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Post by ffestiniogsoapbox on Apr 13, 2014 2:32:03 GMT
www.facebook.com/pages/Bodrodz-Xtreme-Gravity-Racing/687754924576556"2014 BODRODZ NEED FOR SPEED CHALLENGE" link"It's official, the 2014 Need For Speed Challenge is on now! Current Top Speed: 84.4 MPH Atomic Splinter Atlanta, GA This challenge is open to all gravity cars". So we have one potential challenger from the uk. What are we looking for ? What length of run / steepness of gradient to achieve 80+ mph ? Perhaps we need to have a technical discussion - ukgsa forum ? And yes, plenty of big hills around here (snowdonia) for an early morning run. We would be happy to help. Perhaps a Cartie Sim would be helpful. cheers, Steve P.
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Post by woody on Apr 13, 2014 7:28:40 GMT
My favourite course would be Crimea Pass , from the top down to roman bridge , dont know how quick a soapbox can go down there but my pug 406 would roll from a standing start to 90 mph ! our soapbox only got 45mph but i think that was because it had the drag of a garden shed !
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Post by Scottish Cartie Association on Apr 17, 2014 13:54:38 GMT
First off, and most importantly, you're going to need access to a private road or a public road that has been closed for the purpose with the permission of the relevant authorities.Assuming you've done that, then the key things you'll need are length and straightness. It takes a surprisingly long distance to get up to terminal velocity, and any bends that you need to slow down for will hinder you. Unfortunately, as roads get steeper they also tend to get twistier, and you'll need to be lucky to find anything steeper than about 10% that is straight enough. At 10% gradient, it'll take somewhere around 4Km to reach your top speed, and of course you'll need to slow down and stop afterwards. So you're looking for about 4.5 to 5Km of very straight road at a gradient of about 10%. The other thing you'll need is elevation, since the higher you are, the lower the air density. This makes a significant difference. You'll go faster at 2000m than you will at sea level. You'll also need a very quick cartie. The difficulties in reaching that sort of speed should not be underestimated. You'll need a mass to drag area ratio (M:CdA) of at least 1000 Kg/m2. Bodrodz did their fastest run on the Burkhalter Gap Road just south of Chattanooga, which is about 4Km at an average of 9% and finishes about 1000ft above sea level with a slightly uphill run out at the end. Based on their quoted top speed I've used SCA CartieSim to estimate that they have an M:CdA ratio of about 1050 Kg/m2. And finally - if you want any kind of credibility then don't measure your speed with a GPS. GPS speed measurement is problematic at best, and some consumer GPS are shockingly inaccurate. Your phone, for instance, will almost certainly be using some form of averaging and filtering to give the appearance of an accurate and stable reading, but the reality is that it will be a processed figure which may well be quite good for measuring relatively constant speeds but less accurate when measuring rapidly changing speeds. If your GPS uses doppler speed measurement it is potentially very accurate. If it uses time and distance calculations to get an instantaneous speed then it is likely to produce wildly variable results. For a better verification I'd be looking for a GPS logged run at a minimum of 1Hz including time stamps, latitude, longitude, position, elevation, speed, number of satellites, horizontal and vertical dilution of precision at least. Preferably from two separate loggers. The gold standard for speed verification would be using break beam sensors or similar to time the cartie over a fixed known distance of at least 50m. To be honest I'm pretty ambivalent about the whole thing. This "challenge" won't show who has the fastest cartie. It'll show who has the longest, steepest, highest and straightest hill. Or - more likely - the person with the most wildly inaccurate GPS. So - that's what you're going to need. I suspect the hardest part of it is going to be finding a suitable road and then getting permission to close it. Good luck.
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Post by ffestiniogsoapbox on Apr 17, 2014 22:33:58 GMT
Nice one Stephen,
Good technical info to give some perspective. Thank you.
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