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Old 05-25-2001, 11:28 PM   #1
driver
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Question Will upgrading to heavier wheels make the car feel slower?

Hi. I'm considering getting a 2002 2.5 RS and was also thinking about the possibility of putting on Prodrive P7 17" wheels. From what I've read on the boards..I believe the stock 16" wheel is 16 pounds and the 17" Prodrive P7's are 21 pounds. So, I was wondering if this will make the car feel slower or not?

Another possibility I was considering was the OEM 17" UK wheels. Those are 19 lbs. Not as heavy as the Prodrives....but still heavier than the stock wheels.

What do you think?
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Old 05-25-2001, 11:54 PM   #2
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Well, it depends on how well ya know the car whether or not it will make it feel slower. Heavier, and larger diameter wheels, will MAKE it slower.
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Old 05-26-2001, 01:28 AM   #3
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Like Rev said - heavier, larger diameter wheels will make your car slower (in a straight line). The larger wheels, with shorter sidewalls on the tires, will make the car faster through corners.
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Old 05-26-2001, 07:37 AM   #4
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...unless it's a bumpy corner, because the suspension can't deal with the added weight as well.
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Old 05-26-2001, 08:07 AM   #5
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What does the diameter have to do with it? I can obviously see why a heavier wheel would have an effect but how so the diameter?
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Old 05-26-2001, 09:09 AM   #6
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Heavier wheels WILL make your car accelerate more slowly. Wether you notice it or not depends on your sensitivity. It was noticeable for me when I did it to my mustang years ago.

There are two reasons people go with larger (Vertically) wheels.

1. The look
2. By then using a tire with a short sidewall, you have a 'stiffer' tire that may be more responsive.

So when you go to a 17inch wheel, you have a tire with a thinner sideall. The total Wheel+Tire height shouldnt change much.

When you turn the steering wheel, less time and energy is spent bending the sidewall of the tire. So you start changing direction quicker.

Now, wether this small difference will reall matter or be noticeable depends on a lot of factors, including the particular tires in question ,and the driver.

It is *not* a profound difference, in the way that better tires are.

Also keep in mind that heavier wheels means MORE unsprung weight. The more unsprung weight you have, the more bumps will upset your car. You could offset this by adding weight to your car inside, but that kinda sucks.

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Old 05-26-2001, 09:29 AM   #7
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I have driven an RS with 15 inch wheels and an RS with the stock 16 inch wheels. The 16 inch wheels felt slower to me. However it was a bit more precise in the corners. I prefer smaller wheels, to a point. 15s or 16s on the impreza is what I prefer.

I agree with the points everybody here has made.
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Old 05-26-2001, 10:05 AM   #8
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What does the diameter have to do with it? I can obviously see why a heavier wheel would have an effect but how so the diameter?
The farther the weight is from the center of a rotating mass, the more force that is required to make it turn.

Take a pole. Clamp two weights to the ends of it. Grab it by the middle and twist it. Now take the pole and clamp the same two weights halfway between the middle and each end of the pole. See how much easier it is to turn it?

For the same reason, a larger diameter wheel that weighs the same will take more force to turn.
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Old 05-26-2001, 11:27 AM   #9
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yes it will make it feel slower and turn weird i put chrome on mine big diffrence but then u adjust to it !! http://www.pitt.edu/~kappasig/.temp/...ckdooropen.jpg
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Old 05-26-2001, 11:57 AM   #10
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Another thing about the large wheels, isnt just the larger rotating mass. That plays a large part, but another part is the leverage of the wheel to the car. The larger the diameter of the wheel, the more torque it will take to move the mass of the car. Because you are using a longer lever. Sounds difficult to understand. But it makes sence.

Also another problem, it takes the same extra exerted amount of energy to slow doen that mass as it does to start it. Becuase of the larger diameter wheels, yout brakes will REALLY suffer. With the larger diameter wheels, the amount of mass pressing against the brakes will increase. Which will mean longer stopping distances, and higher brake fade.

I really dont recemend anyone go above the recemended wheel diameter for the car. IF you want to inch up the wheel, and remove and ince of sidewall, and keep the roatating diapeter the same, thats great, it will im prove the stability of tha car. However, going overboard with wheel diameter size will only cause problems. Especially if you plan on driving "spirited".

For my integra project i had, i found that the best wheels for it where the stock forged aluminum wheels that came stock with it. They where relativly light, had brake cooling ducts built into them. And where very rugged. And they didnt look like ass.

Improving your tires will help alot more then increasing your wheel diameter.
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Old 05-26-2001, 06:03 PM   #11
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let me just add some of my observation. This afternoon i attended a lengthy Auto-x school were we practice different manuvers repeatedly. One of which was an acceleration course. My buddy runs a 2000RS with 18" motorsports on 35 series tires, i run a bone stock 2001RS with stock size Kuhmos. After about 10 to 12 runs our times were darn near identical to each other in acceleration and in braking. Within a 1/2 second almost everytime. Timing was don with a stop watch so there was some user error. We also took first and second place overall with our times just over a second apart.
Although what everyone has said is true about the theory, the real world driving has shown me that there is very little effect on the cars performace due to the larger wheels. Unless you are trying to be extremely competative or are such a good driver that you notice the slightest change you do to your car, i wouldn't worry about going to the larger wheels. I don't think it'll hurt you either way.
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Old 05-26-2001, 06:22 PM   #12
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there are some very smart people in I-Club
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Old 05-26-2001, 08:45 PM   #13
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i kept mine to factory standers but had to get that bling bling
<IMG SRC="http://www.pitt.edu/~kappasig/.temp/gregbackdooropen.jpg" border=0>
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Old 05-26-2001, 08:59 PM   #14
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Quote:
The larger the diameter of the wheel, the more torque it will take to move the mass of the car. Because you are using a longer lever.
Right you are Buck-O. (I actually aggreed with you. wow) That's why it's important to keep the overall wheel-tire diameter the same after the switch. Even if the diameter stays the same, my previous example still applies, as more of the weight moves farther from the center of the wheel.

That said, I'm still putting 17's on my car.
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Old 05-26-2001, 09:31 PM   #15
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for every inch above 13 in a wheel diameter you slow your 1/4 mile time by 1 tenth of a second, that's why everone races with 13 inch bogarts and lensos, not to mention a three year old could pick them up even with a drag slick on them.
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Old 05-26-2001, 10:00 PM   #16
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I just went to 17" Team Dynamics Monzas with 215/40x17 S-02 and noticed no adverse effects on acceleration or handling - but I think the turbo and the Tein coil-overs help with that.

Larry
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Old 05-26-2001, 11:23 PM   #17
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You can just get some cool replacement 16' wheels, not have to buy tires at the same time, and you have an extra set to powdercoat or put R-comps or snow tires on.
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Old 05-27-2001, 12:38 AM   #18
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Sanguine, yeah, shoking isnt it. Kinda hard to beleive that i actually know what im talking about, eh?

Beleive it or not, i have quite an array of first hand experience in the tuning feild, from big V8's, to small four bangers.

But anyway, there was a discussion about this not to long ago (maybe a month?) about rotating mass, and the inirtia of the wheels.

I think part of the problem that would be experienced by most cars is SLIGHTLY reduced by the fact that the torque is being distrobuted to all four wheels. Therefor the combined torque bing applied to the road will help in initiating the movement of the car. Thats totally theoretical, i have nothing to back that up. But im willing to bet there is a definate, if not slight, advantage becuase fo the AWD.

Where as any normal FF car would have all the power to two wheels, and most of the cars weight, BEHIND the driving wheels. Becuase of the inertia of the car on acceleration making the rear end squat, with large diameter heavily loaded wheels, you get more wheel spin becuase they got from heavy loading, to lightened load as the car squats, and you get more load on the tranny and clutch as it struggles to deal with the jarring from the extra wheel spin, and it all adds up to a loss in performance.

For short sprints, i dont think the larger diamter wheels size will effect the brakes that much. Such as a short auto cross etc. But long term stop go city traffic, with alot of brake "riding" will certaintly do you in after a while.

For the msot part as long as the stock rotating diameter is maintained, you should be fine. Gearing will be proper, and performance should be better, with a smaller sidewall tire, providing a bit more lateral hold.

As with everything, there are two dozen factors involved with it, and there really is no perfoect setup.

Personally, bigger wheels made my integra feel sluggish, and it was no slouch. The best feel for the car came with the stock forged wheels. And a nice sticky set of Dunlops.
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Old 05-27-2001, 12:54 AM   #19
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The example of the pole with weights at the end isn't really valid, as in a car, the wheels are (or should be!) in contact with the ground at all times.

Imagine having a wheel and tyre combination connected to a driveshaft and hub, sitting on the ground. Measure the torque that is needed to accelerate the wheel at a certain rate (or imagine turning it by hand).

Now get a wheel and tyre combination with 1 inch larger wheels and tyres, but the same rolling circumference. Measure the torque required to accelerate the wheel at a cartain rate, or again imagine twisting the driveshaft by hand.

There will be a difference, but it will be very small. Now sit a 3,000 lb car on top of 4 wheels, with a very torquey engine, and you can imagine the difference in rotational inertia will be almost negligible.

If they made the cars slower, why would the WRC (and for example BTCC cars) run large 18 inch wheels and tyres for tarmac events I know they can fit bigger brakes under them). In events where thousands of a second counts, surely bigger wheels would be a major disadvantage ?


If you fit ones that are too big, then you have effectively fited taller gears to your car, and you will notice a drop off in performance.

I have run my car around numerous race tracks, and compared it to dozens of other Imprezas with different sizes and weights of wheels(I have no engine mods at all). In terms of straight line speed, there was absolutely no difference between any of them, and the biggest difference was down to driver skill in changing gears more quickly, or having better brakes and being able to brake a bit earlier. Having followed los of cars through the corners, I would say that cars running 17 inch wheels are visibly more settled when turning fast into a corner, much more so than those running 15 inch wheels.

Same thing goes with unsprung weight. We are all agreed that reducing unsprung weight is a good idea, but I doubt very much that most people could even notice the effects of wheels and tyres a few pounds heavier. I have tried 5 different wheel and tyre combinations on my Imprezas over the past 4 1/2 years, with some being "lightweight" 15 inch rims, and some being the "far too heavy" Prodrive PD7 alloys. I can't say I've noticed much if any difference in handling, and steering. Sure the 15 inch tyres gave a softer ride, but turn-in and steering response was woolier, but that's to be expected. I have run the Prodrive OZ P1 wheel on my car, back to back with the Prodrive PD7 wheel. Same type of tyres (Toyo T1S), same tyre pressures. Drove them over the same (smooth and rough roads), and I can honestly say, that I could not tell the difference. Thinking about it, by the time you add up the weight of all the suspension and steering components, plus the wheels and tyres, a few lbs is only going to make a single percentage difference. Yes it will be noticable, but not a night and day difference. You could get more of an effect on handling by adjusting the tyre pressures by a few psi!

Also, there can also be a few percent difference in rolling resistance of tyres, and you have to be careful of comparing brand new larger wheels and tyres, with well worn smaller ones. Remember that some tyres are marketed with fuel savings in mind, and offer up to 5% fuel savings, achieved through improvements in rolling resistance. However, these "economy" tyres tend to be of the lower grip type, and would rarely be fitted to a performance car.

I certainly would be prepared to pay twice as much for wheels which were a few lb lighter, as in real terms the differences on the road and track.

I am currently running with the Prodrive PD7 wheel, as I think it looks great, and its a good strong wheel for a reasonable cost. When I was running the more expensive P1 wheels, I was paranoid about hitting pot-holes, kerbs etc, for fear of damaging them (50% more expensive to replace!)

I would recommend that people fit the wheels and tyres that fit their budget, and they like the look of. Unless you are going to be competing regularly in competitions where 1/100th of a second makes all the difference (ie not any sort of driving on public roads), you won't notice any performance hit, as long as you keep the rolling circumference the same. So go ahead and fit those "slighty heavier" wheels, and spend the few hundred dollars you have saved on other useful mods for your car, or simply spend it on fuel and enjoy your car a bit more
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Old 05-27-2001, 01:24 AM   #20
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Quote:
The example of the pole with weights at the end isn't really valid, as in a car, the wheels are (or should be!) in contact with the ground at all times
The example is perfectly valid. In the example the pole never touches the ground at any time, it should be turning horizontally.

A wheel on a car is nothing but a series of levers. Each spoke acts as a lever, with the center of the wheel as the fulcrum.

Take two levers, both exactly the same weight and length. One has a weight near the fulcrum, the other has a weight near the end. The one with the weight near the end will require more force to move.

Quote:
If they made the cars slower, why would the WRC (and for example BTCC cars) run large 18 inch wheels and tyres for tarmac events I know they can fit bigger brakes under them). In events where thousands of a second counts, surely bigger wheels would be a major disadvantage ?
Using a larger wheel with a narrower tire improves lateral performance. If you can exit a corner faster, you can more than overcome the small loss of acceleration caused by the larger wheel. There is a balance to be found, as you need enough sidewall to absorb imperfections in the road while maitaining an optimal contact patch.

Read this article - http://www.gr8ride.com/cgi-bin/pm/co...oss&oid=104682
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Old 05-27-2001, 07:49 AM   #21
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Bear with me here.

It's my guess that most BTCC and WRC cars have enough power to smoke their tires in two or three gears if not driven carefully. On that assumption, the biggest tarmac factors are cornering (thin sidewalls) and braking (big brakes). Acceleration takes care of itself with adequate contact patch and a judicious right foot. Therefore, the positives of more precise cornering and more powerful/durable braking outweigh the negatives of heavier unsprung weight and rotating mass.

As I've posited before: Look at the SCCA Showroom Stock racers - rarely do they go over 15" wheels. Same goes for the lower classes of Solo II. Those cars have less power and generate lower top speeds. My guess is they are more affected by unsprung weight and rotating mass and less affected by braking needs.

WRC and BTCC just seem to be more violent sports - even on tarmac.

So, if you are driving a 350+hp car, cornering and braking at 10/10th's, you might consider 18's. And a good lawyer.

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Old 05-27-2001, 09:28 AM   #22
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JohnS, you got it down man!

Finally someone I can agree with

Obviously an engineer!

I'm considering the Prodrives as well - either the 17" PD7s or 17" P1s. While they may be more expensive to replace by only some 15 - 20%, the P1s look more resistant to bending.

Count the number of bracing points along the PD7 (7 ) compared with the 20 or so along the P1s distributed over much shorter intervals. Surprise, less distributed load! Less bending moment between each webbing! Less likely to fail in bending!

Of course assuming the same Ey values for both wheels - probably not true. Anyway, if you've got the money, you drive a lot of ****ty roads, and you like the P1's styling, it might be a better value to buy the P1s.

Dave.

[This message has been edited by Dave99 (edited May 27, 2001).]

[This message has been edited by Dave99 (edited May 27, 2001).]
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Old 05-27-2001, 02:34 PM   #23
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Hey, that article from GR8RIDE posted by Sanguine is really good!

It goes through a blind experiment using different rim diameters and balasting loads under reasonably controlled conditions - well worth the read!

Dave.

BTW Ey = Young's modulus of elasticity

I meant that if you hit a pothole, the 10 spoke rim (not 20 - whoops) is supported at more points than a 7 spoke rim so it'll be stronger in bending around the outer rim circumference.

[This message has been edited by Dave99 (edited May 27, 2001).]
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Old 05-27-2001, 04:13 PM   #24
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the reasons most race cars use big wheels is very simple.

to fit around big brakes.

Ive read some books on suspension design and it suggested the idea of bringing breaks inboard so you could use really small wheels.

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Old 05-27-2001, 05:45 PM   #25
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I agree with all of you guys. Though...in this particular case (WRX), due to the advantage we have over many cars from the line...17 or 18 wheels will make the car reach high speeds faster once the car is relatively fast. Thus helping in the "rolling" start department, besides curves, etc.
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