Bike Geometry and Ride

[Miq]

Ok what about these?

 

[Schwinn Sales West]

Hi John, I now see the link @Headset Guy linked to at Calfee. It has great info. I will add pics for Rake and Trail to our thread. I think the rest of my drawings match. I'm not specifically calling out "front center". Haven't seen that one before. I've been getting confused at this blog.

Hi @J-wagon. Thanks for hopping in.

Other things that don't make sense to me yet.

Some of the measurements are based on the seat post height. But that is totally dependent on the size of the rider setting up the bike. Seems like every bike has some adjustment of the "geometry" or a range of possible geometries.

Shouldn't we be talking about the height of the grips vertically from the center of the seat bolt as well as distance from the grips horizontally to the center of the seat bolt? That makes a big impact on how your weight is distributed on the frame and how it feels.

Front Center is important if you are designing a very tight bike like a track bike or one with Criterium frame geometry. The number will determine if you can actually turn the front wheel without your toes or toe clips hitting the front tire. It was sometimes called "over lap" and on many track bikes (modern frames anyway) the rider toes will hit the front tire. You never turn that far in a race.

John

 

[Miq]

Hi John, I disagree with the actual top tube length vs the effective top tube length. Seems to me like the effective one is really all we care about, especially as we start to compare wildly different shaped bikes. In general I like the idea of seeing how the points our body interacts with the bike relate to each other. Where are the rider's hands, butt, and feet? Stack and reach get me closer to understanding that than actual top tube length IMHO.

 

[Miq]

 

[Miq]

Headtube length doesn't seem that important to me either, not nearly as important as grip height.

This chart is going to change, and things will get added and deleted, but this is a start with actual numbers from real bikes.

 

[J-wagon]

@Miq , I'm more familiar with mtb, and those frame measurements are all relevant and good starting point. As mentioned, distances, angles can be modified for rider fit by accessories spacers, handlebar rise, bar sweep, stem length/angle, saddle position, seatpost height, layback, changing fork, etc. Or shorter crankarms reduce pedal strike on low BB klunkers.

At the end of the day, we all adjust to personalize fit. Practically for me, unless the frame is uber large or uber small, I can do the above for preferred fit.

My main issue is I'm not tall like those Marin klunker pioneers so very little space between me and top tube standover. I've built couple girl klunkers give me uber standover space but their geometry funky especially long HT length have to invert bars creating negative rise to match boy bike stack fit and girl BB seems lower so pedal strikes galore on singletrack. Klunkers are awful for mtb but super fun because they are awful.

 

[Drosentreter]

(Sorry @Schwinn Sales West and @Miq) our threads are similar enough I thought this was mine for a minute

 

[Schwinn Sales West]

Headtube length doesn't seem that important to me either, not nearly as important as grip height.
View attachment 1792990

This chart is going to change, and things will get added and deleted, but this is a start with actual numbers from real bikes.

Your correct head tube length is not critical, it is actually determined by the bottom bracket height. The grip position will be determined by the handlebar rise, and the handlebar reach, the stem length and the stem reach also are varibles. Just look at a very old Paramount adjustable stem to see how far these measurements can change. I still think it's two different discussions. The bikes frame geometry, and the riders comfort geometry is two different things, but they play together because you will run out of seat and bar adjustments.

John

 

[Miq]

@J-wagon I'm similar at only 5'7". I'm with you on the awful fun of Klunkers. I'm really just interested in learning more about what things have the biggest impact on the ride. From the measurements of my two klunkers, much of it seems really similar, but they ride completely differently.

@Schwinn Sales West I agree with you that there are really two kinds of measurements we are interested in, the ones fixed at the factory and the ones we can adjust for personal fit. We can arrange the columns at some point to group them or use different text colors to differentiate them if we really want to. I'm pretty flexible. I think we could add frame material (steel, vs Al, vs Carbon, etc.) just so we include that aspect when we talk about the ride. The Tire sidewall and profile that John mentioned earlier seem important to me.

If we can get a few bikes measured and start discussing how they ride and why, it should lead to me wrapping my head around more of this, and some fun discussion.

 

[J-wagon]

@bloo