speedometer recalibration - possible?

[gearjunkie]

Hey all,

I just got some winter tires for my 2000 outback wagon. They are a
bit smaller than the stock (they are 205-55-r16 vs 225-60-R16). This
causes about a 7% discrepancy in the speedometer reading as well as
the odometer reading. I was wondering if anyone knew of some sort of
way of recalibrating the speedometer so that it reads correctly? It's
not a huge worry asI can just keep it in mind while I'm driving, but
it wouldn't hurt to have it reading back to normal if possible.

-Nathan

 

[Jack Countryman]

In the old days of cable driven speedometers, there were mechanical adapter
boxes that fit between the transmission and the cable. Local International
Harvester dealers parts depts were always good source...if they didn't have
the ratio you wanted, they could get it for you. Their trucks must have
used those, because I could always find one close to what I needed there.
More often I'd scrounge the wrecked scouts in the local parts yard to get
them cheaper. I don't know what they use now that speedometers no longer
have cables...and confess I haven't looked... I'd suspect that the ones IH
used were SAE while the Subarus likely have metric fittings?

 

[clare]

Hey all,

I just got some winter tires for my 2000 outback wagon. They are a
bit smaller than the stock (they are 205-55-r16 vs 225-60-R16). This
causes about a 7% discrepancy in the speedometer reading as well as
the odometer reading. I was wondering if anyone knew of some sort of
way of recalibrating the speedometer so that it reads correctly? It's
not a huge worry asI can just keep it in mind while I'm driving, but
it wouldn't hurt to have it reading back to normal if possible.

-Nathan

You don't want to have to recalibrate it again next sprong when you
put the summers back on..
As far as the tire size, you went the WRONG WAY, anyways. You really
wanted a set of something closer to 205 70 tires for the winter - a
tad larger diameter, and NARROWER.

Even better yet, something like 235 70 15 tires on 15" rims. (I didn't
check the actual tire interchange for equivalencies, but it should be
close and shows the direction you SHOULD be going. High profile narrow
agressive snow tires on the smallest diameter rim that is available
for the car - with rolling diameter either equal to or slightly larger
than the factory tire.
Particularly on a vehicle with anti-lock brakes.

 

[weelliott]

 You don't want to have to recalibrate it again next sprong when you
put the summers back on..
As far as the tire size, you went the WRONG WAY, anyways. You really
wanted a set of something closer to 205 70 tires for the winter - a
tad larger diameter, and NARROWER.

Even better yet, something like 235 70 15 tires on 15" rims. (I didn't
check the actual tire interchange for equivalencies, but it should be
close and shows the direction you SHOULD be going. High profile narrow
agressive snow tires on the smallest diameter rim that is available
for the car - with rolling diameter either equal to or slightly larger
than the factory tire.
Particularly on a vehicle with anti-lock brakes.

Actually, the tires he got were narrower. The 205 number is the width.
He bought a tire that was 20 mm narrower. I agree that it would have
been a good idea to go with a 205/70 since the extra sidewall makes
them a little squishier, and thus grippier on slippery surfaces.
Although, he'd still be off by about 6 or 7 percent, but in the other
direction.

A 235/70 would actually be wider, and much much taller. The sidewall
would be 22 percent taller than the 225/60, which is way too tall.
That size is typically a truck/SUV tire, so would probably be pretty
heavy too. So the meagerly powered subie would then have a noticeable
gearing disadvantage, and more rotational mass and unsprung weight.
Not a good combination. Although the extreme gearing might help on
highway fuel economy.

 

[JD]

You don't want to have to recalibrate it again next sprong when you
put the summers back on..
As far as the tire size, you went the WRONG WAY, anyways. You really
wanted a set of something closer to 205 70 tires for the winter - a
tad larger diameter, and NARROWER.

Even better yet, something like 235 70 15 tires on 15" rims. (I didn't
check the actual tire interchange for equivalencies, but it should be
close and shows the direction you SHOULD be going. High profile narrow
agressive snow tires on the smallest diameter rim that is available
for the car - with rolling diameter either equal to or slightly larger
than the factory tire.
Particularly on a vehicle with anti-lock brakes.

A 235 anything R15 is a very wide tire. I agree with the 205/70 and even a
215/65. But a 235/70 would be a very large tire; assuming it even fits in
the wheelwell, it would be like riding on snowshows.

 

[Bob Bailin]

Hey all,

I just got some winter tires for my 2000 outback wagon. They are a
bit smaller than the stock (they are 205-55-r16 vs 225-60-R16). This
causes about a 7% discrepancy in the speedometer reading as well as
the odometer reading. I was wondering if anyone knew of some sort of
way of recalibrating the speedometer so that it reads correctly? It's
not a huge worry asI can just keep it in mind while I'm driving, but
it wouldn't hurt to have it reading back to normal if possible.

-Nathan

If you bring it to the dealer they might be able to reprogram the ECU to
accommodate the new tire size. Make sure you know how many revolutions
per mile these tires are rated for. It will probably cost you the dealer's
minimum diagnostic charge, and you'll have to get it reset in the spring.

Bob

 

[gearjunkie]

If you bring it to the dealer they might be able to reprogram the ECU to
accommodate the new tire size. Make sure you know how many revolutions
per mile these tires are rated for. It will probably cost you the dealer's
minimum diagnostic charge, and you'll have to get it reset in the spring.

Bob

Thanks for all the info guys. I figured it was going to be a bit of a
pain to recalibrate everything since everything is electronic now, I
had seen references to the gear changes other places, but it looks
like a pain to change the electronics, especially if I can't do it
quickly and easily.

FYI, I found a site that shows you the difference in tire sizes,
rotations, etc. etc. to compare if anyone is interested in how much a
different size effects the speeds, etc.

http://www.1010tires.com/tiresizecalculator.asp

Yes, the tires I got are narrower. The first number is the width in
mm, so I went from a 225 to a 205. The dealer I went to didn't have
205/65/r16s in stock (which would have been about the same diameter as
my 225/60/r16s), so I went with the 55s instead. Probably should have
gone a bit bigger on the diameter, but it's not too big a deal. I
lost a bit of clearance (a little less than an inch), but the narrower
profile will make a big difference. I guess on the bright side, I
gained a little wheel well clearance.

The speed difference at 70mph is about 5mph, so my speedometer will
read about 5 mph high in that range. Oh well.

 

[clare]

Actually, the tires he got were narrower. The 205 number is the width.
He bought a tire that was 20 mm narrower. I agree that it would have
been a good idea to go with a 205/70 since the extra sidewall makes
them a little squishier, and thus grippier on slippery surfaces.
Although, he'd still be off by about 6 or 7 percent, but in the other
direction.

A 235/70 would actually be wider, and much much taller. The sidewall
would be 22 percent taller than the 225/60, which is way too tall.
That size is typically a truck/SUV tire, so would probably be pretty
heavy too. So the meagerly powered subie would then have a noticeable
gearing disadvantage, and more rotational mass and unsprung weight.
Not a good combination. Although the extreme gearing might help on
highway fuel economy.

Like I said - I had not done the calcs -

PROPER size snow tire is 215-70 15.
Rolling diameter 26.85" vs stock 26.62, making the speedo error -
0.96%

Or better yet a 195-75 15 (26.51 diameter. and 0.44% speedo error)
The tire weight will be a bit higher, but the 15" rim is lighter,
particularly if you can get a light alloy design.. Likely ballance out
almost even.

 

[weelliott]

 Like I said - I had not done the calcs -

PROPER size snow tire is 215-70 15.
Rolling diameter 26.85" vs stock 26.62, making the speedo error -
0.96%

Or better yet a 195-75 15 (26.51 diameter. and 0.44% speedo error)
 The tire weight will be a bit higher, but the 15" rim is lighter,
particularly if you can get a light alloy design.. Likely ballance out
almost even.- Hide quoted text -

- Show quoted text -

Well, I don't want to sound like a smartass, but there are no
calculations necessary to see that 205 is less than 225. The extra
weight I was talking about from the 235 isn't due to the tire being
larger--although that would be a contributing factor--but rather to
the fact that tires in that size are made to be put on trucks and
SUVs, and typically have more belts and plies and deeper tread. They
are built for heavy use and therefore are heavy. I will admit that I
didn't notice that you had suggested a 15 inch rim. That would help,
but it wouldn't overcome the taller sidewall and heavier tire.

I run 205/65 all season radials on mine, and I like the way they look
and handle, but that is just my opinion. We rarely get more than 6
inches of snow here in MD, and I've been out in it with my subie with
nary a worry of getting stuck. The car is very predictable in the
snow.