Up-sizing alloy wheels from standard

[nicecar]

Hi my Astra Conv has 205/50 16 87 tyres (50 profile) as standard on 16" alloy wheels

Can someone tell me the profile size of tyre I would need if up sizing the alloys to:-

17"

18"

19"

Take it that the overall diameter of the tyre will be the same, just the bigger the wheel, the smaller the profile of the tyre. (so speedometer not out)

Also if clearance, can you put a higher profile tyres and have the speedometer re-calibrated (as say tyres for 19" have to be ultra low profile and cost the earth) Is this legal?

[SmellyTofu]

http://www.miata.net/garage/tirecalc.html

[Benny-o]

Not sure of the profile q, I'm not sure how low a profile can go 25 - Maybe (in regards to 19")?? Somebody to confirm please. 50 means that the wall of the tyre is 50% the width of the 205.. so as your profile reduces you're in for one hell of a bumby ride, with or without lowering etc. I'm pretty sure 17" = 45(235/215), so maybe 18" = 40..?? Keep an eye on the width as well as the hight too, don't want to have to widen your wheel arch or whatever they do, that's pretty costly..

The legal side of things you can only increase your rim size by 2", so really your max is 18". 18" fill the wheel arch real nice & tight as you've probably seen on other astras..And the lowest point of the car must be no less than 100mm.

not sure if that helped you any, im sure somebody with more xp will post something pretty soon!

[Benny-o]

hey that's a cool little site SmellyTofu! nice find!

[Nem]

Use the same fitment as the Turbo 17's for them. 205/45/17's IIRC. Offset needed is between 38 and 49 I believe.

If you go 18's:
225/35/18 or 215/35/18 in order to keep as close to your rolling radius as possible. Load rating should be minimum 86V so remember that when purchasing your tyre. You probably wont find a 215 wide tyre with a LR greater than 84.
You'll also need an offset around 45 to 49 in order to keep the vauxhall fitment and keep any scrubbing to a minimum. Absolute maximum width of the wheel is 8" but I suggest you get 7.5's if you can find them. (They're not widely available however)

IMHO 19's arent illegal (at least up here :D) as long as you get them engineer certified. You will however you will require major arch modiification.

Having said all that, the luckiest thing about owning the cabriolet (the convertible) is that I believe it has more room in the wheel arches than the hatch/sedan models. So you might even get a bit of leeway there.

All this information is purely from what I've learnt having researched for myself. I would advise that it's all purely guidelines and you may experience different results to what I'm expecting. But at least find some comfort in the fact that I ordered $3600 worth of wheels and tyres so I like to think that I've done my homework. Potentially an expensive lesson but I'll be sure to post whether I pass or fail. :lol:

[break]

Just using this: http://www.miata.net/garage/tirecalc.html

205/50/16

You can get any of these legally as they are no more than 16mm bigger in diameter than your current wheels, and they arn't more than 1.3x wider than your current wheels.

205/45/17
225/40/17
215/40/18
225/35/18
215/35/19
225/30/19
215/30/20
225/30/20

[Nem]

For some reason most of the UK boys run 215/35/18 instead of the 215/40/18 as prescribed by the calculator. :?

[GOZOFF]

For some reason most of the UK boys run 215/35/18 instead of the 215/40/18 as prescribed by the calculator. :?

I do too :)

[RK]

i think its because 215/40s are hard to find. or not mainstream enough to be a financially viable option.

[leon1982]

according to some members from astra-sport.co.uk 19s are find as long as you have the correct wheel spec..especially in a convertible..I think the only mod you need to the guard is rolling the arches...I wouldn't call this a major mod though
so..if I were you..I'd go for 19s

[ultim8DTM5]

The search button answers all your questions!!!!!

[nicecar]

Thanks for all your help :D , I am going to get tyre prices and see what up-size fits my budget

[dug74]

For some reason most of the UK boys run 215/35/18 instead of the 215/40/18 as prescribed by the calculator. :?

Corsa are suppose to run 205/35/17 to be true and correct as well...but 205/40/17 are cheaper and more mainstream..and only puts the speedo out 2kms ;)

[ultim8DTM5]

Hmm anyone knows the the Barina runs an electronic speedo? I know the mechanical ones were over-compensated from the factory so they would be more consistant over time...taking into account wear.

[JasonGilholme]

My Corsa's only got 14's stock.... Does that mean I can only go up to 16's??? legally that is 8) I'd like 17's but i wanna know if it will effect my insurance if i have a crash....god forbid

[Nem]

Corsa are suppose to run 205/35/17 to be true and correct as well...but 205/40/17 are cheaper and more mainstream..and only puts the speedo out 2kms ;)
I agree with what you have said. :) Although I would like to be a little more explicit.
It is recommended that you're within 2.5% of your original diameter. But as you say the availability and price (as well as a marginally better ride) that is provided by the 40 profile tyre would make it slightly more appealing. Not so much that it is the "wrong" tyre. Unless it puts your speedo out too much and then you should get it recalibrated.

[ultim8DTM5]

Width is the greater concern than diameter. Get a 25/30/35 series profile with 17x6.5 and should be alright.

But do the maths I'm generalising

[Nem]

Yeah I find its getting the right combination of everything. Width when concerned with scrubbing. Rolling Radius/Diameter mainly for speedo. (but also scrubbing) Availability of the tyre in a particular load and speed rating. Recommended width of the tyre on what width wheel. Hell it gets pretty damn confusing. So stop listening to me and talk to a professional. :lol: