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zetor

15" And 17" Wheels

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Ok I know the 17" wheel is bigger:) from my previous thread I will now have to buy new wheels with winter tyres for the Auris, there are 2 wheel sizes, 15" and 17", I know using 15" you get better fuel economy but what is the actual differences when it comes to handling and stopping? Would winter tyres perform better on 17" wheels? At present I have winter tyres on 15" wheels on my Corrola and they seem ok to me.

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Well for winter conditions i.e., rain or snow I would say it is best you use the 15'' rimms. Smaller tires provide better traction in wet conditions specially in snow that's why you see Rally cars whith such small tires. For dry conditiond 17'' would be better offcourse but only because it allows you to have a bigger tires. If I were you I would probably get the 17'' rimms for summer and keep the 15'' for winter. This if the difference is minimum off course. 17'' rimms make the car look more sportive but were are not talking about a sport car so 15'' or 17'' in a normal Auris will provide you some improvement but not that much.

Resuming if they are almost the same price take the 17'' for summer. If you like the looks of a 17'' take it. If you are trying to find a major improvement only take the 15''

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Ok I know the 17" wheel is bigger:) from my previous thread I will now have to buy new wheels with winter tyres for the Auris, there are 2 wheel sizes, 15" and 17", I know using 15" you get better fuel economy but what is the actual differences when it comes to handling and stopping? Would winter tyres perform better on 17" wheels? At present I have winter tyres on 15" wheels on my Corrola and they seem ok to me.

what about 16" as fitted to some models.a compromise maybe.

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I can't quite understand how bigger wheels give lower mpg, a 17" wheel moves further than a 15" with each complete rotation so in effect you would think it would improve mpg as you travel further for the same engine imput rather than the opposite

Maybe someone can enlighten me ?

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I can't quite understand how bigger wheels give lower mpg, a 17" wheel moves further than a 15" with each complete rotation so in effect you would think it would improve mpg as you travel further for the same engine imput rather than the opposite

Maybe someone can enlighten me ?

You have more contact surface with the road friction increases and therefore consumption too. Not to say that in terms or aerodynamics a larger tire also makes more air resistence and increases the heigth of the car unless you get low profile tires. In teory having a 15'' or 17'' with the same size let's say 205 but lower profile on the 17'' tires you could probably get a better consumption but you wouldn't even notice it probably. But in this case comfort would decrease a lot and that you would notice you can be sure.

But this is teory no one buys a 17'' rimms and uses the same size of the ones you were using on the 15'' because it will make the rimms look stripped. I know this because when I had my Saxo I bought bigger rimms and I tought I would n't need a 195 tire and I said 175 was suficient the guy immedatly told me it would look bad. Sometimes it depends of the rimms width not all are the same and on some you can fit smaller width tires on other you just can't

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It will all depend on the tyre aspect ratio......

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I have now just discovered that the environmental bonus that I can get has now changed which means to get the €1500 bonus the car has to produce less then 90g/km, it was 100g/km so with the 17" wheels (93g/km) it only qualifys for the €750 bonus, I think I will call in the Toyota garage and see if I can have the 15" wheels (89g/km), I don't take delivery until the begining of March, any extra they may cost I can offset with the bonus :) I can then also buy the 2nd set of wheels with winter tyres later.

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capnbirdseye - There are a couple of factors that come into play, I will give a bash at explaining -

For the purposes of illustration the tyres discussed will be a 195/65 R15 and 225/45 R17.

First thing to note would be the similarities of the tyres - that is that both have a diameter of ~ 634 mm, and a circumference of 1993 (195/65) or 1992 mm (225/45). This is important for clearances of the wheel arches and suspension on full lock (a taller tyre may foul, although fitting too wide a tyre may also result in fouling). It also means that your speedo will remain accurate as the gearing hasn't be drastically changed. General advice is to stick within +/- 2.5% of the original circumference. Thus most of the time you will see people go up in rim size and down proportionally in aspect ratio.

On to the differences -

Tyres - as others have mentioned the 225s will have a different contact patch than the 195s. It's going to be wider, and shorter front to back, the exact shape will be dependant on the pressures used. This will probably result in an increase in rolling resistance (decreased fuel economy). Now the lower A/R of the tyres mean that they will generate less heat from sidewall deformation, and tyre manufactures typically use this opportunity to use a softer compound (compared to the 195s not compared to super soft track/race tyres etc.), which will increase the amount of grip and friction, again likely increasing the rolling resistance (< fuel economy). Finally, because wider tyres are often "sportier" manufacturers may use different tread patterns on their 225s compared to their 195s - bigger tyre blocks, different groves and pitch, which enhances the tyres traction at the expense of noise and rolling resistance (< fuel economy).

Wheels - the 17" is bigger... yes you all know that 17 > 15, but that isn't the whole story.

As we all know metal is heavier than rubber so the 17" wheel is going to weigh more than the 15" wheel... but the 195/65 R15 tyre will probably be fitted to a 6" wide rim (range is 5.5 to 7"), while the 225/45 R17 tyre will likely be fitted to an 8" wide rim (range 7.5 - 9"). So the wheel is not just taller, it's wider, which will increase it's mass even further... and weight is the enemy of fuel economy...

Also in play is inertia, a heavier object is harder to move, but of more specific concern for wheels is rotational inertia. As the weight moves further from the axis of rotation (the hub), its rotational inertia increases, so not only is the 17" wheel heavier and harder to turn, its weight is further from the hub compounding the problem. If I recall correctly it's about a 12% increase per inch - so if the 15" and 17" wheels weight were identical, the 17" wheel would still be 25.4% harder to rotate. So bigger wheels require more work to rotate, and where does this energy come from? Yup the car's fuel... (< fuel economy).

Finally you have the aerodynamics of the wheels themselves, the wheels aren't as smooth as the tyres, so a larger wheel is likely to cause more turbulent air than a smaller wheel (depending on spoke pattern/design), which will produce more drag, which saps fuel economy (< fuel economy).

As for the OP -

15" should be fine for winter tyres, it will really come down to cost/space - do you want to keep a spare set of 15" wheels (if it's on 17" at the minute), with winters tyres on them? The cost of purchasing the 15" wheels should be offset against cheaper 15" tyres (check first! certainly this winter all winter tyres have been expensive regardless of being R15 or R17) and not having to pay to mount/remount winter/summer tyres.

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