Speedometer/Rev difference between 15" and 17" Wheels
03-30-2001, 11:31 AM
#1
New Member
Thread Starter
Join Date: Mar 2001
Posts: 90
Likes: 0
Received 0 Likes
on
0 Posts
Speedometer/Rev difference between 15" and 17" Wheels
I just picked up my new 2001.5 A4 1.8TQM on Wednesday, and I'm already sorry I didn't go for the sport package. So, I'm now thinking of upgrading to 17" ACE Lolas this summer, and perhaps upgrading the suspension a little later.
For those of you who also had 15" wheels and upgraded to 17", did you see a noticeable difference in your speedometer vs. actual speed. I haven't done the calculations (to include tire size, also) but logically I would think that the 17" wheels and tires would give you a slightly higher speed at a given RPM, when compared to the 15" wheels.
Has anyone noticed this difference? If so, did you get your speedometer recalibrated to compensate?
For those of you who also had 15" wheels and upgraded to 17", did you see a noticeable difference in your speedometer vs. actual speed. I haven't done the calculations (to include tire size, also) but logically I would think that the 17" wheels and tires would give you a slightly higher speed at a given RPM, when compared to the 15" wheels.
Has anyone noticed this difference? If so, did you get your speedometer recalibrated to compensate?
03-30-2001, 11:47 AM
#5
New Member
Thread Starter
Join Date: Mar 2001
Posts: 90
Likes: 0
Received 0 Likes
on
0 Posts
Re: Speedo will read 1% too slow.. try this website... very helpful
Thanks. That's a great site!
My alterior motive in moving up to 17" wheels/tires is to lower the RPMs at 70 mph. I've noticed that at 70 mph, I get enought engine noice and slight vibration through the tranny in the shift **** that it annoys me. So, I end up driving a little slower. 67 mph seems to get rid of most of it. So, I was hoping that by going to 17" wheels/tires, I might not only make the car look better, but also drive smoother at 70 mph.
Just a thought.
My alterior motive in moving up to 17" wheels/tires is to lower the RPMs at 70 mph. I've noticed that at 70 mph, I get enought engine noice and slight vibration through the tranny in the shift **** that it annoys me. So, I end up driving a little slower. 67 mph seems to get rid of most of it. So, I was hoping that by going to 17" wheels/tires, I might not only make the car look better, but also drive smoother at 70 mph.
Just a thought.
Trending Topics
03-30-2001, 12:05 PM
#9
New Member
Thread Starter
Join Date: Mar 2001
Posts: 90
Likes: 0
Received 0 Likes
on
0 Posts
Re: what kind of tires are you runnin? I have no driveline vibration etc. up to 120mph
It arrived with Goodyear Eagle LS tires -- not the best in the world, to be sure!
The vibration isn't that pronounced, but I can certainly feel it in the shifter if I keep my hand on it. I don't really feel it in the steering wheel or floor.
The vibration isn't that pronounced, but I can certainly feel it in the shifter if I keep my hand on it. I don't really feel it in the steering wheel or floor.
03-30-2001, 12:08 PM
#10
AudiWorld Super User
Join Date: Nov 2000
Posts: 6,270
Likes: 0
Received 0 Likes
on
0 Posts
A couple things...
a 225/45R17 in two different brands may be two different sizes. They can vary widely from brand to brand.
Also, the rolling diameter of a tire will change too. Compare 205/65R15 (25.49") and 225/45R17 (24.97) the 15" tire has a taller, therefore less stiffer, sidewall, so it will compress more under the weight of the car, reducing it's actual diameter.
This is why they are considered the same diameter, even though off the car the 15's will be taller.
If you want to calculate the speedometer difference, measure both wheels (installed) from the ground to the center of the rim.
Let's say your 15" has R1=12.25, and the 17" has R2=12". (Speedometer reading)*R2/R1=Actual MPH
So at 80 mph, you're actually going 78.4 - Not a big difference.
Also, the rolling diameter of a tire will change too. Compare 205/65R15 (25.49") and 225/45R17 (24.97) the 15" tire has a taller, therefore less stiffer, sidewall, so it will compress more under the weight of the car, reducing it's actual diameter.
This is why they are considered the same diameter, even though off the car the 15's will be taller.
If you want to calculate the speedometer difference, measure both wheels (installed) from the ground to the center of the rim.
Let's say your 15" has R1=12.25, and the 17" has R2=12". (Speedometer reading)*R2/R1=Actual MPH
So at 80 mph, you're actually going 78.4 - Not a big difference.