Pcd Diameter

[rcs_888]

Hey guys,

Appart from owning a R34 i also have a BMW E34. Highly modified and going through regency currently etc but what i am doing is converting the front hubs to 5x114.

What im needing to know is can anyone actually tell me the bolting diameter of the 5x114 pcd so i can spin up my hub on the lathe lay down a grove so from there i can measure out where my holes have to go. So then i can drill and tap the hub.

Thanks guys

[GTRPSI]

PCD114 is a 114mm circle diameter......

PCD means Pitch circle Diameter.

Look below.

http://whichwheelsfit.com/index.php/pcd-explained

[rcs_888]

I understand pcd and that the rough way to measure is from outer of one stud the the centre of the adjacent stud but that doesnt actually give you the diameter so for a 5x114 the studs arent actually in a 114mm diameter circle? Im confused its too late lol ill grab the verniers tomorrow and have a play

[Ben C34]

Diameter is diameter.

Based on your measuring method you don't understand what pcd is. Google it.

Mark a 114 diameter circle and drill your holes on that. Seems pretty dodgy to me..I would prefer to use a mill with a digital read out or an indexing head, or a cnc .

Edited January 4, 2015 by Ben C34

[jiffo]

Wheels mount on the centreing spigot, studs simply hold wheel onto hub, spigot does the work.

Studs are set out using an indexing head.

PCD is 114.3 (4.5")

[Ben C34]

I was happy to ignore the .3 for now.....

How far out of you think the studs can be out before it matters? I know the spigot takes the load, but realistically if the studs aren't all correctly on the pcd they will be getting flexed slightly sideways.

No way would i simply scribe a circle and then drill for studs.

Edited January 4, 2015 by Ben C34

[jiffo]

In these metric days we forget the origins of many measurements, hence the 4.5" reference.

[rcs_888]

I inderstand pcd guys. I can tell the difference between my bmw wheels and my skyline wheels and that the bmw is 5x120 and nissan is 5x114.3 so what i want to do is fit the skyline wheels to the front of the bmw and that means that the studs dont meet up yes the centrebore measurement is the same so thats fine but im not loading up studs and just ratling them on that just asking for failure. What im trying to workout is if you get a sheet of metal and scribe out a circle what does the diameter have to be to meetup with the holes on a 5x114.3 stud pattern. Doesnt matter i have answered the question myself lol and ill update this as i do the wheel hub. So this is a 114 diameter circle and that goes through the cross section of each stud so ill clock up the hub in the lathe to the centre bearing mount then come out and spin a line in it at 114.3mm diameter and then split it into 5 sections so i can then drill the hub. Hopefully its starting to make abit more sence now

[rcs_888]

This is how u can measure to get an idea if u have 5x100,5x114, 5x120 etc....

[rcs_888]

[Ben C34]

You can't say you understand pcd and then ask the most fundamental basic of what it means. Pitch circle diameter.

Any way, good luck with it.

There's a formula for figuring out what to set calipers to scribe a circumference into equal segments. Can't remember it cos never had to use it, but it would help you. Even though like I said it should be done to Co ordinates or using a dividing head.

I know a guy in holden hill who would charge stuff all to do it properly if you want.

[warps]

What scares me is that you're allowed loose on a lathe. If you can't grasp the basics of a PCD then how the hell can you even work out how to start a lathe, let alone set it up for machining?

I think I grasp your original problem - you can't get a 114mm by measuring across any of the studs on a 5x114 stud pattern. That's because none of the studs are diametrically opposite, so you're always measuring one of the sides of the triangle but not the hypotenuse.

To calculate your PCD by measuring across 2 of the studs on a 5 stud pattern is as follows:

D = Measured distance between centres of 2 studs "opposite" each other (ie not 2 studs next to each other)

PCD = PCD (DUH)

PCD = D / cos (sin-1(sin 36)/2)

Or to make it a bit simpler:

PCD = D/0.9558

So, for a 114.3mm PCD, the longest measured centre distance between any 2 studs (for a 5 stud pattern) would be 109.25mm

For a 120mm PCD the measured centre distance will be 114.7mm

Now if you're measuring between 2 adjacent studs, then the calculation will be:

PCD = D/sin36 (much simpler calculation)

or

PCD = D/0.58779

HTH

Edit: just looked at the image you posted above. It's a reasonable approximation, as it allows about 6mm for a 12mm stud. In reality, the measured distance will be between 5mm and 6mm smaller than the actual PCD, so this method is a fairly quick approximation (though it probably wont be accurate enough to tell you whether it's 108mm PCD or 110mm PCD for example, and certainly not accurate enough for machining purposes

To answer your question, forget about any measurements you've taken, as they won't tell you anything without applying some maths. These measurements are just confusing you, so throw the verniers away.

Set up the lathe to scribe a 114.3mm diameter circle. Then you can mark the positions on this (5 equidistant positions) and these will be your stud centres.

Much more accurate to do it on an indexing head on a drill or mill. I'd be happy to manually drill brake rotors (have done this plenty of times) but actually drilling and tapping for wheel studs I'd want a bit more accuracy.

Edited January 5, 2015 by warps

[rcs_888]

Shouldnt be allowed near a lathe! Cheers dude i work in a fabrication workshop and i use a lathe and mill a fair amount so thanks for that vote of confidence.

Im sorry that im not the smartest cookie in the class and im sorry that to you this was asking a stupid question but my issue was the fact that when you measure opposing studs you never actually measuring a circle. The information that you have kust given is what i have been trying to find.

So thanks guys i appreciate being told that i have no idea. I may not be able to explain what im after well but im sure not an idiot like you guys are assuming so thank was joining this forum hoping for help from members not what i seem to have gotten

[Ben C34]

Lol

[warps]

Haha settle down - just a friendly dig. No need to get upset (wasn't calling you stupid, either). But yes, your question did surprise me a bit, given the machinists I work with usually have a fairly good grasp of measuring stuff - in fact I've been taught a lot of tricks over the years by some of the older machinists I've worked with.

Don't let the abrupt manner of some (myself included) put you off - there are some smart cookies here, with great advice from time to time. Sometimes you just have to wade through a bit of crap to find it.

[rcs_888]

Yeah unfortunatley i have been brought up in a family of noone mechanical and have no mates mechanical and so far i have managed to teach myself everything to build my BMW and now im trying to teach myself about the skyline. The BMW forums i have been on have been massivley helpfull as ive never had anyone teach me anything my whole life has just been reading and trying to do it myself and ive had alot of fails but ive also managed to build this over the past 2 years

I have also bagged the front but trying to get it another 15mm lower so trying to go from 19x9.5 fronts to 18x9.5 fronts to get the sils down and level. And unfortunatley i have a set of 18x9.5 wheels in 5x114.3 and cant afford to buy wheels but i do have the time to experiment with drilling front hubs to the different stud pattern

[niZmO_Man]

Good on you for trying and doing stuff/learning.

The circle should go through the centre of the stud/hole so just set a compass to 2.25 inches and draw a circle?

Looks like you already did that.

[Ben C34]

No worries man. We are all happy to help.

It's hard to get an idea of what people are really thinking on here!

Keep on writing decent posts and people will always help. It's guys who write short, poorly written posts requesting help who are annoying!

Car looks sweet.

If you have access to to a mill use that for the hole positions to be sure.

[warps]

Another option if you only (!!) have a lathe is to use the wheel as a template to redrill your hub. Knock the old studs out of the hub, and if the hub is a snug fit into the wheel (centre bore) then you can set the wheel onto the hub and use the bolt holes to locate the new stud holes. For this, I'd make up a set of mandrels that go into the bolt holes (machine them up on the lathe out of some 4140 or old grade 8 bolts if you have any big enough lying around). These can either be used as a guide for the pilot drill bit, or sharpen the bottom and use them as a centre punch to give you the location for the stud holes.

Make the mandrels nice and snug in the wheel holes (light tap in fit is better - about 0.001" - 0.002" clearance) so they locate exactly in the wheel holes. Also make sure that nothing can move as you go from one hole to the next so that none of the holes move out of the pattern

A bit of stuffing around, but more accurate than measuring. I always find that measuring and executing are 2 different things.

[djr81]

Why not a brake rotor or just the hat?