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Tire pressure does effect MPG - How much is too much ?
I'm at about 2000 miles on an '05 Auto HCH. My MPG has remained around 40-41. I do mostly to/from work (13 miles) stop and go plus short spurts on the hi-way and have several hills to deal with which makes it difficult to increase my MPG. Before the last tank I increased the tire pressure from 30 to 35 psi. The mileage on this tank (180 or so miles) is hovering between 47 and 48 MPG (per the guage, which I believe to be a bit overstated). I hesitate to go much higher being concerned with tire wear and traction - mostly traction. I hear of folks at 40 psi and above and wonder how tire wear and traction are effected ??
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That is a raging debate (has been forever) and I think there is no solid answer. Everyone has their opinions, here are mine:
1. Honda engineers have a reason for recommending 30 PSI. I do not know for sure what that is, but it's probably the best "compromise" for merging traction, tire longevity, and safety. 2. Higher PSI will affect traction to a degree, and will affect tire wear to a degree. Personally, living in Phoenix AZ (home of 320+ days of Sun) I am not concerned with traction problems. I do not drive my HCH like a sports car, and wet weather rarely affects us at all. Tire wear is not that much of a problem if I rotate the tires enough and these tires are pretty cheap to replace (at $65 each) if the wear is uneven enough to make me replace the tire after 30 to 40 thousand miles. 3. The main thing I have to worry about in overfilling tires is HEAT. It gets HOT in Phoenix, and if I over-inflate to say 40 PSI on a tire rated at 44 PSI max, the heat expansion will take that PSI up over 50 on the hottest days if I have driven on the highway for a few miles - I saw that last year in August. So I need to be careful in Summer to keep it about 35-38. I have braved 40 PSI this Winter and have seen no problems. 4. I inflated down to 32 PSI on my recent trip to Texas, where I knew I had a loaded car and would be driving in snow/rain/ice on occasion. I sacrificed max MPG for max safety. So each person should consider their own circumstances and base their PSI on how their life is. I can generally over inflate a little in the Winter and I have to be more careful in the Summer. |
Hi RoyalF:
___ Start here … Tire Pressures ___Always fill cold (whatever the ambient is) and expect a 1 # increase for every 10 degree increase above ambient or straight tire heating due to the drive. Burst pressures of today’s tires are well over 100 #’s so unless you are really crazy, you won’t blow them out. In fact, over inflated tires produce far less heat then the same tire when under inflated. Longevity will improve tremendously. The 30,000 mile Bridgestone RE92’s when inflated per the Insight manual/door sticker last just about that amount of time. When inflated to 50 +, there are those that still have not replaced them and are well south of 100,000 miles now. The Corolla’s GY Integrity’s lost 5-6/32 over her first 30,000 miles at < 40 #’s and just 3-4/32 over last 40,000 miles at 50 – 52 #’s if that helps? ___To much? When I drove for the record distance on a single tank last June and repeated it back and forth to work last September, I jacked them up to 60 #’s and haven’t ever looked back. ___Increasing tire pressures improve FE, tire longevity, and turn in. What higher pressures hinder is stopping distances and ride comfort. ___An HCH’s minimum would be 50 #’s if you are looking to maximize your FE. If it were mine, I would be running 52 - 55 #’s myself. ___Good Luck ___Wayne R. Gerdes ___Hunt Club Farms Landscaping Ltd. ___Waynegerdes@earthlink.net |
Do not overinflate HCH tires due to safety
___An HCH’s minimum would be 50 #’s if you are looking to maximize your FE. If it were mine, I would be running 52 - 55 #’s myself. Any HCH owner who overinflates their tires that much is risking safety for a couple of extra MPG - I would say that's not a good tradeoff. I can safely run mine at 44 PSI in the winter, but in the summer, the heat drives the inflation pressure up like a hot air balloon. Like I said, I checked them after a short highway drive and they were up over 50 PSI. |
Hi Larsb:
___You are making statements that do not hold true in the real world in the least. Burst pressures as stated above are in the neighborhood of 100 - 125 #’s. You will never reach that unless your car was on fire. Guess what the Insight’ers Bridgestone RE92’s and HCH’s Bridgestone B381’s (many HCH’s include these as OEM stock) MAX sidewall state? 44 #’s as most any other tires do. Do you know how many millions of miles have been driven in Insight’s with the RE92’s and HCH’s B381’s at 50 + #’s? Just to let you know, there are quite a few Insight’s and HCH’s in the desert southwest besides your own. ___You can run whatever pressures you want but you will never reach the FE that your automobile is capable of by running at the std. as listed inside your front door or by running max sidewall of 44 #’s. Which you decide to choose is up to you but bringing up the safety card when you are tooling down the road with 2 children at 70 + mph is far more dangerous imho. ___Good Luck ___Wayne R. Gerdes ___Hunt Club Farms Landscaping Ltd. ___Waynegerdes@earthlink.net |
Originally Posted by xcel
..... but bringing up the safety card when you are tooling down the road with 2 children at 70 + mph is far more dangerous imho.___Good Luck ___Wayne R. Gerdes ___Hunt Club Farms Landscaping Ltd.___waynegerdes@earthlink.net
I had a blowout in my Chevy Avalanche pulling a U-Haul at 70 mph and it was not a lot of fun. When I was a kid, my crazy stepdad had a front blowout going 70+ and almost killed us by slamming on the brakes. So I am justifiably a little paranoid about blowouts. Because of your "guru status" Wayne, I will indeed investigate the possibility of running at higher pressures, but I admit when I checked my pressures on a not so hot August day and saw an extra 10 PSI in my tires, I got a little concerned. I want neither a blowout nor a tire which needs replacement early because of undue wear on the middle section, which CAN and DOES happen in long periods of overinflation - I found that out with my Avalanche tires. |
Max sidewall cold pressure rating
In my own experience, all my cars since I began driving have been inflated to the max cold pressure rating of the tire. My father runs his the same as well.
I've never had a blow out which I would describe as a complete & sudden tire failure, but have picked up my share of nails & screws and one left a hole large enough to flatten it in less than 30 seconds. I've never had to replace a tire prematurely for running them on max pressure as long as the other tire maintenance points are not ignored..like rotation, balancing and alignment. The only downside in my experience in Max rated sidewall pressure is a harder ride. I've dropped my pressure to the suggested 32PSI a couple of times but it feels like I'm slogging through wet sand and I drop 7-10MPG. Here in Atlanta we don't usually get very much wintery mix, but in the case of a rare ice or snow storm I'd likely drop it off of the Max setting a little for that paticular trip. |
Hi Lars-ss:
Originally Posted by lars-ss
Are you implying that driving 70 + mph in a modern car is unsafe? Or just with overinflated tires? I would never put my kids in danger unnecessarily. But when you are driving on a freeway trip of 14 hours plus and you are accomplishing it in one day and the speed limits are 75 mph on the Interstate, you do what you have to do.
___The proof of higher speeds being less safe can be proven with simple physics … Besides the increased emissions, increased fuel consumption, higher wear and tear by traveling at higher speeds, there is the safety issue. Reaction Distance = Reaction Time * Speed Speed is ~ constant during this period because you haven’t touched the brakes yet but you might have slightly pulled your foot from the accelerator? Perception + Reaction time = ~ 1.5 seconds for most. Braking Distance = [(Initial Speed (ft/s))**2]/(2* Deceleration) Deceleration is ~ constant during the severe deceleration phase at ~ 30 ft/Sec**2 using C&D’s 70 - 0 mph braking distance of 181 ft for our Little Beauty’s. This was from C&D’s January 2000 Insight Road Test. 88 ft/sec = 60 mi/hr. Reaction distance + Braking distance = Total distance traveled before stopping. At 50 mph: Total braking distance = 110’ + 90’ = 200’ At 75 mph: Total braking distance = 165’ + 202’ = 365’ ___That is > ½ a football field longer to stop from 75 mph! ___So two things … Would you rather hit something at 50 mph or less (or possibly not at all!) given you might actually have time for some braking or accident avoidance steering correction in any distance > 110’ before the collision or at 75 mph where you have probably already collided with whatever (165’ or less) before you had the chance to touch the brakes or make a correction? Remember that your perception + reaction + actual braking time at 75 is almost ½ a football field longer then at 50 mph. I am not even including the damaging impact energy that has to be dissipated! How many accidents could be avoided with that extra ½ football field of distance anyway? ___Someone else can check my math from the following: http://www.sci-ed-ga.org/modules/dri...stigation2.pdf ___Good Luck ___Wayne R. Gerdes ___Hunt Club Farms Landscaping Ltd. ___Waynegerdes@earthlink.net |
Now, now, boys. Lets not start a flame war! =)
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Hi Lars-ss:
Originally Posted by lars-ss
... I admit when I checked my pressures on a not so hot August day and saw an extra 10 PSI in my tires, I got a little concerned. I want neither a blowout nor a tire which needs replacement early because of undue wear on the middle section, which CAN and DOES happen in long periods of overinflation - I found that out with my Avalanche tires.
___To sum up the Integrity’s wear both before and after driving them to pressures beyond max sidewall, I had uneven edge wear and had lost ~ 5/32’nds of tread at the ~ 30,000 mile mark while running 35 #’s. Over the next 38,000 miles and running 50 #’s, I lost just 3/32nd’s tread wear, edge wear was halted, even tire wear across the entire face, and of course the much enjoyed increase in FE. ___The Insight’s Bridgestone RE92’s are only down 2-3/32nd’s of 9/32’nds after 36,000 miles from new and they are only a 30,000 - 35,000 mile tire to begin with! I just took the RE92’s back up to 55 #’s last night in fact due to the natural bleed off and temperature drops so make sure you check them often … ___Finally, although only a wish right now, I pushed the Continental’s on the Ranger P/U back up to 50 #’s last night from the ~ 44/44.5 #’s I found them at after almost 3 months of not paying attention. With our fluke 52 - 61 degree temps for my drive home tonight, I dropped under ½ tank (per the Fuel Gauge) at the 368 mile mark. Although it is not entirely linear given the extra ~ 1 - 1.5 gallon available at top off, I might actually hit 40 mpg’s on this tank? That is if the head winds are not to strong in the morning and afternoon temperatures do not sink as fast as forecasted. The only way this type of FE is possible is with the tires inflated to 6 #’s above Max Sidewall and the rest of the techniques and setups we all use. Our temperature fluke sure helped out tonight as well ;) ___Good Luck ___Wayne R. Gerdes ___Hunt Club Farms Landscaping Ltd. ___Waynegerdes@earthlink.net |
went from 39 to 43 MPG
I live in Chicago, and I was noticing very poor MPG since the weather turned cold. I hadn't touched my tires since my last oil change in November.
I added 8lbs to each tire, bringing them up to 33 lbs each (yes, they went down to 25 lbs from the cold weather!). My mileage is up to 43 MPG now! (Normally 51 MPG in warmer weather) Stephen |
Hi All:
___A great post by someone who goes by the nick Tempusvn over at Edmunds … Here are published numbers for Goodyear Tires with a Max Sidewall Inflation Pressure of 35 PSI for vehicles that 'recommend' a pressure below the maximum. ############################# Dry Macadam Surface (Stopping Distance in Feet) 2001 Dodge Grand Caravan Sport__20 psi__28 psi__35 psi Full Depth Tread with ABS_________75.5____76.2____75.8 1/2 Depth Tread with ABS__________69.9____68.1____66.3 Full Depth Tread without ABS______98.3____95.9____91.6 1997 Ford Ranger Full Depth Tread with ABS_________80.8____78.2____77.6 1/2 Depth Tread with ABS__________79.0____74.8____71.4 Full Depth Tread without ABS______97.8____96.5____94.1 ############################# 0.02 Inch Wet Macadam Surface (Stopping Distance in Feet) 2001 Dodge Grand Caravan Sport__20 psi__28 psi__35 psi Full Depth Tread with ABS_________79.8____78.5____77.1 1/2 Depth Tread with ABS__________84.7____73.7____81.4 Full Depth Tread without ABS_____111.1___110.2___108.6 1997 Ford Ranger Full Depth Tread with ABS_________83.8____81.5____79.8 1/2 Depth Tread with ABS__________91.5____89.4____84.6 Full Depth Tread without ABS_____131.9___126.0___118.4 ############################# 0.05 Inch Wet Macadam Surface (Stopping Distance in Feet) 2001 Dodge Grand Caravan Sport__20 psi__28 psi__35 psi Full Depth Tread with ABS_________80.0____81.1____82.7 1/2 Depth Tread with ABS_________103.7____99.7____92.2 Full Depth Tread without ABS_____118.0___112.2___111.7 1997 Ford Ranger Full Depth Tread with ABS_________89.7____86.0____81.5 1/2 Depth Tread with ABS_________125.7___118.5___104.5 Full Depth Tread without ABS_____142.9___134.8___125.7 ############################# Specialty snow tires on specific snow conditions are, obviously, a special case, but it has nothing to do with the general behaviour of the average passenger tire in most conditions. It also doesn't cover slush where again, the ability to bring maximum point pressure to bear is more important than a big footprint. Manufacturers set the vehicle 'recommended' pressure for many reasons besides safety and performance. Remember the Bridgestone fiasco with Ford. Ford recommended a low pressure on the Exploder, because it decreased the chance of rollover (at least partially because you couldn't corner as fast with the sidewalls rolling over :) ). But, that caused the tires to blow out. Bridgestone took the heat, but it was Ford's fault. The tires were rated for higher inflation, and should have been run there. Most instances now where the vehicle manufacturers recommend lower tire pressures are for comfort. But, in the vast majority of real world situations you will get better performance and longer tire life by going closer to the sidewall rating. The possible exceptions being mud and some rare snow situations where you are looking more for a snowshoe than a tire. But, Slush, Ice, and Plowed snow all benefit greatly from higher pressure. What's really bad is when people buy into this 'big footprint' myth and let air out of their tires in the winter :( I'm not saying to always inflate tires to the sidewall max, but 99.9% of the time you'll do far better to inflate a bit over what's printed on the vehicle. I know many tire professionals who use the '5 Pounds Over' rule on their own cars. IE, if the vehicle manufacturer wants 28 pounds in the tires, they do 33. If the manufacturer wants 32, they do 37. This has another benefit. It makes sure you don't run under-inflated, because it's ALWAYS far safer to be a few pounds over than a few pounds under. ___Wayne R. Gerdes ___Hunt Club Farms Landscaping Ltd. ___Waynegerdes@earthlink.net |
Update from RoyalF on tire pressure
AT last writing, I had increased tire pressure from 30 psi (as it came from dealer) to 35 psi. The tank trip meter settled in around 49 mpg but over time (and traffic) ended at just below 45 mpg. Measuring at fillup I got right at 45 so the trip meter and fillup calculation were on the money, getting just over 500 miles for the tank full. It got pretty cold for the next tank which ended at 42.0 mpg on the trip meter but only 39 mpg when calculated (and I really did not top off to excess). With the fillup yesterday ( high temps in the 60's - sweet -) I increased the psi to 39, with trip meter mpg around 49 but still too early to tell. Will report back in a week or so. Enjoying the feedback and insight (no pun intended).
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Another thing to keep in mind with regards to tire pressures and inflation pressure is road conditions. If you hit a pothole with your tires inflated to 32psi, they will flex plenty and deform with probably a bit of a pressure spike from hitting the pothole and suddenly compressing the tire far above what it would normally be. If you had the tires at 55psi, the spike in pressure would be far higher; possibly well above 100psi or so. I know I've had friends who blew out tires from hitting potholes and it blew it from pressure alone - no wheel damage.
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Hi AZCivic:
___I know of at least 2 guys at work that have lost tires when hitting pot holes (Blowout) but I have never heard of a hypermiler with MAX sidewall or above losing them when hitting potholes. Even when running the RE92’s at 60 #’s for the Attempt last year I did hit potholes and other such debris. No blowouts have been recorded. ___Those of us that do press up our tires to these levels do apparently suffer from a higher percentage of debris stuck in the tires however. I know at least 3 that have lost a tire due to this. I lost an RE92 late last year from a screw just above the tread at the sidewall. I believe Hot_Georgia_2004 lost a B381 with a screw or similar. Rick Reese lost an RE92 to a screw or similar late last year as well. ___Good Luck ___Wayne R. Gerdes ___Hunt Club Farms Landscaping Ltd. ___Waynegerdes@earthlink.net |
I'm running my stock tires at 42 PSI and my MPG for this tank is currently 49.9 MPG in the past 212 miles. My most recent trip today was about 65 miles and I got 57.5 MPG... I'm using all the tricks I've read here, such as accellerating a bit fast then getting off the gas... Oh, and driving behind semi trucks to help reduce wind resistance. Hot_Georgia_2004 has an EXCELLENT article on this site for driving tips.
Just my $0.02. :) |
Re: Tire pressure does effect MPG - How much is too much ?
I haven't read all the reponsed, but I pumped my up to 36 based on some guy on hybridcars.com's recommendation. It was scary to drive and hard to handle. I dropped it down to around 32 and has been much more stable.
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Re: Tire pressure does effect MPG - How much is too much ?
You may want to check your alignment or something. 36psi would barely even be noticeable. I'm especially concerned that someone who has experience with a Porsche 911's handling could ever characterize a stock Civic's handling as scary and hard to handle. Definitely get that alignment checked!
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Re: Tire pressure does effect MPG - How much is too much ?
I'll admit that at 42PSI my HCH does get a little bit wibbly-wobbly when I hit an awkard area of the pavement. (e.g. Kirby Rd. when it crosses over the 267 Dulles Toll road bridge in Northern Virginia), albeit this is VERY seldom, and it still handles 1000 times better than my 2003 VW Beetle at the same spot. Really the most notable difference is I can feel every bump in the pavement (which I inform all my passengers I have the tires at 42PSI so they dont think all HCHs drive that bumpy). Get that alignment checked.
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Re: Tire pressure does effect MPG - How much is too much ?
Originally Posted by AZCivic
You may want to check your alignment or something. 36psi would barely even be noticeable. I'm especially concerned that someone who has experience with a Porsche 911's handling could ever characterize a stock Civic's handling as scary and hard to handle. Definitely get that alignment checked!
It was perhaps an exaggeration. The Honda has super light power steering for such a small car. Add some extra PSI to the tires and it gets a little weird at 70 or so. :embarass: 911 has no power steering and at 22 years old is rock solid at similar speeds....on the track...well... ;) One of our other cars is a 3 series, which has less power steering input than the HCH, so the HCH seems like overkill when compared to those two. Next to our Cherokee, the Honda is the same. |
Re: Tire pressure does effect MPG - How much is too much ?
Isn't the civic variable power asist? Or am I thinking of another car?
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Re: Tire pressure does effect MPG - How much is too much ?
if you read your civic hybrid's manual in the section about tire pressure, it recommends that you increase cold pressure to 35 psi when driving over 100 mph. in other words, 35 psi in the tires is acceptable by the manufacturer.
i've pumped my civic hybrid's tires up to 40 psi before but found the ride to be too harsh and bumpy. where i live in california, the weather can also be quite unpredictable, sunny and hot one day and cold and rainy the next. for simplicity's sake, i run my tires at 35 psi. it's a good tradeoff between slightly increased mileage and tire wear, handling, and braking. |
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