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MG Midget and Sprite Technical - Tyre size

What maximum width tyre can one go to on a standard 3.5" Frogeye rim?
GuyW

Carbibles site says that 145 width suits a 4" to 5.5" rim which sounds a bit of a high range of rim widths for that section of tyre.
GuyW

I think its 155 but I always worry it may roll off so I have always used 145
Bob Beaumont

...and a 145 on a 5.5" rim must look a bit weird.
Dave O'Neill 2

Guy,
short answer = 145 - but note that's a 145/70 (seventy) R13 tyre.

135/80 R13 tyre would be modern equivalent to original Frogeye tyre, see note at bottom.

Long answer -
according to Carbibles 5.20-13 tyres = 130/100 R13

http://www.carbibles.com/tyre_bible.html#classiccrossply

130/100 R13 gives 165/60/13 - 145/70/13 and 135/80/13

http://www.carbibles.com/vintagetyresizes.html

So to answer your question, the above suggests 165/60
- BUT - Toyo UK with their Nano Energy 3 tyre, just as an example, have for the 165/65 R13 an "Approved Rim Width Range (inch)" of "4.5-5-6.0" with 5 in bold, the table doesn't consider 3.5" rims -
click on "SPECIFICATIONS" tab here - http://www.toyo.co.uk/tire/pattern/nanoenergy-3

And these calculators also contradict 165/60/13 -
http://www.tyresizecalculator.com/tyre-wheel-calculators/wheel-rim-size-calculator

http://www.oponeo.co.uk/advice-and-tips/fit-the-rim-to-the-tyre/165-60-r13


Note 135/80/13 is included in all above and gives rim size of 3.5" which helps to bear out my previous thoughts that a 135 tyre would be fine on a Frogeye at least because it's even lighter than the later Spridgets.

http://www.oponeo.co.uk/advice-and-tips/fit-the-rim-to-the-tyre/135-80-r13

Uniroyal RainExpert 3 - 135/80 R13 70 T

70 = load index gives wieght capacity of 335kg

T = maximum of 118mph for 10 minutes
Nigel Atkins

Thanks Nigel. A 165 is definitely far too wide for a 3.5" rim, that must surely be an error!

I had used the Carbibles site but the table l found on matching tyre to rim widths doesn't go below a 4.5" rim. And the rim width they list for the 145 tyre goes up to a 5.5 which seems a bit wide to me for that section tyre.

From the Carbibles links that you list it looks like they give different results depending on which table is used. Some contradictions there!

I am happy with a 145 width tyre. That will be plenty wide enough for nice handling.
GuyW

Guy,
lots of inconsistencies when comparing web sites.

Short answer, 145/80 R13 seems to be the size you want.

Of course I still think 135/80 R13 would be nicest on a standard(-ish) Sprite with a standard(-ish) engine but it's not my car.

I have 145/80 R13 on 5" rims and the sidewalls do seem (very?) firm (have to allow for variances in makes and/or models of tyres of course).

Long answer -
. according to oponeo -
145/70 R13 - 3.5"-5.0" - 4.5" recommended

145/80 R13 - 3.5"-5.0" - 4.0" recommended

(135/80 R13 - 3.5"-4.5" - 3.5" recommended)

. according to Tyre Size Calculator
145/70 R13 - 3.5"-5.0" - standard 4.5"

145/80 R13 - 3.5"-5.0" - standard 4.0"

(135/80 R13 - 3.5"-4.5" - standard 3.5")
Nigel Atkins

The feel of 155 x 80 x 13 on the 3,5' rim is much better on my 5' rim. More stable in line on the highway, more feel in the curves, more stable under braking.
Flip
Flip Brühl

Yes the recommended size for 155/80 and 155/70 is 5", I've had both of those tyre sizes on my 5" rims and they both work well but I can't see either size working so well on a 3.5" rim, spirited driving would be compromised.

As far as I remember I had 145/80 R13 on my 3.5" steel wheels on my previous pretty standard 1275 Spridget and they were lovely, very enjoyable.
Nigel Atkins

I'm surprised that no-one has mentioned the 'good book'.

This is from the Mk3 (pre-facelift) midget handbook, so 3.5" disc wheels and 4" wires.


Dave O'Neill 2

Dave,
I leave it to Guy to reply to that. :)

Your copy of the good book gives interesting info on the tyres (for that model).

There are two versions of the Sprite Driver's Handbook available if Guy wants to sneak a look, no one need know. ;)

I'll just leave these here for anyone to pick up -

http://www.spridgetguru.com/DriversHandbooks/97H1583A.pdf

http://www.spridgetguru.com/DriversHandbooks/97H1583B.pdf


Nigel Atkins

No need Nigel. Probably of surprise (to you and others) I started by checking my paper copies of both the Driver's Handbook and the Manual. I have copies of both, but they are the pre-clairvoyant publications. They don't include radial tyre sizes, just cross-plys.

I was asking specifically about tyre fitment for 3.5" Frogeye wheels. I had thought the 1098cc cars went up to a 4" rim and then changed again to 4.5" in 1969 with the 1275 cars. But I see that only applied to the wire wheel versions - the steel wheels stayed with the same width rims as the Frogeyes right through until late 1969.

Anyway, I have my answer now. 145 is what I will be using.

GuyW

To be serious the Driver's Handbooks for the relevant models do give lots of info so you can look things up like the wheel and tyres sizes and options. No they don't cover changes up to nearly 60 years later but as we have here you can use them as a base to convert to what's available now.

I knew what you wanted to know but thought it best you told Dave than I.


(not being serious)-

Welcome brother come in and take a seat! :)

I'm surprised you didn't remember I had 3.5" steel chrome hub disc wheels on my previous '69 Spridget I've mentioned it and put the photo up enough times, perhaps I need to repeat myself more often (!?). :)

ETA: I've just noticed how the SWA make the car in that colour look lower and skwat(?)




Nigel Atkins

not squat, I meant sleek

- rushing to beat the edit guillotine again
Nigel Atkins

This thread was discussed between 23/05/2017 and 25/05/2017

MG Midget and Sprite Technical index

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