Tyre pressures

iainment

I ride a Sirrus Sport with 700X28 tyres. They say on the sidewall that the tyre should be pumped up within a range of 70psi (I think) and 100psi. My daily commute is 10 miles each way on roads and paved cycle track.

What pressure should I go to - the upper or lower or mid psi?

In general should you go to the highest or lowest advised pressure?

Many thanks.

danlikesbikes

Umm this could be a lengthy thread.

No right answer is the best I can off.

Personally I like higher pressures and find the feel better for me, but others prefer the softer and possibly better grip offered at lower pressures.

Just use the search function for threads on pressures and you'll see what I mean.

desweller

How heavy are you?

rick_chasey

DesWeller wrote:

How heavy are you?

Makes a big difference this.

My understanding is, the heavier one is, the higher the pressure needs to be.

For commuting I ride about half a bar less than for my road riding.

danlikesbikes

Rick Chasey wrote:

DesWeller wrote:

How heavy are you?

Makes a big difference this.

My understanding is, the heavier one is, the higher the pressure needs to be.

For commuting I ride about half a bar less than for my road riding.

Heavier = higher pressure get that, but surely for commuting you would be heavier (bike/pack/panniers) and need 1/2 more pressure than you run for road riding, or am I missing something.

desweller

Danlikesbikes wrote:

Rick Chasey wrote:

DesWeller wrote:

How heavy are you?

Makes a big difference this.

My understanding is, the heavier one is, the higher the pressure needs to be.

For commuting I ride about half a bar less than for my road riding.

Heavier = higher pressure get that, but surely for commuting you would be heavier (bike/pack/panniers) and need 1/2 more pressure than you run for road riding, or am I missing something.

It's just Force/Area. Force = weight of rider + weight of bike + weight of kit.

Rider could be anywhere between 60kg (e.g. Rick Chasey) and 120kg (my 6'7" mate Neil) - who knows? But kit and bike will not vary by more than a few kilos from one setup to another; even my full-on touring setup (dynamo wheel, 35c tyres, panniers front and rear) is only 8kg heavier (without payload) than my CFRP road bike. So the big deciding factor is the OP's weight.

iainment

I'm a big lad and I carry a reasonably full pannier.

So from the above I guess I should be at 100psi.

Thanks.

warreng

I'm 78kg and prefer 105-110 depending on the bike.

No idea if I'm quicker - just feels "better"

rick_chasey

Danlikesbikes wrote:

Rick Chasey wrote:

DesWeller wrote:

How heavy are you?

Makes a big difference this.

My understanding is, the heavier one is, the higher the pressure needs to be.

For commuting I ride about half a bar less than for my road riding.

Heavier = higher pressure get that, but surely for commuting you would be heavier (bike/pack/panniers) and need 1/2 more pressure than you run for road riding, or am I missing something.

It's more the commute is bumpier then my Sunday rides & I don't always want to be jarred into work

danlikesbikes

Rick get what you mean.

My winter bike I run about 15-20PSI less for comfort over the summer bike so it's the other way round for me.

mr_evil

Start with the 15% tyre drop method. Adjust from there to your liking.

sketchley

Sheldon has a good article on this http://sheldonbrown.com/tires.html#pressure you have to take into account tyre width and wheel weight be sure to click on the link in the article that shows you how to calculate the correct pressure. Note wheel weight is the load on the wheel including rider and bike weight and it's not a 50/50 split between front and rear as depending on the bike and it's geometry the split will vary the best option is to put the wheel on a set of bathroom scales and sit on the bike and measure it. You also need to be wary that tyres do not always measure what they say, for example I use conti gp4 seasons 28s which are more like 26s on my rims. What is true is a wider tyre at the same pressure on the same bike and the same rider will have less tyre drop than a thinner one, so depending on rider weight it's very easy to have under inflated thin tyres or over inflated thicker ones. I'm 108kgs and if I was to run 23s on my bike I'd need to inflate to 140+psi to keep tyre drop to 15% which clearly isn't practical and would be a very harsh ride, hence I run 28s with the rear at 120psi and the front at 110psi which is much better but on the rear is over the tyres rated maximum of 115psi. This is often why thicker tyres are faster despite being heavier, because they have correct inflation for rider weight and therefore have less rolling resistance compared to under inflated thinner one with more tyre drop.

sketchley

Rick Chasey wrote:

Danlikesbikes wrote:

Rick Chasey wrote:

DesWeller wrote:

How heavy are you?

Makes a big difference this.

My understanding is, the heavier one is, the higher the pressure needs to be.

For commuting I ride about half a bar less than for my road riding.

Heavier = higher pressure get that, but surely for commuting you would be heavier (bike/pack/panniers) and need 1/2 more pressure than you run for road riding, or am I missing something.

It's more the commute is bumpier then my Sunday rides & I don't always want to be jarred into work

That probably means your Sunday bike's tyres are overinflated for your rider weight, which in theory means less tyre drop and lower rolling resistance, this is fine on super smooth Tarmac but on anything with bumps the tyre will leave the road which means you are not putting power down as much. Next time you ride the Sunday bike I'd try taking a few psi out and seeing if it faster and more comfortable.