We’ve covered this before, but it was in the old forum so I can’t search on it.
I’m choosing a cassette, and I wondered what top speed do I really need? I’ve almost entirely on the flats so I want a really tight cassette.
A 52x12 at 115 cadence gives about 41 mph. A 52x11 at the same cadence gives about 44.8 mph.
It seems that at 41 mph I should tuck in and rest for a little while. I wonder if continuing to pedal up to 44mph is really going to help that much.
my guess, it’ll help you by about 3 miles an hour on the bike.
Stop pedaling? No way. I say keep it in the 52x11 and keep cruising at 44.8 the whole race. You might considering bumping your cadence up to 120 though, 115 is really kind of wimpy on the flats, unless you’re in a really big gear with a headwind, then it’s ok to back off to 115 in the 11.
I’ll assume you’re referring to descending, and not riding in the flats (please tell me this is the case so I don’t have a complex about riding at 23 mph). I don’t have wind tunnel data to back this up (:-), but I’m suspecting that descending at 40+ mph you are better served cutting wind resistance by getting the cranks in the 3’ and 9’ position and getting low than by continuing to pedal. I also seem to remember reading this somewhere, but I don’t remember where.
Races aren’t won on descents. I’d stick with the 12 as your smallest cog. That way you can have tighter gearing and/or a larger cog for climbs.
Thanks Pooks. That’s where I was going with my post when my brain rudely interrupted me with something enrirely irrelevant and I forgot to finish my train of thought. I totally agree that whatever slight benefit you’d gain from an 11 is probably outweighed by the benefit of tighter gearing.
It’s pointless to pedal above about 35 mph. You’re using up huge amounts of energy to overcome an exponentially rising wind resistance. As you crest a hill, keep working to get back up to speed. Once you’re over 30 mph on the descent, tuck in and get some free time and rest a little.
On a 3-mile descent, 38 mph versus 35 mph saves you all of 23 seconds. Hardly worth blasting your legs over during a 5-minute free ride. The rider that coasted at 35 will pick up those 23 seconds at the bottom in no time.
I hear people talk about going over 50 m.p.h. on their bikes on a descent and have never gone that fast. My top speed has never gone above 47 m.p.h. according to the maximum speed memory on my Cateye. I totally whiped at 47 m.p.h. once too. Not pretty. Anyway, there is a website called “analytical cycling.com” or some such thing where they have this calculator you can enter a gear combination and cadence and it will give you a speed: For instance, 53/11 at 105 r.p.m will result in 39.5 m.p.h. (I’m pulling that number out of thin air- it isn’t accurate, just an example). so that may be of some help. If it isn’t, just do what I do: Stop pedalling, close your eyes and hang on… One way or another you’ll eventually get to the bottom.
Top speed on a bicycle: Saluda Grade Road in North Greenville, SC. Two of us, neither pedaling, but switching out drafting one another down this cliff. It’s really quite hair-raising! As you get behind the guy passing you, the draft area is fairly long. You just stay tucked and then you begin to accellerate rather quickly right up behind the leader…you have to be quick to make sure you don’t touch because you are really accellerating fast, and you switch places. It was fun, and it shows any handling weaknesses! I don’t relish the idea of a wobble or vascillation starting at those speeds.
Oh, back to the question. It’s really no question for me; I tuck. If I ever wonder about it, though, I’ll pedal hard for 4-5 strokes and tuck again. This usually convinces me to just stay tucked! Lots of energy spent for very little gain at high speeds. I consider 35mph to be high speed in a triathlon. In a road race, I might do differently just trying to out-think the other riders, or to get an accordion effect started to shake the pretenders out.
Yes, I’m talking about descending. I don’t even dream 30 on the flats.
I seem to remember somebody saying something about 35mph being a pretty reasonable cut-off. It just makes sense. At 115 cadence, wheel diameter 0.704m, a 52x13=37.93mph. (Is the wheel diameter correct for a 700c wheel?)
So why would I ever want anything smaller than a 13? Even my small ring 42x13 is just over 30mph. I’m about to buy a new cassette (my first gearing change) and I was going to buy a 12-23 but I don’t see why I shouldn’t just use a 13-23. I’ll have to look and see what the differences are in the middle gears.
Tom D: “I hear people talk about going over 50 m.p.h. on their bikes on a descent and have never gone that fast.”
I hit 51 mph on the big downhill at Lake Placid. That was after spinning out in my 53*12, and then lying as flat as possible, with my butt hanging off the back of the bike (my stomach was on the seat). 404 in front, disc in back. In the pouring rain. I was so pissed at how my ride was going by then I didn’t care what might happen to me.
I once hit 61 mph on South Park Drive in the Berkeley Hills without really trying to. That is my speed PR.
Your math is a bit off. That cadence and speed would get you to about 35.8 mph. The rollout distance of my 700 wheels is 2094 mm. Dividing by pi gives you .6675m.