Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

Pedals, French thread?

Notices
Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

Pedals, French thread?

Old 02-04-18, 09:17 AM
  #1  
Senior Member
Thread Starter
 
Join Date: Mar 2015
Location: Connecticut
Posts: 2,000
Mentioned: 28 Post(s)
Tagged: 0 Thread(s)
Quoted: 457 Post(s)
Liked 42 Times in 33 Posts
Pedals, French thread?

Is there a way to figure out if a set of pedal is French thread without French threaded crank to test them on? The pedals are Lyotard, 1970s vintage.
Attached Images
File Type: jpg
20180203_234454_resized.jpg (330.1 KB, 236 views)
vintagerando is offline  
Old 02-04-18, 09:18 AM
  #2  
Senior Member
Thread Starter
 
Join Date: Mar 2015
Location: Connecticut
Posts: 2,000
Mentioned: 28 Post(s)
Tagged: 0 Thread(s)
Quoted: 457 Post(s)
Liked 42 Times in 33 Posts
extra photo
Attached Images
File Type: jpg
20180203_234547_resized.jpg (365.7 KB, 233 views)
vintagerando is offline  
Old 02-04-18, 09:36 AM
  #3  
sch
Senior Member
 
Join Date: May 2003
Location: Mountain Brook. AL
Posts: 4,001
Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 302 Post(s)
Likes: 0
Liked 135 Times in 103 Posts
Certainly not from pix, my personal stash of Lyotard Berthets in Fr and Eng threads have indistinguishable threading
as the 20 TPI of the English and the 1.25M threading is identical for all practical purposes. If you measure the
diameters the English threads will be ~0.03-.05" larger than the Fr threads in actual measure,

Fr pedal threads are 14x1.25M, English nominal 9/16x16TPI. 14mm is ~0.55" where 9/16" = 0.5625" so you
would think the difference to be smaller, but manufacturing tolerances for threading result in a larger difference.

Easiest way IME would be to put the pedals on a junker English crank set and see if they are sloppy fit or tight
when threaded in just short of fully seated, say 1/2-1 turn short. Compare with a 9/16 pedal or several.

Good way to ruin an English threaded crank is to ride it with Fr pedals screwed in. I KNOW this. Fr threaded
pedals mount easily and non-destructively into English threaded cranks, it is only under pedaling stress that
the wobble starts eating the threads in the cranks, which become severely damaged in a few miles.

A few years ago I experimented with lathe turning a new set of axles out of 4140 for my remaining set of
Fr Lyotards, one of which had a bent axle. Experiment was a success, not particularly hard to do, make a
set of 9/16x20 axles for the formerly 14x1.25M ones, hence my interest in the actual diameters needed.

Last edited by sch; 02-04-18 at 09:50 AM.
sch is offline  
Old 02-04-18, 09:39 AM
  #4  
Mechanic/Tourist
 
Join Date: Apr 2007
Location: Syracuse, NY
Posts: 7,522

Bikes: 2008 Novara Randonee - love it. Previous bikes:Motobecane Mirage, 1972 Moto Grand Jubilee (my fave), Jackson Rake 16, 1983 C'dale ST500.

Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 486 Post(s)
Liked 11 Times in 11 Posts
Look to see if the end of the threaded portion is stamped with a D or G (initials of French words for right and left). If present, definitely French, but still possibly French if not there.
cny-bikeman is offline  
Old 02-04-18, 09:46 AM
  #5  
Senior Member
Thread Starter
 
Join Date: Mar 2015
Location: Connecticut
Posts: 2,000
Mentioned: 28 Post(s)
Tagged: 0 Thread(s)
Quoted: 457 Post(s)
Liked 42 Times in 33 Posts
Originally Posted by cny-bikeman
Look to see if the end of the threaded portion is stamped with a D or G (initials of French words for right and left). If present, definitely French, but still possibly French if not there.
Thanks for response.
vintagerando is offline  
Old 02-04-18, 11:02 AM
  #6  
Banned
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 43,598

Bikes: 8

Mentioned: 197 Post(s)
Tagged: 0 Thread(s)
Quoted: 7607 Post(s)
Liked 1,352 Times in 859 Posts
I have the same pedals in 9/16" by 20tpi .. Measure anything yet?
fietsbob is offline  
Old 02-04-18, 11:39 AM
  #7  
Senior Member
 
Troul's Avatar
 
Join Date: Oct 2013
Location: Mich
Posts: 7,192

Bikes: RSO E-tire dropper fixie brifter

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Liked 2,872 Times in 1,857 Posts
what are the case nuts stating for grade & what are there pitch? Wouldnt make sense to be compiled of hybrid machinery. Either all or nothing is my thinkings.
__________________
-Oh Hey!
Troul is offline  
Old 02-04-18, 11:55 AM
  #8  
sch
Senior Member
 
Join Date: May 2003
Location: Mountain Brook. AL
Posts: 4,001
Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 302 Post(s)
Likes: 0
Liked 135 Times in 103 Posts
Amended my first post to actual measurements. Went and dug out the damaged Fr spindles and the
remaining 9/16" Berthets I still have. First, the 9/16 pedals do have R and L stamped on the spindle
wrench flats. The Fr spindles are blank. IIRC the Berthet pedals now sold off were variably marked but I
don't remember any of the Fr threaded ones having a mark.

Now: actual real measurements: Fr: 0.542 and 0.539" diameter threads
Eng: 0.550 and 0.554" diameter threads

My new experimental spindles I made 0.559/0.560" in size. So measuring might help, depending on
unknown variances over the decades in Fr manufacturing tolerances.

Finally, IME putting Fr threaded pedals into a 9/16 aluminum crank and riding will rapidly chew up the
threads in the crank, basically destroying it. I did so back in the '90s. If the threads in the crank were
steel, it might work at least for a time but would be risking the pedals and/or the crank threads.

Last edited by sch; 02-04-18 at 12:00 PM.
sch is offline  
Old 02-04-18, 01:11 PM
  #9  
Old fart
 
JohnDThompson's Avatar
 
Join Date: Nov 2004
Location: Appleton WI
Posts: 24,862

Bikes: Several, mostly not name brands.

Mentioned: 153 Post(s)
Tagged: 0 Thread(s)
Quoted: 3544 Post(s)
Liked 3,283 Times in 1,878 Posts
The "S" and "G" markings are a good indication of metric pedal threads. The definitive proof would be to use a thread gauge. They aren't expensive, and can be useful in other situations as well.

JohnDThompson is online now  
Old 02-04-18, 01:49 PM
  #10  
Friendship is Magic
 
3alarmer's Avatar
 
Join Date: Nov 2010
Location: Sacramento, CA
Posts: 22,780

Bikes: old ones

Mentioned: 304 Post(s)
Tagged: 0 Thread(s)
Quoted: 26071 Post(s)
Liked 9,987 Times in 6,937 Posts
.
...if you don't want to buy a thread gauge (they're cheap, BTW), you can use the threaded end a pedal spindle of known quantity as a thread gauge.
It helps a lot in the exercise that there are only two possibilities, so either your known quantity spindle threads match up or they don't.
3alarmer is offline  
Old 02-04-18, 01:55 PM
  #11  
Senior Member
 
Join Date: Jul 2009
Posts: 790
Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 384 Post(s)
Likes: 0
Liked 6 Times in 6 Posts
Originally Posted by JohnDThompson
The definitive proof would be to use a thread gauge. They aren't expensive, and can be useful in other situations as well.
Seconded. A measurement is worth a thousand internet opinions.

Get one each of metric and TPI. (If you really want to be geeky, you can get a Whitworth one so you can measure Italian threads with the correct gauge....) And get a caliper while you're at it. I personally prefer a vernier because of durability, but some new digital ones can give you the nearest inch fraction as well as inch and metric decimal.

Absent a thread gauge, you can lay the unknown thread on a known one. Many are marked, but it's almost guaranteed that any pedal made since about 1990 will be ISO thread (which differs only from BSC in thread form.) A French pedal thread will "roll" a little in a 20tpi.
Ghrumpy is offline  
Old 02-04-18, 02:01 PM
  #12  
Senior Member
Thread Starter
 
Join Date: Mar 2015
Location: Connecticut
Posts: 2,000
Mentioned: 28 Post(s)
Tagged: 0 Thread(s)
Quoted: 457 Post(s)
Liked 42 Times in 33 Posts
Originally Posted by Ghrumpy
A French pedal thread will "roll" a little in a 20tpi.
This seems important, but I am not sure what it means.
vintagerando is offline  
Old 02-04-18, 02:10 PM
  #13  
Senior Member
 
Join Date: Jul 2009
Posts: 790
Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 384 Post(s)
Likes: 0
Liked 6 Times in 6 Posts
Originally Posted by vintagerando
This seems important, but I am not sure what it means.
Identical pitches will lock together, with no daylight between them. Pitches that are really close but not identical won't mesh perfectly, and the finer one will sort of roll on top of the coarser one. (I don't mean roll around, but back and forth, if that makes sense.)

Once you see it happen, you'll get it.

If you have a Campagnolo 26tpi axle and a metric 1.0mm (25.4tpi) axle handy, lay one down on the other, hold them between you and bright white sheet of paper or your computer screen, and you'll see it.
Ghrumpy is offline  
Old 02-04-18, 03:05 PM
  #14  
sch
Senior Member
 
Join Date: May 2003
Location: Mountain Brook. AL
Posts: 4,001
Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 302 Post(s)
Likes: 0
Liked 135 Times in 103 Posts
Thread gauge useless to distinguish the pedals as they have the same pitch for the length of thread on the
pedal. Now if you measured out to 20+ mm long thread, then some variance will appear.
20 TPI is same as 1.25M thread for thread lengths less than 22 mm or so.
sch is offline  
Old 02-04-18, 03:36 PM
  #15  
Senior Member
 
Join Date: Jul 2009
Posts: 790
Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 384 Post(s)
Likes: 0
Liked 6 Times in 6 Posts
Originally Posted by sch
Thread gauge useless to distinguish the pedals as they have the same pitch for the length of thread on the
pedal. Now if you measured out to 20+ mm long thread, then some variance will appear.
20 TPI is same as 1.25M thread for thread lengths less than 22 mm or so.
My two thread gauges disagree with you. And they are about the length of a pedal thread.
Ghrumpy is offline  
Old 02-04-18, 04:41 PM
  #16  
Senior Member
 
Join Date: Jul 2009
Posts: 790
Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 384 Post(s)
Likes: 0
Liked 6 Times in 6 Posts
Originally Posted by sch
Thread gauge useless to distinguish the pedals as they have the same pitch for the length of thread on the
pedal. Now if you measured out to 20+ mm long thread, then some variance will appear.
20 TPI is same as 1.25M thread for thread lengths less than 22 mm or so.
As a practical matter, what you say be true. But IMO you're overselling it. And I'm not sure I understand your math because you don't show it.

As I said already, I can see the difference over the 10 threads of my gauges and on actual pedal threads. So your first statement may just be a matter of how good one's eyes or glasses are working.

But we can quantify the difference mathematically. Over one thread, I calculate it as 0.020mm:
1/20"=0.050=1.27mm.
1.27-1.25=0.02mm
That's about a 1% error per thread:
0.02/1.25=.016 or 1.6%
That error accumulates for each added thread. ISO spec (and what most modern pedals have) is 10 threads. So the total for a pedal thread is 0.20mm (or about 0.008") and a 16% error:
(You don't really need me to do that math, right?)
I'm no engineer but that seems like that might be a problem. I'll add that after your 22mm length, the threads will be about ⅓ off each other.
Older pedals for steel cranks may have a couple fewer threads, so the error is of course less.
If I have made a mathematical or logical error, please correct me!

Whether that difference is enough to cause fit problems is another matter that depends entirely on tolerances, and as we know, they can be loose. And frankly the diameter difference between French and British pedal threads is usually more of an issue. But pitch is not a non-issue.
Ghrumpy is offline  
Old 02-04-18, 04:50 PM
  #17  
SE Wis
 
dedhed's Avatar
 
Join Date: Apr 2005
Location: Milwaukee, WI
Posts: 10,442

Bikes: '68 Raleigh Sprite, '02 Raleigh C500, '84 Raleigh Gran Prix, '91 Trek 400, 2013 Novara Randonee, 1990 Trek 970

Mentioned: 39 Post(s)
Tagged: 0 Thread(s)
Quoted: 2696 Post(s)
Liked 3,297 Times in 2,002 Posts
Go to a good hardware store and buy a .10 9/16-20 hex nut
dedhed is online now  
Old 02-04-18, 04:59 PM
  #18  
Senior Member
 
sweeks's Avatar
 
Join Date: Sep 2004
Location: Chicago area
Posts: 2,519

Bikes: Airborne "Carpe Diem", Motobecane "Mirage", Trek 6000, Strida 2, Dahon "Helios XL", Dahon "Mu XL", Tern "Verge S11i"

Mentioned: 22 Post(s)
Tagged: 0 Thread(s)
Quoted: 964 Post(s)
Liked 559 Times in 387 Posts
Originally Posted by JohnDThompson
The definitive proof would be to use a thread gauge. They aren't expensive, and can be useful in other situations as well.
For years, I've used a set of metric taps for this. It wasn't the reason I bought the taps, but it turns out I use them more for measuring than tapping.
I'm going to add a gauge to my tool box now, thanks!
Steve
sweeks is offline  
Old 02-04-18, 05:24 PM
  #19  
On Holiday
 
Hoopdriver's Avatar
 
Join Date: Apr 2017
Posts: 1,014

Bikes: A bunch of old steel bikes

Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 394 Post(s)
Likes: 0
Liked 14 Times in 12 Posts
Originally Posted by sch
Thread gauge useless to distinguish the pedals as they have the same pitch for the length of thread on the
pedal. Now if you measured out to 20+ mm long thread, then some variance will appear.
20 TPI is same as 1.25M thread for thread lengths less than 22 mm or so.
Not quite. A single thread gauge may seem to fit both 20 tpi and 1.25 mm but if you have both English and Metric gauges (and you should) you will see that one gauge is clearly a better fit than the other.
Hoopdriver is offline  
Old 02-04-18, 08:08 PM
  #20  
Senior Member
Thread Starter
 
Join Date: Mar 2015
Location: Connecticut
Posts: 2,000
Mentioned: 28 Post(s)
Tagged: 0 Thread(s)
Quoted: 457 Post(s)
Liked 42 Times in 33 Posts
So, ....uhh....a thread gauge will or will not solve the question: are these pedals French thread?
vintagerando is offline  
Old 02-05-18, 09:19 AM
  #21  
sch
Senior Member
 
Join Date: May 2003
Location: Mountain Brook. AL
Posts: 4,001
Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 302 Post(s)
Likes: 0
Liked 135 Times in 103 Posts
Waited til this am to try the thread gauges and found them to be nearly useless as expected over
the 6 threads that actually exist on the pedal spindles. The metric might have shown a little light
at the end on the 9/16" spindle but the 20 tpi gauge fit both Fr and Eng thread spindles
equally. Now if you had a larger # of threads to run the gauge over it might be more discriminating.
The discrepancy over 6 threads is difficult enough to discern that I don't think this is a valid
method of discrimination.
sch is offline  
Old 02-05-18, 10:25 AM
  #22  
Senior Member
 
Join Date: Jul 2009
Posts: 790
Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 384 Post(s)
Likes: 0
Liked 6 Times in 6 Posts
Originally Posted by vintagerando
So, ....uhh....a thread gauge will or will not solve the question: are these pedals French thread?
Will the answer determine whether you buy one or not? Because you won't know until you try. Theoretically, of course, it should, but in this case, as we know, the pitch is very close. Because of loose manufacturing tolerances and a small measurement length, a thread gauge might not be as conclusive as it could be otherwise. If you don't want to spring for an actual thread gauge, then a bolt of the same pitch will function adequately (however, it is subject to the same tolerance errors that the pedal threads are. Thread gauges are made to tighter tolerances than most screws you'll find in a hardware store.)
Or of course you could compare it to any other pedal threads you can find, including ", and see if there's a conclusive difference.

Threads are defined by form, diameter, and pitch, which is why I recommended you get thread gauges AND a micrometer caliper. (Form we need not worry about here, because Metric and BSC have essentially the same form.) If you can't conclusively determine whether it's French or not after making both measurements, then it probably doesn't matter anyway.
Ghrumpy is offline  
Old 02-05-18, 01:17 PM
  #23  
Old fart
 
JohnDThompson's Avatar
 
Join Date: Nov 2004
Location: Appleton WI
Posts: 24,862

Bikes: Several, mostly not name brands.

Mentioned: 153 Post(s)
Tagged: 0 Thread(s)
Quoted: 3544 Post(s)
Liked 3,283 Times in 1,878 Posts
Originally Posted by sch
Waited til this am to try the thread gauges and found them to be nearly useless as expected over the 6 threads that actually exist on the pedal spindles. [] The discrepancy over 6 threads is difficult enough to discern that I don't think this is a valid method of discrimination.
In that case, what reason is there not to simply force the pedals into the crank, regardless of thread spec? IIRC, TA actually cut their pedal threads such that they would work with either metric or English thread cranks.

Or, you could try a fancier gauge, like the VAR #167:

JohnDThompson is online now  
Old 02-05-18, 01:44 PM
  #24  
sch
Senior Member
 
Join Date: May 2003
Location: Mountain Brook. AL
Posts: 4,001
Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 302 Post(s)
Likes: 0
Liked 135 Times in 103 Posts
Well the point is Fr threads very easily go into English cranks, but being a bit loose
they quickly tear up the aluminum crank threads. Vice versa I have never tried
but putting Eng threaded pedals into a Fr crank would probably work, require only a bit
less than Schwartzenegger torque and permanently rethread the crank to Eng threading.
Most people by the 3d turn of the pedal into the crank would conclude something
wasn't right.
sch is offline  
Old 02-05-18, 08:59 PM
  #25  
Thrifty Bill
 
wrk101's Avatar
 
Join Date: Jan 2008
Location: Mountains of Western NC
Posts: 23,547

Bikes: 86 Katakura Silk, 87 Prologue X2, 88 Cimarron LE, 1975 Sekai 4000 Professional, 73 Paramount, plus more

Mentioned: 96 Post(s)
Tagged: 0 Thread(s)
Quoted: 1230 Post(s)
Liked 938 Times in 614 Posts
In my limited experience, french pedals go into English cranks, but English pedals did not thread into a French crank.

I like to start any threading by hand before using a tool. Use a tool and you might be able to force it in.
wrk101 is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.