Wheel Size Effect

[BlackFireN2O]

What does the size of the wheel affect in the ride of the car besides the look. I have heard that 17's make a better ride (in drag racing as well as in auto x) compared to 18's. But the 18's look so much better. Can someone esplain to me how the wheel size affects a vehicle? Plenty Thanks in advance!!

[jim_howard_pdx]

This is not my strongest subject, but I will give this a try. In the beginning Mustangs came with 14 and 15 inch wheel sizes. For about a year Michelin built a 15.5 tire for FORD that are un-obtanium.

16, 17, 18, and 20 inch tires are built mostly for extreme performance. The idea is to reduce the sidewall's influence upon the suspension in order to gain high speed cornering ability. That is why you see 35, 40, 45 ratios so commonly.

It used to be that all street tires were 75 or 70 ratio tires. That means if the tire was 5 inches wide, it was 3.5 to 3.7 inches tall from rim to tread.

With an 18" 35 ratio tire a 7 inch wide tire is just 2.45 inches from rim to tread. So when cornering at 100 mph, the sidewalls produce less distortion to the suspension, allowing the car to groove.

As you go up in rim size, you can retain ride comfort by going a 45 ratio if available. When you get to 18 inch tires, you are going to primarily find 35 and 40 ratio tires. But in 17 rims you will find 45 and sometimes 50 ratio tires.

A ZR rated tire has lots of stick, but don't expect it to last more than 25-28,000 miles. I prefer Z-X rated tires, which go between 35,000 to 40,000 miles. They are a little harder rubber, A GOOD THING ON THE STREET, but will not give you the great stickiness of a ZR.

Hope this helps.

By the way, if you go 17 inch rims, the tires will be much less expensive. If you want to go ZR tires, then 17 inches will be much less expensive over the years.

[BlackFireN2O]

jim_howard_pdx, I'm sorry but i didn't understand half of what you said. I'm am practically tire illiterate (sorry ) Can you explain some of the things you said again and note the meanings of the terms you used. Like explain alittle more how less sidewall is better for turing? I will be mostly using the car to drag race, but i think i will get slicks for that and for the street i want tire/wheels that will take care of those pesky kids at the stoplight , but i would still like atleast some cornering ability? Thanks in advance for all your help!

[Shaggy]

Okay i will try for road racing Jim is fully correct the less sidewall you have the less there is to flex making a lower profile tire responds quicker to turn in. but going from 17 to 18 can actually hinder road race perfomance because you are hauling more tire and wheel weight and a 275/35/?? is going to have the same height sidewall no matter the rim diameter it will just be one inch overall shorter between a 17 and 18 inch rim so as long as you are geared for that tire height then you will be fine.

Now for drag racing a good drag racing slick/cheater has soft sidewalls to absorb some of the shock on launch look at the tires in this picture




Now this is extreme but that is part of the design becuase of this though there is no real great comprise between a corning tire and a drag tire and that is with out talking about tire growth built into drag slicks either. For drag racing a iwould recomend 15's and for the street i would recomend 17's the main resasons being that the 17's are cheaper and if you want a totasl tire hieght of say 26 inches you get a little more sidewall to protect the rims for potholes.

[MiracleMax]

This is not my strongest subject, but I will give this a try. In the beginning Mustangs came with 14 and 15 inch wheel sizes. For about a year Michelin built a 15.5 tire for FORD that are un-obtanium.

Yep, they are metric tires, at one time produced by Michelin, I believe the size was 220/55r390 (I think????) You can probably still get them from Coker (thats the guys Michelin sold the molds to), Ford and BMW used these. unlucky souls

16, 17, 18, and 20 inch tires are built mostly for extreme performance. The idea is to reduce the sidewall's influence upon the suspension in order to gain high speed cornering ability. That is why you see 35, 40, 45 ratios so commonly.

Depends, big brakes, and styles drive this alot in OE and aftermarket situtations. There are a few luxury hi-perf tires out there.

It used to be that all street tires were 75 or 70 ratio tires. That means if the tire was 5 inches wide, it was 3.5 to 3.7 inches tall from rim to tread.

Here you go, this how the service description breaks down.

eg; P245/50r16 XXZ

P = Passenger
245 = Section width in milimeters (not tread width)
50 = 1 of the tires aspect ratios, in this case it refers to the height of the sidewall in relation to the section width. As it pertains to this size, it means the sidewall is 50% of the section width.

r = radial construction

16 = rim diameter.

XX = This would actually be a numeric designation and refers to the maximum load the tire can carry at the maximum tire pressure branded on the side wall (alot of people confuse this with what air pressure the tire needs.)

Z = speed rating (in this case it refers to tires designed for 149+, for passenger use you will see;

S = 112
T = 118
H = 135
V = upto 149
Z = 149 +
W = 178 (??)
Y = 183 (??)
ZR = Doesn't have a maximum speed listed.

The speed rating refers to the tires ability to withstands sustained operation at those speeds for upto 8 hours without failure. In truth it does not denote the actual performance capabilities of the tire beyond its ability to withstand a sustained speed in a defined amount of time.

HOWEVER certain generalizations can be made as to the way the tire affects handling and performance. It IS unwise to go to a lower speed rated tire than the one originally equipped on the vehicle. IF you do, the vehicles maximum speed is limited to the specification listed on the tire AND it will effect vehicle braking and handling.

The most important thing when it comes to selecting a tire is rim fitment and load carrying capability. Tires have approved rim widths which should be observed. As for load carrying capability. You need to figure your gross weight. (ie; You like to cruise with 5 fat chicks in your car with a full tank of gas and an all iron 460 under the hood with the killer S/C set-up. The bass death machine in the back, and over the top hydraulics, plus a trailer hitch and your boat). Bad things will happen if you just throw what looks kewl to you on there.


With an 18" 35 ratio tire a 7 inch wide tire is just 2.45 inches from rim to tread. So when cornering at 100 mph, the sidewalls produce less distortion to the suspension, allowing the car to groove.

Heres how you do this;

SECTION WIDTH x ASPECT RATIO (expressed as a decimal) / 25.4 = height of the sidewall.

SW x AR / 25.4 x 2 + RIM DIA = Nominal unloaded tire dia. (this is useful for making broad comparisons)

As you go up in rim size, you can retain ride comfort by going a 45 ratio if available. When you get to 18 inch tires, you are going to primarily find 35 and 40 ratio tires. But in 17 rims you will find 45 and sometimes 50 ratio tires.

Generally speaking, as you retain sidewall height the tire will ride better (the sidewall is a sort of shock absorber), However it depends on how the sidewall is constructed. There are tires on the market which have very pliable s/w with excellent cornering and turn-in capabilities.


A ZR rated tire has lots of stick, but don't expect it to last more than 25-28,000 miles. I prefer Z-X rated tires, which go between 35,000 to 40,000 miles. They are a little harder rubber, A GOOD THING ON THE STREET, but will not give you the great stickiness of a ZR.

Generally speaking, yep. However there are variations in here. For example BF Goodrich produces a line of ZR tires. The GForce tire line has three models.

KD (Key Design) = there big dog dry handling tire
KDW (Key Design Wet) = excellent wet tire
KDWS (Key Design Wet & Snow) = all season hi-pef tire.

Its interesting to note that there are some Z-rated tires out there with Tread Life ratings approaching 400. Big whoop you say, however a few years ago in the same brand of tire a manufaturer introduced an 80,000 mile warranty on a 400 treadwear tire.

Heck on the 02, my Goodyears are gonna go 40k.

Maintenece, suspension design, vehicle weight in relation to tire size, road conditions, and driving style are a few things that can effect tire life (Honda fits there vehicles for the most part with H and V rated tires which routinely go 40-70k before replacement)

As you move down the line you give up ulitmate handling capability for more balanced tire performance.

By the way, if you go 17 inch rims, the tires will be much less expensive. If you want to go ZR tires, then 17 inches will be much less expensive over the years.

Yep

[jim_howard_pdx]

I will make this easier, knowing you want to drag.

Buy Hoosier brand autocross tires if you plan on driving in the rain and need a sticky tire.

Buy Hoosier brand DOT approved Street Slicks or M/T Street Slicks if you want to race but need to drive the car to the track. Buy M/T Slicks (I prefer the crinkle wall for better launch on a heavy car) if the car is trailered.

Don't worry so much about the aspect ratio. I prefer to go with the tallest slick I can fit under the car without jacking up the suspension. Then go the tallest gears to get you the rpms you want at the quarter mile trap area. Go to the "ANALYZER" on the purple menu bar to plug in the tire circumference, your HP and it will tell you what gears to run.

With my engine, I will pull an 11.9 Quarter with 4.30 gears. But with a C-4 transmission I could not live with the engine RPM. My plan is to go with a Doug Nash or Tremec or an AOD if I decide to keep the ol slushbox style tranny. I want a 5 speed because my car is primarily built to embarrass Corvettes, Porsches, and BMW's. And when I say embarrass, I plain wipe the smile off their smug faces. I can beat a new vette by 20 to 30 car lengths to 100 MPH. That is as fast as I will drive on the street. I do the same to new Cobra 4.6 cars....sorry Ford Dudes......

[88workcar]

Mr Jim, what does your car weigh? Have you ever run 4.30s? Have you acually run 11.9s? I wish I lived near you, the new vetts round here run 12.50s off the show room floor, They give me hell, thats why I keep a full bottle in the car. I have 4.30s, I have a motor only .4 bigger than a 4.6 and I run 12.50s @ 109 with out the NOS. I just bought slicks so that will get better Fri night. I will also be installing a cage soon so I can make a nos pass at the track. I want heads but these stock E7s seem to be pretty good for now. Oh, what is the MPH on your 11.9 pass? I can't wait to get an 11 sec slip.