This Is How To Measure Your Car For New Wheels

[Deep Dish V35]

Just spent 3 hours writing this up, hopefully I havent missed anything...

Here is a simplied way to measure your car for wheel fitment when you want to upgrade.

You can only do this method if your car currently has an open type of wheel which allows easy access to the brake disc.

What i am going to get you to do is measure your car for width, then use a website to calulate the offset.

Tools required

1. tape measure

2. a 60cm ruler or some kind of straight edge like square tube(that long or longer)

3. pen and paper to write your measurements

4. access to the following website on a PC (doesnt work on apple devices)

http://www.jonathanr...fset-calculator

NOTE - It is important to make sure your tyres are inflated properly and your car is parked on level ground!!!

We will do this whole thing for just your front wheel first. When that is done, re-do this whole tutorial for your back wheel.

BEGIN!

While holding the very top of the ruler or straight edge, let it hang so that the upper part is just resting against the highest point of your wheel arch, as seen in picture 1. It must not contact anything else at this point.

pic 1 (click to enlarge)

Using the tape measure, you need to rest the hook end of the tape against the WHEEL MOUNTING FACE of the brake disc (or a part near it which is level with that face) and measure DIRECTLY OUTWARDS to the hanging ruler, as seen in picture 2. If you hold the tape measure on an angle, your measurement will be incorrect - it must not be held on an angle.

note: In my pic I was unable to touch the wheel mounting face on the brake disc so I touched the end of the tape against a part of the brake caliper that I could see was level with that mounting face.

Another thing is to make sure you are measuring to a point that is as close to the centre cap of the wheel as possible, as camber will affect your final result.

pic 2 (click to enlarge)

The point at which your tape measure reaches the inside of the straight edge is your first measurement (which is the distance from the wheel mounting face to your fender) take this measurement off the tape measure and record it in millimeters as "Fender distance to hub" on your notepad. You can see my measurement as being 85mm, yours might be different.

Now using just the tape measure, measure from the top centre of your fender's wheelarch, across the top of your tyre, to the side of the suspension strut or shock absorber. This measurement is the absolute widest you can go between the strut/shock and the fender. See picture 3. You can see my measurement is 245mm (approx 9.5 inches) overall.

All alloy wheels are actually ONE INCH WIDER than the width they state on them - a wheel sold as 8.5 inches wide will actually be around 9.5 inches wide OVERALL as the measurement the manufacturers give you is for the inside where the tyre bead would seal. Now I know that with the right offset I can ONLY JUST fit an 8.5 inch wide wheel as it would physically be 9.5 inches wide.

pic 3 (click to enlarge)

Using your hand, reach around the tyre and feel for anything that comes near the back of the wheel. The shock/strut SHOULD be the closest thing to the back of your front wheel, but on the rear you might also have clearance issues with the trailing arm. All you need to do is check the difference in gaps to see if this is going to be an issue. If it is going to be an issue, you'll need to allow for it by having a narrower wheel.

Now go to the website I mentioned earlier.

http://www.jonathanr...fset-calculator

On this page, the black lines represent the wheel, the blue lines are the tyre, the red line is the fender/wheel arch. We will be using the "wheel one" settings and the left hand picture for the new wheel in this example

1. Insert the rim diameter you want. This is the easy bit.

2. Leave spacer/adapter measurement at ZERO

3. Remebering what I said earlier about wheel widths, enter the width you want PLUS the one inch, making sure you dont go wider than that overall measurement from the fender to the strut that you measured on your car.

4. Enter the Fender distance to hub measurement you wrote on that piece of paper. Now adjust the offset measurement until the points of the black lines touch the red line. When they touch, you have found your PERFECT MEASUREMENT for FLUSH WHEEL FITMENT.

NOTE this website does not allow for camber. The lower your car is, the more camber it will tend to have, meaning you can run wider (ie: less) offset closer to zero or even into negative numbers. I can show you how to allow for camber in another post at a later date.. on V35's the front doesnt camber too much when lowered, but the rear does exponentially.

All you have to do now is set your desired tyre width and profile.

The blue line will show the shape of the tyre you want to fit and whether it will be a stretched fitment or not.

Using the WHEEL TWO settings, enter the width, profile, and diameter of the FACTORY FITTED tyres listed on the tyre placquard on your car.

In the box on the bottom of the page you can now see under WHEEL TWO the standard tyre height and rim diameter that the car came with. You should aim to match these 2 measurements with your new tyres on WHEEL ONE so that you dont upset your speedometer's accuracy.

You have now finished your first wheel and can write down all the settings listed under wheel one. Now go back to the top of this page and do the same thing for the opposite end of the car.

Things to consider:

-Large multi piston brake calipers such as BREMBO or BEAR BRAKES stick out past the mounting face of your brake disc. These will quite often have clearance issues with aftermarket wheels. It is necessary to measure how far your brake caliper sits past the wheel mounting face and make sure that the rear of your desired wheels have this clearance.

-Lowering your car will change the amount of clearance you have as the wheels tend to increase in camber angle, making the top of the wheels "tuck in", especially on the rear of cars with IRS. The lower the car is, the lesser the offset of the wheels can be.

Edited August 8, 2012 by Deep Dish V35

[Deep Dish V35]

Ok here is how to measure the camber and adjust the original offset calculation accordingly

This is a 2 person job unless you were born with 3 arms.

Tools needed:

2x straight edges

Tape measure

First thing is to cut a straight edge from some steel or alloy bar so that it is the same height as the RIM. You will need to measure the height of the rim alone using a tape measure. You will find it is around an inch or 25mm more than the actual rim size. see pic 1

pic 1 (click to enlarge)

After you have made this tool, get a friend to hold it VERTICALLY and directly onto the centre line of the wheel so that it touches the rim lip on the top and bottom of the rim. see pic 2.

pic 2 (click to enlarge)

Now using your second straight edge, hold it so that it JUST TOUCHES the top centre of your fender/wheel arch, and hangs perfectly upright and alongside the first straight edge without touching it. see pic 3

pic 3 (click to enlarge)

now heres the tricky bit... You need to measure 2 places.

First place to measure is at the TOP of the rim, the distance from the wheel side of the first straight edge to the wheel side of the second straight edge. see pic 4. you can see the measurement at my thumb is approx 10mm. Yours will be different

pic 4 (click to enlarge)

Second measurement. Try to do this as close as possible to the same height as you originally measured the mounting face when doing the steps in my first post. Once again, the distance from the wheel side of the first straight edge to the wheel side of the second straight edge. see pic 5. you can see the measurement at my thumb is approx 5mm. Yours will be different

pic 5 (click to enlarge)

Now take the first measurement from the second measurement. It should give you a negative number. For me it is -5mm.

That number is the adjustment you make to the offset calculator for that particular wheel's offset when using the website mentioned in my first post. The website does not allow for camber, so this calculation fixes it. on the website it will show the wheel now poking out that far when the car has no camber. this is correct.

If youve just done your front wheel, you can now go and measure the rear wheel

Hope that is easy enough

Edited August 8, 2012 by Deep Dish V35

[Vimana]

Thank you. This will help when we are ready for new rims.

[Deep Dish V35]

alternatively.... if you want your current wheels to be more flush, you can use the result of the calculation from my second post to buy a spacer that matches that measurement (for me, measurement of -5 means i should fit a 5mm spacer) to make the rim flush with the fender

(slip-on spacers are not something i would use as they will reduce the amount of stud thread inside my wheel nuts)....... which worries me more than the whole "legality" thing

Edited August 8, 2012 by Deep Dish V35

[t5iv]

Excellent write up. Appreciate the effort that you've put in. Admins, pin?

[Seano350GT]

A lot of work gone into this, thank you. Hopefully this educates some fitment noobs like myself

[Seano350GT]

Put in all the measurements of the rims i'm buying, front wheels are going to have .75'' poke and back 1.51'' poke. Although at the front the tyre looks all retarded and triangular with 245F i have to change it to 275 for it to be straight

[Deep Dish V35]

Put in all the measurements of the rims i'm buying, front wheels are going to have .75'' poke and back 1.51'' poke. Although at the front the tyre looks all retarded and triangular with 245F i have to change it to 275 for it to be straight

1.51" ???? dont you mean 1.51mm??

that amount of poke with the wheels you PMd me? on a sedan yes, on a coupe no. 20x10 +25 should be a good fit with minimal poke. i think the poke is shown in millimetres on that website but i cant check on my iphone

just out of interest, what were the mounting face to fender measurements on your coupe?

Edited August 9, 2012 by Deep Dish V35

[Deep Dish V35]

the "stretch look" all depends on the actual tyre you choose to fit. some tyres are made with bulgey sidewalls, some come with extra rubber for rim protection. some have neither. its the hardest bit of getting the right look.

i have had situations in the past where a 265 in one brand was actually wider than a 285 in another brand.

it really helps if you can see the tyre you want already fitted to a another wheel before you buy your own.

my fronts are currently 20x8.5 with a 225/35/20, they have about 15mm stretch each side and it still looks almost square

Edited August 9, 2012 by Deep Dish V35

[Seano350GT]

1.51" ???? dont you mean 1.51mm??

that amount of poke with the wheels you PMd me? on a sedan yes, on a coupe no. 20x10 +25 should be a good fit with minimal poke. i think the poke is shown in millimetres on that website but i cant check on my iphone

just out of interest, what were the mounting face to fender measurements on your coupe?

Haha sorry mate yeah i mean milimetres. Sweet well at least now i know that they won't sit inside my guards which is the look i was after.

I didn't actually measure the mounting face to fender, i just put in all the details i know about the fitment and it came up with a little bit of poke. Thanks for your advice very helpful mate

[Deep Dish V35]

Another point of interest for V35 Sedan owners..... have a read thru the following thread on G35Driver.com.... 55+ pages of fitment pictures with details. My wheel whoreing is listed on page 54

http://g35driver.com/forums/media-share-g35-sedan-v35/225137-03-06-aftermarket-modded-oem-wheel-pics-thread.html

[n15m0]

Another point of interest for V35 Sedan owners..... have a read thru the following thread on G35Driver.com.... 55+ pages of fitment pictures with details. My wheel whoreing is listed on page 54

http://g35driver.com...ics-thread.html

Nice one my wheel whoring started on PG 4 of that thread lol...and more in between...brings back memories...

Hey Deep Dish, what specs are u running on ur sedan? Wouldn't mind seeing some photos of another sedan...

[Deep Dish V35]

F 20x8.5 +35 with 225-35-20 slightly tucked

R 20x10 +42 with 255-30-20 slightly poking

2003 350z shocks and springs all round

car sits at a safe height for everyday driving, could use another inch lower to look better, but im getting a bit old for that...

would be happier if the fronts were +25 offset to match the poke of the rear.

i dont post any full pics apart from the couple in the G35 thread. dont like to advertise.

Edited August 9, 2012 by Deep Dish V35

[GED59]

Great post Dish

[81gSKy]

What about Concave wheels?

[Deep Dish V35]

for concave wheels, its a bit more difficult. requires either a block against the edge of the wheel arch (the width of that you would account for in your calculations) or other tools that most people dont have... a gyprock L shaped square and a spirit level. or an engineers magnetic post and a plumb bob would work too.

generally it requires a bit more specialised tooling that the average person doesnt have. i could write a completely different "how to" using those tools if people want to buy them

i use pretty much a similar method to do my own wheel alignments too

Edited August 10, 2012 by Deep Dish V35

[Deep Dish V35]

^^ thats if the wheels already stick out past the guards..

but i think you were referring to putting the straight edge on the face of a wheel with pokey spokes... which is actually CONVEX

concave means curved inward

convex means curved out

convex faced wheels are yet another small can of worms. you just need to add equal sized spacers to the ends of the straight edge that space the straight edge out from the wheel face. then allow for the spacers in the calculations. once again, it requires another big post with pictures to explain it properly

Edited August 10, 2012 by Deep Dish V35

[81gSKy]

for concave wheels, its a bit more difficult. requires either a block against the edge of the wheel arch (the width of that you would account for in your calculations) or other tools that most people dont have... a gyprock L shaped square and a spirit level. or an engineers magnetic post and a plumb bob would work too.

generally it requires a bit more specialised tooling that the average person doesnt have. i could write a completely different "how to" using those tools if people want to buy them

i use pretty much a similar method to do my own wheel alignments too

^^ thats if the wheels already stick out past the guards..

but i think you were referring to putting the straight edge on the face of a wheel with pokey spokes... which is actually CONVEX

concave means curved inward

convex means curved out

convex faced wheels are yet another small can of worms. you just need to add equal sized spacers to the ends of the straight edge that space the straight edge out from the wheel face. then allow for the spacers in the calculations. once again, it requires another big post with pictures to explain it properly

Yes, please do write up a 'how to' for concave wheels as well, it would help heaps. My first mod was my concave wheels and they don't sit spot on flush, but slightly inside and its frustrating.

Nah nah I'm talking about concave (from lip to centre is inwards), not convex (from centre to lip is outwards). I don't like convex and it would be harder to fit BBK with them too.

[Deep Dish V35]

concave wheels are measured exactly as ive described.... not sure what your drama is, maybe post a pic

[Deep Dish V35]

just noticed i hadnt gone into detail

on this one...

THIS is a convex wheel. the spokes stick out further than the rim lip, which makes it harder to measure if using my instructions

THIS is a concave wheel. the spokes across the face do not stick out past the rim lip.