Heavy steering problems

but isnt overall diamater about the same in 19 with 55s as opposed to 20 with 45s. IDK

(17-10-2011 09:20pm)exigejoe Wrote:  but isnt overall diamater about the same in 19 with 55s as opposed to 20 with 45s. IDK

19" with 235/55 Dia 741mm
20" with 245/45 Dia 729mm

No guarantee this is correct by the way!

They shoud use 255 to close up the gap or use a 50 profile. I might use 50 instead of 45 when i get my 20s.

Surely the rolling diameter of the wheels has to be the same whichever size of wheel is used, otherwise the speedometer accuracy goes out the window...

I dont think speedometers are very accurate. At least not compared to my tomtom. I thought this was one reason why the police turn a blind eye to people doing 10percent more than the limit. In my mini 77 on the speedo is 72 on the Tom Tom.

(17-10-2011 11:05pm)LP Wrote:  I dont think speedometers are very accurate. At least not compared to my tomtom. I thought this was one reason why the police turn a blind eye to people doing 10percent more than the limit. In my mini 77 on the speedo is 72 on the Tom Tom.

Speedos are nominally set to read 4% fast to give a margin for error.

Circumference of 19" 235/55 is 2,329mm and the 20" 245/45 is 2,290mm (rounded) so the difference in distance covered with each revolution of the wheel is ±39mm (more by 19") or 1.73%….. which considering that over the life of a tyre the tread reduction from new to the minimum legal depth (±20% of new) will have pretty much the same or slightly greater impact on the circumference and hence accuracy of speedometer I would not worry too much about this.

PDI?

Pre-Delivery Inspection. The dealer is supposed to check the car and take it for a short test drive to ensure all is well.

I guess that's why mine had 28 miles on the clock and a CD in the player when I picked it up.