Felge und Nabe messen, um Speichenlängen zu berechnen

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Eine Messung ist soviel wert wie 50 Expertenmeinungen
--Howard Sutherland

Merke Dir Howard Sutherlands weisen Worte ! Um die richtige Speichenlänge für den Laufradbau zu bestimmen, muss man die Dimensionen der Felge und der Nabe genau kennen. Die Hersteller liefern auf Ihren Webseiten oft Listen mit Spezifikationen zu den jeweiligen Naben und Felgen. Auf den Seiten von Sheldon Brown findet man Damon Rinards Spocalc Excel Anwendung mit Maßen (englisch). ABER erst nach man die meisten Speichen in ein Laufrad eingezogen hat, kann man erkennen, ob die Speichenlängen stimmen. Daher solltest Du messen - selbst wenn Du Dir sicher bist, die richtigen Maße zu kennen. Online präsentierte Informationen können nur dazu dienen, Bauteile richtig zu identifizieren und möglicherweise Messergebnisse zu plausibilisieren.

Dieser Artikel beschreibt das Vorgehen beim Messen mit dem Schwerpunkt auf möglichst einfache Methoden, einfache und preiswerte Werkzeuge. Zudem wird ausgeführt, wie genau die Messungen sein müssen.

Speichenlängen werden in Millimetern angegeben. Daher sind natürlich Messungen in Millimetern notwendig. Da der Artikel ursprünglich aus dem amerikanischen Sprachraum kommt, werden teilweise Messungen in Zoll beschrieben. Die Umrechungen werden ebenfalls erläutert, auch wenn es hier im europäischen Umfeld wenig Bedeutung hat.

Was wird gemessen?

Wenn Du möchtest, kannst Du diesen Abschnitt überspringen. Man muss die Formel zur Berechnung der Speichenlänge nicht exakt kennen. Speichenlängenrechner nehmen einem die Rechenarbeit ab.

Der erste Schritt zur Berechnung der Speichenlänge

Aber falls Du Interesse an Mathematik hast, kannst Du hier lernen, wie die Speichenlänge berechnet wird. Es handelt sich um eine Trigonometrieaufgabe, die in zwei Schritten durchgeführt wird.

Der erste Schritt ist das Ausrechnen der Länge der dritten Seite eines Dreiecks mit der Cosinus Funktion.

Speichenlaenge 1.png

bei der

  • A und B die bekannten Seiten und θ (Theta) ist der Winkel zwischen den Seiten sind.

A wird mit der violetten Linie der links stehenden Illustration dargestellt. B ist die Orange Linie. C ist die gesuchte dritte Seite (in rot) - deren Länge muss ausgerechnet werden.

Die beiden bekannten Seiten (A und B) bilden den Radius (halber Durchmesser) des Speichenlochkreises im Nabenflansch (B) und den Radius den Speichenlochrings in der Felge (A). Der Winkel θ hängt von den Speichenlochabstand des Nabenflanschs zur Mitte der Nabe und vom Einspeichmuster ab.-

Zweiter Schritt für die Berechnung der Speichenlänge unter Berücksichtigung der Speichenneigung gegenüber der Mittellinie

Der erste Schritt erzeugt einen virtuellen Messpunkt direkt unter den Speichenlöchern der Felge. Hier gibt es Nichts direkt zu messen, daher ist ein zweiter Schritt vonnöten.

Der zweite Schritt ergibt die Speichenlänge, indem der Abstand des Nabenflansch seitwärts von der Mittellinie des Fahrrads mit einbezogen wird. Dieser Schritt wendet den Satz des Pythagoras für rechtwinklige Dreiecke an (Berechnung der Hypotenuse). Hierbei gibt es eine winzige Korrektur, um die Größe der Speichenlöcher im Nabenflansch mit einzuberechnen.

Speichenlaenge 2.png

hierbei:

  • ist C das Ergebnis der ersten Formel. Diese Seite sieht man in rot in der Illustration rechts.
  • ist w der Abstand des Flanschs von der Mittelinie (blaue oder grüne Linie im Bild rechts).
  • ist d der Durchmesser der Speichenlöcher der Nabe.

Beide Flansche der Nabe haben wahrscheinlich einen unterschiedlichen Abstand zur Mittellinie, wie man an der blauen und grünen Linie erkennen kann.

Mach Dir Notizen

Wenn Du misst, solltest Du Dir folgende Informationen aufschreiben. Du benötigst diese Informationen für die Berechnungen und um Korrekturen für den nächsten Laufradbau zu machen, falls die Speichenlänge leicht inkorrekt ist.

  • Zahl der Speichenlöcher in Felge und Nabe (beide Seiten zählen!)
  • Außendurchmesser der Felge und die Distanz von diesem zum Speichenloch, und/oder
  • Außenumfang der Nabe und Distanz von hier zum Speichenloch
  • Speichenlochkreisdurchmesser der Nabe
  • Durchmesser der Speichenlöcher der Nabe
  • Abstand des rechten Nabenflanschs von der Mittellinie
  • Abstand des linken Nabenflanschs von der Mittellinie
  • Beabsichtigte Kreuzungszahl der Speichen

Zahl der Speichenlöcher

Man benötigt die Zahl der Speichenlöcher in Felge und Nabe. Normalerweise müssen die Zahlen übereinstimmen, jedoch kann es manchmal nützlich oder notwendig sein, Laufräder mit nicht passenden Lochzahlen zu bauen. Wenn die Nabe einen besonders großen Durchmesser hat (wie beispielsweise bei manchen Pedelecs), erklärt der unten verlinkte Artikel, wie man die Speichenwinkel an der Felge verringert, um Speichenbrüchen vorzubeugen.

Zudem haben manche Naben und Felgen unregelmäßige Abstände der Speichenlöcher. Diese werden allerdings hier nicht diskutiert und werden möglicherweise Teil eines zukünftigen Artikels.

Siehe auch

Die Felge messen

Eine Felge zu messen, wird üblicherweise in drei Schritten durchgeführt:

  1. Messe den Durchmesser der Felge oder berechne den Durchmesser basierend auf dem Felgenaußenumfang. [[John Allen] empfiehlt, Beides zu tun.
  2. Falls nötig, miss die Tiefe vom Außenumfang zum Speichenloch
  3. Falls nötig, berechne den Durchmesser an der felge, an dem die Speichenköpfe in den Speichnlöchern ruhen (das nennt man auch den Einspeichdurchmesser, dieser ist äquivalent zum Felgenwirkdurchmesser bzw. ERD).
  4. Außer die misst bereits über die Enden der Speichennippel eines bereits eingespeichten Laufrads, addiere zweimal die Höhe eines Speichennippels (typischerweise 2mm je Speichennippel, also 4mm insgesamt).

Eine Felge kann einwandig oder doppelwandig ausgeführt sein, wie man folgendem Bildern entnehmen kann. Eine doppelwandige Felge hat eingelassene Speichenlöcher: Die schmaleren Löcher zur Naben hinweisend halten die Speichen. Die größeren Löcher, die in Richtung Reifen weisen, ermöglichen die Arbeiten an den Speichen beim man das Laufrad baut.

Schritte zwei und drei in obiger Aufzählung benötigt man bei Speichen mit eingelassenen Speichenlöchern, weil man den Einspeichdurchmesser nicht direkt messen kann.

Felgenquerschnitte
Felge ohne Öse Felge mit Öse Felge mit eingelassenem
Loch und ohne Öse
Felge mit eingelassenem
Loch und mit Öse
Felge mit
Speichenbuchse

No-eyelets.jpg

Not-recessed.jpg

Recessed-no-eyelets.jpg

Recessed-with-eyelets.jpg

Recessed-with-sockets.jpg

Die unten stehende Illustration zweigt den Au0endurchmesser und den Einspeichdurchmesser. Die dargestellte Felge ist eine doppelwandige Felge mit eingelassenen Speichenlöchern mit Ösen.

Felgenquerschnitt zeigt den Außendurchmesser und
Einspeichdurchmesser einer Felge. Die Speichen werden in den
tieferen, schmaleren Löchern dieser doppelwandigen Felge befestigt.

Felgenaußendurchmesser und -einspeichdurchmesser

Den Außendurchmesser messen

Lay a measuring tape or ruler across the rim between two points directly opposite one another. Slide one end of the tape back and forth along the rim until the measurement is largest. Measure at three or four different angles spaced equally around the rim and take the average, in case the rim isn't perfectly round. (Spoke tension will make the rim round later, unless the rim is really bad. Then start with another rim.) Measure to the nearest 1mm or 1/32 inch, or better. If the diameter falls partway between millimeter or 1/32 inch marks on the tape, you could estimate the fraction.

Measuring rim diameter

If you measured in inches, multiply by 25.4 to get the diameter in millimeters. Convert the fraction after the last even inch to a decimal before multiplying: for example, 1/4" is 0.250, so a rim that measures 24 1/4 inches is 24.250 inches in diameter, or rounded to the nearest 1/10 millimeter, 616.0 mm. .

Den Umfang der Felge messen

If you are working with an empty rim, it is easy to measure the outside diameter, but if you need to measure a built-up wheel, the axle gets in the way of the tape measure. You then need to measure the circumference (distance around the rim). Also, measuring in two different ways is possible, and a good idea. As carpenters say, "measure twice and cut once" or in this case, measure twice and select spokes once.

You can measure the circumference of a rim by wrapping a measuring tape all the way around the rim. You then derive the diameter from the circumference.

A narrow, metal tape measure -- 1/4 inch or 6 mm wide -- will fit into the well of the rim (the deepest part of the rim's channel). (A wide metal tape measure won't fit into the well of most rims and won't curve smoothly around the rim.)

Don't trust a fabric measuring tape as used in fitting clothing. The fabric stretches.

Use the metal tape measure as shown in the image below.

Measuring circumference

Here are the steps to measure a rim using the circumference:

  • The tape has a tab at the end. Hook the tab into the valve hole and wrap the tape all the way around the rim, measuring the total circumference at the bottom of the well.
  • Divide the circumference by π ("pi" in English, pronounced "pie") to get the diameter of the well. In case you were sleeping in 6th-grade math class: π is a a Greek letter denoting the ratio of the circumference of any circle to its diameter. π is a single-button function on scientific calculators, carried out to a large number of decimal places, but 3.142 is close enough if you have a four-function calculator or are working on paper. On paper, take your calculation out to tenths of a millimeter or hundredths of an inch..
  • If the tape measure is divided in inches, also multiply by 25.4 to get the diameter of the well in millimeters. To make paper calculation quicker, you could combine steps 2 and 3, multiplying by 8.085.

If you don't have a narrow tape measure, you could wrap a bicycle cable inner wire around the rim, hooking the ferrule into the valve hole. Mark the wire, stretch it out flat and measure the length. If measuring a built-up wheel with non-recessed spoke nipples, the cable will sit next to them and the measurement is that for a bare rim.

Die Tiefe bis zu den Speichenlöchern

You must measure the depth to the spoke holes if they are recessed, or if you measured the outside diameter of the rim.

You can use an improvised tool, as in the image at the right -- a bolt and nut, and a small metal ruler. Lay the ruler flat across the flanges of the rim. IMeasuring recess depth using bolt and nutnsert the bolt. If the rim has recessed spoke holes, the bolt will extend to the bottom of an eyelet. Screw down the nut until it rests against the ruler. Then use the ruler to measure the length between the nut and the end of the bolt. Subtract the thickness of the ruler (here, about 0.5 mm). Again, if your ruler only measures in inches, you need to convert to millimeters.

Measuring depth of a recessed spoke holeTo avoid having to remove the rim tape of a built-up wheel, you may measure at the inside of the valve hole, as long as you can see that the spokes rest at the same diameter.

If you measured the circumference of the rim at the well, then measure the depth from the well to a recessed spoke hole, if the spoke holes are recessed.

If you are good at holding objects steady in your hands, you can even do the depth measurement with a bare bolt or bicycle spoke, as shown in the image at the left. Insert the spoke to the bottom of the spoke-hole recess, and slide your hand down the spoke until the fingernail of your index finger rests lightly against the side of the access hole.Transferring measurement from thumbnail to ruler

Then as shown in the image at the right, transfer this measurement to the ruler, resting your fingernail lightly against its end.

The dimension you measured using the bolt or spoke is a difference in the radius --the distance from the center of the wheel to the outside. Spoke calculators use the diameter, which is twice the radius, because there's nothing to measure at the center of an empty rim. So, as you move on to final calculations, you'll be subtracting twice the depth you measured with the bolt or spoke.

Berechnung des Einspeichdurchmessers

Now you need calculate the spoking diameter. Get out your pocket calculator or smartphone app (or a paper and pencil if you're retro or the battery is dead).

We'll calculate our spoking diameter using both of our sets of measurements, and see how the results compare.

The measured outside diameter of our rim is 20 7/8 inches, or 20.875 inches. Multiplying by 25.4 gives 530.2 mm. The measured depth from the outside of the rim to the spoke hole is 11 mm. Twice that is 22 mm, and so the spoking diameter measures as 508.2 mm.

The circumference of the well measures as 64 1/8 inches, (64.125 inches). Multiplying by 25.4 converts to 1629 mm; then dividing by pi, the diameter at the well is 518.5mm. The depth of the recessed spoke holes is 5mm; twice that is 10mm and so the spoking diameter measures as 508.5mm.

So, we got 508.2 mm by measuring the diameter and 508.5 mm by measuring the circumference. Close enough!

Finally: If you measured over the tops of spoke nipples, you are done. If you measured an empty rim, add twice the height of a spoke nipple -- about 4mm total. This measurement should agree with the one according to Damon Rinard's method (see below).

Damon Rinards Methode

Damon Rinard describes another method to calculate rim diameter, but I think it is more complicated.

Sutherland Felgendurchmessersystem

The handy Sutherland Rim Diameter System simplifies measurement of the rim. By using a tape with a special scale, this system calculates the diameter for you -- saving time, and time is money if you build a lot of wheels. The Sutherland system includes a tool to find the effective rim diameter for spoking.

Howard Sutherland demonstrates the Rim Diameter System in the video below:

Die Nabe messen

To determine spoke length, you also need measurements of the hub: the diameter of the circle of spoke holes, the diameter of a spoke hole, and the flange spacing from the centerline.

Der Speichenlochkreis und der Speichenlochdurchmesser

Hub flange dimensions

The axle gets in the way when measuring the diameter of the circle of spoke holes (d in the image at the right). The spoke hole diameter (S) also affects spoke length.

The traditional way to measure the spoke hole circle diameter is with a caliper, as shown in the image below, center to center of the spoke holes, but it's easier to measure from the right side to the right side, or left side to left side. You can't get a "contact" measurement this way, but inaccuracy of a small fraction of a millimeter isn't going to be important here. If you're a real stickler, you could insert the outside-measuring blades of the caliper into the spoke holes to take a smaller measurement, and the inside-measuring blades (at the top in the picture) to do a larger measurement, then take the average. Subtracting the smaller from the larger measurement and dividing by two would also give you the diameter of the spoke holes -- but that is usually 2.5 to 3 mm, and the resulting difference in spoke length isn't large enough to matter.

Measuring hub flange diameter with a caliper

improvised measuring tool You don't need a caliper. You could cut a C-shaped recess in a piece of cardboard, mark the spoke-hole spacing as shown in the photo at the left, and then measure it with a ruler.

Flanschabstand von der Mittellinie

A hub flange farther from the centerline requires longer spokes, but only slightly longer with most wheels because the spokes approach the hub at a high angle.

Usually with a front wheel or the left side of rear wheel, you can go with a typical spacing of 35 mm, and with the right side of a rear wheel that has multiple sprockets, 20 mm.

The drawing below is of the same hub shown in the previous two photos (a SRAM DualDrive hub, a 3-speed with a cassette body for hybrid gearing). The dimension in red is the OLD (overlocknut distance), and the dimensions in blue and green are the flange spacings. They are very near the generic ones already given. Drawing of DualDrive hub showing flange spacing

With unusual hubs, and especially with a large hub in a small rim, you must measure the flange spacing, or read dimensions from hub specifications. If both flanges are the same distance from the centerline, measure the spacing between the flanges and divide by two. If the two flanges are different distances from the centerline, measure them independently. Resting the locknut against the edge of a workbench or table makes measurement easier. An example is shown below, using the same hub.

Both ends of the hub are measured. First, let's measure from the right end. The right flange is 50mm to the left of the right locknut, and the left flange is at 100mm to the left of the right locknut.

Measureing flange spacing

Next, turning the hub over and measuring the other end, the left flange is 35mm from the left locknut.

Measuring flange spacing

Calculating now, the overlocknut distance is 135mm, as in the manufacturer's specification in the drawing above. Half that is 67.5mm. The right flange, at 50mm from the right locknut, is 67.5-50mm or 17.5mm from the centerline of the hub and the left flange at 35mm from the left locknut is 67.5-35mm or 32.5mm from the centerline. These measurements are not an exact match for the manufacturer's specifications, but are close enough for all practical purposes.

Some rims have spoke holes closer to one side than the other, to reduce dishing when the hub has unequal flange spacing. Then subtract the offset of the spoke holes from the hub flange spacing of the same side as the offset, and add it to the hub flange spacing for the other side. For example, if the left flange of the hub is 35 mm from the centerline, the right flange 20 mm from the centerline and the spoke holes in the rim are offset 3mm to the left, then the effective flange spacing is 32mm on the left and 23mm on the right.

Damon Rinard has another description of hub measurements on this site.

Jetzt zur Speichenlängenberechnung

The final measurements you need to calculate spoke length are

  • Number of spoke holes
  • Spoke hole circle diameter of rim
  • Spoke hole circle diameter
  • Hub spoke hole diameter
  • Spacing of right hub flange from centerline
  • Spacing of left spoke flange from centerline
  • Intended cross number

Spoke length calculators are online or downloadable.

Some spoke calculators, including Damon Rinard's Spocalc on this site, perform only the mathematical calculation described earlier in this article. Other spoke calculators account for the stretching and seating of spokes and shrinkage of the rim in a tensioned wheel -- about 1 millimeter of spoke length in a typical wheel. If the spoke calculator already accounts for tension, then specify spoke length based on where you want the ends of the spokes to reach.

Messwerkzeuge und die Genauigkeit der Messungen

How accurate do your measurements need to be, and what tools are good enough?

Maßband und Lineale

A tape measure to take the circumference of a rim should be 1/4" or 6 mm wide, and must be at least 8 feet or 2.5 meters long to reach all the way around a typical bicycle rim -- longer for oversize rims (32" and 36" wheels, antique high-wheelers...) but you could measure these wheels, or any wheel, using the diameter, or bicycle cable as described earlier.

Generally, metal rulers with etched markings are highly accurate, and tape measures of reputable brands (Stanley, Craftsman etc.) are accurate enough, but do check yours against an etched metal ruler -- and the longer the ruler, the better. A tape or ruler of plastic, fabric or wood cannot be trusted. Plastic and wood expand and contract with changes in temperature and humidity; fabric also stretches.

Speichenlänge prüfen

Spoke length is measured from the inside of the elbow, as shown in the image below, to the threaded end.

When measuring a spoke using a tape measure, a second spoke may be used to hold the elbow of the spoke and the tape measure's tab, as shown.

measuring a spoke

The threaded end of this spoke measures at 11 29/64 inches (halfway between the 11 7/16 and 11 15/32 marks on the measuring tape). A metric tape would make measurement easier, but let's calculate: 29/64 is 0.453125, and so the length measures as 11.435125 inches. (Yes, I know that the number of decimal places exceeds the precision of measurement, but digital calculators give you the extra digits at no extra cost.). Multiplying that number by 25.4 to convert to millimeters and lopping off meaningless decimal places gives 290.9mm. The ruler and the manufacturer's identified spoke length agree very well.

Spoke length measurement

Fehler undiIhre Effekte

As long as your tools are good, selecting the wrong spokes for a wheel is more likely to result from an outright mistake than from a measurement error. Though you should always measure carefully, wheel measurement is more forgiving than you might think.

Errors in measurement of the rim's diameter result in only half as great an error in spoke length. Deriving the diameter from the circumference improves accuracy further by more than 3 times.

With common wheels, errors in flange distance from the centerline are of minimal importance: a 1 mm change in flange distance results in only about a 1/10 mm change in spoke length.

The importance of the hub spoke hole circle diameter depends on the spoking pattern. With a radial spoking pattern, spoke length changes at half the rate of the diameter of the hub flange. With higher cross numbers, the effect on spoke length becomes smaller and smaller. With a 36-spoke cross 4 pattern, the spoke holes are 90 degrees away from those in the rim, and the hub spoke hole circle diameter hardly matters at all. A 36-spoke cross 4 pattern pattern is a good choice when the hub's dimensions aren't known or with flanges of different sizes. With both wheels spoked this way, a bicycle tourist would need to carry only one length of spare spokes, despite different flange sizes on the front and rear hub, etc. etc.

The table below summarizes the effects of measurement errors.

Effect of measurement errors Measurement error in: Spoke length will be off by this many times the error: Note Rim circumference 1/6.28 (1/2π) This is the most accurate way to measure for diameter. Rim diameter 1/2 Must be measured at several angles and averaged Depth from measured rim radius (1/2 diameter) to spoke hole 1 This is a difference in radius and applies to each spoke. Hub flange spacing from centerline About 1/10 Error becomes worse for small wheels/large flanges. Hub spoke hole circle diameter Usually small, but up to 1/2 Small for high cross numbers, 1/2 for radial spoking. Spoke hole diameter 1/2 Unimportant because spoke hole clearance is small. Tensioning compensation -- Spokes will be effectively about 1mm longer when tensioned.

For typical wheels, random errors dominate, but for larger wheels, and particularly, very large wheels such as on antique high-wheeler bicycles, proportional errors -- from the scale of a measuring tape being slightly to large or small, and from spoke stretch under tension -- become important.

The ends of the spokes of a fully-tensioned wheel come to somewhere between the bottom and top of the slots in the spoke nipples. Properly-tensioned spokes stretch by about 0.3%, and rims compress slightly -- so, the 250-300mm long spoke in a typical large bicycle wheel needs to be about 1mm shorter than raw calculations would indicate.

The range of spoke lengths which avoids these problems is about 3mm. The tolerance has become smaller in recent years, because short spoke nipples and matching short threads are fashionable to reduce aerodynamic drag.

Falls Speichen zu kurz sind oder scheinen

  • bending spokes overthe hub flangeSpokes at the outside of the hub flanges may appear too short when lacing the wheel if they bow outward. You may need to tap on spokes lightly with the flat face of a hammer or mallet just outside the hub flange to straighten them so they reach the spoke nipples.
  • A spoke which is too short, or has long threads, will leave threads visible outside the nipple.
  • If the rim covers much of the nipples' length, long nipples may be required so a spoke wrench can reach the nipples' wrench flats. Longer threads prevent a spoke with short threads from screwing in all the way, so check for compatibility.
  • If a spoke does not extend into the head of the spoke nipple, then the weakest part of the spoke nipple is in tension and the nipple is at risk of breaking. Brass spoke nipples are much stronger than aluminum ones and are more likely to survive this abuse.

Wenn Speichen zu lang sind

  • If the spokes extend into the screwdriver slots when the wheel is under light tension, you can't use a screwdriver for initial light tensioning of the wheel. This first warning that the spokes are too long comes after you have laced the wheel.
  • If the spokes of the tensioned wheel protrude from the tops of the nipples and the rim has non-recessed spoke holes, you'll have to file the spoke ends so they don't puncture the inner tube.
  • The threads may also reach their limit and bind, so you won't be able to tension the wheel. You'll feel the spoke twisting instead, as you try to turn the nipple with your spoke wrench.

The threads of all four spokes in the image below extend equally far. The leftmost nipple is threaded on until the threads start to bind. The next spoke nipple is threaded on until the end of the spoke is level with the top of the nipple's screwdriver slot, as far as it can go without risk to the inner tube. The rightmost nipple is threaded on only far enough to conceal the threads of the spoke, risking nipple breakage. Comparing the leftmost spoke with the bare one shows that the internal threads of the nipple extend down about as far as the base of the wrench flats.

Speichenlängentoleranzen

I thank Roger Musson for permission to use the photo below, with cross-sectioned spoke nipples. The spoke threads are the same length in all three examples, but the spoke nipples are of different lengths. A spoke can be threaded in only until the red line in the picture reaches the bottom of the threading in the spoke nipple. Beyond that limit, it will bind. The combination on the left risks breaking the spoke nipple just below the head, because the spoke does not extend up into the head of the nipple. Only the short spoke nipple at the right is really suitable for the spokes shown.

Siehe auch

Quelle

Dieser Artikel basiert auf dem Artikel [Measurements for Spoke Length Calculations https://www.sheldonbrown.com/spoke-length.html] von der Website Sheldon Browns. Originalautor des Artikels ist John Allen.


Roger Musson -- wheelbuilding book, spoke calculator