Oversize tires and larger rims decrease gas mileage

[Victor]

Article in today's LA Times says pimping your car with bigger rims and wider low profile tires decreases gas mileage. Says 20% of your fuel goes to overcoming rolling resistance from tires. The bigger and wider the tire, the more rolling resistance. Article says also to not use rain tires if you drive on mostly dry roads. Also, worn tires get better gas mileage than new tires since they have less tread on them, plus are smaller diameter. The larger the rim size, the worse the performance because of rotational inertia being much higher for a 17 or 20 inch rim than a 15 or 16 inch. The lighter the wheel the better, like the forged rims on a J30T being much better for performance than heavier cast rims. There can be as much as a 10% difference in gas mileage between using best and worst tire for your car. Generally one should stick with the tires that the car manufacturer supplied when new. Large tires are also less aerodynamic than smaller tires, adding extra air resistance to the rolling resistance. Article says the tire industry is fighting a proposed law to make them list the rolling resistance of their tires.

[qship96]

Cant wait to see the boyz in the hood go from the 22" khrome anchor look to 13" wheels with 185/70/13 tires on their whips as the new must have fashion accessory.....can see it now, old caprice,dents and all, with shiny greasy little tires on puny 13" chrome fake wire wheels

[elwesso]

well of course one has to choose between safety and performance. If all one is concerned about is gas mileage, the Q45 forum of NICO is not the place to be, sorry.. However, when one puts new wheels and tires on their car it is assumed they do the NECESSARY research, comparing weights of the wheels and tires COMBINED to make sure that it is not a significant difference.

That article assumes that the consumer goes from a well designed OEM wheel to a boat anchor HUGE wheel with inadequate tires... Which, in all honesty, is the correct assumption to make based on what basically everyone chooses their wheels on..

Strength and weight are definitely a second thought to cosmetic design...

[dormicum]

i do know about itbut i stoll changed my Q into a 19' rims

[Q45tech]

Rolling resistance, friction, and tire wear index are intertwined.

[oldmako]

I am shopping around to purchase three more factory trunk spares for my Q. With those puny things I ought to be able to get 24mpg!!!!!

Now if I can just figure out how to give them gangster whitewalls.....

[mcrews]

I went from the stock 245/45/18 to a 255/45/18 on my F50 02 sport.I drive alot on the highway and saw an INCREASE in my fuel average from 24mpg to 26.2 mpg.

I ran this test over the same stretgh of road in similar weather.....geez, all the weather is the same in CA!!!!!

I also run a higher tire presure, close to 43 lbs.

I agree that much larger tires will hurt gas mileage.I went with the larger diameter because of the amount of time I am on the road

mark

[Rex]

I went from the stock 245/45/18 to a 255/45/18 on my F50 02 sport.I drive alot on the highway and saw an INCREASE in my fuel average from 24mpg to 26.2 mpg.

I ran this test over the same stretgh of road in similar weather.....geez, all the weather is the same in CA!!!!!

I also run a higher tire presure, close to 43 lbs.

I agree that much larger tires will hurt gas mileage.I went with the larger diameter because of the amount of time I am on the road

mark

Are you taking the speedo error into account in these calculations?

[thewaxynoodle]

ive got 20's on my q45theres a noticable decrease in fuel efficiency

[oldmako]

http://www.performanceprobe.co...=tire

http://www.paspeedo.com/calculator.htm

Here are a coupla calculators to determine speedo and odo error when changing tire diameters.

[MinisterofDOOM]

That article assumes that the consumer goes from a well designed OEM wheel to a boat anchor HUGE wheel with inadequate tires... Which, in all honesty, is the correct assumption to make based on what basically everyone chooses their wheels on..

Exactly.I imagine the guy going from stock 15" steelies with 195/70/15s to a set of aluminum 17s with some 225/50/17 on his Accord will see benefits rather than losses in the fuel economy.

[dormicum]

ive got 20's on my q45theres a noticable decrease in fuel efficiency

i want to get a 20but it's not fesable in HK as the road condition is bad

[Qproject]

boys will be boys. people will still sport the + 20" wheels.

[bigdog76]

Well I increased my stock tire size on the Q for the standard 215'S to 225 and there was no noticiable change at all. Rim size did not change.

One should also keep in mind all the other wear items the brakes, the suspension, all that is effected by thoses 20's and up.

I use to have 22" on my Cadillac EXT I took them off and was suprised how much better it could stop when I hit the break and much lighter.

Rims are a thing of the past with all the car manfuactures coming out with nice size good looking rims. Rim companies will have a hard time selling what they did in the late 99's and early 2000's.

[Qproject]

not about size, more about WEIGHT. IMO anything bigger than 20" should all be made with lightweight forged aluminum.

Well I increased my stock tire size on the Q for the standard 215'S to 225 and there was no noticiable change at all. Rim size did not change.

One should also keep in mind all the other wear items the brakes, the suspension, all that is effected by thoses 20's and up.

I use to have 22" on my Cadillac EXT I took them off and was suprised how much better it could stop when I hit the break and much lighter.

Rims are a thing of the past with all the car manfuactures coming out with nice size good looking rims. Rim companies will have a hard time selling what they did in the late 99's and early 2000's.

[Haitian_King]

Article in today's LA Times says pimping your car with bigger rims and wider low profile tires decreases gas mileage. Says 20% of your fuel goes to overcoming rolling resistance from tires. The bigger and wider the tire, the more rolling resistance. Article says also to not use rain tires if you drive on mostly dry roads. Also, worn tires get better gas mileage than new tires since they have less tread on them, plus are smaller diameter. The larger the rim size, the worse the performance because of rotational inertia being much higher for a 17 or 20 inch rim than a 15 or 16 inch. The lighter the wheel the better, like the forged rims on a J30T being much better for performance than heavier cast rims. There can be as much as a 10% difference in gas mileage between using best and worst tire for your car. Generally one should stick with the tires that the car manufacturer supplied when new. Large tires are also less aerodynamic than smaller tires, adding extra air resistance to the rolling resistance. Article says the tire industry is fighting a proposed law to make them list the rolling resistance of their tires.

If I may play Devil's Advocate here.

There can be as much as a 10% difference in gas mileage between using best and worst tire for your car.

Is 10% really that big of a deal? Say you're getting 18 mpg. Is losing 1.8 mpg really that bad?

While larger than OEM wheels/tires decrease fuel efficiency and the like, the car owners probably don't care. If an owner spends $3-4k on big shiny wheels and another $1200 on tires, it might be safe to assume that they aren't the most cost-conscious people in the world.

[qship96]

Strange thing is that the poor people tend to be the ones putting the big shiny wheels on their cars. I have noticed as I drive thru expensive neighborhoods most cars have stock wheels on them, yet when I drive thru inexpensive neighborhoods or the rundown parts of the city, almost all the cars have big shiny wheels- anyone else notice this in their area?

[Haitian_King]

Strange thing is that the poor people tend to be the ones putting the big shiny wheels on their cars. I have noticed as I drive thru expensive neighborhoods most cars have stock wheels on them, yet when I drive thru inexpensive neighborhoods or the rundown parts of the city, almost all the cars have big shiny wheels- anyone else notice this in their area?

I have. It is a very astute observation.

I wonder why that is? What's the sense of putting $2-3k wheels on a 83 Caprice, when their numerous progeny are running rampant, in need of proper food and Pampers?

Ugh. It saddens me. Disgusts me as well. For all their complaining about the "White Man", they're doing a great job holding themselves down and setting themselves back.

Sorry for the slight deviation from topic.

[NightRiderQ45]

Ugh. It saddens me. Disgusts me as well. For all their complaining about the "White Man", they're doing a great job holding themselves down and setting themselves back.

Well I own chrome wheels and I've never complained about the "white man" holding me back so please watch your statement because we "all" don't think like that idiot! I'm a little over a year out of college with my electrical engineering degree and I was blessed with a very nice salary. So I guess there some people in this world who would judge me as a thug or uneducated because I have chrome 20" wheels, but in reality I'm probably more intelligent than they. If people want rims on their car in their poor neighborhoods, then that ignorance is on them. I mean, I feel that people who drive ugly minivans are digusting. Why not just get a nice SUV. But that's their preference not mine.

Same can be said by owning an cheap $2000 Q45 and putting $10k into it so I can perform near OEM specs. Some people like that idea, I on the other hand don't and think it's silly. I'm sorry, I would purchase something else instead of throwing so much money into an old outdated car.

Sorry, I had to speak my mind after Haitian's comment. I hate ignorance.
Modified by NightRiderQ45 at 12:21 PM 5/6/2008

[Rex]

Not to stir the pot, and yes, he used the phrase "white man", but please be aware there are Caucasians (and other races) that feel they're being "held down" by the "white man". I won't speak for Haitian_King, but I read his post to be one about people living in economically depressed areas, not about race.

That doesn't mean it wasn't "ignorant", just might not have been ignorant in the manner you took offense to?

[Haitian_King]

I'm not looking to have this thread locked, but I feel compelled to defend myself against allegations of ignorance.

References to homeboyz and 40 ounces and dub wheels are constantly made on the board, especially in regards to people that try to slap large wheels on Q's and other sedans.

I've never seen you up in arms about that.

My previous post was about people living in economically depressed areas (statistically a majority of the inhabitants are of African-American descent) spending thousands of dollars on big wheels, while their home, families, and communities are in terrible states of disrepair. After such ludicrous expenditures, they then turn around curse "The White Man". (I know, I've heard them do it.)

If sorry if my post hurt your feelings. I thought I was on a board populated by adults. My mistake.

[Jeff Williams]

I have 285/40/18 rear tires and 245/45/18 front tires on my 1994 Q45t, and I still get 20 MPG on the highway. Of course, when my speedo says I am going 72, the car is really going about 80, so the reduction in RPM has helped offset the excessive width and weight of the rear tires.

My car came from the factory with the light weight BBS wheels, and I am running the light weight ASA (BBS) wheels.

[NightRiderQ45]

I'm not looking to have this thread locked, but I feel compelled to defend myself against allegations of ignorance.

References to homeboyz and 40 ounces and dub wheels are constantly made on the board, especially in regards to people that try to slap large wheels on Q's and other sedans.

I've never seen you up in arms about that.

Because there is nothing wrong with the term "homeboy". I have quite a few back home in Alabama. I just realize that people have different taste so I stopped arguing about it. I have 20" wheels and I love it. I do notice during the winter months that I save a small amount of gas because of the weight load taken off of my car. At the end of the day, it's all about different people preference (e.g. VIP styling)

My previous post was about people living in economically depressed areas (statistically a majority of the inhabitants are of African-American descent) spending thousands of dollars on big wheels, while their home, families, and communities are in terrible states of disrepair. After such ludicrous expenditures, they then turn around curse "The White Man". (I know, I've heard them do it.)

True...Back home in the southern states especially Alabama, Mississippi, and some areas of Georgia, there are rural broke down areas they are constantly getting busted for the production meth. So do I go out on the limb and think that all of them in the area are "country bumpkin meth heads" because of the negative connotations of a few shown on tv? No; that's what I stated was ignorance thinking. Back to my previous post...if they decide to do stupid stuff like that then that's their choice. What I'm trying to get you to understand is that "all" don't curse "The White Man". I mean, they might be happy in that type of environment.

No hard feelings Haitian. Your avatar is the Dipset symbol so I think we have some things in common with music !

[Haitian_King]

I have 285/40/18 rear tires and 245/45/18 front tires on my 1994 Q45t, and I still get 20 MPG on the highway. Of course, when my speedo says I am going 72, the car is really going about 80, so the reduction in RPM has helped offset the excessive width and weight of the rear tires.

My car came from the factory with the light weight BBS wheels, and I am running the light weight ASA (BBS) wheels.

Has that gotten you in trouble with the law?

I wonder what the speedometer/actual speed variance would be if I installed the 4.11 differential with larger wheels. Would the J30 speedometer gear even be effective?

[Q45tech]

3.90 speed gear/4.083 diff = 0.955 or 4.5% error vs 15.4% with stock 3.538 speed gear.

[Jeff Williams]

That was my plan exactly.

I have the 4.08 rear ready to go in, I have the 3.90 speedometer gear ready to be installed in my new transmission, and I oversized the rear tires to compensate for the difference. It is not exact, but much closer than with the OEM tire diameter.

The only isue, is that the 18 x 9 ASA wheels I got from Tire Rack with the 285/40/18 tires rb on the outer fenders. I have done some rolling so there is no sharp edges, but it still rubs a bit on dips in the road or hard cornering.

I have not gotten in trouble with the law yet, because I usually compensate for the speed difference. Plus, I drive like an old lady most of the time.

I get my wild hair when I am in the Vette, stretching out the LS-1 !

[mcrews]

Are you taking the speedo error into account in these calculations?

Rex,maybe I'm making a false assumption.But a larger tire will roll farther than a smaller tire.Thus for the same rpm you get more distance?I realize that to start rolling there is probably more energy(rpm) used, but once you are on the way, the larger tire would give better mpg?

mark

[Rex]

Rex,maybe I'm making a false assumption.But a larger tire will roll farther than a smaller tire.Thus for the same rpm you get more distance?I realize that to start rolling there is probably more energy(rpm) used, but once you are on the way, the larger tire would give better mpg?

mark

I was just inquiring about the "correction". Since those 2 tires have different diameters (thus different circumferences), the speed and distance traveled as shown on the speedo will not be accurate for both without "correction". It's not a significant error given the sizes you listed, but nonetheless there's an "error". If my mind is working correct today, your speedo will be over stating both speed and distance, thus your number may be even better than your calculations reflect by ~1.3%.

[gjh20]

i just put custom built/painted NC Forged 7-spoke 22" wheels (3-piece forged) on my '98. (http://ncforged.com/images/wheels/7spoke.htm) i replaced the staggerd 20" Asanti setup i was running. the front tire is a 235/30-22 (9" wide, 4inch lip), the rear is a 265/30-22 (10.5" wide, 6.5inch lip). the overall tire diameter is within approximately 1" of stock. the speedo error is 2mph less @100mph (according to the above listed links to figure out conversions). thus the speedo being off isn't a major factor. however, the weight penalty is instantly apparant on acceleration & during braking. you can just feel it... my gas mileage also suffers, but such is to be expected with a +6 fitment on any vehicle in my estimate.

i haven't posted pictures due to the fact that oversized wheels on Q's ALWAYS turns into some kind of socio-economic or racial discussion that truthfully i find more ignorant than spending money you don't have to lift your F-150, put Mickey Thompsons & Weld wheels on it only to park it next to your single wide & your 7-year financed Harley (oh sorry, ignorant vehicular purchases are limited to "the hood" right?). anyway, i had to get that off my chest. and like it or not my custom painted 22's with 4" front lip, 6.5" rear lip setup is SICK! let the rhetoric continue....