BB height. Isn't a +70mm bb stock frame supposed to feel like a +146mm mod? 26 inch wheels right?

[Mr_Orange]

Do stock bikes feel like they have a very high bb?

I'm mainly concerned with lateral (side to side) stability/balance. Tracking standing. Riding through narrow sections.

A mod bike with a bb of +70mm is really placing you 70mm + 10 inches (from ground to axle center of a 20" wheel) off the ground right?

But a stock bike frame with +70mm bb would be 70mm + 13 inches (from ground to axle center of a 26" wheel). Like this frame: http://www.tartybikes.co.uk/26_inch_frames/b1k3_eklipse/c14p12701.html

That's an additional 3 inches right?

So isn't that supposed feel like riding a mod with +146mm bb?

Are stock's just way harder to balance side to side than mod bikes?

[monkeyseemonkeydo]

Nope. You're physically higher but it makes very little difference to basic balance etc. Your feet might be like a mod with a +146mm BB but remember the height of the bars. A mod with a +146mm bb would need to have a 250mm x 40 degree stem or whatever to make it possible to ride (which would make it fine to balance- though still horrible to ride!).

[Mr_Orange]

So you're saying as long as your bars/stem is in an ideal position, that'll make all the difference in balance, despite being physically higher up?

What if you really exaggerate this idea and made a bike with 60 inch wheels. Your saying as long as your bar/stem position is ideal, the lateral stability is really not going to be affected by you bb being that high up?

Are you really not loosing any lateral stability by being higher up in terms of actual physics, or are you just saying that this 3 inch difference isn't so hard to get use to as long as your bars are in your comfortable ideal position; even though there actually is a slight loss in lateral stability.

Edited December 16, 2015 by Mr_Orange

[craigjames]

Yes you're raising the centre of gravity when the bike is on two wheels, so yes it will be slightly more unstable. As Dave has said bar/stem set up makes a large difference to how much of a difference a high BB makes.

But with respect to your comment " So isn't that supposed to feel like riding a mod with +146mm bb"... No, there are many other geometry factors that affect how the bike rides and feels, so it's not as simple as what you've asked.

[Mr_Orange]

I ride bmx bikes and the bb height range is from 11.5 inches to 11.8 inches off the ground, and people even have particular preferences between such a small spectrum. 

When looking at even just mod frames, it goes from +50 all the way to +90mm. And when you factor in the extra height of 24" and 26" wheels, it seemed like trial riders are on a huge range of bb heights. 

I was originally looking at 26" dirt jump bike frames like this http://octane-one.com/void/, which has a bb rise of just 3mm. I assumed the reason the bb rise was so low was to take into account the extra wheel height, lowering you to a more tolerable elevation closer to where the bb's on bmx bikes or 24" bikes are. 

Then when i looked into 26" trial frames with bb's ranging from +10 to +70mm, it seemed like that all went out the window. 

 

[peter_t]

Im not sure why you are comparing trials to bmx and dirt jump frames. They share almost nothing in common when it comes to fuction or desirable features.

In trials the height of the bottom bracket from the ground is not relevant. The height in relation to the wheel hubs will have the same effect on the way it handles regardless of wheel size.

[CC12345678910]

I might not word this correctly, but I think you are looking at this a bit skewed. In my mind stating/using how high the BB axle center is from the floor is irrelevant/not comparable to the default measurement I am used to. Trials measures the distance from an imaginary line strung across the wheel bolt/axle centers, upwards (if it goes down the frame ain't gonna be any good for trials realistically) to the center of the BB bolt/axle.

20 hours ago, Mr_Orange said:

I'm mainly concerned with lateral (side to side) stability/balance. Tracking standing. Riding through narrow sections.

This is what I mean by your point of reference being skewed, you're focusing on two wheel riding, not hopping about on the back wheel like a pogo stick.

So isn't that supposed feel like riding a mod with +146mm bb?

No. For example. A short stock with the right bar and stem rides like a jumbo size mod, 24in trial, i.e. 24in wheel, no seat, NOT street frames like inspired, blend the best of big wheel capability with the agility of a mod - you don't get on a sorted one and go "Sh*t! 24in wheels! I can't ride that cos it's sooo much taller", you go actually tend to go "F**K ME this thing hops like a f***ing flea!"

 

Are stock's just way harder to balance side to side than mod bikes?

And no again, completely irrelevant. You've either got the basic skills down or you don't, the size of bike ain't gonna make a sh**e of difference.

 

4 hours ago, Mr_Orange said:

 was originally looking at 26" dirt jump bike frames like this http://octane-one.com/void/, which has a bb rise of just 3mm. I assumed the reason the bb rise was so low was to take into account the extra wheel height, lowering you to a more tolerable elevation closer to where the bb's on bmx bikes or 24" bikes are.  

Nope! That frame is designed for high speed two wheel and mid air based stability, again irrelevant to trials and a completely skewed idea.  

Basically in simplistic practical terms think of the stated BB height measurement as this (beware that head angle has a great effect on this analogy, as does stem angle, bar angle and even crank arm length);

A low BB frame will have a balance point on the back wheel similar to a manualing bmx. A high BB trial frame will have a very upright balance point on the back wheel with the front wheel high in the air. The former will spin, manual and bunnyhop and the latter simply won't, but will sit up and beg on the back wheel, gap and sidehop better/easier than a low BB bike ever will.  

Is that any clearer??

Edited December 16, 2015 by CC12345678910

[FamilyBiker]

just realize that as long theres bb height being measured as "above the line your wheelbase is drawn with" theres always the "relative to other points" thing

what you feel is changes in relation of geometry values to each other and the contact points you have to your bike.(not just points inyour rider/bike system relative to the ground or the ceiling )

that being said,like other people said,the real difference in trials will show once you get on the rear wheel,which is basicallyy the stance modern pure trials frames are designed for.

Edited December 17, 2015 by FamilyBiker

[Mr_Orange]

I only have vague glimpses into the trials world from just browsing videos online so please excuse my naivete.

I definitely get the whole 'trials is more about being on the back wheel' thing though. And yes i get that BB rise refers to height above the imaginary line across the two wheel axles.

Isn't there stuff though where guys are riding across really thin hand rails or thin train tracks. Doing 180s and landing back on the same thin rail. That's why i thought 2 wheel balance might've been equally important.

Also, there's guys doing pretty much street bmx tricks on those 26" octane frames. It's not just a dirt jumping thing.

So what's the deal with those Inspired frames. I guess it would be nice to have something where i can do street bmx type tricks along with trials stuff too. Is that what I'm looking for? Are there other companies like Inspired?

 

[peter_t]

Riding skinny lines etc on two wheels isn't easy but it is easy compared to hopping around on the rear wheel. This is why frames have the have high BBs as it helps with the hard stuff.

street bikes such as insprired are a compromise between trials and bmx frames. It will do both but wont be as good as a bmx or a dedicated trials bike. When you see videos of danny mac etc. it shows how tallented they are as a rider, not how easy the frame makes it.

If you had a street style bike im sure you would be able to manual and bunnyhop pretty well as you probably do with your bmx background but you may struggle with the more trials focused moves such as pedal kicks.

 

Personly im not in to bmx type stuff so have a full on trials bike. It is hopeless for manuals etc but that is not what its for. I was mucking about with a mate yesterday who has a jump bike and it just felt so wrong. Problem was i was trying to ride it like a trials bike. For a laugh I tried to pedal kick and hop about and i couldn't do it for shit.

Trials riding is hard enough so a nice frame designed to be user freindly is all too welcome

[Mr_Orange]

Got it. you, when reading through threads, it seemed like most people say the higher BB is easier for trials stuff, but there were also a few people defending the lower bb too.

Is there such a thing as short chainstay + very low bb? How that would feel like?

I ran across this: http://www.pinkbike.com/news/Bike-Check-Stout-Sigma-136-2012.html. It's a 26" bike with 13.6 chainstays. They did this by cutting a groove into the BB (you can see in the pics).

Say you took that same style frame construction (with the BB cutout thing) and did a 24" wheel version. This means you can have a 24" bike with 12.6" chainstays (there are bmx frames this short and commonly used too). However, unlike a bmx frame which has BB rise, you give this a 20mm BB drop.

So 24" tires, with 12.6" chainstays, and a 20mm BB drop.

I wonder if the BB drop will give you the same extra leverage bunnyhop feel of a longer chainstay bike, while short chainstay gives you the benefit of a much shorter wheel base for spins.

 

 

[AndyT]

No idea about mods.

 

my +70?80? 26" Gu cannot handle the balance lines that my +20? Hex can with ease... Both wheels on ground, Rollin forward- think trying to balance while riding a rail. The hex excels at this, the gu just wants to gap 3m past the rail and is very awkward while balancing on both wheels.