wheel offset/spacers

[Davidppp]

Hello all.

The search for compatible wheels continues.

The early Saabs used the 170mm PCD and will fit, but are hard to find..any ideas please?

Also, can we ft thin wheel spacers to assist us using the 7/16 studs from old Ford..much stronger than the ancient 3/8 rusty one which are snapping already.

I reckon 8mm will be enough..we are running standard wheels with Avon Turbospeeds.

At some point wider track is bound to create body fouling issues..how wide can we go?

David

[Keith Clements]

I use Land Rover studs which are much stronger but require opening out standard holes in the wheels but NOT the drums.
For the rally wheels that have been widened and have offset so I can adjust contact patch/king pin alignment using spacers made from disks of 2 mm aly. I have up to 6 discs inserted. The widened wheels give a superb flatness to the tread, probably doubling the contact patch area.

Alloy wheels are available made to order but at a price. See Richard Gane and Julian Crossley race cars.

Please note that you should only tighten standard studs to 50NM. Must garages severely stretch Jowett studs with twice that torque.

[David Morris]

Hi David,

You ask about spacers and whether their use would cause fouling of wheel arches?

I can only speak for Javelins. I reckon you would only need to worry about the rear wheels. The clearance between the tyre and the wheel arch rims is narrow and further compounded by the possible 'off-centre' location of the rear axle. The 'centering' of the axle is, I believe, mainly controlled by the Panhard rod, and that in its self is a pretty flexible location, depending on the condition of the end rubbers. These do perish and need to be replaced when worn or just plain tired.

I completely endorse the comments made by Keith regarding the torque applied by tyre fitters. Don't let them near your Jowett!! Their 'windy hammers' apply a massive torque and although they will say that they use torque wrenches, in my experience they use a torque wrench AFTER tightening! Of course the nuts are tight enough, in fact they are near shearing!

That's why, on whatever car you are using, trying to undo a wheel nut by the roadside is almost impossible. I carry a long breaker bar in my modern. I tighten my Jowett nuts myself, and really all you need is for them to be reasonably tight. My Jowett handbook for the WW2 stationary engine uses two nice Jowett terms for tightening nuts on the engine, either 'Tight' or 'Dead Tight'....!!!

Take care,

David

[Keith Clements]

I doubt if you will find ANY wheels that are compatible, but please let us know if you do.
On a Javelin there is very little room for error in the location of the rear axle. Probably only 2 cm either way will cause fouling of the arches. With wider tyres there is no room for error and forceful cornering will cause rubbing. On the front you may also find the wheels rub on full lock and full bounce with a slightly larger tyre.

All my wheels have been welded around the stress points to stop the cracking. On one Monte Carlo Rally we had to cut the knobbly bits off our mud/snow tyres because they fouled the arches just before the start in Holland.

see CAD

[Davidppp]

Thank you both, very much.

We can therefore go up to about 10mm using standard wheels on the Jup. without fouling, if I am rightly interpreting?

The Landy studs are certainly beefy enough..16mm!!

We already have a full set of the 7/16 studs and nuts, from Grayston, so ideally would like to use them..but the knurled portion under the head is 8mm longer than on the original studs and sticks out of the drum by 8mm ..so either we counter bore the nuts or we fit 8mm spacers.

Looks like we can go a LOT wider on the back, but not so sure about te front and also dont want to upset the streering geometry too much.

Can we fit 8mm spacers with standard Jup wheels?

Kind regards
david

David

[Davidppp]

PS.

I have read that the PCD of the wheel studs is 170mm..measuring it comes nearer to 190..which is correct, if either!?

David

[Keith Clements]

See the CAD drawing in my previous post. 7.375 inch

The spacers I use are to get the contact patch at the correct point NOT to widen the track. The steering will be heavy and not give good road holding if the contact patch is not bisected by the king pin inclination line. Camber and castor are very important to get correct.

The width of the tyre is very critical as it will rub on the top suspension boots or the bonnet at the front and the wheel arch at the rear. Back axle travel on cornering is also a factor and depends on condition of panhard bushes. Note, under load, things move.

I am afraid it is a case of trial and error.

[Davidppp]

Ah! Thanks, Keith. I had missed that link you provided..just the job.

What great resources you have assembled here!

David

[Keith Clements]

I currently have 10mm of spacers with standard wheels on the rear with no issues. The same on the front gives heavy steering.
I am currently sorting vibration issues which may be due to the refurbished wheels that have been welded up to stop cracking.
I will probably revert to the known good wide 16 inch rally wheels or 15 inch (ex SAAB modified) racing wheels to confirm.

[Davidppp]

Long delay, sorry.

Current proposal.

Use new steel rims, which are available in 16 by 4, chuck to part off centres, and machine concentric inside with an abutment on the wheel well. .
Laser cut then turn ali 6 series discs to shrink fit inside rims, drill countersink and tap maybe 20 M8 socket screws through steel into ali to join.

Make a drill guide, (thanks Drummond!), registering on machined inner of steel rim, with hardened steel drill guide bushes for 18mm od 60 degree centre drill, for 7/16 wheel nuts then another bush, 15.5mm clearance hole for studs.

Quite a bit of work.

What advice and critique can people offer please?

I know we have plenty of advanced engineers here.

Kind regards
David
David

[Davidppp]

PS My very amateur guesstimate is we need a 15mm thickness of ali at the rim to centre joint, and maybe 18 at the wheel stud fixings.

But I suspect this is very overengineering it.

An alternative would be a step drill..but I dont know where to get them in UK...

David

[Keith Clements]

Few things to consider.
Make the wheels with an offset that can be adjusted with shims.

Mixing aluminium and steel may cause issues with the difference in thermal expansion. On my rally wheels a steel disk was welded in the centre, This is also a lot stronger.

A steel disc may well be lighter than aly with all its fixings.

If aly is used I would think it would have to be a high tensile alloy. Do not underestimate the forces on a wheel . They are considerable and most steel wheels flex. Modern alloy wheels are very thick and the forces are absorbed through CAD designed structures.

Consider insurance implications of modified wheels. They will have to be declared, even though they are probably safer than the originals.

[Davidppp]

Thanks, Keith.

Ali steel composites are not new, although currently out of fashion.

The D type used them, then in the sixties the Reliant scimitar and others.

Dunlop made them.

The idea is to freeze the ali centre,to give say 40 degrees difference in temperature, and this equates to about 0.3mm over the 16 inch of diameter.

So we'll machine the parts to an interference fit of ten thou at room temperature. Steel expands about half as much as ali so should be ok..

Good point about offset, I plan to use shims as you suggested.

The main reason to choose ali is stiffness, and ease of machining and fabrication..

A steel centre would be easy if laborious to weld, but the distortion might be an issue..and it would need to be quite thick to be equivalent in stiffness or strength to 18mm of 6 series ali, which is quite strong.

I had not considered any insurance issue..the car is already modified..

David


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