If it doesn't fit, then I must quit

[pdonk]

Originally Posted by scottcw2

Yes, this is a perfect description. I feel like a part of the Kvale, but on top of the DeSalvo.

Looks like I have my answer.

This is exactly how I feel about my speedvagen vs my moots. Sit in the SV and on the moots. I have set up saddle height and setback the same on both, bar drop on the moots is slightly less as is saddle to bar reach.

The feeling is even more exaggerated on my dekerf mtb, which definitely has a sitting on top of feeling.

[Mark McM]

Originally Posted by jtbadge

With your crank length and saddle height set the same, between the difference in BB drop and tire height, you're riding 15mm-ish closer to the ground on the Kvale. That's a huge difference in a feeling of stability.

I have a bike with a (proprietary) carbon seatpost. During a ride (and before I used carbon assembly paste) the seatpost slipped down about 15mm. I distinctly noticed a difference in leg extension while pedaling - but I never noticed even a minor difference in a feeling of stability, let alone a "huge difference"

If a 15mm makes a "huge difference" in a feeling of stability, then does that mean that taller riders (whose centers of gravity are much higher than shorter riders) will never feel stable on a bike?

[Black Dog]

Originally Posted by scottcw2

I realize that is true, but I know what I feel. My Kvale with a 60 c-t ST feels extremely stable. The DeSalvo with a 61 c-t ST feels like I will tip over.

The only things that I can think could cause this are:

• the Kvale is running 23c tires and the DeSalvo is running 32s. Maybe the wider tires are also causing the bike to feel a bit higher.
• the Kvale has a BB drop of 8cm, the DeSalvo is 7cm. Maybe the higher BB makes the DeSalvo feel less stable.

Well this and differences in geometry will make it feel different, the ST length is not a factor as long as your contact points are the same.

[jtbadge]

Originally Posted by Mark McM

I have a bike with a (proprietary) carbon seatpost. During a ride (and before I used carbon assembly paste) the seatpost slipped down about 15mm. I distinctly noticed a difference in leg extension while pedaling - but I never noticed even a minor difference in a feeling of stability, let alone a "huge difference"

If a 15mm makes a "huge difference" in a feeling of stability, then does that mean that taller riders (whose centers of gravity are much higher than shorter riders) will never feel stable on a bike?

You didn't notice a difference in stability because your cranks were still the same distance from the ground. The BB drop and tire height didn't change.

And, yeah. A lot of bigger bikes have more BB drop and longer chainstays to help with stability.

[tv_vt]

Read Tom Kellogg's blog on the first time he used a compact frame and then talk about level top tubes vs sloping...

There's a fair difference in fork trail between those two bikes, too. Handling might feel quicker on the one with 56mm trail and maybe more stable on the one with 59mm trail.

[colker]

Originally Posted by Mark McM

Even if the two bikes have the same BB height? BB drop is just a frame dimension, and doesn't affect handling directly. .

It may be the opposite.. BB height only affects pedal clearance. Change the crank length and you fix it. BB drop is the center of gravity against wheel axles.

[colker]

Originally Posted by pdonk

This is exactly how I feel about my speedvagen vs my moots. Sit in the SV and on the moots. I have set up saddle height and setback the same on both, bar drop on the moots is slightly less as is saddle to bar reach.

The feeling is even more exaggerated on my dekerf mtb, which definitely has a sitting on top of feeling.

BB drop on your 26in MTB is way less than on a road bike.
SEat tube length effect is placebo of the highest order.

[Mark McM]

Originally Posted by jtbadge

You didn't notice a difference in stability because your cranks were still the same distance from the ground. The BB drop and tire height didn't change.

So wait a minute - if I were to have swapped to shorter cranks - say, gone from 180mm to 165mm (15mm higher from the ground), the shorter crank bike would be less stable because they put the feet higher off the ground?

Originally Posted by jtbadge

And, yeah. A lot of bigger bikes have more BB drop and longer chainstays to help with stability.

Can you give any examples? I just checked a few Trek (Domane and Checkpoint) and Specialized (Roubaix and Tarmac). In all of them, the larger sizes had less BB drop (higher BBs). I suspect that the reason for lower BBs on smaller bikes is to decrease standover, and higher BBs on bigger bikes to maintain pedal clearance (with longer cranks).

[pdonk]

Originally Posted by colker

BB drop on your 26in MTB is way less than on a road bike.
SEat tube length effect is placebo of the highest order.

Agree about BB drop, just another point of reference.

Seat tube lengths vary greatly between the bikes, saddle heights are within mm's of one another. Relationship of bum to BB is about the same, relationship of bum to ground is very different.

[colker]

Originally Posted by pdonk

Agree about BB drop, just another point of reference.

Seat tube lengths vary greatly between the bikes, saddle heights are within mm's of one another. Relationship of bum to BB is about the same, relationship of bum to ground is very different.

I am not an authority but from what i know it´s the BB acting as a pivot against the wheel axles. It´s one of the reasons 29ers corner better than 26inchers. A low bb or bigger bb drop gives stability and less resistance when changing direction so cornering feels like the bike is gripping the ground better.