Tyre Pressure - 25mm

[bpsmith]

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?

 

[RedRider]

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.

 

[Jon George]

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.)

 

[Accy cyclist]

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?

 

[RedRider]

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.

 

[Accy cyclist]

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.

 

[RedRider]

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.

 

[Accy cyclist]

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!

 

[RedRider]

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.

 

[Accy cyclist]

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!

 

[ColinJ]

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.

 

[Accy cyclist]

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!

 

[rb58]

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 .

 

[Globalti]

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.

 

[John the Monkey]

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