how do tires/wheels size affect performance?

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Many people have been telling me if I really want to upgrade performance on my car or any car that I should invest in bigger tires and wheels.


I have also heard that TOO BIG can actually take subtract from performance and potentially create a lot of unstrung weight.



So my question is how do larger wheels/tires affect performance and how big is too big?

posted by  Bronxie

Yeah, be real careful about having too much "unstrung" weight. :banghead:

Now I remember one of the reasons I stopped logging in. :doh:

posted by  vwhobo

Because no one liked you?:wink2:

posted by  67Coronet383

Because of me?

posted by  Bronxie

vwhobo beat me to it, but it's "unsprung" weight...and another term that relates to it is rotational mass. I don't know much about tires, but fatter tires do equal greater traction, and smaller ones consequently mean less traction, but at the same time less energy is required to spin them...

posted by  chris_knows

Like it ****ing matters. Only vwhobo would be such a woman about something like that.


At least unstrung is a word. Unsprung isn't even in the dictionary!

posted by  Bronxie

"Unsprung" isn't, "unsprung weight" is :laughing:.

posted by  chris_knows

Oh definitely. How could I have missed that?


If you get bigger wheels would your speedometer be offset by a few MPH?

posted by  Bronxie

I might be wrong here, but I think larger wheels (diameter, not width) give you less power. I'm picturing them like gears, and the tires are the gears at the end. The axle will spin more or less at the same speed no matter what the tire/wheel size. If larger tires spin at the same rate in RPMs, they will cover a greater distance because of the larger circumference. However, just like using larger gears at the end, they will be easier to stop moving, therefore creating less power. By this thinking larger wheels would give you a higher theoretical top speed, and it may account for incorrect speedos when people greatly change their tire size. Anybody confirm/deny this?

posted by  giant016

I see you're still honing the art of being a moron to a fine edge. Good job. :banghead:

http://www.google.com/search?hl=en&q=unsprung+weight

Apparently at least 143,000 others haven't read your dictionary.

http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=unsprung

posted by  vwhobo

HMMM...


I guess you're right, that definitely is relevant here.


NOT.



Talk about being a moron!


And mind you, dictionary.com says, "I know every single word in the english langauge and I have no idea what 'unsprung' means."

posted by  Bronxie

I thought about that too but I wasn't so sure. :(

posted by  Bronxie

It depends on the size, but I think it was said on here that for every inch that you increase your diameter, you have to decrease your sidewall bu 10%, although it would depend on how thick your wheels are then lol. The ECU can be programmed for another size though.

posted by  chris_knows

I really am just looking at wider tires. My car has 18" "S" wheels and I think that's adequate... I think 19" would make for a really uncomfortable ride as well.

So is it the width that will increase traction?

posted by  Bronxie

More suraface area = more traction.

posted by  giant016

And if only you had 10% of the intelligence you believe you have, you'd know that it is exactly relevant.

The tires are not supported by a spring.

The wheels are not supported by a spring.

The (outboard) brake assemblies are not supported by a spring.

The lower control arms are not supported by a spring.

The (live) rear axle assembly is not supported by a spring.

Etc.

Etc.

Therefore they are unsprung.

Therefore any weight associated with them is unsprung weight.

Is that simple and relevant enough for you... MORON?

posted by  vwhobo

Bronxie, Hobo's right. You're trying to find argument in something that has no room for argument. Why is that always so important for you? Quit arguing and learn something.

Additional unsprung weight will reduce suspension efficiency, though relatively small amounts will be unnoticeable to the driver.



Increasing the width of the tire does not increqase surface area of the contact patch, it only makes the contact patch wider, but skinnier front to back. (given the same tire pressure and the same vehicle weight). This reduces accellerative traction slightly, but improves lateral grip.


But the bit about the increase on overall diameter reducing the overall gear ratio is spot on.

posted by  ChrisV

It's so fun getting info out of you :D

posted by  Bronxie

If wider tires reduce accelerative traction, than skinnier ones would improve it correct? Perhaps dragsters should run skinnies all around:mrgreen:

I'm not completely arguing with what you're saying, mostly in that I can see that the contact patch would be skinnier from front to back if a wider tire were put on. The only thing is that if you put on a tire that was identical except one inch wider I don't think that the small loss in front to back area would account for all the area gained by adding one inch to the width. I dunno, maybe I missed something.

posted by  giant016

Yeah, that's what it looks like to me.

http://www.car-forums.com/talk/showthread.php?t=25835

posted by  vwhobo

the only way i can see larger tires and wheels making performance better is by getting bigger wheels and tires you would be able to get a big brake kit for your car, which would increase your braking performance by decreasing stopping distance.

posted by  V-Tec

Wrong answer. More urban myths and wives tales. The standard brakes on ALMOST ALL CARS and trucks built for the last 25 years are strong enough to overpower and lock the tires during braking, even in the best of tractive conditions. Hence the addition of 4-wheel ABS to most new cars/trucks. Bigger brakes will just lock those tires sooner and easier. The simple fact is that the tires stop your car, the brakes only slow the rotational speed of the tire. Sorry.

That being said, bigger brakes generally give you better control of your braking along with being less likely to fade after repeated use.

posted by  vwhobo

You guys are making it easy for vwhobo and ChrisV to appear uber-intelligent. Most of you...lack....knowledge.

Most of you guys joined this car forum months ago because you like cars...why haven't most of you researched about cars during those months? Do you really like cars? Some of your answers are just completely wrong...but you are so sure of them.

posted by  My Life, My Era

thanks for clearing that up... took a guess and was wrong

posted by  V-Tec

Amen to that one...

posted by  67Coronet383

I don't understand how...Increasing the width of the tire should increase the surface area of the contact patch, but according to the diagram below, it's wrong lol...?

posted by  chris_knows

The "bend/sag" at the contact patch is less in a wider tire which makes the contact patch smaller.

posted by  67Coronet383

Chris,

You're forgetting the two conditions that make that statement true... Identical vehicle weight and tire pressure. For any given weight/pressure combination, it will require the same amount of surface pressure to hold the car off the ground. If you change one of the two, the contact patch size will change. Otherwise, only the shape will change.

Of course, we haven't explored what happens when the tire outside diameter is increased along with having a wider section. Hmmm. Anyone?


Note: Isn't it funny that two of the people with the least knowledge are telling you guys how you're making ChrisV and I look smart? I wonder why they haven't wieghed in on the situation yet. Oh yeah, I know. :wink2:

posted by  vwhobo

I get it, the weight is more dispersed, so the contact patch isn't flattened as much as with a narrower tire.

posted by  chris_knows

So a bigger contact patch is more desirable? And if so, why are larger tires more desirable than smaller tires?

posted by  Bronxie

They look cooler...:laughing:
.
.

posted by  BavarianWheels

because you wear boxer shorts?:wink2:

posted by  Wally

Holy Crap he's right this time!:doh:

posted by  elchango36

Notice that dragsters run tires with extremely low tire pressures. And ALSO notice that when a dragster actually runs, the tires increase in diameter and the contact patch gets narrower..

Notice the wrinkles in the sidewalls:

http://www.eurodragster.com/live/susannecallinlicence/images/launch.jpg

The tires are running very low air pressure (and they have to be screwed to the rim, as well). The ultra low air pressure allows more of the front to back contact patch to be utilized for accellerative traction.

But when running hard, the tire expands and the contact patch gets skinny side to side:

http://professorginz.com/TopFuel/racecar.jpg

posted by  ChrisV

Larger wheel size with shorter tire sidewalls give increased cornering/steering response, at the expense of ride quality, up to the point where the wheel itself adds too much unsprung weight and you go backwards. The shorter sidewall is like having a short pencil eraser: it flexes less side to side, thus being more precise in it's response to your input. Wider tires increase lateral grip due to the shape of the contact patch, and in general, larger tires are also designed more for performance with better rubber compounds and tread block design.

Lots of factors go into the choice of tire. For road racing, a very short sidewall tire, allowing room for the largest brakes, and the best cornering/steering response is ideal. For this reason, so many sporty cars follow this pattern.

Now, often, the rubber is heavier than the alloy of the wheel, so by increasing diameter of the wheel but using a lighter alloy, the overall weight can go down, giving less unsprung weight. And by reducing the weight of the tire by having it have shorter sidewalls (at the same or similar overal diameter) you reduce rotational mass at the farthest point from the hub, reducing the effort necessary to turn it, freeing up some horsepower. Thus a larger diameter wheel with a short sidewall tire can free up horsepower AND increase cornering response AND improve overall suspension efficiency.

At some point however, you run into the law of diminishing returns, and can actually go backwardfs, so you have to be careful IF you are looking for ultimate actual performance. In real life on the street, however, the difference between slight improvement and slight detriment is small, and often unnoticeable. So a slightly heavier large diameter wheel will not really hurt the performance enough to be noticeable, but might look better enough to the owner that it's negative effects are immaterial.

posted by  ChrisV

:clap: :clap: :clap: :clap:
one of the best has spoken again

posted by  V-Tec

Here's (http://spikedhumor.com/articles/61539/Slow_Motion_Drag_Cars.html) a video of a drag car taking off in slow motion (1000 FPS)...Pretty interesting.

posted by  chris_knows

So basically, these things have a range of effectiveness, and too much in either direction can hurt the objective at hand.


How can you calculate if you are getting the most out of your tires & wheels, for example, if you are in the market for these things.


How heavy is too heavy, how short is too short and how big is too big relative to the vehicle it goes on?


Like I'm sure this set up isn't very effective.


http://www1.istockphoto.com/file_thumbview_approve/836059/2/istockphoto_836 059_low_profile.jpg

posted by  Bronxie

Learn something new everyday. Who needs school when you've got CF?

posted by  giant016

I suggest you and other members cross-reference what you have "learned" in this topic with a more reputable source, preferably a book.

posted by  My Life, My Era

Thanks for the advice, but I know enough about the subject not to reference books. Perhaps you have a recommended reading for the others though?

posted by  Wally

It all depends on what you are going to be doing with your car. if you are going for that extra hundredth of a second on an autocross course, or road race course, then as light as possible, with as sticky a tire as you can find is what you are looking for, preferably as wide as can fit under your fenderwells. Like this Miata that Ron Baur drives in SCCA autocrossing:

http://www.bauerspeedracing.com/autocross/P1080249.JPG

275 Kumho's on 18x9.5" wheels. A bit on the radical side, but it works. Of course, with any racing, you have to work within the rules, and stock class cars are limited in wheel sizing. One thing about this, there are usually experts that have gone through the calcualtions and teh trial and error phase of testing to tell you what will work best on your car. Of course, you can get a few different recommendations based on who's done the actual testing and their particular location/surface/event, but it'll give you an idea of where to start. Your own driving style will also play a part in determining the best setup. I personally prefer a slightly taller sidewall for a bit of flex. This gives me a more gradual breakaway at the limit, making driving at or past the limits easier. Thus I'll use a 50 series tire on a 1 or 2 inch diameter smaller wheel, rather than a 45 or 40 series tire on the larger wheel when going for autocross performance. On the street looks are more important to me, so I might go for that 40 series tire on the larger diameter wheel.

On the street, if you are into corenring, you can go in a similar route, butremember, street tires are different and that much change may be worse for your car than something closer to stock. Again, on the street, for most people, the negatives are not usually enough to actually notice.



For a race car, no. For a street car, it'll have a slightly jarring ride, and be subject to hitting potholes and getting damaged. For a show car, it's plenty effective.

posted by  ChrisV

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