Tyre pressure conundrum
Discussion
On a 9-5 auto. Recently had new tyres from Michelin Pilots to Primacy latter reckons to be as good for the MPG (150 miles door to door mostly on the Mway). OK, manual (the book not the gear box) and door sticker mention minimum pressure and advisory for certain loads. If I run at the minimum recommended the MPG is awful (32 odd). OK, up the pressure etc to a point that gets a good return, I can get 40. Prior change I was on 40mpg with around 36 psi.
So, the question. At what point is the upper pressure dangerous? Obviously handling and wear is affected but you just don't pump them up till bulging and let a bit out. Have to check the sidewall wall marking but sure they are the heavier duty.
Being tight I know but with the distance and conditions would like to maximise it.
So, the question. At what point is the upper pressure dangerous? Obviously handling and wear is affected but you just don't pump them up till bulging and let a bit out. Have to check the sidewall wall marking but sure they are the heavier duty.
Being tight I know but with the distance and conditions would like to maximise it.
Your tyres should be able to cope with 40psi. I've been driving a 9-3 estate for the last 3 years and was advised by the dealer to run the tyres at 40psi. However, even with running at the book pressure I was having problems with wear down the centre of the tyre. Running at 32 all round solved that problem, and I can still get high MPG. How you exercise your right foot will have more effect than tyre pressure IMHO
Thought this one was destined for the no reply bucket. Cheers. Not had any dealings with a dealer and was getting 39-40 prior tyres changed then it went down hill. I get lower mpg with 32psi and far better the higher I go. Just a bit wary of 40. Will pump them back up, around 37 at the moment. Re Right boot, I take it easy as hoofing it at the lights makes no difference really on a 150 mile trek to the office. Set cruise control to 70 and get the book out. Obviously forget that around town but I do not do that often, its the arm chair to get to work a long way away.
My 9-5 Aero Auto Estate tends to have a fair amount of kit in it so I usually run the tyres at max recommended pressure or close to it. I can never remember which way round it is but I think 43 front and 42 rear.
I don't do the long haul stuff often but would be really surprised at such a difference as you have noticed just through a change of tyre. Especially when they are basically the same. I'm running Michelins with, of course, the 'Extra Load' spec.
When empty of the kit I carry the ride is harsher with the tyres at higher pressure but the steering response improves. The dealer at service always seems to set the pressure about 4lbs under the recommended. (Recomended iirc is low 30s).
I think the best I have seen was around 34mpg. That was on a summer motorway run with some queuing and heavy use of the aircon but cruising, when the road conditions allowed, perhaps a tad faster than the limit. Which I thought was not bad, all things being considered.
Short runs, winter starts and around town stuff, even with a very light foot and avoiding sport mode, will drop it into the high teens quite readily - as one might expect.
How is the handling since the new tyres were fitted?
I don't do the long haul stuff often but would be really surprised at such a difference as you have noticed just through a change of tyre. Especially when they are basically the same. I'm running Michelins with, of course, the 'Extra Load' spec.
When empty of the kit I carry the ride is harsher with the tyres at higher pressure but the steering response improves. The dealer at service always seems to set the pressure about 4lbs under the recommended. (Recomended iirc is low 30s).
I think the best I have seen was around 34mpg. That was on a summer motorway run with some queuing and heavy use of the aircon but cruising, when the road conditions allowed, perhaps a tad faster than the limit. Which I thought was not bad, all things being considered.
Short runs, winter starts and around town stuff, even with a very light foot and avoiding sport mode, will drop it into the high teens quite readily - as one might expect.
How is the handling since the new tyres were fitted?
Handling is pretty much the same but then its door to door up the motorway mainly so not pushed it and bear in mind it is not an Aero or modded suspension so it wallows a bit. Not the best car to have in the twisties but then I have another for that. On the motorway it is good as it gets but then there are no corners to try it and the arm chair does what it does best and a very comfortable ride. Better in the wet I fancy but then I was down past 5mm when I bought it and it took two years to wear them out.
They (tyres) were pilots now they are primacy. They are the higher loading rating according to the marking on the wheel, 97. Think the older ones were 94. Would that make a difference?
Blurb and tests say they (Primacy) get the best mpg. On leave at the moment so will see what happens in a few weeks. I leave the climate control on but it seems the system is quite smart so not necessarily drawing full power all the time. Will up the pressure and see what happens.
Maybe I am being too picky
They (tyres) were pilots now they are primacy. They are the higher loading rating according to the marking on the wheel, 97. Think the older ones were 94. Would that make a difference?
Blurb and tests say they (Primacy) get the best mpg. On leave at the moment so will see what happens in a few weeks. I leave the climate control on but it seems the system is quite smart so not necessarily drawing full power all the time. Will up the pressure and see what happens.
Maybe I am being too picky
I would think the mid point - mid 30s - is about right for your commute.
The considerations are for safety and tyre wear. Tyre wear seems consistent on mine with no obvious oddities related to pressure - but them my mileage is low compared to yours so not so easy to be certain of changes. My fronts last about 10k miles but then I think that is down to a lot of short runs, too many roundabouts (wear on the outer shoulder of the NSF) and a lot of maneouvering per mile covered in relative terms. The rears wouold seem to go on for a long time although the last pair ended up making a rather annoying thrumming sound whan just over half worn. Something to do with tread patterns it seems.
Mine is on Primacy these days (always been on Michelin but started out on the one before Primacy) - the tread pattern seems to change every couple of years though so whether directly comparable is difficult. The highest MPG improvement figure I can recall seeing claimed for 'Energy efficient' tyres wss 5% so to go from low 30s to 40MPG seems a little high. It might be worth checking with Michelin to see what they say.
I suppose it is just possible that some combination of circumstances means that for you commute a higher pressure aids the auto's decisions and leads to significantly different operation and so fuel saving. However when I was doing long weekly commute runs in previous cars (132 miles door to door 98% motorway plus a couple of miles a day back and forth to the office) the biggest effect on consumption for a tankful of fuel was cruising speed (using cruise control mostly) and what traffic conditions were like. Heavy but moving traffic or an extended section of speed limited roadworks on the run - such that speeds dropped into the 50-60 mph range for extended periods - made an measurable difference to the figures. As did setting a higher than normal cruising speed by, say, 5MPH. Tyre pressure - a little, but not so much as ling as they were not really too low to start with.
The considerations are for safety and tyre wear. Tyre wear seems consistent on mine with no obvious oddities related to pressure - but them my mileage is low compared to yours so not so easy to be certain of changes. My fronts last about 10k miles but then I think that is down to a lot of short runs, too many roundabouts (wear on the outer shoulder of the NSF) and a lot of maneouvering per mile covered in relative terms. The rears wouold seem to go on for a long time although the last pair ended up making a rather annoying thrumming sound whan just over half worn. Something to do with tread patterns it seems.
Mine is on Primacy these days (always been on Michelin but started out on the one before Primacy) - the tread pattern seems to change every couple of years though so whether directly comparable is difficult. The highest MPG improvement figure I can recall seeing claimed for 'Energy efficient' tyres wss 5% so to go from low 30s to 40MPG seems a little high. It might be worth checking with Michelin to see what they say.
I suppose it is just possible that some combination of circumstances means that for you commute a higher pressure aids the auto's decisions and leads to significantly different operation and so fuel saving. However when I was doing long weekly commute runs in previous cars (132 miles door to door 98% motorway plus a couple of miles a day back and forth to the office) the biggest effect on consumption for a tankful of fuel was cruising speed (using cruise control mostly) and what traffic conditions were like. Heavy but moving traffic or an extended section of speed limited roadworks on the run - such that speeds dropped into the 50-60 mph range for extended periods - made an measurable difference to the figures. As did setting a higher than normal cruising speed by, say, 5MPH. Tyre pressure - a little, but not so much as ling as they were not really too low to start with.
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