2bitpython

Hi all, brand new here and not very car-wise, so I'm hoping to get some advice on tyre selection and start to improve my knowledge on Scooby matters.

I have an 05 STi with its original 17" wheels and tyres. As the tyres are approaching the end of the line I thought I might take the opportunity to swap wheels too, as I fancy a change from the standard gold multi-spoke alloys - they take so long to clean!

When I shop around I find a much bigger choice of 18" alloys over 17". So my question is this really: are there any downsides to having 18" instead of 17"?

I can only guess that it might affect things like ride, turning circle, road noise, etc - maybe it won't make any difference to anything, I don't know.

I'd appreciate any help on wheel/tyre selection that you can give, so I don't spend a lot of money doing something I'll regret.

Right, I'm off next to google what 225/45/R17 means, 'cos right now they're just magic numbers to me!

Cheers
Si

ScoobP1

iTrader: (1)

18's should give you better handling but a bumpier ride. Tyre will be more expensive with 18's and they will be damaged easier on potholes.

18's will look far better and are worth getting.

The numbers you mentioned mean in this order, tyre width (in mm) wall height Or aspect ratio (in % of tyre thickness) and rim diameter (in inches).

Hope this helps.

Gary WRX

Bear in mind if you are running 225/45/17 the 45 part relates to the depth of the tyre wall so if you are changing the rim size to 18 you need to drop the tyre depth to 40 to keep the circumference the same.

2bitpython

Thanks ScoobP1 for the info, it's good to be aware of the downsides as well as the up.

And although I'd guessed the 225 was probably the tyre width in mm, for the life of me I couldn't work out what the 45 meant! millimetres? no. cm? no. inches then? no. erm...

So thanks for shedding light that it's a percentage!

And thanks Gary on the extra advice on dropping the tyre depth - invaluable tip. I'm starting to feel like I'm in a better position for picking the right wheel/tyre choices when it's time for a replacement.

While we're on the topic, can you quickly explain what the numbers mean that are listed against the various wheel choice on the websites selling them: numbers like 17x6.5, 17x7, 18x8 etc?

Cheers again
Si

Themanatforss

Hi - just bougt a P1 with 18" and 215 x 35 tyres and hit a pot hole on M74, blew out the tyre which I had to replace. Some thing for you to consider.
(Now looking for original P1 17" OZ Racing wheels)

2bitpython

Hi and thanks for the warning. Dunno if 17" tyre would have popped too, but it would seem that with very low profile you increase the chance of damage.

Tough call: safer 17" or cooler 18"

stef_2010

iTrader: (3)

I'd go for 17s

18'' wont handle better than 17'' as you need to decrease the size of the tyre wall to keep the same rolling radius

I have a classic that came with 16'' standard, i also have a set of 17'' for it, while I keep the 17'' on most of the time the ride is much nicer with the 16'' and the bigger sidewall

Rob Day

iTrader: (78)

I personally dont think there is a lot in it. Now if you had a car running on standard 16's ad then went to 19's that would be different.

I have a simular car to you, Silver with Gold STI wheels, and I find them a bit gory gainst the silver paintwork. So i have just gone for 18's in anthracite, the ride doesnt eel to be much different, but the handling is much sharper. As for tyres, yes they are a little more expensive, but not by enough to worry you unless you eat through them frequently?

Have a look in the for sale section as there is generally someone selling wheels with tyres, tyres or just wheels.


Rob

2bitpython

Thanks guys for your thoughts, it's all helpful.

I'd imagined that it would be the tyre tread pattern that would affect handling rather than wheels, so this is good to know. Certainly I'm looking forward to changing the tyres, as these tramline worse than anything I've experienced before (I'm on my third Scoob and the other two didn't tramline).

I guess I'll end up with 18s mainly because there seems to be a much bigger choice available. I'll have a look next at the sale section though and see what's on offer.

Cheers again
Si

PS Can someone explain what 17x7, 18x7.5, etc means? The first number is clearly the wheel size, but what is the 7 or 7.5?

ScoobySteve69

iTrader: (13)

Rim width.

BlobEyedRex

the 7 or 7.5 is width in good old imperial, whereas tyres are measured in metric e.g 215 is 8.5" and 225 is 8.9".

Also something going with bigger alloys is they'll way more so increase in un-sprung weight which is not good, but a compromise but going to 225 over 215 is minimal gain in traction, whereas keeping to a 17" size but going with an even lighter wheel and then spending more on a quality tyre will give you better traction and less un-sprung weight which is good.

On a newage going from 215/45R17 to 225/40R18 your increasing the diameter (speedo error =1.44%) which although minimal slows down accelleration but will give better cruising performance and another downside you'll have increased possibility of chipped/cracked rim edge from all these pot holes we now have everywhere.


Personally i prefer the 17" for road use as;
tyre price less on 17" than 18" for performance tyres (going 18" and then using budget tyres WHY?)

17" will give better ride everyday and if you want stiffer sidewall buy PZero Nero's and then increase tyre pressure (allows soft & hard tuning) as only dropping to 40 profile from 45 is like a reduction of 7mm only

also to get zero speedo error's you'd need to run either 245/50R17 or 245/45R18 which is why i never understood for 18's everyone pushes 225/40

This is a good site for both working out offset and plus sizing of both wheels and tyres - java based calculators, and so far seem spot on

http://www.rimsntires.com/specs.jsp
http://www.rimsntires.com/tireplussizing.jsp

somehting i forgot to say is go 17x7.5 and use a 225/45R17 it's radius is still less than a 225/40R18 so less speedo error (although both still within the 2.5% limit) and contact surface on the 17" will be better and still lighter/cheaper than 18" option

2bitpython

Wow thanks for the detailed info and insight, this is really useful. My car already has 225/45/R17, which is the same as your recommendation, so at least I know I'm on a good choice while I work out what their replacement should be.

I hadn't thought about the weight of bigger alloys, so that's a good tip. And the rimsntires link is a good one, as they clearly explain all the dimensions involved.

With the wheel and tyre widths being measured in different places (rim vs tread), I guess there is some margin to play with when picking a wheel for the desired tyre. Like it seems 225/45/R17 tyres might/ought to fit on wheels with rim sizes 17x6.5 to 17x8.5, with 17x7.5 being a handy average.

It's been really helpful getting insight and experience from all the replies here, so again I'd like to thank all the contributors.

I think despite the wider range of 18" to choose from, and arguably that they look better on the car, on balance 17" replacements are probably my best bet.

Si

BlobEyedRex

As you've seen on the calculator using a too small a rim for a tyre will cause the sidewall to do this \ / and will wobble under cornering and then going to a too wide a rim for given tyre size will stretch the tyre and i know the Hellaflush guys love this, it's dangerous for everyday use as unless you keep the very high pressures required (80-100psi) the tyre will push off the rim easily under corner forces.

Also if you can keep the sidewall | | as much as possible it reduces sidewall temps as again these get to high then sidewall will fail

Gary WRX

I changed from 215/45/17 to 225/40/18 and to be honest didn't notice much difference

The ride is a little firmer and I feel the bumps a little more bu it's not significant. Handling is slightly better due to a thinner tyre wall however again little difference.

I did notice acceleration was not quite as sharp (could have been in my mind due to everyone saying this could be affected) however I had the car remapped shortly afterwards which sorted that out.

I guess what I'm trying to say is there is little difference so if you do like the look it's worth the change I'm more than happy with mine.

Speak to mags from rts tyres (M44GY) i bought mine from him and he can give you good advice on fitment etc. He fitted mine aswell

Rob Day

iTrader: (78)

Ohh and something else I got caught out that you need to be wary of, make sure the new rims dont fail on the Brembo's. I bought a second hand set of wheels with tyres that came of a blobeye STI, as such I bought them and when they arrived went to fit them but they were failing by about 2mm. This is because the Blobeye was running with AP Racing calipers which are much narrower. I bought a set of hubcentric spacers which solved this for the short term..


Rob

BlobEyedRex

usually ET48-50 good for big brake kits and a good reason to then not sticking to 17's for the reasons I've given above is that big brakes won't fit, but going to 18" they will. Like everything we do to our cars it's all pro's & cons and what were prepared to accept as the trade off for what we want, but always spend the time to research it rather than impulse buy seen too many people over the years waste thousands £ on mods that with a bit of research could of got it right first time.

New_scooby_04

iTrader: (4)

On a newage car, 18s better, but bare in mind the above advice about getting quality lightweight alloys to avoid a big increase in unsprung weight and reducing the tyre depth to keep the rolling circumference the same.

If you can afford them, I HIGHLY recommend OZ ultraleggeras they look lovely on a scooby and are lightweight

Best to stick to 17s on a classic IMHO.

Ns04

BlobEyedRex

OZ's Ultra's, superleggeras and the good old Prodrive/OZ P1WRC look good on all generations (timeless wheel designs) & good range of offsets, plus strong and light

2bitpython

Yup this is something that would not have occurred to me, but luckily when I found there were far fewer 17" options than 18", I emailed one of the suppliers, performancealloys I think, to ask why, and they replied that it was the Brembos being a problem for many 17" that would otherwise have fitted.

Those OZ's look good BlobEyedRex, and they're in the sort of colour I think would go well with my silver car. But I prefer 5 or 7 spokes, so I guess this is an opportunity for anyone's suggestions/favourites for what wheels they think I should consider; they've got to be: 17" or 18" that fit over Brembos, 5 or 7 spoke, gunmetal/silver/anthracite/etc. All pics welcome

Thanks again
Si

Rob Day

iTrader: (78)

Si I assume you have a blobeye STI, have you looked in the Blobeye threads for some pic to ive you an idea of your options?

2bitpython

Good idea, I'll do that. If I spot the ideal set I'll ask the owner if he had problems fitting over his brakes, so I'll know if they should go straight onto my car without grief.

Tazman861

iTrader: (2)

Is it just me or is the disc in this pic on the wrong side of the car? The cooling grooves look wrong?

cster

Doh!

BlobEyedRex

LOL, they mine Alcon/prodrive anchors - & grooves not for cooling they for scrubbing pads & gas removal, cooling is by the 2.5cm inch fins you can see running through centre if u know wot I mean, check my garage photos out

BlobEyedRex

I'll have to load some new images of cross section of disc which wat I was trying to think of before in last post 2.5cm wide multi fin things run through cross section of disc, think that explains

Tazman861

iTrader: (2)

Call them what you like my question still stands - aren't they on the wrong side of the car?

BlobEyedRex

No, that is the optimal way that PRODRIVE & Alcon designed it to be. Why would u think it was the wrong way? As it's purpose is for releasing gas pressure and scrubbing pad surface, I don't know what engineering knowledge you have but if you break it down the angle of attack & flow thru direction makes it optimal for reasons I've given

BlobEyedRex

4got to say if your referring to why caliper is in the rear side of disc instead of front again it's optimal position look at porche

Tazman861

iTrader: (2)

The reason I ask is because I have grooved discs and the instructions on fitting were that the grooves went the other way. I have seen many cars with grooves and they all go the other way.

Didn't mention calipers

BlobEyedRex

Ok, well whoever makes yours decided for their reasons to place otherway. Prodrive in their wisdom placed them the way they did. & to be honest I've never questioned because I've never built/designed WRC winning cars they have so their chose of doing this is for optimal reasons. BTW what make are your brakes