Focus Fanatics Forum banner

1 - 12 of 12 Posts

·
Registered
Joined
·
336 Posts
Discussion Starter #1
2 different ways to measure the same thing.

I've always gone by Backspacing and always used Inches because.... Merica. [headbang]

The whole Offset from centerline of the wheel in mm has always bugged me LOL.
 

·
Registered
2006 ZX3 2.0, 2006 ZX5 2.0, 2004 ZX3 SVT
Joined
·
1,205 Posts
2 different ways to measure the same thing.

I've always gone by Backspacing and always used Inches because.... Merica. <img src="http://www.focusfanatics.com/forum/images/smilies/icon_smile_headbang.gif" border="0" alt="" title="Head Bang" class="inlineimg" />

The whole Offset from centerline of the wheel in mm has always bugged me LOL.
1mm = .03937 inches
 

·
Thats What She Said
Joined
·
10,704 Posts
or 1" = 25.4mm (or 2.54cm) ;-)

Wheel diameter and width is done in Inches and bolt pattern is in mm offset is in or mm.

Tires have width in mm but then have a in diameter also...

Whole thing is fun to work with.
 

·
Registered
Joined
·
336 Posts
Discussion Starter #5 (Edited)
or 1" = 25.4mm (or 2.54cm) ;-)

Wheel diameter and width is done in Inches and bolt pattern is in mm offset is in or mm.

Tires have width in mm but then have a in diameter also...

Whole thing is fun to work with.
Yeah, it's the mixing of UOM's that bugs me. Both wheel and tire measurements can be this way.

Whoever came up with the whole "Aspect Ratio" for tires needs a swift kick.
Tread Width and then a sidewall that's a percentage of Tread width just doesn't make sense. It's the way it is, but doesn't make it Logical.

I prefer tires to measure Dia x Width like most offroad tires. 37x12.50-17 are what's on my truck. Wheels are 17x9 with 4.75" Back Space

Most of my background is in American Muscle Cars, Drag Racing, Circle Track, and Off-Road Desert Racing. Most of the Wheel/Tires in these genres are Inch measurements all around and use backspace for wheel offsets rather than the offset from centerline
 

·
Registered
Joined
·
179 Posts
I agree that the way that tire sizes are done is crazy.

Really, what you should care about is overall diameter. The aspect ratio means something to people looking at handling characteristics, but it's not really useful information without the rest of the wheel size for context, in which case...

Well, for passenger cars, that's what we've got.

Offset from centre is a more useful measure for suspension purposes. Keeping the offset similar means that the suspension lines are where they're supposed to be for steering geometry and in cases where the suspension allows the camber to change with deflection, that this is placing weight on the tire as expected. Often you can get better skidpad results with a narrower wheel and tire with a good offset than you will with a wider tire that's "flushed out" -- you'll also usually get better bump-steer characteristics.
 

·
w/ my magic bag
Joined
·
29,452 Posts
As well as scrub radius^^^..... Lettering size to metric. BFG's LR50x15's on 10'' Ansen's...
 

·
Registered
Joined
·
2,807 Posts
. Often you can get better skidpad results with a narrower wheel and tire with a good offset than you will with a wider tire that's "flushed out" -- you'll also usually get better bump-steer characteristics.
More tire is always better. Always. Even with messed up geometry.
Signed, everyone who has actually raced a car
 

·
Registered
Joined
·
336 Posts
Discussion Starter #11
Wheel off/back spacing changes scrub radius.
I'm aware, but ALSO tire height will change your scrub radius. Unless your SAI is perfectly vertical...... which I hope it's not LOL

It might be minimal on little cars like our Foci, but on Baja Trucks and Buggies like I'm used to, everything is magnified. Dealing with Taller tires, more wheel travel, etc. When you change tire size by several inches, it shows.
 

·
Registered
Joined
·
336 Posts
Discussion Starter #12
On a mcpherson strut car you will also change your scrub radius by raising or lowering the car since you are moving the relationship between the lower balljoint and the top of the strut. Again, this is minimal, but still a change to your scrub at static ride height

Unlike a double a-arm suspension where the SAI is fixed
 
1 - 12 of 12 Posts
Top