Skinny Tyres=Good Grip?

[sasman]

Just read Car & Driver Drive data on The i3..I have read endless reviews of how skinny tyres don't give much grip..

The i3 went round a slalom course max speed 39.3 Mph Braking Distance 163 Feet

Ford Fiesta ST 41.3 mph Tyre 205/40R-17 Braking Distance 172 feet
Mini Cooper S 39.9 Mph Tyre 205/45-17 Braking Distance 191 feet
Fiat abarth 500 40.4 Mph Tyre 205/40Zr-17 Braking Distance 195 Feet

Wow!! who would have thought the I3 would post such impressive figures from such Skinny rubber...and Autocar reports that wet handling is very good as well..Brilliant!!

 

[DAZ]

I'm really impressed with the ride quality of my i3. I have the front and rear tire inflated to 40 psi, and still a smooth ride. Those skinny tires remind me of the song by Joe Tex, "Skinny Legs and All".

 

[WoodlandHills]

My car was delivered at 28psi all around, I changed it to the recommended 33/41 and it rode better! The bumps seemed to be transferred to the suspension in a smoother fashion as if the tire sidewall had more impact dampening ability at a higher pressure.

 

[jadnashuanh]

WHen you compare the actual tire contact patch between those cars listed and the i3, the i3 is about on par with the i3's longer and the other's wider - it's total contact patch that makes the grip, not how it is arranged on the ground. The larger diameter means a longer patch is in contact with the road than a smaller diameter, wider tire. A narrow tire is better for drag and wet or snowy weather, too, as the path to clear the water or dig down through the snow is more efficient.

People that complain about the narrow tires on the i3 don't really understand the depths BMW went to to try and make the vehicle efficient while retaining that fun to drive element.

 

[mrsmith]

We've had lots of rain recently and I can confirm the BMW's skinny
tyres are pulled off line a lot less than a regular wide tyred car.

 

[Goldcj7]

I can confirm that the i3 is awesome in heavy rain conditions, was caught in a very heavy downpour on the M4 yesterday and the tyres cut through approx. 4 inches of water with no problem, at 50mph! The car doesn't pull towards the kerb in puddles like most cars I've owned too
I do find the traction control a bit intrusive though, when accelerating hard it cuts in regularly on me, but maybe I'm a bit over enthusiastic! Maybe I'll upgrade to the wider rear tyre with time.

Just ordered some winter tyres, I feel the i3 will a useful tool in difficult conditions in the coming winter......

 

[noakey]

I can confirm that the i3 is awesome in heavy rain conditions, was caught in a very heavy downpour on the M4 yesterday and the tyres cut through approx. 4 inches of water with no problem, at 50mph! The car doesn't pull towards the kerb in puddles like most cars I've owned too
I do find the traction control a bit intrusive though, when accelerating hard it cuts in regularly on me, but maybe I'm a bit over enthusiastic! Maybe I'll upgrade to the wider rear tyre with time.

Just ordered some winter tyres, I feel the i3 will a useful tool in difficult conditions in the coming winter......

Hi.. Why do you think you will need the winter tyres in the uk? I had not considered buying any as our winter is quite tame with only the occasional snow flurry.

 

[nowtta60]

WHen you compare the actual tire contact patch between those cars listed and the i3, the i3 is about on par with the i3's longer and the other's wider - it's total contact patch that makes the grip, not how it is arranged on the ground. The larger diameter means a longer patch is in contact with the road than a smaller diameter, wider tire. A narrow tire is better for drag and wet or snowy weather, too, as the path to clear the water or dig down through the snow is more efficient.

People that complain about the narrow tires on the i3 don't really understand the depths BMW went to to try and make the vehicle efficient while retaining that fun to drive element.

Longer... there's an interesting thought.. not only is the longer patch physically longer, it will also be in contact with the ground longer as the rotational wheel speed will be lower than a smaller diameter wheel. Something not normally discussed when talking about grip, is how long each mm2 of the tyre actually stays in contact with the ground, rather than being spun up in the air and back down again.

You've then got factors like a larger diameter tyre will have a higher angular momentum so it's "throwing itself" at the tarmac a bit more.

Not sure what the effect would be if any? Still it shows that grip is not a singular dimensional parameter governed by tread width.

 

[PhilH]

You've then got factors like a larger diameter tyre will have a higher angular momentum so it's "throwing itself" at the tarmac a bit more.

Angular acceleration is mv2/r, so with a larger radius (r) acceleration will be lower.

 

[ecoangel]

It is how the orientation of the tyres contact patch that is all important here. The MINI etc will have better cornering potential than the i3 IN THE DRY because the low profile tyres provide angular grip whereas the i3 and all skinny tyres will be better in braking because the orientation of the contact patch is larger in the fore/aft sense.

As for winter tyres in the UK - highly recommended - my car came with to sets of magnesium wheels from Gerrmany - one with summer tyres (Bridgestone B381 145/80R14 eco tyres with aerodynamic sidewall improvements like Honda Insight Mk1) and a set of winter 145/80R14 Continentals.

Anything below 10 deg C the winter tyre wins in terms of braking, less prone to aqua-planing, and overall grip in mud and snow.

There is far more natural rubber in winter tyres so they provide 3 TIMES the grip of summer tyres - this does have around a 10% impact on fuel consumption compared to the ECO summer tyre.

Have a look at the tyres on the 1970s Lancia Stratos driven by rally champion Sandro Munari in the Monte Carlo rally:

http://www.pistonheads.com/gassing/topic.asp?t=786933

Compare those to the regular low profile tyres used for tarmac/ dry dirt road rally stages:

http://www.telegraph.co.uk/motoring/classiccars/6560330/Classic-Lancia-Stratos-buying-guide.html

 

[jadnashuanh]

In most places, they stopped calling them snow tires years ago for a good reason...while some tread designs are really aggressive and great in heavy snow, not all are, but all of them are much better when it is cold. The i3, with the 20" wheels has summer, performance tires and will be much less 'performance' when the weather turns cold, regardless of any precipitation that may be around in liquid or solid form. All-season tires are a compromise, all seasons - the tread can't be as responsive in cold because they'd wear out and be squirmy in the hot, so they end up being a compromise, all seasons. On my other car, I have some Michelin PA2's, and those ride and handle very close to the stock tires that came with it. IN fact, on some surfaces, they are quieter!

FWIW, I'm picking up my set of winter tires/wheels this afternoon...by the end of the month or so, it will regularly be cold enough where I live where they will become useful. I like that extra bit of safety margin that they provide and have run snow/winter tires most of my driving life. THen, I don't live in Southern California, or Florida where it rarely gets cold, and almost never snows, so your results may differ!

 

[jadnashuanh]

Grip, assuming the load is evenly distributed, is based almost completely by the area, and it doesn't matter much the shape of it. It depends on the tire's construction while turning if the contact patch distorts much how well it works.