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MG Midget and Sprite Technical - 155/80 or 165/70 - much difference?

Morning all, currently have some 155/70 Pirelli P2500's on my 74 midget, and want to get something a little fresher / softer for the coming winter months.

Looking at Goodyear Efficient Grip in 165/70 13 or Toyo NanoEnergy3 in 155/80 13 (or similar). Now, I understand the difference in aspect ratio between these and my current tyres, and that this can also vary between different tyre manufacturers etc etc. So, either option should fill the arches a little more and likewise will probably increase the ride height a little too, the 155/80 more so than the 165/70. In theory...

I'm interested to hear from those of you who have / have had one or both of these tyre sizes on their Spridget. In the real, any real difference to handling, ride comfort etc? Or are they just too close in size to notice much difference at all?

In case it has any bearing, car is a 1275 with 5spd box, 266 cam, 1.5 rockers, Cooper S valves, luminition, FL telescopics F&R, Maniflow single box.

M Weller

I have Pirelli P3000 165/70 R13s fitted to my modified 1973. Excellent tyres in every respect. I have hardly ever lost grip - and I don't hang about, they seem fine enough in winter/rain, and they do seem to fill the arches nicely for a 13 inch.

Do you get winters in Devon?

Not compared to you guys!!! But up on the moor early mornings it can get fairly 'interesting' this time of year...

Will take a look at the P3000's, thanks.
M Weller

Hi Mike,
also consider with comparisons your wheel rim width would be relevant too, to some extent at least.

If you change your tyres, especially in winter bear in mind new tyres can be 'greasy' so take it reasonably easy on them for the first 100 miles (200 miles in damp/wet weather).

Also remember to check the tightness of the wheel nuts after about 30-50 miles of use.

Don't let the tyre fitters over tighten the wheel nuts, they're at a lower setting than they're used to, I've twice had wheel studs damaged, first lot told me second lot didn't, info in Driver's Handbook - 44-46 lb. ft. (60-62Nm).

After you've used your new tyres for a good while it'd be interesting to know how you find them as tyre choice is ever changing.

Nigel Atkins

Cheers Nigel, I'll make sure wheel nut torques are as per handbook (which I do have!!!), as I'll be taking the wheels in loose - don't trust a non classic minded tyre fitter not to put the trolley jack through my 'lightened' floorpan...
M Weller

I can't comment on Goodyear Efficient Grip on a Spridget, but I have run them on a (FWD) daily driver at 1000 miles/week and they performed very well.
Dave O'Neill 2

I really rate Uniroyal tyres. Very very good in damp and greasy conditions, and pretty cheap too. I have had 155 80 13 and 175 70 13 and the 155s were fine, 175s more mechanical grip but lost a little of the fine edge. I currently have 185 60 14 and they would be too wide for a standard car.

On a standard car I'd go 165 as a compromise.
Rob Armstrong

Hi Mike,
I don't think most tyre places are that bad (but some might be) they just need informing/reminding of the differences. I must admit through to hanging round them as much as possible to check things and prefer to go to a specialist tyre place rather than the general ones.

I think as the car is newish to you that you should take it in to have the tyres fitted and have the tracking checked at the same time as it's amazing how quick you can wear new tyres if the tracking is out (plus of course handling).

As you have FL front suspension the 'good book' figure won't be so relevant and you want the FL figure ("approximately 1/16" (1-2mm)(??) toe in" on my paperwork), unless BBSer David Billington has a different figure as the initial design was *borrowed* from him.

Make sure to stress TOE IN as some places seem to be used to toe out.

And I wouldn't trust the pressure gauges at some (most?) places and would check them with a proven reliable gauge (pays to have one for yourself).
Nigel Atkins

.....and if changing out tyres and running on Rostyles, then surely the inclination to sinful expenditure must present itself via the temptation to splurge on more aesthetically pleasing wheels? I do like my shiny gloss black Minilite style alloys with polished rims....

Hi Mike,
I have used both sizes in the past with both Uniroyal rain masters and the current preference which is Vredstein snotracs.The latter are proper winter tyres and are very popular for the classic rally brigade up North.They are a very soft compound but I do not know how they would last purely for road use as mine tend to get destroyed doing autotests.They are fairly cheap but I have heard they were in short supply,my last ones came from Germany or the Netherlands at extra cost.The other thing of be aware of is that they are directional so not so easy to swop over,I keep an old non directional tyre as a spare.I could not tell the difference between the two sizes but that may partly be down to the LSD dialing out loss of traction.
Any decent new tyre will be Miles better than an old tyre.I tend to run at higher pressures that standard,around 28 in the rears and 25 for the fronts but play around and see what feels best for you.
John S.
J Sloan

Thanks for all the replies, looks like any new rubber in any size will be preferable to my 5 yr old boots!

I have 5" Minilite style wheels already, though the spare is still the Rostyle.

Hadn't thought about tracking... probably would be a good idea to get that done at the same time. I use Mid Devon Tyres in Exeter, seemed OK on the Focus, but they get a few more of those through the door than Midgets.
M Weller you have adequate wheel nut thread engagement on the studs? - ie around 11 turns on a standard 3/8 UNF?

I have used various 165/70 x 13 tyres over the years (currently Yokohama, previously Toyo) and that is my preference. This size has the advantage that the rolling circumference is virtually identical to the original 155/80 tyres so the speedo is unaffected. However, when I fitted 165/70s to early Rostyles (4.5J rim) I felt that the tyres flexed too much on cornering. They were much more stable fitted on my Minilites (5J rim) and fantastically stable on some 5.5J rims (although the latter fouled the wheel arch on hard cornering).
Chris Hasluck

Sounds encouraging re the 165/70 x 13, will get some Goodyear Efficient Grips in this size and report back in due course. And a tracking too.

Not thought about wheel nut threads before, will check that as well.
M Weller

Not sure why you would bother having the tracking checked unless they were offering to do it for free rather than doing it yourself. The only thing you can change easily is the toe in/out setting and that is easy to check with a homemade gauge or one such as made by Guyson? Camber angle is easy to check also using the likes of a 12" spirit level and a bit of trigonometry although you can't change it on a standard car.
David Billington

Beware also certain well known tyre firms who advertise "Free tracking check" who then (inevitably?) find that adjustment is needed for which there is a charge.

I had just that experience with a car (not an MG) for which I was charged for adjusting the tracking. Only when I got home I checked and the TRE locknuts were completely unmarked and hadn't been moved at all. I went back and complained. At first they swore blind the job had been done until I produced photos! I got a refund + a "goodwill" payment and someone lost their job.
Guy W

Due to the greater boss/PCD thickness of the alloys, I found that I only obtained 6 turns on the nut until tight. Wholly inadequate for sufficient purchase on the stud. Recommended thread engagement is around 1.2 x stud diameter - standard being 3/8 UNF. I had to change the studs for longer.

Worth a check I feel....

Something else to remember

If this is on the roystel wheel and not an has to be balanced different then the regular modern wheels other wise there going to load up about 3 stones (pounds) of counter weights on the wheel to balance it then claim bad old wheel


1 Paper

I had the same experience with wheel stud length when fitting Minators, although others claim to have not had this issue.

MSA 'blue book' used to recommend 1.5 x stud diameter IIRC.
Dave O'Neill 2

my Midget went from some poor quality powdercoated unpainted Rostyles to Minator (Minilite replicas) without the need to change the studs.

The wheel nuts take 12+ turns to tight, whether that's (1.2 or 1.5 x 3/8") depth I don't know.

Mind when I first saw my car it had some (to me turgid) Cosmic wheels that suited the boring (for a Spridget) colour and look of my car but the Cosmic wheels/tyres made the steering feel wooden so had to go so perhaps the studs where changed before I got the car.
Nigel Atkins


Some wheels give adequate purchase, others do not. Personally I would simply remove/replace a nut to check.

I would hazard a guess that your studs were changed out for longer ones.

Incidentally the guidance - for tightening of flanges in the offshore O&G industry at least is to allow for "protrusion of at least 3 sound threads from the nut" 1.2 x D or thereabouts usually achieves this, 1.5 x D more so.

....and 12 turns to tight on a 3/8 UNF is around 1/2 inch thread engagement - which is 1.33 x D.

The MSA 'blue book' is now available online...

Here's the bit relating to wheel studs. This is obviously for competition vehicles, but I don't see why it shouldn't also apply to road vehicles.

Dave O'Neill 2

Hi Oggers,
I totally agree you need to check, after all who wants their nuts loose.

What would 13 turns be please?

As 12 is tight using socket then I use a cheap torque bar that adds less than a full turn (the torque bar is a simple thing and not certificated ever let alone regularly).

My front wheel studs at least are standard length, I know as I had to replace one on my current Midget and the wheel nuts I have are supposed to be suitable for my MGOC Spares Minator wheels.

I can't do the 3 sound threads as the wheel nuts are the Rostyle closed ones.
Nigel Atkins

whilst I remember - a while back I read that the performance of summer tyres drops (dramatically?) when the weather is below 10c so expect your new tyres to be better in the warm weather.

Yes the chances are more likely than less likely (depending on quality of the tyres of course) that new tyres will be better than 5 year old used tyres so you have to allow for that too in general assessment.
Nigel Atkins


Standard stud is a 3/8 inch UNF of 24TPI. 13 turns is thus 13/24 of an inch ie 0.541 inches, which is 1.44 times the diameter of the stud. If correct torque is achieved after this number of turns, I would say you have nothing to worry about. Therefore, 1.2 x D thread engagement is equivalent to 11 turns, 1.5 x D thread engagement is equivalent to around 14.

Use a similar calculation to ascertain how much thread engagement you have on the closed nuts.

Another thing for you to consider is the mating face profile of Rostyle nuts - closed or otherwise. They may - or may not - be the of same profile as the countersink of your Minator wheels. The nuts need to be the same conical profile of the wheel countersink. Otherwise the the clamping force will be inadequately applied, and the nut may come loose.

Thanks for that.

I've not checked the profiles but the nuts seemed to have kept the wheels tight for seven and a half years, about 35k miles and far too many cycles of removing and refitting by me and others so I'll go with what MGOC Spares say - of course a wheel will now fall off because I've put this.

I should have put my Minators are MGOC Spares Club Sport wheels, perhaps other Minator Spridget wheels have a different profile for the wheel nuts, or MGOC Spares have it wrong but it's (now also) on their web site -

As with other stuff on our Spridgets there are so many variables it is always better to check than not to check.
Nigel Atkins

"As with other stuff on our Spridgets there are so many variables it is always better to check than not to check"

So therefore check the profile n'est pas?

I am not sure why the wheels being of MGOC origin would signify. They would surely be bought in from elsewhere originally and thus may well have a completely different countersink profile to Rostyles.

The fact that your nuts have been tight for some time is certainly encouraging, but personally I would still check it out. My wheels certainly came supplied with correct profile nuts - which were different to the original Rostyle nut.

Check it with what and how, cardboard, blu-tac. Being a non-mechanic/engineer the only measuring instruments I have are a plastic or tape (not that I can see the increments properly even with my glasses on), measuring jugs, spoons, containers etc..

I have real world tested them and posted evidence here that the seller claims their fit so if all goes wrong there'll be blame on which to base the claim.
Nigel Atkins

I am sure there will be some drawing or specification of the wheel and nut on the internet somewhere. Supplier websites are often very informative. You may even be able to see any discrepancy visually when putting conical nut end into countersink of wheel and feeling for a decent fit along the conical sides. It should be a mating face fit rather than a mating edge.

I'm not so sure that the internet always has the information you want, don't believe the hype.

Next time I take a wheel off I'll try offering a nut up but I'll probably forget. If a wheel falls off or a nut come loose before that I'll let you know.
Nigel Atkins

You may not be able to let me know if a wheel falls off.....

Good point, in that case the only way is to let you know each day that a wheel hasn't fallen off, take this as today's confirmation.

Don't worry it'll be someone else's turn tomorrow and not you :).
Nigel Atkins

Alternatively, If I don't see a post from you on this board within in the next 2 weeks, I will assume the worst :)...

The worst will be that I return to posting after two weeks. :)

The Driver's Handbook advises to check wheel nut tightness every week so obviously I do this religiously.
Nigel Atkins

Just returning to Prop's point about Rostyles, a had a couple of new tyres on the front of my MGBGT, put on and balanced by my local garage.

The first time I went on the motorway, I discovered a vibration at 70 mph.

When I got home, I swapped the front tyres, left to right, right to left.

Problem sorted!
Geoff MG-TF

On the subject of wheel studs can someone please confirm for me what the standard length and part number is for rear wheel studs for steel wheel axles. Car is a MkII Sprite.

And the length and part numbers for the front hubs too.

My reason for asking is that I have had fun trying to buy the correct standard rear studs, to replace bent and stretched studs, getting supplied ones with too few splines on and not sure if others are too short. Also not sure what is standard as one side of my axle the wheel nuts are only about 3/4 on the studs on standard steel wheels with the hub bolted on properly and the halfshaft in fine; while the other side the wheel nuts are on OK.


PS on the subject of winter tyres I have found Continental WinterContacts good on my modern and note that you can get them in sizes for Spridgets. Try Camskill Tyres.
M Wood

I can't do it now but if you've still not got the answer later today I'll try to find out rather that rely on my very poor memory.
Nigel Atkins

it sounds like maybe you possibly have one side with steel wheel studs and the other side with perhaps wire wheel studs - but obviously I'm not sure, see info below.

I hope this helps, as there are too many hyperlinks for one post I've split over two posts -

Wheel studs for Sprite Mk2

Rear (steel wheel)
Part number - 2A7089 – (? same size as 2A7089 and NAM5645 ?) –

Part number – BTA492 – “Short stud used in rear hub. 1-1/8' long x 3/8" ” -
Nigel Atkins

Front Drum brakes (steel wheel)
Part number – 2A4066 – “studs are 3/8" UNF thread and each measures approximately 35mm in length” -

(needs three posts)

Nigel Atkins

looks like I need to put in a post without hyperlinks as site won't let me post too many together(?)
Nigel Atkins

Front Disc brakes (steel wheel) (also see next post)
Part number – BTA339 – “Stud, 1.1875", 30mm, shaft length” –

Nigel Atkins

I'm sure the subject of wheel studs and their lengths cropped up a few months back.
Dave O'Neill 2

sorry it just won't take that hyperlink, must have been the problem all along

Front Disc brakes (steel wheel)
Part number – NAM5645 - this bolt has a 30-32mm long shank from under the head and has a 23mm thread length –
(link not added)

yes it did, I found that thread whilst searching
Nigel Atkins

I've just reactivated the thread from July entitled 'Wheel Studs for Minilites'.

I also found another thread in the archives entitled 'Wheel studs - extra long?' started by a Mr M Wood of Strathclyde.
Dave O'Neill 2


Many thanks for the info on wheel stud part numbers - just what I needed.

I reckon now I have wire wheel length studs on one side of my car with steel wheels - time to get the correct length ones. What was confusing me was they came with the car and I was getting the same length new ones supplied!

Dave O - yes, it was me asking about longer studs on an earlier thread. It is a problem been bugging me for a while, not helped by long periods away from the garage.

Thanks all
Best wishes
M Wood

glad to help.

I try to get info cross-referenced from at least two reliable (usually at least) sources but details were a bit thin on the ground especially dimensions.

So check all the measurements you can on the studs you have and want.

It can now be that despite having the original (or later) part numbers that non-original parts are not the same specification or dimensions so it's very difficult to say what you (or any of us) might have already fitted or get when you order new.

Also I've known in another line of parts (not cars) for there to be three or four different original part numbers, and prices, for what was always exactly the same part.

As parts are so often "superseded", or substitutes used instead, or error with storage location, that it wouldn't surprise me now to order two different parts with different part numbers for them to arrive and be exactly the same part.

So double-check what you order, double-check what they send you as soon as it arrives and double-check the part is the one you want before you start the work - I've been caught out more than once by having an unsuitable part halfway through the work.

Good luck.
Nigel Atkins

This thread was discussed between 05/12/2016 and 12/12/2016

MG Midget and Sprite Technical index

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