Hey guys,

So i would like 18inch rims but i've been told they would weigh too much and drag down my preformance and gas milage. The experts tell me to stick with 17inch; but i see you guys have 18inch rims. Is the performance loss worth the sex-appeal?



<-- lol

 

That's a load of crap, all the sport models mine included come stock with 18s.

Back in the day of steel wheels but likely the difference in weight between a 17 and an 18" alloy wheel is not enough to affect gas milage.

 

Myself, I have the stock rims. But sit and think of this, with a 17 inch wheel the wheel turns one rotation, with a 18 inch wheel the wheel turns about or lets say a 1/8 of the way more so your getting 1 rotation plus about an 1/8 more per rotation. I would think you would get better gas milage with a bigger wheel and tire. Just my 2 cent, but to me it makes sense that you would get better mileage with bigger rims and wheels.

 

Not really gas mileage but it will negatively effect handling, ride quality and braking. Car and Driver did a test a few months or maybe a year back and found 16s or 17s were the ideal wheel and tire combination. Of course that applies to cars that come with these sizes from factory or a plus one sizing. Ever pick up a 18 inch tire vs a 16 inch tire? There is a big differnce in weight. You're talking upwards of 50lbs all around.

I've owned plenty of steel racing wheels that were lighter than stock alloys.

 

Ive heard many different arguments about wheel size. Also, I have owned about 11 cars total, 5 of which I modified fairly heavily. I can tell you this, you wont notice a big enough, if any, difference with gas mileage by putting 18 in. wheels on your car. As a matter of fact with the 18's you will more than likely have low profile tires which will be almost identical to the diameter of a stock 17 in wheel with stock tires.

The pros: better look

The cons: you WILL bend a rim with 18's on low profile tires. Its inevitable. The lack of tire combine with an aluminum wheel will bend.

As far as braking, cornering, etc. goes, you wont really notice to much of a difference under normal driving. Keep in mind the X-type sport offered 18 in. wheels stock but no brake modifications. They used the same brake setup with each of the wheel options. Cornering really depends on the tire. You will notice better cornering as long as you use a good tire.

I had stock 17 in. wheels on my 02 X-type sport and changed them to the 18 in. stock wheels from an 05. The 17's had a better ride and were better in the snow. The 18's look a lot better IMO.

 

Not true. You have to take into account unsprung weight which is a killer for performance, handling, and gas mileage. Sure the 18" wheel is going to have more metal than the 17" but if the overall weights of the two packages aren't too far off then it's not going to effect it that much. Don't go cheap with rims; quality, lightweight brand name is the way to go. Skip the replicas and AutoZone rims. You're gonna be dealing with bent rims and finish problems later on.

 

It's all about rolling mass. An 18" rim and tire package should if all things are equal weigh more than a 17" package, but you switch to a lower weight 18" rim and the rubber is less weight since it's lower profile at the same height so you should average out.

And unless you are planning on off roading I can't see how under normal use you would bend the rim. Even up here in Canada we pave our roads and because we're mildly socialist if I were to bend a rim in a massive pothole, I go to my insurance company along with a pic of the pothole and they repair or replace the rim for free. And then charge back to the city because our gasoline prices include a tax to maintain the roads in the city. So if they don't and it causes damage they pay. Sweet deal but rarely is there ever a giant pothole.

Canada, home of universal medical and rim replacement.

 

What difference does it make whether it's 17" or 18"? You want to know miles per gallon, not miles per rotation. Who cares how many times it rotates? Plus, like Sidewalkman says if you are going to a bigger wheel diameter chances are you are going to a lower aspect rario tire anyway, so the rolling circumfrance is pretty much the same. Weight? That depends on the wheels and tires, but again, probably not that big of a difference.

Performance? That depends on your definition I guess. All I know is I have the 18" Arubas like Sidewalkman and I love the way they look, love the way the car handles and am content enough with the mpg not to keep me awake stressing over any real or perceived 'nth degree of performance I'm reaping or losing.

If you want to do the math if you drive 15K per year and were getting 20mpg and all of a sudden found a way to get 1mpg more, at $3 per gallon you would save $108 a year. To me, not even worth taxing my feeble brain. Buy what makes you happy.

 

Meh. These cars aren't economical and don't perform well anyway. They are all about appearance and the 1-2% variance in gas mileage, ride quality (which depends on the tire and air pressure) and performance hits are trivial compared to how effeminate these cars look with <=17s on them.

 

The only way to do the test is to use the same wheel, same tire just different sizes. If this is done the 18s fail miserably in all catagories except for bling and increased price of your tires. You need to keep in mind that the "sport" package on the X type is nothing more than a lip service sportieness. Give the masses what they want even though it does little for performance (minus of course the big honking rear spoiler). Coming from a racing background, I rely on lap times not look for determing what the truth is.

 

Having done something similar to this but with simply a larger diameter tire, I can provide this knowledge from first hand experience. I will admit, this is on the extreme side of things. I went from a 30" diameter tire to a 35" diameter tire on my truck keeping all other things constant. Obviously, the bigger diameter tire results in more unsprung weight. The larger tire also resulted in an error in the speedo (16.7% error to be precise). Even taking into account the speedo error, the mileage of my truck went from 17 mpg down to 12 mpg doing the same driving. I also noted that the truck did not shift right due to the computer not receiving the correct speedo signal. Installing a new drive gear to make the speedo indicate correctly (still had the same gears in the differential), the mileage of the truck picked up by 2 mpg for the same driving (back up to 14 mpg.

As for braking, night and day difference. With the bigger tires, the amount of foot that needed to be applied was dramatically more to get the same braking. Acceleration was obviously slower too. By how much, I never did any measurements. But it was definitely noticeable.

As for my Jag, like a lot, I have stepped up 1 size in the tread width of my tires (up to 235/40R17's from the factory 225/45R17's) while using the factory rims for both sets of tires. While they are very close in overall diameter, there is a slight increase there. Braking wise, I can't say that I have noticed any difference. Weight wise, the newer tires weight in only slightly more (2 pounds or so). I can't say that I have seen any negative effects other than maybe a slight drop in mileage (0.5 mpg). But, even that I can't attribute beyond a doubt to just the tires.

Newer vehicles are very sensitive to tire diameter. Small changes can affect how the car shifts, which then affects the overall mileage.

 

LOVE my 19's.....

2 winters.... no bent rims.

 

Wow guys thats alot of information.
But to clear something up, I know better then to go bigger rim and not decrease the tire size. Id like to keep the height of the tire the same, which is the smart thing to so (just fyi the taller the tire the more time, gas, and torque it take for the motor to turn it)

So i think goin with an 18inch rim and a low pro tire. lets say a 205/35R18 tire is the best of both worlds.

I had a 2000 Merucry Cougar that came with 16inch rims and i put 18s on it. Huge mistake, the car had no torque and couldn't take the weight. I saw huge difference in preference and gas mileage. But im sure this kitty will do just fine.

 

The OEM fitment is 225/40/18. Anything smaller is too small diameter or will have insufficient load rating.

205/35/18 is the tire you would put on a newer Mini Cooper or Golf/Jetta/Civic pre-2000 model year for example.

As a general rule, old people like more sidewall. That's where you'll see the highest correlation when people get in religious debates like this. If you tracked the car that's one thing, but if you want something that looks presentable, then do at least 18s.

 

true.
we put 225/30/20 on my girls jag and it drives fine. watch out for potholes but thats a given.
gas mileage, i dont really drive it but she hasnt mentioned any change. and it only makes a difference in the city, once you are on the hwy you get the same if not better mileage.

 

weird, my currrent tire size is 205/35R16. But its not uncommon for someone to stretch the tires width. So if i do go with 18's ill get a tire with rim lips so i dont curb them. Making the tire size around 225/35R18.

Now i just gotta pick a rim... but thats a thread for another day.

 

stock 17 inch rims are 225/45/17

 

Seat of your pants performance measurements the differences will be nil as Exexpat stated.

Really comes down to looks, and perhaps the slightly cushier ride and/or rim protection offered by a 17" wheel. The Car and Driver article does make some good points about 17's but unless you are gonna really run the car hard the difference is negligible.

So if you like the looks, go with 18's. No biggie.

As for rim protection, around here it's not a matter if if, but when, you bend an aluminum wheel on the horribly maintained road infrastructure. I buy my wheels in sets of 5 anyway to have a properly sized spare ready to go and another wheel in the event (read: when) one is bent.

Sidewalkman, I'm jealous of your rim replacement socialist regime.

 

This whole discussion is making little sense to me...

My 18" Proteus with Pirellis weigh noticeably less than my 17" Sports with Nokian winter specials, pick one up in each hand and you can tell immediately; less rubber + less alloy = less weight. Makes sense...

OK not every brand/make of tire will weigh the same. Not every size of wheel will weigh the same.

But if you match the tread width, and the rolling circumference, and more/less the weight, then there will be absolutely no difference to the MPG...

 

But your 18" Proteus with pirellis would weigh noticably more than 17" Proteus with the same Pirellis.