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MG MGF Technical - Tyre sizes

Can someone clarify this for me please

TF135 cool blue, 16 inch wheels

Front tyres are 195/40 R16
Rear tyres are 215/45 R16

Now I understand the difference between 195 and 215, but why the difference between /40 and /45?

and would it make a difference if I changed the rear to 215/40?

thanks
Colin Ashworth

The 40 or 45 is the aspect ratio of the tyre, i.e. in this case the side wall height is either 40% or 45% of the tyre width. Changing the profile of the rear tyres will change the rolling circumference of the tyre, affecting the accuracy of the speedo.
Ralph Gadsby

thanks Ralph, is it normal for front and rear tyres to be different ratios? or has the "previous owner" fitted the wrong tyres?

Guess I need to check my owners manual
Colin Ashworth

The front and rear tyres are correctly different sizes. What I'd not really thought about here is that I'd assumed the different profiles gave the same total diameter of the wheel + tyre.

However, for the front tyres the wall height is 195*0.4=78mm whilst the back ones are 215*0.45=97mm. If the profiles were the other way round (i.e. 45 at the front and 40 at the rear) then the tyre walls would be almost identical at 88mm and 86mm giving the same overall wheel diameter (and thus circumference).

Perhaps you've mixed up some of the numbers?

Chris
Chris Rudge

195/45 R16 front, 215/40 R16 rear - well spotted there Chris :o)
Rob Bell

yes yes I did :(

thanks folks
Colin Ashworth

I have got 215/40 R16 tyres fitted to all wheels on my Abingdon is this correct?
S J Sibthorp

well its correct for a TF135 .....
Colin Ashworth

I can't remember where I saw it, but I read recently about someone who had problems in France getting a replacement tyre because he had non-original sizes. Apparently in France it's illegal to supply anything but the originally specified sizes. So if you've fitted 17" wheels, you'd be up the spout! There might even be a problem persuading them that 16" on a '96 1.8i was OK. And what's the correct size of the various ones listed?!
205/40x16 front, 215/40x16 rear work OK. The photo also shows the car on its TF suspension with the 'comfort' (relatively speaking!) Bilstein dampers. They're set mid-height at the rear, and lowest at the front, but it's still only just below standard ride height. (I seem to be straying from the original topic!)

M Cunningham 1

>> And what's the correct size of the various ones listed?! <<

215/40 R 16 or 195/45 R16 front, and 215/40 R16 rear :o)

Nice looking car there - how much modification needed to get the TF suspension in (particularly regarding the front and rear damper upper mounts)?
Rob Bell

I let Mike Satur loose on it last year, and he probably learnt or invented quite a few new swear words getting the old stuff off. All the bolts were well and truly rusted solid! The only body mod required is to cut a pair of clearance holes above the front damper mounts, where there is already a raised 'dimple' in the pressing. At least for the money, I now have an unbelievably clean underside - everything Waxoyled, Coppaslip on all the fasteners &c &c - see sample pic attached! (One rather rusty-looking lower engine steady bracket, though!)
I know you've had a look at my website, Rob - if anyone else is interested in that conversion, go to http://www.lejambonfute.f2s.com/m2dyk_home.html to read all about it. I apologise if all the apostrophes have gone funny - f2s have just moved my site onto a new server, and I've been too busy to update.

M Cunningham 1

All other countries in Europe abide by the EEC Rule that you may not vary your car from the Original Design Approval to a varying extent. Most are very strict except UK where nobody cares a toss.
If you take your car into Mainland Europe and are involved in an accident, the Police will inspect your car and if it does not comply, then you are totally liable despite whoever caused the accident. viz. your car is considered to not be roadworthy.
Geoff F.
G. Farthing

I know that the guys who designed the TF had in the back of their minds the conversion of hydragas to conventional springs - but it is very interesting that the body modifications are very minimal! :o)
Rob Bell

I was originally going to get various goodies like a new hood, leather seats &c, but I went to Alan Phillip's (ex MG/Rover, now Vehicle Handling Solutions) talk at MGF10, and he explained why the TF rear suspension was fundamentally better geometrically than the F; also that it was indeed designed as a retrofit. It convinced my engineering designer's mind, so I blame him for forcing me to pay for the monster mod. I'm not in the least sorry though;o)
M Cunningham 1

ROFLMAO! Don't blame you! :o)
Rob Bell

This thread was discussed between 04/09/2007 and 08/09/2007

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