UnThreaded | Threaded | Whole Thread (11) | Ignore Thread Prev Thread | Next Thread
Author: wheypat Big red star, 1000 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: of 54264  
Subject: Volvo V70 Tyre Pressure Date: 10/08/2012 11:25
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 0
Good Morning,

I've just been to fill up my tyres and got very confused about what is the correct pressure. The sticker on the inside of the door states that for 1 to 3 people at 0-160 km/h is 30 front and 32 rear. And then underneath this it has "Eco" and quotes 0-160 tyre pressure as 38, front and rear. The manual states that "at speeds under 160 km/h the general tyre pressure is recommended to obtain optimum fuel economy".

Anyone got any idea what tyre pressure I should be putting in!
Print the post Back To Top
Author: geebee2 Big gold star, 5000 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 45659 of 54264
Subject: Re: Volvo V70 Tyre Pressure Date: 10/08/2012 15:44
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 0
I don't have specific information, but I would guess that 38 front and rear will give you the best mileage per litre of petrol.

If that's what you are after, I also suggest checking the sidewall of the tyre, and inflating to the maximum.

Basically rolling resistance is reduced the more air you put in a tyre. The ride may be slightly noisier.

Print the post Back To Top
Author: geebee2 Big gold star, 5000 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 45660 of 54264
Subject: Re: Volvo V70 Tyre Pressure Date: 10/08/2012 15:57
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 0
The above is of course very much simplified, it's my rough conclusions from when I looked into this a few years ago.

You should be aware that grip could be very slight reduced in the dry, but this is really only relevant if you drive very aggressively.

You may find there is no sidewall max.

My general rule of thumb is that 40psi is fine, 44psi is also fine, but I wouldn't go much beyond that, unless perhaps I was in a MPG competition (!)

Off-topic : for bicycles, you do need to stay within limits. I had a clincher tyre blow off the rim after inflating to just over the 115psi limit.

Print the post Back To Top
Author: WessexMario Big gold star, 5000 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 45667 of 54264
Subject: Re: Volvo V70 Tyre Pressure Date: 11/08/2012 12:01
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 5
If that's what you are after, I also suggest checking the sidewall of the tyre, and inflating to the maxi<mum.
Basically rolling resistance is reduced the more air you put in a tyre. The ride may be slightly noisier.


Can I say that's not good advice.

The maximum pressure for a tyre is that which will carry the maxium load, also stamped on the outside of the tyre. If the load on a tyre is less than the maximum limit for that tyre, then the pressure should also be less to ensure that the tyre profile in contact with the road is as designed.
At pressures above the correct range for the load, the tyre will be over-inflated which will make the centre bulge, and the edges loose contact with the road. You'll get increased tyre wear in the centre part of the thread, and the tread pattern will not be contacting the road across the width of the tyre so you'll get more tendency to loose grip. Yoe, you'll get less rolling resistance, but you'll also get worse handling and worse braking distances.

The correct pressure for a particular tyre is dependant on the load on that tyre - this is a combination of the weight of the vehicle, the front to back weight distribution and the maximum speed that the vehicle will be travelling at.
There will be a range in which you can safely vary the pressure, from a slightly softer more comfortable ride, to a harder more responsive ride, but advising to inflate to the tyre's maximum without knowing what the ratio of the actual load to the maximum load for a tyre is, is dangerous.

Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Print the post Back To Top
Author: WessexMario Big gold star, 5000 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 45668 of 54264
Subject: Re: Volvo V70 Tyre Pressure Date: 11/08/2012 12:22
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 0
I had a clincher tyre blow off the rim after inflating to just over the 115psi limit.
Should we be surprised at that?
For any vehicle you need to stay within the manufacturer's limits.
With a motor vehicle, it's even more important, on a bicycle you're only going to hurt or kill yourself.

Some safety advice about over or under inflating on the ROSPA site:
http://www.rospa.com/roadsafety/adviceandinformation/vehicle...

It is a legal requirement that tyres have both the maximum load, and the maxmimum pressure stamped on the sidewall.
They are there because both are needed to calculate the correct pressure for safe partial loading.

Print the post Back To Top
Author: ahenry Big gold star, 5000 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 45669 of 54264
Subject: Re: Volvo V70 Tyre Pressure Date: 11/08/2012 17:48
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 0
Sheldon Brown was a well-respected poster on Usenet in the 1990s and early 2000s. He ran a bike shop

Sheldon wrote this http://sheldonbrown.com/tires.html#pressure about tyre pressures, basically saying that value on the sidewall is a balance between the requirements of the legal and marketing departments.

I remember a Usenet post where he mentioned that a rep from Specialized (a bike company that also sold tyres), who said that the maximum pressure ratings on the sidewall of a bicycle tyre were pretty conservative, and that you could typically inflate them to double the "maximum" value.

Tyres have to be good at lots of different things, and the pressure is a compromise between properties like ride comfort (high is bad), resistance to pinch flats (low is bad). On a smooth surface, high tyre pressures help fuel economy, but on a rough surface, the tyre can end up bouncing between the bumps in the road, so a lower pressure is better.

Personally, I would start with the values which are recommended for the driving that you're doing. If you are going to Germany and are planning to cruise at high speeds, then the higher pressures might be worthwhile. For lower speeds and lower loadings, then I would stick to the lower values.

Print the post Back To Top
Author: ajc5001 Big gold star, 5000 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 45670 of 54264
Subject: Re: Volvo V70 Tyre Pressure Date: 11/08/2012 18:02
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 0
If you are going to Germany and are planning to cruise at high speeds, then the higher pressures might be worthwhile

As far as I am aware, tyre pressures are supposed to be set when the tyres are cold (i.e. at whatever the temperature is at the time, with the tyres not having been used beforehand thus causing them to have warmed up). This seems to be confirmed by all the hassle in Formula 1 with tyre warmers and comments on losing temperature and therefore pressure when behind the safety car etc. So, If you use a car on German autobahns, would the increased speed not cause the tyres to run warmer and thus automatically at a higher pressure? Or is this effect negligible in the real world of ordinary cars and tyres.

Adrian

Print the post Back To Top
Author: ahenry Big gold star, 5000 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 45672 of 54264
Subject: Re: Volvo V70 Tyre Pressure Date: 12/08/2012 14:07
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 0
If you are going to Germany and are planning to cruise at high speeds, then the higher pressures might be worthwhile

As far as I am aware, tyre pressures are supposed to be set when the tyres are cold (i.e. at whatever the temperature is at the time, with the tyres not having been used beforehand thus causing them to have warmed up). This seems to be confirmed by all the hassle in Formula 1 with tyre warmers and comments on losing temperature and therefore pressure when behind the safety car etc. So, If you use a car on German autobahns, would the increased speed not cause the tyres to run warmer and thus automatically at a higher pressure? Or is this effect negligible in the real world of ordinary cars and tyres.

If you measure the temperature in Kelvins (ie 0C is 273K, 25C is 298K), then* if you double the temperature, you double the pressure. This holds for an "ideal gas" http://en.wikipedia.org/wiki/Ideal_gas_law However, the change in the pressure isn't that big - for instance, even if the air in your tyres went from 25C to 100C, the pressure would increase by ~25% (373K/298K)

In practice air in tyres is not an "ideal gas" but it is a small difference. You can get your tyres filled with Nitrogen if it worries you.

The size of the contact patch for the tyre depends on the load on the tyre and the pressure. If you had a 600lb load on a tyre at 30psi, then the contact patch would be 20 square inches. The smaller contact patch, means that you get less grip for all-out braking an acceleration when the tyre pressures are high.

The advice is to run tyres at higher pressure when you run at high speeds, even when you measure the pressure with cold tyres.

A tyre at low pressure deforms as it rolls. This flexes the tyre and makes it warm up. This energy reduces the fuel economy, but can also cause the tyres to overheat if you are running at high speeds for a long time. If you double the pressure, then the contact area halves, and this doesn't need the tyre sidewall to flex as much.

Car tyres have a maximum speed rating, which is the letter at the end of the tyre code. Some cars require tyres with a higher speed rating than their top speed, because they put a higher than normal load on the cars.

Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Print the post Back To Top
Author: ajc5001 Big gold star, 5000 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 45673 of 54264
Subject: Re: Volvo V70 Tyre Pressure Date: 12/08/2012 15:20
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 0
The size of the contact patch for the tyre depends on the load on the tyre and the pressure. If you had a 600lb load on a tyre at 30psi, then the contact patch would be 20 square inches. The smaller contact patch, means that you get less grip for all-out braking an acceleration when the tyre pressures are high.

The advice is to run tyres at higher pressure when you run at high speeds, even when you measure the pressure with cold tyres.


Perhaps it's just me, but it seems counter-intuitive to want a smaller contact patch at higher speeds. I'd prefer to have better grip and braking.

Print the post Back To Top
Author: ahenry Big gold star, 5000 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 45674 of 54264
Subject: Re: Volvo V70 Tyre Pressure Date: 12/08/2012 16:58
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 0
The advice is to run tyres at higher pressure when you run at high speeds, even when you measure the pressure with cold tyres.

Perhaps it's just me, but it seems counter-intuitive to want a smaller contact patch at higher speeds. I'd prefer to have better grip and braking

Everything is a compromise. High pressures help to limit the heat build-up. If the tyres were to get hot, then they wear rapidly, and are more likely to have a blow out.

If you were choosing a car specifically to be able to cruise at high speeds, then its best to have wheels with a large diameter, which then mean that the tyre doesn't have to flex as much to get a given size of contact patch. Low profile tyres have stiff sidewalls, which don't heat up as much. This also leaves lots of space inside the wheel for big brake discs, which are less likely to overheat under heavy braking. You then need stiff suspension, or the big wheels will bash into the bodywork.

The problem with this, is that you get a car which is great on an Autobahn, but with poor handling on rough roads and a rock hard ride. tyres will be expensive, and give a poor turning circle.

Print the post Back To Top
Author: ivahunch Three stars, 500 posts Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: 45675 of 54264
Subject: Re: Volvo V70 Tyre Pressure Date: 12/08/2012 19:40
Post New | Post Reply | Reply Later | Create Poll . Report this Post | Recommend it!
Recommendations: 0
I normally use 34psi front & 32psi rear, unless heavily laden in which probably 34psi rear

Print the post Back To Top
UnThreaded | Threaded | Whole Thread (11) | Ignore Thread Prev Thread | Next Thread