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MG Midget and Sprite Technical - Modern tyres for an old Frogeye

I need some decent rubber on my wheels but want to retain the original rims (3.5 inch) which are really for tubed tyres.

I have searched through the archives but not found much information, apart from one thread where a few posters have said they have used tubeless tyres on tubed rims.

I had a look at some tyres at my local Black Circles depot and all modern tyres are heavily sculpted inside so it doesn't look like a good idea to run tubes inside them.

Someone must have had this problem recently so if you have can you share some of your knowledge with me.

The tyres I would like to fit are Uniroyal Rainmaster, Dunlop Streeet Response or Goodyear Efficient Grip. I can get these in 145/80 R13 T or 155/70 R13 T. I know the modern equivalent size is 145/80 but as I have a 3.7 diff I could have the 155/70's instead if suitable for a 3.5 inch rim.

Rob

Rob aka MG Moneypit

Rob,

I've got modern tires, General Altimax RT, on my 77 MGB. This is a wire wheel car, so it runs tubes. I agree with you that the inside of the tires look pretty course for inner tubes. So, I can't say I recommend running tubes in these course tires, but I have been doing it without problems. So far that is only about 6000 miles, but did include one 3500 mile round trip to Utah.

I believe there are differing inner tube qualities. If you decide to go this way, see if you can get some thick ones. I have noticed significant differences lately in inner tube thickness for my tractor.

I guess if you have lots of $ you could have new bands welded to your wheels.

Charley
C R Huff

Are your rims porous? Mine are original frogeye and are fine with tubeless
Bob Beaumont

Bob and Charley. This all started when I took a deflated tyre to a tyre supplier. The tyre was a tubeless type but used a tube. I asked him to take the tube out and repair the tyre. He said the wheel didn't have a safety bead on the rim (he could tell by the rim profile) so the tyre needed a tube. I got a tube and he replaced it for me. He said, in an expert type of way, you can't put tubeless tyres on that rim without tubes.

So I have spent a good few days ringing round tyre suppliers and visited my local Black Circles depot to find tubeless tyres I can put tubes into, as the expert said.

But, I've just read my 1959 workshop manual and it says the original tyres were 5.20x13 TUBELESS tyres. So much for the many "experts" I have talked to!!!

A case of RTFM?

So I can put any tubeless tyre on my original rims without a tube. Sorted.

Bob, the wheels are like new inside so my worries are not really worries. So much for so called experts.

Rob
Rob aka MG Moneypit

Yes tubeless tyres were fitted from day one back in 1958. Don't you just love 'experts'
Bob Beaumont

Safety rims are nothing to do with whether they are tubeless tyres or not.

They were first used by Chrysler with tubed tyres. Have a look at this article:

http://news.google.com/newspapers?nid=698&dat=19410129&id=neRTAAAAIBAJ&sjid=94kDAAAAIBAJ&pg=2993,2431602


Jim
J Smith

I've been fiting tubeless tyres to steels on older cars for decades and have never had a problem. I'm sure there are exceptions but I haven't encountered them.
N.C. Nakorn

Yes, experts. Say no more.

Interesting snippet in the link you posted Jim.

So a 5.20 crossply as originally fitted would be about 135mm so I suppose 145 being 1 size up is probably the biggest for a 3.5 inch rim. So, would 155 be too wide??

There is an ebay auction on at the moment (251546476786) with a set of 5 Frogeye wheels with tyres. The tyre size quoted is Avon 175/70 x 13 which must be dangerously over size.

Rob
Rob aka MG Moneypit

tyre sizes were discussed recently and the fact that 5.20 is equivalent to 135/80/13 (well 130/100/13 actually) and from linked table also 145/70/13

I assume you want tyres for your frog with steel wheels

I also postulated that given an original Frog's weight that 135s would be fine for the weight and handling of the car plus that lighter vehicles need less loading index and generally the narrower the tyre the less load index

whatever tyre width you put on you need to check it's within the manufacturers recommended rim width range see here as an example of the range, clink on to the link for 350, then the size and specifications tab, you'll see that this particular model of tyre suits a 135 and is within range for a 145 but out of the manufacturer's recommended range for 155 for this particular model of tyre - http://www.toyo.co.uk/tire/category/passenger-&-eco-car

btw you don't want the Toto 350 on a Spridget, I made that mistake

see here for tyre sizing and loads more useful info - http://www.carbibles.com/tyre_bible.html

a tyre size comparison calculator is three-quarters of the way down this page - http://www.carbibles.com/tyre_bible_pg4.html
Nigel Atkins

missed the edit, it should have read -

> ... you'll see that this particular model of tyre suits a 135 on a 3.5" rim and is within range for a 145 ... <
Nigel Atkins

and this link covers a calculator that includes 135 size which the other doesn't

the 135/80/13 has a greater rolling radius than the 145/70/13

but the 135/80/13 has an almost identical rolling radius to the 155/70/13

but obviously the 145/80/13 has a greater rolling radius than the 135/80/13 and 155/70/13 (and obviously also the 145/70/13)

- http://www.kouki.co.uk/utilities/visual-tyre-size-calculator
Nigel Atkins

I wouldnt put the full blame on the this "expert" tire guy

This is very old technology... Id bet he dosnt see many old cars like ours with tubes...the guy probably does know tires very well... modern that is, on top of that, this is justone modle from one car company...theres probably 1000 cars out there made be for 1978, that use differant tires and wheel combos

I think this is very similar to taking our cars to a modern shop and having a 22 year old fresh out of tech school to adjust the carbs and install no points and condensors then clean and calibrate the mechanical regulator

If this was a classic car mg shop ....my thoughts would be differant... string the idiot up, over a good fire...haha
Prop and the Blackhole Midget

Well I have ordered 4 off 145/80 x 13 tyres to be fitted Wednesday at the local Black Circles depot. Uniroyal Rainmasters seem to have come back into stock after being unavailable for a while.

Found another wheel calc website that still has crossply sizes.

http://www.exploroz.com/Vehicle/Tyres/SizeCalc.aspx

Interestingly, 5.20 x 13 crossply tyres are 590mm diameter and 145/80 x 13 radials are 562mm diameter. This means this size radials are 95% the size of the original crossplies, which is a big difference.
It's interesting that 145/80 x 14 tyres are 588mm diameter which is a closer match. I wonder if there is an alternative 3.5 inch steel wheel available in 14 inch diameter? Some other BMC car perhaps?

Rob


Rob aka MG Moneypit

Rob,
interesting stuff, early MGB wheels were 4J-14", they ran on metric size 155/80/14 but the B is a heavier car and a 145 tyre would normally fit to a 4" rim

the later MGB Rostyle wheels, 5J-14", on the roadster still had 155/80/14 tyres, BGT had same wheels but 165/80/14 tyres

just out of interest I crunched a few number but if there are errors it's because my elderly electronic calculator sometimes makes mistakes, my mate say it's something called GIGO

rolling circumference (tyre 'rolls along the ground' like a caterpillar tank tread does) - read more: http://www.carbibles.com/tyre_bible_pg4.html#ixzz34HCxHTdq

5.2 x 13 = 1791.94mm rc

135/80/13 = 1646.94mm rc (8% out on speedo to 5.2 x 13)

145/80/13 = 1695.55mm rc

145/80/14 = 1772.16mm rc
Nigel Atkins

was just about to throw my scribblings away when I noticed I'd copied a figure down wrong, sorry

correct figures for rolling circumference -

5.2 x 13 = 1792.55mm rc

135/80/13 = 1647.30mm rc (8.1% out on speedo to 5.2 x 13)

145/80/13 = 1695.55mm rc

145/80/14 = 1772.16mm rc
Nigel Atkins

Hi all, been happily running on 145/80 Uniroyal Rainmaster (tubeless) tyres for a week or so and so far so good. Had to lower tyre pressures down to minimum stated in drivers manual. As they left Black Circle depot they were much too hard and felt like driving on rubber baloons. They even torqued the wheel nuts to the correct torque for me which would have been ok but their torque wrench was reading 10 lb/ft over so I had to do it myself when I got home.

Too Black Circles over an hour to fit 4 tyres due to quite heavy corrosion inside. Took a lot of grinding out and lashings of rubberised sealant to seal the tyres. I looked at the inside of the tyres and they have ribs inside but just on the side walls so I reckon I could have used tubes with them.

Going to Le Mans for the Classic event so will take a couple of new tubes just in case.

Rob
Rob aka MG Moneypit

This thread was discussed between 04/06/2014 and 18/06/2014

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