What if ?

When fitting PPP Prodrive recon you get better use of the additional torque by fitting 18" wheels. What I want to know is why ? and what is better ?

I am bemused as larger wheels change the ratio and make it harder to turn the wheels and would normally slow the acceleration on a car. Usual effect is a slower car off the mark with a slightly increased top end and a speedo that is further out than usual. So why is it better on a Subaru ? I am going to need new tyres soon on my MY05 STI PPP and have manager to get a price of £495 supplied, fitted and precision balanced (With the weights on the inside) and though I could upgrade the wheels if it was of a noticable benefit. The thing is it is alot if cash to spend when there is no information to say what difference to expect.

jbwrx300

good question - it is in the PPP documentation (downloadable as PDF) from Subaru site.

I think this may simply be an angle to selling more prodrive wheels as they are supplied by the dealer and it is easy to up the spec when ordering new. From a technical aspect, simply saying 18" is ideal is not good enough, as this will obviously have positive/negative effects on the handling depending on actual wheel size/width/tyre profile and a negative effect on ride quality.

so is the next step then - once you have upgraded to 18" wheels you need the prodrive springs?

I dont know, mine works fine and the only reason I would consider changing my wheels is
a: because they are rather gold and gay
b: they are too skinny at the rear and dont fill the arch - they actually look silly.

T4molie

Oddly enough I have the PFF7's and the Spring kit on mine and they really did improve the handling - however I couldn't say whether it was the wheels or the springs or both cos I got them at the same time

16vmarc

Surely youre bound to lose handling quality though with 18s.

T4molie

TBH I'm not really in the know as far as handling dynamics and so on cos I bought them because I thought that the Bugeye sat too high and I prefered the 18's

But as I mentioned above the car certainly feels more planted with less body roll

Mother Theresa

As the tyre will have a smaller aspect ratio (40 vs 45 for the 17's I think) the rolling diameter will be more or less identical so no torque change ???

16vmarc

so smaller tyre, imo that means harsher ride ad more prone to tramlining.

What if ?

hmmmmm! a mixed bag of thoughts there - 40% profile on the same width wouln't be much different as standard diameter, If a wider tyre was fitted it would be bigger, sam if a 45% profile was fitted. If the diameter of the tyre is kept the same - what is the difference adn the rolling size would be the same and the ratio unchanged. The main negative effect would be a higher centr of gravity and porrer handling. What a mess this is turning out to be !!!!!

jbwrx300

If Prodrive recommended 18" for any technical reason, the cars would be sold with 18" wheels. A mate of mine commented on this the other day when I told him the book said I was supposed to have 18" alloys according to Prodrive. His answer was succinct - "Then why the **** did it not come with 18" wheels?"

If the correct upgrade means that the wheel diameter does not change at all, the only thing I can see changing is that the ride would deteriorate which would naturally lead to you getting a set of springs fitted as your next port of call.

T4molie

I wonder whether Mike Wood would care to comment on this one?

jbwrx300

Also - just an afterthought -

If Prodrive recommend 18" wheels fitted with PPP, surely the dealers would be pushing you to upgrade when you buy. I told them I didnt like the gold wheels on the WRX300 and they never made a peep about upgrading to 18" Prodrives, which I would probably willingly have done.

Now we all know that car dealers will use any excuse to get you to add an option, especially where they are dealer fitted. If I was a dealer selling the car to you, I would be telling you all the technical advantages of 18s over 17s with this pack and provided it was not complete BS, someone who was into their cars and doing things properly would probably cough up.

As they dont try to push the wheels, I can only assume that there is no technical justification behind the claim.

nakedjem

If you're gonna fit 18's and get a step down in prfile of tyres then you keep the rolling circumference the same almost always. Different tyre maufacturers will have slightly different sizes of tyre even though they're given as the same, and even batches may vary. So there should be no change to the speedo or gearing or acceleration or top speed.

The only conceivable way that the transfer of torque could be improved is because the tyres would be a lower profile, and less able to flex or distort under hard acceleration. The difference would have to be negilgible, but nevertheless does theoretically exist.

I can't see how the Prodrive spring kit would change the ability to deliver more torque if that is what people are suggesting. It would probably feel better, though!

Jerry

What if ?

When I ordered the car and PPP they did offer 18" wheels for silly money and said it was recommended by prodrive if you got PPP fitted, They didn't know why though.
Personal I wouldn't trust Dealer sales guys as mine told me the MY05 STI with PPP was definately (and even challenged him several time and said I didn't belive him) 320 PS (316 BHP) (they said 320 BHP) as they now fitted the WR1 pack for the performace gains on the engine. As such I would technically have a better / faster car than the WR1 as it was a 2005 model with the extra mods !!!!!!! WTF ! it's 305 PS (301 BHP) - I asked Prodrive !

jbwrx300

Jerry, was thinking the same about flex, but really cant see this making any noticeable difference to getting torque to the ground throughout the power band, as it pulls pretty evenly all the way through the range rather than a massive pull when the turbo kicks in and dying at 5500 revs like a standard wrx.

Re springs, not commenting on a performance difference, just saying that if 18s give you a poorer ride, surely your next step would be to upgrade the springs as a next step to improve the handling all round.

What if ?

That would be very handy right now

steve05wrx

Hi
I suppose new springs could help - when reapplying the throttle as you come out of a tight bend.
All 4 wheels will be more firmly planted - giving you better traction!
I intend to have the ProDrive springs fitted ASAP on my 05WRX - as the car seems to roll excessivley on corners (however the car is so quiet and smooth - you are often travelling a tad quicker than you might think!)
Cheers!
Steve

MikeWood

There are various reasons for recommending 18" wheels and tyres to go with the performance package.

Lets start with the WRX. The std 17" tyres are OK when you've got the std levels of torque to cope with but with the increased torque available with the PPP, traction at the front in the wet becomes a limiting factor in the lower gears. A better (& wider) tyre on an 18" wheel helps.
On the std tyre the grip in the wet or dry isn't that great so a better (& wider) tyre on an 18" wheel helps.
The ride on the std tyres could be better so fitting the tyres we recommend (PZero Rosso or Nero depending on the wheel chosen) helps with this. This is not a wheel diameter issue it's much more about the actual tyre fitted so fitting a larger but lower profile tyre can actually help if the OE fit doesn't have such a good ride.

On the STi there are no real traction issues due to the front LSD but this can give worse problems in the form of tramlining and torque steer. Adding the extra torque that the PPP gives obviously would make this worse on the std tyres so we recommend that you fit larger wheels and more importantly different tyres. If you've ever driven the same STi on std Bridgestones and then our 18" wheels you will immediately notice the the car is much calmer and tolerant of uneven surfaces for just this reason.
The std Bridgestones also give a very firm and unforgiving ride as they have very stiff sidewalls. Fitting our 18" wheels and tyres improves this.
Any concerns about increased diameter etc are unfounded as the overall diameter of the tyre is the same as std.
One important gain however is that our 18" wheel and tyre assemblies are between 1.5 & 3kg LIGHTER than the std 17" STi wheels and tyres so improving unsprung mass and reducing the rotational inertia of the assembly.



There seems to still be the misapplied rule that fitting the lower profile tyres that a larger rim needs, will degrade the ride quality, but this is simply not the case if either the original tyre gives a firm ride or you can choose a replacement tyre that gives a better ride. Both apply in this case with the 18" wheel and tyre packages we supply......


If your dealer hasn't recommended you change wheels and tyres it probably most likely that he hasn't driven a car so equipped. His comment that the ride is worse is probably down to experience based on other cars that simply don't work on bigger wheels and tyres, normally small fwd ones.......

Hope this helps

Mike

mid_life_crisis

Could not agree more, going 17”>18” on a PPP WRX worked wonders; both ride and handling were improved significantly.

Just done the same on my 2005 STi PPP and the effect is ever greater. The stock RE070 make for an exceptionally nervous car that sticks like sh*t to a blanket on a dead flat dry road but tramlines and hops about all over the place the rest of the time. 18 x 8” + 224/40/18 is within 0.46% (theoretical) of the same diameter as the stock 17 x 8” + 225/45/17, but the ride and handling is completely transformed.

I can also confirm Mikes weight figures, being quite sad I weighed the standard wheel/tyre against the new ones; they were just on 3Kg per wheel and tyre lighter (OZ Superleggera + Marangoni Zeta Linea).

T4molie

Mike,

Cheers for answering the above queries

I've recently test driven both an 03 STi and an O5 STi (both with PPP) and did notice a very big difference in the drive - while there are of course mechanical differences between the 2 cars I found that the 03 felt more sure of where it was supposed to going and as you say more calmer on uneven surfaces.

The difference? The 03 had the PFF7's and the spring kit on while the 05 was std.

The big question for me now is "am gonna stump up the cash to upgrade my MY02 WRX to an 05 STi + PPP + Springs +18's"?

TBH I would have liked to have driven an 05 to the above spec, to compare, but the dealer didn't have one in

abc

Thanks Mike for a helpful post.

I notice that the argument for fitting 18" wheels and tyres (ie better grip and ride) is based in large measure on criticism of the standard tyres. This is borne out by the statement that "This [ie ride quality] is not a wheel diameter issue it's much more about the actual tyre fitted so fitting a larger but lower profile tyre can actually help if the OE fit doesn't have such a good ride." If it is a matter of the tyre fitted, it doesn't obviously follow that you should also change the wheel diameter. In other words, when read carefully, the argument seems to be this: fit a better tyre and you'll get better ride and grip! Although this option might not be as good as fitting new tyres and wheels, it'd be a lot cheaper.

I don't want to nit-pick, but there does seem to be a flaw in the reasoning! Or perhaps I have misinterpreted your argument...

Cheers,

Andrew

mid_life_crisis

IMHO the RE070 spoil a very fine chassis. I upgraded from a 2004 WRX PPP on 18” PFF7 to the 2005 STi PPP and it came as quite a shock just how nervous the car was on our small bumpy Norfolk roads. The car was actually hard work to drive and not really pleasurable at all. Going to 18” was such a transformation it took some believing initially. The RE070 have immense grip on dry flat surfaces but any bumps cause the car to hop all over the place, and they are close to dangerous in the wet. To be honest I’m surprised Subaru fit them for UK driving conditions, they’d be fine if we had roads like billiard tables and it rarely rained

What if ?

Cheers for the concise report Mike. Which Tyres would you recommend on a MY05 STI PPP ? Also is there a gold wheel available from Subaru dealers of the same weight reduction ? and if so what is it called ?

Almost forgot:- is the space saver wheel still usable, or does it need to be changed ?

Thanks,
Simon

MaDaSS

Post removed due to high BS content! LOL.

MikeWood

Simon

We do a Gold 18" P-FF7 and it is still possible to use the space saver spare as the overall tyre rolling radius is still within the tolerance range.

Mike

MaDaSS

So Mike, would you say on an MY03 WRX with Eibach spring kit which i must say with standard wheels and T1-R tyres seems to be rather twitchy, even though i have had geometry done, that i would maybe, in your opinion, get better 'service' if i had say the 18" P-FF7 with your recommended P-Zero Nero tyres?
If so, what size would the tyres be? 225*40 or wider?
Thanks.

MikeWood

I haven't driven a WRX on std sized T1-R yet but having driven STis on them I would be very confident that what you suggested would be a better proposition.

Mike

What if ?

Cheers Mike. I take it they are still lighter ? I will ask today when I pick my car up form dealers

T4molie

Mid Life,

Sounds like (well I know) that roads around norfolk are just as cr@p as the ones in Bedfordshire

Are you pleased that you upgraded from your WRX to the STi? I test drove the 05 last weekend and tbh have been offered a very good deal from the dealer to change up

The STi seems to me to be a more "aggressive" drive compared to the WRX which feels more relaxed. I only use my Scoob as a weekend car and motorway driving when I travel north to see the olds but obviously have not experienced how the STi compares to the WRX on a long drive

Andy

mid_life_crisis

PM responded to

Short version, am I pleased? Yes very

MaDaSS

It looks like my next 'spend' is accounted for then! LOL.
Some P-FF7's for my tweaked MY03 WRX.