Steering Ratio Information

[MicroNut]

After some more digging, I found specific information relating to the steering ratio of the smart's manual and electric power steering systems.

The manual system has a ratio of 22:1 (meaning one degree of rotation at the front wheels requires 22 degrees rotation of the steering wheel). The EPS system has a ratio of 21:1. So technically it is quicker, but by a very small margin.

Here are the theoretical steering inputs (i.e. steering wheel rotation) required to execute a 30 ft radius turn in each case, with the MINI Cooper thrown in for comparison:

Car......................................Wheelbase .......Ratio.......Steering Input
smart with manual steering...........73.5 in..........22.0:1........254 degrees
smart with EPS...........................73.5 in..........21.0:1........242 degrees
MINI Cooper...............................97.1 in..........13.2:1........199 degrees

This is a crude comparison that does not account for speed, steering geometry or tire slip angles, but it gives a clue as to why the MINI feels more agile.

I think the real world difference between smarts with and without EPS on the same tires will be minimal. I also suspect that the improved agility noted by some jounalists for smarts fitted with EPS may have more to do with bigger tires and reduced slip angles than the steering system itself.

The article referencing the steering ratio information can be found here (it contains some other interesting technical info too): http://www.duemotori.com/news/auto_n...riving_fun.php

[lhoboy]

[QUOTE=MicroNut;2763]
Car......................................Wheelbase .......Ratio.......Steering Input
smart with manual steering...........73.5 in..........22.0:1........254 degrees
smart with EPS...........................73.5 in..........21.0:1........242 degrees
MINI Cooper...............................97.1 in..........13.2:1........199 degrees

QUOTE]


The Smart does feel like steering a truck compared with the MINI, and maybe that's why I wasn't too excited about the handling. Maybe an improved power steering unit with a radically reduced ratio would turn the Smart into what it really could be: a modern replacement for the classic Mini. The new MINI is too much of a pig to fit that bill.

[SmartAmerica]

[B][COLOR=black][FONT=Arial][B]Doesn

[lhoboy]

[QUOTE=SmartAmerica;2781][B][COLOR=black][FONT=Arial][B]Doesn

[Lewis]

I think the steering cannot be too quick on the Smart because of stablity control issues with such a short wheelbase and tall body. Safety is the reason I think the Smartcar will always be less agile than the squat Mini. The Mini I think of as a cut and thruster and the Smart more as a relaxed cruiser.

All the euro car reviews on the new models mention that the power steering really helps though so there must be something to it. Perhaps just being able to turn the wheel easier gives the feeling of more agility since the ratio will always have be quite ponderous for the stability control system not to be constantly cutting in?

Sure would be nice to have a showroom full of Smarts to test drive both back to back! Well I can dream. :-)

[lhoboy]

Originally Posted by Lewis

I think the steering cannot be too quick on the Smart because of stablity control issues with such a short wheelbase and tall body.

You're probably right on that. The handling on the Smart may not be stable enough to handle a quick ratio. Certainly a concern on wet pavement:Smart on the Skidpad

[nader]

Originally Posted by lhoboy

You're probably right on that. The handling on the Smart may not be stable enough to handle a quick ratio. Certainly a concern on wet pavement:Smart on the Skidpad

While that clip was pretty funny it is a little disturbing. First thing I do will be a set of high performance tires.

[jonnysan]

Originally Posted by nader

While that clip was pretty funny it is a little disturbing. First thing I do will be a set of high performance tires.

And a beefing up of the sway bars may help alittle bit, too. But the tires in a situation like that can make all the difference.

[Old smart]

Originally Posted by jonnysan

And a beefing up of the sway bars may help alittle bit, too. But the tires in a situation like that can make all the difference.

Different tires would likely help, but a little piece of motor racing practice is this: in wet weather suspensions are SOFTENED-UP, not stiffened-up. A stiff suspension transfers too much weight to the outside tires and the result is excessive oversteer.

BTW, a person at the road show I attended had a "Brabus-ized" G&W 450. He admitted that the fatter tires cost him 10%-15% of his gas mileage.

[Lewis]

I think that buyers of the Smart are not really performance oriented and what with the height and short length stability issues perfer to have the safety margin of slow steering. In fact the Euro journals describe the stability control system in the Smarts program as brutal to keep it stable. For the small group of performance oriented folks there's always Brabus mods.