Original tyre diameter?

[haircutmike]

Can someone let me know what the original tyre diameter was for the original fitment tyres?

I have bought a set of wheels for the road and will be changing the tyres.

The rears are good, 225x45x17's

The fronts, I am sure are too small being 205x40x17's

I am tempted to put the same size all round and adjust ride height accordingly.

What do you guys think?

[J400GED]

Original fit on non PAS cars is 205/55/15 = 112.75mm (205mm x 55%) + 190.5mm wheel radius (7.5inches) giving a nominal rolling radius of 303.25mm (11.94 inches).

205/40/17 equates to 205mm x 40% + 215.9mm wheel radius = 82mm + 215.9mm = 297.9mm nominal rolling radius. Difference in nominal rolling radii = 5.35mm which is approximately the amount of wear from a new tread to a worn out one.

HTH

Ged

[SMB]

J400GED said:

Original fit on non PAS cars is 205/55/15 = 112.75mm (205mm x 55%) + 190.5mm wheel radius (7.5inches) giving a nominal rolling radius of 303.25mm (11.94 inches).

205/40/17 equates to 205mm x 40% + 215.9mm wheel radius = 82mm + 215.9mm = 297.9mm nominal rolling radius. Difference in nominal rolling radii = 5.35mm which is approximately the amount of wear from a new tread to a worn out one.

HTH

Ged

Not strictly true, 205/55/15 was for later cars, early cars had 205/60/15 as standard.

[haircutmike]

Guys, I should have said, car has pas, does that make a differance?

[J400GED]

ok, Haircut Mike, what age is your car?

If it has 205/60/15 that equates to 123mm + 190.5mm = 313.5mm against 297.9mm giving a difference of 15.6mm.

As fronts are not driven, it will have no effect on your speedo or anything like that.

So it's a question of taste regarding wheelarch space to the wheel - obviously this will also vary dependant on what ride height the car is set at.

[J400GED]

Early PAS cars had 215/50/15 (unless anyone can correct me) equating to 107.5 + 190.5 = 298mm and the later PAS cars had 225/50/15 equating to 112.5 + 190.5 = 303mm.

The reason for the narrower tyres on non PAS cars was to reduce the effort required to turn the steering wheel and having narrower tyres on a PAS car will do no harm.

HTH

Ged

[haircutmike]

I have never had original wheels.

I currently have been running Toyo triple 8's

Rear, 255 x 40 x 17's
front, 215 x 45x 17's

Newly purchased, (s/h) wheels.

They have 225 x 45x 17's on the rear, similar overall radius I believe

Front rims are the same size.

These have the 205 x 40 x 17's but are too small in diameter.

I fancy going up to the same size as the rear or probably, 215 x 45 x17's or am I barking up the wrong tree?

[J400GED]

The 205/40/17 will give 297.9 radius very close to early PAS wheel/tyre size 215/50/15

The 215/45/17 will give 312.65 radius - very close to the early non PAS wheel/tyre size of 205/60/15.

The 225/45/17 will give 317.15 radius - slightly larger again and will probably fit in the wheelarch and the extra loading on the PAS - if fitted - should not be a problem since the later Chim 500 with PAS had this width. If PAS is not fitted, you will notice heavier steering.


Ged

[haircutmike]

Just found one of those new fangled tyre calculators!

The original 225x50x15's would equate to either;

225x40x17, 6mm larger dia. or

215x40x17, 3mm less dia.

Is the smaller width desirable, if so for what reason.

I would have thought to go for the wider 225mm for a tad more grip?

[J400GED]

Mike,
As you have PAS, the extra tyre width shouldn't be a problem for the steering weight as 225s were fitted to later Chim's.

Do you need more grip at the front?

As I said earlier, at the end of the day it comes down to personal taste.

Ged

[SILICONEKID340HP]

closet match for 17" wheels are
Front 215/40/17 about 3mm smaller in diameter compared to 205/55/15 0.5% difference
Rear 245/40/17 about 3mm smaller in diameter..compared to 225/50/16 0.57% difference

Giving you very close to 1" differene between front and rear..

Edited by SILICONEKID340HP on Monday 27th June 23:14

[haircutmike]

I always need more grip!

I will go for the 225x40x17's then as these are close to my triple 8's that the suspension is set up for.

Thanks for your help.

Peter, (not Mike) .

[haircutmike]

Dam, the 225 isn't available, suppose it will have to be the 215's then.

[J400GED]

Yeah sorry Peter, just looked at your profile