SUB-4 MINUTE MILE ATTEMPT....DOWNHILL!!!

BUMP

Ok so here's the deal guys. The only wheel I know of anybody having is my coach, a good gps is expensive I think, and a surveyor might take some time. And frankly I don't want to go out and buy a gps or ask my coach for his wheel because, well, I'm lazy. And plus, if breaking 4 really is as easy as everybody is saying it is, then a few tenths of a second shouldn't matter.

We're gonna stick with the bikes, but what we're gonna do to calibrate them is to ride a mile on the track, which is as accurate as we can get I imagine. We'll do this with two bikes, and then measure the course with two bikes. If there's still any difference, we'll just put the finish in between the two finishing spots like I said earlier.

My new goal, due to the posts stating how much time downhill takes off, is to break 3:50. It should be a good show.

Don't ride a mile on the track to calibrate. You would be much better off riding 100 meters (straight) a few times to calibrate. It will be too hard to keep the bike on the inside line of the track for a full mile. Riding down the straightaway will be easier and more accurate.

Good idea. Thanks dude.

You can usually rent a wheel from a survey shop or a rental store. They typically cost about $15 a day.

There's no reason to rent a wheel. Real certified courses are measured on bikes, not using hand pushed wheels. The difference is that the real certifiers use a counter that clicks many times per wheel revolution and most bike computers count only once every full wheel revolution. You will only be off by a full wheel revolution a most if you have the computer calibrated right.

For the initial calibration on the bike, you can do a rollout of one full revolution along a straight line on the ground with a rider on the bike - the tire pressure and rider weight on that wheel should be as while riding. To help locate a full revolution, put a piece of masking tape on the tire, mark one edge of the tape as the reference mark and set that edge of the tape on the starting point on the ground. Then get on the bike, and follow the line on the ground for one revolution. Get off the bike you can roll the wheel the last few mm to get the exact roll-out distance to the mm. If you repeat this several times, you'll find that you can be confident of the rollout to within a mm or so. Look at the bike computer instructions on how to input this rollout distance.

Then you can check the result along a 100 m straight section of a track as suggested above. To get the measurement closer than one wheel revolution, set the wheel on the starting line so that the wheel magnet is just on the side of the pickup so that you will have to do almost a full revolution before passing the pickup for the first time. Always use this as the starting position. Reset the odometer. Roll the 100 m. You can mark the partial wheel revolutions needed to turn the numbers over. Conversion factors to use: 1 mile = 1609.344 meters (exactly)

If you don't want to bother with partial wheel revolutions, you can be up to two wheel revolutions off or about 4.2 meters. Measure the distance about 6 meters (adding .1 percent or 1.6 m) longer than a mile to make sure that the course isn't short.

The Dude1 wrote:

Don't ride a mile on the track to calibrate. You would be much better off riding 100 meters (straight) a few times to calibrate. It will be too hard to keep the bike on the inside line of the track for a full mile. Riding down the straightaway will be easier and more accurate.

The Dude1 is right. Also, a track isn't supposed to be measured at the inside lane. I think most tracks are measured 8 inches from the line/rail, but I can't remember for sure. There is at least one expert on this topic on the boards, but all of a sudden I can't remember his name.

Calibrating on the straights is a much better idea.

My high school cross country coach always had us run downhill as a peaking workout. My sophomore I ran a downhill 800m in 1:59 (ran 2:12 the year before and 2:05 that spring)over a course that was about 65 feet downhill. Senior year I ran a 4:26 1600m (ran 4:30 the year before and was injured that spring) on a course that was only about 60 feet downhill. 200ft down seems pretty crazy, seems like you should have no trouble breaking 4:00. My only suggestion would be to mark out quarter miles (or even eighths of miles) because it will be very important mentally to have those checkpoints. Also, I would go out a lot slower than you think you should. When it's long, straight and downhill it's hard not to go out too fast. In my 800 I split 55, and then 64 and in my 1600 I split 2:09, 2:17. Good luck.

Generic pooch wrote:

If you don't want to bother with partial wheel revolutions, you can be up to two wheel revolutions off or about 4.2 meters.

Just to be clear about that, you could be off by as much as 4.2 meters EVERY 100 meters! You probably won't be off that much, but you're very likely to be off by at least 1 meter every 100 meters, and that will mean your mile measurement will be off by 16 meters. You will have to bother with partial wheel revolutions on your calibration rides to have any hope of being accurate. But if you do follow that guy's procedure for partial wheel revolutions you will end up with a pretty accurate measurement.

Another option would be to say where you live. There might be somebody with a Jones counter reading this that lives near you and is willing to measure it for you.

Considering that the race is tomorrow night, there is too little time for someone on this board to volunteer to measure if with a Jones counter.

Why are people getting so anal about the distance? This isn't going in any record books. So what if it's off by a percent.

It's because he'll be able to legitimately say he ran sub-4, albeit downhll, so you want to make sure it's right. Just curiousity, why doesn't anyone just go out with a 100' tape measure. I know it's a pain, but at least it'll down to a few inches.

lights, camera, action! wrote:

Why are people getting so anal about the distance? This isn't going in any record books. So what if it's off by a percent.

dukerdog wrote:

Just to be clear about that, you could be off by as much as 4.2 meters EVERY 100 meters!

No, no, no! That's not what I meant. It depends on the particular bike computer and how precise they let you input the rollout measurement, but if calibrated well, the computer should be at least 99.9% accurate for long distances or no more than 1.6 meters off for a full mile. The 4.2 meters that I'm adding is potential error at the start of 2.1 meters (approximate rollout distance of a road bike tire) and another potential error of 2.1 meters at the end of the measurement. Most bike computers use a magnet on the wheel and the computer counts a revolution every time it goes by the pickup. But if you just randomly put the bike on the start line, the magnet will go by the pickup anywhere for the first time between 0 and 2.1 meters from the start line and record 2.1 meters completed when the actual distance is 0 < x < 2.1 That's a one time potential error at the start.

Now that I think about it, the potential error at the finish from this magnet factor can be zero as long as you stop the bike as soon as the computer reads 1.00 miles - slow to a crawl as when you are at .99 miles. So the total error for a well calibrated bike computer is about 2.1 + 1.6 or about 4 meters.

Alright everybody, the distance thing has been settled. We calibrated two bikes around the track one lap and both read out .25 miles a little past 400m (about 2 meters) which was good enough for us. We then measured out the actual course with two bikes and both stopped at the same spot. Also, that very same spot is where google earth said the mile was (well off by 5 feet...but still damn good).

Like posters said before me, it doesn't really matter if the course is 4meters or whatever off. This is all just in fun, and I plan on breaking 4 minutes convincingly enough that the potential error wouldn't matter anyways.

All in all though, thanks for all your help guys. I will now rest up for my big night (did I mention this was gonna be at like at 1am?) and I'll try not to let everybody down with a performance that will haunt me for the rest of my life.

Generic pooch wrote:

No, no, no! That's not what I meant. It depends on the particular bike computer and how precise they let you input the rollout measurement, but if calibrated well, the computer should be at least 99.9% accurate for long distances or no more than 1.6 meters off for a full mile.

I agree. As long as he counts partial wheel revolutions during the calibration he will be pretty accurate for the course ride. I just wasn't clear whether you were referring to the calibration rides or the course ride when you mentioned partial wheel revolutions. Regardless though, I don't think you can measure your bike's rollout distance with your technique to with 2mm (2.1 meters x 0.1%).

Big Wave wrote:

Also, that very same spot is where google earth said the mile was (well off by 5 feet...but still damn good).

Well, like I said, if you aren't going to calibrate your bike properly you may as well just use the Google Earth measurement. I think you'll have to run under 3:56 to be sure you ran a 4:00 mile.

Just out of interest is Google earth accurate at measuring courses? I take it you have to be very careful when marking out the course so that you do not cut any bends off with straight lines?

Google Earth is accurate if you take the time to measure your course carefully. Don't believe me?? Measure your local track and Google Earth--it will be .25 miles.

Hey Big Wave, I am aware of this event and its location--what time exactly will it start: I don't want to miss it? I've heard 1am and 2am???? Which is the correct time?

We don't know yet. Whenever the lights turn yellow so that it would be easier for the car to go down the street and me not worry about other cars. Just call us around 10 or so tonight and we should know by then.

Hell, I've been thinking about trying the same thing for a couple of years now. As I'm in my early 60's I'm going to need a mountain and possibly some wings, but whatever.