Toe overlap calculator, anyone?

[simplemind]

I looked for a simple online calculator, but failed to find one that looked right.

[ultraman6970]

Never seen one...What frame size and shoe size are we talking about here?

[Kontact]

Hard to calculate because there isn't a metric for how far the toe of your shoe goes past the pedal spindle. You have to just measure that part.


If you have a bike with acceptable toe overlap, the Front Center measure will tell you what other bikes will be similar given the same crank arm length, same Q, shoe center over the pedal and tire size.

Move your cleats, install fenders, get pointer shoes or make your tread narrower and the overlap will change.

[false_Aest]

BikeCad Pro. Maybe it's offered with the online version?

[David Kirk]

If you can find a dealer who still has the Serotta design spreadsheet it will do the job. I wrote the formula that calculated the exact clearance and it took in account the center of the bottom bracket to the tip of the toe measurement.

It was dead accurate but you need to have good solid numbers for the rest of the bike.

dave

[Nooch]

Originally Posted by David Kirk

If you can find a dealer who still has the Serotta design spreadsheet it will do the job. I wrote the formula that calculated the exact clearance and it took in account the center of the bottom bracket to the tip of the toe measurement.

It was dead accurate but you need to have good solid numbers for the rest of the bike.

dave

I believe I can email this if you need -- I appear to have one saved on google drive.

[ergott]

Originally Posted by David Kirk

If you can find a dealer who still has the Serotta design spreadsheet it will do the job. I wrote the formula that calculated the exact clearance and it took in account the center of the bottom bracket to the tip of the toe measurement.

It was dead accurate but you need to have good solid numbers for the rest of the bike.

dave

I have my original spreadsheet, but it tries to refer to dead links (file:///Serotta02/company/DRAFTS/Ottrott ST/) so I can't see any calculations.

[John H.]

Small to medium bike- You will have it unless you have small feet, run cleats forward on the shoes, short cranks, really slack front end, long top tube, or some combo of all of these.
Big tires (like on gravel bike) also add to potential overlap.

I ride around 55cm bikes- I have never owned a road bike with zero toe clip overlap.
Never had a problem with overlap either.

In my opinion this is one of the least important factors in designing or selecting a bike.

[NHAero]

Could you post it as an attachment?

Originally Posted by Nooch

I believe I can email this if you need -- I appear to have one saved on google drive.

[cmg]

front center dim - (Wheel radius + crank length + shoe length pass pedal axle) = overlap. No need to calculate if you have bike, just measure it. 51 or smaller frame will have overlap.

[Kontact]

I am also a bit puzzled about what kind of calculation we are talking about, here.

[djdj]

Originally Posted by cmg

front center dim - (Wheel radius + crank length + shoe length pass pedal axle) = overlap. No need to calculate if you have bike, just measure it. 51 or smaller frame will have overlap.

OK, I'm not engineer but, to get the exact measurement, wouldn't you need to take into consideration that the toe will likely be lower than the front hub (because the bb center is below), and that the wheel must turn slightly to come into contact with the toe? In other words, using just the wheel radius measurement would overstate the amount of overlap.

[David Kirk]

Originally Posted by cmg

front center dim - (Wheel radius + crank length + shoe length pass pedal axle) = overlap. No need to calculate if you have bike, just measure it. 51 or smaller frame will have overlap.

That will get you in the ballpark but if you want to be 100% of the numbers it won't be right.

The first reason is that as the front wheel is turned to the side the tire actually swings in an arc and this buys you some room. The head angle and fork rake will determine how much room is gained as you steer off-center.

The second odd variable is how much pedal stack there is and how thick the shoe sole is. Basically the more vertical displacement one's shoe has from the pedal axle center is the concern. How does this matter? Well if you pedal with a level foot is matters little....but if you pedal toe down/heel up then this moves the toe forward a real amount. And the higher off the pedal axle center the shoe is the more it moves forward when you point the toe down.

This second thing was a big surprise to me 25 years ago when I wrote the formulas to predict overlap. Old school look pedals were really tall and if you lifted the heel even a small amount it moved the toe forward almost 10 mm. So if you crossed your T's and dotted your I's and got good solid numbers and then the rider pointed the toe down they could easily go from no overlap to overlap.

Nitpicky for sure but it all depends on how accurate you want/need to be.

dave

[Nooch]

Originally Posted by NHAero

Could you post it as an attachment?

Let's try!

[cmg]

Originally Posted by David Kirk

That will get you in the ballpark but if you want to be 100% of the numbers it won't be right.

The first reason is that as the front wheel is turned to the side the tire actually swings in an arc and this buys you some room. The head angle and fork rake will determine how much room is gained as you steer off-center.

The second odd variable is how much pedal stack there is and how thick the shoe sole is. Basically the more vertical displacement one's shoe has from the pedal axle center is the concern. How does this matter? Well if you pedal with a level foot is matters little....but if you pedal toe down/heel up then this moves the toe forward a real amount. And the higher off the pedal axle center the shoe is the more it moves forward when you point the toe down.

This second thing was a big surprise to me 25 years ago when I wrote the formulas to predict overlap. Old school look pedals were really tall and if you lifted the heel even a small amount it moved the toe forward almost 10 mm. So if you crossed your T's and dotted your I's and got good solid numbers and then the rider pointed the toe down they could easily go from no overlap to overlap.

Nitpicky for sure but it all depends on how accurate you want/need to be.

dave

But could'nt you just draw a circle representing the toe at it's most extension and every time it crossed the wheel circle was a point of potential contact? or the rider could just learn not to pedal through sharp turns....