Don
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Joined: Thu May 10, 2012 3:55 pm
Location: Biloxi MS

Re: 140 kph

Fri Jan 18, 2013 7:29 pm

Joe,

I don't see how such high pressures could possibly improve handling - Higher pressures reduce the sidewall flex which also reduces contact patch and that reduces the friction with the road surface - Less friction there means the tire loses traction sooner than if you were using the recommended pressure. I suppose you could be getting a percent or two greater range due to the decreased rolling resistance, but I'd bet any improvement is too small to measure

If extreme tire pressures were better for handling, all racecars would be doing this . . . . but they're not. They all run pressures much lower than the manufacturers maximum. (NASCAR cars leave the pits with cold pressures in the low teens) The long established method for determining the best pressures for handling is to chalk all the tread from sidewall to sidewall and then keep adding pressure gradually until the tire no longer rolls the edge of the tread when cornering hard - In other words, the lowest pressure which keeps you from rolling over on the sidewall is the best pressure for handling. If you're a driver who corners hard, then you'll need two or three more pounds than someone who doesn't drive as hard as you do

Good on you for not recommending anyone else try pressures higher than the maximum recommended by the tire manufacturer - Running pressures so high that the sidewalls cannot flex in a pothole is certainly one way to ruin a tire by damaging the tread plies. They do publish a max pressure and mold it into the tire sidewall for a reason

That said, my experience is that almost all vehicle manufacturers recommend pressures on the low side of optimum (I'd imagine this is so you'll be happy with the cushy ride) so I always run my tires harder than the vehicle manufacturer recommends. Great handling is why I bought my Miata and I've found that 32 to 34 PSI works best for handling when I drive it hard . . . . as in occasionally sliding all 4 tires in a corner hard :D Mazda recommends a ridiculously low 26 PSI

With my iMiEV, I use 45 PSI while Mitsu recommends 36. Personally, I would never go higher than the max rating molded into the tire - There's nothing to be gained and it could result in a damaged tire

Don
2012 iMiEV SE Premium, White
2012 iMiEV SE Premium, Raspberry Metallic
2012 iMiEV SE, White
2017 Chevy Volt Premier
2014 Ford Transit Connect XLT SWB wagon

JoeS
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Posts: 3816
Joined: Thu Dec 15, 2011 5:47 am
Location: Silicon Valley, California

Re: 140 kph

Fri Jan 18, 2013 10:14 pm

Don, I defer to your experience in the handling department - perhaps the liveliness I feel in my iMiEV is simply due to the minimal contact patch :roll: , yet I consider the iMiEV very stable at speed. However, when it comes to mileage gain, I believe there were a number of tests which showed a significant improvement at higher tire pressures. For example, I briefly looked at EcoModder and they repeated the Mythbusters results as being a 7.6% reduction in fuel consumption in going from 35psi to 60psi:

http://ecomodder.com/forum/showthread.php/mythbusters-tests-tyre-tire-pressure-17151.html

Translate that 7.6% into a range increase and that gives us close to five more miles of range for the iMiEV.

My Gen1 Honda Insight lifetime of over 77mpg isn't only due to featherfooting. :geek:

Nevertheless, as you pointed out, we don't want anyone to treat this as a recommendation to exceed the manufacturer's tire pressures, which are posted on the driver's - side door.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

emissionimpossible
Posts: 10
Joined: Tue Oct 09, 2012 5:14 pm
Location: CURVE LAKE, ONTARIO, CANADA

Re: 140 kph

Sat Jan 19, 2013 6:53 am

I don't know how to post pics, but I'll give it a try...My bumper sticker:

https://fbcdn-sphotos-e-a.akamaihd.net/ ... 4799_n.jpg

emissionimpossible
Posts: 10
Joined: Tue Oct 09, 2012 5:14 pm
Location: CURVE LAKE, ONTARIO, CANADA

Re: 140 kph

Sat Jan 19, 2013 6:59 am

Ha Ha, Merci, Steph.

JoeS
Site Moderator
Posts: 3816
Joined: Thu Dec 15, 2011 5:47 am
Location: Silicon Valley, California

Re: 140 kph

Sat Jan 19, 2013 10:34 am

emissionimpossible wrote:I don't know how to post pics, but I'll give it a try...My bumper sticker:
Image

Thank you for posting. Very creative, I thought! 8-)

To post the picture, you highlight the link and click on "Img" in the edit menu.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

emissionimpossible
Posts: 10
Joined: Tue Oct 09, 2012 5:14 pm
Location: CURVE LAKE, ONTARIO, CANADA

Re: 140 kph

Sat Jan 19, 2013 5:05 pm

Thanks Joe. That's great!

Don
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Posts: 2942
Joined: Thu May 10, 2012 3:55 pm
Location: Biloxi MS

Re: 140 kph

Sat Jan 19, 2013 8:20 pm

JoeS wrote:Don, I defer to your experience in the handling department - perhaps the liveliness I feel in my iMiEV is simply due to the minimal contact patch :roll: , yet I consider the iMiEV very stable at speed. However, when it comes to mileage gain, I believe there were a number of tests which showed a significant improvement at higher tire pressures. For example, I briefly looked at EcoModder and they repeated the Mythbusters results as being a 7.6% reduction in fuel consumption in going from 35psi to 60psi:

http://ecomodder.com/forum/showthread.php/mythbusters-tests-tyre-tire-pressure-17151.html
Your link was to a test with a car using 'normal' tires - I would expect the benefits of overinflating LRR tires to be much less. Even so, the benefit of 60 PSI vs 40 PSI was only 1.4% and I'll bet the difference between your 60 and my 45 with our LRR tires is well less than 1% . . . . way too little to be able to measure and next to no gain achieved by going beyond what the tire manufacturer considers safe

Don
2012 iMiEV SE Premium, White
2012 iMiEV SE Premium, Raspberry Metallic
2012 iMiEV SE, White
2017 Chevy Volt Premier
2014 Ford Transit Connect XLT SWB wagon

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