Morris Minor Owners Club

Sorry for bringing the delicate subject of tyres up yet again but having trawled through the
numerous posts on the subject I am no wiser. Normal for me I suppose.

I have found some replacement tyres 155 x 80 x R14

The ones that are on at the moment are showing as 145 x R14 76T

One member stated he has used the 155 size for 35 years with no problems.

I need to Phone A Friend (or 2) Can I fit the 155 x 80 x R14

To be fitted to a 1953 split screen.

Thanks in anticipation

Shane

Ignore what others may say, I have been running 155/80/14 tyres on my 1952 split screen since 1978

Thanks Mike

I will press ahead and get a set ordered.

Shane

You will need to run them at about 28 psi and if they are tubeless make sure that the tyre fitter has the correct size valves before removing the old valves

aagree wwith mike on this one

Is there any advantage to running 155s over 145s or is it mostly down to price as 155s look like being a few quid cheaper than 145s probably because they are wider used.

just the cost for me and also my local tyre place can get the 155 but not the 145
so it does work out cheaper for me for them to supply and fit

155 tyres have a larger diameter than 145s so will raise the gearing to nearer the original crossplies and will probably give a more accurate speedo reading.

just go with the 155s it will be fine .

145s = 872.2 revs/mile
155s = 849.1 revs/mile

145 R14 is really the limit for a 3" rim but so many are using 155's without problems how could your insurance company argue? As far as pressure goes, you don't need excessive 30+psi and recommended was 22/24 for a saloon on 145R 14. They are MUCH more comfortable at recommended settings (and no reason to overheat!). Remember also that Bridgestone 145's are dearer than some 155's but are a superior tyre.
Don't know where you get your revs/mile from Mike but only the manufacturer
could give you that info for a particular tyre. It isn't possible to calculate it from nominal tyre sizes.
John

John Naylor, it is indeed possible

I worked it out to be (quick napkin and phone maths (so quite a bit of rounding poorly)):
145 = 874.8 revs/mile
155 = 848.7 revs/mile

I'm going to use the latter as an example. These calculations do not take into account how the tyre and wheel slightly overlap on the bead.

155/80-14
155mm width, 80% wall height, 14 inch internal diameter.
Wall height = 155*0.8 = 124mm, double that makes 248mm.
Internal diameter = 14" which = 355.6mm
Total diameter = 248+355.6 = 603.6
Circumference = πd = 3.14159265*603.6 = 1896.3mm.
1 mile = 1,609,344mm.
1609344/1896.3 = 848.7, which is the amount of revs the tyre 'should' do in one mile - providing the driver does not wheel-spin.

Albert

EDIT: I'm not actually sure if the height of the tread is included in the tyre size. SO that may be a contributing factor which would lower the revs/mile.

There are tyre size comparison charts on the websites
Original tyre pressures were 22 psi on crossplys which have a stiffer sidewall. If you run radials at those pressures you can feel the sidewalls flexing when cornering enthusiastically

Not that simple.
There is a flat bit at the bottom!
The rolling diameter of a radial tyre is at the rigid belt beneath the tread. The rigid belt is as a result of triangulation of the radial ply and two opposing metallic plies. This is inextensible and it's circumference gives the rolling circumference of a loaded tyre. Interesting to note that tread wear will have no effect on speedo reading. The standard for tyres and rims is ETRTO which requires membership to browse but somebody has kindly put the 2003 document on line ETRTO STANDARDS MANUAL 2003.
The usual factor for approximating rolling circ is 3.05 instead of pi but as tyre designers have a tolerance around the tyre designation it isn't possible to calculate with any accuracy.
As regards tyre pressure, quoting from ancient Minor Matters, Michelin recommended 20/22 for their 145 R14 MX on a Saloon but suggested 22/24 for other manufacturers radials. Increasing pressure radically to give 'better steering response' and to 'avoid overheating' are a nonsense. Just beware of excessively low pressures (10-14psi???) as our rims are not tubeless and therefore don't have a retaining diameter which may result in a tubeless tyre coming off the rim with high cornering forces.
John

I found this site very useful when selecting tyres for my 5 1/2" J's. I managed to get some with a circumference within few mm of the 145's fitted to the original wheels.

Edit
Would help if I attached the link

https://www.mcgrefer.com/sizeinfo/#page-1=page-1-width

Hi, must add my penn'orth. Where do members with 155s store their spare wheel? I raised the question a year ago (to the day!) and was advised to obtain a 145 to fit in the aperture on my 1967 four door saloon. Do others do this?

http://www.mmoc.org.uk/viewtopic.php?f=5&t=56223

Just when you think that you know it all someone produces a gem of information
My 155 spare fits under the boot floor with room for a set of gaskets on top

I run 155/80/14 tyres on mine (Nankangs, which are inexpensive and suit the car well) and have no trouble housing the spare wheel & tyre in the correct position
Maybe some owners have a bent boot floor platform

ManyMinors just what I wanted to hear as I have just taken
delivery of a set of Nankang CX688 for my Series 11.

Really really, good price with Free Delivery.

The courier did leave another box with 2 tyres 205's, by mistake. Someone
will be waiting for these but the firm said they will pick up tomorrow.

Shane

I totally agree with Mike 155x14 running at aprox 30 psi. if you run at recommended pressure on 155's the volume of air inside doesn't inflate the tyre correctly thus damaging the side wall. Think of it this way larger tyre more air to inflate smaller tyre less air. We run our 54 series 2 on 155's at 30 psi all round.