Speed gains of 650c wheels vs 700c wheels
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2012-11-25 9:57 PM |
Expert 1130 Fernandina Beach, FL | Subject: Speed gains of 650c wheels vs 700c wheels I have a friend who is considering buying a new bike. He has an older QR with 650c wheels. There isn't anything wrong with the bike but thinks the purchase to a newer bike with 700c wheels would make considerable speed gains, which makes some sense to me. Our argument is: I purchased a road bike when we both started with tri's and he purchased this QR. I have since gotten hooked and made the decision to buy my tri bike last year after my first year of tris. He didn't really take to it and does 2-3 local sprints and is MOP swimmer/biker BOP runner. I noticed gains in my first year going from road to tri. I don't think with the limited number of races he does he'll notice that much of a difference just based on wheel size to justify buying a new bike for little to no reason. Long story short, for arguments sake, what gains over 40k could be expected just based on the wheel size? |
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2012-11-25 10:03 PM in reply to: #4509674 |
Expert 1375 McAllen | Subject: RE: Speed gains of 650c wheels vs 700c wheels Wheel size is a physics problem. Because you have a smaller wheel, you'll need less power to get it spinning at the same angular velocity (higher torque). However, it "tops out" a bit sooner than a larger wheel just because you can only spin your cranks so fast, right? Long number crunching short, its easier to accelerate on smaller wheels but once you get going the 700's are faster. You can easily remedy this with a change of your gear ratios. Just a guess take a minute to a minute and a half off the final time. I've never been on 650's though so my guess is poorly based. |
2012-11-25 10:10 PM in reply to: #4509678 |
Champion 10668 Tacoma, Washington | Subject: RE: Speed gains of 650c wheels vs 700c wheels odpaul7 - 2012-11-25 8:03 PM Wheel size is a physics problem. Because you have a smaller wheel, you'll need less power to get it spinning at the same angular velocity (higher torque). However, it "tops out" a bit sooner than a larger wheel just because you can only spin your cranks so fast, right? Long number crunching short, its easier to accelerate on smaller wheels but once you get going the 700's are faster. You can easily remedy this with a change of your gear ratios. Just a guess take a minute to a minute and a half off the final time. I've never been on 650's though so my guess is poorly based. Yes, it accelerates more easily because of the lower moment of inertia, but it doesn't "top out sooner". You use gears the same on either wheel size. Going from a 700 to a 650 wheel size, you lose about the equivalent of 2 teeth on the chainring. Meaning using a compact 50T on a 700-wheel bike is about the same as a standard 52T on a 650-wheel bike. Aerodynamically, it's a wash, unless you're short enough that the larger wheel limits your ability to get into a good position. 700's are not faster than 650's by any means. |
2012-11-25 10:10 PM in reply to: #4509674 |
Champion 10668 Tacoma, Washington | Subject: RE: Speed gains of 650c wheels vs 700c wheels rjrankin83 - 2012-11-25 7:57 PM Long story short, for arguments sake, what gains over 40k could be expected just based on the wheel size? Approximately zero. Or less. |
2012-11-25 10:18 PM in reply to: #4509674 |
Expert 1484 | Subject: RE: Speed gains of 650c wheels vs 700c wheels Fit is king. If the 650c bikes fits and your friend is aero on it, it is worth looking at. I raced and trained on an older Litespeed Tachyon for years, it was a 59cm frame with 650c wheels. I did my fastest IM bike time on that bike. Things to keep in mind with 650c wheels: - If you flat, be self sufficient. Not going to find many people to bum an inner tube off of. - Wheel choices are limited, there are not that many 650c wheels out there. - Used 650c race wheels are cheap. I had several sets of race wheels, sold them all for what I paid for them too. I converted my 650c face to a fixie and love it that way. I even raced a local sprint tri on it fixed, ran a 55x17 gear, put my aero bars back on it and averaged 24.99 mph on the course. I still ride my 650c fixie with the wife, running a 50x17 gear to help keep the spin up and climb the local hills. (TachyonFixie.jpg) Attachments ---------------- TachyonFixie.jpg (49KB - 23 downloads) |
2012-11-25 11:09 PM in reply to: #4509674 |
Expert 1130 Fernandina Beach, FL | Subject: RE: Speed gains of 650c wheels vs 700c wheels My thoughts were little to none. Changing his gearing would be a better, and much cheaper, route. He's convinced that he's slower due to the fact that he has the smaller wheels. When in reality he only rides in prep for a race (3-400 miles a year give or take haha) |
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2012-11-25 11:43 PM in reply to: #4509678 |
Regular 285 Missouri | Subject: RE: Speed gains of 650c wheels vs 700c wheels odpaul7 - 2012-11-25 10:03 PM Wheel size is a physics problem. Because you have a smaller wheel, you'll need less power to get it spinning at the same angular velocity (higher torque). However, it "tops out" a bit sooner than a larger wheel just because you can only spin your cranks so fast, right? Long number crunching short, its easier to accelerate on smaller wheels but once you get going the 700's are faster. You can easily remedy this with a change of your gear ratios. Just a guess take a minute to a minute and a half off the final time. I've never been on 650's though so my guess is poorly based. the smaller moment of inertia of the smaller wheel is going to such a slight difference when taken into account the total inertia of the entire system (rotating and non rotating objects). that is such a small amount though. not only that, but how often are you really accelerating in a TT? and on top of that, the acceleration by be harder, but it will also take longer to slow down, so there will not be as much accelerating. no matter though, the argument is not even worth making as the difference in inertia is so slight. it's not enough to make a single second of a difference on a 40k TT. shoot i could even venture to say that it could decrease your time due to many other factors. no matter what your gear ratio is you can only output a certain power and that power will translate to the road the same way. the bicycle does not become more efficient by changing gear ratios. That is up to you. wheel size alone in no way can make anyone go faster. |
2012-11-25 11:53 PM in reply to: #4509715 |
Expert 1484 | Subject: RE: Speed gains of 650c wheels vs 700c wheels rjrankin83 - 2012-11-25 9:09 PM My thoughts were little to none. Changing his gearing would be a better, and much cheaper, route. He's convinced that he's slower due to the fact that he has the smaller wheels. When in reality he only rides in prep for a race (3-400 miles a year give or take haha) ya, bingo on the lack of time in saddle. |
2012-11-26 4:42 AM in reply to: #4509685 |
Champion 9407 Montague Gold Mines, Nova Scotia | Subject: RE: Speed gains of 650c wheels vs 700c wheels briderdt - 2012-11-26 12:10 AM Approximately zero. Or less. X2. Unless there is some problem with the bike or wheels, for any element where physics would tell us that there is an improvement with a larger diameter wheel, there will be a corresponding trade-off that would make a smaller diameter wheel a better trade off. Physics tells us that there is no free lunch so if an athlete is producing a given wattage on bikes with different wheel sizes, their performance will be within any margins of error for the test. Now, with better tires and latex tubes available for 700c wheels than 650c wheels, your friend should be able to see some speed increases there on the order of probably 1s/km. Shane |
2012-11-26 5:03 AM in reply to: #4509674 |
Pro 5892 , New Hampshire | Subject: RE: Speed gains of 650c wheels vs 700c wheels From the wheels themselves, nothing, no difference what so ever. You may be faster with 650 wheels though if that allows you for a better fitting bike. This is especially common for shorter women, where you simply can't make a well-fitting bike small enough without compromising angles, etc. As noted, you will need to change the gearing to make up for the smaller wheel diameter (note that this will not make it any harder, the effort will be identical to that of a 700c wheel with the corrected gearing). You can calculate about 2 teeth difference (being larger for the 650c wheel, so if you usually ride a 53/39, you would need a 55 front ring) |
2012-11-26 5:47 AM in reply to: #4509839 |
Extreme Veteran 643 , Guam | Subject: RE: Speed gains of 650c wheels vs 700c wheels OP--all of the above intel is/was the reason I bought a 650 wheeled bike 30yr ago. Back then it just made sense to me that a smaller wheel was an advantage. I too ran a Litespeed with 650cc wheels (still have it, is for sale now) for years til I bought a custom Litespeed build to my specs. All the advantages of a 650 wheel are countered by above mentioned disadvantages. To this day I'm not sold that a 650 wheeled bike is better. A 650 wheel built specifically for A rider (weight/power) is going to be way lighter than a 700 wheel built for that same rider. (Back in the day we would build/spoke wheels for each individual rider). A much lighter wheel is going to climb and accelerate way faster and have less wind resistance than a 700 wheel. BUT, IMO the chronic disadvantages of the 650 being an ODD/non standard size wheel is the reason I now ride 700 wheeled bikes after 50yr of riding. Just my opinion. Disclaimer--I am just an old tri converted roadie with NO engineering degree. Summary--drink the kool aid and stick stick with 700cc Hope this helps |
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2012-11-26 6:34 AM in reply to: #4509674 |
Expert 1375 McAllen | Subject: RE: Speed gains of 650c wheels vs 700c wheels 650 wheels are lighter |
2012-11-26 10:06 AM in reply to: #4509674 |
Champion 7136 Knoxville area | Subject: RE: Speed gains of 650c wheels vs 700c wheels fastest bike I own is a 650c The downside to 650's is a much more limited selection of wheels in general. Most companies are 700 only these days. (or a very limited selection of 650's) |
2012-11-26 10:33 AM in reply to: #4509674 |
Veteran 740 The Woodlands, TX | Subject: RE: Speed gains of 650c wheels vs 700c wheels Attached is a link to a good article discussing pros & cons of 650 vs 700 wheels and debunking some of the common myths. It's a little old, but still rings true... http://www.slowtwitch.com/Tech/Yet_more_wheel_size_debates_223.html |
2012-11-26 10:39 AM in reply to: #4509685 |
Sensei Sin City | Subject: RE: Speed gains of 650c wheels vs 700c wheels briderdt - 2012-11-25 8:10 PM rjrankin83 - 2012-11-25 7:57 PM Long story short, for arguments sake, what gains over 40k could be expected just based on the wheel size? Approximately zero. Or less. Yep. Plus, (also mentioned), harder to find tires/tubes. And in an emergencey, less likely to be able to borrow tubes on rides if needed. |
2012-11-26 10:40 AM in reply to: #4509674 |
Minneapolis, MN | Subject: RE: Speed gains of 650c wheels vs 700c wheels How tall is the OP's friend. my partner rides on 650's because that was the optimal bike that would fit her. she is 5'2" on a good day..... |
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2012-11-26 11:07 AM in reply to: #4509674 |
Elite 3498 Laguna Beach | Subject: RE: Speed gains of 650c wheels vs 700c wheels The story of how 650c's wound up on triathlon bikes at all is an interesting one. Remember that when Dan Empfield founded Quintana Roo the company was intended to make predominantly, or perhaps exclusively, bikes for females. Empfield was married to a top pro female triathlete then and had worked to produce a wonderful assortment of bikes around gender specific geometries. Many of those had 650c's. Empfield worked on a project with a fellow named Ralph Ray to develop a bike made "from the aerobars back" with a 90 degree seat tube angle. I don't know the reason, or even if, the first bikes had 650c's. They likely did due to issues with wheel clearance in the rear triangle but again, I am not sure. In any case early triathlon bikes trended with 650c's. That is what we had, so we sold them. They were a headache since we had to have 56 tooth chainrings, rotten front shifting because of the big chainrings, we had to stock new size tires and tubes and get 650c race wheels. Lots of extra work. A little known fact is that one season 650c road bikes actually trended in the Tour de France when a few top riders, including Laurent Jalabert (who did Ironman after he retired from cycling) used a 650c wheel size road bike on mountain stages for the lower gearing and stiffer wheels the wheels size offered. It didn't catch on though, mostly due to logistics. Bottom line: Wheel size is dependent on torso length. That's it. Torso length is also influenced by overall height. Most people below 5'2" tall, male and female, are relegated to 650c's since their torso is not long enough for 700c's. It would be like a size 5 foot wearing a size 10 shoe. 650c's are neither faster nor slower. A good set-up has gearing adjusted for the 650c size with larger chainrings and smaller cogs to achieve "gear paraody" with 700c wheel bikes. It's worth noting that the Ironman World Triathlon Championship was won a few times, quite a few actually, on 650c's and there have even been top results on 24" wheels (Paula Newby Fraser). When it comes to wheel size, if the wheel fits, ride it. Edited by Tom Demerly. 2012-11-26 11:07 AM |
2012-11-26 11:30 AM in reply to: #4510225 |
Champion 10668 Tacoma, Washington | Subject: RE: Speed gains of 650c wheels vs 700c wheels Tom Demerly. - 2012-11-26 9:07 AM They likely did due to issues with wheel clearance in the rear triangle but again, I am not sure. And this is still an issue today for any one who rides steep. |
2012-12-05 4:10 PM in reply to: #4509674 |
Expert 2373 Floriduh | Subject: RE: Speed gains of 650c wheels vs 700c wheels If bigger wheels made you faster, than shouldn't a dump truck be faster that an Porsche? |