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View Full Version : What difference do different wheel diameter and tire heights make?


Savij
10-12-2007, 03:33 PM
I'm thinking about getting a set of winter tires and putting them on my current 16" wheels for this winter. I was thinking of getting the optional 17" wheels that were available for the car and putting the appropriate tires on them next spring.

I looked at tirerack at the wheel tire packages to get an idea of what I would be spending, and I noticed that they had some 18" and even 19" wheel packages for the car. It looks like the tires are much smaller on the larger wheels so that the overall diameter stays the same; they wouldn't be rubbing against the fenders when turning or anything like that.

Do larger wheels and smaller tires make any real difference to the way the car drives? Do you have to worry about the wheel getting damaged with those lower profile tires? Does the car handle or drive better? Thanks

Demon-Xanth
10-12-2007, 03:47 PM
Larger diameter tires allow for more traction, however they come at the cost of taller sidewalls, lower effective gear ratio (sometimes a plus, can be compensated for in the differential), and increased rotating mass. Going to a larger rim allows you to keep the sidewall short, which is good for handling, but bad for ride quality, forward bite, and protecting the rim from damage. Another side effect of a larger rim, which is often the necessity in the first place is more room for brake discs and calipers. An example of this is that a 16" rim will fit a '99 Dodge Ram just fine but a similarly equipped '03 is a no go.

One thing to note: going to a larger rim adds stress on the drivetrain, suspension, and brakes. It's been said that the Avalanche based Escalades can handle upto 22" rims, past that they start getting cracked rotors. Some tire shops love selling people large rims with skinny tires because then they can sell replacement rims to that customer on a regular basis. With the shorter sidewalls, there's less tire and air to absorb the impact of things like curbs, potholes, speed bumps, and whatever else happens to be in the road. Tire combinations with shorter sidewalls also tend to have the tire stick out less, which makes "rubs" become scratches and bent rims. More care must be taken when driving with a short sidewall because of this.

Unless you get light rims made for racing, your car WILL be slower with a larger diameter rim.

Savij
10-12-2007, 04:17 PM
Originally posted by: Demon-Xanth
Larger diameter tires allow for more traction, however they come at the cost of taller sidewalls, lower effective gear ratio (sometimes a plus, can be compensated for in the differential), and increased rotating mass. Going to a larger rim allows you to keep the sidewall short, which is good for handling, but bad for ride quality, forward bite, and protecting the rim from damage. Another side effect of a larger rim, which is often the necessity in the first place is more room for brake discs and calipers. An example of this is that a 16" rim will fit a '99 Dodge Ram just fine but a similarly equipped '03 is a no go.

One thing to note: going to a larger rim adds stress on the drivetrain, suspension, and brakes. It's been said that the Avalanche based Escalades can handle upto 22" rims, past that they start getting cracked rotors. Some tire shops love selling people large rims with skinny tires because then they can sell replacement rims to that customer on a regular basis. With the shorter sidewalls, there's less tire and air to absorb the impact of things like curbs, potholes, speed bumps, and whatever else happens to be in the road. Tire combinations with shorter sidewalls also tend to have the tire stick out less, which makes "rubs" become scratches and bent rims. More care must be taken when driving with a short sidewall because of this.

Unless you get light rims made for racing, your car WILL be slower with a larger diameter rim.


In that case, I'll be sticking to the original/optional sizes for my car.

Demon-Xanth
10-12-2007, 04:35 PM
Originally posted by: Savij
In that case, I'll be sticking to the original/optional sizes for my car.

Good plan :)

I put 295/65R16's on the back of my car (stock is 255/65R16s) after I had I had been running 285/60R16s. Even though it was only 30.5" vs. 29", I absolutely HATED the 295s. If I had the 3.92 rear end it might've been okay, but with the 3.55 I had to downshift more often and gas milage went down a half a MPG.

Savij
10-12-2007, 04:39 PM
Originally posted by: Demon-Xanth
Originally posted by: Savij
In that case, I'll be sticking to the original/optional sizes for my car.

Good plan :)

I put 295/65R16's on the back of my car (stock is 255/65R16s) after I had I had been running 285/60R16s. Even though it was only 30.5" vs. 29", I absolutely HATED the 295s. If I had the 3.92 rear end it might've been okay, but with the 3.55 I had to downshift more often and gas milage went down a half a MPG.

Well, I was thinking about keeping the total size the same and just having more wheel and less rubber, but it sounds like even that has its issues. And it's more expensive.

jagec
10-12-2007, 04:52 PM
It's not like there are NO advantages to larger rims (with the same overall tire diameter)...in theory it will corner slightly better, and of course there's the larger brakes angle. But it really depends on where you are stock. For example, I certainly wouldn't increase the rim size from stock on a Corvette, since it already has very low-profile tires. My MR2, on the other hand, has 14" rims stock, and that really constrains your performance tire options. Bumping it up to 15" or 16" isn't enough of a change to endanger your rims, but it allows you a much greater selection of quality rubber. If I finally buckle down and buy new rims, they'll probably be lighter as well...this is a 1989 with 80's wheels. Not heavy, but certainly not light.

But that's a much older car...modern cars are really buying into the "big wheel" look, so oversizing is more risky now.

ValValline
10-12-2007, 05:36 PM
My roommate just got a set of track wheels for his '05 MazdaSpeed Miata.

The new wheels are 15x8 and his stock wheels are 17x7. We weighed both tire/wheel combos when swapping them out for a track day, and they were within 2 ounces of each other. The Miata is a very light car and the additional sidewall on the 15in wheels allows enough flex to keep a larger contact patch when cornering at speed. His lap times have improved.

So bigger wheels and a lower profile tires do not always mean better performance or a weight savings.

imported_Truenofan
10-12-2007, 11:43 PM
hm....valvalline, is his bolt pattern 114.3x5? is he thinking of selling those? would i be able to get a good look at them? I'm looking around for a decent light set of rims that would do my car justice for track use. I'd prefer rims like what he got, where did he get them and how much did they weigh?

beat mania
10-12-2007, 11:51 PM
Originally posted by: Demon-Xanth
Larger diameter tires allow for more traction,

No, wider tires allow for more traction. 255/40/18 and 255/45/18 would have the same contact patch with the road.

Zenmervolt
10-13-2007, 01:59 AM
Originally posted by: Demon-Xanth
Larger diameter tires allow for more traction, however they come at the cost of taller sidewalls, lower effective gear ratio (sometimes a plus, can be compensated for in the differential), and increased rotating mass. Going to a larger rim allows you to keep the sidewall short, which is good for handling, but bad for ride quality, forward bite, and protecting the rim from damage. Another side effect of a larger rim, which is often the necessity in the first place is more room for brake discs and calipers. An example of this is that a 16" rim will fit a '99 Dodge Ram just fine but a similarly equipped '03 is a no go.

One thing to note: going to a larger rim adds stress on the drivetrain, suspension, and brakes. It's been said that the Avalanche based Escalades can handle upto 22" rims, past that they start getting cracked rotors. Some tire shops love selling people large rims with skinny tires because then they can sell replacement rims to that customer on a regular basis. With the shorter sidewalls, there's less tire and air to absorb the impact of things like curbs, potholes, speed bumps, and whatever else happens to be in the road. Tire combinations with shorter sidewalls also tend to have the tire stick out less, which makes "rubs" become scratches and bent rims. More care must be taken when driving with a short sidewall because of this.

Unless you get light rims made for racing, your car WILL be slower with a larger diameter rim.

Larger diameter tires do not provide additional traction. You're thinking of greater width.

The only inherent advantage that a larger wheel has is the ability to fit larger brakes. You can have a 6" wheel diameter and still have the same short sidewall if you wanted to do it that way. There'd just be no room for brakes. Sidewall height has nothing whatsoever to do with wheel diameter. It's a completely independent variable.

ZV

Zenmervolt
10-13-2007, 02:01 AM
Originally posted by: Demon-Xanth
Originally posted by: Savij
In that case, I'll be sticking to the original/optional sizes for my car.

Good plan :)

I put 295/65R16's on the back of my car (stock is 255/65R16s) after I had I had been running 285/60R16s. Even though it was only 30.5" vs. 29", I absolutely HATED the 295s. If I had the 3.92 rear end it might've been okay, but with the 3.55 I had to downshift more often and gas milage went down a half a MPG.

The 295/65s are taller and would have given you better mileage on the freeway (though in town it would have dropped, true). Furthermore, since you kept 16" wheels through both sets, it's really not a valid comparison to the OP's question about fitting larger wheels.

ZV

Zenmervolt
10-13-2007, 02:04 AM
Originally posted by: jagec
It's not like there are NO advantages to larger rims (with the same overall tire diameter)...in theory it will corner slightly better, and of course there's the larger brakes angle. But it really depends on where you are stock. For example, I certainly wouldn't increase the rim size from stock on a Corvette, since it already has very low-profile tires. My MR2, on the other hand, has 14" rims stock, and that really constrains your performance tire options. Bumping it up to 15" or 16" isn't enough of a change to endanger your rims, but it allows you a much greater selection of quality rubber. If I finally buckle down and buy new rims, they'll probably be lighter as well...this is a 1989 with 80's wheels. Not heavy, but certainly not light.

But that's a much older car...modern cars are really buying into the "big wheel" look, so oversizing is more risky now.

You're close, but not quite. You've forgotten that the larger wheel is not what causes the better cornering. It's the shorter sidewall of the lower-profile tires used to maintain the same rolling radius. While it's true that the cheapest way to accommodate shorter sidewalls is to simply use a larger diameter wheel, the best way, all else being equal, is to fit the lower-profile tires to the smallest-diameter wheels possible and compensate for the difference in gearing by altering the differential or the transmission ratios themselves.

Of course, I'm being a bit pedantic here. :P

ZV

MovingTarget
10-13-2007, 03:45 AM
Maybe it is just an urban legend, but won't a large enough increase/decrease in wheel size affect the calibration of your speedometer? IIRC, the diameter of the wheel/tire is directly proportional to the circumference, which is the linear distance travelled per revolution of the wheel. So, changing this ratio of linear distance to number of wheel revolutions would affect how it registers for your speedometer/odometer. Of course, I'm not too familiar with the way the car "reads" or measures speed/distance, just seems pretty easy to measure the rpm of one of the non-powered wheels and use a known ratio to calculate these. Somebody please correct me if I am wrong here.

But yes, it does affect the handling and ride quality of the vehicle as previously mentioned by others here. Personally I don't like low profile tires for this reason. I travel a lot on the interstate, so ride quality is very important.

jagec
10-13-2007, 06:12 AM
Originally posted by: Zenmervolt
You're close, but not quite. You've forgotten that the larger wheel is not what causes the better cornering. It's the shorter sidewall of the lower-profile tires used to maintain the same rolling radius. While it's true that the cheapest way to accommodate shorter sidewalls is to simply use a larger diameter wheel, the best way, all else being equal, is to fit the lower-profile tires to the smallest-diameter wheels possible and compensate for the difference in gearing by altering the differential or the transmission ratios themselves.

Of course, I'm being a bit pedantic here. :P

ZV

I suppose I SHOULD have specified that I wanted to keep the overall diameter constant, not wanting to dig into my transmission if not absolutely necessary.:P

Besides, I'd be doing it more to open up my tire options than the gain cornering ability.

Originally posted by: MovingTarget
Maybe it is just an urban legend, but won't a large enough increase/decrease in wheel size affect the calibration of your speedometer? IIRC, the diameter of the wheel/tire is directly proportional to the circumference, which is the linear distance travelled per revolution of the wheel. So, changing this ratio of linear distance to number of wheel revolutions would affect how it registers for your speedometer/odometer. Of course, I'm not too familiar with the way the car "reads" or measures speed/distance, just seems pretty easy to measure the rpm of one of the non-powered wheels and use a known ratio to calculate these. Somebody please correct me if I am wrong here.


If the total diameter (wheel+tire) changes, then yes, the speedo calibration changes too.

FeuerFrei
10-13-2007, 10:50 AM
Originally posted by: jagec

Originally posted by: MovingTarget
Maybe it is just an urban legend, but won't a large enough increase/decrease in wheel size affect the calibration of your speedometer? IIRC, the diameter of the wheel/tire is directly proportional to the circumference, which is the linear distance travelled per revolution of the wheel. So, changing this ratio of linear distance to number of wheel revolutions would affect how it registers for your speedometer/odometer. Of course, I'm not too familiar with the way the car "reads" or measures speed/distance, just seems pretty easy to measure the rpm of one of the non-powered wheels and use a known ratio to calculate these. Somebody please correct me if I am wrong here.


If the total diameter (wheel+tire) changes, then yes, the speedo calibration changes too.

Switching to a larger diameter also makes the odometer read low, which throws off your mpg calculations, and generally makes your vehicle look like it's traveled fewer miles than it actually has.

ValValline
10-15-2007, 10:53 AM
Originally posted by: Truenofan
hm....valvalline, is his bolt pattern 114.3x5? is he thinking of selling those? would i be able to get a good look at them? I'm looking around for a decent light set of rims that would do my car justice for track use. I'd prefer rims like what he got, where did he get them and how much did they weigh?

Not sure on his bolt pattern. He is keeping both sets of wheels, so nothing is for sale.

He got the 15x8s from 949racing. http://www.949racing.com/

alkemyst
10-15-2007, 12:30 PM
Originally posted by: Zenmervolt

Larger diameter tires do not provide additional traction. You're thinking of greater width.

The only inherent advantage that a larger wheel has is the ability to fit larger brakes. You can have a 6" wheel diameter and still have the same short sidewall if you wanted to do it that way. There'd just be no room for brakes. Sidewall height has nothing whatsoever to do with wheel diameter. It's a completely independent variable.

ZV

QFT.

Most are just looking for looks so it doesn't make much difference, but all things being equal you'd want the lightest wheel and lowest diameter possible to get the tire characteristics you need. There is a whole science behind this dealing with inertia, unsprung weight, etc.

What most racers do is up the wheel to fit more brake. In some instances you want more sidewall (drag) and others less.

To answer the OP, increasing overall height reduces gearing numerically, making you engine/trans spin less to get to the same speed.

Demon-Xanth
10-15-2007, 12:34 PM
A larger diameter produces a longer contact patch than a shorter one. Compare a big rig's tire footprint to that of a Camaro and you'll see what I mean. :)

JulesMaximus
10-15-2007, 02:16 PM
Originally posted by: Savij
I'm thinking about getting a set of winter tires and putting them on my current 16" wheels for this winter. I was thinking of getting the optional 17" wheels that were available for the car and putting the appropriate tires on them next spring.

I looked at tirerack at the wheel tire packages to get an idea of what I would be spending, and I noticed that they had some 18" and even 19" wheel packages for the car. It looks like the tires are much smaller on the larger wheels so that the overall diameter stays the same; they wouldn't be rubbing against the fenders when turning or anything like that.

Do larger wheels and smaller tires make any real difference to the way the car drives? Do you have to worry about the wheel getting damaged with those lower profile tires? Does the car handle or drive better? Thanks

Yes
Yes
It depends
You're welcome

;)

Lower profile wheels will give you a rougher ride and because of the narrow sidewall it is easier to damage a rim or rough roads.

Handling will generally improve because lower profile tires don't flex as much in the sidewall. Be careful though because cheaper 18 or 19" wheels often weigh more than a stock 17" wheel and increasing unsprung weight will degrade handling and increase braking distances.

Tremulant
10-15-2007, 02:26 PM
Originally posted by: FeuerFrei
Originally posted by: jagec

Originally posted by: MovingTarget
Maybe it is just an urban legend, but won't a large enough increase/decrease in wheel size affect the calibration of your speedometer? IIRC, the diameter of the wheel/tire is directly proportional to the circumference, which is the linear distance travelled per revolution of the wheel. So, changing this ratio of linear distance to number of wheel revolutions would affect how it registers for your speedometer/odometer. Of course, I'm not too familiar with the way the car "reads" or measures speed/distance, just seems pretty easy to measure the rpm of one of the non-powered wheels and use a known ratio to calculate these. Somebody please correct me if I am wrong here.


If the total diameter (wheel+tire) changes, then yes, the speedo calibration changes too.

Switching to a larger diameter also makes the odometer read low, which throws off your mpg calculations, and generally makes your vehicle look like it's traveled fewer miles than it actually has.



http://www.miata.net/garage/tirecalc.html

and if you're changing your wheels, I'd also suggest http://www.1010tires.com/WheelOffsetCalculator.asp to make sure the new wheel fits right.

alkemyst
10-15-2007, 06:49 PM
Those wheel offset calcs are good if you know how to use them...most of the time you don't want to match your old wheel stats. Brakes and coilovers also can greatly impact wheel choices.