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I have two Specialized Langster (one brand new 2013 model (54 cm) and the other a couple of years old unique London model (52 cm)) - both are single speed. Got sick of getting punctures on my daily commute so on Monday I got Durano Plus 700x25c tyres - the bike shop owner said go for 25c as the 23c is good but for daily commuting he would recommend 25c - he did acknowledge you will go slightly slower but not that you will really realise.

Well, he was wrong and I have realised! Anyway, the problem is the London model seems to be a lot slower then the the one - both are slower now but the London one lot more.

I am able to really pedal the heck out of the London one but it just does not seem to go too far I know I can pedal more but there is no need as it just does not cope to go further (hope I am making sense as it is hard to explain!). Could it be the chain is just not good enough on the London model then the other bike? Or something else - there is nothing much else I can think of as it just has one chain and no gears and stuff - except for the new tyres??

One point - the chain is painted (as it is a unique London model) so could it be that? I only bought the London model two weeks ago and am only now riding it around now for my daily commute.

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A chain would have to be really bad to slow you down noticeably -- generally the chain will start skipping or jumping off well before friction becomes an issue. Certainly tires can make a difference, especially if heavily lugged and/or underinflated. Make sure your tires are inflated to near the "sidewall" pressure. For 25c this should be at least 60PSI. Also be aware that, in particular, the Schwalbe belted tires tend to have higher rolling resistance, due to the nature of their belts. –  Daniel R Hicks Nov 13 '13 at 12:00
    
From the question it's pretty difficult to tell what the problem is. Have you measured your average speed on the two bikes in similar conditions? What has changed besides the tires? Is there any obvious noise coming from the bike when you ride? Is the speed difference most apparent up/down hills or into a headwind? I think we need more information. –  James Bradbury Nov 13 '13 at 12:14
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Inflate your tires to the maximum allowed pressure. –  Vorac Nov 13 '13 at 12:52
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60PSI would be the minimum. Probably around 100 is a good number. –  Daniel R Hicks Nov 13 '13 at 15:50
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Sheldon Brown does a wonderful job of describing how to determine your proper tire pressure. –  jimirings Nov 13 '13 at 20:57

2 Answers 2

One note is that the gearing is different, assuming they're still stock.

The Specialized Langster London has a 42t chainring and 16t cog, the 2013 Langster has a 48t chanring and 17t cog. With 700x25 tires that means they are 69.6 and 74.6 gear inches respectively.

What that means is that spinning at 100rpm, you're going ~22mph on the Langster and only ~20mph on the London. So it will feel slower when you're trying to go flat out.

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When I read the OP's description of the problem I was thinking it sounded like a gearing problem, but I didn't have time to do the research at the moment to verify. –  jimirings Nov 13 '13 at 20:54
    
I also suspect the bike size, and if they are both set up correctly for you. That 2cm difference in frame size can mean a lot (10%) of power difference. That combined with the other factors (gearing, tire pressure) will give a very different experience! –  andy256 Nov 14 '13 at 6:24

The difference between 23c and 25c will be pretty much imperceptible (there's some argument that wider tires at the same pressure are faster up to a point anyway). You will notice more of a difference between correctly inflated tires and underinflated tires, but even that shouldn't be enough to make the bike feel sluggish unless they're extremely and obviously underinflated.

It's also unlikely that the chain is adding any significant friction: they're extremely efficient when properly lubricated. It should start making metal-on-metal squeaking noises well before you start feeling significantly increased drag from the chain.

Changing the tires would have involved removing the wheels and resetting the chain tension. On a single-speed an overly taut chain could cause some of the symptoms you described, including increased resistance. Sheldon Brown gives a good description of the issues around chain tension: http://sheldonbrown.com/fixed.html#tension .

It could also help to diagnose the problem if you check that the wheels are spinning freely: if you lift the wheel off the ground and give it a gentle spin, it should rotate freely for a while.

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I have noticed that the back wheel is touching the brakes a lot more then it used to - I will try and adjust the brakes to not touch (or should they touch?). Inflation of the tires will be something I will do tonight and see how it goes. –  lara400 Nov 13 '13 at 14:13
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The brake should not be touching the wheel rim, except when braking. If they intermittently touch the wheel, then the wheel is out of true, something that can also cause the symptoms you describe. –  Drew Stephens Nov 13 '13 at 15:05
    
Yeah, there should be no contact between the brake pads and the wheel rim unless you're squeezing the brake. A couple of mm of clearance between the rim and the brake pads on both sides is about right for your double-pivot brakes. If you spin the wheel and look at the gap between the pads and the wheel rim you can get a sense of what's wrong: * gap between wheel and rim changes as wheel turns => wheel is out of true * gap is much bigger on one side than other => brakes are misaligned and need to be rotated * gap is too small on both sides => brake cable is too tight –  user611910 Nov 13 '13 at 19:25

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