Hi guys,
Want to swap my 20s for 19s but my car is on H&R springs and hence pretty much as low as I can safely go already.
Wondering whether those of you that have experience about this can tell me whether there is a material difference in clearance on 19s vs 20s? I'd expect some of the diff in the size of the actual wheel itself to be offset in increased tyre wall, but not sure how much.
Thanks in advance.
Dan

 

You can use a tire calculator to get your height difference. I assume you are running 235/30/20 and 325/25/20?

And not you want to run the stock sizes of 235/35/19 and 305/30/19 again?

235/35/19 vs 235/30/20 = <TABLE style="BORDER-COLLAPSE: collapse" border=1 cellSpacing=0 borderColor=black cellPadding=4 background=images/spacer.gif><TBODY><TR style="BACKGROUND-COLOR: #ffffff" onmouseover="style.backgroundColor='#D3D3D3'; window.status='Diameter: overall height of the tire';" onmouseout="style.backgroundColor='#FFFFFF'; window.status='';"><TD bgColor=#eeeeee><TABLE width=280><TBODY><TR><TD width=100>Overall Diameter:</TD><TD width=80 align=right>25.47 in</TD><TD align=right>646.93 mm</TD></TR></TBODY></TABLE></TD><TD><TABLE width=280><TBODY><TR><TD width=100>Overall Diameter:</TD><TD width=80 align=right>25.55 in</TD><TD align=right>648.97 mm</TD></TR></TBODY></TABLE></TD></TR></TBODY></TABLE>

305/30/19 vs 325/25/20 =
<TABLE style="BORDER-COLLAPSE: collapse" border=1 cellSpacing=0 borderColor=black cellPadding=4 background=images/spacer.gif><TBODY><TR style="BACKGROUND-COLOR: #d3d3d3" onmouseover="style.backgroundColor='#D3D3D3'; window.status='Diameter: overall height of the tire';" onmouseout="style.backgroundColor='#FFFFFF'; window.status='';"><TD bgColor=#eeeeee><TABLE width=280><TBODY><TR><TD width=100>Overall Diameter:</TD><TD width=80 align=right>25.96 in</TD><TD align=right>659.38 mm</TD></TR></TBODY></TABLE></TD><TD><TABLE width=280><TBODY><TR><TD width=100>Overall Diameter:</TD><TD width=80 align=right>26.39 in</TD><TD align=right>670.30 mm</TD></TR></TBODY></TABLE></TD></TR></TBODY></TABLE>

www.1010tires.com if you need the calculator.

 

You are correct. The overall tire diameter is what is important. The 911 is very particular about this but going to the right sized 19" tires won't cause any problems even if lowered. Regardless of diameter you need to keep them as close a possible to the factory overall diameter. Going to the factory sizes is always the safest.

Use the calculator or use this:

305/30-19

305 = width in mm
30 = profile measured as 30% of width
19 = diameter of wheel in inches

305*.30/25.4 = 3.6 (width of sidewall in inches as 25.4mm/in)
Two sidewalls = 2* 3.6 = 7.2 inches
19" + 7.2 = 26.2 inches overall diameter

I'm not sure why this comes out different in the above post. I think a typo occurred and a 295 was entered instead of 305.

The overall diameter is not the same as the rolling diameter but for this type of calculation as long as you're comparing apples to apples you will be okay.

Not applicable to you but the overall factory diameter for the 996 and earlier cars is about 1" smaller overall than the 997s.

 

Thanks very much for the informative responses.
I think, however, I have found the solution to all my problems

www.cargraphic.co.uk/?/o,article,4632/

Woohoo no more scraping!

 

I would scrape a few spoilers before paying 13K for it or 9000/10000 Euros.

 

No i typed in 305. Maybe their calculation tables are off.