Interesting, but at ~$300 everywhere (Tire Rack, Amazon, etc.) I'll probably stick with my analog gauge.Originally Posted by mark elder
Interesting, but at ~$300 everywhere (Tire Rack, Amazon, etc.) I'll probably stick with my analog gauge.
Dave Weitzenhof
It's really disappointing to hear that Longacre agrees they sold you a tool that is not up to the task and they aren't offering any help. I expect they should either replace it or offer you a substantial discount on a different model. I feel bad I suggested they were a good source.
Today I went out to the shop and fooled around with it some more. It seems to be very sensitive to sudden movements, getting zero-shifts up to 1 psi. I cleaned all the battery terminals, but that did no good. I also cut a 5/8" hole in the center of the battery box to make sure it did not touch anything. Made no difference. The zero point still wanders around at up to 1 psi off and most times resists re-zeroing. Maybe, although there is nothing that looks questionable, there is a bad solder joint or something like that.
After 2 hours of screwing around I gave up before I got pissed enough to maybe throw it at the wall, and will maybe revisit it when I have more time.
Last edited by DaveW; 01.09.23 at 7:23 PM.
Dave Weitzenhof
Dave,
I think your digital gauge is duff. I have the smaller Longacre digital gauge. The gauge turns on and is always zero. It does have a zero function by holding the "on" button for 3 seconds. I used to calibrate my digital and analog gauges at work in the instrument shop and always did a pressure comparison at the start of the day at the track.
I've found the digital gauge to be nearly useless if the air temperature is below 45F. The little button cells don't like low temps.
“Racing makes heroin addiction look like a vague wish for something salty.” -Peter Egan
Yeah, I agree with you. But I hate to give up on something I paid ~$141 for. At least it's good for non-racecar stuff since a psi or so makes little difference for a street vehicle.
Dave Weitzenhof
Hey, most folks have had good luck with them, so I certainly don't blame you. It seems like mine is just a luck-of-the-draw bad exception. Crap happens. It's too bad I didn't realize the issue until after my warranty expired.
See post #50. Longacre is going to send me a new gauge !
Last edited by DaveW; 01.15.23 at 2:01 PM. Reason: added last sentence
Dave Weitzenhof
JACO Products 100 psi digital gauge
Highly rated, all brass construction, ~$32 including tax & shipping from Amazon. ~$110 less than the Longacre that I've been talking about above. Lifetime warranty and, per a LOT of reviews, excellent customer service! I just ordered it.
https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1
For that price, what do I have to lose? Since it is good to 100 psi, I can even use it on my Chevy G30 van (tow vehicle) tires (60-80 psi).
Last edited by DaveW; 01.10.23 at 11:19 AM.
Dave Weitzenhof
I went back out today to further examine the Longacre gauge. I may have finally determined the issue.
Since the transducer is in a brass fitting located in not very tight-fitting slots in the somewhat flexible plastic gauge body at the gauge end of the hose, wiggling the hose deflects the fitting and puts a little stress on the stiff strip of 4 wires leading from the transducer to the circuit board. These wires had no potting around them in the hole leading to the transducer. That means that the wires may have been putting some side or bending load on the transducer when the fitting deflected, maybe enough to cause the random, uncorrectable, zero-shift issue. This is the most reasonable probable cause I've found to date.
So I potted the part of the wire strip entering the brass fitting with Dow 832 non-corrosive RTV. It's fairly stiff (Durometer 35A) when it cures.
I'll give that a week or so to thoroughly cure and see what results. If that doesn't fix it I may separate the 4-wire strip into its 4 individual wires, reducing the strip's stiffness and its resultant stress on the transducer.
Last edited by DaveW; 01.13.23 at 4:11 PM. Reason: added more info
Dave Weitzenhof
I received this today and calibrated it against gauges that I have used in the past. It calibrates almost identically to the Longacre.
Last edited by DaveW; 01.11.23 at 8:45 PM.
Dave Weitzenhof
Guess what? Today, after several emails to Longacre describing what's been going on with the gauge, I got an email from them saying they're sending me a new gauge ! That certainly restores my faith in them.
I also told them I'd update them on whether my latest "fix" did any good.
Dave Weitzenhof
I have had several of my digital Longacre gauges go for a crap recently after many years and will have to replace at least one. Does anyone have any current recommendations for the lower priced digital gauges?
Yes, I have some very good old analog gauges around, but would rather have some variance in a .1 psi digital gauge than trying to eyeball an analog gauge. Thanks!
Greg Rice, RICERACEPREP.com
F1600 Arrive-N-Drive for FRP and SCCA, FC SCCA also. Including Runoffs
2020 & 2022 F1600 Champion, 2020 SCCA FF Champion, 2021 SCCA FC Champion,
2016 F2000 Champion, Follow RiceRacePrep on Instagram.
https://www.apexspeed.com/forums/sho...l=1#post648238
I calibrated this against gauges that I have used in the past. It calibrates almost identically to the Longacre. The only issue is that because it keeps the recent reading displayed when pressure is removed, it doesn't always exactly follow the pressure drop as you bleed off excess pressure. That issue was noted in the reviews.
Last edited by DaveW; 01.13.23 at 9:27 AM.
Dave Weitzenhof
I did what I said above - it had no effect. So the issue will remain a mystery. Very nice that Longacre sent me a new gauge to replace it.
Dave Weitzenhof
I calibrated the new gauge in the shop which is currently at 55-60F. It read within reading errors (0.1 to 0.2 psi) of what it should. However, this time (~1.5 hr after I brought it out to the shop) it displayed a similar zero-shift issue as the older one, but about 1/2 as bad. Instead of as much as 1 psi shift, it was limited to ~0.4 psi. When I first tried the new one earlier it had previously been sitting in the house at ~70F, so it was still warm and even at this point it was still a bit warmer than the shop.
When the weather gets warmer, I'll see if it still does that. The 2019 gauge seems to be less subject to this at warmer temps, so I assume the new one will also. I guess when it's cold out (below 60F) I'll still use my Ashcroft scientific analog dial gauge which doesn't have this issue.
Dave Weitzenhof
We use super-accurate pressure gauges in my company's line of work (service/calibration of laboratory instrumentation) and, over the years, I've learnt a lot about their accuracy and influences on that.
Digital/electronic gauges are highly responsive which is great most of the time, but this can be their very downfall. Even the slightest flex in the sensor mounting can create an error/offset in reading. Our sensors are generally in machined-from-solid, stainless steel housings to minimise this.
Another influence - and one that can affect analogue gauges too - is any change in atmospheric pressure. A 'vented' gauge will have an opening in the housing, so any change in atmospheric pressure doesn't affect the zero point (this applies to 'gauge pressure' instruments far more than 'absolute pressure' ones). Without a vent, the zero level is dependent on the atmospheric pressure at the time of build. If this changes, which it will quite normally, it can create an offset. That internal pressure within the housing can also be influenced by changes in temperature since, if the housing gets colder and thus the material contracts, the internal pressure can increase as the volume decreases.
In practice what does this all mean? Gauges are only as accurate as their construction allows. That does not mean they are 'wrong', simply that their 'rightness' is not perfect!
The liquid filled "shock and vibration resistant" analog gauges are even more susceptible to the above. There was a thread on this many years ago.
“Racing makes heroin addiction look like a vague wish for something salty.” -Peter Egan
The Longacre gauges have plastic 2-piece housings, so they are definitely not sealed. It appears to me now that there are components that as they warm up change their output, and those are not temperature-compensated. The rapid movements zero-shifts likely are a side effect that if the outputs didn't continuously shift with temperature after starting out cold would not be noticed.
The more expensive digital tire gauges are likely temperature-compensated to minimize the effects of changing gauge temperature.
Last edited by DaveW; 01.16.23 at 11:16 AM.
Dave Weitzenhof
Is the sensor inside vented, Dave? I'm not familiar with the specific internals of Longacre gauges but the 4-wire sensor is likely to be a silicon diaphragm Wheatstone bridge. These need to be in a very rigid housing to prevent physical deflections, eg. pcb flex, but with a vent to eliminate variance due to changes in atmospheric pressure. By way of comparison, the sensors we use in the workshop are similar to this:
http://www.southeastern-automation.c...ssure/2200.pdf
Temperature compensation on gauges can mean two things, either:
a) The readout is compensated to allow for tire temperature
b) The resistances in the Wheatstone bridge are compensated to allow for component temperature
The pressure transducer was open at its internal electrical connection, but in my experimentation on the 2019 gauge, I did pot it with Dow 832 RTV in an attempt to minimize the effect of the wire strip's stiffness on transducer output. Now that I know that didn't help and is likely counterproductive, I'll drill a small hole to make sure it's vented again.
a&b) It's apparent now that neither of these 2 choices is present in these 2 gauges.
Dave Weitzenhof
Looking at the literature in the link I see the company Druck is located at 4 Dunham Drive in my town. I actually rented garage/workship space at 4 Dunham drive! Our town is known for having a decent high school lacrosse program, not serving the world with state of the art transducers!
Cool. Was expecting to learn something by lurking on Apexspeed, but not this
I had a quick look at Longacre's website and it's only their more expensive gauges that will give a "tire temperature" corrected pressure. For component temperature compensation, the Wheatstone bridge will often have a built-in thermistor to perform this function.
It's interesting your $32 Amazon purchase was just as accurate as the Longacre gauge. Unless a manufacturer is using a high-quality transducer from a supplier like Keller, it's likely both will be using standard plastic-cased component, so the functional similarity isn't too surprising.
As a little light relief, the link below is from Wika who make excellent gauges, and illustrates beautifully (too beautifully, in some cases!) common failure modes:
https://blog.wika.us/knowhow/8-commo...gauge-failure/
Does gage accuracy really matter?
I found a NHTSA study that tested sliding friction vs tire pressure for a Goodyear Eagle street tire. The coefficient of friction between 24 and 17 psi only varied 1.2%. So that is about .2% per 1 psi. I am pretty sure a driver cannot sense a .2% change. This test used a special towed test trailer on a Goodyear test track.
Note: I fully accept that there are aero/ride height implication for tire pressure settings. What I am interested in is the change in the level of grip.
Brian
I can tell you that I can feel a distinct change in level of grip with a 2 psi difference in front tire pressure in the SCCA FC spec bias tires on my Citation F2000. At 17 they're very good. At 19 they're skating. Since pressure rises as they warm up, I want to know within 1/2 psi where they are when I leave the grid.
Last edited by DaveW; 01.17.23 at 9:35 AM.
Dave Weitzenhof
I can’t speak to race cars, but in karting a pound off on the gauge was noticeable and could be detrimental — and we also ran pressures in the mid- to upper-teens.
We had the luxuries of sponsorship covering everything except the chassis itself, and thus a virtually-unlimited tire budget to test for days with if we wanted to (and we did).
What we learned was the sweet spot was finding hot pressures as close to 2 psi gain from cold to hot as possible on the outside tires, and whatever inside pressures it took to match outside pressures at full hot. Three pounds (outside) gains created overheated tires, one was underheated. We ran 10% less pressure on the outside front cold, and 20% on outside rear cold. The first lap was very tricky in feeling like the outside rear had gone flat, but after two laps the grip was much better than when starting with matched pressures.
None of this would have worked at all with an inconsistent gauge — especially if 15 now showed as 17 a second later, and inverse on the other side. Sounds to me like a guarantee for getting whooped, which is never a worry on the street — not to mention the dynamics of carcass, compound, and weight transfer are entirely different.
Last edited by E1pix; 01.16.23 at 5:51 PM.
Once we think we’ve mastered something, it’s over
https://ericwunrow.photoshelter.com/index
What type of gauge do the F1, Indycar, World challenge ect use?
Will
It's been a few years since I've been in the pits for an Indycar race, but it was majority of Intercomp, a few Longacre, and there were one or two others.
I can believe that for a street tire. However the differences in friction/grip characteristics for street vs race tires and compounds are huge. Street tires are designed to be as consistent as possible across a very wide range of contact pressures, tire pressures, ambient temperatures, tire temperatures, etc. Race tires are designed to have much higher grip levels, but that means they operate properly in a relatively small range of ambient and tread temperature, slip velocity, contact pressure, etc. I.e., race tires operate optimally in a very narrow range of use, and tire pressure is one of those critical variables.
Last edited by DaveW; 01.17.23 at 12:11 PM.
Dave Weitzenhof
I'd be more concerned about the impact on tire spring rate, I should think.
We actually dial in pressure on our ITB/HP car to the tenth, it matters - even for Regional (sorry, Divisional now?) racing. Been doing that a LONG time, many wins to show for it.
No argument there.
Tire spring rate is a BIG part of the handling equation and is of course directly affected by tire pressure. To not over-complicate things, I just didn't include that in my previous response comparing street to race tires.
Last edited by DaveW; 01.17.23 at 12:27 PM.
Dave Weitzenhof
Analog dial gauge range vs usage pressure
Most authorities say that a tire pressure gauge should be used near the middle of its range for accuracy.
That is generally good advice, but I have a slightly different take on it in relation to dial analog gauges:
While gauge accuracy will be better in the middle (near 30 psi in a 0-60, near 15 psi in a 0-30 gauge, etc.), one has to factor in being able to read the gauge needle with accuracy w/o taking more than a second or 2 to do it. This means to me that finer gradations and more space between each psi is as important in quickly obtaining the desired pressure as the intrinsic gauge accuracy.
So I prefer a 0-30 dial gauge for the tire pressures on my F2000, which may be from 13 cold to 22 hot, depending on position and ambient conditions, as much for readability as accuracy.
Dave Weitzenhof
Repeat pressure gauge comparison - edited 1/23
I compared readings from my 8 tire pressure gauges, including the Longacre 52-53000 I bought in 2019 and the one Longacre just sent me on warranty - these have zero-point issues (discussed previously) below 60F. The Ashcroft is a lab quality gauge I bought 20+ years ago, mated to another gauge's hose and end fitting and have been using since I got it. None of them was hugely off from the others especially considering their ranges.
The Ashcroft is very accurate, but my issue with it is that reading it correctlly (it has 1/2-psi hash marks) is a bit difficult, especially when one is rushing; 1/4-to-1/2-psi misreads are hard to avoid. The new Longacre analog dial gauge is nice, but no easier to read, oil-filled (so it is slow to react), and it holds the reading (keeps its internal pressure) so you have to re-zero between different tires. Reading the RaceQuip (no longer used for racing) was difficult since it has only 1-psi hash-marks. The JACO I just bought is surprisingly accurate (I used it as the baseline), and only cost $32. It also holds, so extra re-zeroings are sometimes necessary.
I submitted an online communication with JACO asking if the hold feature could be switched off. The answer is no, it can not be disabled. Unfortunately, that means to me that it'll not be practical to bleed down racecar tire pressures in a hurry because for small smooth pressure changes, the display doesn't always follow the actual pressure. That's really too bad - it's very accurate and doesn't appear to have the low-temperature zero-shift issues of the 2 Longacre digitals.
Bottom line - I now have 4 gauges that calibrate essentially the same. So if I need to switch, there will be no errors induced.
Repeated comparison/calibration below:
Last edited by DaveW; 01.28.23 at 10:22 AM. Reason: Recalibrated Ashcroft gauge - moved pointer
Dave Weitzenhof
I think the main takeaway from your testing is what I've been told in the past - always use the same gauge!
Garey Guzman
FF #4 (Former Cal Club member, current Atlanta Region member)
https://redroadracing.com/ (includes Zink and Citation Registry)
https://www.thekentlives.com/ (includes information on the FF Kent engine, chassis and history)
Or if possible, make sure all of the gauges you will possibly use are calibrated the same, within your desired accuracy. Today I made a pointer puller (below, uses a 1/4-20 Allen screw) and reset the Ashcroft to match 3 other gauges, all in yellow background in post 71. The Ashcroft will likely be my preferred gauge except at warmer ambient temperatures where I can use the Longacre digital.
Last edited by DaveW; 01.22.23 at 5:36 PM.
Dave Weitzenhof
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