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Discussion Starter #1
What tyre pressures are you running on your Ampera?

I am always reluctant to deviate much away from manufacturer's recommendations with regard to issues such as this that have a direct bearing on safety.

Manufacturer's spend a lot of time testing what is the best compromise between safety and wear and so I would not recommend going above the 39psi that is the recommended maximum. If you do, and have an accident as a result of a blow-out or failing to stop in time then having tyre pressures outside the recommended range might compromise your position with insurance or police. Just a thought.

Having said that, I can see no reason why we shouldn't have the pressures as high as possible within the recommended range. High pressures will reduce rollong resistence and reduce our energy use extending our electric mode range.

My car was delivered with pressures set to 35psi but today I am upping them to 39psi. If I feel happy with the ride then that is where I will keep them from now on.
 

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Discussion Starter #2
OK. Just back from pumping up my tyres.

I thought I would see if I could use the onboard tyre pressure system to pump them up instead of using a tyre pressure guage. I don't know how accurate they are but I am sure it is within 1 or 2 psi so it should be fine. The pressures seem to be sampled every 30 seconds or so. I didn't ime it but as I was pumping up the tyre the reading didn't change immediately and then only changed every 30 secs or so. It works but you have to be a little patient.

My tyres are now at 38psi. I aimed for 39 but ended up at 3 at 38 and one at 39 so rather than inflate the 3 an extra 1psi I just let the 1 down instead. 38psi is fine.

I will report back on the ride when I have done a few miles.
 

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Took delivery with 36 psi all round, please advise what you think running on 39 psi. thanks.... Just had car detailed so will post pictures at the weekend. Had to build a make shift ramp to get the car into the studio as front spoiler was catching as we tried to get car into the garage.....
 

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Discussion Starter #4
Driven about 10 miles so far at various speeds and not really noticed a lot of difference between 35 and 38psi.

So I will be keeping mine at 38-40 in future I think.
 

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Some of the on board tyre pressure indicators are sometimes different by 1psi to the actual tyre pressures, according to my digital tyre gauge. The manual states the on board system is only a guide, therefore have decided that my digital gauge is more accurate, as it is one unit rather than 4 seperate units with their indivudual tolerances of accuracy, although it is a bit disconcerting to have different tyre pressures on the display. Tried inflating them to the on board system at 35psi but my gauge shows either 35 or 34psi, cannot get them the same :(
I'm inflating the tyres to 35 psi (comfort level) but may try the higher pressure to get better economy, thanks.
 

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Ignore the following if you are only interested in the high-level user details of the tire pressure system (ie. what is communicated in the user manual that comes with the car).

Some related service manual technical details:
Tire Pressure Monitoring System Operation

The tyre pressure monitor system warns the driver when a significant loss or gain of tyre pressure occurs in any of the 4 tyres. It allows the driver to display the individual tyre pressures and their locations on the driver information centre.

The system uses the body control module (BCM), driver information centre, instrument cluster, remote control door lock receiver, tyre pressure indicator module and a radio frequency transmitting pressure sensor in each tyre assembly. Each sensor has an internal power supply.

When the vehicle is stationary, the sensors internal accelerometer is inactive which puts the sensors into a Stationary state. In this state the sensors sample tire pressure once every 30 seconds and do not transmit at all if the tire pressure does not change. As vehicle speed increases, centrifugal force closes the sensors internal roll switch, which puts the sensor into Wake and then Drive mode. The remote control door lock receiver receives and then sends the tyre pressure and temperature data to the body control module (BCM). The tyre pressure indicator module sends sensor ID and location data to the BCM. The BCM translates the data contained in the tire pressure sensor radio frequency transmissions into sensor presence, sensor mode, and tire pressure. Once vehicle speed is greater than 40 km/h (25 MPH), the remote control door lock receiver waits for the sensors to go into Drive mode.

Each sensor has its own unique identification (ID) code which it transmits as part of each RF message and must be learned into the BCM memory. Once all 4 ID's have been learned and vehicle speed is greater than 40 km/h (25 mph), the BCM continuously compares ID's and pressure data in the received transmissions to the learned ID's and pressures to determine if all 4 sensors are present and if one or more tyres are low. If the BCM detects a low tyre pressure condition, a variation in pressure between 2 tyres on the same axle, or a malfunction in the system, it will send a serial data message to the instrument cluster requesting the appropriate tyre pressure monitor indicator illumination and also to display the appropriate data message on the driver information centre, if equipped.

The sensors continuously compare their last pressure sample to their current pressure sample and will transmit in Learn Mode-Pressure Triggered if a 8.3 kPa (1.2 PSI) change in tyre pressure has been detected in either a Stationary or Drive state. When the tyre pressure system detects a significant loss, or gain of tyre pressure, the tyre pressure monitor indicator icon is continuously illuminated on the instrument cluster and if equipped, a check tyre pressure type message is displayed on the driver information centre.

Both the indicator icon and driver information centre message can be cleared by adjusting the tyre pressures to the recommended kPa/PSI and driving the vehicle above 40 km/h (25 MPH) for at least 9 minutes.

If power is disconnected from the BCM or if the vehicle battery is disconnected each tire pressure sensor ID is retained but all of the tire pressure information is lost. Under these circumstances the BCM cannot assume that the tire pressures were maintained over an unknown period of time. Cars equipped with the driver information centre will display dashes and the scan tool will indicate a default tyre pressure value of 1020 kPa (148 PSI) for each tyre. To reactivate the sensors, the vehicle must be driven above 40 km/h (25 MPH) for at least 9 minutes. When the sensors are activated, the driver information centre displays the current tyre pressures.

The BCM has the ability to detect malfunctions within the tire pressure monitor system. In the event a DTC is set, the tyre pressure monitor indicator icon on the instrument cluster will flash for 1 min. and then remain illuminated after the power switch is turned ON and the instrument cluster bulb check has been completed. Any malfunction detected will cause the driver information center to display a service tire monitor system type message.
 

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I have had my Ampera for 16,500 miles now and have since new run the tyre pressures at 40psi (39 indicated on the display). I have always thought that the ride over roughish surfaces was a little harsh and that the tyre noise evident on some road surfaces, whilst reasonable, could be better.
While filling the car with petrol after returning from Cornwall I decided to use their tyre inflation equipment as one of the tyres was consistently showing 1 psi less than the other three. Recognising that GM recommends 35 psi for a comfortable ride, rather than inflate the low tyre I decided to reduce all tyres to 35 psi. The improvement in ride smoothness and tyre noise has been surprising and remarkable.
I know there will be a penalty in terms of battery range but the payoff is well worth it.
If you share my thoughts on the Ampera's ride and tyre noise give 35 psi a try.
 

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Interesting... like you I've run at 39/40psi from shortly after day 1. Might give 35psi a try and see what the difference is for me. Wonder what sort of difference it'll make to the range.
 

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I'm still running on the 36psi it came with. Seems about right:

  • Over inflated - poor grip/braking, hard ride, lower 'fuel' use and uneven tyre wear (in the centre)
  • Under inflated - improved grip/braking, softer ride, higher 'fuel' use and uneven tyre wear (on the outer edges).

That a fair summary?
 
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Does the monitor prompt if the pressure is too low as I'm sure I'm nearer 32 or less but nothing saying this is a problem ?
I understand you will only get a prompt if the tyre pressure reduces at more than a predetermined rate (suggesting a puncture)
I'd rather not experiment by gradually reducing the pressure to see if it shouts!!!

Big Paul
 

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My
Does the monitor prompt if the pressure is too low as I'm sure I'm nearer 32 or less but nothing saying this is a problem ?
my understanding is that a warning is triggered if a tyre is more than 'x' psi DIFFERENT to the others, not to an absolute value. It may be the rate of reduction that triggers it as the previous poster said though, I'm honestly not sure as I've not seen the logic described.
 

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Interesting... like you I've run at 39/40psi from shortly after day 1. Might give 35psi a try and see what the difference is for me. Wonder what sort of difference it'll make to the range.
I travelled to Tewkesbury area on Saturday, 252 miles round trip taking 5 hours of driving. I used all the battery on 'A' roads travelling at the speed limit wherever possible, only restrained by traffic. Motorway sections, M25 and M4 were travelled on petrol again at the speed limit where possible (145 miles approx.) . I achieved a battery range of 47.2 miles and petrol consumption of 51.5mpg.
I don't think the drop in tyre pressures have made a significant impact. The battery range exceeded my expectation but petrol consumption compares favourably with my usual figures of 49 to 52. for motorway and 'A' road journeys.
 

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Over inflated - poor grip/braking, hard ride, lower 'fuel' use and uneven tyre wear (in the centre)
This may have been true in the olden days of cross-ply tyres, but not any more.
I didn't know, and I'm pleased to learn, that the Volt / Ampera recommends a high tyre pressure.
 

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Interestingly there is a huge disparity on my system. Using the supplied tyre compressor, I have inflated the tyres to 41psi - then when I get in the car and drive for a few minutes (to update the sensors) they are all sitting at 37-38psi! I think I need to get a (relatively) accurate tyre pressure gauge to calibrate the system so I know actually what pressure I'm running at.

I've found that the car has a bit of a tendency to wander on the road with the pressures up (not surprising, but more than I'd expect) so I might try dropping the pressures a bit and assume that the tyre pressure monitors are about 3-4psi low on the actual value.

In any case, apart from proper digital tyre pressure monitors, all others are generally only good to +-3 or 4psi, even petrol station ones, let alone analogue "needle"-type gauges.
 

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I was very grateful for the tyre pressure warning system a week or two ago when it warned me of a "un-balance" in the rear tyres (normally 39 psi, but one had dropped to 34psi). The tyre didn't look any different to the others visually, but the local tyre centre found a nice 2 inch nail embedded in it... Luckily it was repairable.
 

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That sounds familiar :) Ruddy nails....so many about. My tyres are still the originals after 22k but two of them have had plug repairs because of nails...
 

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Think yourselves lucky the tyres aren't too expensive... one trip to Cornwall cost me a front tyre and a puncture repair on a rear tyre - on an old Jag XKR, which is about £350 a corner :eek:
 
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