Smart Car of America Forum banner

621 - 640 of 675 Posts

·
Registered
Joined
·
847 Posts
Welcome to SCoA! There is a reason the rear tires are wider than the front tires. smart engineers have done everything they can to make sure the car doesn't oversteer so my advice is to leave well enough alone. :)
All 4 tires the same a mistake?
Seeing as how I just bought 2 rear 5.5 rims & tires to replace the front, so that all four tires are the same.

Was that a mistake?
 

·
Premium Member
MY08 cabrio MY09 cabrio Brabus MY15 ED
Joined
·
7,701 Posts
Seeing as how I just bought 2 rear 5.5 rims & tires to replace the front, so that all four tires are the same.

Was that a mistake?
No, not at all!

Running 4-square (4 rears on all corners) is a very popular modification.

4 fronts on all corners, an accident looking for a place to happen...
 

·
Registered
Joined
·
847 Posts
No, not at all!

Running 4-square (4 rears on all corners) is a very popular modification.

4 fronts on all corners, an accident looking for a place to happen...
Why? I really don't understand why it would be so dangerous?

Just because it is a popular modification doesn't Make it Safe.
 

·
Registered
Joined
·
922 Posts
I am seriously considering running four front wheels, as rear wheels are hard to find or very expensive from the dealer. I'd intend to go 165/65-15 at all four corners, or possibly use that same size at all four corners using the existing rear wheels.

The Smart has a slight rearward weight bias, but the rear suspension is fixed at significantly more negative camber than the front. This will make the grip at the rear end greater than the front, which will balance out the slight rearward weight bias.

Also, the standard ED shocks and spring rates would likely be overwhelmed by the grip available from a 185 or 195 width tire, so a 165 width tire will allow it to approach and exceed the limits of grip in a much more controlled fashion because the suspension will not be overstressed by the wheel forces created by the smaller tires. Once you have more tire than suspension, things get ugly at the limit.

The more familiar I am with this suspension, the more I think this is the way to go. I've changed the front toe now to 1/32 in at each front corner, which should give me dynamic zero or a slight dynamic toe out at speed. This has significantly helped it to turn in better with neutral throttle, and it is much better behaved under braking.


Sent from my iPad using Tapatalk
 

·
Premium Member
MY08 cabrio MY09 cabrio Brabus MY15 ED
Joined
·
7,701 Posts
I have run 145/65R15 winter tires all around since 2008, I'm still here to tell the tale.
Lefors was ISO "fuel economy."

Totally different dynamics if your "purpose" is to plow through the tundra of winter.
 

·
Registered
Joined
·
847 Posts
I am seriously considering running four front wheels, as rear wheels are hard to find or very expensive from the dealer. I'd intend to go 165/65-15 at all four corners, or possibly use that same size at all four corners using the existing rear wheels.

The Smart has a slight rearward weight bias, but the rear suspension is fixed at significantly more negative camber than the front. This will make the grip at the rear end greater than the front, which will balance out the slight rearward weight bias.

Also, the standard ED shocks and spring rates would likely be overwhelmed by the grip available from a 185 or 195 width tire, so a 165 width tire will allow it to approach and exceed the limits of grip in a much more controlled fashion because the suspension will not be overstressed by the wheel forces created by the smaller tires. Once you have more tire than suspension, things get ugly at the limit.

The more familiar I am with this suspension, the more I think this is the way to go. I've changed the front toe now to 1/32 in at each front corner, which should give me dynamic zero or a slight dynamic toe out at speed. This has significantly helped it to turn in better with neutral throttle, and it is much better behaved under braking.


Sent from my iPad using Tapatalk
OH NO Don't do it....you'll be driving an 'Accident looking for a place to happen.':D:D
 

·
Registered
Joined
·
847 Posts
Why the smart has narrower front rims and tires. Per Evolution.co.uk

As for me I don't give a rats behind about MPG, that was post #615 by skye3001. That I gave my opinion on.
The hell with design and physics. I haven't done a J-turn or bootleg turn in 40 years. I'm going to run 4 rear size wheels and tires. Sounds as if it is more dangerous than 4 skinny tires all the way around.
Will I die if I put two front wheels on the rear for the better fuel economy?
https://www.evilution.co.uk/wheels/wider_front_wheels.htm

The front wheels on the fortwo are narrow, so subsequently the tyres are also narrow. This was a design bodge to allow the car to pass the elk test (sometimes called the moose test). This is a driving field test that is a measure of stability when you throw the car into a quick left then right swerve as if you were avoiding something (like a moose, child or car reversing into the road). To pass, the car has to be doing 42mph or more and not flip over.

Elk Test Failure

This test had been undertaken since the 1970's and unfortunately for Mercedes (who ran smart at the time), the first car to fail the elk test was the 1997 Mercedes A Class which just fell over instead of swerve.

Mercedes immediate reaction was to panic and give the A Class narrow front wheels and tyres to increase understeer because the original tyres were gripping so much that the centre of gravity was being pushed outside
the envelope of the car. Being a tall and narrow car, it fell over.

As the smart city car (renamed to fortwo in 2004) was just a small version of the A Class, Mercedes had to do the same with the thin wheels and tyres. They also adjusted the front suspension setup which is why the 450 was rolled out with different front and rear wheel offsets. There was no time to fix it properly.

J Turn

This isn't a proper regulated test, it's just something you see in movies and car shows.
However, as with the elk test, having a tall car with wide front wheels is bad news.

You drive backwards as fast as the car will go, turn the wheel 180 degrees (356 fahrenheit) and the front
of the car spins around to face the other way. As is spins you put the car into 1st gear and straighten the
steering as the slide brings the front of the car around to the direction you want to face. Or in the case of
the fortwo, the front wheel grips and the car flips over on its side.

Conclusion

So, putting wide front wheels on your fortwo improves the way it handles by giving the front more grip.
Just remember that there is a limit to front wheel grip usefulness. If you swerve heavily at high speed in a
fortwo the car may fall over (instead of skidding uncontrollably in any way it wishes).

Don't swerve uncontrollably, slam your foot on the brake and let the ESP (or Trust) and
ABS do their thing before swerving around anything. As for the J turn, just don't do it.

Wider Tyres, The Easy Way

The obvious route to take for all of the smart range is to just fit wider tyres.
Depending on the width of the alloy, you have a range of tyre widths you can choose.
It is important not to exceed the minimum or maximum widths.

Check your existing wheel width and see how wide you can go.

Ideally, as the tyres become wider, the number depicting the profile (height) of the tyre should decrease.
The number on the tyre will be WWW/PP/DD where W is the tyre width, P is the tyre profile and D is the alloy
size in inches. For example 145/65/15. 145mm wide, 65% of the width is height, on a 15" alloys wheel.

In this instance, the alloy is 4" wide so using the table you can go up to 165mm wide.
The general rule is reduce the profile number by 5 every time the width increases by 10.
So, in this example you could consider 165/55/15 tyres.
 

·
Registered
Joined
·
1,938 Posts
Have never seen an elk in South Carolina..... perhaps I should have my eyes checked. Never saw any in Ohio either..... all I can say is putting rears on the front takes the car from being an understeering PIG and makes it enjoyable to drive. But what do I know.....
 

·
Registered
Joined
·
847 Posts
It is Official as of 1pm 07-15-17 I am now a member of the "I can Rotate My Tires Club"
Put the New ones on the rear and the rear on the front.
Same Brand tire, model and size all the way around.

MY cost to join the club. $359.00 Yours may differ.

Rims.. 2 2010 passion 9 spoke 5.5 ........$125
Tires..2 Kumho 175/55-15 ...................$170
TPMS.2 Mercedes Benz 433MHz.............$32
Installation and Balancing ....................$22
Tip ..................................................$10
Total..........................................................$359
 

Attachments

·
Registered
Joined
·
180 Posts
Just got these mounted up today. Alutec Grip 3 from Tire rack. (4) 15x6" with Hankook H737 185/60/15. Ride is definitely smoother so far, but they've only been on less than 2 hours. No rubbing when turning, even at full lock but will rub over larger bumps slightly. I don't think it is going to be an issue. Plus, as time goes on an the tires get worn a bit there'll be that much more room to play with in the fenderwell.

I needed these for my back as the ride is pretty harsh on these with the OEM rubber even set at the recommended tire pressures. I got these set at 34F and 36R now. Feeling good so far.
 

Attachments

621 - 640 of 675 Posts
Top