700 vs 650 tires - Triathlon Week

mdmorden · 11-28-2005, 10:21 AM

Is there an advantage to haveing 650c tires? I see a lot of tri bikes go with the smaller tire, but most road bikes go with a 700 tire? Is the 650 faster? The reason I am asking is because I am looking into buying a tri bike and the one I am keen on has 650's, but I don't want that slowing me any. Do you think it will help or hinder??

sfricks · 11-29-2005, 12:25 PM

I haven't run into many articles comparing wheel sizes but those I have suggested there's little difference between the two. A lot of tri bikes use 650s for geometry, not for any increase in speed. There will be a gearing difference due to the wheel size.

That said, my advise is forget the wheel size and F O C U S on bike fit. Without proper alignment and coordination of all applicable muscle groups any perceived gain from bike componentry is just that; perceived.

I've watched many a foolish friend skip the $300 fee for a professional bike fit and then spend $1000 trying to "upgrade" their ride to be more competitive.

Hope this helps and good luck!

mdmorden · 11-29-2005, 02:09 PM

Yes, thanks it does help. Today however I was in at a local bike shop and the bike expert there helped me out a little as well. He confirmed what I had a hunch of. The 650 is going to be better for acceleration, but when you are up to speed the 700 tire is better. It has to make less revolutions and therefore less friction of moving parts and so forth. The other note worty bit of info he gave me was that if you need a tire, the 700 is more available say if you were in a small town. Well I will take my knew knowledge and be a more informed buyer. Thanks for the help. Oh, why is it so expensive for a proffessional bike fit? What all do they do? Can't be that complex to see if i need a 56 or a 58 can it? Thanks again though.

Matt

sfricks · 11-29-2005, 02:53 PM

Yes Matt, a pro can help. For example, my daughter and I are both 5' 9.5". I ride a 56cm and she rides a 58cm, both professionally fitted. I was also advised to (and did) exchange my factory installed 172.5mm cranks for 170s. Inseam length, torso length, arm length and many other factors affect bike fit. Seat position (fore and aft), seat angle, crank length, stem length, bar height and aero bar position (fore and aft) all make a difference. You can get an "out of the box" bike at K-Mart. Let your local bike shop do their job. Talk to the tech about fit. If they can't help you, find another shop. If you're cycling properly and efficiently, you'll use dozens of muscle groups. You can't get the max out of all those if your body needs to compensate for some maladjustment, right?

For the record, I don’t buy the 650 thing. It’s just different gearing. Over 100 miles, I bet it wouldn’t be noticeable. I rode 650s until about 1.5 years ago. As far as flats… On long training rides I carried (and carry) 3 tubes, a patch kit and a cell phone. In a short Tri I carry one, 70.6 two and 140.6 three. I never had problems finding a tube.

pyschosyd · 11-29-2005, 04:20 PM

I agree with fricks. 650's seem to be more of a fad than actually worth it. If you are looking at frames 49 or 50 or less they will often switch to the 650's for aerodynamic purposes. But on frames any larger than that, I don't believe they are beneficial. Acceleration is such a small part of triathlon. No sprints.
syd

Tri-Goodell · 12-09-2005, 01:13 PM

Hey Gang,
Let me help a little with the mystery of 700 vs. 650 dilemna. The only thing that 650's are good for are: faster acceleration and wind resistance by keeping you lower to the ground. If you think about it for a second....700 vs 650 mm...

700mm translates into more than 6 inches of forward movement over 650 mm wheels during a single revolution. (700mm - 650mm = 50 mm x 3.1416 = 157.08mm/ 25.4 = 6.18")

In order to calculate a difference, I will need to make some assumptions. Assume the wheels are exactly 700mm and 650mm, the rate is fixed at 100 rpm for both sizes. This means the 700mm wheel will travel 700mm x 3.1416 x 100 = 219912 mm, which equals 721.5 ft. This also means that the 650mm wheel will travel 650mm x 3.1416 x 100 = 204204 mm, which equals 670 ft.

So, in just this example, for only 100 revolutions of the rear wheel, 700 mm wheels travelled 51.5 feet further than the 650 mm wheels within just one minute. You do the math....you must spin much faster on 650's than on 700's to get the same distance in the same amount of time.

I hope that clears things up a bit!