650B Conversion Misconceptions


1980 Meral sport touring frame

A while back I received a hostile diatribe in my comment queue about my Meral 650b conversion.  I spammed the comment, but then thought it was potentially illustrative, albeit rude and obnoxious.   The moron’s comment appears at the end of this post, and because it is full of misconceptions and mythologies couched as “expertise”, I’d like to thank him for inspiring this post.

I purchased my 1980 Meral 700c sport touring frame after researching the ideal geometry and clearance requirements for a wheel size conversion. I consulted Sheldon Brown’s 650B conversion guide, as well as resources available from many other cyclists, mechanics, and frame builders. A particularly easy to read guide is available at Rivendell’s site. Since that time, I have done a number of other wheel size conversions, from 650c to 26 inch, and from 700c to 650c.


Mafac Raid brakes-to supply adequate reach to the 650B rims.


Before building up the frame I dry mounted many of the components to check for clearance and chain line.

Those of us who have undertaken 650B conversions understand the brake reach, tire clearance and other considerations that must be explored when contemplating whether to convert a bike to 650B.  My spammer, however, believes that one can alter the geometry of a frame by changing the wheel size.  Without a blow torch, that would not be possible.


After the conversion to 650B, the bike looks beautiful and eats up the miles.


Wine cork spacer for the rear fender.

The outer diameter of a 38 mm 650B tire is only a bit smaller than that of a 700c x 20 tire.  The effect of the 650B conversion is to give one a chance to ride on wider tires, making the bike more useful and comfortable, and to provide for fender clearance that didn’t exist with the larger wheel size.  And, as I have stated in past posts, you don’t want to convert a frame to a smaller wheel size if your frame has a lot of bottom bracket drop.  Rivendell recommends no more than 70 mm, but you may be able to get away with a bit more drop if you are using shorter cranks.  Many bicycles from the 1970’s on have way too high bottom brackets to begin with, so lowering the bottom bracket a bit will improve the bike’s handling and cause no negative side effects.

My own Meral has very little bottom bracket drop, so the conversion improved the handling, by dropping the bottom bracket height DOWN to 27.5 cm, still very high, and much higher than recommended by some frame builders.  My trail went from 43 mm to 41, and my wheel flop stayed the same at 12.  The world did not stop spinning due to my audacious acts.  What are the factors at work that cause these changes?


Rake and Trail, drawing courtesy of Dave Moulton.

When you install smaller diameter wheels, there will be a change in the distance from the center of the axle to the ground, thus reducing the distance of the horizontal line between a straight line following the fork/headtube angle, and a vertical line from the wheel axis to the ground.  Smaller wheel diameter = less trail.  More rake also = less trail, which you can determine from the above drawing by imagining the vertical line through the axis, moving forward, reducing the trail line.  Less trail almost always equals less wheel flop, which can provide improved handling for carrying front end loads.  Wheel flop is a function of head angle and trail, so you can alter wheel flop also by changing to a longer or shorter fork, and/or to a fork with less or more rake.  But in a well thought out 650B conversion, there’s no need to worry about changing the fork.

Another misconception is that a 650B conversion causes fork shimmy.  Even though no one seems to know what does cause shimmy, I think we can say for certain that it is not caused by the “wrong combination of rake, trail and head angle.” which of course a 650B conversion does not affect anyway (rake and head angle being impossible to change without changing the fork).  Fortunately, I eliminated the shimmy on my initial build by using different tires – I switched from the ponderous Panasonic Col de la Vie tires to the comfortable, delightful and fast Loup Loup Pass tires from Compass.

Finally, here is the comment which inspired this post, in full and unedited, with misspellings and grammatical errors intact:

“As you state, the frames is well designed and its construction very well crafted; it was mostly likely built by Francis Quillon the head framebuilder at Meral..and he would be proud of it. However..he designed the bike around 700c wheels and would be astonished that you have fitted 650B, thereby upsetting all the correct design features that he had used in the frames constructions ie head angle, front end clearance, fork rake and trail…all those important features that govern how a bike handles..OH! not forgetting the height of the bracket.
Shimmy is often a result of the wrong combination of fork rake, trail and head angle..compounded, without doubt by using the wrong wheel size. So what you have managed to do is to take a delightful frame that was intended for fast road riding ie sportif use, and try to turn it into a type of randonneur…which it was never designed from the box of frame tubes , lugs etc to be.
As for the massive amount of handlebar stem quill that protrudes dangerously out of the fork column, Quillon would be alarmed at the thought ..and the sight it presents. The least you could do would be to buy one of those elegant Stronglight extra long headset lock-nuts that would both add about 30mms of extra grip to the quill while at the same time making the bike look less ridiculous than it does now…
Never mind the chrome hilights, the wonderful deep purple flamboyant paintwork..you have turned the bike into a travesty of what the designer/framebuilder intended and,
in doing so, insulted his skills.
If you really need so much seat pillar projecting from the seat cluster and such a high riding position, I suggest you get a frame that is more appropriate to your inner leg and body length.
Just a footnote…no French builder, large or small would ever let a bike with toeclip overlap leave their workshop or factory.”


Shockingly tall seatpost?

This diatribe points out how narrow minded some cyclists are –  adhering to the idea that if they do not personally experience something, then it must not exist.  One of the reasons the seat post and stem are tall is because I am using 160mm cranks, which help to eliminate toe overlap.  Shorter cranks means a taller seat post, which in turn means a taller stem.  And yes, this frame had toe overlap with the larger 700c wheels, and it was indeed designed that way – something that happens when small and even medium sized frames are built around 700c wheels.  Whether the builder considered this a necessary compromise to please a particular customer, we will never know.  Most disturbing about this rant is the ridiculous concept that style trumps comfort when setting up a bike for a particular rider.  Many riders know that taller stems mean more hours of comfortable riding.


NItto Technomic stem, sanded to French size, a la Sheldon Brown, Shimano 600 French headset.

2015-05-07 019

A travesty?

Apparently, the original Shimano 600 French headset is an absolute eyesore, when paired to the tall Nitto stem.

So hideous is the bike that it is now a “travesty”.  Well, me and my travesty will see you out on the road.  Happy riding!

29 thoughts on “650B Conversion Misconceptions

  1. Nola –
    Not withstanding your critic’s generalizations, the Meral looks like a fine example of a 650B conversion. There is at least one error with his comment “…no French builder, large or small would ever let a bike with toeclip overlap leave their workshop or factory ” as it is just flat out wrong. First, there is the example of your Meral. Also, I own a 60 cm, Bernard Carre built, 1973 Bertin C 37 with 170 mm cranks and medium clips. There is overlap. Your reader needs to become aware that being certain is not the same as being right.

    • Agreed, Jim. I have encountered many frames of all sizes with toe overlap. There are even “experts” who argue that toe overlap doesn’t matter. I and many other cyclists know the truth: toe overlap is to be avoided if possible as it can set you up to crash when you least expect it. However, one way builders avoid toe overlap on smaller frames is to slacken the head tube angle, which I think is even worse than dealing with toe overlap. A too slack head tube on a small frame will lead too excessive trail and wheel flop, making for a handling mess.

      • Funny that you mention that. My wife rides a 49-52 size (700c). She has a Guerciotti “racing bike” that she purchased new in 1981. We think it has close to 100,000 miles on it now. She loves that darn thing! I was having trouble getting her to ride other bikes, and she said they all “steered funny” so I checked the trail on the old “racing” bike (a 49 cm. size). 83 mm of trail! I measured it three times because that seemed nuts, but it is that much. A very short-offset fork, with a very slack head angle (and a very steep seat tube angle, plus a high BB, by the way, just to get the ST and TT numbers to look good on paper). Took a long time to wean her off of that crazy geometry!!!! That’s all she rode, for decades…… Now her main bike is a 51.5 cm. size, 73-degree HT, with 55 mm of rake, yielding about 45 mm of trail. Way better than 83….!

    • Absolutely correct. The nutter was just plain wrong, in so many ways…..

      The good news is that he inspired this thoughtful explanation, which lots of us can now share! So, his ignorance begat some enlightening……

  2. My Velo Orange (while not a conversion) has all sorts of stem and post sticking out but by doing so, I was able to knock 5cm off of my reach. That’s a lot! When I poste my bike on a popular facebook page, I got a lot of flak for that but who cares? Dude, you have a sweet ride there and the haters can say all they want but in the end, you did your research and now you have a more comfortable and versatile bike to show for it.
    Screw that troll, enjoy your bicycle.

  3. Great Post, beautiful bike. I will certainly refer to it in the future for my own potential conversions. Ive personally never found toe overlap to be anything worth worrying about. The only time it ever presents itself is at very slow, very tight u-turns anyway.

    • Thanks, Al. Toe overlap is never an issue until it’s an issue, and then it is too late. Ask any smaller rider and you’ll get a very different perspective. Toe overlap is an important issue for commuting riders who navigate tight turns in the rain on steep hills. Avoiding toe overlap is the goal of any mindful builder, but mass produced frames for small riders achieve a bad result by slackening the head tube in order to shove 700c wheels into a small frame, thus avoiding toe overlap. The result is terrible handling. Some people adapt well to a small amount of overlap, but ideally there should be none.

  4. I myself will soon belong to the “sinners club” of 650B converters !. But when I see that JP Weigle is already a member , it soothes my soul !
    The frame is most probably a Special CNC 700C frame with superb workmanship, unfortunately my present purse would not allow me to have such a frame built to such a high standard. I will nevertheless have cantilever pods added and some racks fixtures brazed on. And it will give a second life to this frame which had been sleeping for the last 30 years in a barn.
    Surely, its a blasphemy in the eyes of certain worshipers – beware of the zombie frame brought back to life by witchcraft ! – but as usual, religion to the extreme is harmful and I am happy to fight against it !

  5. Nola, great work on both this 650 conversion and your beautiful Peugeot Mixte!
    I agree with the other commentors and will not echo what’s already been said but wanted to add a ‘conversion’ of sorts experience of my own for perspective.
    Last summer I built up an early 70’s Japanese made ‘Crystal’ road bike project that I purchased from a hoarder’s stash missing one of its wheels to resell. It was obvious to me the bike was a scaled down road bike for smaller/younger riders with one 26″ wheel still attached. Not having 26″ wheels on hand, I installed 27″ (27″x1-1/14″ tire size) rims and set the bike up for riding. I believe the geometry was very ‘Schwinn Racer’, not Masi GC, so the bike rode comfortably with toe overlap for my size 12-1/2 feet attached to my 6’3″ frame. When I finally sold the bike, it was purched for a boy of about 11-years old and of average proportions who loved the bright yellow color. I relayed my experiences with toe overlap and cautions about old, ‘delicate’ 70’s bikes in general, although her son was an ‘ideal size’ for the frame. Some weeks later I met his mom in the super market who was delighted to relay her son’s exploits on the bicycle, including what sounded like the makings of a future cyclocross racer!
    If you have the knowledge and skillset to make something functional and useful for yourself and no one gets hurt in the process, I’d call that a good day!

  6. How curious, why do people even read blogs or articles about things they don’t agree with or have any interest in? Your blog has a focus on bicycles for smaller riders and is full of wheel size conversions. It is a common way for people to get into 650B without trying to find a 650b frame. As a shorter person you are well aware of the lack of quality small frames and show how you can make frames work better with smaller wheels for smaller people. I have had to really hunt down small higher end bicycles, but they all have 700cc wheels. I still have yet to tackle any conversions, but in order to make the bicycles work for me, they have goofy set ups in order to work for me and sometimes know it all men have the nerve to critique them. My husband made a 650B conversion with a too big 80’s japanese bianchi that did not have a great ride quality or so he moaned. 650b transformed it. He cannot fit wider than 38mm tires which is fine. He did use the honjo fenders meant for one of my bikes. He gets loads of compliments on it.
    Your Meral is stunning.

    • Thanks, Heather. Wheel size conversions are appropriate for all sized riders – allowing one to use wider tires and fenders. The bicycle manufacturing industry has still not stepped up to the plate in terms of optimizing frames and wheel sizes for all riders of differing heights. And, with the quality of older vintage frames, there is an ongoing advantage to taking a vintage frame designed for 700c wheels and converting it to 650b.

      • I agree, but I will say that, as someone that has and still does sell high-quality lugged-steel frames, the market for anything smaller than the smallest 700c frame (so, about a 52 cm c-t) is very near zero. As is the market for anything larger than about a 63 cm c-t size.

        I own the Heron brand, and from 1997-2007, precisely zero of the smallest-size frames (50 cm c-t) were sold. I received all two of the ones that were built, when I purchased the brand! Ditto the 65 cm. size. Zero sales in a decade. That said, for the new Heron Sportif frames that are debuting in January, 2017, we will offer a 50 cm size, as well as a 64 cm. size. The 50 cm. one, however, will be built to order (but cost no extra because of it). 64s will be stocked.

      • Thanks, Greg. I love your your bikes – I have been aware of your builds and have admired them. There is much to do to educate cyclists – especially new riders – about frame geometry and wheel size. I think your comments reflect the sad result of the cycling industry’s recent focus on the male gender and on racing, to the exclusion of all else. That wasn’t so true back in the early days of frame building. I think we will get there, with patience.

      • No, it’s pretty much always been true…… Similar issue with crank arm length. Everyone SAYS they want shorter ones available. I stock them (165s) in just about everything I carry, and sell maybe two per year, total, vs. dozens of the other sizes. The truth is there just is not even a modicum of folks that will buy super-small “good” frames or short “good” cranksets, sadly.

  7. Your Meral is one of the most beautiful and well proportioned looking steel restorations I’ve ever seen (if you ever decide to sell it…). Last year you helped convince me it was ok to
    ‘Petersen-ize’ the stem on my 1982 TREK 710 frame. Sometimes form does need to follow function.
    Hope your leg is better.

    • Hi Michael,
      It sounds like your Trek 710 is working out. I love to hear these stories – so much is gained by using what has already been produced, reinterpreting as needed. Happy riding!

  8. Hi Nola, I own a 753 Meral racing bicycle from ’82. It is beautifully crafted just like your 531 frame. I applaud your ingenuity, inventiveness and perseverance with this build. What is most pleasing [about the the frame] is that someone is still putting it to good use and still enjoying it – not matter what it may or may not have been originally designed for. Chapeau sir.

  9. enjoyed this series of articles on the Meral conversion ,, Mercian cycles KING of MERCIA model comes with an interference front end unless specified otherwise , many other makers have models that are of the same ilk where a specific ride characteristic was favoured over ultimate rider convenience or user friendliness . i think your complainer just isn’t getting out on his bike enough 😉

    • Agreed. Toe overlap can be eliminated by the builder, but there are sacrifices when building a small frame around 700c wheels. This Meral is an example of that – where the builder chose not to eliminate toe overlap in favor of other frame characteristics and geometry.

  10. Thanks for all the info! I have a quick question– how wide do the Loup Loup tires actually measure with calipers? I’ve mounted Col de la Vie’s to discover they measured a width of 32.5mm, not quite 38mm. I’m curious to know if Compass’s stated width for the 38mm Loup Loup is actually 38mm. This info is pertinent to a potential build. Thanks!

    • Hi Justin, the actual width of any tire will vary with the rim you have selected. And, tires may actually widen over time. On my Velocity Synergy 650b rims, these tires are about 37 mm wide running them at 46 psi rear and 42 psi front.

  11. I know that this is an odl post – but I found that this is very useful and instructional! I have only built up 1 vintage bike (an old Mercian) and that was for 700c and for L’Erioca use. I am interested in perhaps one day building an old style 650b rando bike from an older steel frame and this is quite inspiring.

  12. All my bikes have high Nitto stems and seatposts that stick up. I am 6’0 with a very short torso and i ride mostly in the “fitness” stance. I hope to do a 650b conversion to a Trek 400 over the winter. Any advice gladly listened to. Cheers!

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