For those concerned about wheel size versus weight.. interesting observation.

[Steve1968LS2]

I swapped back to my "showy" wheels today, so I took the time to do a little weighing with my digital scales.

Many people say to go with a 17" wheel to save on rotating weight, but I found there's not much of a savings. Here's the data:

18x12 Forgeline WC3 with 335/30/18 R888 tire = 57 lbs
17x12 Forgeline ZX3 with 315/35/17 R888 tire = 52 lbs

So going with the 17 only saved 5 lbs off the assembly. I guess some of the weight savings of the smaller 315 tire was lost to the taller sidewall.

The savings were even less up front.

18x10 Forgeline WC3 with 275/35/18 R888 tire = 50 lbs
17x10 Forgeline ZX3 with 275/40/17 R888 tire = 49 lbs

So, a savings of one pound by going 17... Just something to ponder when you are shopping for rollers. :)

https://static1.pt-content.com/images/noimg.gif

[GBodyGMachine]

Interesting. I do think you will get a bit more tire selection with a 17" wheel. That is one advantage I can see.

[BonzoHansen]

Good info. I thought a big part of the discussion regarded moment of inertia, which my little layman brain interprets as where the weight resides.

[brans72]

fancy toy you got there!

[dannyho]

it would be interesting if people were to post the moment of inertia of the wheels and tires. it's a pretty simple test and calculation. I remember doing it in HS Physics. logic obviously tells me the 17 would have a lower moment of inertia than the 18, but it also tells me that the larger you go the less difference it's going to make between sizes.

[68sixspeed]

MOI is of course a bigger concern than static weight, but I would consider a 10% savings in rear rotating weight is significant, especially with the old rule of thumb that 1lb of rotating weight is worth 10lbs of static weight as far as acceleration/deceleration. (plus 10lbs the unsprung weight difference is significant too.)

Think of all the money spent on an aluminum center section for the rear end to save unsprung weight, or lightened gear sections, aluminum flywheels and driveshafts (granted more critical because they are before the rear end gears), all to give it back on bling. Now 18's aren't as bling as say 20's, but that the whole ongoing debate on this site, now isn't it?

[Steve1968LS2]

fancy toy you got there!

Not mine.. I swiped it from our tech center.. handy for all sorts of stuff. ;)

[FirstGenZq8]

sweet, you got a real nice scale there!

go to this thread and start posting some wheel weights; anything to get that FirstGenZq8 guy to STFU w/ his ranting and raving about wheel weights!

https://www.pro-touring.com/forum/showthread.php?t=48248

[parsonsj]

Mazda Racing posted a spreadsheet that I played with for a while.

Rule of thumb: 1" diameter bigger wheel "costs" about 50 lbs, even if the wheels weigh the same. Per wheel. So your 18" wheels cost you the equivalent of 200 lbs. 2 tenths in the quarter mile. 15 feet 60-0.

MOI: It's real, and it always demands payback. :)

jp

[dstryr]

You drove both the 17's and the 18's...notice a difference in the seat of your pants?

[Steve1968LS2]

Mazda Racing posted a spreadsheet that I played with for a while.

Rule of thumb: 1" diameter bigger wheel "costs" about 50 lbs, even if the wheels weigh the same. Per wheel. So your 18" wheels cost you the equivalent of 200 lbs. 2 tenths in the quarter mile. 15 feet 60-0.

MOI: It's real, and it always demands payback. :)

jp

Yea.. but isn't overall diameter the real deal. The 315/35/17 was almost as tall as the 335/30/18 (a few tenths) and isnt a lot of the weight in the tire rather than the wheel? (at least the weight out the outer edge of the assembley).

Just thinking out loud here ;)

And the 275/40/17 was actually taller (i think) than the 275/35/18.

I know there are other payoffs for the 17s... that's why i dumped a bunch of $$$ on a set for the track. 5 lbs in the back isn't bad, sorta surprised on the fronts.

[Steve1968LS2]

You drove both the 17's and the 18's...notice a difference in the seat of your pants?

Yea, easier to fry the tires with the 17s...

The big payoff on that combo was a slightly taller sidewall that yields better feedback and response on the track. The weight was a bonus :)

[dstryr]

Hmm. Im still up in the air about getting 17's or 18's...car will be a DD that hits the local autocross up probally once a month. I do like the looks of 18's better too.

[Damn True]

I know there are other payoffs for the 17s... that's why i dumped a bunch of $$$ on a set for the track. 5 lbs in the back isn't bad, sorta surprised on the fronts.


5lbs static. And the main thing is where that weight is relative to the hub.

[parsonsj]

the main thing is where that weight is relative to the hub.That's it. Since wheel weight is concentrated in the hoop portion, bigger wheels take their bite.

Another way of looking at it: going from 17" to 18" wheels affects performance about as much as having a passenger ride along with you. If you went to 20" wheels, it would be like adding 3 passengers.

jp

[XLexusTech]

Mazda Racing posted a spreadsheet that I played with for a while.

Rule of thumb: 1" diameter bigger wheel "costs" about 50 lbs, even if the wheels weigh the same. Per wheel. So your 18" wheels cost you the equivalent of 200 lbs. 2 tenths in the quarter mile. 15 feet 60-0.

MOI: It's real, and it always demands payback. :)

jp

X2 :yum:

[T_Raven]

Crap now I wish my profile 5s 18s were 17s, oh well they were slightly used and cheaper than new 17s woulda been.

[1969CamaroRS]

Very glad I went with 17" now :smoke: The minimum I could go, fit my brakes and get modern rubber.

[Vegas69]

Still glad I have 19's out back because they look killer and I spend more time cruising and looking at it than I do down the drag strip.:1st:

[TonyL]

yep. came for the MOI comments. Think of swinging a ball on a string over your head. The further out you let the ball go, the harder it is to get it going.

There's interesting research to be done in the hoop weight area.

[Damn True]

If you have two 9" wide wheels one @ 17" and one @ 18" there is a 3.2" greater circumference in the 18" hoop. That means there is an additional hunk of metal in the wheel that is 3.2"x9"x___ . With the ___ representing the thickness of the wheel material. This does not of course account for the additional material in the center of the wheel. And...of course this material is .5" further away from the hub.

[Steve1968LS2]

If you have two 9" wide wheels one @ 17" and one @ 18" there is a 3.2" greater circumference in the 18" hoop. That means there is an additional hunk of metal in the wheel that is 3.2"x9"x___ . With the ___ representing the thickness of the wheel material. This does not of course account for the additional material in the center of the wheel. And...of course this material is .5" further away from the hub.

But if the wheel is light.. and the 17-inch tire is heavier then isn't the tire the factor since it's at the furthest distance from the hub?

[Vegas69]

You know what... I was thinking it would be a great story the other night to run 17,18,19etc back to back with the same tire width on the drag strip or road course and see how much difference it makes. What do you think Steve?

[1969CamaroRS]

You know what... I was thinking it would be a great story the other night to run 17,18,19etc back to back with the same tire width on the drag strip or road course and see how much difference it makes. What do you think Steve?

Oh great idea. Even better would be if you could get the same brand/size tires and wheels, so the only real difference is the size of the hoops. A real apples to apples comparison.

[1offwizard]

But if the wheel is light.. and the 17-inch tire is heavier then isn't the tire the factor since it's at the furthest distance from the hub?

My thoughts too. Most of the weight of the tire would be the steel belts which would be the same distance from center if the diameters were the same.

[68sixspeed]

Steve- you have the contacts to get this through over any of us-- contact the engineering guys at one of the major wheel mfg's and get the MOI #'s on the same design wheel in different dia's, same on the tire mfgs. On the wheel, if they'd share solid models we could pull the info off those as well as take a good stab at modelling the tire based on it's weight and cross section info.

or, the 1/4 mile dyno doesn't lie, same car, make it an automatic for consistency, try the tire combos and watch the mph drop as you go bigger.

[wiedemab]

The weight of the wheel/tire combo is probably a pretty good "real world" indicator that the heavier setup will have a higher moment of inertia, but to really know the moment of inertia you need the density as a function of the radius. I'm pretty rusty on my ME skills, but it would be really difficult to hand calculate this (at least for me) as the wheel design and tire profile are not easily geometrically represented.

If someone wanted to solid model the wheel and tire combo in a 3D modeling software (ie: Solidworks) you can assign different physical properties to the wheel (aluminum) and the tire (I'm not sure what the density of this would be - it could be figured out I guess).

Experiment - Weigh (well technically I should say "mass") the tire and then submerge it into some sort of a graduated liquid container and see how much volume it displaces -> density = M/V.

The software will tell you what the moment of inertia for that combo would be. My brother-in-law is a Solidworks guru. Depending on how busy he is at work, if I see him this weekend, maybe he can get some measurements Steve's wheels and at least roughly model them and see what the software says.

OK - I'm done rambling.

[68sixspeed]

Kind of along the lines of what I as thinking, but I hate to just draw a rim, a real world design section is needed to get accurate results. We can discount the tread area and OD of the tire as it would be virtually the same on either setup and calcualting the density with steel and other belts is a pain. So then we need to calculate the sidewall and bead for the tire, and then the wheels. Anyone have a SEMA membership and access to the CAD data?, we could use an OE wheel for the comparisons. I have the solid modeler and some time if we can get the info. -Dan

[The WidowMaker]

id like to see the numbers as well. i see what steve is saying, but although the tire is the same "x" dimension, the "rim" of the wheel is still further out. id be suprised if it was 50 lbs per inch, but then again im suprised a lot.

tim

[Steve1968LS2]

Steve- you have the contacts to get this through over any of us-- contact the engineering guys at one of the major wheel mfg's and get the MOI #'s on the same design wheel in different dia's, same on the tire mfgs. On the wheel, if they'd share solid models we could pull the info off those as well as take a good stab at modelling the tire based on it's weight and cross section info.

or, the 1/4 mile dyno doesn't lie, same car, make it an automatic for consistency, try the tire combos and watch the mph drop as you go bigger.

Good idea... saving weight in the wheel doesn't help if you run a heavier tire since the tire is farthest out.. wow, a math guy could really geek out on this stuff. lol

[silver69camaro]

Anyone have a SEMA membership and access to the CAD data?, we could use an OE wheel for the comparisons. I have the solid modeler and some time if we can get the info. -Dan

Yep. I'll request a model for a '08 Z06 wheel and tire. But I don't have a similar wheel to compare to in a 17" form.

[silver69camaro]

Good idea... saving weight in the wheel doesn't help if you run a heavier tire since the tire is farthest out.. wow, a math guy could really geek out on this stuff. lol

I could be mistaken, but on a specific volume basis (lbs/in^3), the tire is lighter. I think.

[bbcc]

I could be mistaken, but on a specific volume basis (lbs/in^3), the tire is lighter. I think.

You are correct. But, as stated before the steel belts do complicate things mildly.

Just as a logical analysis of this: We have two tires, both of the same diameter and width, are compared with the only variable being the wheel size. Following with the theme, lets say 18" and 17" are used. This means that 0.5" more sidewall material exists on the 17" tire. Having said that, the substantial mass of the tire is on the outer extents of the tire, aka the tread. The tread will obviously have the most impact on MOI. The increased amount of material on the sidewall of the 17" wheel won't account for a whole lot considering it is adding minimal material closer to centroid.

We can say that the significant portion of the wheel is the hoop. It contributes to (insert educated guess) 40-50% of the wheel mass. And this mass is the furthest away from the wheel centroid. So a step up to an 18" wheel means that this 40-50% mass is now 0.5" further away from the centoid. Considering that aluminum, and steel for that matter, are going to be a denser material than the tire, the increased MOI of the 18" wheel will not be ofstet by the decreases MOI of the 18" tire. I think it is safe to say that the 17" wheel and tire combination has a distinct performance advantage over the 18" wheel and tire.

So I think that combined with lower mass of the 17" wheel/tire, which helps the unsprung weight and so on, the 17" wheel/tire needs less force to be accelerated.

But, I think Steve should totaly do a real world test on this. A drag strip test would be cool, but a few to many open variables to notice what could be a very small change in performance. Maybe a chassis dyno test would be a much more accurate quantitative test.

Ryer

[dannyho]

somebody should probably check my math on this. I did this using the energy method.
in order to determine the MOI of anything, support it axially and wrap a string around it. fix one end of the string to the wheel and the other to a weight. the idea is when you let go of the weight the wheel will spin, lowering the weight to the floor. the information you're going to need is the radius of the object being measured, the mass of the weight you're using, the distance that the weight drops, and the time it takes to do that.
MOI units are kg*m^2, which is SI (I doubt anyone is interested in finding slugs*in*in)
which means you have to convert all your units over to meters and kilograms.
if you want to find out the MOI of your tire/wheel, it's not really a hard thing to do. Just takes a little math.

and a diagram

[bbcc]

Math looks good. That's a pretty practical test to get the MMOI. The only uncontrolled variable will be the bearing drag. The drag will increase with an increase in weight. That will have to be kept in mind when looking at the results of the test. But I can only see this further accentuating the MMOI of the heavier 18" wheel.

[sik68]

I didn't bother to "geek it out" too much, but here is a simplified analysis I came up with. I don't see a need to make it too complicated.

Please proofread for anything incorrect. 17" on the left, 18" on the right

https://static1.pt-content.com/images/pt/2009/01/a-1.jpg

https://static1.pt-content.com/images/pt/2009/01/b-1.jpg

Average HP from 0-60 may not be the best indicator of the power-sapping nature of weight and rotating intertia; but it gives you something to wrap your head around.

[Steve1968LS2]

Update:

I put 335/35/17s on my Forgeline track wheels..

The weight.. 60 lbs

My 335/30/18 combo weighs 57lbs

So the 17s are heavier.

Now I know the wheels are lighter so that weight must be far from the hub and caused by the heavier tire (due to the increased sidewall.

Now to be fair I know the R888 is typically lighter than same sized other tires but still.

My front 275/40/17 combo was withing a pound of the 275/35/18 combo.

Food for thought...

[68sixspeed]

Steve- can you run some track or g-tech accelleration and braking tests to see any performance difference? It might take 17's vs 20's to see a noticeable difference though.

[parsonsj]

My Mazda Racing spreadsheet put the cost of a 1" bigger wheel at somewhere around 50 lbs. Bigger wheels make the car behave as though it weighs more, which takes into account braking performance as well.

jp

[Vegas69]

Not sure a Mazda spread sheet is a good comparison. They can't be running 335mm of rubber.

[parsonsj]

Not sure a Mazda spread sheet is a good comparison. They can't be running 335mm of rubber.Not sure why you would make that conclusion. The actual size of the tires doesn't really matter, what we are talking about is the difference between sizes. The Mazda Racing worksheet is germane since I am assuming actual engineers with experience in such matters designed it.

But anyway, I was wondering if some calibration with those findings and what the calculus above shows would be interesting.

jp

[Vegas69]

If the rubber weighs more than the aluminum, the wider the tire the less factor a bigger wheel has.

[Damn True]

Not sure a Mazda spread sheet is a good comparison. They can't be running 335mm of rubber.

O'RLY?

https://static1.pt-content.com/images/noimg.gif

Besides, I think the premise is the comparison of a tire of a given dimension on two different diameter rims is it not. If the premise holds true on 215's on a Miata it would be just as true with the 335's on the back of a Camaro would it not?

[sik68]

There were a bunch of posts deleted from this thread???

[Ralph LoGrasso]

There were a bunch of posts deleted from this thread???

They weren't deleted; unfortunately, they were lost due to a forum error. See here:

https://www.pro-touring.com/forum/showthread.php?t=54070

[Steve1968LS2]

My Mazda Racing spreadsheet put the cost of a 1" bigger wheel at somewhere around 50 lbs. Bigger wheels make the car behave as though it weighs more, which takes into account braking performance as well.

jp

If we were talking just wheels I would agree.. but we are talking wheels/tires.

Since I know my 17's are lighter than my 18s then the extra weight now MUST be in the tire.. which is further from the hub than the wheel. So, my 18 rear is more performance oriented than my 17" wheel combo.. right?

[Steve1968LS2]

O'RLY?

Besides, I think the premise is the comparison of a tire of a given dimension on two different diameter rims is it not. If the premise holds true on 215's on a Miata it would be just as true with the 335's on the back of a Camaro would it not?


Math is math.. :shrug:

[Vegas69]

My post was lost with the server problems. After a little research the moi has to go up with a larger wheel. You are moving the hoop out with a larger wheel and that is a heavy portion of the wheel. The tires are all about the same weight. I looked up the three most popular size mini tub sizes and weight in a PS2.
335/35/17 34lbs 335/30/18 33lbs 345/30/19 34lbs Keep in mind the 19 is 1.2" larger in diameter and 10mm wider.

[sik68]

I posted this yesterday...

Since braking is a faster process than accelerating, wheel weight and inertia play a bigger role than accelerating (which I posted last page).

https://static1.pt-content.com/images/pt/2009/03/braking_power-1.jpg

From these calculations I'm doing, I have several ideas:

1) Your lightweight wheels aren't going to free up enough power to let you pull around someone on any one particular turn. The benefit comes over many turns and many laps of reduced unsprung weight and inertia.

2) If you're trying to reduce inertia, start with the motor side of your drivetrain; IE, rotating assembly, clutch, flywheel. Switching from a 30lb flywheel to a 13lb flywheel is worth about 40hp in 1st gear, and 25hp in 2nd. Try getting those numbers with lightweight wheels. I think Penny has an aluminum flywheel? So that's good. :)

[Damn True]

Math is math.. :shrug:

Indeed. It would be really interesting though to examine it in detail. I found the spreadsheet JP mentioned yesterday for the math bit. So how about this.

Nick's engine has recently been dyno tuned prior to installation right? Thus we have an accurate picture of the crank HP (yours has been changed since install if I'm not mistaken right?) prior to any drivetrain losses. I propose the procurement of two sets of rear wheels of the same model and construction, (I'm sure you can get some blem's or something no?) one in 17" one in 18" and two tires of the same model/size save for rim diameter (with tire diameter being as close as practicable).

Measure/weigh each according to the parameters in the model and see what the math says. Then, mount both sets of tires/wheels on the car and run them on a chassis dyno.

If there is an appreciable difference in the MOI between the two there should be a commensurate reflection in the rate of acceleration of the wheel and perhaps even a loss/gain in the wHP measurement.

If nothing else it would be interesting to see it actually examined rather than postulated on amongst a bunch of nerds (myself included) on a message board.

[Vegas69]

I just chassis dynoed my car yesterday with the mammoth rear tires and he said they have played with different wheel sizes for fun on Corvettes. 3-4 horse is about it between small and large on a high horse application. It may change the curve somewhat but the peak numbers won't be much different. I think a real world test like a 1/4 mile or a lap around the road course would give a better indication because of the real world loads.

[sik68]

amongst a bunch of nerds (myself included) on a message board.

I'm highly insulted! :)

I'd say, test it on a drag strip, as a chassis dyno won't tell the whole story. In a 4th gear pull on a dyno, wheel acceleration is very slow in proportion to the amount of power going through the drivetrain. My guess is you won't see the difference at all...plus, it's only 2 wheels, and the car isn't moving.

[Damn True]

Measuring the rate of wheel acceleration on the dyno would eliminate some significant variables. 1/4 mile times may be impacted by differences in the ability to effectively launch the car due to tire compliance but I think those datapoints would be interesting to add to the mix. An auto-x with a very, very consistent driver (I think we know one or two...cough-Pozzi's-cough) would be good as well.

Test 'em all. Mathmatical model, chassis dyno, 1/4-mile and auto-x.

[Damn True]

I just chassis dynoed my car yesterday with the mammoth rear tires and he said they have played with different wheel sizes for fun on Corvettes. 3-4 horse is about it between small and large on a high horse application. It may change the curve somewhat but the peak numbers won't be much different. I think a real world test like a 1/4 mile or a lap around the road course would give a better indication because of the real world loads.

I think the difference in rwHP would be pretty small, especially at the peak since at that point, the "work" has in large part been done. The average rwHP and rate of acceleration would, IMO be more profoundly impacted.

[silver69camaro]

I actually have very accurate models of some Intro wheels that I can modify the diameter and width as I choose, as well as some accurate BFG tire models that can be modified as well. If I can find some time, I'll calculate the HP required to spin to, say, 60MPH and compare that to a smaller diameter rim.

[Vegas69]

I think the difference in rwHP would be pretty small, especially at the peak since at that point, the "work" has in large part been done. The average rwHP and rate of acceleration would, IMO be more profoundly impacted.
Agreed

[Damn True]

I actually have very accurate models of some Intro wheels that I can modify the diameter and width as I choose, as well as some accurate BFG tire models that can be modified as well. If I can find some time, I'll calculate the HP required to spin to, say, 60MPH and compare that to a smaller diameter rim.

I have a couple of interesting models as well. Shoot me a PM with your email addy.

[sik68]

I actually have very accurate models of some Intro wheels that I can modify the diameter and width as I choose, as well as some accurate BFG tire models that can be modified as well. If I can find some time, I'll calculate the HP required to spin to, say, 60MPH and compare that to a smaller diameter rim.

Looking forward to seeing this!

[79-TA]

I actually have very accurate models of some Intro wheels that I can modify the diameter and width as I choose, as well as some accurate BFG tire models that can be modified as well. If I can find some time, I'll calculate the HP required to spin to, say, 60MPH and compare that to a smaller diameter rim.

Shouldn't that be in terms of energy, not power? Sorry to be nitpicky. If you're doing sort of an acceleration test, the power required would not be constant and it would be dependent upon how quickly you accelerate. Of course, you could just pick a random amount of time to divide the total energy (at 60 mph) by to find an average horsepower.

That sounds really interesting though, best of luck.

[parsonsj]

Just pick a nominal 0-60 time. Say: 6s. That should normalize the data.

jp

[sik68]

My "guess"

linear 0-60mph 4 sec, rotation + translation

17" wheel+tire: 4.6hp
18" wheel+tire: 4.9hp

Negligible.

[parsonsj]

Negligible.

Ah. You've been perusing the Mazda Racing spreadsheet. :)

I'm hoping to see model data for 19, 20, and 22 inch wheels too. Is that a possibility?

jp

[sik68]

Ah. You've been perusing the Mazda Racing spreadsheet. :)

jp


Haha, nope. It's what my nerd-self came up with back on pg 2

https://static1.pt-content.com/images/pt/2009/01/b-1.jpg

[parsonsj]

Oh, ok. The MR spreadsheet has similar values, though it translates it to mass/weight. About 60 lbs or so.

[zman1969]

maybe try filling them with Helium? :spank2:
giggle

[Steve1968LS2]

I have no doubt that a 17" wheel offers more performance than an 18" wheel..

However, I also feel most, if not all, of that gain is lost since 17" tires generally have taller sidewalls.

Of course there are lots of variables since tires and wheels both vary quite a bit in weight even if they are technically the same size.

[BonzoHansen]

I have no doubt that a 17" wheel offers more performance than an 18" wheel..

However, I also feel most, if not all, of that gain is lost since 17" tires generally have taller sidewalls.

Of course there are lots of variables since tires and wheels both vary quite a bit in weight even if they are technically the same size.

Too short a sidewall can be problematic...on the street they increase susceptibility to sidewall & rim damage, and (at least in my limited experience) short sidewall tires seem less forgiving at the edge, giving the driver less feedback. I'm not sure I am articulating my thoughts correctly.

[Steve1968LS2]

Too short a sidewall can be problematic...on the street they increase susceptibility to sidewall & rim damage, and (at least in my limited experience) short sidewall tires seem less forgiving at the edge, giving the driver less feedback. I'm not sure I am articulating my thoughts correctly.

All of that is very true..


I was just speaking in terms of weight.. if weight further out from the hub is bad then more attention needs to be give to tires since, in my case, they weigh more than my wheels.

[parsonsj]

This Mazda Racing spreadsheet I'm referring to takes the tires into account. I think the effect of wheel size from one size to the next isn't that bad. It's when you go up 2, 3, or 4 inches that the effects really start to show up.

jp

[Twentyover]

Think Vizard did something like this with flywheels on a sbf a number of years back, think it was in PHR. IIRC, the with a 10 lb flywheel (vs stock, I don't remember weight), it would take 50 hp less to accelerate the lightweight flywheel at the same rate as the stock flywheel in 1st gear, like 30 hp in second, 15 in 3rd, and 5 or 6 in direct.

[sik68]

Think Vizard did something like this with flywheels on a sbf a number of years back, think it was in PHR. IIRC, the with a 10 lb flywheel (vs stock, I don't remember weight), it would take 50 hp less to accelerate the lightweight flywheel at the same rate as the stock flywheel in 1st gear, like 30 hp in second, 15 in 3rd, and 5 or 6 in direct.

Here's a great Vette magazine article with the flywheel comparison.
http://www.vetteweb.com/tech/0407vet_lightweight_flywheel_install_information/index.html

Like you're saying, in the low gears, a lightweight flywheel is a tremendous power "adder." And the effects can be seen even at relatively moderate engine accelerations, like a dyno pull.

[Vegas69]

I just weighed my wheels and tires tonight.

345/30/19 on a 19x12 3 piece ZE Boost Wheel 67.8 lbs Tire 34 lbs
255/40/18 on a 18x8.5 " 50.2 lbs Tire 25 lbs

[71OLDS]

If all this is true, why aren't we all running the stock 14" rims and tires? why stop at 17? I know we want the big brakes but if 17 will out perform 18 in the 1/4 mile and 60-0, why stop at 17? why not 15 or even 14. Also why would they make new production cars with 18/19/20s?

[1969CamaroRS]

If all this is true, why aren't we all running the stock 14" rims and tires? why stop at 17? I know we want the big brakes but if 17 will out perform 18 in the 1/4 mile and 60-0, why stop at 17? why not 15 or even 14. Also why would they make new production cars with 18/19/20s?

I think it is a trade off between braking performance, weight/speed and looks. Small disc or drum brakes just don't stop a car fast enough and so the upgrade cycle starts. I think the sweet spot is around 17/18 sized wheels with like 13/14" rotors.

As far as new cars with 18/19/20 partly a look thing and clearance for the very large brakes.

[Vegas69]

It's mainly looks ,but brakes do come into play on sports cars.

[silver69camaro]

Did anybody get the latest issue of Car and Driver? Had a very interesting comparison of various wheel diameters vs performance. I'll bring it in tomorrow.

Basically, the larger wheel size made a pretty dramatic hit on fuel economy and 0-60 time, but improved ultimate grip (up to a point).

[John Wright]

so..... what if you lower the tire from 38# to 33#....do you save 5#?....LOL...(j/k)

[gold79ta]

So you are saying if I have 15's and my cars is a dawg if I put on 17's it will move like a turtle?

[BonzoHansen]

New Super Chevy has an article on a new Camaro SS they have been modifying. This month they dropped the wheels and brake size. They wanted 17s on it to use tires with more sidewall. As with most mods, there is more than 1 change happening so it is not exact apple for apples. Here is a summary.

Front:
Removed
OE cast front wheels: 20x8, 245/45/20 PZero - 64 lbs each!
OE front 14" brakes
Added
4th gen front brakes
New 17x4 Bogarts with 4.5/26-17 tires:
front wt savings - 100 lbs

Rear
Removed:
OE cast rear wheels: 20x9, 275/40/20 PZero - 68 lbs each!
OE SS 2010 SS rear brakes
Added:
2010 V6 rear brakes
17x9 SLP 4th gen 5-spokes and 274-40-17 hoosier d/rs - 34 lbs each
rear wt savings - 82 lbs

Total wt savings - 182 lbs - all unsprung

Running at atco they dropped:
60' time by .06 (1.86-1.8)
1/4 ET by .19 (11.81-11.62)
MPH up by 2.06 (199.27-121.33)
(last test used nitto 274/40/20 d/rs, so the trap gain was not all tire)

Those OE sizes are ridiculous. But I digress.

It appears no one makes 'skinny' 18s to clear the OE 14" rotors, thus the reason they de-braked on this boat. De-braking is not for me! Especially in a 4000 pound car driven on the street.

[mc84_zz4]

I would have rather invested in some low-weight wheels instead of de-braking the car.
They spent a small fortune undoing the most common upgrade....:hmm:
Nitto makes drag radials in 18" which 'should' clear the rear brakes, if they wanted more sidewall,
but that is not the same as Hoosiers, I know.......

[T/Aaron]

Larger wheels(17,18,etc) are not for decreasing the weight of the wheels.
1. Larger wheels give the ability to run low profile tires for decreased tire deformation during cornering while keeping the tire diameter the same.
2. Larger wheels are used to give you the ability to run larger rotors.
3. You don't want to run low profile tires for drag racing. You need the high profile tires to flex during dragstrip runs.
If you want to lose weight, you run lightweight racing rims.

[Procharmo]

Wheel size is only half the story. Tyres play a bigger part....
Trackday Toyo R888 17/315/35, Street MT/ DR 17/315/35 and Strip MT/ DR 15/315/60. That's my wish list, if I knew weather 10 x 15's could fit over my rear Baer discs!!

[BonzoHansen]

I would have rather invested in some low-weight wheels instead of de-braking the car.
They spent a small fortune undoing the most common upgrade....:hmm:
Nitto makes drag radials in 18" which 'should' clear the rear brakes, if they wanted more sidewall,
but that is not the same as Hoosiers, I know.......

no front 'skinnies' clear those brakes, it seems.

[TnBlkC230WZ]

You know what... I was thinking it would be a great story the other night to run 17,18,19etc back to back with the same tire width on the drag strip or road course and see how much difference it makes. What do you think Steve?

This was actually done by one of the car mags (Motor Trend or Road and Track) using 16, 17 and 18 inch tires that were the same width and diameter. I believe they were The 16s where clearly the fastest tire, but they gave up some in the handling department. The 17s were slower, but were significantly better handling tire. The 18's were slower still and only slightly better than the 17s in handling.