If it doesn't fit, then I must quit

[scottcw2]

One frame 2-3 cm too big:

https://i.imgur.com/TPHCmoN.jpg


And another 3 cm too small:

https://i.imgur.com/dud6RTp.jpg


The search continues...

[XXtwindad]

One frame 2-3 cm too big:

https://i.imgur.com/TPHCmoN.jpg


And another 3 cm too small:

https://i.imgur.com/dud6RTp.jpg


The search continues...

Plenty of people would enter a guilty plea for those frames …

[scottcw2]

Agreed, and I wish I could also.

I was surprised how much an extra 2 cm in the ST made a difference in ride feel. Even with my crank length and saddle height set the same, I just don't feel as stable on the longer ST. It's like my center of gravity is too high.

[colker]

Agreed, and I wish I could also.

I was surprised how much an extra 2 cm in the ST made a difference in ride feel. Even with my crank length and saddle height set the same, I just don't feel as stable on the longer ST. It's like my center of gravity is too high.

Seat tube length has zero effect on bike feel for me. It´s all about where´s the wheels, where i sit and where are the bars.

[Blown Reek]

I was surprised how much an extra 2 cm in the ST made a difference in ride feel. Even with my crank length and saddle height set the same, I just don't feel as stable on the longer ST. It's like my center of gravity is too high.

That's fascinating, because your center of gravity is the exact same. Maybe you just don't like how it looks.

[scottcw2]

That's fascinating, because your center of gravity is the exact same. Maybe you just don't like how it looks.

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.

[SPOKE]

bb height (or drop) is a huge factor in how a bike feels underneath you.....

[mhespenheide]

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.


Other people on this board disagree, but in my opinion BB drop is quite important. At one point I had two 'cross bikes that were otherwise quite similar; one with 68mm of drop and the other with 73mm of drop. I definitely enjoyed the ride of the bike with 73mm of drop more. It felt more planted, like I was part of the bike, while I felt like I was riding "on top of" the bike with 68mm of drop.

Like I say, plenty of people here think that 5mm can't make that much of a difference, but it seems important to me.

That said, 8cm of drop is a lot. Absolutely on the high end of the range for road bikes. Although I think Richard Sachs uses drops in that range, too...

[scottcw2]

It felt more planted, like I was part of the bike, while I felt like I was riding "on top of" the bike with 68mm of drop.

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.

[Blown Reek]

the Kvale has a BB drop of 8cm, the DeSalvo is 7cm. Maybe the higher BB makes the DeSalvo feel less stable.

bb height (or drop) is a huge factor in how a bike feels underneath you

Perhaps this is the discrepancy. If the bikes were apples-to-apples, I'd call shenanigans. You'll definitely feel the difference between two identical bikes with different bb drop.

[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.

[vqdriver]

If it doesn't fit, then I must quit

you should get a johnnie cochran frame

[Clean39T]

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.

Second that opinion. Plus pnuematic trail is a thing, right? So those 32c tires are going to contribute to a different feel underway as well.

FWIW, I like the way my Kirk rides with 28s much more than how it rides with 32s...

[Mark McM]

That's fascinating, because your center of gravity is the exact same. Maybe you just don't like how it looks.

Or maybe there are many more differences than just the seat tube length; but because the other differences aren't as plainly visible, all differences in feel have been ascribed to the most visible difference (seat tube length).

[Mark McM]

Perhaps this is the discrepancy. If the bikes were apples-to-apples, I'd call shenanigans. You'll definitely feel the difference between two identical bikes with different bb drop.

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

The bike with 23mm tires and 8cm BB drop will have a BB height close to 2cm lower than the bike with 32mm tires and 7cm BB drop. If that's enough to make you feel like you're going to fall over on the higher BB bike, then you'd never keep from falling to the the ground on a suspended MTB, which can have BB height 8cm or more higher than a road bike.

[pdonk]

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]

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]

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]

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]

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]

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]

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?

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]

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]

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.