Changing Wheels For The V8

Just to clarify, is this how we're all measuring offset?

offset.gif


Edit: Found a more detailed diagram here.

WheelOffset2.gif
 
Good diagrams Paul! Yes, that's how I'm measuring. The bottom diagram does emphasise how unhelpful backspace is - doesn't include the tyre overhang for one thing. On the P6 it's "frontspace" if such a term has ever existed, that is the critical dimension, I've not found a wheel yet that's capable of getting the tyre near to the back of the mudguard etc!

Chris
 
So the backspace measurement on it's own is useless, but when you know the overall rim width it can be used to work out the offset very easily. Out of pure curiosity I might measure my own wheels later if it stops raining.
 
Offset is a function of backspace and overall rim width. In isolation both backspace and offset are indeterminate hence the need to know rim width. With a constant backspace and an increasing rim width, offset will reduce.

I would be very interested to know all three from your wheels Paul. Fingers crossed it stops raining for you!

Ron.
 
On the contrary, Ron. Offset is extremely useful on its own. This is cecause it sets the centre point of the tyre - which is what you are really interested in. The ideal offset for the P6 rear mudguard area is aready established at 44mm +/- 2mm. This derives from the Denovo tyres which were fitted as an option in the mid 70's. They were the widest tyres ever fitted to a P6 at 205mm at the standard diameter, and even then, occasionally needed the D post fettling to get them not to foul. knowing this you can confidently assess the likely difficulties with various wheel types. From this point on the rim width becomes irrelevant to the fouling issue, albeit must still be selected to suit the chosen tyre size. ie a 7" wide rim wearing 205 tyres will leave the tyre sidewall in exactly the same place relative to the foulling points as a 5.5" rim wearing the same tyre, provided they both have the same offset. The difference is then down solely to the sidewall shpe on the two wheels, on the 5.5" rim a 205 tyre will be extremely bulbous and prone to roll off the rim under cornering, on the 7" rim the beads will be rather stretched and you risk deflation and a very hard ride.

Chris
 
I tend to agree with Ron, knowing the rim width is essential really, otherwise you have no idea of the overall width of combined tyre/wheel. And once you know the rim width it doesn't matter if you have backspace or offset as you can calculate one from the other.
 
this: http://www.jegs.com/i/Percy%26%23039%3B ... 1/10002/-1

is quite handy for simulating wheels and tyres - haven't used it yet on my p6, but I did on one of my Mazdas, worked a treat. Might be of use to us for measuring things?

Surely American Racing or one of the billet wheel mobs in the states would be interested in doing a batch of suitable p6 wheels if some of us organised a group buy?

Failing that, are there any other suitable mag wheels out there in a different PCD that don't require bodywork? Maybe getting the wheels re-drilled or the Rover stud pattern changed to something else is an option...
 
chrisyork said:
Richard and I have a difference of opinion on measuring offsets - your measurements agree with mine - so Richard's quoted offset to be treated with caution (sorry to resurrect this Richard :oops: ).

Chris
Click to expand...

:D

I think we have the same way of measuring them Chris, but got different answers on the steel wheel in Sparky's boot.

The Minilite was 30, (I checked with Minilite) and the Vitesse is 40, (I checked with Rimmers and it actually states it on the wheel) so I can only surmise that the spare wheel I had, was off a 2000, or a different car as it was 40.

To reiterate, IIRC Chris maintains that the standard offset on a P6B is 53, but I measured my spare wheel at 40. Either way, the Vitesse wheels are a lot closer than the minilites, and do make a difference to the handling of the car.

Richard
 
Could someone please tell me the diameter of the grease caps, (both across the flange and around the base just above it) residing on the front hubs? Rather than pulling a wheel off I thought that I would ask first.

Thanks in advance,
Ron.
 
The Minilite Sport in that size still has in my opinion an offset range which is too small. Ideally with a 6.5" I would be looking at an offset of 40mm or a touch more. Enter the Minilite EV2000 which in that width has an offset range of 32 to 52mm. That will allow the perfect wheel to be obtained for the P6 in terms of offset, provided of course that the correct stud pattern is available. If not, the bolt holes can always be welded up and new holes drilled in the correct place by a suitable wheel modifying business of which there are numerous in Australia. If the hole in the centre is also of the correct size then they will be one to consider.

Ron.
 
^ it was your thread I was referring to Chris!
So if you ran 15x6 Fuchs alloys with something like a 185 or 195 tyre, would you still need to alter the D post or other bodywork?

There are some other problems with the 5x130 pattern, again it's one that apart from porsches, it doesn't seem to be popular and 15x6 Fuchs wheels are thin on the ground in Aus by the look of it.
 
Well I reckoned the mismatch was about 1/2". So lets say those Fuchs would be OK with the D post moved about 10mm to 15mm. The tyre size - 205/55 X 16 - on them isn't too far out for diameter, so it is a real comparison. Since the first number, 165 etc, is the width of the tread in mm, all you have to do to get a rough idea of the maximum tyre size without mods is subtract twice the mismatch from the tyre size currently. So if the error is 10mm that takes a 205 down to a barely acceptable 185. If the error is 15mm.... Unfortunately the photos are on the side of Lucky that I have already moved out to the maximum I am comfortable with, so the remaining mismatch is going to be hard work to lose.

Chris
 
SydneyRoverP6B said:
I would be very interested to know all three from your wheels Paul. Fingers crossed it stops raining for you!

Ron.
Click to expand...

As requested the measurements of my Minilite wheels:-

Diameter 14"
Measured overall rim width, 178mm
Backspace, 125mm
Offset, 36mm
D post clearance at ride height is about a finger width with a 195 tyre.

Stamped into the rim next to the width and diameter is VR35 which I assume means 35mm offset.

I'm not sure I understand how different offset wheels affect the handling of the car though?
 
You must log in or register to reply here.
Back
Top