jeffkruse

I currently have 255/45/18 on my 2004 Audi A8, I was thinking about changing the tire size to 245/45/18. Just more options. Any ramifications? I found a tire size calculator on line and below are the differences. Seems very minimal. Any help would be appreciated.

Tire Size Comparison

Specification Sidewall Radius Diameter Circumference Revs/Mile Diff
255/45-18 4.5in 13.5in 27.0in 84.9in 746 0.0%
245/45-18 4.3in 13.3in 26.7in 83.8in 756 -1.3%

TSHong

Yes, the tire is not that much different but I would never recommend going with a smaller size. The load carrying capacity is reduced, speedometer incorrect, and would look small on a D3. These would be very small difference but there.

On a side note, not sure about legalities of being sued in an accident if either insurance or lawyers found out that you were not running proper size tire. Although this would be an infinitesimally small liability.

MP4.2+6.0

Audi's tire range on the D3 is between 27.0 and 27.7," so if anything you are going the "wrong" way here. No it won't melt though, but I would not do it either. If they were winters and maybe you went to 245/50s (or better size wise 235/50s probably), then perhaps. I think you will find speedo error is already pronounced (check it with a GPS app on a phone if you want); at least with a W12 a Euro road test showed up to a 5% error with the 255/45 18 base fitment, and the sizes toward 27.7 "true" this up better.

Maybe most importantly you are pulling down braking performance some. Most any road test on any decent vehicle will find braking distances drop as tire width goes up within reason, and certainly within a manufacturer fitment range. Also was my experience when I ran 255's a bit on some 18's when my 20's (275's) were getting refinished. I value that 5-10 feet debatable range (assuming same tires) when the stops from common (USA) highway speeds out of nowhere come up. True emergency ones sure, but also in increasingly common sluggish freeway traffic with drivers in front doing God knows what besides focusing on driving before they late panic. And you will inevitably get the blame and the insurance points if you go into the car in front and weren't driven there by the car behind. I see 'em literally every few days on the side of the highway with the CHP car, good weather or bad, typically with bunching up traffic.

Last small point is you exposing the rim lip a little more to curbing damage as you narrow down any tire on any given wheel.

jeffkruse

Thanks for the info, the car came from the factory with these tires(255/45/18), I have the sticker, and I did notice that my speedometer is slower than actual GPS about 5 MPH at 60MPH. I think I will stick with the correct size.

MP4.2+6.0

If you want, look at the tire pressure sticker (pre 2007, fuel door) to see if these were even a listed size, or (calendar) 2007 on the specific size listed on the then mandated door pillar sticker.

255/45-18 is really the known baseline fitment (ignoring early 17s), and back in the day I saw many a set of take offs on EBay with that set up too. Your spare size could be a further cross check, since few swap outs go into the spare too. Some early D3 Audis have down to 17's for the spare, but except for 20's the spare set up typically matches the others.

TSHong

I just looked at what our main distributor carries and there are plenty of choices from budget to premium tires. I do know that the 245/45R18 do have more choice but the the 255 have a pretty good range of choices.

jeffkruse

do you mind sharing who your distributor is? Thanks. It is listed on the fuel door(255/45/18), also I wish I had a spare, I bought the car and did not bother checking for a spare. Lesson learned.

MP4.2+6.0

So it was 255 as I expected. Somewhere the tires got switched.

On the spare, you can find beater OE 18's down to about $100 on EBay. Twice that if you get clean/refinished. If you have a scratched one now you could pony up more, or just get by w/ a beater, especially if you are about to spin off some old tires anyway. Search string to get down to a pretty tight search is something like: Audi 18" (stock, OE, factory, OEM) A8 wheel -a4 -s4 -tt -s5 -a5 -a6 -a7

Having tried that string, there is one a ways down in the hits w/ a complete tire that looks clean that might be plug and play and get you back to 255's all the way (assuming the basic 5 spoker is what you have), spare and all: http://www.ebay.com/itm/03-04-AUDI-A8-A8L-QUATTRO-WHEEL-TIRE-RIM-18X8-5-18-CONTINENTAL-255-45R18-OEM-/301231827643?pt=Motors_Car_Truck_Wheel_Packages&hash=item4622d0eabb&vxp=mtr Won't have TPMS sensor, but that would be next to never now anyway, let alone kept up. And if the wheel is correct style, might be cleaner than one of your existing ones you could move to spare position if you get tire remounted.

TSHong

Our main distributor is ATD. They have a Tire Buyer program and you can get them installed by a local installer near you. ATD has distribution centers across the US. I'm a brick and mortar tire store chain in ATL.