View Full Version : Mis-matched tire (front/rear)
acjx880
01-03-2007, 02:04 AM
Hi guys,
I've read on many threads here that you guys seems to have a concensus that mis-matched tires on AWD is BAD.
I know there are issues coz of traction, but will that actually damage the AWD system?
Reason
01-03-2007, 02:30 AM
Hi guys,
I've read on many threads here that you guys seems to have a concensus that mis-matched tires on AWD is BAD.
I know there are issues coz of traction, but will that actually damage the AWD system?
So it is said, I'm one to fight the "tails" and find out myself, but this is one I'll take their word for ir. :wink:
Plays_with_Toys
01-03-2007, 08:32 AM
Usually mismatch tires on any set of drive wheels is bad (hence why spare tires should never go on a drive wheel for more than 50 miles if it is not a full size spare). Some say that even a few thousandths of tread difference can cause problems. I don't know if that is true or not. I can't imagine the thousands of old woman drivers who drive subarus know this and pay any close attention to it (even with respect to rotating their tires), and they're driving around fine.
But like reason said, I'm not exactly going to be the guinea pig.
d1giPhux
01-03-2007, 08:52 AM
I really doubt it does much, but i dont recommend it. Most tire shops wont even mount different set of tires now days, but I really doubt it would do MUCH hard. Although i cant say for sure, because i have never done it. If you need to get some new cheap tires, i recommend tire rack. I got some Sumitomo HTR+ tires off there for like $60 each, and they are awesome. They are 'all season', but have been great in the snow / ice so far, and awesome in rain / dry weather conditions! Plus.. the tread is sick looking! :cool:
Yes, mismatched tires will put an abnormal amount of stress on your center differential, since they are viscous coupling, and work based on speed differences betwen the front and rear tires.
rougeben83
01-03-2007, 11:07 AM
I'll let you know when I take my snows off this spring :wink:
Wiscon_Mark
01-03-2007, 11:14 AM
If the front wheels are turning at a different rate than the back wheels, the center diff will try to compensate. Now this sort of thing is ok if you're just slipping around a bit here and there, but if it's happening the entirety of your drive, you will eventually wear out the center differential.
Sarra
01-03-2007, 05:34 PM
If you have open front and rear diffs, you could put different size tires on one side of the car than the other, but I wouldn't suggest doing that. :twisted:
If you really want to run smaller tires in front, you could always do some advanced math and swap your rear diff for one with a slightly larger final drive. The different ratio would even out due to the differences in diameter. Some AWD tractors have smaller tires up front, and they use a different front and rear diff to compensate for the difference in diameters.
Regardless, due to traction, safety, and longevity of the car, I'd suggest sticking to a matching set of tires anyway. :)
rougeben83
01-03-2007, 08:53 PM
Read the owners manual. Should be a quib about subaru's allowing only up to a 1/4" in CIRCUMFERENCIAL difference between the tires, which translate to about 1/32" in tread.
There you go.
acjx880
01-04-2007, 03:11 AM
Hmmm...
I'm wondering if there's any damage on the centre differential of my newly acquired Brighton... As the previous owner had different tires in the front than the rear, although the tires are all the same dimension. (I think...) :-?
On my gf's Outback Ltd wgn, eventhough its a year older with slightly lower mileage, I feel the car accelerates so much smoother, but that might just be because I had flushed/replaced all the fluids in her vehicle.
I may just have to wait till there's some snow on the ground to test it out. Too bad my tire shop had sold out of the GT Radial snow tires I got for her; if both cars had the same tires, the comparison would have been alot easier...
Wiscon_Mark
01-04-2007, 09:56 AM
While it might be the same diamter, you know that not all companys have the same manufacturing processes, and one 195/60/15 tire might be different than another 195/60/15 tire.
rougeben83
01-04-2007, 11:38 AM
Measure the tire diameter yourself.
Wiscon_Mark
01-04-2007, 01:44 PM
Measure the tire diameter yourself.
Measure with the micrometer, mark with chalk, split with an axe :lol:
(make sure you measure very accurately)
acjx880
01-04-2007, 03:05 PM
Measure the tire diameter yourself.
Measure with the micrometer, mark with chalk, split with an axe :lol:
(make sure you measure very accurately)
lmao...
I think I'll pass on that and just go to a local Crappy Tire to pick up a pair of matching tires in the spring, as the previous owner had done all his service there. I've put on Gislaved NordFrost5 185/65/15, which should have the same diameter as the OEM 195/60/15 for now.
I don't think I can stand opening another can of worms since I've only had the car for 2 weeks....
Thanks guys for all your inputs!
MoclovFlop
01-04-2007, 03:53 PM
I'm running two different sets of tires (unfortunately) and there is a difference of a few 32nd's between the two, I inflated the more worn ones a few PSI more in hopes of some sort of compensation. I'm probably doing damage, but I can't afford new tires yet. :-(
Wiscon_Mark
01-04-2007, 03:54 PM
A new viscous coupler is more expnensive than a set of tires....
acjx880
01-04-2007, 04:21 PM
This may be a little off topic, but what's the front and rear torque split on these cars, and are they variable?
Even if the torque split was even, hard corning will usually wear out the front tires more quickly, so wouldn't that make a difference already to the tire dimension and cen. diff., even if one had the same tires on all four corners? :-?
Wiscon_Mark
01-04-2007, 04:24 PM
The 4EAT is 90/10 (F/R) in D unless slipping occurs. Then it will start at 50/50 and vary by how much the front/rear wheels are slipping. If you lock it in 1st or 2nd, it'll be 50/50
The 5MT is 50/50 unless slipping occurs. Then it's variable.
shazapple
01-04-2007, 04:32 PM
Even if the torque split was even, hard corning will usually wear out the front tires more quickly, so wouldn't that make a difference already to the tire dimension and cen. diff., even if one had the same tires on all four corners? :-?
Thats what tire rotation is for :wink:
rougeben83
01-04-2007, 06:54 PM
Yup, but again, were talking about worse-case scenario's here.
I've seen a couple of WRX's with more worn front tires (especially on the inner shoulders) and I'm assuming the owner has had them that way for a long time and the car is still chugging along.
Seriously, don't overthink it; get the tires to within the specs and you're fine.
backpack09
01-22-2007, 12:33 PM
And if you want to get a better compairison of tire size, measure the circumfrance not the diameter. The circumference will show differences in sizes easier than measuring diameter.
As (correct me if I am wrong, it's been a few since geometry class...)
circumfrance=3.14X2Xradius
Which means a 1/32 of diameter difference = 3/32 of circumference difference...
ugg too much math, back to my burrrito.
LeggoMyLeggy
12-20-2008, 02:35 PM
The 4EAT is 90/10 (F/R) in D unless slipping occurs. Then it will start at 50/50 and vary by how much the front/rear wheels are slipping. If you lock it in 1st or 2nd, it'll be 50/50
The 5MT is 50/50 unless slipping occurs. Then it's variable.
Since we've been getting a little bit of snow out here in Seattle, WA I've had a chance to go play in the snow a little bit. It seems to me that when the 4EAT is 4th the bias feels like 90/10 split. When I'm 1st or 2nd it feels more evenly split. The question is when I'm in 3rd. I feel more rear bias than the in 4th gear. Can someone confirm if they've experienced this also?
Thanks and happy holidays to you all!
Leggo
PS...What do you all do about stuck doors??? Prevention and opening.
decke48
12-20-2008, 02:41 PM
PS...What do you all do about stuck doors??? Prevention and opening. vasoline on the weatherstrip. just a light coat. works in weather from 32f to 10f as far as i know not sure about lower temps
LeggoMyLeggy
12-20-2008, 02:50 PM
Thanks. Will try when the doors thaw out later today.
birukun
12-20-2008, 09:13 PM
All I know is that I know when I have a tire low on air (slow leak, fixed after I got tired of checking all the time) my car does not COAST as well as if all the tires are the right PSI.
I imagine the same will happen with mismatched tires. Not good for gas mileage and probably not good for the drivetrain. I don't have solid proof that this will mess things up, but this is an expensive experiment!
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