choddo

Those flares are so getting caught up in that chainset.

Troul 

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.

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.

eduskator

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

PeteHski

Maybe the software is doing some temperature compensation.

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.

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.

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.

PeteHski

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.

eduskator

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.

Alan K

Fastest possible pressure!
That must be a new concept.

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.

PeteHski

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.

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 :-)

jadmt

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...

DaveSSS 

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.

tomato coupe

What term do you prefer for the pressure that minimizes resistance?

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.

PeteHski

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.

RChung

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.

Alan K

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. 😉

Alan K

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. 🤪

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,

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.

PeteHski

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.

rclouviere

tubeless?