Narrow tires on wider rims

[Aircooled4evr]

I have come to the Porsche world from the WV Cal look scene.
And maybe therefore, have a somewhat different approach than others?
And this is related to my next question: Does anyone in here have experience with narrow tires on wide rims? eg. 195 / 205mm on 8 "rims, And 225 on 9" rims? How much does it affect the driving characteristics?.
I probably also go for slightly higher tires than most today. However, I know the properties of high tires well, and likes the early warning they give. I'm also not a race car driver anyway!, and the little I get to drive on the track ... it probably doesn't matter anyhoo.....

[Joe Bob]

I think your biggest issue is getting a tire shop to mount them. Those sizes are a bit marginal.

[Tyson Schmidt]

Generally speaking any given tire size on a wider rim will increase stability and directional response, and have a firmer ride.

On a narrower rim it will give a softer ride but but less directional stability. It’s very tire-dependent as to how wide you can stretch a tire on a rim before it decreases performance. I’m running 225 on 9’s in back of one of my cars and it looks and performs perfectly. Even treadwear. But the number on the sidewall doesn’t tell the whole story. There are big differences between tire brands and models and even between sizes of a given tire.

For example, I once ordered a set of 225 front, 245 rear Bridgestone RE-11 tires. You couldn’t tell the difference between the 225 and the 245. It was about 5mm difference.

So it’s hard to make a blanket statement on what the limits are without knowing which specific tire you are dealing with.

[Cheshire Cat]

Originally Posted by Aircooled4evr

I have come to the Porsche world from the WV Cal look scene.
And maybe therefore, have a somewhat different approach than others?
And this is related to my next question: Does anyone in here have experience with narrow tires on wide rims? eg. 195 / 205mm on 8 "rims, And 225 on 9" rims? How much does it affect the driving characteristics?.
I probably also go for slightly higher tires than most today. However, I know the properties of high tires well, and likes the early warning they give. I'm also not a race car driver anyway!, and the little I get to drive on the track ... it probably doesn't matter anyhoo.....

I was driving on 10 and 12 with 225\40 and 295\35 tyres, so, to make it work you have to have some pressure, 2.5- 3 bar so it`s stiff

[kent olsen]

And don't complain when you park next to the curb and rub the wheel against the curb.

[Aircooled4evr]

wow! well well... It doesn't look like I'm getting into big trouble!
Super, thanks for the reply!
I will not get an issue with getting a tire shop to mount them, I do it myself.

I've never made a curb rash, and i don't plan to start on it now!

I had dreamed of drive with Michelin TB 15, But they don't fit in width for 8 & 9X15 " rims ... Sigh

[Bill Verburg]

Originally Posted by aircooled4evr

i have come to the porsche world from the wv cal look scene.
And maybe therefore, have a somewhat different approach than others?
and this is related to my next question: Does anyone in here have experience with narrow tires on wide rims? Eg. 195 / 205mm on 8 "rims, and 225 on 9" rims? How much does it affect the driving characteristics?.
i probably also go for slightly higher tires than most today. However, i know the properties of high tires well, and likes the early warning they give. I'm also not a race car driver anyway!, and the little i get to drive on the track ... It probably doesn't matter anyhoo.....

195 / 205mm on 8 "rims, and 225 on 9" rims? How much does it affect the driving characteristics?.

55
A lot, tires and the wheels they are mounted on is just like the Goldilocks story, not too this and not too that

A tire is designed and built with a certain characteristics, such as the foundational stiffness which allow it to distort in a controlled linear fashion in use, the tire needs to distort, that's why we don't run on wooden or metallic wagon wheels any more.









The tire distortion determines the slip angle that the tire runs at, this in turn determines the handling characteristic that the wheel/tire combo impart to the chassis

over steer is when the slip angles in back are bigger than the slip angles in front


under steer is the reverse








every tire has a design spec for the wheel width

here's a 205/50x 17 on an 8, this tire's spec is 5.5-7.5, on an 8 is is stretched to .5" over, the stretch does 2 things
1) stiffens the sidewall and sharpens steering response
2) reduces flex and makes the ride harsher

besides that the aluminum edge of the wheel is vulnerable to curbing


here's another .5" over install showing the exposed wheel edge


w/i the tire's spec you can tune for the desired handling trait, use the widest spec wheel and you sharpen steering response and maximize grip because the slip angle is minimized while reducing ride comfort, use the narrowest spec width and you do the opposite

I've gone .5" over in the past and been ok if a bit uncomfortable w/ it, I'd never go 1" over

[Aircooled4evr]

Thanks Bill Verburg.
[QUOTE I've gone .5" over in the past and been ok if a bit uncomfortable w / it, I'd never go 1 "over QUOTE]
I'm not afraid of uncomfortable!

(my brain withers over your graphs ... So I settle for your written comments)

So, ok with .5 "and never over 1". Good usable guideline!

[Cheshire Cat]

p.s. Singer wraps their cars with stretched tyres

[Bill Verburg]

Originally Posted by Cheshire Cat

p.s. Singer wraps their cars with stretched tyres

for street packages they do go .5" over front and back

for their track packages the only go to the max spec wheel

Why? to get max performance you go to max spec width to allow the rubber to work, max grip comes from min design slip angle which is obtained at max design spec, either side of max design width is either too hot or too cold

[Cheshire Cat]

Originally Posted by Bill Verburg

for street packages they do go .5" over front and back

for their track packages the only go to the max spec wheel

Why? to get max performance you go to max spec width to allow the rubber to work, max grip comes from min design slip angle which is obtained at max design spec, either side of max design width is either too hot or too cold

absolutely agree
yet, recommended size on 11" is 285-295 with minimum 275 - their race package while on the street they go with 265 with 40% wall though which is plenty on this size

[Flojo]

I did smt similar at front.
regular spec: 7x16/205-55
changed spec: 7x16/205-50

I even could have chosen to a 45 but that would change way too much (harsher steering and even lesser "comfort" as the Toyo R888R sidewall is already reinforced)

(bare in mind, at rear I ride 245-45 on a 9x16)

[Driven97]

Also note that the rim width range is the same for each listed size (eg, all 225/50-15 have a 6-8" recommended wheel) but the actual tire sizes can vary quite wildly for the listed size.

I put a 225/50-15 Yokohama A052 on a 15x9. It looks completely normal despite being 1" out of the recommended range, because it runs really wide for a 225. The tire shop even goofed the first time and mounted the 205s I bought for the front on my 9s. That did look like a stretch, FWIW.

Tire Rack has a pretty good set of data for section widths (sidewall) and tread widths. You can also find this data on the tire manufacturer's web pages.

Tl;dr usually a good idea to look up the actual tire you want to use and compare the specs to others, even of the same size.

[panzerfaust]

i run both 225 50 15 on 9x15 e50 BBS and 225 50 16 on 8x16 fuchs on fronts.

no issues on 9s... typically the wider rim give better turn in and tire response. manufactures now are cautious in recommending overly wide rims due to rim scuffing or damage from curbing, carwash rails or pot holes due to liability in replacing or repairing wheels

225 50 15 were fully TUV approved on 9 inch wide rims before all these warranty concerns. TUV was and is still the most stringent of all the government certifications in terms of safety since there are still no speed limits in germany

anybody remember here the ludicrous usa lawsuits with the NSX rear tires? now that's another manufacture liability story that had very little to do with safety

[Flojo]

Originally Posted by Panzerfaust

225 50 15 were fully TUV approved on 9 inch wide rims

all depending to spec tolerance regarding the circumference of a wheel and the speedo signal

German law: Paragraf 57 der Straßenverkehrszulassungsordnung (StVZO) darf der Tacho eine höhere Geschwindigkeit anzeigen, als der Wagen tatsächlich fährt, erklärt der Tüv Nord - aber niemals eine niedrigere.

in Germany cars prior 1991 may even have a up to 10% deviation but NEVER less than real speed.

so a smaller wheel to spec diameter would show you higher speed: OK
a wider wheel would show you slower speed: NOT OK (*)

(* unless you adapt the speedo)

[panzerfaust]

Originally Posted by Flojo

all depending to spec tolerance regarding the circumference of a wheel and the speedo signal

German law: Paragraf 57 der Straßenverkehrszulassungsordnung (StVZO) darf der Tacho eine höhere Geschwindigkeit anzeigen, als der Wagen tatsächlich fährt, erklärt der Tüv Nord - aber niemals eine niedrigere.

in Germany cars prior 1991 may even have a up to 10% deviation but NEVER less than real speed.

so a smaller wheel to spec diameter would show you higher speed: OK
a wider wheel would show you slower speed: NOT OK (*)

(* unless you adapt the speedo)

i have had well over a dozen alfa, fiat, lancias and ferrari's. if any those veliga borletti, or jeager gauges are anywhere near 10% on stock size tires id be ecstatic yes its always safer to overestimate rather than underestimate the speed. a good explanation why the speedo readings were glorified.

i wont even mention my french and british cars... lol

which brings up an interesting point, i recall lots of people were upgrading their cn36 on 215 60 15 to the then new 225 50 15's on the early 75-76 930s. there is a massive difference in the tire diameters between the two being a low profile 15 incher before the 16 became available. i reckon the vast majority didnt go through the trouble of replacing their speedos or speedo gear or tranny to account for the 2 inch or more height difference?

[Aircooled4evr]

Hi fellow pelicans.
I just looked this thread through again. Lots of good, informative posts!
Can see that 195/205 at 8 ", and 225 at 9" (X15 ") aren't over the top.

In particular, I'm glad to see, in this thread, and in the thread "Please post photos of fat Fuchs rims on your low SC", that you CAN use 8 "with 205 in the front, as long as you roll the wheel arch! I'm more confident in my project now ... But .. am I the only one these days, who would think of choosing "old-fashioned tire height"?
I was thinking of 195/65 and 225/60 at 8 & 9X15 ".. .....
I love it when the tires sit really close to the "edge", and "up high in the shadows"!
P.S. I do not care ... the Tires will be without rim protector edge! I like my tirewalls "clean" and simple ....

[Bill Verburg]

Originally Posted by Aircooled4evr

Hi fellow pelicans.
I just looked this thread through again. Lots of good, informative posts!
Can see that 195/205 at 8 ", and 225 at 9" (X15 ") aren't over the top.

In particular, I'm glad to see, in this thread, and in the thread "Please post photos of fat Fuchs rims on your low SC", that you CAN use 8 "with 205 in the front, as long as you roll the wheel arch! I'm more confident in my project now ... But .. am I the only one these days, who would think of choosing "old-fashioned tire height"?
I was thinking of 195/65 and 225/60 at 8 & 9X15 ".. .....
I love it when the tires sit really close to the "edge", and "up high in the shadows"!
P.S. I do not care ... the Tires will be without rim protector edge! I like my tirewalls "clean" and simple ....

I see several issues w/ your choices

assuming you have an SC/Carrera chassis
issue 1 there are no 8x15 Fuchs that fit the front, all are ET10.6 and you need ~ET25-30 for an 8 on the front of a 911

issue 2 195//65x15 is generally spec'd for a 7" wheel max

issue 3 There are no 9x15 Fuchs for the back, all 9x15 Fuchs are ET3 you want ~ET15 for the back
issue 4 a 225/60 x15 is spec'd for an 8" wheel max

issue 5 compared to a more usual tire choice 7 & 8 a15 w/ 205/50 & 225/50 x15 your choice is going to cost ~ 38lb-ft of torque that comes from the cars ability to accelerate

[Aircooled4evr]

Damn damn damn! ....
OK. thank you Bill Verburg.
So my problems ARE just started then.....
Hmm .. It can be done on a SC, with 8 "ET 25 .. has ET10.6 .. I am short of 14.4mm then...
Again, it can be done with 9 "ET15 has ET3 .. here I'am short of 12mm.
So: short of 14.4mm in the front
short of 12mm in the back
How the hell can that be done, (when you don't want to widen your car!)
1) you can stretch your tire further .. (195X65 & 225X60 compared to 205 &245). gives you 2-3mm?
2) you can give it more camper ... 2mm?
3) machine 1-2mm of the contact surface on the rim .. Very dangerous ..
at this point you are missing approx. 10mm in front
and approx. 7mm in the back
4) Can you convert your spindle to new type of ball bearing in the front? You should have enough space to move the rim in a little ... (if you take the old double concave system on the Porsche, and compare it with, for example, a WV golf wheel bearing, you will have a few mm)
5) can't think of anything other than moving the actual suspension points now .... and it will be approx. 7mm both front and rear ...
6) suggestions? ideas? am I REALLY going to drop my dreams ...

[Bill Verburg]

Originally Posted by Aircooled4evr

Damn damn damn! ....
OK. thank you Bill Verburg.
So my problems ARE just started then.....
Hmm .. It can be done on a SC, with 8 "ET 25 .. has ET10.6 .. I am short of 14.4mm then...
Again, it can be done with 9 "ET15 has ET3 .. here I'am short of 12mm.
So: short of 14.4mm in the front
short of 12mm in the back
How the hell can that be done, (when you don't want to widen your car!)
1) you can stretch your tire further .. (195X65 & 225X60 compared to 205 &245). gives you 2-3mm?
2) you can give it more camper ... 2mm?
3) machine 1-2mm of the contact surface on the rim .. Very dangerous ..
at this point you are missing approx. 10mm in front
and approx. 7mm in the back
4) Can you convert your spindle to new type of ball bearing in the front? You should have enough space to move the rim in a little ... (if you take the old double concave system on the Porsche, and compare it with, for example, a WV golf wheel bearing, you will have a few mm)
5) can't think of anything other than moving the actual suspension points now .... and it will be approx. 7mm both front and rear ...
6) suggestions? ideas? am I REALLY going to drop my dreams ...

What can be fitted is constrained by;
the available hardware
the available space
the effects on the vehicle dynamics

Here is what is available that can be fitted to an SC/Carrera

note that only the wheels in the green sections are oe Fuchs