Tyre widths 16" vs 17"

[ziggyboy]

The stock 16" my car came with had 205/55R16 while the recommended 17" I've now got are 225/45R17.

The question is, why have VW chosen a width of 225 over, say, 215, when obviously there will be more tyre space touching the ground making the car "slower". I have noticed a slight decrease in fuel economy and attribute this to my presumably increased wheel weights and the tyre width.

Is it safe to put on 215 tyres? I'm assuming it will be, unless there are other reasons I'm not aware of...

[Diesel_vert]

The stock 16" my car came with had 205/55R16 while the recommended 17" I've now got are 225/45R17.

The question is, why have VW chosen a width of 225 over, say, 215...

To maintain a similar rolling circumference - as would any other vehicle manufacturer. So 225/45 R17 is actually the next logical step up.

A 215/45 R17 tyre is quite a bit smaller than a 225/45 R17 tyre in terms of physical size and diameter, which impacts its load carrying capacity.

I have noticed a slight decrease in fuel economy and attribute this to my presumably increased wheel weights and the tyre width.

Yes and yes - just put up with it.
Welcome to the exciting world of big wheels and tyres.

You've already fitted 17" wheels to it; swapping over to 215/45 R17 tyres isn't going to do much IMO.

Is it safe to put on 215 tyres? I'm assuming it will be, unless there are other reasons I'm not aware of...

Be aware of the load index.
You need to buy the extra load version, i.e. 215/45 R17 91W XL, not the standard load version, i.e 215/45 R17 87W.

Note - it won't be as compliant a 225/45 R17 tyre, you'll have less dry/wet grip, the speedometer will overestimate more, and you'll certainly need to increase the inflation pressure to achieve the equivalent load capacity.

[kaanage]

Compared to the 205/55R16, 225/45R17 has a 0.41% larger rolling circumference while 215/45R17 is 1.05% smaller so neither is a huge difference. Note that the larger rolling circumference of your current tyres will reduce odometer readings by the 0.41% and therefore reduce the mileage calculations by that degree, so your car thinks it is using even more fuel than what is caused by the extra drag (both rolling and air).

Here is my favorite site for checking this as it allows multiple sizes to be compared: Tire Size Calculator - tire & wheel plus sizing

Just to explain the effect on the load rating - air volume provides the primary support for a vehicle's weight and with all other things being equal, when tyres are of the same width and rolling circumference, the one with the larger rim size will have a lower load rating as the enclosed air volume is smaller. Manufacturers can strengthen a tyre's sidewalls to a degree to create the extra load version but due to the extra material required, you get the downsides as mentioned by Diesel_vert.

[ziggyboy]

I was thinking of putting 215/50R17, which is even larger in diameter than the 215/45R17 you guys have suggested. Yes my speedo will be "2.374% too slow" as the tyre calculator has indicated, but that is OK as speedos are normally overestimated anyway. When I'm doing 100kph my GPS is telling me I'm doing 94kph. Adding 2.374% will give me around 96kph when doing the same speed.

And Diesel_vert mentioned the 215's will get less grip than the 225's I've got now, but isn't that still more grip than my 205 stock on 16"??

[Diesel_vert]

I was thinking of putting 215/50R17, which is even larger in diameter than the 215/45R17 you guys have suggested. Yes my speedo will be "2.374% too slow" as the tyre calculator has indicated, but that is OK as speedos are normally overestimated anyway. When I'm doing 100kph my GPS is telling me I'm doing 94kph. Adding 2.374% will give me around 96kph when doing the same speed.

215/50 R17 is quite a big tyre compared to 225/45 R17, so accordingly, you'll add 9 mm to the ride height when compared to a 205/55 R16 tyre (225/45 R17 adds 4 mm).

I'd guess they wouldn't be much different in weight either, so expect very little difference in fuel consumption, if any. It may even increase a tiny bit, due to the increase in ride height.

I'd also expect they'd be more compliant than a typical 225/45 R17 tyre.

And Diesel_vert mentioned the 215's will get less grip than the 225's I've got now, but isn't that still more grip than my 205 stock on 16"??

Generally yes, but the choice of tyre plays role as well.

Also, 215/50 R17 is so big that the section width is essentially the same as 225/45 R17. It's overall diameter lies between 235/45 R17 and 245/45 R17.

You might like to consider 205/50 R17 93V XL as well.

...

Again, it appears to me that reverting back to your original tyre an wheel setup is the simplest solution. There's always a price to be paid by going with bigger wheels and tyres. Physics, eh?

[ziggyboy]

Hehehe... my original objective was to keep the wheel size (17") but get the same fuel economy I did with my 16"...

Doesn't seem like that's going to happen though. Hmmmm...

[Diesel_vert]

Hehehe... my original objective was to keep the wheel size (17") but get the same fuel economy I did with my 16"...

Doesn't seem like that's going to happen though. Hmmmm...

You can counter this by fitting wheels which weigh no more than the originals did.

Or fit low rolling resistance (RR) tyres, though you probably won't recoup the difference if the tyres you currently have are still new. Perhaps try increasing the inflation pressure by 2-3 psi.

What tyres are currently on the car?

[Ryan_R]

GTI being more powerful would need more grip. I've considered bigger wider 17's for my car for this reason since loading APR Stage 1 gives me the same power as the GTI (and more torque) and it's quite easy to run out of grip even when spending over $200 per tyre.