i'm not 100% sure if the stability program takes rotation into consideration, if it just monitors "rotation" period, i'd make them all the same size (then you can carry a spare, if you like), i'd go with 195/50-16's, the 50 profile will give you protection against curbs and potholes and you'll have almost 16" of rubber on the road (tire contact width) with a 61" wide car.
i put 195/50-15's on a geo metro, that was about the same weight of a smart and it stuck like glue to the road, and made no tire noise in the harshest cornering, the original tires would scream in turns over 15-20mph.
the fronts are skinny to "knife" through snow, the rears are fatter for traction (rear drive) they are all small for lighter weight and provide incredible coasting ability (low rolling resistance) if i see that i might have to stop or slow down in 1/8-1/4 mile, i nudge the shifter forward to N, this car coasts like no tomorrow! beats the snot out of my old geo metro. i put fat tires all around on my metro and only suffered from slight tire noise (bad tire choice, for a few $$$ more i could have had quiet tires!)
We did a lot of research and talked to a lot of people at smart about tires as this was an issue for us while driving in the Cannonball race. So I have some answers for you.
First off, while you don't need to stagger the front and rears, you will want to as the rears can be bigger then the fronts. The reason they come staggered is 100% for fuel economy, they get better MPG with smaller tires and they don't expect people to drive the smart like a race car so they went with the smallest tires they could, the rears are 175 as to keep traction, weight and a little bit of style.
This is because putting to big of a front tire puts oversteer, putting to small of a tire creates understeer. The best sized tire on the front is a 175 width, the height should always be matched to original height to ensure clearance. Also getting into anything more then 175 on the front and you can run into major issues with the tire being to big for the fenders. With our BRABUS suspension the 175 tire is in the fender at all times and some of the 185 tires are wide enough to rub even without load into a corner.
On the rear, this is where you have a little more room to play. With the power that the smart has from the factory and with 175 up front the recommended tire width out back is 195. This will give a nice contact patch on the rear and will fit within the stock fender area, while you can go up to a 205 without too much issue other then a little more tire outside of the fender, this extra tire is just for show and won't give any better performance, in fact it might give to much stick to the rear and produce more understeer.
To summarize, the best option is 175 on the fronts and 195 on the rear, height is determined by the size of rims, but you want to make sure you match as close as possible to the factory sizing.
I have 175 front and 195 at the back, and i'm very happy with it, but the brabus smart has 175/50 R 16 tyres at the front and 225/35 R 17 tyres at the rear. That is not a nice combination, the front tyres are really to small, the difference is to big, and it doesn't look nice. But i think smart doesn't want wider tires, cause they prefer understeer.
Many thanks. Advice to me from the importers of Schmidt wheels is that the best combo for is 195/40x16s all around. Also, since tire pressure monitor sets cost $350.00 USD, can you remove them from the factory 15"s and install them on new rims? And can you just not install monitors at all? Without them, do yoju screw up your compuer settings? Inquiring minds want to know.
You can remove the monitors without issue on other things with the car, just have the warning light on all the time, but they can be switched to other rims, as long as they fit in the wheel, which they should.
We bought aftermarket wheels and put the tire pressure sensor in.
As for your idea on 195 all around, you might/probably will find issues with the front, the front with 175 already just fit into the fender, while going to a 185 is possible with the right tire a 195 will require a very narrow 195 to ensure no rubbing/exploding tire while cornering happens.
i noticed a small sheet metal screw in my right front tire, it was about 1/4" long (threads) i unscrewed it and drove the 15 miles home, i poured some liquid on the hole and it didn't bubble, but i guess i imagined a tiny leak with the tip of my finger.
after parking for an hour i checked the tire pressure all around (4 months of driving and 3200 miles) and the fronts were 31.5 & 32.5 and the rears were 37.5 each, maybe that helps with the coasting, i think i'll up the fronts to 34 psi and the rears up to 40 psi. should get a little extra mpg!
I FOUND THE ANSWER ALL BY MYSELF WITH HELP FROM FOG CITY PERFORMANCE IN SAN FRANCISCO. HERE IT IS: 16X6.5" FRONT WITH 195/45X16 YOKOHAMAS, 16X7" REAR WITH 215/40X16 YOKAHOMAS. THESE ARE SCHMIDT WHEELS FROM GERMANY. WOW!!! WHAT A DIFFERENCE!!!
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