The manufacturer may want to know the lowest safe pressure so that it can specify a pressure substantially higher than that to give a substantial margin of safety against drivers who never check and adjust pressures as needed.
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Why 42 PSI ?
- Thread starter enemji
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The manufacturer may want to know the lowest safe pressure so that it can specify a pressure substantially higher than that to give a substantial margin of safety against drivers who never check and adjust pressures as needed.
Candleflame
Active Member
that myth has been debunked. this is only true on a perfectly mirrorflat road. on a normal road lower tire pressures glide over obstacles easier and therefore can actually be faster.
zoomer0056
Active Member
comanchepilot
Member
Yes - but only to a point - on a bicycle you will have less pedaling effort at the upper limit of the recommended pressure than at the lower limit - not necessarily at the highest vs lowest useable pressure - two totally different concepts,.
So many great moments in the Hitchhikers Guide to the Galaxy series. RIP Douglas Adams.
Candleflame
Active Member
This is my first Tesla and I was shocked to see 42psi recommended - all cars I've owned have been somewhere around 32-34psi. I found the ride 'pingy' and harsh, so after a few hundred miles with the car, I dropped the pressure to 38psi. Sure enough, the ride is noticeably smoother over small, high-frequency road imperfections. Might be a touch quieter too, but that is more subtle. Haven't noticed a large increase in wh/mi used around town.
But yeah, to answer the question, 42psi is definitely about reducing rolling resistance and increasing range. I plan on keeping it at 38psi except for road trips, when I'll bump it up to 42 and re-install my aero wheel covers.
But yeah, to answer the question, 42psi is definitely about reducing rolling resistance and increasing range. I plan on keeping it at 38psi except for road trips, when I'll bump it up to 42 and re-install my aero wheel covers.
Yes, this - for minimum rolling resistance you have to match the tire pressure to the road surface. Smoother surface - higher pressure; rougher surface - lower pressure. Lower pressure reduces rolling resistance over obstacles but increases rolling resistance in the form of energy wasted in deforming the tire itself. On the other hand, you're wasting energy deforming a low-pressure tire if you're on a smooth surface.
stopcrazypp
Well-Known Member
I looked up the video, if you are referring to the below video, it actually supports the argument of @comanchepilot (avoiding the absolute maximum and minimum usable):
First of all, the type of tire/wheel he is using is fairly specific (may not be applicable to other road bikes) and he is testing on rough roads. 28mm tubeless tires on Zipp hookless 303 Firecrest Wheels which are 25mm wide. He is 72 kg, and he is doing the test on chipseal roads which are rougher than typical asphalt or concrete roads (conditions were also damp, although not fully wet).
Chipseal - Wikipedia
Even so, the results he got was at 62.5 psi he was 0.3-0.4 kph faster than at 72.5 psi (the max allowed on his tires). He then lowered it to pressures recommended by the manufacturer's tire pressure guide for his conditions (53.7 psi front, 57.1 psi back) and only gained 0.1 kph (which he mentioned was probably not statistically significant). He then lowered it to 42.5 psi and actually went slower than at the pressure guide based pressures (although not slower than at 72.5 psi). So basically he only gained something significant when he went below the absolute maximum allowed by the tires, otherwise it was either not statistically significant or he actually went slower when he lowered pressures below manufacturer recommended.
In the end, he referenced the document here, which is mainly based on rough roads (poor-condition asphalt or dirt roads). Basically the idea is that the power required from the rider is both from rolling resistance and vibration losses (which play a bigger role on rough roads). This graph (which he showed in the video also) basically illustrates the idea:
https://www.sram.com/globalassets/p...emeffeciency/pdf-downloads/tse-explained2.pdf
As you can see, rolling resistance goes down with tire pressure increases. Vibration loss goes up. There is a sweet spot that optimizes both. That sweet spot pushes downwards on rough roads, and upwards on smoother roads. So basically due to the fact that a road bike has limited suspension to absorb vibrations, loss from that can be higher on rough roads. This may not be applicable to cars where the suspension system that supports most of the weight of the car can do a lot more absorption of road vibrations.
If you apply those results to this thread on Tesla tires (which as above may not be applicable in the first place due to major differences in the suspension design), all that tells you is to avoid pumping your tires up to the max allowed by the tire (50 psi or 51 psi) to reduce vibration losses on rough roads. It doesn't say necessarily that reducing pressures further lower than manufacturer recommended will help improve efficiency (instead it resulted in the opposite, going lower than manufacturer recommended was less efficient), especially given rolling resistance goes up as tire pressure goes down.
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rpiotro
Active Member
Do you have those awful MXM4 tires. I got rid of them after only 10K miles. And I am a dyed in the wool Michelin man. The foam liner gets stiff in cold weather and it feels like you are riding on a square tire. Then in spite of that acoustic liner the noise level can be quite high on certain road surfaces. Then there is the traction. OK at best on dry roads. So so in the wet and awful in the snow. With a dusting of snow I could not get up my not very steep driveway without a good running start. And yes, the ride is a tad harsh.
Replaced them with CrossClimate2s. Much better. Not much noisier but at least consistent on various road surfaces. Very minimal hit in range. Dry traction equal or better. Wet and snow performance off the charts for an "all season" tire. At 40 PSI the ride is much better than the MXM4s.
In 50+ years of driving I have never had a new car that the OEM tires weren't crap. The main criteria seems to be A.) low rolling resistance to maximize EPA economy testing. And B.) Low bid.
Interesting about the cold weather making the liner stiff. I got the car a couple months ago so I haven't had a chance to see what it's like in warm weather, but I'll be looking out for that. And yes, the MXM4 do not feel impressive in any conditions, they seem completely focused on efficiency. I am also a Michelin fan, usually Premier A/S on the family car and Pilot Sports on my fun cars.
Funny you mention that you did an early replacement of the MXM4s with CrossClimate2s - I was just on TireRack doing some research with the same idea in mind! The CrossClimates get incredible reviews everywhere you look; they seem to be the new all season king. However, this (incredibly relevant) TireRack test did put a damper on that idea a little bit - they used a Model 3 to compare the OEM Tesla MXM4 vs the CrossClimate2 and found that the CrossClimate2 is a better tire in almost every way, but that you pay for that in a significant range hit.
It made me a little hesitant about ditching the MXM4s since I was hoping to do some road trips this summer. It'd be a bummer to lose 10% of my range just to tires. Have you had the CrossClimates on a road trip?
Funny you mention that you did an early replacement of the MXM4s with CrossClimate2s - I was just on TireRack doing some research with the same idea in mind! The CrossClimates get incredible reviews everywhere you look; they seem to be the new all season king. However, this (incredibly relevant) TireRack test did put a damper on that idea a little bit - they used a Model 3 to compare the OEM Tesla MXM4 vs the CrossClimate2 and found that the CrossClimate2 is a better tire in almost every way, but that you pay for that in a significant range hit.
It made me a little hesitant about ditching the MXM4s since I was hoping to do some road trips this summer. It'd be a bummer to lose 10% of my range just to tires. Have you had the CrossClimates on a road trip?
stopcrazypp
Well-Known Member
That was a good read. Basically CrossClimates handle slightly better, also slightly better in wet, and absolutely dominates the MXM4s in snow, but the huge con is a big hit on range (plus a bit more noise). So I guess unless you see snow, MXM4s still remain a fairly good choice due to the efficiency.
Please do try out the Lexus OE tire - Michelin Primacy Tour AS (MFG Part# 06522 - MICHELIN® PRIMACY™ TOUR A/S 235/45R18 94V LEX BSW). I have those on my Mercedes, and they are absolutely luxurious. Make sure you don't choose the ones with 44PSI Max Load. Of course if you don't like it, you can always get a free return under the Michelin Promise Plan which includes 60-Day Satisfaction Guarantee. Michelin Warranty Information | Michelin
https://www.tirerack.com/tires/tires.jsp?tireMake=Michelin&tireModel=Primacy+Tour+A/S&frontTire=345VR8PTASV2&i1_Qty=4&autoMake=Tesla&autoModel=Model 3 AWD&autoYear=2022&autoModClar=235/45-18 SL (Standard Load)&vehicleSearch=true
The MICHELIN Primacy® Tour A/S has the quietest tread design among leading competitors based on internal objective interior noise tests measuring dBa from 500 to 2000 Hz on asphalt (weathered and smooth) and smooth concrete comparing the MICHELIN® Primacy™ Tour A/S versus the Bridgestone® Turanza™ Serenity Plus, Continental® PureContact™, Pirelli® Cinturato P7™ ALL-SEASON Plus, and Goodyear® Assurance® ComforTred®.
or the new Pirelli P Zero Elect AS tire... slightly cheaper than the MXM4s but I'm getting slightly better efficiency and less noise. Also ... running 40 psi increases comfort at minimal range hit. 42 psi cold with the temps warming up while driving gets fairly "stiff" soon
SalisburySam
Active Member
The 255/45R20 105V, Michelin Primacy Tour A/S is OEM tire on our 2023 Ioniq5 Limited, as well. Wonderful ride, very quiet. Hyundai recommends 34psi on the door jamb, max for tire is 50psi. Even with the relatively low profile 20” tires, the ride is also smooth and not at all jarring, though I’m not sure how much of that is the suspension.Please do try out the Lexus OE tire - Michelin Primacy Tour AS (MFG Part# 06522 - MICHELIN® PRIMACY™ TOUR A/S 235/45R18 94V LEX BSW). I have those on my Mercedes, and they are absolutely luxurious. Make sure you don't choose the ones with 44PSI Max Load. Of course if you don't like it, you can always get a free return under the Michelin Promise Plan which includes 60-Day Satisfaction Guarantee. Michelin Warranty Information | Michelin
https://www.tirerack.com/tires/tires.jsp?tireMake=Michelin&tireModel=Primacy+Tour+A/S&frontTire=345VR8PTASV2&i1_Qty=4&autoMake=Tesla&autoModel=Model 3 AWD&autoYear=2022&autoModClar=235/45-18 SL (Standard Load)&vehicleSearch=true
The MICHELIN Primacy® Tour A/S has the quietest tread design among leading competitors based on internal objective interior noise tests measuring dBa from 500 to 2000 Hz on asphalt (weathered and smooth) and smooth concrete comparing the MICHELIN® Primacy™ Tour A/S versus the Bridgestone® Turanza™ Serenity Plus, Continental® PureContact™, Pirelli® Cinturato P7™ ALL-SEASON Plus, and Goodyear® Assurance® ComforTred®.
rpiotro
Active Member
Have not had them on a road trip unless a 110 mile round trip to see a client counts. The fact that it still has been a bit cool around here makes it difficult to get a definitive answer. I make that trip about twice a month. My gut feeling is that the range hit is pretty minimal. My guess is 5% or maybe even less. If that holds true a small price to pay.
For those here that mentioned Michelin Primacy I have to agree it is a good tire. I had them on my Q50 hybrid. Good in all conditions except snow. I had a set of dedicated winter tires. Hakkapeliittas. Unstoppable.
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