Why do prodrive recomend that 18" wheels should be used on the sti 8 ppp ?

Are there any performance gains to be had by adding the larger rims ?

Has anyone done this modification ? any pros ? any cons ?

cheers


chris.

 

££

Probably something to do with the unsprung weight of the new wheels......... can you tell I'm guessing??

 

Apparently they help reduce understeer, with the P Zeros on. See the comments in Fast Fleet in this months' EVO magazine if you've got a copy.

 

They want your money !!!!

No real need for them except they look the bollocks !

 

18's are likely to weigh more than 17's. Tyre wall will be considerably shorter, which is not necessarily a good thing on british roads, despite how well it will seem to go on smooth tarmack race track. I suspect it is, at least moderately, a profit based recommendation.

 

I don`t care what they say about the 18" wheels, I think the standard wheels are tops! Also they must be the easiest wheels ever to clean, unlike most of the 18" options with corner bits that`ll hold brake dust and grime.

I imagine by putting the spring kit on, it will give sharper handling than any 18" wheel upgrade

 

re: unsprung weight. You obviously need to take in to account the tyre as well as the wheel, so if you are able to make a wheel larger but keep the weight the same, the unprung weight may be reduced.

The reason for the recommendation will probably be purely that the set-up has been developed for that specific wheel, etc. The benefits of a shorter tyre wall include things like sharper / quicker reaction, less deformation of the contact patch with slip angle, etc. There are negatives too, but the whole set-up has probably been designed to make the most benefit of that wheel.

Cheers

Simon

 

I've got 18s on my classic - they lok the NUTS!

Turn in is much improved over 17s, but some bumps can feel harsh. Not as bad as I was expecting though..!!

 

Had 17" Oz wheels on mine.

Moved on to 18" prodrive and i take corners much better

And i can still get 5 people in the car with no rubs

 

I didn't go for Prodrives when I went 18 (did for the 17s)

BK Racing shiny blinging chrome ones...

Still haven't stopped smiling about them...!!

 

Hi Simon,

"re: unsprung weight. You obviously need to take in to account the tyre as well as the wheel, so if you are able to make a wheel larger but keep the weight the same, the unprung weight may be reduced."

I was kind of taking this into account. IIRC, lower profile tyres with tiny short sidewalls tend to need much more material in the sidewalls in order to form a useful tyre shape, hence bumping weight up. Also, in general, larger wheels seem to like to be wider too, which adds on the weight again. And this extra mass is added closer to the outside of the wheel, thus making a larger impact in dynamic mass (if thats a relevant term). IYSWIM

 

Hi Moray

A taller sidewall tends to need more material due to it needing to add stiffness (for obvious reasons).

It's a common consideration in development to consider the addition of mass in larger wheel compared to the reduction in mass due to lower profile tyre.

The "dynamic mass" thing is not a consideration in pure un-sprung weight discussion.

My personal gut feeling is that 17 is a large as I would want to go on a scooby, but I didn't develop the set-up so I can't recomend either way.

Cheers

Simon

 

Simon, I always said I'd never go large than 17s - but nice 18's do look the muts nuts!

 

I have the 18" on my STi PPP but never drove it with the 17's however I don't notice much in the way of understeer apart from in the wet. Understeer seems to be talked about with STi when running on 17's hence I assume from this that the 18's go someway to remedy this problem

Or maybe I'm braking too early

 

I have the Prodrive FF7s on my STi 7 and I *think* that the ride actually improved slightly (placebo anybody? ). IIRC, the OE STi wheels are rather heavy and that the FF7s are a couple of kilos lighter per corner, which would probably explain the ride thing - I have no idea if the 18" tyres are heavier or lighter than the 17s however, but I would imagine if the wheel weight is correct, it is a net gain.

I like them and would recommend them to any STi owner considering them.....

Matt

 

Moray & Mutant
I weighed the std. STi7/8 17" wheel/tyre and the Prodrive 18" FF7/Toyo 225/40 combo and the bigger wheel was knocking 3kg lighter! My sons 18" OZ 10 spoke/P-zero Nero was a little heavier but still noticably lighter than the standard set-up.
The PPP version that Clarkson raved about (and the "Stig" flogged around the track) on Top Gear a few weeks back had the standard set-up!
JohnD

 

John,
What are you doing online at 3pm. Get back out and finish cleaning your car, there's a meet tommorrow!

Failing that if yours is already done I will drop mine round.

 

Hi Tony
Get off this BBS and do some work! I don't go back until the 1st These long hols make it really hard when you have to go back, and you know the little b******s I "teach" (sympathy please - anyone?)
Car will be washed tomorrow. If I clean it too soon it might get some dust on it!
JohnD
PS they're both PPP'd

 

Didn't weigh my wheels (BK238), but I bet they're heavier than my old Prodrive 7

Bet my cars heavier than John's too with all the extra dirt I carry around

 

And the answer is ?

 

Bear in mind i'm on a classic but:
better turn in and road holding with my 18's, over the 17's.

But the cons are it's a little bit bumpier (but not as bad as I'd imagined) and they're EXPENSIVE!

So I guess Prodrive recommend them cos they get more money off ya and the car handles better.

 

John,
How Wilsons must love it when you walk in!

 

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