diff --git a/client/bicyclesim-meteor.html b/client/bicyclesim-meteor.html
index 4ac9480..7fbe388 100644
--- a/client/bicyclesim-meteor.html
+++ b/client/bicyclesim-meteor.html
@@ -101,6 +101,8 @@
           <legend>Asetukset</legend>
           <label>Liikekerroin. Vaikuttaa kuljettuun matkaan mutta ei nopeuslukemaan.</label>
           <input type="text" value="{{settings.multiplier}}" id="settings_multiplier"/>
+          <label>Renkaan koko, tuumia</label>
+          <input type="text" value="{{settings.diameter}}" id="settings_diameter"/>
         </form>
       </div>
     </div>
diff --git a/client/lib/settings.js b/client/lib/settings.js
index 4a48fa4..9abd16e 100644
--- a/client/lib/settings.js
+++ b/client/lib/settings.js
@@ -10,11 +10,21 @@ window.settings = {
   'staticmaps_key': 'AIzaSyDtGhiAnSdg9TaGZC_daNcQe43BS8Ws7Iw'
 };
 
+window.c = function () {
+  return Math.PI * localStorage.diameter * 2.54 / 100;
+};
+
+if (_.has(localStorage, 'diameter') && !_.isNumber(localStorage.diameter)) {
+  delete localStorage.diameter;
+}
+
+
 if (_.has(localStorage, 'multiplier') && !_.isNumber(localStorage.multiplier)) {
   delete localStorage.multiplier;
 }
 
 _.defaults(localStorage, {
+  diameter: 28,
   multiplier: 2.5
 });
 
diff --git a/client/main.js b/client/main.js
index b8eb22d..fe5dfc3 100644
--- a/client/main.js
+++ b/client/main.js
@@ -83,6 +83,9 @@ Template.settings.settings = function () {
 Template.settings.events({
   'change #settings_multiplier': function (event) {
     localStorage.setItem('multiplier', parseFloat(event.target.value));
+  },
+  'change #settings_diameter': function (event) {
+    localStorage.setItem('diameter', parseInt(event.target.value, 10));
   }
 });