Tyre pressures

[Canardly]

Should these be the same for both front and rear, or not? If not why not?

[bumper]

more weight through the bum than the hands

60/40?

[Kim]

Weight distribution depends on the bike geometry and luggage, but assuming the same kind of tyres, I'd generally try to follow it.

The exception is on a mountain bike, where it may be prudent to have the rear a *lot* harder than the front.

[Canardly]

There is a lot of conflicting info regarding this. One site (there is an App apparently) recommends a two bar difference for touring which seems an awful lot. For marathons that represents minimum and maximum pressures for a 700 x 32c. @4.5 and 6.5 bar.

[bumper]

you could have an extra 30kg over the rear loaded, that would need a fair bit of extra pressure than just carrying say a 60kg* rider


*can't remember what 60kg was like, I was probably aged 10 when I was last that weight 

[zigzag]

the weight distribution i have is 38/62 (just me on the bike, hands on the hoods). i normally put 10psi more in the rear tyre. this weight distribution explains the rear tyre wear, which is normally twice as fast as the front (and rear tyre also wears more due to the torque when riding out of saddle).

[sojournermike]

more weight through the bum than the hands

60/40?

Might be a bit low for my weight;)

As noted depends on your weight and the overall weight distribution. I'm 85kgs and am currently running 80/60 using 28mm Schwalbe One Tubeless on 19mm internal rims (they come up to 30 or 31mm). I tend to start high and then slowly try lower pressures until I think it's nice, without being any slower.

Edit: The Berto Tyre Pressure app wil give you a good starting point, based on research suggesting the optimum pressure allows for a 15% 'drop' under load. You can go a bit lower with tubeless.

[Ningishzidda]

http://www.bikequarterly.com/images/TireDrop.pdf

Uniform 'Tire drop' front and rear.

[P Walsh]

If you have the same pressure front and rear you will have the front tyre less squished (technical term) than the rear when in use. You need about 10psi less in the front. And unless you are particularly heavy you do not need to inflate to 100psi+, unless you want to shake your fillings loose. With Grand Prix 4 Seasons (25mm) I have about 95psi rear and 85psi front, and having them any firmer only makes me back off on coarse road surfaces (i.e. most of the time).

To get the right tyre pressure for you, first find a quiet bit of road with a uniform surface of coarse chippings. Inflate your tyres to max pressure, then ride around and feel the vibration in the bars and saddle. Then stop and let out some air. Ride around a bit more. Repeat as many times as you need, possibly pumping more air in if necessary, until you feel that you have found the right pressures. Then measure the pressures with a gauge that you trust, and make a record for future reference. Takes about 20 minutes and is well worth while.

[Ningishzidda]

You could of course just sit on your bike and see how far the tyres flare out.
Left side flare + right side flare = Tyre drop.

[Canardly]

Thanks all, will have a look at the info.

[fuaran]

I think it makes sense to have wider tyres on the rear, than the front (for a road bike).
So the pressures are about the same in both.

[Ningishzidda]

I think it makes sense to have wider tyres on the rear, than the front (for a road bike).
So the pressures are about the same in both.

As in the Continental Force/Attack pair. 23 rear, 22 Front.

Or the Schwinn Stingray?

[Highlander]

Why not measure your front/rear axle loads by sitting on the bike with one wheel at a time on a set of bathroom scales.  You probably need an assistant to do it and you need to keep the bike level.  The total should add up to the total weight of bike/rider.  Once you know the proportions you can adjust tyre pressures accordingly.   I've done some subjective testing and though it sounds counter intuitive, running the front tyre at a lower pressure seems more efficient.  But you don't want to run too low, that's why you need to measure the respective front/rear loads.

[jsabine]

I think it makes sense to have wider tyres on the rear, than the front (for a road bike).
So the pressures are about the same in both.

I think the problem with that is that, IIRC, the size of the contact patch (which is presumably what you're trying to affect) is dependent on the pressure and the weight applied, and entirely independent of carcass size.

Accordingly, you end up running a higher pressure than ideal (for ride quality, efficiency, grip) in terms of weight distribution on the front in order to compensate for the smaller carcass and minimise the risk of pinch punctures.

Although it's initially attractive, I reckon you're better sticking with the same size tyres front and back, and reducing front pressure in relation to the weight distribution.

[Biggsy]

I like more difference of pressure between front and rear than the weight ratio would dictate - to minimise the chance of the front tyre skidding (by having it soft) while minimising the rolling resistance of the rear (by having it hard), as rear skidding isn't so dangerous.

My theory is that a harder tyre is more likely to bounce up from a bump and skid when it comes back down.

I ride with about 70psi front and 100psi rear in 28mm, for example.

[Nelson Longflap]

When I'm feeling brave I run F4 bar and R6 bar (or about F:R = 60:90). On a good day in summer I weigh around 65kg (but not today). The bravery is needed to overcome fear of pinch punctures, but in practice this hasn't been a problem. Sometimes I ride 70:90; but tbh I think 60:90 is more comfortable (which is what I'm aiming for). Tyres are either 25 or 28, usually, sometimes 32.

[Samuel D]

The alternative theory, espoused by Jobst Brandt and many racers, is that you need a much higher front pressure than suggested by its typical load, since under hard braking almost all your weight is borne by the front wheel and fast cornering is safer with less tyre flop.

I weigh about 65 kg and currently run pressures around 70–80 PSI at the front and 100 PSI at the back with 23 mm tyres. This does vary a bit with different tyres, terrain, and mood when pumping.

[Jakob]

Running tubulars, so usually about 110 in the front and 120 at the rear.

[Ningishzidda]

Why not measure your front/rear axle loads by sitting on the bike with one wheel at a time on a set of bathroom scales.  You probably need an assistant to do it and you need to keep the bike level.  The total should add up to the total weight of bike/rider.  Once you know the proportions you can adjust tyre pressures accordingly.   I've done some subjective testing and though it sounds counter intuitive, running the front tyre at a lower pressure seems more efficient.  But you don't want to run too low, that's why you need to measure the respective front/rear loads.

Did you read that Bikequarterly article I posted ?

If you didn't, I congratulate you on your Design of Experiments skills and logical thought processes.
If you did, I commiserate you on your poor powers of recall.

[Ningishzidda]

The alternative theory, espoused by Jobst Brandt and many racers, is that you need a much higher front pressure than suggested by its typical load, since under hard braking almost all your weight is borne by the front wheel and fast cornering is safer with less tyre flop.

I weigh about 65 kg and currently run pressures around 70–80 PSI at the front and 100 PSI at the back with 23 mm tyres. This does vary a bit with different tyres, terrain, and mood when pumping.

On hill descents, you need sufficient tyre 'footprint' without the tyre being laterally unstable. Too little tyre 'footprint' on hard braking downhill can tear up the centre of the front tread.
Only experimentation and experience will find you the optimum pressures for both tyres. ( 'all' tyres on a trike ).

[T42]

With 23mm GP4000s I use the old rule of thumb: 1/10 the weight of the cyclist at the rear and half a bar less at the front.  Roughly 7.5 rear and 7 front.  With 25s I use pretty much the same.  Used to run 23s on 8/8.  Dunno why I changed, really.

[Ningishzidda]

With 23mm GP4000s I use the old rule of thumb: 1/10 the weight of the cyclist at the rear and half a bar less at the front.  Roughly 7.5 rear and 7 front.  With 25s I use pretty much the same.  Used to run 23s on 8/8.  Dunno why I changed, really.

Where that old rule of thumb falls down is when the bloke who rides Thursday evening with the local club is 22 stones.

This would require his rear to be 14 bar, or 200 psi.

His Conti 23mm tyre flares out a little more than recommended at 120 psi.

[Highlander]

Why not measure your front/rear axle loads by sitting on the bike with one wheel at a time on a set of bathroom scales.  You probably need an assistant to do it and you need to keep the bike level.  The total should add up to the total weight of bike/rider.  Once you know the proportions you can adjust tyre pressures accordingly.   I've done some subjective testing and though it sounds counter intuitive, running the front tyre at a lower pressure seems more efficient.  But you don't want to run too low, that's why you need to measure the respective front/rear loads.

Did you read that Bikequarterly article I posted ?

If you didn't, I congratulate you on your Design of Experiments skills and logical thought processes.
If you did, I commiserate you on your poor powers of recall.

Believe it or not I came up with the idea after getting my van MOT'd some years ago.  The tester informed me that I was over the weight limit for that particular make of van and explained how you can be prosecuted on three separate counts for being over weight, front axle, rear axle and overall.  Until then I didn't realise that the MOT equipment calculates the overall weight by adding the two axle loads together.  So I thought I'd try it on the bike and realised there was quite a big variation between front and rear loads. 

I've done the exercise on the recumbent trike as well where as you might imagine, there is a huge difference in the loads on each of the three wheels. That's how I deduced you can run with ridiculously low pressures in the front tyres on a "tadpole" with no loss of performance but a massive increase in comfort.   

Up to this point, like everyone else I knew, I had been studiously maintaining my tyres  front and rear, at the maximum pressure.

It's frustrating and delightful in equal measure when you suddenly find out you have been doing something wrong for several decades...   

[T42]

With 23mm GP4000s I use the old rule of thumb: 1/10 the weight of the cyclist at the rear and half a bar less at the front.  Roughly 7.5 rear and 7 front.  With 25s I use pretty much the same.  Used to run 23s on 8/8.  Dunno why I changed, really.

Where that old rule of thumb falls down is when the bloke who rides Thursday evening with the local club is 22 stones.

This would require his rear to be 14 bar, or 200 psi.

His Conti 23mm tyre flares out a little more than recommended at 120 psi.

Yebbut a 22-stone rider would break my bike, never mind the tyres.  I think the nominal limit on GP4000s is 8.5 but it could be 8, in which case if you're over 80 kg (*2.2/14 for stones) hard luck.