DVC45

How important are Bottom Bracket height on Touring bikes? How much does BB height affect handling when fully loaded?

The reason I asked, is because I am thinking of building a tourer, based on vintage MTB. Being what they are (MTB's), I was wondering if the high BB clearance on this type of bike is suitable for touring.

bradtx

DVC45, Bottom line is very little, if any effect to the handling. The older rigid mountain bikes make excellent touring bikes with the exception that large to very large rear panniers could crowd the rider's heels as the chain stays aren't often as long as those on an expedition level tourer. There are work-arounds for this.

Brad

tcs

You can make anything work, but purpose built DF touring bikes over the last 100 years have tended to relatively low bottom bracket heights vis-a-vis their tire size.

Remember, a vintage mountain bike frame was most likely nominally designed for 26x2.25" (559x55~57mm) tires. If you fit 26x1.375" (559x35mm) tires - which would still be wide-ish as road touring tires go - the bottom bracket height would drop almost an inch (~20mm).

DVC45

Alright..the hunt for a suitable candidate begins...


Thanks!

fietsbob

The sound of Dragging the toe clips Upside down as you start off ,
until you flip them over and put your foot in, is avoided, If the BB is a bit Higher.

My Bike Friday Pocket Llama took a bit of getting used to as the stopping seated , with its higher BB,
putting a foot out tippy toed , no longer worked, so I had to learn to slide off the seat,

If you always start off pushing down the right pedal, but dismount your left foot for the stop from that pedal.

the right one will be at the bottom . so maybe a bit push off to get going will be a learned adaptation..

seeker333

The difference in BB height between a tourer at 275mm and a mtb at 295mm won't be felt much in handling of the bike in a loaded touring scenario. Unlike road or mountain bikes, touring bikes generally lumber along without much leaning into curves or sudden directional change.

BB height does determine how easy it is to hold the bike with one leg down at a stop, which is critical when the bike happens to be loaded with gear. For a given saddle height, the higher the BB, the higher the saddle, and the further your leg/foot has to reach to plant on the ground. A high BB means you may get only a toe onto the ground, especially if it's an uneven surface. This may necessitate leaving the saddle at every stop, both feet grounded to keep the bike standing.

Touring frames have a very low BB height, partly for a lower center of gravity to improve load control, partly so you can get a foot down at stops easier, and partly because there's no reason for it to be any higher. Road frames have a higher BB than touring frames to give them more pedal clearance when the bike is leaned into curves. MTB frames have the highest BB, to avoid pedal strike on rocky singletrack.

djb

another voice heard of not feeling any diff in handling with my old mtn bike with 25-30lbs on it due to bb height.

Booger1

I like the higher BB for my touring bike.....I can get on and off of curbs easier without bashing the big ring.

I found no noticable difference in handling between BB heights on my 2 touring bikes.1 old school type 27" tourer,the other a newer 26" disk mountain frame.

There's an 1 1/2" difference between bikes.........I like both of them.I'd ride either one anywhere.

Doug64

I may have not understood the comment, but for most of us the saddle height would be way too low if I could get even a toe on the ground from the saddle. Stand over heigght is stand over height regardles of bottom bracket height.

Contrary to conventional wisdom, my cyclocross bike, Bianchi Volpe, which is touted as having a higher bottom bracket height is within a couple of mm's of the bottom bracket height of my LHT, Cannondale T800 and a Cannondale T2 (all 58 cm frames, except T800). The T2, T800(50 cm frame) and LHT bottom bracket heights are are also amost the same as my road bikes. My wife's road bike, a small frame, is actually a few mm's lower than all of them. My wife's custom frame is the only low one at 250 mm's.

I don't have a mtn bike to measure, but almost all the bikes I measured were +/- a couple mm's of 275 mm from the ground to the center of the BB spindle. The 26" wheels also tend to put the bike closer to the ground.

djb

This got me curious, I went and measured my mtn bike, its at 290 with 26x1.5 Schwalbe.
My Tricross, the cross-bike like Dougs Volpe, or should I say mine is a faux cross bike, its never seen tires other than 28 slicks, its bb is at 275ish

the diff btwn the mtn bike and the Tricross is most likely a certain amount due to the 1.5 tires being taller than the 28 Gatorskins.

My wifes tiny XS Giant Avail road bike is 270ish.

I was too lazy to take a kids bike, and old tires off the hooks to get to my hanging old touring bike, so dont know what it is.

Interesting, not a big difference between them, even though the mtn bike is a somewhat large size.

seeker333

I can get toes on the ground with 700x35s, and I have to lean plus shift on saddle to reach the ground with 700x45s. I would guess the majority of bicyclists can reach the ground better than you and I because their saddle is too low.

I didn't comment about stand over height in #6. You are correct in that it obviously has no direct relationship to BB height or saddle height.

I'll try to clarify what I wrote earlier: for a given saddle height X (as measured from center of BB to top of saddle along seat tube center line), and a given BB height Y (as measured on flat horizontal surface, from ground to center of BB), the distance from saddle top to the ground is X+Y. If you hop on a second bike with a 5% higher BB and everything else identical, then the distance from saddle to ground is 1.05X+Y, which is obviously further to reach with the foot. In other words, a higher BB means it's harder to reach the ground.

If the OP builds a touring bike from a typical mtb frame, he will be less likely to reach the ground from a seated position than if he had built a typical touring frame with the same components and same saddle height.

bradtx

djb, More telling would be to measure BB drop, what the frame is designed with to achieve a desired BB height with a spec. tire. Run a string from the fork's drop out to the rear drop out on the same side keeping the fork straight ahead. Measure from the string to the center of the BB.

Brad

Doug64

David, I have to confess. Mine has never seen a wider tire than 28 mm slick either. Well, except when I brought it home from the LBS

seeker333, Thanks for the clarification. I see your point.

seeker333

Yep, if you don't account for tire height differences then there's not much point in measuring BB height.

Bekologist

Saddle height from the ground is directly related to BB and crank length, not the standover.

And a lower BB (drop) makes a bike handle differently, i can tell the difference in handling between a cross and a touring bike, and how they descend. a bike with a lower BB takes to downhills at speed better, along with the additional wheelbase a touring bike provides, and they are quite stable frames at speed, probably one of the most stable of the prototypical diamond frame angles.

djb

Doug, mine got the tires switched out AT the LBS when I bought it, so other than the test ride I did on it with the stock 32s I guess, its always had 28s. I really like them for on road stuff, and just have never gone anywhere with enough dirt riding to warrant getting a pair of wider tires.
I always say thats one of the advantages of a cross bike, to be able to put wider stuff on, but my riding just doesnt include enough of it to be worth it to buy a pair. Im comfortable on 28s on dirt roads that we see around here, ie not lots of loose stuff, so its not an issue.

Brad, to be completely honest, Im too lazy to do that. What I do take out of this discussion of bb height (or drop that you refer to) is that for me it doesnt really change the feel of riding, other than going up over curbs and such, which I do find handy on the mtn bike if I go over really high ones as one runs into once in a while in a city.

cheers

ps, Bek , it would appear then that both my Tricross and Dougs Volpe dont really have high bb, as they are pretty much the same as a LHT or a Cannondale Twhatever.
I have to say the diff between my two bikes, despite 15mm of bb height diff, really isnt that diff. I figure its hard to compare when I take the same corners fast with both, simply because of the diff bars, so my weight distribution is different. They certainly feel diff but I cant say that one really thhhat different. In slower turns, 20, 30, 40k the mtn bike is nice and nimble, quick steering and really transitions nice and fast from side to side.
So for me, its certainly not like I feel one is diff, especially with the bar differences and my body stance difference coming into play.

robow

I go along with the camp that if the height is within reason, it won't matter very much. Interestingly Trek's touring bike's BB is 8mm higher than their similar sized cross bike. So I guess they don't feel it needs to be excessively low to work well.

seeker333

Check again! The BB drop is greater, but the BB height is lower.

Touring bike bb drop = 70-75 mm

Road bike bb drop = 68-72 mm

Cyclocross bike bb drop = 62-64 mm

Mountain bike bb drop = 53-53 mm

Bekologist

yes, and until that sinks in, the concept of stability correlating to how far a BB is dropped below the plane of the axis of the wheels isn't going to be understood.

robow

You're correct, I was going by Trek's "g" measurement illustration which appears to correlate with not drop but total bottom bracket height. Even so, it shows inter lap with the road bike sizing so no large difference there, I guess is a better point.

bradtx

I forgot to make a point here. Mountain bike's top tubes lengthened over time, if you wish to use drop bars, find a late '80s or early/mid '90s rigid bike where the top tube length is more or less equal to the seat tube's length. This era of mountain bike also generally had a level top tube.

Brad

fietsbob

A load in lowrider racks on the fork helps a Lot.


and Bending the pedal and crank arm, if it strikes the ground in a corner
or a high spot , has a greater possibility with a Lower BB..

seeker333

That is a poor illustration.