Specialized Sirrus tube / tyre query

jonnyguitar

New Member
Hi there lovely cyclechat folk.

I have a Specialized Sirrus Elite 2009. I pump up my tyres to around 110psi but often I find after a cycle for 1-2 hours they've deflated down to around 70psi. Rather annoying! Is this normal? I know I'm pumping them up correctly and closing the valve fully.

I am rather heavy though at about 18 stone. (big bones :-)

Any advice would be appreciated.

Also I have a long cycle through France coming up and wondered if changing the tyres from the supplied 28c tyres to 25c or even 23c would help. Is this possible?

What pressure would I run the tubes at on a thinner tyre?

Lastly, any advice on comfy saddles would be good too!

Any help would be fab as I feel a bit out my depth right now!

Thanks

Jonny
 
Pressure loss of that magnitude is not normal IME.

Putting narrower tyres on is definitely doable (I have 25's on mine, others have 23's)

Basically the narrower tyre will roll faster/ easier but you lose some comfort.

I usually run my 23 and 25's some where between 105 and 120 psi (near or at the maximum recommended for the tyre.

We are each to our own when it comes to saddles; I prefer a narrower saddle but this might not be good for you.

PS Welcome to the forum
 
OP
J

jonnyguitar

New Member
Thanks HLAB! I think I will try 25c tyres then. If the bike/rider/accessories is particularly heavy, does that mean I should inflate MORE than the average, or less?

Also I was wondering what innertube you'd reccommend? Tough ones with good quality valves are in order I think!

Thanks again for the friendly and quick response! Nice to find a friendly forum. :-)
 

Globalti

Legendary Member
Does the deflation also happen overnight or between rides?

Saddle comfort is so subjective; less experienced riders prefer a more padded saddle until they get hardened up. I used to have a Specialized Body Geometry saddle, which had two gel pads for the sit bones and was very comfortable but quite heavy.
 
Dunno about the 2009 Sirrus Elite, but Mrs wrx has a 2006 Sirrus with the same Alex rims as my 2004 Allez came with : her Sirrus is running 28 tyres, my Allez has 23's.

I've never known tryes go down the way you describe - sometimes they might go down like that if you left the bike unused for 2-3 weeks, but not 2-3 hours.

If you are replacing your tyres, the existing tubes might be OK inside 25's but will probably be too big in 23's.

But for the sake of a few quid, I'd replace the tubes anyway.

You do need higher pressures if you're heavier (go over a bump with them under-inflated and you may get a 'snakebite' puncture where you have two parallel cuts in the tube where they were squashed flat against the wheelrim), so if you're heavier or carrying luggage etc then the pressure is higher.
You also have higher pressure on thinner tyres.

See what the late, great Sheldon Brown says about tyre pressures http://www.sheldonbrown.com/tyres.html#pressure
 

jay1lk

Active Member
I use these on my sirrus. Not had a problem as yet. Hoping they'll get me across France later in the year.

http://www.jejamescycles.co.uk/specialized-all-condition-armadillo-tyre-id37589.html
 
OP
J

jonnyguitar

New Member
HLaB said:
Innertubes are much of a muchness. Having said that I avoid Specialized tubes after having a few fail (where the valve meets the tube) and after asking here/ googling it seems its a common problem.
it's funny you say that. the tubes i've been using are specialized - the ones i've had a problem with loss of pressure. could it be the same problem?

i changed last weekend to a Bontanger tube and I _think_ it's holding pressure better than the specialized tubes.
 

battered

Über Member
If a tyre is losing pressure over 2 hours then either the valve or the tube is faulty. As others have said get it in a bowl of water and look for bubbles. Alternatively just replace the tubes, any brand will work.

You should need to blow up your tyres every week or two, not every 2 hours.
 
OP
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jonnyguitar

New Member
battered said:
If a tyre is losing pressure over 2 hours then either the valve or the tube is faulty. As others have said get it in a bowl of water and look for bubbles. Alternatively just replace the tubes, any brand will work.

You should need to blow up your tyres every week or two, not every 2 hours.
Thanks. I'll try the water idea but I'm thinking that it's because of my weight (18 stone) that is forcing out the air when I sit on the bike. If that's the case then it won't show up in a bowl of water.
 

battered

Über Member
Your weight has nothing to do with it. Your car weighs over a ton and doesn't squeeze the air out of its tyres. There are 120 pounds on every sq inch of that bike tyre, static. That air wants to get out. If there's a hole, it will find it. If there isn't, it won't, whether you are an 8 stone size 10 woman or 20 stones of 6ft6 bloke who makes Jonah Lomu look like a bit that dropped off.:biggrin:

A bowl of water will show up a leak even if you only put 30psi in.
 
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