Tire pressure: continuous high speed driving?

[Jonathan]

What does "continuous high speed driving" mean to you?

The owner's manual calls for tire pressures to be 23 psi in the front and 30 psi in the rear during normal driving. It calls for 29 psi in the front and 34 psi in the rear during continuous high speed driving.

Just wondering what people use in their tires and what you notice if you go from the lower pressures to the higher ones.

Is it more of a long term wear and tear idea? Or is the handling better with lower air pressures at low speeds and better with higher pressures at higher speeds?

Most of the time I have 23 and 30 psi in my car and I generally drive around the countryside here where the roads are 80 km/hr zones (speeds at 90 km/hr typically). I don't drive around in town very often at the slow speeds or in traffic. For anyone going to DCS, spending hours on the Interstate in a 75 mph zone (120 km/hr) would surely qualify for the higher air pressures. Is there any advantage or disadvantage to just leaving them at 29 and 34 psi all summer?

[Bitsyncmaster]

I run 28 PSI front and 32 PSI rear all the time. I check pressure cold and it will go up a little when tires heat up. I don't know why everyone recommends higher pressure for highway unless they mean to set that pressure with warm tires.

Using 23 PSI in front just does not seem safe. I feel to risky for the tire to pull off the bead with a hard turn.

Lower pressures give a softer ride and less MPG.
Higher pressures increase puncture risks.

[Patrick C]

With my low profile tires I run 30psi in the front and 35psi in the rear.

[Jonathan]

23 seems low to me too, Dave. I know the car was designed for that with the weight distribution, but it does seem a little low for some reason.

Good point Patrick. Stock wheels versus non is important. I should have mentioned my car is stock in both the wheel and tire sizes as well as suspension.

[Michael]

I run 28 - 30 up front. I remember thinking that the factory recommended pressure for the front seemed way too low. I personally think this was done for the same reason the front tires were 14" to begin with...to keep the front end as planted as possible and keep oversteer to a minimum. I think with the improvements in tire grip that the low pressures on the front is no longer necessary.

[David T]

I run 28 - 30 up front. I remember thinking that the factory recommended pressure for the front seemed way too low. I personally think this was done for the same reason the front tires were 14" to begin with...to keep the front end as planted as possible and keep oversteer to a minimum. I think with the improvements in tire grip that the low pressures on the front is no longer necessary.

The manual gives no specification as to what is meant by sustained high speed driving. The higher pressures are meant to prevent rolling the tire off the bead in high speed turns. I would suggest if you are driving over 65 for more than 20 minutes or turns (like on a track) you should increase the tire pressure. It will wear the tires more in the middle and should not be done in the rain. Keep an eye on the sidewalls and if you start seeing wear on the sides you do not have enough pressure in the tires to keep them from rolling under the rims.

[DMCMW Dave]

Is there any advantage or disadvantage to just leaving them at 29 and 34 psi all summer?

It will ride harder.

[NightFlyer]

Primarily a ride comfort concern. Look at any era owners manual and they all have a similar recommendation regarding tire pressures.

That said, this is what I run year round for a nice balance between comfort and responsiveness:

Front - 26 LB F/IN2
Rear - 32 LB F/IN2

[David T]

Primarily a ride comfort concern. Look at any era owners manual and they all have a similar recommendation regarding tire pressures.

That said, this is what I run year round for a nice balance between comfort and responsiveness:

Front - 26 LB F/IN2
Rear - 32 LB F/IN2

If you are going to experiment with tire pressures go buy a tread gauge. They are not expensive. Regularly measure across the tread, the middle and each side of each tire. If you find you are not wearing evenly the sides and the middle, adjust the air pressure to even it out. More pressure wears the middle and less wears the sides. I have found the recommended pressures to be a good place to start and you should not find it necessary to vary from them more than 2-3 psi. Always compare cold before you start driving for the day. On one car the owner complained the doors shook and banged a lot. He needed door seals but he was filling the tires up to what it said on the sidewall, 32 psi. Once I lowered the pressures the doors were a lot better. One side benefit of keeping a lot of pressure in the front tires is it makes it easier to turn the wheels at low speeds. They will ride harder and the middle of the tread will wear out faster though. If you are serious about experimenting with tire pressure get a good tire pressure gauge. Not one of those cheap pencil types. You can buy a good digital one for around $15. You should also have a good infra-red thermometer. Too low and the tires will run hot. Very bad for tire life but it makes it very sticky for good traction.

[Bitsyncmaster]

Front tires will always wear more on the sides because of steering forces. With radial tires tire pressure does not make much difference with tread wear like old bias ply tires did (I'm showing my age with that comment).

So why does one car recommend 23 PSI and another car with the same tire recommend 34 PSI?

[Jonathan]

Thanks for the feedback guys. I pumped up the tires to 28 in the front and 32 in the rear last night and I'll test out the ride this week and see how it is.

[David T]

Front tires will always wear more on the sides because of steering forces. With radial tires tire pressure does not make much difference with tread wear like old bias ply tires did (I'm showing my age with that comment).

So why does one car recommend 23 PSI and another car with the same tire recommend 34 PSI?

It is all about load bearing and capacity. To handle less loads you require less pressure up the the rated capacity and max tire pressure. Yes, front tires will wear on the sides but so do the rears. That is why it is recommended to rotate the tires on cars that you can do it on. Even with radial tires you still get crowning and wear on the sides and the middle based on tire pressure.

[Farrar]

This is an interesting discussion. What do your tires' manufacturer recommend? On my car, I noticed that steering was easier at low speeds when the tires were inflated to the higher "sustained high speed driving" pressure.

I found the information in this chart to be informative, as well: http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=72

[David T]

This is an interesting discussion. What do your tires' manufacturer recommend? On my car, I noticed that steering was easier at low speeds when the tires were inflated to the higher "sustained high speed driving" pressure.

I found the information in this chart to be informative, as well: http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=72

It is not about what the tire manufacturers recommend. The automaker designs the car and selects the appropriate tire and then drive tests the car to determine the optimum tire pressure. That becomes a compromise involving load bearing, wear, ride comfort, wet weather driving, fuel economy, handling, etc. Since Lotus Engineering did all of this and all of the major manufactures go to them for advice, I would tend to go with what is on the tire sticker.

[Dangermouse]

I use about 28 in the D front purely for low speed steering effort.

On my DD, it's recommened pressures are 32 all round which is great for handling at 40mph+ but makes my daily commute <25mph bone shaking. The door jamb sticker recommends 32, but I reduced them to 30.5 at the weekend which resulted in a much more comfortable low speed ride, but even with a 1.5 psi reduction I could detect much more movement in the side to side maneuverings.

Incidentally, when my tires were hot, the pressure was 35, as compared to 32 when cold, a 10% increase, so I am surprised that the recommendation for high speed driving is 29/34. It's not clear whether you are supposed to inflate to these pressures before commencing a high speed drive, measuring when tires are cold, and then you can expect them to increase to 32/37.5 when hot (I think my tire max rating is 40)? Or that the hot tire pressure should be set at these and then they are what they are when the tires cool?

fwiw, buy a good tire pressure gauge and use it consistently if experimenting. Just using the ones on the compressors at the garage will lead to inconsistent readings

[dmc6960]

Been running 29F/34R for 14 years and over 100k miles. Its done me good. Never once wore out the middle of the tread first.

[David T]

I use about 28 in the D front purely for low speed steering effort.

On my DD, it's recommened pressures are 32 all round which is great for handling at 40mph+ but makes my daily commute <25mph bone shaking. The door jamb sticker recommends 32, but I reduced them to 30.5 at the weekend which resulted in a much more comfortable low speed ride, but even with a 1.5 psi reduction I could detect much more movement in the side to side maneuverings.

Incidentally, when my tires were hot, the pressure was 35, as compared to 32 when cold, a 10% increase, so I am surprised that the recommendation for high speed driving is 29/34. It's not clear whether you are supposed to inflate to these pressures before commencing a high speed drive, measuring when tires are cold, and then you can expect them to increase to 32/37.5 when hot (I think my tire max rating is 40)? Or that the hot tire pressure should be set at these and then they are what they are when the tires cool?

fwiw, buy a good tire pressure gauge and use it consistently if experimenting. Just using the ones on the compressors at the garage will lead to inconsistent readings


Be very careful going below the car manufacturer's recommendations. If there is not enough pressure in the tire and you hit a pothole you can destroy the tire and bend the rim. Can happen even with the proper tire pressure but more likely when you go lower. Going low also makes the tire flex more and that makes it get hotter. Hotter is bad, remember the Ford Explorers rolling over? In that case everything went wrong. The tires were undercapacity and made bad (cheap). Owners let the tires get low by not checking them regularly. Cars were overloaded with people and stuff. Caused the government to mandate tire pressure sensors on new cars. If you have to get the tire pressure wrong more is not as bad as less.