Weight of Stock and Aftermarket Wheels

[fmaxwell]

Increasing the unsprung rotational mass (tire, wheel, disk/drum, etc.) is one of the most detrimental things that can be done to a car's handling. I certainly don't claim to be the first to point this out:

Kahn RS-R Alloy Wheels - Made for Smart

Has 18" wheels ever been put on a smart..ever?

There could be other issues, too:

Voided Warranty

The Miata guys get it and there are plenty of resources listing the weights of various wheels for the Miatas (for example, see: Table of Wheel Weights).

The book "Mazda Miata Performance Handbook" by Norman Garrett points out that one popular 15" aftermarket alloy wheel shod with a 205/50 tire weighs 48lbs compared to the stock 14" factory wheel/tire weight of 27lbs -- an 82" increase that will have horrible effects on handling. And don't forget that it also affects braking and acceleration as the brakes and drivetrain fight the higher rotational mass.

The stock Passion/Cabrio wheels and tires:

Front Wheel: 10.5 pounds
Front Tire: 14.0 pounds
Combined: 24.5 pounds

Rear Wheel: 14.5 pounds
Rear Tire: 17.0 pounds
Combined 31.5 pounds

Does anyone have figures for the various aftermarket wheels and tires being used on the smart fortwo (Schmidt, Team Dynamics, Pulse, Rial, etc.)?

[pghjake]

Do you have the weight for the stock steelies?

[fmaxwell]

Originally Posted by pghjake

Do you have the weight for the stock steelies?

No, unfortunately, I don't. Extrapolating from Miatas, I would expect them to be about 50% heavier (5-6 lbs. per wheel).

Early Miata alloy wheels weighed 12.3 lbs. and the steel wheels (of the same 14x5.5" size) weighed 18 lbs. Most people who bought steel-wheeled Miatas replaced the steel wheels with lighter weight alloy wheels.

As I tend to drone on and annoy people, I didn't initially go into the issue of vehicle weight to wheel mass, but the lighter the vehicle, the more sensitive it is to changes in wheel mass.

[donnyonee]

ive also heard of where the "heavier" is located in relation to the center of the circle has a lot to do with this issue. do you concur or am i mistaken?

[VinceLA]

good job, fm. This should definitely be a sticky. I started thread on stock/aftermarket exhaust weights a while back. The thing about upgradeing to aftermarket wheels is the weight penalty. I'd love to have Kosei K1 in 15s but they appear to weigh the same as stocks. Maybe lighter tires?

I hate the idea of adding extra weight to the smart and experience that lag off the straight line. I recently drove a smart with 16s and another with 17s. Very slow start. Our smart weight/power ratio is already quite pathetic at about 27. Pushing that towards 30 is definitely not sound.

UPDATE:

Sport Edition SM3
15x6 [14.5 lbs]
15x7 [15.0 lbs]
16x6.5 [16.3 lbs]
16x7.5 [17.6 lbs]

Rial LeMans
15x5 [13.0 lbs]
15x6 [14.0 lbs]

[fmaxwell]

Originally Posted by donnyonee

ive also heard of where the "heavier" is located in relation to the center of the circle has a lot to do with this issue. do you concur or am i mistaken?

The further the mass is from the center, the greater effect it has on acceleration and braking. It requires more power it change its rotational speed. Also, it's mass added to the car. If you put wheels and tires on that add 80 lbs. to the car, you are now trying to spin up/down an additional 80 lbs. of wheel/tire as well as pushing a vehicle that's 80 pounds heavier.

It also makes steering heavier and slower -- think about how a gyroscope resists when you try to rotate it around an axis perpendicular to its direction of rotation.

Don't let people tell you that wheel/tire weight doesn't matter on the street. Sport Compact Car magazine took a 2001 Sentra SE that the owner had fitted with 19" rims and measured a 0-60 mph time of 8.6 seconds. Then they mounted a set of 15-inch wheels with 195/60R-15 tires, dropping 13 pounds at each corner while changing overall tire diameter by only 0.3". The reduced weight and rotational inertia dropped the 0-60mph time by a full half of a second to 8.1 seconds.

There's a saying in the Miata community about wheels. Light, strong, cheap: You can have no more than two of those things when buying wheels.

[Fredvon4]

Light, Strong, Cheap.... pick any two

Light and Strong = not Cheap
Light and Cheap = not Strong
Cheap and Strong = not Light

Another factor with wider then stock tires on a very light car, like our 2000Lb with driver smart, is increased hydroplaning potential. Much of that can be mitigated by a rational width choice and tire tread design

I hope by buddy Fred is NOT suggesting the only proper fitments is factory weights and widths.

As I am sure he is aware the entire smart line is factory configured with a very wide range of wheel and tire choices.

His data is relevant and his cautions above are relevant.

Modifying suspension, wheels, and tires with good sound engineering principles in mind can make the car better.

But hanging heavy Chrome plated with spinner Bling Bling 18" rims with real heavy 245x35x18 tyres can have some real nasty side effects as well as be exceptionally costly

In the end though it all comes down to owner preference. I think many of the mods I have seen so far are real hidious... and some others were very cool and functional

About 6~7 years from now, when I retire for daily 8~5 work days. I would like to take one of my high mileage smarts (I will probably have 2 or 3 at any give time for the foreseeable future) and up the power to the 112~125 range, lower it, Aero it, wide tire it, fart pipe it, and go drifting with anew testosterone toy.... maybe even a shot or two of NoS just for tire shredding fun!

[fmaxwell]

Originally Posted by Fredvon4

Light, Strong, Cheap.... pick any two

Light and Strong = not Cheap
Light and Cheap = not Strong
Cheap and Strong = not Light

Sadly, some only get one or none, paying a lot for a wheel that's heavy, weak, or both.

Originally Posted by Fredvon4

Another factor with wider then stock tires on a very light car, like our 2000Lb with driver smart, is increased hydroplaning potential. Much of that can be mitigated by a rational width choice and tire tread design

VERY good point. Thanks for pointing that out.

Originally Posted by Fredvon4

I hope by buddy Fred is NOT suggesting the only proper fitments is factory weights and widths.

I'd be much more careful on the smart than on other cars.

1. In 1998, just prior to the product launch, Mercedes discovered that the smart city-coupe (predecessor to the fortwo) handling at the limit was not stable and that it could result in roll-over in high-speed cornering. To address this roll-over problem, Mercedes changed to asymmetrical rim and tire widths and stiffer suspension. The wrong changes could lead to a reintroduction of that instability. Remember, this was something discovered only after thousands of hours of testing. You might rediscover it late at night as you try to avoid a deer if you choose the wrong tires and rims.
2. The high Cg, short wheelbase, narrow track, rearward weight bias, and rear wheel drive make it inherently less stable than a conventional sedan. Therefore, it's more sensitive to changes than is a more typical car.
3. Because the smart fortwo is so light and has such limited horsepower, it is much more sensitive to changes in wheel weight. The kind of change that would go unnoticed in a Buick sedan might be really detrimental to a smart fortwo.

Bottom line for me: If I were hell-bent on changing the rims, I'd probably limit my choices to rims and tires that were no heavier or wider than the heaviest/widest factory choices. If Brabus offers a wider rim/tire, I'd also opt for any of their suspension changes that accompany the tire change (anti-sway bars, springs, shocks, etc.).

[Fredvon4]

Fred I know where you are coming from but your posts seem to me to be overly cautious and worriesome.... This car, as presented to North America is NOT inherently dangerous and unstable... You seem to argue that a wider track and heavier wheels tries will upset some stability of the car...

I see it 180 out from your view... I think Wider, even to the point of absurdity will only do one or both of two things:

Promote wet road hydroplaning due to the light weigh and over large contact patch....

Further increase the potential of under-steer or upset it enough to induce some oversteer...

In my opinion, not really a problem because the Nanny Electronic Stability Program (ESP) and Traction Control programs will work to counter either condition

That's it from a control and stability point of view...

What is left are Warranty impacts caused by potential to exceed the Front Hub bearings side load tolerances.

Additionally, as you stated above, the factory brake system will be under performing due to the more mass of the heavy wheel/tires and larger moment of mass due to larger diameter wheels....

This is simple to correct by more aggressive pads, multi piston calipers, and better designed rotors... I doubt any mods to the rear brakes other then better pads is necessary

They have some interesting coil over suspension components and a few better then stock shocks, springs, and sway bars....

I have been in Germany a LOT since the introduction of the smart car. I can tell you German TUV (annual safety inspections) are much more strict then anything we experience here in the USA. Also many of the mods I might recommend INCLUDING the 3 to 5 stud adapters are TUV approved....

Point is, I have seen some wickedly wild modified smart cars with serious HP and lots of cool suspension and drive train mods. They SAFELY compete at Autobahn speeds with many of their MB/Porsche/BMW brethren zooming past me at 160Kmph+ in my pedestrian rental Opal..... grin

[xcrew229x]

Just cause I'm curious Fredvon....... how many cars, over your driving lifetime, have you put wider tires/wheels on? I've lost count of mine.... Never had one short as this one, but never saw handling anything but improved on the RWD platforms, and greatly improved on the FWD ones, though sometimes at the expense of front tread life. Comment?