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MG Midget and Sprite Technical - Rostyle center bore...

im thinkg about a PCD adapter to allow the use of 15" or 16" MGF 5 spoke wheels.

Specs are:
P.C.D. 95.25 mm
Offset 30 - 35 mm
Centre bore 56.6 mm
15" wheels: 6J 15
16" wheels: 7J 16

Whats the center bore and offset of the std rostyle wheels?

Need this info for a quote from Superlite-wheels.com
Rob McGeown

If you go ahead, I might be interested in a couple of sets!
Mick - trying to sort the wiring

There isn't a centerbore on Rostyles, that being the source of much trouble about balancing. And, since the wheels (not even pre Rostyles) were not located off a hub spigot, there isn't really one of those too. There is a spigot of sorts, but it is an artifact of hub machining and may or may not be consistent from hub to hub. On the (front) hub I have available to measure, the flat surface is machined into the hub casting with a fairly large (1/8-3/16")radius tool, but the radius is not fully formed so you can't really measure it. Were it fully formed, the spigot would be about 2.680. The OD of the hub flange is at least fully machined, but since nothing located off that either, there is no reason to suppose they are any more than "rough machine" tolerances. It's about 5.930".

I don't know exactly what you are trying to do, but before ordering any odd & costly bits, study the actual parts and take all responsibility upon thyself.

My recommendation would be to either machine the hub center to one of the common sizes, or to cut the OD to something convenient to locate an adaptor plate from.
Common modern spigot sizes are 54, 56, 57, 60 64mm. You can JUST get it down to 54 (2.124"), but 2.36" or 60 mm would be more convenient and appears to be a standard for aftermarket wheels, which get fitted with reducing rings for the smaller sizes. At 60 mm you should still get a useful height of spigot to locate from. And if you plan on hanging big sticky feets off it, consider upsizing the studs, screws or whatever you are using.
FRM
FR Millmore

you might give this guy a try and do anything...apperantly he is like mikey....he'll try anything....he likes it. he likes it....LOL.

prop

http://www.wheeladapter.com/index.php
Prop

Rob,
Have your hub re driled or buy some nice ally ones with what-ever PCD you want on them? Just a thought.

Best Regards,

Howie.
Howard Wright

Redrilling would be a tight fit with 95.6 PCD on existing 4" i think...worth looking into tho.
Rob McGeown

Rob,

I mentioned to a mate that has a Caterham, 3.75" (95.25mm) PCD due to the Triumph stubaxles, like Spitfire etc, that the MGF uses the same PCD and he is looking around for a spare set of wheels possibly off an MGF. I wouldn't have thought it would be much of an issue drilling holes 1/8" further inwards but you won't know until you measure the hubs.
David Billington

ive had a quick look but dont have any accurate measurment device!

Attached an image of where the new holes could go. Dont know if the stud diameter would be the same?


Rob McGeown

Rob,

Triumph stud bits like Spitfire & GT6 were 3/8" UNF like the sprite IIRC. The main issue I think these days may be that these small high tensile studs are a liability for the tyre fitters as most now use larger bolts/studs, and these smaller ones can be easily be overtightened.
David Billington

I havent taken my studs out yet, but IIRC they have a square cutout to lock them in? How would one form this square on the rear face of new holes? Larger studs may be the best way to go, 11/16?
Rob McGeown

I guess these would be ideal...they dont have a square section like i thought, just stepped diameter the the thread.
Rob McGeown

Rob,

IIRC no square cutout but rather a seration on the stud stem under the head which is an interference fit in the hub holes. You just have to drill the holes the right size and the studs will hold when pressed in.
David Billington

Ok,so the front hubs look like they can be re-drilled, but im not sure about the rear. Would have to drill the half shafts and drums too.

Can a PCD adapter plate be used on the outside of the drums?

If used on the rear, would it be best to use on the front too, else the rear will be wider...?
Rob McGeown

<<Can a PCD adapter plate be used on the outside of the drums?>>

Should be the same as using one on the front.

<<If used on the rear, would it be best to use on the front too, else the rear will be wider...?>>

The rear track is narrower than the front as standard, at least on the frogeye, I think on the later cars also. I run, or ran as the cars not been on the road for a few years, 7/8" spacers on the rear of my frogeye to get the track front and rear more equal.
David Billington

So, here's a scale hub adapter model...may need some tweeking and redesigning for the rear.

4x4" to 4x95.6mm with a 56.5mm centre boss. Larger stud holes for MG F studs.


Rob McGeown

Rob-
Did you read what I sent you back at the start?
Or look at a hub with some kind of measuring device in hand?

Part of the problem is how much spacer thickness do you need/want/tolerate.

Another part is whether you are using through studs or a deal where the plate bolts to the hub and the wheel bolts to the plate. The second is what your drawing looks like, and in general it's a hokey, heavy, and frequently weak way to do it. I think it's why wheel spacers are banned in some places, along with the Mickey Mouse "stud extenders".

Your proposal will not fit over the ROUGH cast/machined hub unless the plate is greater than about .750" thick, with a huge counterbore on the back, PLUS enough thickness for the center spigot of your choice. Say 1" minimum thickness, the hub center + grease cap is .750".

And it STILL will not locate anywhere on a true center unless the hub is machined to suit.

The hub can easily be machined to 56.5 with some (variable by the casting) useful center spigot, if you can/want to mount the wheel on the hub direct or with a thin spacer.

What's the deal with MGF wheels anyway? We don't have them. How much do they weigh? Personally I don't really care for very small PCD, as stresses go way up. The fact that big, wide, sticky feet seem to work means that the wheel has more metal than it would really need with bigger bolt patterns.

Makes more sense to me to go to 4x100 PCD, lots of cool cheap wheels about and the Spridget stud positions can very easily be moved that far using common 12mm studs, which are readily available longer if needed for spacers and such. But you still have to machine the hub!

FRM
FR Millmore

FRM,

Thanks for your responses. I have read and understood you comments.

I asked Guy to take some measurements for me and has porvided them using a dial guage with tolerance to 0.005". This is what my draing is constructed from.

I agree that this would not be the strongest method, but given that there is not enough material on the rear hubs to drill the new PCD, and that i would have to drill the half shafts and the brake drums, spacer/adapters looks the easiest option.

We all have our particular likes, and mine is MGF Trophy 160 wheels (see http://www.mgf.ultimatemg.com/group2/suspension/wheel_options_for_the_mgf.htm)

I could machine the front hubs and use a spacer/adapter on the rear.


Rob McGeown

The idea is the spacer/adapter bolts to the hub using the existing studs. The new MGF studs are in the spacer and the wheel is bolted to these.
Rob McGeown

the centre boss needs to be only 0.65mm smaller to accomodate the MG F centre bore - if all castings are the same, which from what you say they arent, but could be lathed if they are all over size.

The 12mm studs from the MG F cant be drilled over the existing holes as the PCD gives a 1.8mm overlap. They will have to be offset between the existing stud and brake bolt holes.


Rob McGeown

I hadn't realised that the PCD of the MGF wheels was so much smaller than the Sprite one. It seems odd when the normal on 4-stud moderns is much more often 4 X 100. Certainly on the 4 X 100 size it is a much neater and better solution to get the studs re-drilled oversize onto the new pattern with the increase in stud diameter accommodating the slight overlap of the holes.

What size studs are you going for? You mention 11/16 but that sounds large for the stud. If you really are using 11/16" (17.5mm) studs then their diameter is sufficient to redrill the existing holes off-centre at the new PCD of 4 X 95.25
Guy Weller

I pretty sure they are M12 studs, i dont have one to measure at the moment.

Re-drilling the existin hoes is a much easier and cheaper option for the front, but im sure it wont work for the rear.

A problem shared is a problem nearly solved! Keep the comments coming!
Rob McGeown

Are there any issues with slotted holes like attached? They are not available in a 4x4 PCD, but if they were they could adapt from 95.25 to 114...


Rob McGeown

Well M12 is 15/32", nearer to 7/16 than 11/16" !!

Using M12 studs, you could recentre buy up to about 1.5mm , giving a reduction in PCD of 3mm, not enough to reduce the current 101.6 (4") to your required 95.25.

I wonder if the edge of the present stud holes could be filled with weld before re-drilling? Or would the heat have some dire consequences? - I don't know enough about these things. If it could be done at the front, then I don't see that there is any more of a problem at the rear, just more layers of steel to drill through. Anyway if this is for a K-onversion why aren't you planning on discs for the rear?

Guy
Guy Weller

the MGF (and TF) shares its PCD with the Maestro and Montego and some Metros, and many earlier Triumphs, probably an ex-Triumph designer in the BL conglomerate, set in his ways.
David (davidDOTsmithAT stonesDOTcom)

Thats a good pont Guy! Besides the cost, i was under the impression that rear discs are too powerful and upset the balance quite a lot more...but i donntk now having never driven one.

There would be <2mm to fill with weld, and with the thickness of the hub, in not sure heat distortion would be an issue. I do have a spare rear hub so i could play around.
Rob McGeown

Rob,

I wouldn't consider welding unless you know what the hub material is. I would think it is malleable iron or cast iron and wouldn't respond well to welding.
David Billington

well im truley confused.. Been researching offset and backspace etc.

I have no idea if the 30-35 mm offset on MG F wheels will work on std midget hubs.

Can anyone offer some adivce?
Rob McGeown

Rob-
Lots of pretty MGF wheels I will grant you. Have some suspicions re the data posted there, as weights don't make any sense - the very expensive super light wheels being the same as a lot of not super light ones.

As David says - DO NOT try welding the cast hubs - they will get v brittle right where it's most critical.

Re Guy's notes, there are various sizes of stud that might work, 7/16", 12mm, 1/2", 14mm. Studs will have a knurled underhead section of varying diameter, always a bit over the stud size, and sometimes a lot. This can be used to advantage, once you quit slacking off and measure & calculate what you need. 12mm or 1/2" are the most suitable.

Ex: Many Mazda 12mm studs are 12.9mm OD at the knurl, which means the drilled hole size will be about 12.6-12.7 before you press the stud in. Some Nissan are 12.8, and people have successfully used the Mazda studs in Nissan hubs without any redrill. Lots of long studs for Miata and RX7.
A lot of 1/2" studs have knurled areas much larger than the stud, like up to 3/4" or more. It's a matter of looking up catalog data in suitable places, like ARP or any racecar supply place.

Note that stud holes cannot be "drilled" off center. To do this accurately, you need a machine setup that uses either a single point tool (best)or an endcutting tool. If done with a drill, then you need a jig with a hardened guide bushing, and probably a good supply of drill bits.

"Are there any issues with slotted holes like attached?"
Indeed! This goes with my comments re spacers/adaptors in general, previous. An adaptor like this is weak, esp, in aluminum or more likely, potmetal. (note that major factor is that many aluminum alloys have no definable fatigue life, so what works today can kill us tomorrow! Using these in a poorly designed and clearly highly stressed application is poor thinking.)
If we assume that the big wheels & sticky feets are to be used and not just "pretty boy", then weak is NFG. A big point is that as pictured, the width of bearing surface radially outboard of the stud is very narrow, right where the major load from the wheel is supposed to be supported. Some wheels, like most steel wheels, will not even make contact there.

"I have no idea if the 30-35 mm offset on MG F wheels will work on std midget hubs.

Can anyone offer some adivce?"

Been doing that - research, measure, think, experiment!!!


I have investigated various schemes, and had a lot of numbers, now lost in a computer's psychotic episode. Roughly, you can {{!!for test measuring purposes only!!}} fit 4x100 wheels, which are readily available in a zillion different sizes/widths/offsets by borrowing, on the Sprigdet. 13 x 5 35mm offset Mazda steel wheels fit depending on the tire. I figured that 14x6 45 mm alloys would just work, probably using some spacers at the rear, after redrilling the PCD and machining the hubs. (In order to test fit without the hub remachine, it is necessary with these wheels to fit big washers between the wheel & hub to avoid false readings from the rough hub center - don't forget to include the washer thickness in the calcs!)
But I haven't done it yet, and there is no Spridget on site just now.

Wider wheels will alter the offset calcs, larger diameter wheels give more clearance for suspension bits - which may be required as a consequence of the width increase. If you can borrow something close, you can quickly arrive at a reasonable solution.

Have fun!
FRM
FR Millmore

well as luck will have it I'm doing the back brakes on the Midget today, and have lots of spare MGF wheels for the Montego. And the answer seems to be no, the inner rim of the wheel touches the leaf spring when there is still about 5mm between the inner face of the centre and the axle hub face. With a tyre fitted it would be a much larger amount, and then you have to allow for sidewall flex under cornering. With 175/60x13 Yoko 48s on 5" miniltes I can occasionally see signs of contact between sidewall and leaf spring when checking after a race.
David (davidDOTsmithAT stonesDOTcom)

David-
Real Data - thanks!
What's the offset on the Minilites?
Clearance to both inner and outer wheel arch?

Somewhere I have seen oddly laterally deformed springs to cure your tyre/spring interference. They have squiggles to avoid wide tyres.

As far as Rob's questions, I suppose he needs to know the same info for the MGF wheel you tried. It seems they also come in different widths.

And of course I have no idea what Rob's car is like as to bodywork mods and such.
Thanks,
FRM
FR Millmore

Thanks for the info and advice. Im getting the jist that this is a lot more hassle than its worth!

However, im able to make any required body mods as im still in the shell stage. I have already removed the front inner arches. I am willing to run spacers, but i do take on board the info on risks and stress/fatigue.
Rob McGeown

Rob-
If you will have the power, get out the hammer and go at it! 16x10 with matching rubber! Did I get the impression somewhere that you are going K series?
Spacers per se are not the problem with correct studs, but the adapters scare me. I've seen them broken, seen "extender studs" (on a Mini) loose and threads worn.

FRM
FR Millmore

Yep in doing a K!

Rob McGeown

This thread was discussed between 19/06/2009 and 30/06/2009

MG Midget and Sprite Technical index

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