Wheel spacer question?

[Lance924]

I have an 86 2.5 944 and i have just bought a set of boxter s alloys to compliment it.
The fronts are 7x17 ET55 (Part Number 986.362.124.00)
The rears are 8.5x17 ET50 (Part Number 986.362.124.00)
I am trying to find out what size spacers i should use to safely put these wheels on my car.
I estimate the fronts should be 9mm and the rears about 18mm,but would like somebody to confirm or correct me as to the right ones to fit.
I would also like some advice on tyre sizes as the tyres on the wheels are 255/40/17 rear and 205/40/17 fronts. Would it affect the handling if i used these profiles or should i drop in the sizes.

Many Thanks in advance.

[hpservertech]

26 for the rear & 31 for the front

Not sure where you got your estimates from. What you do is subtract the difference between what you have (23.3) and what your going to go with (50/55)

[Dantilla]

Massive understeer. If all you want is the car to look good while sitting in front of Starbucks, go ahead.

But with that much more rubber in the rear of the car, it will plow through turns like a pig.

[Lance924]

The reason for my question is to try and avoid the problems with understear.
The tyre sizes i have mentioned are the ones that are on the wheels already.I have fitted the rears on the car but they seem to sit alittle to far in the arches.
The fronts need spacing because the bearing cap will not allow the wheel to sit flush with the hub.
I gave the wheel sizes and porsche part numbers because i would like to know what size tyre i can fit without it looking sily on the rim. ie Too small or to fat.
Thanks for the reply,but im still unsure how to work out the spacer sizes.
It is not just about it looking good ,i also want to keep the handling of the car.
I want to order tyres today,But dont want to replace all treads to find out the car drives unwell.
Would a 205 front and 225 rear be better?

[Dantilla]

A 944 handles best with equally sized tires front/rear.

Just about every car manufactured has a bit of understeer engineered in, because it is considered safer for the average (poor) driver.

Porsche used the staggered setup, 205/225, and later the 225/245, to induce understeer.

With it's near perfect 50/50 weight distribution, having the same size tires front & rear makes for a beautifully neutral handling car.

While the 944 looks great with wide tires in the rear, it really messes things up. It's possible to swap suspension parts to return to neutral handling, but all your doing is putting band-aids on the problems caused by mis-matched tires.

With 7 and 8.5 wide wheels, you're probably best to go with 225 in front, and 245 in the rear. This will keep the handling with slight understeer, but close to factory specs- Not a bad place to be.

Just for comparison, I've got a heavilly modified 911 for autocrossing- With it's extreme rear weight bias, I tried a 205/255 combination. Even with the entire engine hanging out behind the rear axle, this provided way too much understeer. So far, I like driving my 911 best with 225 fronts, and 255 rears. My street tires are 225/245, and it's a bit tail-happy.

Hope this helps....

[Lance924]

Originally Posted by Dantilla

A 944 handles best with equally sized tires front/rear.

Just about every car manufactured has a bit of understeer engineered in, because it is considered safer for the average (poor) driver.

Porsche used the staggered setup, 205/225, and later the 225/245, to induce understeer.

With it's near perfect 50/50 weight distribution, having the same size tires front & rear makes for a beautifully neutral handling car.

While the 944 looks great with wide tires in the rear, it really messes things up. It's possible to swap suspension parts to return to neutral handling, but all your doing is putting band-aids on the problems caused by mis-matched tires.

With 7 and 8.5 wide wheels, you're probably best to go with 225 in front, and 245 in the rear. This will keep the handling with slight understeer, but close to factory specs- Not a bad place to be.

Just for comparison, I've got a heavilly modified 911 for autocrossing- With it's extreme rear weight bias, I tried a 205/255 combination. Even with the entire engine hanging out behind the rear axle, this provided way too much understeer. So far, I like driving my 911 best with 225 fronts, and 255 rears. My street tires are 225/245, and it's a bit tail-happy.

Hope this helps....

I spoke to porscheshop uk today asking them the same questions.
They have recomended that if i am using 255/40/17 rear's,then i should also use 215/50/17 on the fronts to keep a natural balance.This is also to keep the speedo accurate as possible.
My concern was what the large front would do to steering wait,but they have also told me that it shouldnt be a problem.
Any feedback on this would be gratefull.

[Dantilla]

First of all, everything has to work together as a complete system- Springs, shocks, sway bars, torsion bars and tires all work together.

At an autocross school a while ago, I drove a student's 944- He found a bargain on some used aftermarket 944 suspension parts, and bolted them up to his car, and came to the track.

It was the most evil-handling car I've ever driven.

While each individual part was an "upgrade" over the factory part, they were incompatable with each other.

The factory did a great job- Start there. What do they recommend? If you deviate, you may want to adjust something else to get your neutral handling back.

In 1986, your car probably came with 215/60/15 all the way around. That's what the factory engineered the suspension for. And the car was universally praised for being such a great handling car.

What do you expect when you put skinnier tires up front, and wider tires in the rear? It's not reasonable to expect the handling to remain the same.

You're taking away grip from the front, and adding a bunch in the rear. Recipe for understeer.

[Lance924]

I just wanted to say,thanks for the advice recieved,im just waiting for the spacers to arrive now so the wheels can be fitted.
Thanks again