Your speed on the downhill is dependant on how fast you allow yourself to go. If I see lots of bikes around me then I just ride the brakes on the downhill. The fastest I’ve gone on a downhill on RAGBRAI was 41 mph. I really slow it down if it’s raining. The first few times you go fast on the downhills it may make you uneasy but with time you will get used to it. Stay relaxed and don’t tense up your muscles on the way down.