*rt* said:
maybe the spin bike you were on isn't calibrated correctly because based on the math if you go 18 mph you should cover 3 miles in 10 min (i.e., if i go 3 miles in 10 minutes how many miles would i go in an hour? there are 6 10 minute periods in an hour, so multiply 3 (miles) x 6 and you get 18 mph).
i'm not familiar with this exercise. is it meant to be done on a trainer (or spin bike)? or it is assumed that you're going to get out on the pavement on a road bike? i suppose on a trainer with a correctly calibrated computer you could spin at 18 mph for 10 min but, IMO 18 mph is not a beginner's pace. particularly if the exercise is meant to be done on the road using a road bike (using a mtb it would be even more difficult because of increased rolling resistance and less advantageous gearing). i would think that 3 miles at 18mph would be sprint pace for most beginners.
just my $0.02
rt
IIRC it is a fitness evaluation test, to be peformed on a road bike, flat, windless day, well rested and warmed up. It should be at "race" pace.
If you are following the LA programs, I'd suggest by starting off with the beginner weight loss plan (9 weeks to lose 10 lbs) this will get some structured riding in (40-80 miles week) to adapt your body, and you *will* drop some lbs. Then, try the fitness test, and move on to an appropriate "development" 7-week plan. If you start now you'll be in good shape for spring!
Tying in with what rt said, I do a 20 mile relatively flat loop sometimes at lunch as a workout (ie not at "race" pace) and I do it ~3-4 mph faster on my roadbike (avg. ~20 mph) vs. my locked out FS MTB (avg. ~16 mph) with the same or just slightly more perceived effort...so if you are trying the road test on a MTB, I'd say 18 mph roadbike pace = about 15-16 mph on a typical MTB as far as "equivalent" effort. I keep my cadence in the low 90's on road for the most part. When I did TT's many moons ago in HS and college my cadence was more around 105-110. So have a look at your cadence and see if it is too slow, this could tire your legs out prematurely causing a slow time on the test.