Toe overlap and front-center? 58cm f-c?
 

I think Patarek says 58cm avoids most problems, but it isn't clear if that means 700x23 with 170mm cranks. Would a 165mm crank mean that it only needs to be 575mm? What does mostly mean for someone with say, a size 44 shoe? Is it gone or just minimized?

As a short rider with an even shorter inseam I'm finding many new bikes don't seem to have enough front-center for me, especially when I gravitate towards the XS for the low stack height so I can get at least a little saddle to bar drop (short inseam = lower saddle = little saddle to bar drop). I'm not interested in test riding bikes to intentional toe rub and risk faceplanting and buying a bike that will give me problems. I know some people like to just use 73/73 for everything but that leaves me with either my toes rubbing my tires or lots of reach, as much as a L size bike due to the shortened head tube.

I am a slow rider when I get tired, and I spend a considerable amount of time riding at under 10mph and doing tight turns for toe overlap to be important to me. Sometimes I have to zig-zag and I usually can't stop pedaling to turn. Rarely I have to get off the bike and take a breather. The following starts are especially wobbly. My transitions to standing can also get a little wobbly.

Most of the advice on front center seems to be tall people telling short people to deal with it, buy special frames, wheels and tires, or short people that go in straight lines faster than 10mph not having a problem or expert strong climbers who don't get slowed down by hills at all.

Thanks

It seems to me that only have given us an implied question. In particular, you haven't told us any body dimensions. For some people, there are compromises. If you want to sit in a fairly high-performance position on the bike, it's possible that smaller wheels are the only solution. I understand the logistical problems this can raise. I'm short enough and I like to have my cleats far enough back on my shoes that I live with a little bit of toe overlap. I am as wobbly as the next guy sometimes. Think about waking up at 4 am in a ditch in France and trying to ride your bike :) I also use fenders most of the time. What I find is that I can just wobble back the other way. I have never face-planted due to toe overlap, although the time I did a track stand with my right foot forward and my wheel turned left got really close.

I'm a short person telling a short person to "deal with it." As a "slow rider" maybe you're looking at the wrong bike for your needs. Or you need to improve conditioning so you're not so slow?

You could take a page from the Terry bicycles book and do a smaller front wheel. That would require a different fork so geometry doesn't change. Or you could shop for a used Terry. I don't think they are doing smaller front wheels anymore. Maybe you don't need a 700c performance type bike. A mountain or hybrid will likely have enough clearance.

http://www.bikeforums.net/showthread...gged-BB-Angles

Look at this concurrent thread. Andy.

Crescent Cycles- A fuller answer about what is acceptable toe overlap/clearance is to find a bike that has the amount you wish and measure it's front center. Adjust for the crank arm lengths if different.

When designing frames I go by the existing bike as a start. Then i ask about the differences wanted. The components that will be used next. I ask for the current fit dimensions and the changes wanted. Of course if the person is in front of me then i can make many of these fit judgments myself.

You'll find production bikes suffer from so many decisions that are for the brand/manufacturing needs and not the rider's. This is why custom exists. Feel free to PM me if you wish. I'm happy to push possible designs through BikeCad for you and see where it leads things. Andy.

Sorry, the specific question is what is the front center needed for no toe overlap, given a size 44 shoe, 700x23 tires

Yes, well I have to be able to climb the hills in order to get faster at them. I've measured some of them with an inclinometer, 8-10 degrees. Some feel even steeper. I doubt I'll ever be in good enough shape that I'll be able to speed up them, or at least it isn't happening any time soon. When I'm on the flats I can at least pass more roadies than those that pass me. If I didn't live in the hills like most people, then toe overlap probably wouldn't be much of a problem.

It is hard to measure and get everything perfectly straight, but one bike with 170mm cranks is ~590mm and the other is 165mm cranks with ~585mm, so pretty much the same, not really sure how much shorter I can go. A lot of small non-custom bikes seem to have less than ~580mm f-c and 170mm cranks.

One of the bikes is rather large but with a slack HTA at 57cm c-t, and it much too tall for me. The other is 48cm c-t, and I'd like the 75mm HT to be shortened by a hair, and the STA is a steep 76 degrees limiting my saddle choices. I did run large fenders at one point and it wasn't that unusual for me to knock the safety release out.

It is pretty easy to do the math to figure out what you need for clearance. Measure from the center of bottom bracket to the toe of shoes/toe clip, and from center of front hub and outside diameter of tire. There will be a bit more clearance than that, once you figure in the lateral angle offset. If you do want fenders, measure the fender offset from tire and add that on.

As for ways to make things work, shorter crank arms are a good option, as going shorter doesn't lead to any fit problems, it just requires different technique in pedaling. A frame set up for 650B wheels, or putting 650B wheels on a 700C frame and install extended reach brakes would likely be the next best option. You can fiddle with foot position on the pedal, but there is only so much that can be done here before fit becomes a problem. If you do find a frame that has a longer top tube than seat tube, and feel too stretched out, a shorter stem is a good trade off in my opinion, although that might make steering a bit more unresponsive/tricky.

Low trail frames should also help with this. 650B and low trail is pretty popular right now, so there is a lot of options out there for off-the-shelf. Low trail should also help out at slow speeds with stability. Look for frames that have a lot of bottom bracket drop (say over 70mm), combined that with 165mm cranks and clipless pedals/shoes, that should be the best way to minimize overlap.

steep head angle and short rake brings the wheel back , lower head angle and more rake moves it ahead .. (as would an offset fork crown + raked blades.. ) ..

with either you can create the same trail dimension, though th the feel may be different.. no I cannot describe the feeling..


Oh and smaller wheels.. no TCO on my Brompton :beer: it's low trail.. Handles best with a load of stuff.. over the wheel .


In 65, I built a 58 with a 60top tube , generic touring theme .. 72's no TCO with Mudguards .. .. It currently has Paul's Flat bed Porteur rack on it..




TCO on a go fast bike is OK because the overlap is only apparent at slow speeds .

I gather from the last paragraph in your original post that you don't want to go custom. I think that would give you the best result. You should at least contact Mr. Stewart to see what he could do for you. However, if that's not the direction you want to go, take a look at some vintage bikes. There are some nice ones out there for good prices. I may be wrong but my perception is that many frames in the 1970s tended to run longer top tubes than in later years. It'll take a good bit of looking but the right one is out there somewhere.

To set the record straight I don't do anything for people, I give advice and my experience. i am not insured. Do not have a fly by night builder do you anything.

M earlier comments stand though. Test ride, test fit bikes until the front center min dimension you need is known and design around that. it's not rocket science, just math. Andy.

FWIW - one generally can not say that you will need a certain front center number to clear a given shoe/crank size combo. Since overlap is a 'go/no go' deal if you do the figuring and end up being off by even a few millimeters you could easily go from thinking you will have enough room to finding out that you don't.

Bike Cad as a pretty good estimator in its software where you can plug in all the pertinent numbers along with shoe size and crank arm length and it will show you have much room you have. But even this could lead you astray as it doesn't figure in cleat position on the shoe...........so if its close you could end up on the wrong side of this.

All that said if you have a bike with the cranks as you will use them and the shoes/cleats you will use you can come up with a pretty good number for the front center you will need. Put the shoe in the pedal and put the pedal at 3:00 and turn the front wheel until it's at it closest point. Measure the room you have (or the amount of overlap you have) and then measure the front center of the bike in question and you should be able to do the math to get the min front center you'll need.

Keep in mind that if you pedal in a toe down position you will need more front center. When you are doing the measurements about play with the angle of the shoe (rotate heel up/down) and you will see that because of the stack height of the shoe/pedal that the toe will move for/aft a good bit. So if you pedal with your toes lower than your heels by a good bit this could make or break the deal.

I hope that helps more than it muddies the water. I just wanted to be sure that you knew that one can't pick a front center number and be sure it will all clear unless you pick a really big number that will clear by a lot.

Good luck,

dave

So there are two things that technical people do, and most other people don't do:

1) This you may or not be doing, is take responsibility for your own stuff. There are experts here, but for the most part people are non-technical about their stuff and don't really know what they are talking about. So become your own expert, you only have one customer and set of issues to master and it is normally easy for the individual to master their issues relative to the pro.

2) Get some numbers. This is the beginning of everything. Math is possible but not really required. I like math, but I don't really use it all that much for bikes. I measure stuff, acquire a data base. Why doesn't everyone measure up the various frames they own. Later you can move on to bikes you are testing out, or otherwise have access to. The pattern of what you need becomes pretty obvious when you start to log bikes. Numbers in catalogs are not reliable.

Sorry bout that. You've mentioned that you don't do that and I forgot. Too bad though, you've posted some nice work.

Thanks for the complement. I will continue to post my personal work (next up are two full touring bikes, may take two Winters though...) and my advice. Some day when i get totally financially free I'll get insurance and then really start to learn this craft. The more i do the more i know I need to know more. Andy.

I got financially independent in 2002ish. Feels really good for about a week, then you start to think, "what if they take it all away" financial independence is not the time to rely on insurance, and the gratitude of clients. Of course it varies by state. Check out what OJ did.

Realized that I wasn't aware of any TCO problems on my current riders so measured them. My '86 Univega Gran Turismo has a 55cm ctc TT and a 52cm ctt ST. Parallel 72's. 34mm, measured, tires and m/g. FC is 65mm! 170 cranks. No TCO. The '84 Trek 620 w/ 52 ctc st & 54 ctc tt, 28mm ms'd tires w/60cm fc, 167.5 crank, has noTCO. Size 8 1/2 US-42 shoe. After checking the 3 that are here at the house, seems none have TCO!

I stumbled across this thread and thought I'd post some work I did a while back on toe overlap calculation. Forum won't let me attach an excel file so I'm including a screenshot (PM me if you want an emailed copy to play with)
Toe overlap bothers me so I created this analysis. Super simplified general rule: with 700c you need a front center distance at least over 600mm. Even more simplistic but still a reasonable summary says wheelbase minus chainstay length needs to be greater than 600mm. Neither are the exact measurements needed but both are reasonable approximations. The spreadsheet considers lots of details (like asking for measurements of: shoe extension beyond pedal, and pedal offset (Q), etc) and tries to include them in measurements and calculations.

I will probably purchase BikeCad Pro just because it seems like an interesting tool that appeals to my slightly OCD nature. Maybe I'll modify the spreadsheet if bikecad has stuff that could contribute.

http://bikeforums.net/attachment.php...hmentid=401676

The next thing I might think up is just slack off the head tube angle a bit. Is it required to have such a tight head tube? You might consider dropping down to a 72 in front and a 73 in the back. I suppose If you want to ride a unstable bike you could rase the bottom bracket higher until you get that "racer feel".

Since I am built like a gorilla (short legs long arms) My personal frames don't have much overlap.

Mike Frye AKA Frye Bikes