# Gravel bikes and BB drop, opinions?



## robt57

Lots of CX bikes get used for gravel/adventure. Lots of non CX offerings these days. Lots of question as to BB height of some CX and best use etc.

I have Custom Steel with 8CM BB drop as an example. I happened on a Trek Tour/Adventure offering I noticed the BB is 8.5CM. Most I have ever seen on a 700C bike personally.

The 920 comes with 2.0 29er tires... I guess running something smaller with that BB drop. Might this be cause for deeper digging and 'what use' one may have in mind if the desire to ride on pavement is prevalent? Especially the longer the crank arms get, yes? Not to mention MTB shoes and pedals etc.

Oh, and disc and non disc offering as well.

I kind of like what Trek is doing here. Leaning so far from the road side of the equation VS what most seem to be doing? And certainly to the touring side if pave. Except some Salsa stuff perhaps.

Discuss?

920 Disc | 920 | Adventure | Road | Bikes


----------



## cs1

@Robt57 it does look like Trek is taking a page from the Salsa book. They are turning a MTB into a road bike like the Fargo. Whereas a CX bike more a road bike with MTB aspirations. This all strictly opinion of course.


----------



## bigbill

My Gunnar Crosshairs has a 7.5 bb drop. It's closer to a road bike than a classic cross bike. I commuted on for years in the PNW and now use it for a gravel bike. The lower bb means it's more stable and since I'm not going over barriers, it works for me. It's a do everything bike.


----------



## GOTA

Trek isn't looking at Salsa. They are looking at their own Domane. In the smaller to medium sizes the Domane has an 8.0 bb drop. Guitar Ted who is the gravel bike guru has always preached lower bb drop makes for better gravel riding. Stability on a loose surface is a lot more important than ability to go over obstacles which is why gravel bikes aren't CX bikes.

Unless you are racing the Trek 920 would be great for most applications. It's awesome commuter and would probably be pretty comfortable on the gravel.


----------



## cxwrench

Lots of bb drop for some added stability when loaded up and going slow? We've got one in the Marin shop if you are close enough to come check it out.


----------



## Rashadabd

If you look across lineups, Trek, Specialized, and Felt are big believers in lower bbs. They like the stability it provides even on their pure road lineup. Trek also tends to go with longer chainstays on race bikes than some of their competitors.


----------



## robt57

Rashadabd said:


> If you look across lineups, Trek, Specialized, and Felt are big believers in lower bbs. They like the stability it provides even on their pure road lineup. Trek also tends to go with longer chainstays on race bikes than some of their competitors.


I think a lot custom builders too. I have two Carl Strong bikes, BB drop is 75mm and 80mm. And my Portland made in the 90s Reynolds 753 RMA Custom is 80mm. I like low BBs myself for all the reasons mentioned. The RMA and the Road Strong have tight chain stays in the equation of things. But I kind of feel more in the bike that on top of it, in my minds eye or in reality ??


----------



## Rashadabd

robt57 said:


> I think a lot custom builders too. I have two Carl Strong bikes, BB drop is 75mm and 80mm. And my Portland made in the 90s Reynolds 753 RMA Custom is 80mm. I like low BBs myself for all the reasons mentioned. The RMA and the Road Strong have tight chain stays in the equation of things. But I kind of feel more in the bike that on top of it, in my minds eye or in reality ??


I like it too and I would probably be riding a Trek if all of their reasonably priced bikes (5 Series) didn't come with an H2 fit.


----------



## robt57

Let me add that IMO for an All Road setup that you might use both 40 Nanos and 27mm Paves like I am on my Strong. . . Point being how much higher the BB will be VS lower depending on a 25-7mm road tire VS a 40mm Nano should be considered.

I have to imagine @ 8.5CM on the Trek 920 that comes with 2.0 29er tires, putting 25-28mm road tires may be an exercise in pedal striking possibly. Especially with MTN double sided pedal VS an uber low profile road pedal system.


----------



## looigi

I kinda hate to bring this up, but a lower CG is not more stable for a two wheeled vehicle. Riding a bike or motorcycle is like balancing a pole in the palm of your hand. With the pole, you move your hand around to keep it under the CG. On a bike or motorcycle, you keep the contact patch under the center of gravity by steering left or right. The taller the pole, the higher the center of gravity, the easier it is to balance and the slower something falls over.


----------



## Lelandjt

looigi said:


> I kinda hate to bring this up, but a lower CG is not more stable for a two wheeled vehicle. Riding a bike or motorcycle is like balancing a pole in the palm of your hand. With the pole, you move your hand around to keep it under the CG. On a bike or motorcycle, you keep the contact patch under the center of gravity by steering left or right. The taller the pole, the higher the center of gravity, the easier it is to balance and the slower something falls over.


Irrelevant. Take a corner a few times on a 15 year old MTB with a sky high BB. Then try the corner on a modern MTB with a ground scraping BB. Lower BBs handle better. The MTB world realized a few years ago that lower is always better until clearance becomes unacceptable. Different riders have different ideas about what is acceptable. Priorities.

With road/gravel/CX tires varying over a half inch in height that has to be taken into account as well as crank arm length and if you want to be able to pedal when leaned over (crit racing). Think about all that, then get the lowest bike you think you can get away with.


----------



## aclinjury

looigi said:


> I kinda hate to bring this up, but a lower CG is not more stable for a two wheeled vehicle. Riding a bike or motorcycle is like balancing a pole in the palm of your hand. With the pole, you move your hand around to keep it under the CG. On a bike or motorcycle, you keep the contact patch under the center of gravity by steering left or right. The taller the pole, the higher the center of gravity, the easier it is to balance and the slower something falls over.


firstly,
a lower center of gravity makes an object more stable, not less stable.

schoolphysics ::Welcome::

Secondly,
the reason why the taller pole is easier to actively balance compared to a shorter pole is because the taller pole has a lower angular speed. But the shorter pole is actually more stable if left stood alone (I'm assuming both poles have the same base diameter, just differ in length).

Balancing sticks ? choose a longer stick ? Dot Physics

about motorcycles. Lower center of gravity means more stability. That is why cruisers are low and stable compared to sports bikes. But for sports bikes, you do not necessarily want too much (standing) stability because this means that it will be harder to make it tip into corner. An "agile" bike usually means a twitchy bike with less stability (in a straight line). There has to be a fine balance between too much stability and too little stability.


----------



## kiwisimon

robt57 said:


> I think a lot custom builders too. I have two Carl Strong bikes, BB drop is 75mm and 80mm. And my Portland made in the 90s Reynolds 753 RMA Custom is 80mm. I like low BBs myself for all the reasons mentioned. The RMA and the Road Strong have tight chain stays in the equation of things. But I kind of feel more in the bike that on top of it, in my minds eye or in reality ??


I actually asked Carl to put me *in* the bike not *on* it, and he did just that. Higher HT and an 80mm drop on my gravel road bike works perfectly, it feels low and on the sketchier stuff you have to remember pedal strike but handling wise and cornering it is dialed.


----------



## robt57

Let's see your Strong, have you seen mine in threads?


----------



## kiwisimon

robt57 said:


> Let's see your Strong, have you seen mine in threads?


Yeah, both yours and your Dad's. Nice bikes. This is mine in one of the configurations. The cabling has now dropped below the BB now, much cleaner look but not as clean practically. I will throw up the SS version as well.


----------



## robt57

Just mine, my Dad is.. well, has long left the planet. What year is the red road made? I recognize the decals pretty early 90s?


----------



## Enoch562

I recently dipped my toe in the Gravel Bike water. I bought a Raleigh Willard 2. It has a 71 head and 73 seat angle with a 75mm bb drop. I'm having a blast on it. Super stable on gravel and equally fun on the road. It may not be that bike for crit racing but it nice to ride a road bike that doesn't change lanes everytime I raise my eyebrow.

I'm betting 80 mm drop is pretty low, most all the production gravel bikes I looked at were @ 70.


----------

