Changing Wheels For The V8

SydneyRoverP6B

SydneyRoverP6B

Well-Known Member
Staff member
The OEM steel wheels that I have along with my Rostyles both have a total width of 166mm, backspace of 132mm and an offset of 49mm. Since 1987 I have been running 205 section tyres, with clearance between the D post on the o/s being closer than the n/s.

So, if I were to go to a wider aftermarket wheel but continue to run the same width tyre, then in order to offer the same support to the bearings, uni joints etc and to minimise possible steering changes, would I not need to run wheels with the same backspace? The offset will reduce as the wheels width increases naturally, although if I were to run the same offset, then the backspace must increase which brings the tyre in closer to the suspension components.

Here in N.S.W, the track in order to remain legal must not increase by more than 25mm.

Chris, I would especially welcome your views on this matter.

Ron.
 
The wheel needs to increase in both directions at the same rate, i.e. use a wheel of the same offset

So if you increase the wheel width by half an inch (lets call it 13mm), you would have a back space of 138.5.

Minilites in the UK have an offset of 30 btw, which is why I removed them

Richard
 
Hi Ron

The difficulty with using backspace as a measure is that it only tells you about the position of the rim of the wheel relative to the suspension etc. It tells you nothing about where the tyre finishes up. And you have already noted that the tyre is your critical dimension. So, to maintain the tyre that you currently use in the same position in the wheelarch you need to match the offset of the wheels you currently use. No matter what the width of rim, this will leave you with the same clearance at both back and front of the tyre as you currently enjoy, and it will leave the track unchanged. This is to say that offset is all about the centre line of both tyre and rim. And It's the centre line you are really interested in.

I'm actually quite surprised you are managing to run 205's without fouling issues - remind me what the diameter rim and aspect ratio are - or in other words are you running under diameter tyres and if so by how much? If you ever wanted to increase tyre diameter back to oe spec, remember that the tyre widens rapidly fom its maximum diameter as you go down the sidewall, so an under-diameter tyre does give you more space to play with against the D post. You do have a little leeway from where you are now by moving the offside D post sllightly. As often discussed, you can insert a scissors jack between D post and boot sidewall and get the D post to move outwards by up to about 15mm completely without drama, some have gone as far as 25mm, but at that you might have to adjust the door shut.

So to what you can get that will fit. If you are allowed up to 25mm track increase that means you can reduce the offset by up to 12mm per side. So your pssible range of wheel offsets goes from 49mm to 37mm - that's why I'm reasonably happy with SD1 Vitesse cross spoke at 40mm. But every time you come down on the offset you increase the risk of having to "modify" the D post. I wouldn't be inclined to increase the offset, as my knowledge of the Vitesses wheels suggests you are already as close as you can stand to the boot side wall etc with the back of the tyre. To check jack the car up so that the wheels and suspension hang - ie narrowest track, and see how much clearance you have then. Note that the rear track changes according to suspension compression - fully extended is narrowest track and fully compressed is widest track. That's why the critical test for a new wheel and tyre fitment is roundabouts well heeled over! The state of your back springs is also a key determinant of what you can get away with. Factory ride height allows the narrowest offset, anything less than that implies needing a D post mod or larger offset wheel.

Hope that helps.

Chris
 
Sorry to jump in here with a question for Chris, but seeing as I haven't seen the underside of a running P6 for quite a while I have a question....

Shouldn't the factory setup be such that the driveshafts lie virtually straight and level (i.e. at greatest track) when the car is in a stationary un-loaded position ? Thus avoiding excessive losses through the UJ's.

The only reason I can see for not having it setup so is to avoid collisions between brake discs and road, and maybe that answers my own question :LOL:
 
Hi Rick

No, the driveshafts lie at a considerable downwards angle from the diff to the hubs - ie the diff is much higher than the hubs. This is clearly to allow clearance for the discs - you may remember that the Irish rallying P6 actually bottomed out onto the discs recently and destroyed a disc.

This has one major drawback in that the hook joints (UJ's in common English) are running at an angle and the rotational velocity therfore varies cyclicly. This did cause problems during the car's development with vibration. There were a number of changes to compensate for this, one being the substitution of hollow driveshafts for the original solid ones. I've wondered whether it is now possible to substitute constant velocity joints for the hook joints, but I can't think of any other vehicle that transmits lateral loads through cv joints, as would be necessary in the P6 - remember that the cornering loads pass up the driveshafts into the diff. The 2200 had a new design of diff rear mounting using a voided bush, which I suspect was also designed to tackle this issue. This bush didn't spread to the V8 though, so I suspect they are not as tough as the normal solid rubber type.

Chris
 
CV joints can't take side loads by their nature, the inner and outer races must be allowed to slide relative to one and other or else you'd be back at the same problem of the angle change altering the angular velocity.

Can't help on the wheel spacing issue though unless you want me to take any measurements from my wheels?
 
I ought to add, Ron, that 14" rims have the unfortunate side effect of a very poor choice of tyres. This was my main motivation for fitting the SD1 Vitesse rims - they are 15" and allow a much wider choice - as, I imagine do larger sizes. It is not evident looking at the car that the rim size is larger at 15" - the tyres are still quite bulbous at 205/65 X 15, so the car looks "right" on them. If you are going to the trouble and expense of sourcing wider alloys, then I really would recommend going up at least one size on rim diameter. The Vitesse rims would not be my first choice, I finished up in them because they were readiiy available and (relatively) cheap.

Chris
 
Hi Chris,

Appreciate your reply... :) My 205 tyres have an aspect ratio of 70, so as close to the original 185/78 or 185/80 in terms of rolling radius. Very true on the 14" tyre selection that is currently available, they have almost disappeared, in 205 section at least. Michelin have stopped production of the XM1 tyres that I have been using for quite some years, and they are not offering an alternative in that size. Goodyear has done the same. The only tyres that I can source locally in 205/70 are from Toyo in a T rated offering and from Maxxis in a H rated offering. The latter I have purchased a set of for use in the coming months.

I am investigating alternative wheels at present (quattro and TokyoP6B have both been extremely helpful, thanks ever so much gents). The downside of using the Vitesse wheels is the need to change the studs to metric and I would still like to be in a position to use my Rostyles for Rover display days etc, so I imagine sourcing suitable chromed nuts with metric threads would be more than difficult.

Ron.
 
No worries Ron1

Don't some of the Amrican wheel makers do something that looks very much like a Rostyle in 5 X 5 stud [attern? If you cooould get those in the correct offset they'd look the part?

Chris
 
Hi Chris,

Cragar make some lovely looking wheels, but unfortunately the offsets available are either negative or those that are positive are too small. While increasing the track by more than 25mm from running wheels with an offset that is much too small may be illegal here in N.S.W, my main concern is the increased load placed on the wheel bearings, ball joints, suspension components and the change in handling that such wheels will promote.

These wheels....http://www.cragarwheel.com/wheels/?id=3&first=0&fid=1 I really like the look of. Almost a modern day Rostyle, but even though it says that custom builds and backspacing options are available, upon emailing them I was advised that none were offered.. :( Only those listed are available.

Ron.
 
I've had a hard time trying to get suppliers to confirm what sizes they can make vs cost.

Had a thought the other day, what about those Dunlop Alloy wheels that Jaguars and the Rover BRM team used?
 

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Hi Geoff,

Yes I did, sorry for the delay in replying. No go I am afraid.. :( they do make a range of offsets, but the largest is 24mm positive which means that on a 6" wheel the backspace is 113mm. The track thus increases by 50mm give or take making them illegal everywhere in Australia when fitted to the P6. We could probably get by with that, but the changes in steering geometry and the increased loading that the bearings etc will be subjected to I am not at all happy about.

I did ask as to whether they could custom make some with an offset of 49mm give or take but was advised that at $20,000 for the cost of a die that would not be happening any time soon. As for increasing the offset with their existing wheels, that is a non starter as well as the wheel would no longer be strong enough nor would it meet the required Australian safety standards.

So looks like we have to keep looking....

Ron.
 
Interesting, because

a) when I went to the tyre place where I got my 14's from, with them doing a lot of prep work for rally cars and muscle cars for the Biante series, quite a few of them run Superlight wheels (as does the guy I know there on his racing XW Falcon), so he made a call for me to Performance Wheels and they literally said "yep, no problems".

b) at the Dyno day, I was chatting to a Rover club member who told me that Bob Jane in Bendigo sourced him a set of 15in Superlights for his p6b, I'm assuming that they've just ordered Superlights in. So that means his wheels must not be an ideal fit either.

Maybe the supplier that DamianZ28 went through for his wheels (viewtopic.php?f=21&t=8425&start=165#p83729) could assist?

What type of wheel were you thinking of Ron? If all else fails I think I'll just get my Rostyles repaired.
 
Hi Geoff,

These are the wheels I am referring to.....http://www.performancewheels.com.au/Hom ... at=Classic

The 15" X 6" is available in a range of offsets from 3mm to 24mm positive. I spoke to Ray at their Sydney office who appeared to know the P6 quite well. He said that the 24P offset was the wheel to use. I also phoned the Head Office in Adelaide and was told exactly the same thing. I passed on the information that you had been provided with in that these wheels were available with custom offsets to which he said "yes, from 3 to 24P and anything in between". He said that offsets greater than this are not possible as the design of these wheel precludes any further increase. "To offer greater offsets would require another die to cast the wheel which would cost $20,000, so that won't be happening any time soon" he said.

Ron.
 
Ron, I wouldn't get too concerned about bearing loads and tracking just yet. Your main challenge remains to get something that will go inside the rear arches! If you achieve that, then bearing loads etc will look after themselves, because it will be very close to standard offset. Unless you were planning on a major chop operation on the rear D posts?

I'm afraid I have no concept of what 113mm backspace looks like or how it would affect track, but I can assure you that 24mm offset won't go near the rear arches!

Chris
 
Hi Chris,

I appreciate the link that you kindly posted, the only downside though is that those wheels are also 14".

The difference between the standard V8 OEM steel or Rostyle wheels and the Superlite wheels that Geoff and I are talking about is,...the latter are 0.5" wider with a reduction in both backspace and offset of 19mm and 25mm respectively. Richard (quattro) said that when he purchased Sparky, he was fitted with Minilites which had an offset of 30mm and consequently the steering didn't feel right, so he took them off. I am going to have to do more homework.. :?

Ron.
 
In addition Chris,..a reduction in offset of 25mm or so, would the tow in and / or camber need adjustment to compensate? I understand that the scrub radius will change, but I don't know what affect that will have on handling, braking etc.

Ron.
 
I simply wouldn't go there Ron. 25mm off the inset will have the car simply look wrong. And there's no way you will get them inside the D posts without significant mods. 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
 
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