Whats the correct tire size

[David Ambrose]

Hi,
I need to replace 2 of the tires on my 1967 wirewheel MGB GT.
The problem I have is that the current tires do not state the size of the sidewall and only have the number 175HR14 88H

I have contacted a few tires places to try and find out what the equivalent modern day size would be with some telling me they will be 175/75/14 and another saying they will be 175/80/14
As I'm only changing the 2 fronts I want them to be as close to the size on the back as possible.

Can anyone tell me what the correct size would be or if there is any other way to check?

Many thanks
David

[Peter Cresswell]

Hi David,
The number you have quoted - 175HR14 88H is the tyre size you have, and these tyres have an aspect ratio of 80% - which means the tyre sidewall height is 80% of the tread width. So in your case the tread width is 175mm and the height of the sidewall will be 140mm. HR is the 'old' speed rating of the tyre dating back to when tyres were simple and used SR for up to 113mph; HR for 114 - 130mph and VR for over 130mph. This rating has nothing to do with how fast the car will go or how fast you drive, but was designated as the tyre by the manufacturer. The MGB roadster used 155SR 14 tyres and the GT used 165SR 14 the extra width probably was dictated by the GT being a heavier car. Nowadays, and for your tyres 88 is the load rating, and H is the speed rating and is 130mph maximum.
The correct tyres for your car are 165 x 14, which will have an aspect ratio of 80%. The MGB GT on steel wheels had a 5" rim width, whereas with wire wheels the rim width was 4.5in on both the roadster and GT. So 175 tyres on wire wheels are a bit too big for the rims. Also the 175 tyres you have will make the speedometer under-read a little. the suggested tyre of 175/75 x 14 will make the speedo read correctly but they will have a wider tread width than the 175 x 14. You don't want to put the 175/75 x 14 tyres on the front and the 175 x 14 tyres on the rear as this will mean you have wider tyres on the front than the rear which is an unstable combination. The other way round will be fine.
Better would be to stick to 175 x 14 with an aspect ratio of 80% until you can afford a set of 4 and then put 175/75 x 14 tyres on. This is quite a popular tyre with alloy wheels such as Minators with 5.5in rim width and help prevent the tyres rubbing on the rear wheel arches.

[David Ambrose]

Hi Peter,
Thanks for you reply.
The tire shops i have gone to don't seem to stock 175 14's i'm assuming this is an old style of tire which is why they are suggesting 175/75/14 instead.

So ideal option sounds like replacing all four with 175/75/14's
Would that be better then 175/80/14's which some other garages have recommended?

Is it also recommended to change the tubes as well or do these not need to be changed each time you change the tires.

Thanks
David

[Peter Cresswell]

Hi David,
Yes 175/75 x 14 tyres all round would be better, but I feel that even better would be 165/80 x 14, as the car was designed for this size, and they would fit better on the 4.5in rim of your wire wheels. The 175/75 x 14 would be fine on a 5.5in wide rim. The tyre choice is up to you, but from personal experience Toyo work very well on an MGB and they do make a 165/80 x 14. (see http://www.toyo.co.uk/tirefinder/index/ ... /80/rim/14 ). Another popular tyre in this size is Barum. Most tyre shops won't stock MGB sizes so will have to get them in for you.

Modern tyres don't have ribs on the inside which were designed to stop an inner tube from moving inside the tyre (they were designed to be tubeless!), so yes replacing the tube is a good idea. Some years ago I had a 1970 MGB with wire wheels, and I had three flats in one day caused by the tubes rubbing on the inside of the tyres. This was not convenient! You should also have the rubber band that protects the inner tube from rubbing on the end of the spokes replaced at the same time, especially if they are showing signs of wear.

You should also make sure that whoever balances the wheels after the new tyres are fitted knows how to do this correctly and that they have the correct cones for the balancing machine to do them. See this article for more information on this:
http://www.mossmotors.com/SiteGraphics/ ... heels.html
This article also covers the checks needed to ensure the hubs are in good condition.

[Roger Boys]

Really interesting articles on wheels and tyre sizes. I have been plagued with punctures during the last few years using 60 spoke wheels fitted with 175x14 Pirelli P6 tyres and tubes, I tried new rubber spoke protection bands and new heavy duty inner tubes to no avail. This problem got so bad that recently following yet another puncture on the M50 around Dublin I have replaced the complete set of 60 spoke wheels with new ones designed to take tubeless tyres 4.5 x 14 60 spoke chrome finish, these were supplied by Motor Wheel Services of Langley. During a long talk with this company I was reassured to know that tubeless wire wheels have been supplied to Morgan and Jaguar along with MGC for some years with success. I had a new set of Barum Brillantis 165TR14 tyres fitted and balanced using all the correct equipment by MWS. I was very impress with the quality of service particularly the fitting and balancing of the tyres using the correct cones it was so easy that I was allowed to balance one myself! In the passed I have experience lots of problems with getting wheels balanced, the correct equipment it would appear is vital. Most high street tyre company's do not have the equipment, skill or the interest in doing the job correctly. This project was not cheap but from experience I believe that you get what you pay for in this life and MGB parts fall firmly into this category.

[Adrian Oliver]

Interesting Roger.
Do MWS only sell tubeless wire wheels or do they make both?

[David M B Leggeat]

Roger,
How do you rate the performance of the tubeless wire wheels after a further year of use?
Regards,
David.