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I've got a simple city bike that needs some new tires. The bike has been fairly hard to ride lately, and I would like to speed it up a bit. The rims are 28' 622x19C, the current tires are 47mm or 1.75' according to the imprint (although 47mm = 1.85').

It feels like the rolling resistance is too high, compared to similar bikes with thinner tires. Now I've read that thinner tires should have a higher resistance in theory (because there is a larger contact area in rolling direction). But my feeling from comparing several bikes (not MTB or racing, but very similar ones with differnt tires) is that thinner tires feel faster and seem to have less resistance (probably because thick tires have a larger contact area perpendicular to the rolling direction - think of a car tire as the extreme case). Note when I say "thinner", I don't mean like a racing bike, but 37 or 40 mm instead of 47.

So, how to decide what tires to put on the bike? Will thinner tires (optimally inflated) reduce or increase the percieved resistance?

Or do you think I've just been riding with too low pressure all the time, and the current tire size is fine? If thicker really = faster at optimal pressure as they say, maybe the thicker tires also tempt people to use not enough pressure? Otherwise I can't explain my gut experience that the thick tires feel slow.

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This question may help: bicycles.stackexchange.com/questions/611/…. –  Wayne Johnston Apr 7 '13 at 1:10
1  
Thicker isn't faster. Nor is it necessarily slower. At a given tire pressure, width doesn't affect rolling resistance very much. But narrower tires can be run at higher pressure, and higher pressure does reduce rolling resistance. –  Daniel R Hicks Apr 7 '13 at 2:32
    
a 28' wheel would be pretty massive. youtube.com/watch?v=_Zdyo4vJuCU –  whatsisname Apr 7 '13 at 4:54
    
@whatsisname: Yeah, I meant 28 inches :-). I just read it off the tire, guess the second ' has worn off. Europeans and imperial units... –  jdm Apr 9 '13 at 20:12

3 Answers 3

I have replaced 2.0 (50mm) Schwalbe Marathons for 1.35 ones, and that made an ABSURD difference in my roling resistence. I was feeling burnt out by commuting, and since then I started to feel "exercised", getting to destination much faster and/or with less effort.

Then I got a bike with 700x23 tires, and THAT is good, concerning speed and low effort.

The only thing I think is very important: these skinny tires work fine, even with not-ideal road condition, if the bike has a more performance-oriented position (a firmer grasp on the handlebar - which is lower - , less weight on the saddle). If you take a more upright citybike (the first bike I described), the extra speed gained from thinner (not skinny) tires can make the bike too uncomfortable if road condition is not good.

I have also heard those theories about "balloon is the new fast", but that seems very non-scientific, since the "studies" never describe the parameters that varied versus those that remained constant, not to say other methodologic steps. As for me, narrower is obviously always faster (which doesn't mean always better).

Hope this helps!

(by the way, I think 32mm is a good number to try)

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Did you change the tire pressure? What is your average cruising speed (i.e. not counting the stops)? –  Vorac Oct 10 '13 at 14:34
    
I used a pressure that provided enough cushioning without the tire bulging or bottoming out easily. That means the narrower tire had higher pressure. Usually I ride at 20 mph (30km/h) cruising speed. –  heltonbiker Oct 10 '13 at 14:37

You don't indicate what pressure you're carrying, or what sort of tread you have. Pressure and tread are a bigger factor in rolling resistance than tire width.

For a given pressure, a tire will have essentially the same "footprint" area, regardless of its width. And, to a first approximation (and ignoring tread), rolling resistance is proportional to footprint area. For a given tire width there is a range of feasible pressures, but that range generally spans about a factor of two, and a narrower tire will have a higher max pressure.

Additionally, the heavier/knobbier the tread on the tire, the higher the rolling resistance.

Your current tire is probably limited (sidewall rating) to about 50psi. Dropping down to a 35mm tire you can get up to 80-110psi (depending on the tire). In addition, you likely have a fairly knobby tire. You don't need a "slick", but look for tires that have a "bald spot" down the middle with tread on either side.

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Disagree on the last sentence. For city riding, he'll want a slick. Additionally, those 'combination-tread' tires are bad news. The sudden transition from smooth to treaded often happens suddenly on hard turns, and will make you wipe out more than it will ever give a 'boost' in traction. –  whatsisname Apr 7 '13 at 7:04

There's been some very helpful research done for the Dutch cyclist union in 2012. The way it was measured was quite scientific, with G-meters to measure comfort, rolling resistance was measured in Watts and anti-puncture strength in both N and Nm, etc.

One of the cons of the test is that all measurement are done at 4.0 bar, where balloon tires are more likely to be used at +/- 3.0 bar and narrower tires at 5.0+ bar. With pressures around 2.5 bar, all tested tires scored approx. 25%-30% worse on rolling resistance, however that would result in only 1 km/h difference at 20 km/h.!

Test results 28" tires

The newer test from 2013 declared the same winner, the Vittoria Voyager Hyper Folding 37-622 B/B-SK+RT Triple Shielding, but a new runner up, the Schwalbe Big Apple 55-622 B/B-SK+RT HS430 Performance Line, Race Guard, Lite Skin, as seen here: http://www.fietsersbond.nl/node/5907.

With some online shopping, these tyres can be bought for less than $ 20 each.

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Could you provide the English meanings of those terms? –  Daniel R Hicks Oct 10 '13 at 15:38
    
It would be nice to see more bike parts evaluated this way. –  Carson Reinke Oct 10 '13 at 16:38

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