Correct offset when changing Beta wheel rims and converting to wheel studs

[mangocrazy]

We've (at last) made it to the moneypit house in France, and been reunited (after nearly a year) with the Beta Spider. One of the things I intended to do was to measure up the standard wheels/hubs with a view to converting from wheel bolts to studs, and do the same for the 15" Thema wheels and larger 284mm discs I'm intending to fit (at some unspecified time in the future).

I'm also aware that I need to consider wheel offset in this conversion, even though I don't have much idea of how it works (wheel offset isn't a 'thing' on motorbikes, you just have to make sure they're in line...). So here are the measurements I've taken. for the standard OE beta hubs/discs, I've measured the two as one piece - I had no desire to do battle with rusty discs/hubs to separate the two. For the Thema, everything is separate and in boxes, so it's an easy matter.

Beta 14" wheels:

Marking on wheel: - 5¹₂x14H2-34
Combined depth of hub and brake disc: - 23mm
Wheel mounting hole depth (to top of taper): - 17mm

Thema 15" wheels:

Marking on wheel: - 6Jx15AH2-37
Depth of hub: - 12mm
Depth of brake disc - 6.5mm
Wheel mounting hole depth (to top of taper): - 17mm

I'm assuming that the last two characters of the marking stamped on the wheel refer to offset (34 for Beta, 37 for Thema). What does this tell me? Also, it appears that the mounting flange on the (Ferodo) brake disc I've bought for the Thema wheels is substantially thinner than OE Beta (I'm making the assumption that Beta and Thema hubs are the same depth here).

From the above I'm guessing that I will need a spacer between wheel and disc, but the question is, of what depth? If it was purely a matter of keeping the centre line of the wheel the same distance out from the hub in both cases, then a spacer of 4-5mm would seem to be indicated for the Thema setip. But how does the different offset play into this?

All advice gratefully received...

[WestonE]

Hi Graham

Head for the Compomotive website which has a nice explanation and diagrams. For mounting the 284 discs I used Integrale hub centres in place of the Beta ones fitted to Beta. They locate the disc perfectly and they are in perfect condition. But they are spaced further out counteracting the thinner Integrale disc. I also used SKF Integrale bearings because they are great and very easy to buy. After a lot of testing and measuring including with a 7x15 ET30 wheel and fitted tyre. I have 13mm front spacers and no rear spacers for running 195 x 55 x 15 Yokohama AD08 sticky tyres. I have rolled rear arches for improved tyre clearance.

NB the beta track is narrower at the rear than the front by 10mm from the factory on later cars and 14mm on earlier cars. OE cars used 5mm spacers all round.

Enjoy!!

Eric   

[mangocrazy]

Hi Eric,

Thanks for the pointers and website - I've had a look at the tech info and diagrams and can conclude that I should have asked this question before putting tyres on the rims...

I'll do the measurements tomorrow rather than with half a bottle of good French red inside me. 

Given that I will need spacers of some description, I assume that the spacer(s) will fit between disc and wheel? This has the twin benefits of giving more caliper to wheel clearance and keeping heavy components as inboard as possible. I intend to follow the path of least resistance and use equal size spacers all round, unless there are good reasons not to. Please correct me if my reasoning is faulty.

[WestonE]

Hi Graham

You will need to compensate for the narrower disc thickness with the Integrale discs with thicker hub centric spacers otherwise the logic is fine. Start from the back with what will clear the arch and the strut then look at what you need to match it at the front.
BTW search Fiat 500 wheel spacers on ebay and go alloy as weight matters with suspension.

Eric

[mangocrazy]

Hi Eric,

Thanks again. I was definitely intending to use alloy spacers; motorcyclists understand the importance of minimising unsprung weight... The thought occurs that the back wheels will be simpler to fix than the front, as I'm only changing rims/tyres and retaining the perfectly satisfactory (for my purposes) OE rear brake arrangement. So for the rears it's just a case of catering for a change in wheel offset. However I might take the opportunity to space the rears out slightly to more closely match the fronts visually, although it's not of great importance to me. Tyre sizes (F & R) will scarcely change with the conversion. I'm going from 185/65 R14 to 185/60 R15 tyres.

Your tip on searching for Fiat 500 spacers yielded a wealth of results - many thanks.

Graham

[flex]

I've looked into wheel options for the beta. Main restriction is strut assembly clearance at the front: both the strut and the bolts to the hub carrier. there are issues or clearance of the wheel spokes of the caliper depending on the design (though standard does not give much space compared to many).

The factory setup is a 14x5.5" wheel, offset [ET]34mm, using a 5mm steel spacer bolted to the hub (that holds the disc on and gives enough clearance for the caliper from the back of the spokes) resulting an effective offset of 29mm. Not sure why they didn't use a wheel with a little bit more material on the hub face to give it the correct offset and clearance so that the spacer isn't required... The inside lip of the wheel is only a few mm clear from the hub/strut bolt area. any deeper in and there is a good chance you will foul this. Not all wheel are exactly the same shape so clearance might vary slightly depending on type.

if you go to 15"  or bigger wheels, the inside lip sits clear of the hub, so your restriction becomes the strut alone. This probably means 5-10mm more clearance than 14" wheels.
A maximum sensible size is probably 15x7 ET20 - enough clearance inside, but doesn't poke miles out. The Thema Wheels ar 15x6 (I think) ET37, so should just be safe?

Arguably, any change in offset will change the geometry and steering feel. It probably wise to not deviate too far from the standard, but generally fitting wider wheels mean you have to reduce offset to avoid inner clearance issues.

Once you start changing hubs, discs and calipers it all changes - but I you should aim for keeping the wheel centreline close.

http://www.betaboyz.myzen.co.uk/forum/index.php?topic=1059.0

Useful calculator and example
https://www.willtheyfit.com/index.php?width=185&aspect=65&diameter=14&wheelwidth=5.5&offset=34&width2=185&aspect2=55&wheel_size=15&wheel_width=7&offset2=20

[mangocrazy]

Many thanks for the information, I'm slowly assimilating it...

I've been using some offset calculators avaiable on the interwebs and am probably now more confused. I get different results depending on whether the calculator asks for rim width or tyre size (see below). Calculation based on rim/wheel size is first, followed by the calculation based on tyre section:

[mangocrazy]

And just to complete the set, I found a calculator which required me to enter both rim/wheel sizes and tyre sizes. These are the results:

[WestonE]

Hi Graham

When I did this with a 7x15 ET30 Azev A wheel I had an old 205 x 50 x 15 tyre fitted for £5 and used an assortment of bolts spacers and washers with the springs removed from the struts so I could move the wheel through the full range of motion for arch clearance checking. Remember some tyres project beyond the edge of the rim as is the case with 205 on a 7x15. You also need to be sure your bolts fully engage in the hub threads without jamming on the hub. Remember decent McGard Locking wheel bolts come in a couple of lengths only and cutting them down is a pain.

Also consider and try your spare if it is a space saver because some steel ones come with a thick spacer or are a thick casting like the Integrale Alloy one which need longer bolts! This is great if it matches the Thema wheels depth of bolt engagement.

I bought another space saver with a perfect larger tyre and switched it over to a Fiat spacer saver which has no spacer welded on so the car is not down on one corner with a spare fitted and the spare fits in the boot!   

I will run with 195 x 55 x 15 AD08 Yokohma and I know the Azev As clear the R132 6 front Caliper. I fitted 6 x 15 Thema Wheels to my previous Spider but have no records of the bolt sizes or spacers. 

Currently the car is on my trailer space saver set done so the car will go on narrow trailers until I am ready to get the real wheels built up.

Eric

[mangocrazy]

Hi Eric,

As you and flex point out, the only foolproof method is to fit the wheels and measure up, so I'll be doing that in the next few days/weeks. I think I've made life a bit easier for myself by going for conservatively sized tyres, but it had completely escaped my notice that Betas had spacers fitted as standard. Every day's a school day. I have a full set of 5 Thema wheels, so I don't need to worry about different dimensions of a space saver spare. I'll be measuring up thread lengths needed, as I intend to convert to studs with the new wheel/tyre/brake/hub arrangement. I'm using Thema hubs at the front and they are 12mm deep with some fresh air behind before contacting any other metallic components.

I'm planning on starting with the rears first as there are less variables involved. I'm only swapping wheels/tyres at the rear, whereas at the front everything from the uprights outboard will be different. It's going to be 'interesting'. Another concern is whether the 4 pot front calipers will fit inside the Thema wheels without fouling, but that's a matter for another day.

[mangocrazy]

Bit of a thread resurrection, but I've finally got down to figuring out the length of wheel studs I need to accommodate the Thema 15" wheels, offset spacers and different brake discs on the front. And the answer is...

75mm (F) and 74mm (R).

So somewhere between 75mm and 80mm, depending on what I can get hold of. As the Thema wheels are only 6J (compared to the OE wheels 5.5J) there is more clearance to play with than if I'd gone for 7J Integrale wheels. In the course of measuring everything up I also realised that the spacers I'd bought are lacking the bolt holes to mount the spacers to the disc and hub and the front spacers need the lip that fits inside the wheel machining down to suit.

So at least I've found a couple of potential gotchas and can take the spacers back to the UK (I'm in France at present) and get them machined/drilled to suit. Unfortunately that's all I've been able to do to the car, as work on the house has taken priority.

[flex]

Bit of a thread resurrection, but I've finally got down to figuring out the length of wheel studs I need to accommodate the Thema 15" wheels, offset spacers and different brake discs on the front. And the answer is...

75mm (F) and 74mm (R).

So somewhere between 75mm and 80mm, depending on what I can get hold of. As the Thema wheels are only 6J (compared to the OE wheels 5.5J) there is more clearance to play with than if I'd gone for 7J Integrale wheels. In the course of measuring everything up I also realised that the spacers I'd bought are lacking the bolt holes to mount the spacers to the disc and hub and the front spacers need the lip that fits inside the wheel machining down to suit.

So at least I've found a couple of potential gotchas and can take the spacers back to the UK (I'm in France at present) and get them machined/drilled to suit. Unfortunately that's all I've been able to do to the car, as work on the house has taken priority.

Yes, there's always something. Without the stock 5mm spacer I have since found that the hub center will not always fit inside wheels: instead of being a straight 58.1mm, it spreads out wider near the discs, so unless your wheel center bore tapers enough near the mounting face, you can't fit the wheel without either the original spacer fitted of machining a small amount of material from the wheel.

It's not critical that the disc (and spacer, if present) is bolted to the hub IMHO. It will be clamped by the wheel bolts and nuts. It does help lining everything up though. the M8 bolts involved are not doing anything other than stopping the spacer fall off when you take the wheel off.

Its one of those things that can be sorted easily in some spare time when you have it all in front of you for measurements and going back and forth, but there are a few pitfalls if you try and sort it all in one step.

[mangocrazy]

Yes, I realise that the mounting holes for the disc aren't strictly necessary, but they do make life a bit easier, so I'll get them machined. As you say, it's easy to fix when you have specialists near at hand (like I have in Sheffield), but not so easy in rural south of France...

But I'm glad I found the gotchas now rather than when doing the fitting for real.

[mangocrazy]

Another thread resurrection - as I'm still in France with the Spider, I decided to run some mock-ups with the Beta upright, Thema hub, Thema 6J x 15 wheel and the M12 x 1.25 x 80mm studs and wheel nuts I bought. Spacers to correct the offset for the Thema wheels as opposed to the 5.5J x 14 Beta wheels are 16mm deep front and 10mm rear. The standard 5mm spacers on the Beta hubs will be removed and placed in the 'might be useful sometime' pile.

I'm glad to report that all the above components play nicely with each other (especially now I have had disc mounting holes machined in the spacers) and that the 23mm deep wheel nuts I was using for the test engaged on all their length with the studs, with about 2-3 mm protruding out from the nuts (this is on the front hub with 16mm spacer). On the rear hub, the protrusion will be 6mm greater, due to a slimmer 10mm spacer. I'll probably get the 8 studs destined for the rear hubs machined down by the 6mm difference, just to keep everything uniform.

So I think I can call that a result on the stud front. I now need to ensure that the Thema wheels don't foul bodywork or suspension, but that is a task for another day (probably when the car is back in the UK). I'm optimistic that there won't be any rubbing, as the increase in wheel/tyre depth/height is fairly modest compared to what others have done, but I await final confirmation...

[JohnFol]

Yet another resurrection.


On my front hub I have a "worn" thread that just grips the bolt. It's at the point of needing thread lock to stop bolt flying out

Plan A is to get thread drilled / filled / tapped whilst on the car (as no access to special tool for doing hub bearings).

Open to recommendations for a garage or engineering company who can do it in Thames valley area...


Plan B is to fit studs as that feels a bit more DIY.

So was there a conclusion about how to fit studs without having to swap hubs, disks, spacers etc?

[JohnFol]

Decided to go the Helicoil route

[peteracs]

Hi John

Sounds like a sensible solution and saves having to remove the hub.

Peter

[mangocrazy]

Much to my surprise (and relief) a helicoil insert recovered the stripped thread on my 2 litre cylinder block and withstood the final cylinder head tightening torque of 60 lb/ft, so I'd say a Helicoil is/was definitely the right choice.