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Discussion Starter #1
Morning!

I was looking for the correct tyre size for my 17" wheels on my 156 and looking at the Reg checker on Kwik Fitts website it states 225/45/R17 front and rear.

The car was running 215/45/17 on the rear and 205 on the front and was a very harsh ride. So I ordered 225/45/17s all round and the mobile fitter just arrived and we discovered that the fronts won't fit!

I have now re-ordered a 205 for the front and kept the 225 for the rear.

Just in case anyone else is caught out - or am i just stupid? Who knows.

Have a nice day - (Tyres by the way are the Falken 912s - to replace P7s on the rear and potenza on the front (P7s have started to crumble but have lasted years - the potenzas have lasted 6 months)
 

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Should have gone with 215/45R17 as the best and most effective compromise.

Remember to fit the new tyres to the rear, and rotate the original rears to the front so you don't end up with crusty age hardened tyres on the rear and new grippy ones on the front. Oversteer city when you least expect it.
 

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Discussion Starter #3
will the 215 fit on the front without problem and will it give a better ride than the 205. They are returning tomorrow to fit the fronts so I can change the order. I used Event Tyres and I must say they are really good guys.
 

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The correct size is 215/45R17 all round.


Don't use different size front-rear.
 
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215/45x17 is the correct size but a few have fitted 225/45x17 without problems - I guess it depends on the tyre as well as the offset of the wheels.

I assume the fronts are 205/45, considering the harsh ride, and not 205/50 ?

The 225/45's I have give a noticeably less harsh ride than the 215/45's that were on before - probably the brand makes a difference too
 

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The wider 225 tyre will have a slightly larger sidewall, hence the less harsh ride. Remember the profile is a percentage of the tread width so 45% of 215 is 96.8mm and 101.2 on the 225.

Then the speedo will also register slow (at 70 you are doing 71) and the mileage will be recorded incorrectly as you are travelling further per wheel rev than the odometer is recording. Not much in each trip but over the life of the car it could be a lot. Going to the 205 width means the speedo is fast (70 is 69).

You can check tyre sizes at miata.net or Car Bibles.
 

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Gazza's comments obviously assume that the speedo is reading correct on 215/45R17, which it probably isn't because they are noticeably smaller in diameter than the std 205/55R16.
225/45R17 are very close in diameter to 205/55R16, only 1mm difference.

225/45R17 will fit with the std Alfa 7" rims, but clearance will vary between different makes.
 

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Discussion Starter #8
Thanks guys, however I agreed to have the 225s fitted on the rear and have ordered 215s for the front. As the car was previously running 215s rear and 205s front this should be ok.

Why is it wrong to use larger tyres on the rear? I know my BMW did and this is obviously because its rear wheel drive.
 

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Why is it wrong to use larger tyres on the rear? I know my BMW did and this is obviously because its rear wheel drive.
You have answered your own question there!
They have larger rears because they are RWD.

No point at all having larger rears on a FWD car.
You will also have different diameters, which will mean the ABS/EBD won't work properly.

Just fit the correct size all round.
 

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The different sizes shouldn't be an issue. For instance, the rear could be worn and the front brand new. Even if they are the same size, they would have differenct rolling circumferences due to wear. Also consider the effects of cornering whith regard to distance traveled. The rear takes a slightly tighter and shorter route whilst cornering so it won't through the chassis electronics out. Had the size differences been greater, then I'm sure it would.

A good and relevant point though.
 

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Gazza's comments obviously assume that the speedo is reading correct on 215/45R17, which it probably isn't because they are noticeably smaller in diameter than the std 205/55R16.
225/45R17 are very close in diameter to 205/55R16, only 1mm difference.

225/45R17 will fit with the std Alfa 7" rims, but clearance will vary between different makes.
I don t think 205/55R16 is the homologation tyre dimension for the 156. The car was homologated in 15 inches and for the 17", 215/45 is the closest diameter and aslo Alfa dimension. Actually 215/45 is meant for a 7" width while 225/45 for 7 1/2". The increase of diameter is acceptable for a GTA since the power is there ... on a 1.6 it must be a nightmare !

In return i am very surprised you are allowed in UK to run two different dimensions on front and rear ... :wow: (if ever you are?)
 

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205/55R16 is the most common tyre size on a 156, IMHO.

We can have differnt sizes front and rear. You can too as obviously BMW and Merc sell over there.:rolleyes: I think it is perhaps it is a French law that you cannot change the relative sizes if the same size for front and rear was originally homologated. Talking of which, as so many 156s were supplied new with the 205/55R16 size, then this had to be homologated. If not, the cars would not have had a certificate of conformity, and the 205/55R16 size would not appear in the owners' manual.
 

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The original homologated sizes were:
15": 185/65R15 & 205/60R15
16": 205/55R16 (std for all Sportpack/Veloce & all Selespeeds)

Optional 17": 215/45R17
 

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205/55R16 is the most common tyre size on a 156, IMHO.

We can have different sizes front and rear. You can too as obviously BMW and Merc sell over there.:rolleyes: I think it is perhaps it is a French law that you cannot change the relative sizes if the same size for front and rear was originally homologated. Talking of which, as so many 156s were supplied new with the 205/55R16 size, then this had to be homologated. If not, the cars would not have had a certificate of conformity, and the 205/55R16 size would not appear in the owners' manual.
205x55/16 is the equivalence in 16" ofr the homologated basic size as stated above of 185x65/15

diameters are :

185x65/15 = 621.50mm
205x55/16 = 631.90mm
215x45/17 = 625.30mm
225x45/17 = 634.30mm

So to get back to the topic above and according to the diameters, 215x45/17 is certainly the closest to 185x65/15 with the closest accuracy on the speedometer.

As for the law ... if you carry 2 different sizes even homologated, what would be your spare wheel ? If you get the different diameters on the same axle, even temporarily, ... your transmission might not like it ! It is the same in Italy , Belgium ... we MUST follow an homologated dimension on 4 wheels not 2 since we obviously do not drive a Formula 1 ... ;)
 

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Well, | run 225/45/17 tyres with Eibach springs and koni FSD dampers without any fit or clearance problems at all. Not exactly sure why you would have problems.
 

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It's perfectly legal to use different widths in all European countries, all Porsche & BMW Msport cars have wider rears. A Boxster has a 40mm difference between front & rear. Obviously you should only use different widths if it is a manufacturer factory spec.
I don't think any manufacturer has ever fitted different widths on a FWD car as standard though.
 

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"It's perfectly legal to use different widths in all European countries, all Porsche & BMW Msport cars have wider rears. A Boxster has a 40mm difference between front & rear."

... if the car is homologated that way ... no 156 are homologated with different size on front and rears .

Cheers
 

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"It's perfectly legal to use different widths in all European countries, all Porsche & BMW Msport cars have wider rears. A Boxster has a 40mm difference between front & rear."

... if the car is homologated that way ... no 156 are homologated with different size on front and rears .

Cheers
I agree that's exactly what I said, as you missed my last sentence out which was

"Obviously you should only use different widths if it is a manufacturer factory spec." :thumbs:
 

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Well, | run 225/45/17 tyres with Eibach springs and koni FSD dampers without any fit or clearance problems at all. Not exactly sure why you would have problems.

I suppose it is possible if the wheels have a different offset to the homologated or OEM wheels.
 
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