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Tyre pressure and fuel economy
#1
I pumped my tyres up the other day, then got 61.7mpg on a 200 mile trip - 100 of which it was carrying a 300kg load too, as well as my hefty 100kg+ weight. I'm very happy with that - previously I was just nudging under 60mpg. Mine's a 90bhp automatic multispace XTR. It has plastic wheel trims - I think they're 15" wheels, but could be wrong.

I was previously pumping all four up to 38psi, but this time I took them to 42psi. Both these figures are well within the very wide range on the door plate. It's all in bar units - I can't remember the numbers but I had to convert them for my old gauge, which is psi only.

It's noticeably firmer when driving though, so expansion joints thud more but it corners better. I'm pretty sure the mpg likes it firmer though. I'm tempted to go a bit higher still, and see what happens - provided it doesn't start over-wearing the centre of the tread.

It was only about 30psi when I got it new from the dealer - it was like driving a sponge cake.

The possible complication is that mine's at 11k miles, so it may still be running in and slackening up anyway.

What sort of pressure is everyone else running, on what wheels/model, and has anyone else seen similar effects?
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#2
15 inch steels was putting 34 in, the tyre place has uped the new tyres to 38, I may add more if it helps, we get in the 40's MPGwise on our 93,000ml 90 enterprise
63 plate Berlingo working hard.....
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#3
I've been googling since starting the thread, and my conclusion is that harder tyres do give better fuel economy. Even Mythbusters agree with this.

I'm going to try going towards the max given on the door plate. Some people go towards the max on the tyre sidewall or even beyond, but that sounds a bit silly and dangerous to me. You'll probably lose some grip and could possibly invaidate your insurance.

I'm also going to buy a pressure gauge that displays in Bar, as psi is fast becoming a dead unit of measurement. I keep have to google for a converting website every time I pump them up.

Despite the firmness, I prefer the handling now the tyres are hard. But I was going along a stretch of the M25 near Heathrow yesterday where I'm guessing it was previously concrete and it's been tarmacced over, so it has expansion gaps to give that thud-thud-thud as you drive along. It did feel a bit like my ribs were vibrating against the seatbelt at one point!
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#4
I have been running with 38 lbs psi for several months now and it does seem to have improved the handling. vehicle is 90hp multispace with 15 x 205/ . sticker on door quotes the equivilent of 35 lbs psi what ever that is in bars. but, thats it no pressure changes for empty/full load. if the fuel computor is to be believed, economy has improved about 3 - 4% . this is on a new set of tyres so the improvement could be just the increase in diameter compared to the old ones. i am watching for uneven wear - no signs so far.
Mel
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#5
Be careful as over inflating your tyres will have a detrimental impact on your braking distances (as well as tyre wear), especially in the wet.
[-] The following 1 user says Thank You to JT1 for this post:
  • RolyG
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#6
Mine gives a massive range for loaded/unloaded, so I'm currently quite a bit under the higher number. I can't remember the numbers now, but her ladyship's currently out in it so I can't check.

I know from my youth riding a drop-handlebar bike on the roads that harder tyres make a huge difference.

Some suggest that it's due to a smaller contact patch left-to-right, suggesting that the tyre is bulging out in the centre - I don't think that's true at all, IMO it's continuously compressing that squashed spot at the bottom of the tyre as it turns converts a lot of kinetic energy into heat.

Although the contact patch does possibly shrink front-to-back. But under-inflated tyres are also dangerous.

I don't know what I'm meant to do when I'm driving empty to collect a load. Should I pump them up when loading? In which case the tyres will be hot, so the reading will be meaningless.
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#7
I run mine at the top end of that recommended. Tyre wear is normal, handling is good so no reason to run them lower.
MkIII VTR 1.6hdi Modutop, Climate Pack, 16" Alloys
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#8
I reckon every car ive ever had runs on 32/34lb sq in, the upper figure for when er indoors gets in. . . i run my shopping bike on those pressures too. And its comfy until the bike bottoms. .. Had a mini in the 70s and knew when to pump the tires up. Mpg hit 30. . .
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#9
The roads in Notts are awful,as are the millions of speed bumps, so i tend to run my tyres at the softer settings.
Mpg is down into the mid fifty range but the ride is so much better!

 xtr with 16 inch wheels. Smile
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#10
Be VERY VERY carefull of running high tyre pressures just to gain a few mpg (which you will) especially in a Top Heavy Car like a Berlingo and NEVER blow em up to the max in winter. I Learned the hard way last time it froze and still insist the main reason I ended up in a hedge was down to high tyre pressures (officer). If you really want to save some fuel, Rip out all the Air Con, It works Wonders.
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