Tire Size Question for 1.8L 1975 Options

[Superhawk996]

Truth is that I don´t know what I´m doing and that´s why I joined this thread to learn a bit more from more experienced members. My car is non-runner and I haven´t ever driven P914.
On the other hand we have more options than factory some 55 years ago so there may be some options how to make these cars to look and handle a bit better.

Ultimately this is a sports car and I have lots of winding roads nearby so original skinny 155 tires are no option for me despite being outcome of Porsche engineers (IMG:style_emoticons/default/evilgrin.gif)
I will not compete with my car but really like enthusiastic driving.

My car will also get Inner longitudal stifner kit (BTW. Can anyone provide a drawing of the parts, please? Shipping these from US to Europe will cost more that the value of the parts plus custom duty (IMG:style_emoticons/default/ar15.gif) )

I think I will go for 22mm conversion spacers, 15x7 ET40 wheels, 205/60 tires and will make my fenders to fit. There are even more tire options in 195/60.

Do you think this is acceptable compromise? (IMG:style_emoticons/default/idea.gif)

Forgive me for the length of the response. It is not directed at you in any sort of personal way. I'm writing it for the benefit of those that forget how all the little "upgrades" can actually be a degradation.

Since you have never driven a 914 it would be wise to drive it first before deciding that it needs significant upgrades.

The 914's handling (even in near stock form on modern rubber that will fit) when driven at the limit is already beyond the capability of most drivers. I can provide the data to back up this statement if necessary but I'll defer that unless there is truly interest.

This is a bit harsh to say but it is true. I say that as an automotive engineer with 30 years experience that includes having participated in successful Le Mans effort a few decades ago. That includes having personally raced both cars and motorcycles myself and knowing what can be done safely on public roads. Yes, I have driven in Italy, Switzerland, Germany, etc., and I'm familiar with the roads in Europe.

With respect to chassis stiffening. The typical chassis stiffening kits are a great way to add lots of extra weight.

There is very little data on this site to actually provide data on the actual stiffness increase is vs. the massive weight penalty you will incur. Stiffening is one thing for racing at Le Mans, doing a 3.6L powertrain swap, or going club racing on wide super sticky rubber whether it benefits a car that is supposed to be light weight and nimble is another.

Why do you think chassis stiffening is worth the weight gain for a 1.8L with very limited power?

I can tell you with certainty that it is very tough to engineer a 2000 lb vehicle.

Weight creep is real. Just a few pounds for wheel spacers (don't forget the lugs & studs). Then there is going to be approximately 20 lbs (1% of the vehicle weight!!) for the typical plate steel chassis stiffening kit. Don't forget the weight of the new larger wheels to accommodate the wider rubber you are proposing. And of course the new larger tires you've proposed are much heaver and have much more inertia than the original 155 or 165 width tires. Those wider wheels and tires will easily be another 1% weight addition. These seemingly little 1% here 1% there weight additions add up and are lot of extra mass and inertia for the poor 1.8L to have to accelerate.

Then comes the horespower upgrades you'll need to make up for all the weight that was added . . . which in one form or another almost always . . . you guessed it . . . adds yet more weight. The list just keeps growing, brakes, oil coolers, etc.

With respect to wheel offset. The original offset is 40mm on the 5.5" steel wheels. So the 23mm referenced for 5 lug Fuchs already has a scrub radius increase built in that degrades steering effort. I will agree most people find this to be OK but keep in mind, that entails rolling fenders and it isn't uncommon to get some inner wheel well rubbing too depending on chassis build variation . . . that is with wheels and tires smaller than you want.

The moral of the story being there are lots of things that urban mythology and internet lore will tell you are good things and "must do" but they are rarely done knowing the full set of tradeoffs that go along for the ride.

As always . . . its your car. Do what makes you happy. Don't follow internet advice (including mine) blindly.

[Jamie]

after 4 decades of this question.

the 6inch wheels almost always fit
7inch wheels hit or miss... some people are able to fit them... 60% of the time they do not fit stock fenders.

16inch fuchs there is a better chance that 7s will fit as the offset is different from a 15 to a 16

regarding is it worth it?
up to you
it becomes an appearnace thing as both cars can handle well on 4 or 5 bolt..
and stickie-ness of tires makes more difference on handling than the 1/2 inch difference of 5.5 to 6's

so really its about what appearance you want as to whether the 5 bolt upgrade is worth it. Stock 4 bolt brakes with good pads can absolutely brake the car fine .

I've never understood the passion for 4 to 5 lug conversions for a street car? Maybe a leftover from the NARP mindset, and a fashion statement with rim art replacements? (IMG:style_emoticons/default/poke.gif)

[mepstein]

after 4 decades of this question.

the 6inch wheels almost always fit
7inch wheels hit or miss... some people are able to fit them... 60% of the time they do not fit stock fenders.

16inch fuchs there is a better chance that 7s will fit as the offset is different from a 15 to a 16

regarding is it worth it?
up to you
it becomes an appearnace thing as both cars can handle well on 4 or 5 bolt..
and stickie-ness of tires makes more difference on handling than the 1/2 inch difference of 5.5 to 6's

so really its about what appearance you want as to whether the 5 bolt upgrade is worth it. Stock 4 bolt brakes with good pads can absolutely brake the car fine .

I've never understood the passion for 4 to 5 lug conversions for a street car? Maybe a leftover from the NARP mindset, and a fashion statement with rim art replacements? (IMG:style_emoticons/default/poke.gif)

I get it. The 5 lug Fuchs is a pretty wheel and you pretty much have to go 5 lug to get wider wheels for flares. but...the 4 lug Fuchs is really a perfect wheel with either a 195x65 or 205x60 (if you want max tire width). That combo fits 99% of the stock body cars out there. The 2.0 Fuchs are 12.5 lbs and forged aluminum. They sell for less than $1K a set and look right on the cars. It's a really nice wheel without spending a lot to convert.

[Pyetookh]

Forgive me for the length of the response. It is not directed at you in any sort of personal way. I'm writing it for the benefit of those that forget how all the little "upgrades" can actually be a degradation.

Since you have never driven a 914 it would be wise to drive it first before deciding that it needs significant upgrades.

The 914's handling (even in near stock form on modern rubber that will fit) when driven at the limit is already beyond the capability of most drivers. I can provide the data to back up this statement if necessary but I'll defer that unless there is truly interest.

This is a bit harsh to say but it is true. I say that as an automotive engineer with 30 years experience that includes having participated in successful Le Mans effort a few decades ago. That includes having personally raced both cars and motorcycles myself and knowing what can be done safely on public roads. Yes, I have driven in Italy, Switzerland, Germany, etc., and I'm familiar with the roads in Europe.

With respect to chassis stiffening. The typical chassis stiffening kits are a great way to add lots of extra weight.

There is very little data on this site to actually provide data on the actual stiffness increase is vs. the massive weight penalty you will incur. Stiffening is one thing for racing at Le Mans, doing a 3.6L powertrain swap, or going club racing on wide super sticky rubber whether it benefits a car that is supposed to be light weight and nimble is another.

Why do you think chassis stiffening is worth the weight gain for a 1.8L with very limited power?

I can tell you with certainty that it is very tough to engineer a 2000 lb vehicle.

Weight creep is real. Just a few pounds for wheel spacers (don't forget the lugs & studs). Then there is going to be approximately 20 lbs (1% of the vehicle weight!!) for the typical plate steel chassis stiffening kit. Don't forget the weight of the new larger wheels to accommodate the wider rubber you are proposing. And of course the new larger tires you've proposed are much heaver and have much more inertia than the original 155 or 165 width tires. Those wider wheels and tires will easily be another 1% weight addition. These seemingly little 1% here 1% there weight additions add up and are lot of extra mass and inertia for the poor 1.8L to have to accelerate.

Then comes the horespower upgrades you'll need to make up for all the weight that was added . . . which in one form or another almost always . . . you guessed it . . . adds yet more weight. The list just keeps growing, brakes, oil coolers, etc.

With respect to wheel offset. The original offset is 40mm on the 5.5" steel wheels. So the 23mm referenced for 5 lug Fuchs already has a scrub radius increase built in that degrades steering effort. I will agree most people find this to be OK but keep in mind, that entails rolling fenders and it isn't uncommon to get some inner wheel well rubbing too depending on chassis build variation . . . that is with wheels and tires smaller than you want.

The moral of the story being there are lots of things that urban mythology and internet lore will tell you are good things and "must do" but they are rarely done knowing the full set of tradeoffs that go along for the ride.

As always . . . its your car. Do what makes you happy. Don't follow internet advice (including mine) blindly.

Proper race engineer answer (IMG:style_emoticons/default/smile.gif) Thank you

My passanger will add another 7% so I´m not much worried about 2-3% extra. (IMG:style_emoticons/default/icon_bump.gif)

I´m gonna give my engine extra 20% power so hope to compensate for a bit of extra weight. (IMG:style_emoticons/default/sunglasses.gif)

It would be nice to try a narrow and a wider car and compare (IMG:style_emoticons/default/driving.gif)

Now I´ve got more to think about

[chmillman]

I get it. The 5 lug Fuchs is a pretty wheel and you pretty much have to go 5 lug to get wider wheels for flares. but...the 4 lug Fuchs is really a perfect wheel with either a 195x65 or 205x60 (if you want max tire width). That combo fits 99% of the stock body cars out there. The 2.0 Fuchs are 12.5 lbs and forged aluminum. They sell for less than $1K a set and look right on the cars. It's a really nice wheel without spending a lot to convert.

Yeah, for me the main point is that the 5-lug Fuchs are way nicer looking than the 4-lug ones - which iMHO are the result of some unfortunate aesthetic design decisions. The 'spokes' are way too squared-off and there's not enough depth. I wonder if the design was dictated by economics as these had to be for a "VW" branded car.

I have a set of four in pretty much pristine condition which have been up for sale for more than a year now - and until recently no takers. I think I have finally found a buyer though.

My favorite aesthetically for 4-lug remains the Mahle's, cast not forged so probably weigh more than the Fuchs. They are pretty rare these days, I have never understood why someone like Maxilite has not made repros of those.

[Superhawk996]

My passanger will add another 7% so I´m not much worried about 2-3% extra. (IMG:style_emoticons/default/icon_bump.gif)

Again a fair point

However, adding a passenger does change the way a small, light sports car like a 914 or a Miata handles and accelerates. If the driver cannot feel that change then they will have a much wider window of degradations that they won’t mind.

It’s not fundamentally different than adding a passenger to the back of a sport bike at a track day. Can it be done? Yup. Does it change the handling of the bike? Absolutely. Are there riders that can pull it off (ie turning a pretty fast lap) with a good passenger on the bike? Yup - I’ve seen it several times. Regardless, it slows the lap times and drastically changes the way the bike handles.