don't think a 5mm difference in BB drop would make a measurable difference, but the Spectrum's lower CG should theoretically yield a quicker handling bike; easier to lean over to initiate a turn and easier to make mid-corner adjustments. It will also generate a slightly higher lean angle than a high CG bike in an equal cornering situation.

(2) The longer top tube and shorter stem on the Spectrum will put a little more rider's weight over the front wheel. Could this help in high speed descents? My '85 Fuso has a short tt and long stem, and I think this was intended for weight distribution and stability.

JackL

[Michael Katz]

I appreciate everyone's input. Some interesting takes on this. After sifting through the various posts, I'm inclined to think the answer may be in comparing saddle to bar drop, overall setup of the front end and weight distribution over the front end. I'm going to make some more measurements. Then I may throw in the specs for my CSI which seems to fall between the Seven and the Spectrum in responsiveness. Since it's been raining for the last few days and appears that it's going to rain all weekend, I've got nothing better to do!

What's kind of interesting about all of this is that I used as the point of reference, when ordering all 3 of my bikes, a IF Crown Jewel I used to own. I wanted a bike that had the responsive handling of the IF, without the twitchiness the IF had for me, with more stability and stiffness through the bottom bracket and dirvetrain. I ended up with 3 bikes all with very different and distinctive feels.

[JackL]

Michael,
I also have a Crown Jewel, and found the handling a little twitchy. My size 56 c-c had a 73 head angle and 45mm fork offset. I changed to a 43 mm fork offset and this seemed to help.

I have another 56 c-c bike (called an Ebisu) with same 7cm bb drop, 73 head angle and 45mm fork offset that seems steadier than my CJ with the 43mm fork offset, but the Ebisu has 1.5 cm longer chainstays and 1 cm shorter top tube. The only thing I can think of (other than slightly longer wheelbase) is that the Ebisu geometry moves my weight forward, which dampens the steering.

JackL , Getting Anal in Seattle