Space Saver Spare O.K. With Different Tires Than Original?

[Jim]

Read in automotive column today something that made me wonder. The
writer was contemplating getting "plus" size tires due to clearance
problems with his Legacy. The answer included a caution to get 5 new
tires because running the "plus" size with a the space saver spare on
one wheel could cause "major drivetrain damage".

My question is this: Last year I replaced the standard 215x70x15
tires with Goodyear Triple Treds in size 195x60x15 (replaced the
wheels as well). I don't know if these are "plus" size tires; in fact
I don't know what that means. Since no adjustment in the speedometer
was required, the distance travelled per tire revolution must be the
same and thus it would seem there should be no more problem using the
space saver spare on these tires then on the OEM sized tires. Correct,
or incorrect?

TIA
Jim.

 

[Rick Courtright]

wheels as well). I don't know if these are "plus" size tires; in fact
I don't know what that means. Since no adjustment in the speedometer

Hi,

Not sure I understand how a 195-60 and a 215-70 in the same wheel size
can have the same diameter or rolling radius. Did you actually mean your
195-60s are on 16" wheels?

My understanding is "plus" sizing, properly done, results in a larger
wheel size than stock, with a correspondingly "shorter" tire so the
overall diameter and RR remain as close to identical as possible. Many
manufacturers now show "revs per mile" for their different tires so you
can compare. So, for example, you have a stock 15" tire that gives, say,
812 rev/mi, and you replace with a 16" that gives 810 or a 17" that
gives 809 (all numbers made up for comparison only), you're about
"perfect" in your "plus" sizing. This assumes, of course, you don't
create other fit problems, such as going so wide on your "plus" wheels
that you experience chassis interference and such. If you achieve that,
your compact "donut" spare should be fine (with the usual considerations
for using a "donut.")

Rick

 

[Here and There]

My question is this: Last year I replaced the standard 215x70x15
tires with Goodyear Triple Treds in size 195x60x15 (replaced the
wheels as well). I don't know if these are "plus" size tires; in fact
I don't know what that means. Since no adjustment in the speedometer
was required, the distance travelled per tire revolution must be the
same and thus it would seem there should be no more problem using the
space saver spare on these tires then on the OEM sized tires. Correct,
or incorrect?

Plus 1 conversions usually refer to increasing the wheel diameter
by an inch and sizing tires to be the same effective diameter.

The numbers give the effective diameter for the 215s as 26.9 inches
and the 195s as 24.2 inches. That is a whopping 10% difference.
The diameter of the new tires is quite a bit smaller than the
previous ones. It lowers your ground clearance by 1.5 inches.

The distance travelled per tire revolution is only 90% compared to
the previous tire. I would NOT use the spare.

Did you give the incorrect wheel diameter for one of the numbers?

 

[Jim]

Hi,

Not sure I understand how a 195-60 and a 215-70 in the same wheel size
can have the same diameter or rolling radius. Did you actually mean your
195-60s are on 16" wheels?

My understanding is "plus" sizing, properly done, results in a larger
wheel size than stock, with a correspondingly "shorter" tire so the
overall diameter and RR remain as close to identical as possible. Many
manufacturers now show "revs per mile" for their different tires so you
can compare. So, for example, you have a stock 15" tire that gives, say,
812 rev/mi, and you replace with a 16" that gives 810 or a 17" that
gives 809 (all numbers made up for comparison only), you're about
"perfect" in your "plus" sizing. This assumes, of course, you don't
create other fit problems, such as going so wide on your "plus" wheels
that you experience chassis interference and such. If you achieve that,
your compact "donut" spare should be fine (with the usual considerations
for using a "donut.")

Rick

Sorry I read the Owner's manual wrong. On my Brighton the stock tires
were 185x70x14. The new ones are 195x60x15. So it appears there
should be no problem if I ever need the donut for a few miles. Have
not had a flat in 8 years (knock on wood).

Jim

 

[Jim]

Plus 1 conversions usually refer to increasing the wheel diameter
by an inch and sizing tires to be the same effective diameter.

The numbers give the effective diameter for the 215s as 26.9 inches
and the 195s as 24.2 inches. That is a whopping 10% difference.
The diameter of the new tires is quite a bit smaller than the
previous ones. It lowers your ground clearance by 1.5 inches.

The distance travelled per tire revolution is only 90% compared to
the previous tire. I would NOT use the spare.

Did you give the incorrect wheel diameter for one of the numbers?

Yea, misread the manual. The original on my Brighton was a 70X14"
tire, the new is 60x15. According to the previous post, I should be
ok.

Jim

 

[Bonehenge]

Read in automotive column today something that made me wonder. The
writer was contemplating getting "plus" size tires due to clearance
problems with his Legacy. The answer included a caution to get 5 new
tires because running the "plus" size with a the space saver spare on
one wheel could cause "major drivetrain damage".

Is the car an automatic or stick shift? It matters for the correct
answer.

 

[Jim]

Is the car an automatic or stick shift? It matters for the correct
answer.

Automatic...

 

[B a r r y]

Automatic...

Most Subaru automatics are capable of 2WD (Front wheel drive) with the
insertion of a fuse. Check your manual.

If your car has this capability, you have no worries using the stock spare.

 

[S]

Hi Jim, All!

Most Subaru automatics are capable of 2WD (Front wheel drive) with the
insertion of a fuse. Check your manual.

If your car has this capability, you have no worries using the stock spare.

Barry is correct. If you must run the space saver, or a significantly
different sized tire on one corner, put it on the _back_ (I know . . .
this is a pain if you have a flat on the front, nevertheless . . .),
and disable the AWD. Keep speeds below 50MPH, and replace ASAP.
This is acceptable for cars with LSD rears (WRX, some older Legacys,
???) as well, but realize that you are abusing the LSD by doing so.
The space saver spare is only designed to get you to the nearest
service station in any event; usage beyond that is contraindicated.

ByeBye! S.

Steve Jernigan KG0MB
Laboratory Manager
Microelectronics Research
University of Colorado
(719) 262-3101

 

[k. ote]

Most Subaru automatics are capable of 2WD (Front wheel drive) with the
insertion of a fuse. Check your manual.

If your car has this capability, you have no worries using the stock
spare.

I just wanted to point out that the WRX is *NOT* capable of being put into
2WD by moving the fuse. Absolutely not.

 

[Carl 1 Lucky Texan]

B a r r y wrote:




I just wanted to point out that the WRX is *NOT* capable of being put into
2WD by moving the fuse. Absolutely not.

I know the auto is an option on the 'limited' WRX but i have no idea
what the owner's book recommends. maybe the lsd rear diff prevents use
of a FWD fuse? I dunno

Carl

 

[Bonehenge]

I just wanted to point out that the WRX is *NOT* capable of being put into
2WD by moving the fuse. Absolutely not.

Hence the "check your manual" statement.

There are at least THREE distinct Subie drive trains. Since most
Subarus with automatic trannys aren't WRX's...

Wait... You have an AUTOMATIC WRX? Why? That's like an automatic
TR6! <G>

Barry

 

[k. ote]

Barry is correct. If you must run the space saver, or a significantly
different sized tire on one corner, put it on the _back_ (I know . . .
this is a pain if you have a flat on the front, nevertheless . . .),
and disable the AWD. Keep speeds below 50MPH, and replace ASAP.
This is acceptable for cars with LSD rears (WRX, some older Legacys,
???) as well, but realize that you are abusing the LSD by doing so.
The space saver spare is only designed to get you to the nearest
service station in any event; usage beyond that is contraindicated.

Wrong: The automatic WRX is *not* capable of being put into 2WD by moving
the fuse! Only those vehicles that have the fuse mentioned explicitly in
their manuals can be put into 2WD like that.

 

[k. ote]

Wait... You have an AUTOMATIC WRX? Why? That's like an automatic
TR6! <G>

I drive a 2004 STi. I did have a 2002 WRX; however, the only reason I know
for sure that the auto *can't* be put into 2wd mode is because this was
already hashed out about a year or more ago in this very newsgroup, and I
called up the local Subaru Master Mechanic to ask about it, whereupon he
told me very specifically that the fuse slot does absolutely nothing in an
auto WRX.

 

[B a r r y]

I called up the local Subaru Master Mechanic to ask about it, whereupon he
told me very specifically that the fuse slot does absolutely nothing in an
auto WRX.

Nobody's debating that.

The real question is WHY buy an automatic sports car? <G>

 

[k. ote]

Nobody's debating that.

The real question is WHY buy an automatic sports car? <G>

Oh. I dunno: maybe they drive in the city and don't want to screw around
with the clutch all day long? Or--maybe they don't want to learn to drive a
standard on a car like a WRX?