Apple Head are now taking entries for our Woralby event on Sunday 22nd July. The event will be held at the small Village Worlaby, North Lincolshire, which is between Grimsby and Scunthorpe just off the A15. We will be running competitions for Soapbox, Sidecar and Gravity Bike.
What a fabulous event! One of the best tracks we have tackled, with a smooth, grippy surface and challenging bends. Fast enough at 51mph to give a thrill and potential to extend the track to make things even better next year.
Great organisation and smiles all round. Definitely one for 2013.
Sorry to double-post, but it looks as though either the OS map or Cartie Sim may need a minor tweak. The quickest sidecar team consistently achieved a sub-52 second time with 50+ mph maximum speeds. The soapboxes were not far behind and the fastest gravity gravity bike ran under 50 seconds. I wonder whether the apparent discrepancy is due to the very grippy road surface that allowed unusually high cornering speeds?
Post by Scottish Cartie Association on Jul 24, 2012 9:10:40 GMT
The calcs were based on ballpark typical figures for drag coefficient, mass, etc for a typical cartie going from a standing start and guesstimates on where the start and finish line were. Clearly the normal push start for a sidehack is going to have a siginificant effect on the times. According to CartieSim, a push start at Worlaby is worth about 10 seconds, which would seem to agree pretty well with your observations. Also, if the start and finish are in different places then the times will be different and perhaps the top speeds too.
Top speed seems to be at the braking point for turn one, so the top speed depends mainly on how late you can leave braking. Good brakes and a grippy corner would certainly help with that.
The "tweaks" needed are the input data (mass, Cd, frontal area, etc) and the elevation profile. The more accurate they are, the better the results will be. Do you have a decent GPS data file with good elevation data? If so, why not load it into CartieSim and see what it looks like? You can alter the lateral grip and brakes to model how that affects top speeds and times.
Edit: Also - a tail wind will make a difference too. The default assumes no wind.
Interesting stuff. Unfortunately, we don't have any GPS data for the Monkey Business sidecar. However, mass is approx 223kg, Cd unknown (not sure how we could measure that - best estimate approx 0.4, but that's probably a bit optimistic), frontal area approx 0.5 sq.m. There was a slight headwind - perhaps 10mph on the run down to the right hand bend. I am sure you are correct that the fastest part of the track was just before the braking point for the right hand bend. We have very good brakes, so can leave braking to the last moment, but as the track was so grippy, we probably only had to knock off 10-15mph to get round the corner.
If this data is loaded up with the current elevation profile, what comes out at the other end of Cartie Sim?
Post by Scottish Cartie Association on Jul 24, 2012 15:16:52 GMT
I must admit that, based on data I have (from either SRTM or ASTER GDEM) I'm struggling to get 51mph top speed while remaining within the realms of the realistic for Cd, etc. The best I can simulate is ~45mph, and that gives a course time much faster than you were getting. I would guess that either the elevation profile is off or - more likely - the start and finish points for the course are wrong. The formula used is shown in the help file so you can, provided you can remember enough of your A-Level physics, check it out yourself. It's pretty straighforward stuff really.
The version of CartieSim I'm using (not released yet) can estimate your Cd for you, but it needs good quality GPS data. The data you normally get from your phone logger, garmin or tomtom is usually way too coarse to be useful. If anyone has a decent set of logged data for their runs I'd be really interested to see it.
Post by Scottish Cartie Association on Jul 30, 2012 10:39:03 GMT
Thanks - I didn't want to say it, but I was struggling to make your speed observations fit with the physics and a badly calibrated speedo did seem to be a possibility.
It's worth mentioning that GPS speedos are not always so brilliant either. If you store your speeds to a file, the speed profile is often quite "noisy". The general trend is accurate, but there are often many unrealistic peaks and troughs, so while average speeds are usually accurate, the "top speed" figure is often rather higher than reality. For an example, check out our GPS logged speed profile from Border Bogies, and in particular how it gets more spikey when we are in the trees.