Quadriceps pain after mile 30

"quadriceps pain."

Do you mean cramps? If so, that's been beat up in here: replace lost electrolytes. OR it could be that you are mashing big gears for too long. The possible remedies are numerous. Learn to like pedaling fast(er) not just to recover from the pain, but as a rule. Get fitted professionally. It may be your positioning on the bike (coupled with your gearing). I can only assume from your post that having to "slow down" and spin @ 110 rpms implies that you were at some lower rpms, higher speed, which = bigger gearing.

What gearing ratios (& speed) are you typically in when your quads start hurting?

FrankBattle said:

"quadriceps pain."

Do you mean cramps? If so, that's been beat up in here: replace lost electrolytes. OR it could be that you are mashing big gears for too long. The possible remedies are numerous. Learn to like pedaling fast(er) not just to recover from the pain, but as a rule. Get fitted professionally. It may be your positioning on the bike (coupled with your gearing). I can only assume from your post that having to "slow down" and spin @ 110 rpms implies that you were at some lower rpms, higher speed, which = bigger gearing.

What gearing ratios (& speed) are you typically in when your quads start hurting?

I'm not usually in big gears, that's the thing. I'm humming along at about 21-22 mph in the 2nd (middle) chainring, 3rd or 4th smallest gear on the cassette (of a 9 gear cassette). I'm geussing that I'm spinning at about 90 rpms, too.
That's not very big of a gear. Then, I hit the cramps at mile 30 or so, and then have to back off and let my legs cool off.

AmpedCycle said:

I'm not usually in big gears, that's the thing. I'm humming along at about 21-22 mph in the 2nd (middle) chainring, 3rd or 4th smallest gear on the cassette (of a 9 gear cassette). I'm geussing that I'm spinning at about 90 rpms, too.
That's not very big of a gear. Then, I hit the cramps at mile 30 or so, and then have to back off and let my legs cool off.

42-15 ish. True, you should be fine there. Then I would consider either playing with your seat height or getting a fit done at your LBS. I'll make another assumption that you are drinking enough fluids with the appropriate electrolytes over the 30 miles. If you sweat quite a bit, you probably should go through 2 bottles in that distance. Many need less, some need more.

Not getting the right replacement fluids in you while on the bike could also cause cramps.