Geometry question - - - connecting numbers to ride characteristics??

[exapkib]

Question for the geometry/frame building experts in the room:

When I stumbled on to my Yamaguchi, I did not have much experience with different road bikes. I had ridden a Surly Crosscheck that was much too large, and a CAAD9 (size 56) that I loved. Moving from the Cannondale to the Yamaguchi, I was immediately struck by how fast it changed lines, how quickly it moved, yet stabilized at higher speeds. In the years that I have spent on the Yamaguchi, I have come to love it. It just feels right.

In anticipation of a major life event this year, I’ve been saving up slowly for a new frame this summer, and the good news finally came in! As the frame search becomes real, some questions come into sharper focus.

As a prelude to the search, I borrowed my cousin’s Supersix (size 56) to see
if I’d like to go back to an off-the-shelf frame, and also to see if carbon held any interest for me. I don’t think it’s carbon for me (thinking hard about titanium at the moment). While I did at moments have my breath taken away by the weight reduction (almost five pounds lighter than the bikes I typically ride), I missed the handling of the Yamaguchi each time I took it out.

This experience has left me stewing over numbers, and I’m zeroing in on the wheelbase/chainstay/front center measurements, though I’m not sure that’s the right place to explain what I feel on the Yamaguchi.

Just from ‘parking’ the Yamaguchi next to other bikes on group rides, I’ve always known that it has an incredibly short wheelbase for the size. As near as I can, the relevant measurements are:

Top Tube (effective): 54
Wheelbase: 94
Chainstay: 41
Front Center: 54.5

It seems to me that the extremely tight front center is the unusual measurement on this frame. Is that the case? Would that account for the ‘special’ nature of the steering on this bike?

I’ve thought about taking the Yamaguchi to a local builder to get exact measurements on the angles in the frame. Short of that, any other thoughts on which parts of the geometry I should be looking to replicate in the next frame?

Thanks in advance!

[mhespenheide]

Chainstay length, wheelbase, front center, head tube angle, rake and trail, and bottom bracket drop.

Have fun!

[Louis]

Originally Posted by mhespenheide

Chainstay length, wheelbase, front center, head tube angle, rake and trail, and bottom bracket drop.

Have fun!

Or choose a good custom builder who offers frames in the material you like and tell him about the Yamaguchi, why you like it, your body and what you want from the new bike, and have him build it for you.

[ultraman6970]

The short answer to your question is YES.

Yamaguchis bikes are all like that, is the old school italian/japanese school in him... tesch and others from that area of the country built stuff like that, just for racing.

What you have in there is a racing geometry frame... you can compare the whole geometry with modern bikes if you want, but in a 'ultraman" nutshell modern bikes have relaxed angles and pretty much everybody is using the same guidelines, long wheelbase, low headtube angles.

THe issue with modern stuff is that everybody is using large diameter tubes, you cant go smaller than a 52 frame with those, and what you see like Xs or xxs pretty much is a 51 frame with a smaller seat tube, the other reason you have to factor is toe overlap... if a manufacturer has toe overlap in the small bikes they wont sell, another reason to make the stuff longer, for a guy that doesnt race is not a problem, for a racer to fix the issue you pick a smaller frame and put a longer stem... the longer the stem the less you have to swing the handlebar to turn... But again, for an average joe is not a problem to have long wheelbase till they need to maneuver the bike to avoid and accident and the darn bike can't do it.

I guess your yamaguchi is steel right? with steel you can tweak the stuff a lot better... change angles, play with the BB heigh (drop), front tube angle and even the fork trail, with modern stuff unless you are in a full custom is hard to find bikes that handle like yours... at some point you will notice that having a good handling bike is a must specially in situations where or the bike does what you want or you crash. Personally handling is a must for me and i have sold top tier stuff just because the handling wasnt there for what I like, some bikes just fight with you all the time and I doubt that yamagishi does that, it just does what you wants right?

[mhespenheide]

I'd agree except for this: the longer the stem, the more you have to swing the handlebar to turn it.

To clarify, if you want to change the angle of the forks by a certain amount, a longer stem swinging through that certain angle will swing though a greater distance/arc. All other things being equal (they're usually not...), a longer stem on the same bike will be a little more stable since small motions of the handlebars won't rotate the headset as much.

[Peter P.]

I think your love of the Yamaguchi comes from the head angle and fork rake.

The fork rake you could measure if you pulled the fork; the head angle would be harder to accurately self-measure.

While you could argue ALL frame dimensions influence the Yamaguchi's ride, I think the head angle and fork rake predominate.

To ensure you love your next frame, it would be worth the money to bring the Yamaguchi to your local builder to extract the numbers.

Let us know what these numbers are.

[weisan]

exapkib pal, why not just take the Yamaguchi to Joe Bell and give it a royal paint treatment befitting of your "big event"?

[skiezo]

I have one of these to get the bevels correct on my Japanese kitchen knives and it works great to get exact angles on the bikes that I have.
https://www.baileigh.com/index.php/a...4aAqHoEALw_wcB
I know Sarto will do CF in pretty much any custom geo that you could want and the price is not out of line with other customs.
I would take the bike to a really good fitter and let them know what you like about the bike and what you would like it to do better and go from there.

[one60]

why not reach out to Yamaguchi in CO? Its possible he has the original geometry on file and could help you understand the thinking behind the geometry and frame design?

[ultraman6970]

After re reading.... I did not say more.. I said less :P... longer stem the arc prescribed is larger or longer... so you have to swing the stem less to make larger corrections, resulting in a faster reaction at the front wheel... so yes you are right in that part

The steeper the front angle, the same happens...

Originally Posted by mhespenheide

I'd agree except for this: the longer the stem, the more you have to swing the handlebar to turn it.

To clarify, if you want to change the angle of the forks by a certain amount, a longer stem swinging through that certain angle will swing though a greater distance/arc. All other things being equal (they're usually not...), a longer stem on the same bike will be a little more stable since small motions of the handlebars won't rotate the headset as much.

[tv_vt]

Originally Posted by Peter P.

I think your love of the Yamaguchi comes from the head angle and fork rake.

The fork rake you could measure if you pulled the fork; the head angle would be harder to accurately self-measure.

While you could argue ALL frame dimensions influence the Yamaguchi's ride, I think the head angle and fork rake predominate.

To ensure you love your next frame, it would be worth the money to bring the Yamaguchi to your local builder to extract the numbers.

Let us know what these numbers are.

I was thinking along these lines, too. Sounds like you have a low-trail frame there (which is determined by fork rake/head angle numbers mainly).

[Mark McM]

Originally Posted by Peter P.

I think your love of the Yamaguchi comes from the head angle and fork rake.

The fork rake you could measure if you pulled the fork; the head angle would be harder to accurately self-measure.

While you could argue ALL frame dimensions influence the Yamaguchi's ride, I think the head angle and fork rake predominate.

To ensure you love your next frame, it would be worth the money to bring the Yamaguchi to your local builder to extract the numbers.

Let us know what these numbers are.

^^^^^ This.

The front center is fairly short, but the short front center alone is probably not the reason for the quick handling, but it could be a clue to the reason. For a bike with a 54cm top tube to have a 54.5 front center it usually requires quite a steep head angle, and a steep head angle results in a short trail. Short trail bikes can respond quickly to steering inputs (although they tend to have less inherent stability at speed).

[Gummee]

Originally Posted by mhespenheide

I'd agree except for this: the longer the stem, the more you have to swing the handlebar to turn it.

To clarify, if you want to change the angle of the forks by a certain amount, a longer stem swinging through that certain angle will swing though a greater distance/arc. All other things being equal (they're usually not...), a longer stem on the same bike will be a little more stable since small motions of the handlebars won't rotate the headset as much.

We have the opposite thing happening on these super short stemmed mtn bikes: they need super wide bars to slow down the steering.

A narrow bar on a super short stem = twitchy. Wide bar means more it takes more movement at the ends to get the same movement and it slow things down.

I've ridden bikes with 135 stems in the old days. Felt like I saw steering with a tiller.

AFA the OP: a quick ride on bike X just shows you the difference between what you're used to and what you're on. Give it a few weeks and you'll adapt and then the old bike will feel 'funny.'

M

[bambam]

A good frame builder will help you tune it with the right questions.

My customs were built by the same person (Dave Kirk) and he really worked with me to find out my likes and dislikes on certain bikes.

My first I wasn't that familiar with different bikes but my main ride was a Cannondale and I had a DeRosa that I really liked. I was asked about my likes and dislikes of each and many other questions. He knew what to ask and how to translate that into a great riding, then 2 great riding bikes that were slightly different (1 geared and 1 fixed) but both wonderful.

I was worried I couldn't climb as well on the steel bike as opposed tot he Cannondale because of the weight penalty of steel but the way he made and designed it made me realize real quick I was wrong. The framebuilder should be able to snuff out the differences for you.

I have a larger stable now and feeling the difference in the rides. Locking into one brand or handling charateristics is good but some tweaks might end up with a good surprise or expanded knowledge.

I also have a friend that had a framebuilder make a frame where he took the measurements off his favorite frame. That did not turn out like he had hoped.

Great framebuilder are great fo a reason. They have the knowledge.

Love the Yamaguchi BTW.

Good Luck and ride safe,
BamBam

[Ralph]

Get a new Yamaguchi with latest greatest light parts.