Hockenheim

easy, 19's are better

Superfly_A6

Interesting finds:

I've done some digging around which included measuring the weight of both my winter and summer setup. The rims in question are pictures here. Thank you RobC for putting together a tire guide.

The weight of the 20x8.5" OEM Rim + Pirelli P-Zero tire (255/35/20) is 24.3KG or 53.5LBS. Diameter is 27.02". As per Tire Rack's Website, the weight of the tire is 26lbs. So the weight of the 20" rim is 27.5lbs

The Weight of the 18x8" OEM Rim + Continental Contiwintercontact tire (225/50/18) is 24.0kg OR 52.8lbs. Diameter is 26.85". As per Tire Rack's Website, the weight of the tire is 22lbs. So the weight of the 18" rim is 30.8lbs
Please keep in mind that the 20" rim and tire combo have ~ 400km on them, and the winter tires have ~9,500km on them, so thread has worn down and I don't know how much.

I used a bathroom scale to measure both tires (although not very accurate, measurements were taken couple of times)

This being said, although both tires weight the same, I can notice a decrease in acceleration when switching from 18's to 20's. The can seems like it needs to work harder to get moving when compared. So now I'm puzzled. I didn't think that rotational inertia has so much to do with the rim size.

Comments welcome

newmoon

I think you should just sell your 20" wheels + tires as 'near-new', and swap out the tires on your 18" wheels for all-seasons or grand touring tires, at least for this season.

I have the OEM Continental ContiProContact tires in 245/45R18 size and they are very smooth, absorbing bumps solidly, and also very quiet.

Maverick61

Living in PA with crappy roads, i long ago learned not to go eith the lowest profile tires

I ride 19" aftermarket wheels in the summer, 18" in the winter with the sport suspension and both work well for me.

The summer ride is a little stiffer but not harsh IMO on 19" wheels

DeerHunter

Rotational intertia is largely predicated on where the weight is located. In other words, more weight on the outside of the wheel/tire assembly adds rotational inertia (think of a figure skater, whose weight doesn't change during a routine, spinning faster as they draw their arms in towards her body).

So, given that aluminum weighs more than rubber/steel belts, a larger-diameter wheel has more rotational intertia.

2008A6

I noticed you have 225 width tires on the 18in rim...don't they come 245 stock? I'm wondering if the significant difference in contact patch between 225 and 255 may also impact the diff you're feeling.

tenspeed

As snagitseven pointed out in another thread, you can't change the laws of physics.

The contact patch will remain essentially the same. The weight on each tire will remain the same and what is lost on width will be gained on the length. That allows the snow tire to cut a narrower path instead of floating on top of the snow.

Superfly_A6

Composite wheels
http://www.motorauthority.com/news/1...mposite-wheels
http://www.greencarreports.com/news/...w-2015-audi-a8

Superfly_A6

After spending a few weeks with the 20s. I've either got used to it, or tires have soften up. The ride is now nice and I like it.

Thanks for the posts

NABS4

I find the 19" wheels with the sport pkg to provide acceptable ride quality. Immediately after taking delivery of the car I did notice some harshness, but the tire pressure was set as per the door sticker (38/41). I changed it to 36/36 and that has made all the difference.