Balanced tire sizes?

ZOA NOM · ZOA NOM's Garage

Help me out here, I'm trying to do this right. I discovered today that the PO of my '88 Coupe put 16x7's and 16x9's on the car. This is apparently desirable for some, but it seems to be creating a dilemma for me. I seem to be caught between keeping the tire height (and corresponding rev's/mile) stock for the speedo, and making sure the tires are wide enough for the wheels.

The stock tire sizes listed on the plaque under the hood are 205/55/16f and 225/50/16r. The 205's fit the 7 inch rims fine, but I think 225's on 9 inchers is pushing it.

My question after reading through some of the posts on this subject is whether there is a concern about maintaining the balance between the sizes front to rear?

I'm almost settled on buying 245/45/16's for the rear, and I'm wondering if I should try to fit 225/50/16's instead of the 205/55/16's up front to keep the ratio a little closer. I've read that the 245's paired with the 205's can affect under/oversteer.

spinner · spinner's Garage

The PO did you a favor with the 7 and 9 Fuchs (I assume they're Fuchs). The typical sizes are 225/50 and 245/45. Properly lowered and aligned, your car should be real nice

Wil Ferch · 05-06-2003, 09:15 AM

Different spin on this...
Yep...for $ value and such..the "9's" are great...but you have a point.
Originally, you'd have a contact patch using 205 fronts ( on 6's) and 225 ( on either 7's or 8's) on back. Doing nothing for the front and adding 245's in the back will make the car understeer more, especially on low speed corners...all else being equal.

To maintain fr/rr understeer and oversteer balance, you can:
- stay with 225's on back, but these are too narrow for 9's, use 8 or 7.
- go with 225's on front...but use 944 style 7" Fuchs
- get a wider front track with a more stable sidewall support ( compared to stock 6") by using 7" 911 style Fuchs..and 205. This improves the "stock" set up by dialing out some understeer, but you already have these.

---Wil Ferch

Neilk · 05-06-2003, 09:32 AM

FWIW, turbos came with 205s on the front and 245s in the rear. So I am not sure you have to worry about balance.

Don't worry about speedo accuracy. I think most 911s have optimistic speedos to begin with.

thabaer · thabaer's Garage

I improved the balance on my lowered '79 by keeping 205s up front and using 245/45s on 16x8s.

As far as speedo accuracy, you can use the information on some tire mfg sites where they list revs/mile for various tire sizes. As long as your rim widths are within about 1" of what they list as the median rim size for a given tire, you should get pretty accurate predictions.

I like to keep as close as possible to the standard rolling diameter, I just used Bridgestone's data to get a set of 245/45-17s and make sure I didn't poink the speedo in my '91 200q20v.

Wil Ferch · 05-06-2003, 10:55 AM

Turbo's do come with 205 front and 245 rear...but the track width is different too.
--Wil Ferch

Lewis Ledyard · 05-06-2003, 12:42 PM

can I run 16X7s front and rear on a '71 911T? I had hoped to use 205/55 and 225/50. Is that too much w/o adding SC flares (which I do not want to do)?

ZOA NOM · ZOA NOM's Garage

I think I'll go with the 225/245 setup. With the 7's up front, will I have any clearance issues? I appear to be at stock (US) ride height without much negative camber, if any, so there's room to make adjustments. I am interested in a little lower ride, so I'll be messing with the setup anyway.

Thanks again!

Jdub · 05-06-2003, 01:49 PM

I am preparing for the move to the 7 and 9s and thought I would stay with the 205 on the front because 1) they aren't too worn and 2) I always thought a "thinner" tire would provide better feel for steering - is this just my bicycle tire prejudice taking over?

I had intended to keep the Yokohama dB2 205/55/WR16 in front and match it with 245/50/WR16 on the rear. Am I doing wrong here, aspect-ratio-wise?

Much thanks for your replies,
John

avi8torny · 05-06-2003, 01:54 PM

the 225's up front may or may not fit. If you want to be sure...stick with the 205/50/16"s. I have alot of neg camber up front and my Toyo's in the 225 will not fit...not even close. The 205's barely fit with aggressive lowering on my ride. Hope that helps.

ZOA NOM · ZOA NOM's Garage

in order to retain the stock diameter, which will affect the speedo. I currently have 245/50/16's in back, and my speedo is off by 3%.

Wil Ferch · 05-07-2003, 06:13 AM

205/55-16 are 24.8" diameter

225/50-16 are about the same

For 245....you'd want 245/45-16 for nearly same diameter...245/50-16 would be a bit too tall.

---Wil Ferch

Jdub · 05-07-2003, 06:14 AM

Thanks guys!

John

Wil Ferch · 05-07-2003, 06:17 AM

more....

Looking at my car running 911-style 7" Fuchs on the front with 205's...

I would think running 225's for the front would be way too wide...you'd need 944 style 7"..or other brand tires ( I am running Bridgestone S-02's).

---Wil Ferch

AES · 05-07-2003, 06:55 AM

Quote:

Originally posted by Wil Ferch
For 245....you'd want 245/45-16 for nearly same diameter...245/50-16 would be a bit too tall.

---Wil Ferch

I couldn't agree more!

GeorgeM · GeorgeM's Garage

I'm with Avi8torny:

Be careful, 225s on 7s don't fit on my '89 Carrera, I have to use 205s.

I use 245s in back on the track and 225s on the street (because that's before I knew 245s would work). I have had no handling issues.

Mike M · Mike M's Garage

Go to the Early 911S Registry home page.There is a calculator program there where you enter your orginal tire size and your NEW tire size,and it tells you what your speedo will read,revs per minute,tire diameter etc.
Very helpful.

thabaer · thabaer's Garage

The 205/55-16s on the front of my car have rubbed in some more extreme occasions, 225 would be demanding trouble

if I used them on the front. 245/45-16 on the back is the target to match the diameter of the stock 225/50-16s.

The calculators are great for getting what diameter you should get for a given tire size, but double check the mfg data. Some brands deviate from the ideal fraction of aspect ratio based on width. The widths don't even end up the same for a specified number between tire models from a single manufacturer. The number of revs per mile also don't always come out the same for identical sizes; the design, construction and choice of flubber

affect what comes out of the mold.

Chas911 · 05-07-2003, 10:04 AM

I have run all the sizes listed here so I will chime in with my .02. The ultimate setup in 16" Fuch wheels is 8" fronts from a 944 (not 7") with 225/50/16 and 9" on the rear with 245/45/16. The 225/50/16s on the front with 7" 911 offset wheels is pretty tight and usually needs some aggressive fender rolling.
That being said I usually end up running 7" with 205/55/16 in the front. There is a little more understeer in long sweepers but not enough that it is worth the expense for the 8" to run the 225/50/16 (the 944 8" fuchs are getting harder to find). Also the 225/50/16 on 7" seem to have more roll in tight corners than 205s, depending of course on the tire manufacturer. I also think 245/50/16s are too tall for the rear. I would be surprised if your speedo was accurate enough to worry about it.

ohecht · 05-07-2003, 11:01 AM

This makes me wonder about the setup I inherited from my PO:

205/50 17" on 7.5" fronts and 255/40 17" on 9" rears.

Is anyone else running this setup on an SC? The car seems to handle great, but it is the only 911 I have ever driven for any length of time.

Olivier