Simple question as the title implies...how accurate are the distances(and thus the speeds) that they give you?

I don't have any flat routes to base it off of but I just got back from the gym and after a 1/2 hour, it said i was averaging 24mph. I did wear my old cycling shoes w/o cleats & used toe-clips. I can generally average(when I peak fitness wise) at about 20 mph on a rather hilly route, but I haven't really ridden since I came back to school in September.

Are they really dead on or is there some sort of fluctuation like you see with exercise bikes that have electronic resistances?

depending on what you are doing on the spin bike, and what you are attempting to compare it to on a non-spin bike... that's a lot of variables.

in general I'd say, "not especially"

If we're talking the bikes they use in spin classes, the answer would be not at all. Obviously ,just how far you turn the resistance dial would have a huge effect.

I would completely ignore speed, "gear", or anything like that.

Probably the only things I would pay attention to are watts and cadence. Some bikes, like the Keisers we recently got at work, also give a kcal (kilocalorie) number. I just wonder how accurate these numbers are.

Correlations with in-road vs trainer or spin bikes are notoriously incongruent. Even with the best, power-calibrated trainer or indoor bike, you'll have significant variation from outdoor conditions due to airflow, aerodynamics, road conditions, weather, etc. Even my KK trainer, which is probably the highest regarded widely-used trainer out there, which allegedly mimicks road acceleration, is different than road riding - mainly because the roads are so diverse (it's not the trainer's fault!) Unless you ridea perfectly flat, straight stretch outdoors, the results will vary significantly indoors vs out.

On the bright side, you can definitely tell you're improving if you're putting up better numbers between indoor sessions, since those should be very reproducible indoors. I compare my trainer numbers against prior trainer numbers/HR, and that's a good marker for me, but I don't compare them to outdoor rides (I've tried, but it's simply too variable.)

The Keiser M3 Spin bike computer also has a distance display, but it doesn't even tell you what unit of measure it uses! I know I didn't ride 26 miles in 50 minutes during class! I checked Keiser's website and there isn't any info or specs about the computer except that you can use a Polar wireless heart strap.

Sure you did. Obviously, it was just simulating a downhill section...

It might be very accurate in calculated distance, just not at all realistic. IOW it may be using a simple distance calculation, but not take into account air resistance. 24mph average for a half hour would not be too tough with zero air resistance and no hills.

The gym I am a member at has the Keiser M3 indoor bikes and they are great. Our instructor references WATTS and then RPM's, to keep the class on the same path. I often times question the corrolation of spin to live riding, and there are too many variables that are alive on the open road and not in a cooled, indoor, spin room to think they are one in the same.

I have pushed myself to spin for one week, and then ride and do weight workouts the next, until I get firmly back on my bike.

grumble grumble.. you lucky SOB.. mumble grumble...

Heh.. but seriously,

Just curious, but does the instructor want everyone to shoot for the same wattage? I'm no instructor myself, but whenever I "lead" an impromptu class, I just tell them to pick a range of resistance and then have them go light, medium, or heavy (etc), and then to stick within a cadence range (sometimes faster or slower, too). I'm not going to expect a 130-lb kid to put out the same watts as an ex-rugby player, though.

Anyway, just an honest question..

I'm even suspicious of the wattages the spin bikes give. We just got new ones at my gym, and I use it to cool down after lifting. Based on HR and PE the wattages it gives me are WAY too high compared to my powertap. KJ's seem off by at least a factor of two as well.

Our Keiser M3 at work measures in km.

What I want to know is there a calculation to determine what "speed" a certain rpm at a certain resistance is? And yes, to the obvious since I am on a stationary bike the speed is zero. True, but not helpful. Our fitness center is doing an indoor triathlon and I am on a relay doing the biking leg. Since I am not good enough to keep a perfect rpm for a set amount of time and then plug in the distance recorded, I was looking for a chart or calculator.
Thanks,

How do they determine the resistance on the spin bike. Why couldn't you just put the resistance to nothing and spin at 150rpm?

The cadence number displayed on a spin bike is probably accurate. However, compared to a road bike, the cadence number is not the same, since a spin bike has a flywheel and is in effect a fixie on the flat. I usually figure a cadence shown on a spin bike is 10 rpm higher than the equivalent spinning effort on a road bike. I can hit 150 easily on a spin bike, but have trouble getting over 135 on a road bike. Of course watts, speed, distance, and calories are also only useful for comparison between spin bike sessions.

The resistance has to be set at 10. I did find this info finally on Keiser. Must have missed it the first 5 times I looked.

The M Series Computer is a powerful teaching and programming tool. It can assist both the instructor and the participant by providing immediate feedback as well as the ability to track on-going improvement. The M Series Computer displays:
1 – Backlight Sensor – The Backlight Sensor automatically detects ambient light levels in the room and turns on the Backlit Display when needed.
2 – Cadence (RPM)
3 – Power Output (Watts/Kcal)
4 – Heart Rate (HR)
5 – Elapsed Time
6 – Current Gear (Resistance Level)
7 – Odometer / Trip Distance
The Computer gives accurate and precise information instantly, and automatically. It will also display average ride calculations and total distance that has been put on the machine.
The Trip Distance feature was initially intended to be used by gyms and facilities to record how much an M3 was used for a given time frame. The odometer does not reflect distance in terms of miles or kilometers, rather something in between. For every 200 turns of the crank arm the distance will reflect as 1.0 on the display. In the future, we may revise the computer’s algorithm to display a more recognizable distance, which will also be influenced by a rider’s pedaling effort or Power.”

Speed and distance is exactly zero. If it says anything else it's wrong. Only thing that matters is level of effort and duration.

That would appear to be grossly unfair. At 200 lbs, I'd clean up in that competition, putting out more power than the light guys, but with a lower w/kg.

I don't know, my Garmin usually shows a few hundred feet, and a fraction of a mph for most of my trainer workouts.

The main purpose of the spin bikes for me is intervals and training for climbs. There is not any really hilly terrain in my immediate area. I can set the resistance where I want it and then climb until I run out of gas. Same thing on the intervals. The machine forces me to keep up an effort I might not do on a regular bike. Also, you can plug in a smart phone and ride a downloaded route if you desire. As someone stated previously, even if the data is not that accurate you can track progress over a period of time. Similar to a set of weight scales. They may not be that accurate, but they at least can tell if you are gaining/losing weight.

Funny you should mention 200lbs since that is what I weigh. I was trying to calculate what rpm I needed to maintain to beat the best distance(which is currently 5.59 miles for the 15 minutes, but the trainer is mistakenly interpreting the readout as km and converting to miles.)

Thanks Looigi, I knew someone would point that out.

At best, cadence and power are accurate. The rest is garbage on any stationary bike. If you want to use it as a relative scale compared to other efforts on the same bike, that might not be totally useless.

Traditional "spin" bikes that use a flywheel and friction resistance can't report anything meaningful except cadence and time. Stationary exercise bikes that use magnetic resistance have the potential to provide reasonably accurate power readings, but the achieved accuracy depends on the quality of the calibration. If you know power accurately, you (or the bikes computer) can correlate that back to speed on a road bike under specific conditions. One of the big variables is rider weight, so if the computer doesn't ask you to provide that, everything it's telling you (except time and cadence and watts) is a WAG (wild-ass-guess). Conditions also include rider CdA, road surface, air temperature, and barometric pressure. If you don't know what the speed computation is using for those variables, you can't really make any on-road comparisons.

So using this info, 5.59 "miles" that was recorded is equivalent to 9 "kilometers" on the "odometer". For 15 minutes that is an rpm of 120. I need to exceed that for the full 15 minutes to be certain of beating that mark. Also, apparently the M3 stops recording and flashes slow down if your rpm exceeds 140. I will try to test that sometime before my session. I would like to try for 130 rpm for the full 15, but not sure how realistic that is...

any idea what wattage that is?