DSG and rolling radius changes

[Flashollie]

Got standard 17" Devonport alloys and 150 bhp dsg box.
I want to go for 18" probably sportlines as part of dropping it few mm too.
Does the change in wheel size or tge rotating mass have any detrimental effect to performance of the dsg?
I assume Speedo will return correct speed as circumference doesn't change?
Sorry if this is a thick question.

 

[Tourershine]

This might help.

Will They Fit - Online Wheel and Tyre Fitment Calculator

Oh, and i've moved from Devonports, to 19" running 255/45/19 on a DSG, with zero difference in the drive.
At that size the speedo is absolutely spot on with the sat nav, which I wanted, because i've changed my clock centre set up to show big MPH with my Carista, and the nav and clock not matching up is very distracting. (to me anyway)

 

[Flashollie]

That's really helpful thank you.

I'd like to make sure my new set up gives the same speed at 60 or a minor decrease no more than about 1 mph at 60 so I don't get pinged thinking I'm doing 60.
So I think Devonports are 215 x 60 X 17 X 7j wide
So I'm thinking 18" 8j rims with 255 X 45 x 18. This seems fairly stock and give a very minor increase at 60 mph to 60.27mph or 0.45%. I think I can live with that.
I could, to be extra sure (if they fit safely) go for a wider tyre at 260 to get a speed error of -0.2%.
What are most people running and why?

And finally just out of interest, what l don't understand is why does the width of the tyre affect the the speed percentage if circumference / profile stays the same?

Thanks

 

[Deaky]

That's really helpful thank you.

I'd like to make sure my new set up gives the same speed at 60 or a minor decrease no more than about 1 mph at 60 so I don't get pinged thinking I'm doing 60.
So I think Devonports are 215 x 60 X 17 X 7j wide
So I'm thinking 18" 8j rims with 255 X 45 x 18. This seems fairly stock and give a very minor increase at 60 mph to 60.27mph or 0.45%. I think I can live with that.
I could, to be extra sure (if they fit safely) go for a wider tyre at 260 to get a speed error of -0.2%.
What are most people running and why?

And finally just out of interest, what l don't understand is why does the width of the tyre affect the the speed percentage if circumference / profile stays the same?

Thanks

Because the profile is a percentage of the width.

 

[Flashollie]

Ah that makes sense thank you

 

[Pauly]

I switched from standard 17 Devonports to 18 Sportlines with 255/45 tyre (as recommended by VW) and there was no noticeable change
I think there is a tiny increase in rolling circumference (can’t remember my old tyre size ?) and my Speedo went from running about 2-3 mph under actual speed to between 0-1 mph under so worked out more accurate.
Remember manufacturer always seem to install speedos that read on the safer side so will always be a touch under on standard wheels/tyres just be sure to check and compare your speedo speed with gps before and after changing setups

 

[Flashollie]

Great some very helpful advice.
Only futher complication is to future proof. I do want to fit eibach coil overs and lower 30 to 40mm.

 

[Tourershine]

I have 30mm springs currently.
Although will be going a bit lower soon.

 

[Flashollie]

Excellent sounds like all's good to go. Just got choose the wheels now..........