# Tyre Pressure - 25mm



## bpsmith (26 Jun 2014)

Been running my Defy 1 at 120 psi since new as that's what I was advised. Change wheels and tyres and made me go looking for more info and now confused.

Basically, a lot of info online suggests that I am over inflating. I now have GP4000S in 25mm fitment. I weigh 70kg and bike is around 8.5kg apparently.

Online graphs suggest something like 70 psi front and 90 psi back. Is this too low? Any suggestions?


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## RedRider (26 Jun 2014)

I run the same tyres, I'm hovering around the 82 kg mark an my bikes a lttle heavier than yours. I tend to pump the front to 90 and the rear 100 but sometimes go a couple of weeks without refilling when pressure drops to a comfy 70-80. I don't have a problem with pinch flats and my rims are intact.


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## Jon George (26 Jun 2014)

bpsmith said:


> Been running my Defy 1 at 120 psi since new as that's what I was advised. Change wheels and tyres and made me go looking for more info and now confused.
> 
> Basically, a lot of info online suggests that I am over inflating. I now have GP4000S in 25mm fitment. I weigh 70kg and bike is around 8.5kg apparently.
> 
> Online graphs suggest something like 70 psi front and 90 psi back. Is this too low? Any suggestions?


A quick look at the table I use (from Cycling Quarterly) would suggest a tad more in the rear (about 100) and, actually, a little less in the front (65 ish.)


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## Accy cyclist (26 Jun 2014)

RedRider said:


> I run the same tyres, I'm hovering around the 82 kg mark an my bikes a lttle heavier than yours. I tend to pump the front to 90 and the rear 100 but sometimes go a couple of weeks without refilling when pressure drops to a comfy 70-80. I don't have a problem with pinch flats and my rims are intact.



I pump my tyres before every ride. The following day they'll be down from the inflated to 100 psi to around 65-70 psi. I'm curious how your tyre pressure is the same as mine but after weeks not a day?


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## RedRider (26 Jun 2014)

Accy cyclist said:


> I pump my tyres before every ride. The following day they'll be down from the inflated to 100 psi to around 65-70 psi. I'm curious how your tyre pressure is the same as mine but after weeks not a day?


God knows. I reckon it must be almost two weeks since the last time I filled them so I'll check now. I'm guessing it'll still be higher than what yours reduce to in a day. You using latex tubes? Hang on a min.


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## Accy cyclist (26 Jun 2014)

bpsmith said:


> Been running my Defy 1 at 120 psi since new as that's what I was advised. Change wheels and tyres and made me go looking for more info and now confused.
> 
> Basically, a lot of info online suggests that I am over inflating. I now have GP4000S in 25mm fitment. I weigh 70kg and bike is around 8.5kg apparently.
> 
> Online graphs suggest something like 70 psi front and 90 psi back. Is this too low? Any suggestions?



Trying different pressures over a length of time is my suggestion. I've stuck to 100 psi front and back in 23mm tyres for years and it works for me. Each to their own though,you might find that 70 or 80 works for you and you'll stick with it.


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## RedRider (27 Jun 2014)

Accy cyclist said:


> I pump my tyres before every ride. The following day they'll be down from the inflated to 100 psi to around 65-70 psi. I'm curious how your tyre pressure is the same as mine but after weeks not a day?


Back just shy of 70 and front short of 60 according to my guage. Deffo needs pumping tomorrow morning but my ride today felt absolutely fine. I missed my regular weekend (long) rides this last weekend - always pump before them - but have ridden every day along fairly shoddy road surfaces with no probs. Conti race tubes btw.


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## Accy cyclist (27 Jun 2014)

RedRider said:


> Back just shy of 70 and front short of 60 according to my guage. Deffo needs pumping tomorrow morning but my ride today felt absolutely fine. I missed my regular weekend (long) rides this last weekend but have ridden every day along fairly shoddy road surfaces with no probs. Conti race tubes btw.




I use these http://www.chainreactioncycles.com/schwalbe-road-tube/rp-prod26727 I've just checked my pressure. I pumped them up to 110 (as i reckon i lose about 10 psi on the ride)at.3 o clock and they're now down to 75 after 9 hours, and a 35 mile ride. The ride didn't take 9 hours by the way!


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## RedRider (27 Jun 2014)

Accy cyclist said:


> I use these http://www.chainreactioncycles.com/schwalbe-road-tube/rp-prod26727 I've just checked my pressure. I pumped them up to 110 (as i reckon i lose about 10 psi on the ride)at.3 o clock and they're now down to 75 after 9 hours and a 35 mile ride.


Blimey. Thinking about it, I I tend to put 110 into the rear rather than 100. I usually ride 2-300km per week and pretty much never top up between weekends.
Interesting to see @Jon George 's Cycling Quarterly recommendations. That's quite a significant difference between front and rear.


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## Accy cyclist (27 Jun 2014)

RedRider said:


> Blimey. Thinking about it, I I tend to put 110 into the rear rather than 100. I usually ride 2-300km per week and pretty much never top up between weekends.
> Interesting to see @Jon George 's Cycling Quarterly recommendations. That's quite a significant difference between front and rear.




"That's quite a significant difference between front and rear."

I thought that too! Tyre pressure is a big thing with narrow road tyres,compared to mountain bikes where the thick tyres will absorb sharp objects and shock from the poor roads we have to put up with. When i used a mountain bike to get to work on years ago i probably checked the pressure about twice a week,and i only had one puncture in over 6 thousand miles on those knobbly tyres!


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## ColinJ (27 Jun 2014)

Accy cyclist said:


> I pump my tyres before every ride. The following day they'll be down from the inflated to 100 psi to around 65-70 psi. I'm curious how your tyre pressure is the same as mine but after weeks not a day?


Something is wrong! Even if you are using relatively-leaky latex tubes rather than butyl, they only seem lose about 10 psi a day.

If you haven't got faulty tubes or slow punctures in both, then the only other thing that I can think of is that you do not screw down the knurled nuts on the valves after pumping the tyres up, in which case the vales _will_ leak. My butyl tubes only lose a few psi a week.


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## Accy cyclist (27 Jun 2014)

ColinJ said:


> Something is wrong! Even if you are using relatively-leaky latex tubes rather than butyl, they only seem lose about 10 psi a day.
> 
> If you haven't got faulty tubes or slow punctures in both, then the only other thing that I can think of is that you do not screw down the knurled nuts on the valves after pumping the tyres up, in which case the vales _will_ leak. My butyl tubes only lose a few psi a week.



Yes i tighten them up but they still lose pressure. Anyway,it's a small matter to me,i've only had one puncture since last November touchwood,so i'm happy with things at the moment!


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## rb58 (27 Jun 2014)

110 front and rear for me - and I've arrived at those pressures after quite a lot of experimenting. I use the pump once a week, and I generally lose around 25 psi over that period. This is generally the same for all my bikes. If I was losing more pressure than that, I'd be thinking faulty tube or slow puncture .


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## Globalti (27 Jun 2014)

Accy cyclist said:


> I use these http://www.chainreactioncycles.com/schwalbe-road-tube/rp-prod26727 I've just checked my pressure. I pumped them up to 110 (as i reckon i lose about 10 psi on the ride)at.3 o clock and they're now down to 75 after 9 hours, and a 35 mile ride. The ride didn't take 9 hours by the way!



You must be leaking! We pump to 100 on both bikes and must lose about 5 lbs in a week on average.


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## John the Monkey (27 Jun 2014)

I find Continental's recommended pressures are usually about right - the say 110psi for 25c GP 4000;

http://www.conti-tyres.co.uk/conticycle/ti grand prix 4000S.shtml

Seems high to me (last 25c I ran were Pro Race2, at 90psi) but I'd start there and experiment (fwiw, the old Michelin charts reckon 93psi for your wieght on a 25c tyre).

See also;
http://www.dorkypantsr.us/bike-tire-pressure-calculator.html


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## bpsmith (27 Jun 2014)

Thanks for the replies guys!

That last link, in addition to others above, is what I found a few days back and made me think about posting. Some of the rpessures quoted seem very low indeed, but I am keen to take advice and will start with a trial of maybe 75 on front and 90 on back first maybe. How does that sound?

Do you guys notice any difference in speed with lower pressures, or is it just a comfort gain for no speed loss?


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## John the Monkey (27 Jun 2014)

bpsmith said:


> Do you guys notice any difference in speed with lower pressures, or is it just a comfort gain for no speed loss?


Personally, I think a lot depends on the tyre - I've had some that are finicky, and feel dreadful if the pressure isn't just right, and others that will roll fine, even 20 psi off the usual pressure. 

In general, I think stiffer carcassed, more heavily puncture protected tyres fall into the former category, and more supple tyres into the latter.

It's also worth mentioning that that's "feel" - I couldn't say for sure that speed was actually affected.


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## Accy cyclist (28 Jun 2014)

John the Monkey said:


> I find Continental's recommended pressures are usually about right - the say 110psi for 25c GP 4000;
> 
> http://www.conti-tyres.co.uk/conticycle/ti grand prix 4000S.shtml
> 
> ...



I've used the chart and according to it,my front tyre should be 73 psi and the rear 114 psi. I'm going to give this a go and see how it feels.


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## shouldbeinbed (28 Jun 2014)

I've generally stuck to 100 front and rear on 23's & don't see a lot of loss over a week or so. I irrationally worry about the tyre rolling about on the rim in corners with lower pressure in, but I'm sure the load particularly on the front wouldn't be enough to cause such an imagined failure even with a much softer setting.


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## John the Monkey (28 Jun 2014)

Accy cyclist said:


> I've used the chart and according to it,my front tyre should be 73 psi and the rear 114 psi. I'm going to give this a go and see how it feels.


I've never ridden with so much of a diference (10 psi less in the front is as much as I've tried) but then the old chart just gave a recommended pressure, not a front/back pressure.

I'd bear in mind the comments about tyres too in my earlier post - subjective, I know, but some really do feel godawful if the pressure's not right.


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## bpsmith (1 Jul 2014)

Did a quick test ride tonight. Dropped to 85psi front and 105 psi rear over 30 and a bit miles...and it felt more comfortable and grippier at times...but was far too low for my liking. Really went for it and was a lot slower than previous times when it was windier and I gave it less effort. It's trial and error, I know, but the recommended pressure is even lower than that. Certainly doesn't suit my riding it appears. Going up to 100psi front and 110psi rear next and will try the same route probably.


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## boydj (1 Jul 2014)

Interesting info here - http://velonews.competitor.com/2012...-pressures-were-roubaix-riders-running_212925 - on tyre pressures used by pros on the Paris-Roubaix. Lower for the cobbles than they would use on good road surfaces, but it would suggest that <100 psi is not going to hurt road performance on a 25mm tyre.


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## bpsmith (1 Jul 2014)

They are mostly using 27mm or 28mm tyres, which result in a lower required pressure anyway. The pressures they used are similar to mine tonight and would have been higher with a 25mm naturally.

And they are PRO's! Let's see how many of them use those pressure on the Tarmac in the TdF come the weekend...

Interesting article nonetheless.


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## bpsmith (3 Jul 2014)

110psi front and back...so much better!

There might be a happy medium, so won't add air on next ride and see what happens.


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## Accy cyclist (3 Jul 2014)

Well i've been trying 85(ish)front and 115(ish)rear. I can't say there's any difference between that and 100 to 110 front and rear.


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## Doyleyburger (17 Aug 2014)

Going to keep an eye on this thread. 

Been running my new 25 tyres at 100psi for both the front and rear. Perhaps I should drop the front slightly. Used to run my 23's on 110 and iv instantly noticed the difference...... Faster rolling for sure, and much more comfy ride with a lower pressure


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