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Tire Pressure

Old 11-30-23, 11:10 AM
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Those flares are so getting caught up in that chainset.
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Old 11-30-23, 01:08 PM
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I'd prefer to ride at the lower recommended PSI for TL, but with how bad the surface conditions are where I ride, it'd heavily increase the probability of needing wheel servicing.
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Old 11-30-23, 01:12 PM
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Originally Posted by PeteHski
Ah I see now! JLR do have a poor reliability record, but AFAIK it doesn’t mean that all their TPMS sensors read low by exactly the same amount.

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I believe LR is the most unreliable car brand on the planet. Great looking cars, but man, you buy new and get rid of this after 3-4 years of ownership. Resale value must be low too.
If the software is off, all the sensors will be off. By the way, all of the major components that have failed on the Jag have been German. Go figure.
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Old 12-01-23, 06:49 AM
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Originally Posted by DangerousDanR
If the software is off, all the sensors will be off. By the way, all of the major components that have failed on the Jag have been German. Go figure.
And I never liked German cars neither. I always owned Japanese cars up until my current one (Tesla). Most of my friends back when I started driving owned VW and Audis and were often stuck at the garage with hefty repairs bills. Bosch parts here, Bosch parts there, special order here, special order there... But hey, they wanted to be original
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Old 12-01-23, 07:04 AM
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Originally Posted by DangerousDanR
If the software is off, all the sensors will be off. By the way, all of the major components that have failed on the Jag have been German. Go figure.
Maybe the software is doing some temperature compensation.
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Old 12-01-23, 07:26 AM
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Originally Posted by PeteHski
Maybe the software is doing some temperature compensation.
I'm currently using an electronic pressure sensor in a couple of products. The one we use is cheap and it reports temperature and pressure. We do the correction in software.

It is a MEMS sensor and temperature dependence (beyond normal gas physics) is a function of how they work.

​​​​​​The car reads low, but not very much low. Not enough discrepancy to cause trouble either way. Jaguar calls for 47 PSI in the rear, so running 45 on the TPMS set at near freezing will be okay all winter.

I don't see any caveats about temperature in the JACO data. ​​If I wanted, I could check the JACO against a calibrated sensor at work.

Last edited by DangerousDanR; 12-01-23 at 07:32 AM.
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Old 12-01-23, 11:39 AM
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Originally Posted by DangerousDanR
I'm currently using an electronic pressure sensor in a couple of products. The one we use is cheap and it reports temperature and pressure. We do the correction in software.

It is a MEMS sensor and temperature dependence (beyond normal gas physics) is a function of how they work.

​​​​​​The car reads low, but not very much low. Not enough discrepancy to cause trouble either way. Jaguar calls for 47 PSI in the rear, so running 45 on the TPMS set at near freezing will be okay all winter.

I don't see any caveats about temperature in the JACO data. ​​If I wanted, I could check the JACO against a calibrated sensor at work.
A couple of days ago I topped up tyre pressures on our 2 cars using a cheap portable compressor with a built-in digital gauge. I set all 8 tyres to 40 psi on the gauge and all 8 TPMS sensors reported 40 psi. I was actually quite surprised none of them read slightly different! But now when I think back to other cars I’ve owned, I can’t actually remember a TPMS sensor reading low/high relative to my Topeak digital gauge.

The analogue gauges on my 2 track pumps also seem consistent. I often hear about how inaccurate they can be, but mine seem pretty good.
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Old 12-01-23, 12:00 PM
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I think it's beyond the capability of virtually anyone on here to determine ideal tire pressure for speed, any more accurately than +/- 5 psi. Heck, probably 10psi. Too many variables, too many unknowns, too much subjective assessment, not enough good data.

I'd go further and speculate that even with all possible simulation capability, computing power, and eliminating rider weight and road smoothness variables, it's still too hard. Not that a number couldn't be calculated, but there are still variables and lack of good data.
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Old 12-01-23, 12:25 PM
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Originally Posted by downtube42
I think it's beyond the capability of virtually anyone on here to determine ideal tire pressure for speed, any more accurately than +/- 5 psi. Heck, probably 10psi. Too many variables, too many unknowns, too much subjective assessment, not enough good data.

I'd go further and speculate that even with all possible simulation capability, computing power, and eliminating rider weight and road smoothness variables, it's still too hard. Not that a number couldn't be calculated, but there are still variables and lack of good data.
Well that’s why we use decent tyre pressure calculators like SRAM and Silca to help us choose. The pressures they recommend might not be the actual optimum for our specific tyres and road conditions, but they are likely to be much closer than anything we could arrive at subjectively - at least in terms of speed. Comfort is more subjective anyway.
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Old 12-01-23, 12:53 PM
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Originally Posted by downtube42
I think it's beyond the capability of virtually anyone on here to determine ideal tire pressure for speed, any more accurately than +/- 5 psi. Heck, probably 10psi. Too many variables, too many unknowns, too much subjective assessment, not enough good data.

I'd go further and speculate that even with all possible simulation capability, computing power, and eliminating rider weight and road smoothness variables, it's still too hard. Not that a number couldn't be calculated, but there are still variables and lack of good data.
This, + the fact that a lot of pumps read pressure inaccurately.

Not a big deal anyways. Most cyclists only want to feel good on their bikes and they find a certain pressure that suits their needs.
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Old 12-01-23, 03:02 PM
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Originally Posted by Sy Reene
If your tubeless wheels are hookless, you do indeed have to reduce your pressure by a lot to be safe per ETRTO. Make sure you also abide by the tire and rim manufacturers specifications -- ie. go with the lowest of the sources. See Silca disclaimer I pasted below

96R/85F -- that seems like a much larger difference than Silca's calculator usually returns between rear and front. Are you running different width tires in Front vs Rear?
Fastest possible pressure!
That must be a new concept.
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Old 12-02-23, 09:13 AM
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Originally Posted by downtube42
I think it's beyond the capability of virtually anyone on here to determine ideal tire pressure for speed, any more accurately than +/- 5 psi. Heck, probably 10psi. Too many variables, too many unknowns, too much subjective assessment, not enough good data.

I'd go further and speculate that even with all possible simulation capability, computing power, and eliminating rider weight and road smoothness variables, it's still too hard. Not that a number couldn't be calculated, but there are still variables and lack of good data.
The Zipp pressure calculator is what I've been using for the last 3 years, since going tubeless on hooked rims for a year, then on to wider hookless rims. It's simple to put in all necessary information, except for tire casing. I have to decide whether thin or standard is most appropriate for the top level hookless compatible tires like the Pirelli P-Zero tires that I use. Thinner casing, requires more pressure. I've been using something in between thin and standard. It's only a suggestion and up to the rider to decide what they prefer.
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Old 12-02-23, 09:23 AM
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Originally Posted by DaveSSS
The Zipp pressure calculator is what I've been using for the last 3 years, since going tubeless on hooked rims for a year, then on to wider hookless rims. It's simple to put in all necessary information, except for tire casing. I have to decide whether thin or standard is most appropriate for the top level hookless compatible tires like the Pirelli P-Zero tires that I use. Thinner casing, requires more pressure. I've been using something in between thin and standard. It's only a suggestion and up to the rider to decide what they prefer.
I use the same calculator (SRAM/Zipp) and the pressures it recommends never cause any issues. I go with the standard casing pressures on Conti GP5000 and similar tyres.
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Old 12-02-23, 09:26 AM
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Originally Posted by DaveSSS
The Zipp pressure calculator is what I've been using for the last 3 years, since going tubeless on hooked rims for a year, then on to wider hookless rims. It's simple to put in all necessary information, except for tire casing... .
..and road condition and tire's inflated width. And it lets you choose rim type, but not tire type but I guess we'll assume nobody uses tubed tires on a tubeless rim :-)
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Old 12-02-23, 10:17 AM
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Originally Posted by Sy Reene
..and road condition and tire's inflated width. And it lets you choose rim type, but not tire type but I guess we'll assume nobody uses tubed tires on a tubeless rim :-)
I know, on my gp5000's 700x32 the tire width on 20mm inner width wheels is 31mm so at my 232 combined weight there is 2.9 psi front and 3.0 rear difference between listed and actual....not saying that will make any difference that I would notice but also does not differentiate between tubes either I would think a extra hd tube vs latex or tpu would have some impact but maybe not...
I like the silca one but how does one know what speed to put in? what is a fast group ride or moderate group ride? ultimately I end up going with the firm setting from the Rene Herse calculator which is quite a bit higher than either of the other two...
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Old 12-02-23, 10:24 AM
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Originally Posted by Sy Reene
..and road condition and tire's inflated width. And it lets you choose rim type, but not tire type but I guess we'll assume nobody uses tubed tires on a tubeless rim :-)
Since Zipp has your rim internal width, they're at least lowering the pressure as the rim gets wider. With road tires in the 28-30 range, I haven't seen any significant variation between brands. If the manufacturer follows ETRTO standards, there shouldn't be substantial width variations, since there's a standard for rim width. I use 25mm IW hookless rims with tires that are measured on 21mm rims, so they are wider. A 30mm tire measures 33mm.

It would be strange to buy expensive tubeless tires and use tubes in them. The recommended pressure for tubeless might result in pinch flats with tubes. I carry a spare tube, since it might be needed with a damaged tire, but I wouldn't use tubes in them.
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Old 12-03-23, 09:29 AM
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Originally Posted by Alan K
Fastest possible pressure!
That must be a new concept.
What term do you prefer for the pressure that minimizes resistance?
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Old 12-03-23, 10:43 AM
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Like many I have been on this slow increase in tire width and slow decrease in pressure. Currently I am running 30mm (31mm actual) GP5000 S TR tubeless at around 50-55psi for my 170lb me+bike weight. In the summer I will bump that up ~5psi. The Silca calculator says 65psi for me.

When I first got the 30mm tires I was running 70psi which probably gives optimal speed on reasonably smooth pavement, but the handling is so much better at lower pressures, both for smoothness of the ride and for grip when you need it. Especially in winter I really appreciate the lower pressure as the roads are wet much more often and the grip can be minimal at times.
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Old 12-03-23, 02:41 PM
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Originally Posted by scottfsmith
Like many I have been on this slow increase in tire width and slow decrease in pressure. Currently I am running 30mm (31mm actual) GP5000 S TR tubeless at around 50-55psi for my 170lb me+bike weight. In the summer I will bump that up ~5psi. The Silca calculator says 65psi for me.

When I first got the 30mm tires I was running 70psi which probably gives optimal speed on reasonably smooth pavement, but the handling is so much better at lower pressures, both for smoothness of the ride and for grip when you need it. Especially in winter I really appreciate the lower pressure as the roads are wet much more often and the grip can be minimal at times.
Those are the sort of pressures the pros are reported to be running in the spring classics at that width. I run the same tyre at 60-65 psi and I’m a little heavier than you. They ride well on rough roads and I’ve set many local PRs on them. Also did my fastest century event on them last year on relatively smooth roads.
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Old 12-03-23, 04:25 PM
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Originally Posted by downtube42
I think it's beyond the capability of virtually anyone on here to determine ideal tire pressure for speed, any more accurately than +/- 5 psi.
Hmmm. I think it's within the capability of several, possibly many, riders here -- but doing so is kinda tedious and boring. They *could* do it, but they don't want to, and as long as there are reasonably easily accessible online calculators available, there's not much need.
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Old 12-03-23, 09:49 PM
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Originally Posted by tomato coupe
What term do you prefer for the pressure that minimizes resistance?
Pressure can be properly specified by its actual units or subjectively indicated as high or low (as compared to whatever one sets their base level).
But don’t worry, I fully understand bastardization of language. 😉
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Old 12-03-23, 11:48 PM
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Originally Posted by DangerousDanR
Do I really have to explain? OK. Let me try...

In the Beatles movie "Help" there is a scene where the "baddie" points a pistol at Mr. Starkey. He in turn sticks his finger in the barrel and says, "It's British you know...won't work." Like the old joke about warm beer and Lucas refrigerators.

I have owned three British motor vehicles: a Norton Commando (with a Boyer-Bransden ignition that would stop working when the temperature was above 90F), a Series II land Rover, and my current Jaguar XE. All three of them have been absolute hoots to drive in their preferred environment. Not a one of them was what you might call reliable. I have also tried to buy two Lotus automobiles, but the deals fell through.
A good friend of mine is on his 8th Jaguar… he too hasn’t learned from his mistakes. 😉
He should have realized when Ford ownership actually improved the quality of Jaguar. Now it’s ownered by Tata (an Indian company known for its unsafe and unreliable crap vehicles) but the guy keeps going back to it. 🤪
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Old 12-04-23, 01:05 AM
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Originally Posted by PeteHski
A couple of days ago I topped up tyre pressures on our 2 cars using a cheap portable compressor with a built-in digital gauge. I set all 8 tyres to 40 psi on the gauge and all 8 TPMS sensors reported 40 psi. I was actually quite surprised none of them read slightly different! But now when I think back to other cars I’ve owned, I can’t actually remember a TPMS sensor reading low/high relative to my Topeak digital gauge.

The analogue gauges on my 2 track pumps also seem consistent. I often hear about how inaccurate they can be, but mine seem pretty good.
40 PSI? A lucky coinkidink!
I added air to four tires of my car (excluding the spare), each of the four tires were off by 1-3 PSI. An external high quality digital meter was used fill exactly 36PSI. The gauge in the reported inconsistently lower numbers. I’m not sure if individual pressure sensors can be recalibrated,

As for bicycles tire pressure, I have always liked to use a few PSI lower pressure than the maximum. On 25mm I usually use around 70-75 PSI.
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Old 12-04-23, 05:06 AM
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Originally Posted by Alan K
40 PSI? A lucky coinkidink!
I added air to four tires of my car (excluding the spare), each of the four tires were off by 1-3 PSI. An external high quality digital meter was used fill exactly 36PSI. The gauge in the reported inconsistently lower numbers. I’m not sure if individual pressure sensors can be recalibrated,
Good quality modern TPMS sensors are usually accurate within +/-2% so at worst case you might get one reading 1 psi low or high at 40 psi. But IME they usually all read the same when set with the same gauge. I have 2 digital gauges and they both read the same within 1 psi too. Neither of them are expensive gauges.

It also helps my “luck” in that my compressor actually targets 0.5 psi higher than the nominal setting. So it sets my tyres pressures to an indicated 40.5 psi. Which means that the TPMS sensors are less likely to read 39 or 41 psi because they don’t round their readings up or down. So 40.1 and 40.9 both display as 40.
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Old 12-04-23, 07:23 AM
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Originally Posted by WaveyGravey
I ride Gatorskin 700x25 at 100 PSI. I weigh about 160 pounds.
tubeless?
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