Tire Monitor Error

[hcsharp]

Service done. TPMS: Reprogramed.

We should start looking into making our own tool to re-program the TPMS. (Might help the rangers with a smaller tool, give open-source some more functionality, and make it easier to fix the little annoying errors like those.)

I'd support this effort. I know nothing about TPMS systems though.

[markwj]

I'd support this effort. I know nothing about TPMS systems though.

2.5 Roadster / Roadster Sport Tire Thread

The suggestion here is to 'borrow' the tool from Tesla. That would certainly make seeing what it did easier...

Does anyone know what the tool actually does? Is it just CAN bus messages? If so, it is most likely on the same bus as OVMS (which can see TPMS announcements), and it might be feasible.

Any online reference to the tool itself? Manufacturer? Manual? etc...

[hcsharp]

Does anyone know what the tool actually does? Is it just CAN bus messages? If so, it is most likely on the same bus as OVMS (which can see TPMS announcements), and it might be feasible.

Any online reference to the tool itself? Manufacturer? Manual? etc...

I don't know what they're using for a tool but here's the OEM sensor (version 2.x):
http://www.tpmsoutlet.com
If you could find the tool for that sensor...

[hcsharp]

I got an new TPMS warning today. It let me know that my right rear tire was over-pressure. The weather warmed up unseasonably warm today and I still had my tires inflated for winter cold. A few minutes of driving (not hard) and one of them went up to 51psi (from 41 where I last set them). It was a 42 mile round trip which usually takes about 44 ideal miles. Today it only took 35! Amazing what a difference over-inflated tires and warm air makes! The fronts were at 37 psi and the rear 49 and 51 psi.

[Doug_G]

Amazing what a difference over-inflated tires and warm air makes! The fronts were at 37 psi and the rear 49 and 51 psi.

I think it would be advisable to post a warning to others not to deliberately over-inflate your tires to try and get more range. As a minimum your tires will wear out prematurely.

More importantly, it will affect the car's handling, and not in a good way.

[strider]

My car just went into the shop today for a TPMS error. It's been coming and going for weeks now. I had taken it in a year or so ago for the same problem. this time the tech pulled the logs OTA and said it was the rears that weren't being read. Hopefully I'll get the new antenna.

[jerry33]

I think it would be advisable to post a warning to others not to deliberately over-inflate your tires to try and get more range. As a minimum your tires will wear out prematurely.

Adjusting tire pressure for driving conditions is not overinflation. Inflating over the cold tire pressure posted on the sidewall is (when the tires are cold) is.

Tire pressures listed on the vehicle placard are based on a series of assumptions:

1. Ambient temperature (highs for the day) 65F (18 C). If the day is warmer you need to increase pressure to compensate. A 100F day should have a 4 psi increase. Also if you inflate inside during cold winter days (and no one inflates outside), you have to adjust for the warmer air that you put in the tires.

2. A daily pressure check is performed. If you don't check daily, then you have to compensate because you don't want to go under. If set properly (so that the TPMS alerts at one or two psi under where you want to run them, there isn't any need to compensate. If the TPMS is set to alert at 25% low (which is a typical setting for many cars) it's useless in my opinion.

3. Load expected to be carried (this may not be the maximum load that the car is rated for). Inflate more for a vacation trip.

4. Maximum sustained speed. (this varies on whether it's a family sedan or a sports car). Typically sports cars will give a table for speed and are expected to be driven faster so there is no real need to adjust for this. A family sedan is typically uses a 65 mph sustained speed to get the pressure. There shouldn't be much-if-any adjustment for this on the Roadster.

Tire pressures should never increase more than about 10% (or 15% if there is a very large difference in ambient temperature between morning when you check and afternoon).

If your driving deviates from the assumptions (and it would be nice if Tesla spelled out the assumptions) then you need to adjust the pressures. The ambient temperature and daily pressure check are 100% for sure part of the assumptions because that's what all the standards are based on (TRA, ETRTO, JTRTO, etc.). The other assumptions you have to take an educated guess. Using the amount of pressure increase after a couple of hours driving should give you a pretty good clue.


Higher pressures have the following advantages:

1. The tires heat up less so they last longer and are safer. When you are driving the tires heat up to achieve a thermal equilibrium. For example if you start with one tire at 20 psi and another at 30 (for illustration purposes), both tires will flex and create heat. This heat will raise the air temperature inside the tires and reduce the amount of flexing which in turn reduces the amount of heat produced. Eventually both tires will be at about the same pressure because the flexing will have been reduced to the point where heat generated equals heat lost. However the tire starting at 20 psi will be far hotter. It may even get so hot that the compounds start degrading. Heat is what kills tires--not pressure.

2. More resistance to pot-holes. A common tire injury is a "pinch shock". This where the edge of the rim cuts through the sidewall of the tire. It looks like either two parallel cuts or a C shaped cut (depending upon how hard the rim hit the tires). Higher pressure helps keep this from happening.

3. Lower rolling resistance. Self explanatory.

4. Reduces hydroplaning. Hydroplaning is caused by the build up of a wedge of water in front of the tire. When the water pressure in the wedge reaches the inflation pressure of the tire the tire hydroplanes. Note there is also such a thing as visco-planing. This happens when slippery stuff is on the road. There's no real cure for this--other than caution--but higher pressures will tend to wipe the slippery stuff off and dig down to the surface where they can get some traction.

5. Reduces stopping distance. This is true for family sedans with large weight transfers on braking. It won't be true for a Roadster and most sports cars because there is little weight transfer. In a family sedan the additional weight transferred to the front can put the front tires in a temporary under-inflation mode and increase the stopping distance.

6. Reduces uneven wear. Tires have a crown radius. If the crown radius is large (this means the tire tread looks flat in the unloaded condition) then no amount of pressure is going to expand the steel belts to make them "wear in the middle". If the crown radius is small then that is possible. Lower inflation pressures always result in wear on the edges of the tires and shorter tire life.

Lower pressures have the following advantages:

1. Reduces tread damage on gravel roads.

2. Reduces vehicle damage from vibrations on gravel roads and washboard surfaces.

3. Improves flotation off-road.

4. Improves traction in many off-road conditions.

In general, start with the vehicle placard pressures and then adjust them to suit your driving conditions keeping any pressure differential shown. However, no pressure setting can make up for lack of thought . Regardless of the rules you don't want to exceed the maximum pressure on the sidewall when you are inflating the tire. It is not a problem if the tire increases in pressure (to over the maximum pressure shown on the tire's sidewall) while driving.

[Doug_G]

An observation relevant to increasing the Roadster's front tire pressure, which seems to be a bit unusual. I've found during autocross that if I increased the front tire pressure above the recommended setting that it increased understeer. It pushed less when I backed the pressure down. No, I don't have an explanation, but even the books say that the rules work until they don't. This stuff is complicated.

[jerry33]

You got that right.

[strider]

An observation relevant to increasing the Roadster's front tire pressure, which seems to be a bit unusual. I've found during autocross that if I increased the front tire pressure above the recommended setting that it increased understeer. It pushed less when I backed the pressure down. No, I don't have an explanation, but even the books say that the rules work until they don't. This stuff is complicated.

This is perfectly reasonable. Within a normal range, lower pressure offers more grip as the tire will "expand" or "smoosh" (that's a technical term :P) more giving you a larger contact patch and therefore, more grip. Higher pressures will prevent this. Think about a highly inflated ball and push down on it against the ground. You will have a small amount of the deflection so the contact patch won't change very much. If you let some air out the ball will "smoosh" as you put weight on it and the contact patch will grow.