Monday, March 24, 2014

Monday Mailbox: How to Tell If a Bike Will Have Toe Overlap?

Once in a while I get emails from readers who are either planning to buy a bike online, site unseen, or to order a custom frame, and are concerned about the dreaded toe overlap. Is there a way to figure out whether a bike will have TCO short of actually riding it? Can you tell by the frame geometry?

My intent is not to host another TCO debate, but to address this question for those who do want to avoid toe overlap. And the short answer is yes, TCO can be determined by a bicycle's frame geometry. The crucial measurement is what's known as the Front-Center - the distance from a bicycle's bottom bracket to the front axel (center to center), measured as shown in the picture above. Many manufacturers now provide this figure in the geometry specs. It is usually stated in millimeters.

Now, the key is to know what you need that figure to be in order for your toe to clear the front wheel. And this will depend on a number of things. Some of them will be specific to you, and will remain constant: the type and size of shoes you wear, and the way you position your foot on the pedal. Others will be specific to the type of bicycle you are getting: wheel size, tire size, and whether fenders will be used. To figure out your desired Front-Center figure, you will need to factor in all of these variables.

So let's start easy and say you are shopping for a new roadbike with 700C wheels and 23mm tires. Your current roadbike with the same wheel and tire size (that part is key) has a bit of toe overlap, and it's something you want to avoid in your new bike. So you measure your current bike's Front-Center and determine it to be 575mm. How much more room do you need for your toe to clear the tire? Well, put on your cycling shoes, clip in, and measure at the point of greatest overlap (by turning the wheel as if you are making a tight turn at slow speed). Maybe have someone else measure for you as well, to double check. And err on the conservative side just to be safe. 5mm of overlap? You sure? Okay, so this means that on a roadbike with 700C wheels and 23mm tires you need the Front-Center to be a minimum of 580mm.

And what if your current bike has enough toe clearance? Well, great. Measure the Front-Center and then determine how much tighter you can go while still avoiding TCO. That's the minimum figure you want to see in the geometry chart of your new bike.

If you plan to use wider tires, or fenders, or both, keep increasing that figure as appropriate. Because fender fit and true tire size differ from brand to brand, you will be estimating unless you have a chance to try a bike outfitted with the exact same tires and fenders your new bike will have. If you're cutting it close, consistency is key.

But what if you want to switch to a different wheel size? For instance, if you're shopping for a 650B x 42mm bike, and have no current basis for comparison? This is tricky, as you will basically need to calculate the difference between your current wheel + tire combination and that of the bike you're considering. But the numerical information for such calculations is freely available and, if you're mathematically inclined, figuring this out will be fun. And don't forget the fenders!

For a bike that will be ridden without clipless shoes (for instance, an upright city bicycle), toe overlap is more ambiguous. With your foot unattached, you'll be able to plop it onto the pedal every which way - which can result in the occasional fender bump even when there is plenty of clearance. There will also be greater variety in the footwear you will wear on the bike. On a given bicycle, you may have enough toe clearance when wearing sneakers and dress shoes, but find that you scrape the front fender on slow turns in clunky work boots.

So if you absolutely positively do not want any toe overlap what so ever on a non-clipless bike, be sure to wear your most toe-protrudingest shoes and to plop your foot as far forward on the pedal as you dare, when measuring for your desired Front-Center figure.

If you've determined your minimal Front-Center, but the geometry chart of the bicycle you're considering doesn't offer this information, you can always contact the manufacturer and ask. Just make sure you tell them the specific frame size you're looking at, because this measurement is size-specific. And if you are working with a framebuilder, you can of course simply tell them the Front-Center figure you need - or better yet, they can help you figure it out.

There is no substitute for trying a bike before buying. But if that is not an option, hopefully this has shed some light on how to ensure a TCO-free purchase.

32 comments:

  1. And don't forget crankarm length, which can vary from bike to bike. I have concurrently owned bikes with crankarm lengths varying from 165mm to 175mm, which is about half an inch. There's not as much variation there as fenders would cause, but it's probably close to the difference in tire sizes that would fit on a given bike....

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  2. Never buy anything without trying it first. TCO can not be predicted w/o fault.

    Font Center - where typefaces abound.

    5mm is an ok tolerance? That's like a few sheets of paper.

    Anyway front center is a factor of course, as are others (I wonder why you even talk about it though - it has nothing to do with tco's elimination as a guarantee), but you missed on extremely important factor, one that I've suggested (of course) a few times in the past.

    Rather than spoon feed it again, let's see if you can guess what it is.

    I'll say your post does nothing to determine if a bike doesn't have it.

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  3. In regards to wheel sizes and measurements, I think it's cool that typical roadie 700x23c tires, faux-French 650x42b tires, EA3 (26x1 3/8") tires, and balloon/mtb tires @ 26x2.125" are all within a mm of the same 334mm radius. Essentially, all the same size, with varying degrees of rubber involved. And while deflection will make a difference in terms of the axle-to-ground measurement, they will all be exceedingly similar in the dimension related to TCO.

    Now, then, I'm going to end this comment before I start talking about TCO and p'ing folks off..

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    1. Those combos are very similar, but not identical and the style of fenders used with each comes into play as well. So if you're cutting it close that difference starts to matter. For instance, on a 700Cx25mm fendered bike my toe clears with a F-C of sub-600mm, but I need 605mm on a 650Bx42mm fendered bike.

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  4. Most of my bikes through the years had a slight overlap and never was really a problem. I'm 5' 6 1/2". My present frame though has no overlap. Dave Moulton touched on this in a previous post.

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  5. Wouldn't fork rake variations throw out the accuracy of the F-C measurement in determining TCO

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    1. The rake is already taken into account, because the measurement is from the frame's BB to the fork's dropouts (have a look at the first picture). All else remaining constant, as the rake increases the F-C figure increases.

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    2. (…which also means that a bike's F-C can be altered by changing the fork to one with different rake, with the huge caveat that doing this will have other effects on geometry and handling)

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    3. Manufacturing variations play as large a part as anything.

      I've seen expensive bikes with huge measurement, manufacturing errors. Determining tco on paper based on published specs is foolish, in my experience.

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  6. I am excited to read this, because I figured it out all on my own last summer. My first custom bike (which I hoped would be my only custom bike) I specifically asked the frame builder for no toe overlap and that didn't work out. I decided to try again but find a way to make my request quantitatively and that was how I "discovered" the front-center, though I did not know it was called that! I drew a sketch for the frame builder (different builder this time), saying "make sure THIS space is at least THIS much." It worked. I sold my first custom to finance the new one and 2nd time was a charm!

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    1. Glad the second bike worked out for you. The TCO issue is a surprisingly common problem with custom bikes. IMO if a framebuilder says Yes to a no-TCO request but does not take relevant measurements, that is a red flag.

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  7. interesting article. I like how you provide a simple and reasonably accurate way to figure out toe overlap. I could be wrong, but I think the above method is a bit on the conservative side if you consider that the edge of the wheel will move forward away from the bottom bracket as it is turned allowing for additional clearance. Obviously this effect will be negligible if the wheel is only turned a small amount, but a quick "back of the envelope" calculation suggests it might be worth taking into account.

    Say axle to fender is 350 mm and the wheel is turned 15 degrees. The new distance to the axle bottom bracket has now decreased by 350-350*cos(15) = 12mm or ~1/2"

    Sort of interesting since to do this properly you'd have to take into account the distance between pedals (q factor) to figure out how far the wheel turns before potentially hitting your toe with wider q factors giving slightly more clearance.

    That said F-C seems like a great, simple way to do a rough comparison between different bikes that have similar crank lengths, effective wheel sizes, etc.

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    1. Yup. It's on the conservative side, because I figured things like crank length and q-factor would be too much for most to bother with in addition to factoring in wheels/tires/fenders and their own shoe size and foot position. It is in the end a rough comparison method, unless you (a) already have a bike with same effective wheel size, crank length, etc., or (b) are motivated and take into account all the variables and do the relevant calculations.

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    2. Too complicated? The goal is to eliminate tco, not have a discussion about it by disregarding a substantive factor. Crank arm length is too complicated but super relevant. Q factor has a neglible effect on the perpendicular plane, you knew that right?

      You were talking about 5mm before; crank arm length can vary easily 20mm, which is 2 cm, which is almost an inch. It's a HUGE difference when cutting it close, much more so than a theoretical



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    3. I take the q factor thing back a bit - a triple vs. a double can make the dif, but why not just say that vs. q factor is too complicated.

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    4. Jim -
      For riders that always use the same or very similar crank lengths, it's completely reasonable to not consider it. This whole toe overlap analysis thing can be as accurate or as approximate as you want/need it to be. If you run the numbers and find you're bike will clear by an inch or two, why make things unnecessarily complicated by considering smaller factors like crank length or q-factor? On the other hand if it's going to be close or you're a person that has bikes with vastly different crank lengths, these factors might be important. Identifying what plays a role is also great to know if you're going to do something like swap out your fork or crankset.

      If I'm understanding you correctly, you want to dismiss q-factor as only having a theoretical influence on toe overlap, but another person already posted saying that a change in q factor made the difference between overlapping and not overlapping.

      For me personally, all my bikes have 170 or 175mm cranks potentially making q factor just as relevant as crank length.

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    5. Of course it reasonable, but our author dismissed those factors out of hand, got it?

      Didn't read my numbers nor my subsequent q factor comment did you. This post isn't a guide, it's proof one can understand one measurement, some factors, yet not even mention important dynamic ones.

      That it fits your use case doesn't matter - doesn't fit all use cases. It's tantamount to saying, "it works for me b/c I considered it, therefore why complicate things for everyone."

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    6. This is a good place to point out why it is that modern cranks have such enormous q. It's real simple and very specific and only those who were there at the time know anything about it. Shimano did it. They decided that riders who pedal like ducks who were willing to spend money should be catered to. If you pedal like a duck with old square shouldered cranks there is a possibility of cracking your ankle bone on that shoulder. Nearly everyone who does this can learn to pedal better but customers are never to be corrected, never to be instructed. Consumers are to be coddled. The better to get into their wallets. As a result all of us, every last one of us has to ride wide cranks. The only way to ride narrow is to use cranks at least 30 years old. Or to machine your own. And few riders even know what it is they have missed. How would they know?

      I wonder if low q is one of the reasons V is so fond of old English steel.

      I get it that there are riders for whom TCO is a deal breaker. And I get that telling them to figure it out and deal with it will keep some novices off bikes. I also see that designers of consumer product type bikes are more motivated to just get rid of TCO than to figure out good ways to get rid of TCO. I don't see any move to long top tubes and short stems. Short stems work fine but they don't look racy so there are no road bikes with 5cm stems. In fact 5cm stems, if you can find them, are mostly over 50 years old. I don't see mfrs adding fork rake to small frames. All sizes get the same rake because that's cheap and efficient. What designers and mfrs do is slacken the head angle and steepen the seat angle until the bikes are almost unrideable. Because that's the cheap effective way to get rid of TCO. I will wait for the review where a bike is slammed for having a 70 degree hta and 42mm of rake. I will wait for the review slamming a bike for claiming a 74 sta and having 77. When I think of all the fads I've seen and the heaps of ill-conceived bikes no one ever enjoyed I just thank my lucky stars I grew up in a bike town. I always had exemplars of a better way to do things since I was 12 years old and started getting curious about this stuff. There's no one now to lead the way. And no one would follow. The riders think they are customers. The customer is always right.

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    7. Interesting insights.

      My road bike is maybe a size too big for me but fits great with a short stem (the stem is quite old just like you said). I don't even really have an opinion about TCO since I've never had a bike were it was significant even though I've moved my cleats way back since I've found it prevents numbness on my feet on long rides. I feel like it wouldn't bother me for road biking but would be an issue for mountain biking when tricky slow speed maneuvers come up frequently when climbing.

      Given that I do a lot of mountain biking were a large q factor is often needed to clear the frame and/or tire I'm used to a wider stance and I may have gotten where I actually prefer it. I recently got a fat bike and was a bit anxious about the VERY wide q-factor, but after a couple rides to adjust, it feels great.

      Speaking of my fatbike, I had to get the smaller size for increased standover and as you mentioned their solution to TCO was to slack out the head tube angle (69 deg) relative to the other sizes while still using the same fork (45 mm rake). I think the extra trail is great for handling on snow, but does make the handling feel just a bit sluggish on dirt or pavement. When you're average speed for a ride in moderately deep snow is 5 mph, toe overlap becomes a much bigger issue and I'm grateful to have plenty of clearance.

      I can definitely relate to you about hating being forced into fads that I think are stupid at least for the way I ride. Press fit bottom brackets and 10 or more speed drive trains comes to mind for me.

      Please don't take this the wrong way because I thought there was a lot of interesting stuff in your post and I definitely didn't feel like you were trying to force any opinions on me. So yeah, take this as being unrelated to your post, but there was a quote I came across in another forum that I try to follow:

      "Ride your own ride. Don't ride someone else's ride, don't assume you know anything about anyone else."

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  8. As I'm thinking about it, trail, fork angle, fork length, and possibly other dimensions to locate the steerer tube with respect to the bottom bracket would probably also have to be considered in my previous post if you wanted to be extremely accurate since the axis of rotation of the wheel when steering is not vertical and not located at the axle. That said I could definitely see many of these not being important and only accounting for differences on the order of 10ths of a mm. Would be interesting to either crunch through the math or just make some measurements on a bike with the front wheel turned to get an idea of what's significant and what isn't.

    I think it's pretty obvious that these things do matter at least in extreme cases... Imagine a bike with a ridiculously large q factor - the wheel would never hit your feet if they were far enough apart!

    Once again, thanks for the thought provoking post.

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    1. Sure, q factor matters. I've created TCO on a bike that had none by switching from modern (wide) cranks to vintage (narrow) cranks. Fortunately 1mm of overlap does not bother me. It is definitely noticeable.

      That switch reduced q by a full inch. For most practical purposes modern cranks all have similar dimensions. Front-center is still the first measurement to take.

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  9. what mainstream manufacturers offer this information in their geometry charts? seems pretty obscure

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    1. Most of them, last time I checked.
      here's the chart for a Specialized Ruby
      and a Cannondale CAAD10
      and a Soma Smoothie

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    2. hm okay, fair enough!

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  10. One can, of course, clip one's shoe in the pedal and measure without mounting the bike or involving another person. This works for toe clips and, if you can remember, no clips. I have huge feet and toe overlap on very bike I own and never had a problem. Having huge feet may be a blessing, as I have spent an entire life avoiding treading on and catching them on things. Tiny footed people do not have this experience in avoidance and cannot match me in balance, either.

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    1. Yup, the empty-shoed method works - though some people have a hard time clipping the shoe in without their foot in it, or just feel they need to be on the bike to replicate the circumstances of tco.

      Small feet, bad balance here - though probably unrelated.

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  11. Just recently the Senior Production Editor at Cycling Plus magazine had to have the fork re-raked and 160mm cranks fitted to her Paulus Quiros custom bicycle after she’d fallen off as a result of clipping her toe when re-starting on a steep hill. I believe she’d already had the cranks and the front fender shortened, the end of the fender being replaced with a flap (although that’s usually a better arrangement anyway). I suppose re-starting on a steep hill, especially with clipless pedals or toe clips, is when it’s most liable to happen, and you’d never think about that until you hit the ground. It’s a lovely bicycle, though, and she still loves it, especially now it’s sorted.

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  12. It’s interesting how neither Desdemona, your Seven, nor Francesco, your old Moser, have TCO – they probably have just about the same Front-Centre – and yet their front-end geometry is quite different. The Moser had a particularly slack head tube angle, with relatively little rake in the fork, whereas Seven gave Desdemona a slack head tube angle, though not as slack as the Moser, but also raked the fork out with one of their ingenious custom dropouts. Consequently, Desdemona has optimum, ‘neutral’, trail – without the custom dropouts, not only would you have TCO but the trail would have been too high – whereas Francesco’s trail was probably around 70mm, which may account for why its handling spooked you on fast descents. In theory, high trail helps for high speed cornering (motorcycles have around 80mm of trail), but maybe it was just too far out – I have one bicycle with high trail, and compared to other bicycles I’ve ridden it feels as if it corners in a series of swerves. I expect there’s a trick to riding high trail, though – perhaps it just needs you to get down lower, or a lighter touch, or whatever.

    Incidentally, just so’s you know, an awful lot of what I’ve learned about bicycles has been with or through you via this blog, and through those who contribute to it. I’ve even just taken the trouble to find out who Desdemona actually was. :)

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  13. Here, since some of you don't understand metric weighting let me bottom line it:

    Ride the bike, give your money to the person who will let you ride it. If purchased from afar you cheaped out, want what you want, and deserve whatever ill-fitting bike you get.

    If you live in remote Iceland, give your money to the company who will take a return and give good fit guidelines pre-purchase.

    Or quit hooking your heels on the pedals and stop wearing pointy shoes.

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  14. Sure if you have access to the assembled bike or don't care about toe overlap the article and comments are not very relevant.

    For one reason or another, many people do care about toe overlap and also might not have the ability to try the bike out. Some reasons that come to mind include:

    *no local shops sell the bike they're interested in
    *buying a frame only - can't test ride it until the components have been put on in which case it may be too late.
    *working with a frame builder to make a custom bike.

    I think the discussions have also highlighted some interesting facts about what changes to the bike might change toe overlap on a current bike such as bottom bracket width, tire size, fork length (would change F-C), etc.

    Given that toe overlap is pretty much entirely geometric and not nearly as complicated as how the bike handles, durability, etc. I see no reason it can't be figured out ahead of time by a computer extremely accurately. There's a site here that claims to do just that:

    http://www.bikecad.ca/toe_overlap

    although unfortunately I'm having trouble getting my version of java updated and I can't be bothered to figure out what the trouble is.

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  15. I'm coming at this toe clip overlap issue a bit late, but I'll add my two cent's worth. After reading all the comments, I noticed no one mentioned Jan Heine's excellent article in Bicycle Quarterly Spring 2012 Issue "Tall and Short Riders." The wisdom of the French constructeurs was to use the rule: 600mm minimum from BB center to fork dropouts. Adjust frame geometry and fork offset to achieve this.
    My wife has a lovely 50cm Waterford RST-14 bike with such severe toe/fork overlap she has crashed badly several times and is now afraid of riding it. The solution:
    I got her a 54 cm 650 Nordavinden which, with its low-trail fork, has solved the problem nicely. She loves riding it. Guess we'll save the Waterford for our daughter, who is a much more skilled rider, to use when she visits.

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