Tire pressure again

[RAC68]

Hi All,

Today, after changing the oil and filter, I reset the air pressure to 32lbs on the front and 28lbs on the rear as Glenon mentioned. This was after lowering the front end with 3/8" spacers (nuts). Took the Healey out for an enthusiastic ride through the hills and found the car to track and respond great on tight turns and on straightaways. The ambient temperature was quite chilly, around 40F but the Vredestein Sprint Classic 165HR15s held quite well on rough asphalt turns and seemed to settle in and need no constant corrections at highways speed.

Ray(64BJ8P1)

 

[steveg]

I wonder what his tire pressure was? Tee hee.

View attachment 56137

Ha, ha - this pic reminds me of a Donald Duck car that bounces down the road from one tire to another! :welcoming:

 

[BN2guy]

Most often served "hot" I believe.

Yes, Reid knows hot air when he sees it.

 

[Legal Bill]

Sorry. See next post.

 

[Legal Bill]

If it is that important to you, buy a pyrometer. You can use it on all your cars and find the pressure that results in even friction across your entire tread on all four tires.

https://store.windingroad.com/longa...MIkJXJkLTf3gIVnFcNCh2BGwpnEAQYAyABEgIcQPD_BwE

 

[Bob_Spidell]

If it is that important to you, buy a pyrometer. You can use it on all your cars and find the pressure that results in even friction across your entire tread on all four tires.

https://store.windingroad.com/longa...MIkJXJkLTf3gIVnFcNCh2BGwpnEAQYAyABEgIcQPD_BwE

What's the difference between this and your ordinary, garden-variety IR thermometer (besides the name)? Do tires really get up to 1,400deg?

https://www.harborfreight.com/121-infrared-laser-thermometer-63985.html

 

[Legal Bill]

What's the difference between this and your ordinary, garden-variety IR thermometer (besides the name)? Do tires really get up to 1,400deg?

https://www.harborfreight.com/121-infrared-laser-thermometer-63985.html

Quality, calibration, features and accuracy. You can pay $100s for a really good pyrometer. The unit I posted is a unit of good quality at a price that isn't out of reach. You not only want accuracy, but you want a unit that can differentiate the temperatures at points that are relatively close to each other. This is especially true for tires where you want to get a good temperature reading at points across the face of the tire tread. I have seen good ones in use and have used one myself and I can tell you that they will show the difference in temperatures at points less than an inch apart on the surface of a tire. I don't own one myself, so I have not done any experiments with the good units against the bargain units. This video shows the difference in temp readings between a unit of reasonable quality and a bargain bin unit:

https://www.youtube.com/watch?v=LbPpO3xCfBY

Note well that the bargain unit can't measure the temperature of ice while it is near a pot of boiling water.

The unit I posted has uses well beyond tire temps. You can use it to measure temperatures under the hood at a variety of locations: radiator, cylinder head, block, headers, intake manifolds, thermostat sending unit, etc. This can really help when trying to diagnose an engine problem. You can also use it on brake components to determine if one drum or disc is doing more work than the others or is perhaps the victim of over-adjustment or a hanging caliper.

Perhaps the unit you cited would do the job for tires. I don't know. I'm not sure how you would know if it was right or wrong unless you had a good one to compare it with. We pay our money and we take our chances.

 

[Bob_Spidell]

Fair enough. Funny, if you let the YouTube video run it follows with:

https://www.youtube.com/watch?v=cjSbseiVRSA

 

[twas_brillig]

We have a Meyers Manx clone dune buggy, with ours based on a shortened 1962 VW Beetle chassis (our weight is similar to the original Beetle). The original VW used bias ply tires and 4 inch wide rims; we run 7" rims and radial tires. And I don't know what pressure I should be using.
I have a $ 75 US digital standard temperature reader, and took a run on a warm day last summer, starting with about 30 psi and dropping the pressure in a couple of pound increments and driving at highway speeds for ten minutes or so, and then reading the temperatures across the face of the tire, but did not get any meaningful results. I'm not sure if the reader I own was too slow in responding or my hand/eyesight was not consistent enough (I'd painted a stripe across the bottom of the treads to ensure some level of consistency); I would prefer to try a contact (vs laser) gauge to be able to be more repeatable but can't find one to rent.
No particularly useful comments, but figured I'd raise the issue of the difficulty of obtaining reliable, reproducible, readings across the tire tread width. Doug

 

[Randy Forbes]

The optimum tire pressures for our M Rdstr (on Hoosier DOT/R-rated slicks__with "holographic" tread) were obtained by using an older version of this Longacre tire pyrometer, and typically verified during each autocross event.

It is of utmost importance to get the temperature readings__3 per tire, outer, center & inner tread__immediately as the car comes off the track, and do all four (4) as quickly as possible. Sitting for even a minute and the temps across the tread will equalize. Sue got really good at this, usually having all of them done before I could get my helmet off and get out of the car!

This has a memory function, so you can just hit all the tires, recording them as you go. It paid dividends in competition.

 

[twas_brillig]

I'll be picking up a used Snap-On Act-7000 Digital Thermometer/Pyrometer this evening, hoping it'll be better (based just on the brand name rather than true research) than the laser sensor, but it'll be Spring before I can actually use it for the tyres. I've got the tables and equation from the Tire and Rim Association, but the pressure I need to handle the vehicle load on the dune buggy is about 6 psi for the fronts, so nothing real definitive has come out of that exercise. I figure the TRAC stuff can establish the minimum pressures and - touch wood - the pyrometer and measuring tread depth wear (another problem for obtaining reliable accuracy) will allow some level of optimization. And can I borrow Sue come spring? Doug

 

[RAC68]

Hi All,

I seem to be missing something. I appreciate that road adherence is one of a tire's prime uses and air pressure and heat have a great effect. So, from the perspective of a Healey pleasure driver, how would I determine what the general-optimum tire pressure would be for the front and rear pairs of tires? I appreciate that taking pressure readings in combination with 3 heat readings across the treads, at a number of ambient temperatures, would give some data points that could be plotted and could lead to a general tire pressure profile. However, do I relate tread temperature to optimum road adherence? If so, how would I determine the optimum temperature for tire compound road adhesion without resulting in excessive ware (given ware will also increase with increased adhesion)?

Further, I have just changed my tire pressure bias from Front-28/Rear-32 to Front-32/Rear-28 and found the change to be quite good. However, could this satisfaction change with the weather and since my pressure selections were based on general perspectives (no facts), how would you I find facts to base pressure selection upon for each Season (Spring/Summer/Fall)?

I appreciate that there may not be an answer to these questions but isn't what I've asked what we are looking for?

Ray(64BJ8P1)

 

[Legal Bill]

Hi All,

I seem to be missing something. I appreciate that road adherence is one of a tire's prime use and air pressure and heat have a great effect. So, from the perspective of a Healey pleasure driver, how would you determine what the general-optimum tire pressure would be for the front and rear pairs of tires? I appreciate that taking pressure readings in combination with 3 heat readings across the treads, at a number of ambient temperatures, would give some data points that could be plotted and could lead to a general tire pressure profile. However, do you relate tread temperature to optimum road adherence?

Further, I have just changed my tire pressure bias from Front-28/Rear-32 to Front-32/Rear-28 and found the change to be quite good. However, could this satisfaction change with the weather and since my pressure selections were based on general perspectives (no facts), how would you I find facts to base pressure selection upon for each Season (Spring/Summer/Fall)?

I appreciate that there may not be an answer to these questions but isn't what I've asked what we are looking for?

Ray(64BJ8P1)

My contribution to this thread was to point out that those who are seeking a perfect pressure should get a good pyrometer and measure tire surface temperature. The basic goal is to inflate the tires to a point where the temperatures are the same across the width of the tread. This is somewhat tedious, but to the extent people don't understand, a tire that is hot in the middle is overinflated, causing the center of the tread to bulge and make greater contact with the road than the edges of the tire. A tire that is hotter on the edges is likely under inflated and the center of the tread is making less contact with the road. This is very simplistic as you need to take camber and cornering into account. Your car's camber is naturally placing one edge of the tire more in direct contact with the road than another. Cornering will load one side of the tires and drive up the temps over the other side... This is boring, but hopefully everyone gets it. An even reading across the treads may not be best for you situation and you may be looking for a higher temp on one side or part of the tread depending on how you are driving. I could go on, but the measurements are just data points. At the end of the day you need to know how to interpret them and that mostly comes from experience.

Ambient temperature can make a big difference. UHP tires get downright greasy when the temperatures go down to 40 degrees and lower. The compound gets hard and the tires are more like marbles regardless of pressure. But mostly changes in ambient temperature increases or decreases the pressure in your tires and that makes a much bigger difference than the usual swing of temps between 20 and 90 degrees F. for most tires.

My car really needs 32 psi in the front to help with parking lot steering. So you do what works for you.

 

[roscoe]

I have 5 or six pressure gauges, all different types. They read within 5 psi (2.5 psi + or - )when I set my compressor regulator to 35, except for the one I just threw out because it was way off. Do any of you send your tire gauge out for calibration from time to time ( assuming you have a round bourdon tube type gage and not one of those barber pole types that in my experience are not very accurate)? Do your gauges read accurately when it is 32 degrees versus 100 degrees ambient? I sure don't know about mine. Does anyone ever weigh all 4 corners of the car. A scale at each tire might surprise you...full gas versus empty gas with a driver and with a passenger. Perhaps unequal tire pressures would be best. So many questions. So far my tires last OK, I stay on the road but don't really push my driving. I inflate until almost round, with a little bit of a bulge where it meets the road and back off a bit if I hit 35 psi ( or what I think is 35 psi).....works for me. Thank God I don't have On Star sending me tire pressure reports on my Healey, although a digital display telling me I failed to secure the gas cap inside the boot might be nice. I know I'm not a NASCAR driver and for those who really are driving at the edges of the performance envelope this issue is very, very important.

 

[vette]

You pump them up till the centers wear out. Then on the next set of tires you don't pump them up as much. :fat:
In reading about many racers , such as Mark Donahue, it is my belief that different tracks, conditions, and desired results will require different pressures at different times. As Bill has said, "what ever works". I think that applies especially to the track. My take away from reading Donahue's book is that he spent his life searching for the optimum suspension and tire combination and NEVER found it. As a matter of fact. many times after he spent days and nights right up the the start of a race to set up his car he found that it was the worse nightmare he could have put on the track. The reason he won many of his races was because Penske put a good machine under him and because of his shear stubbornness. For public road driving you might just find the best set up for the occasion by just plain trial and error. Obviously, IMUHO, FWIW.

 

[Bob_Spidell]

You pump them up till the centers wear out. Then on the next set of tires you don't pump them up as much. :fat: ...

That's what I do. Started my Mustang on Ford's recommended pressure--35psi front and rear IIRC--and wore the centers out. Went progressively down through about four sets of tires until settling on 29psi front/28psi rear (below 25 the TPMS starts squawking). The car has 315HP and a light rearend and anything higher in the rear makes it all but unmanageable.

Ran a set of Michelin AS/3s on it--All-season, when I'd been running HP summer only--and got 51K miles on them though they were only 'guaranteed' for 45K (and I could have got a few more Ks on them but rain is coming). I've never found two analog (bourdon tube) gauges that agreed exactly, and the 'sliding stick' type seemed to be just as good, but I think the newer digital gauges give more accuracy, but without a calibration standard you have to settle for repeatability.

 

[Randy Forbes]

My contribution to this thread was to point out that those who are seeking a perfect pressure should get a good pyrometer and measure tire surface temperature. The basic goal is to inflate the tires to a point where the temperatures are the same across the width of the tread. This is somewhat tedious, but to the extent people don't understand, a tire that is hot in the middle is overinflated, causing the center of the tread to bulge and make greater contact with the road than the edges of the tire. A tire that is hotter on the edges is likely under inflated and the center of the tread is making less contact with the road. This is very simplistic as you need to take camber and cornering into account. Your car's camber is naturally placing one edge of the tire more in direct contact with the road than another. Cornering will load one side of the tires and drive up the temps over the other side... This is boring, but hopefully everyone gets it. An even reading across the treads may not be best for you situation and you may be looking for a higher temp on one side or part of the tread depending on how you are driving. I could go on, but the measurements are just data points. At the end of the day you need to know how to interpret them and that mostly comes from experience.

Ambient temperature can make a big difference. UHP tires get downright greasy when the temperatures go down to 40 degrees and lower. The compound gets hard and the tires are more like marbles regardless of pressure. But mostly changes in ambient temperature increases or decreases the pressure in your tires and that makes a much bigger difference than the usual swing of temps between 20 and 90 degrees F. for most tires.

My car really needs 32 psi in the front to help with parking lot steering. So you do what works for you.

About a month ago__immediately prior to driving mine nearly an hour north to a car show__I swapped in the Nadella bearing conversion for the king-pins. Night and day!

I've fitted them on loose k-p sets for a couple of guys here, buying them for my car several years ago, but never experienced driving on them before. I'm impressed, and I'm hard to please!

Three (3) times installing these now, and none of my existing stash (included with k-p kits) of shims fit the void; had to make my own.

 

[Bob_Spidell]

BJ8 wheel bearing shims work (some of us aren't expert machinists layful.

 

[Randy Forbes]

BJ8 wheel bearing shims work (some of us aren't expert machinists layful.

Low-tech: mini vise-grips and a drum sander on a Dremel

 

[Bob_Spidell]

Ha ... didn't think of that.

IIRC--don't have it handy--the shop manual calls for a couple thou of end float; never understood why (maybe to let grease in?).