yumseyo

On a Tern folder, would an extra 5mm make riding unsafe from having too long of a crankarm? I could find more used 175mm cranksets out there than 170mm

fietsbob

DO You stop pedaling when you round a corner? keeping Inside pedal Up?

IDK what the Tern BB height is? Do YOU? do you know how much 5mm is?

P7HVN

It's only 1/5th of an inch, so shouldn't be a problem for you...

smallwheeler

ugh.

i would advise everyone to "learn to metric"

fietsbob

It's a southern thing.

fourknees

Obviously not a direct conversion, but it is just shy of 1/5th of an inch. Not a usually stated measurement, but close enough. :-)

smallwheeler

tell a carpenter you want something cut to 37 1/5" and take note of his facial expression.

smallwheeler

true story:

my first job out of uni was working as a "shop boy" at a well-known theatrical production house. we had a very big project with a very tight schedule. the sets were designed by a french designer. we received the drawings.. scaled in metric. the carpenters flipped their lids and the entire project ground to a screeching halt. the owner of the production company called the designer and (no answer- middle of the night) and left an angry message telling him he would have to convert all of his work to english standard. immediately, i dashed to the local hardware store and bought every metric tape measure they had (and ordered 5 more). when i returned to the shop, the owner was preparing to send everyone home. i passed around the tapes and work begrudgingly resumed. i thought i was a friggin hero. later, the owner took me aside and said, "don't ever do that again. it's not how we do things here."

yumseyo

well, I guess that was my 1/5 of an inch story. Sorry, I got everyone so excited..

fourknees

Awesome.

fietsbob

one Mars Lander did a hard-crash landing because measuring were Miles in one camp and KM in the other ..

Houston , We Have a Problem.

P7HVN

Yeah, wow. I guess I haven't been here long enough to realize what gets the members riled up. Maybe I should have said it's only .19685 inches...
I've been on board the metric train for quite some time, but most people who learn it still convert over to inches for practical comprehension. Sort of like ESL users translating things in their head, back to their native language.

If you really want to have fun, or get so frustrated your head wants to explode, go into an auto shop here and start talking tire sizes(P245/50-16, etc.); you wouldn't believe how many people who install them for a living don't really understand the sizing...

On a related note; the shorter cranks(175mm to 152mm) came in for my mini-velo/MTB. No more scrapping the pedals.

lastostrogoth

My Orbea Orca came with 172.5 MM cranks. I am 5'8" with a 29" inseam. I have always ridden 170s. I didn't think that he tiny size difference would matter, but it was much harder to make the transition. After 100 miles of riding I bought a set of 170s and installed them. I am much happier. Another minimal difference was the handlebars. Orbea came with 142. I replaced them with 140s. Again it felt amazingly different. If you are used to riding 170s, stay with them. The length of the crank makes a very big difference in the circumference of your spin. If you are 6' or over 172.5 is fine, though I have friends who are 6' who prefer 170s.
Fit on a bicycle is often the matter of a mm or two. Seat post height can be critical with a MM or more making a tremendous difference.

BassNotBass

Which has blown my mind for decades. It takes more brain power to run a fry-o-lator than to remember the significance of those three numbers.

P7HVN

Certainly true on something like your Orbea, where every component is preferably fitted for optimum performance & efficiency. But we're talking about an around-town runabout, folding bike(one size fits sub-5ft to just over 6ft) and whether an extra 5mm will cause pedal scrape.... Which in this case, shouldn't.
On your 2.5mm difference listed above, you could easily cause that much variance in different shoe sole thickness...

jmm

This concept used to bother me, so I did the maths. It appears that thicker soles decrease the maximum leg extension at the bottom, while increasing leg lift at the top, resulting in the same total stroke overall (or the difference between the extremes). Therefore, the only thing that sole thickness would really affect would be seat height, and I've never noticed enough difference between my normal summer shoes/boots to have to pull over for a readjust. However, when riding my Salsa Mukluk in the snow with thick-soled "mukluks" on, there's no question that my knees are happier with the seat at least 1/2" higher than it is during the summer, or on any of my other bikes year-round.

John

northwood

I have a 175 on my rumble, 170 on the new 420 and 180's on the others. I notice a difference. Granted I am 6'3". I am already looking for 175 or 180's for the 420.

P7HVN

Quite true; a 1/4" sole or a 1" sole is still going to make the same rotation around the crank. However, on the top of the stroke you'd be adding length to the crank and on the bottom you'd be subtracting, which might get a little funky, depending how much different your shoes are, but the distance traveled is the same. That wasn't the intent of my earlier post tho'; more to the point that the 2.5mm(or 5mm in OP) difference is really minute, given the original question concerning a folding bike, rather than a custom-fit road bike...
If I was a math nut, we could get real geeky with all kinds of spin numbers stuff. Throw in some biopace sprockets and I might start getting a headache.
Interesting stuff, for a folding bike thread tho'.
Oddly enough(or not...) I did notice today, riding around on my new 152's, that my calves felt a little more used. No felt difference in upper leg muscles....

lastostrogoth

I stand corrected on most of your points. However, one that I do respectfully disagree with: Wearing thicker soled shoes would not have the same effect as lengthening the crank arm. Quite the opposite. The thicker soled shoes would decrease the distance between the foot and the spindle likely causing the rider to have to raise the seat post.
I spent a good deal of time studying the problem of crank arm length. Mountain bikes almost inevitably come with 175MM cranks. I have had two mountain bikes over the last 25 years. The first was a Specialized StumpJumper which I rode for nearly ten years. I lived in Seattle most of those years and used it mostly for winter training on the roads around Seattle. I would do 40 miles loops through the city on it, and never minded the longer cranks. Shortly after I moved out here I bought a Specialized RockHopper Comp FS frame and built it up with Deore XT components, also 175 MM cranks. Due to some medical problems I was unable to ride for the last two years. I returned to riding last April and have ridden 2100 miles since. I started doing shorter rides on my mountain bike and in nicer weather on my Erickson. Rebuilding after a long lay off is not easy. Remembering the advice of my old coach, I spent those early days spinning in low gears. It was almost two months before I used my large chain rings on either bike. By June I was riding 25 to 30 mile loops and began using my large chain ring on the Erickson which is equipped with old Campy C-Record, retrofriction shifters and a 7 speed block. When on wet days I rode the RockHopper, I noticed that it was distinctly harder to maintain any kind of spin, and that even short rides left me far more tired. Since I only rode the RockHopper infrequently during the summer it didn't much matter. However, the weather began to crap out in September and my experience with the Orbea had made me aware of marked difference in comfort when using shorter cranks. I, therefore, purchased a set of used Shimano Deore cranks in 170MM and installed them on the mountain bike. I had to make a couple other mods to the system, new bottom bracket since the old XT cranks needed 122.5MM spindle and the new ones used 113MM spindle, and also a different front derailleur with a longer throw. I have since done a series of rides with the RockHopper in the 20 to 25 mile range. I have found it far easier and far less exhausting to ride. Maintaining a 60 to 70 RPM spin is almost no work at all. I have not noted any added difficulty when climbing hills with the shorter cranks. The claimed mechanical advantage of longer crank arms may work for taller, longer legged riders, but it is no advantage to a rider my size.
This may or may not be of use to others in terms of selecting crank arm length. I think much of this is very individual. When I was younger, I am now 68, I did not seem to have any problem with the longer arms on my mountain bike. However, there is a very definite difference now, and I am much happier with the 170MM cranks than with the 175s, just as I was on the Orbea with the 170s over the 172.5s.

P7HVN

Yes, this is true. Didn't mean to imply otherwise, on my earlier post. Was only stating that differences of a few mm's could be influenced as much by sole thickness. Thicker shoes will decrease the distance from the spindle on the downstroke, but increase that distant at the top of the stroke... Maybe easier to see what I'm saying, than read it. Pardon my crappy Windows Paint skills. In this illustration, A & B are the crank arms, in the up & down positions. C & D represent a shoe sole thickness of 25mm. In the down position, you'd have an effective arm length of 150mm, but at the top position it would be 200mm.... I'd imagine the competitive road racing teams would have a staggering amount of data on the effects of changing these values, along with everything else on the bikes...

By now, yumseyo is probably thinking 'what the heck did I get myself into..'

lastostrogoth

Excellent points. Not bad artwork either! :-) Ultimately it comes down to what works for you as an individual. I know that Lemond used 175s on his TT bike during the Tour, and he isn't much taller than I am.
Good conversation, respectful and appropriate, unlike many on the forums. Just got back from a 25 mile ride in temperatures below 25º. It was really nice having carbon fiber handlebars as opposed to aluminum.

P7HVN

And here I was, disappointed that the sun didn't materialize today and "had to" ride around in foggy, 58 degree weather... Sometimes the warm winters almost make up for the lack of culture & hills/mountains here.....

yumseyo

it is aw some that there are such hobbyist as you guys around !! thanks for such a great education..