It is currently Tue Aug 14, 2018 6:24 am

All times are UTC - 5 hours [ DST ]




 Page 1 of 1 [ 11 posts ] 
Author Message
 Post subject: Is it possible to run all same tires with different tread..?
Unread postPosted: Tue Nov 06, 2012 4:00 pm 
Subie Tuner
User avatar

Joined: Wed Aug 13, 2008 6:53 pm
Posts: 656
Location: Onondaga Hill
Hey guys long time no talk

I have a decent deal on wheels and tires but 2 tires are worn more than the other (same blizzak). This is probably a no go, eh?



_________________
2011 Satin White Pearl STi #34 ASP

IG -- @shellshocksti
Offline
 Profile  
 
 Post subject: Re: Is it possible to run all same tires with different trea
Unread postPosted: Tue Nov 06, 2012 4:34 pm 
Subie Fanatic

Joined: Mon Sep 24, 2012 5:41 am
Posts: 119
Location: Utica, NY
Not ideal, but it is probably workable. Depends on how bad the difference is. Here's a couple of suggestions:

If it's not that bad, run the meaty ones up front. By the end of the season, that situation will have reversed itself (assuming you're driving what's in your avatar).

If it's really bad, buy two new tires to replace the bad ones, and put those up front. I don't get much rear wear at all on my car, (Civic), so I've got ws-70s at one end, and many-seasons-old ws-50s at the other (finally put them up front just so I could finally wear them out). Just keep them matched on the axles. How bad is too bad? Not sure, but I'd call them done for real snow below 4/32nds.

My $0.02



_________________
-Mike #24 GS
Offline
 Profile  
 
 Post subject: Re: Is it possible to run all same tires with different trea
Unread postPosted: Tue Nov 06, 2012 6:16 pm 
tranny lube party host
User avatar

Joined: Mon Sep 03, 2007 11:01 am
Posts: 2669
Location: Chittenango, NY
The biggest issue you'll run into on the subie is increased wear & tear on the diffs if the rotating diameter is different between the tires. That said though - factory spec has different air pressures front & rear which in itself will change the diameter ever so slightly, so there's obviously an element of fudge factor in there anyways. If it's significant, your options would be to either shave the newer tires to match the old - or to replace the worn tires to match the new (no sense in wearing away more than 50% of two new tires).



_________________
Scott Newton
CNY SCCA Solo Chair
#159 in whatever the class du jour is
Offline
 Profile  
 
 Post subject: Re: Is it possible to run all same tires with different trea
Unread postPosted: Tue Nov 06, 2012 11:38 pm 
Major Trou
User avatar

Joined: Thu May 17, 2007 8:22 am
Posts: 8794
Location: Indypolis
Depends on how different the rolling diameter is. There's a limit spec floating somewhere.



_________________
I couldn't open the door because it was locked, so I used a stick of dynamite to get in.
Offline
 Profile  
 
 Post subject: Re: Is it possible to run all same tires with different trea
Unread postPosted: Wed Nov 07, 2012 12:49 am 
Moar Dew.
User avatar

Joined: Wed May 16, 2007 6:17 am
Posts: 8301
Location: North Syracuse, NY
Mechie3 wrote:
Depends on how different the rolling diameter is. There's a limit spec floating somewhere.

This would be fantastic to know. You can't anticipate that all four tires will have the same tread all the time, and there's no history of tremendous numbers of Subaru transaxles failing. How much of this is myth, barring large variances?



_________________
Disclaimer: The above post is on the internet.
__________________________________

'00 Miata LS, Evolution Orange - Boosty!
'18 Crosstrek, Venetian Red Pearl - Lofty!
Image Image
Offline
 Profile  
 
 Post subject: Re: Is it possible to run all same tires with different trea
Unread postPosted: Wed Nov 07, 2012 3:24 pm 
Subie Fanatic

Joined: Wed Apr 01, 2009 10:01 pm
Posts: 109
It depends on the difference in tread depth. 1/32nds = 0.03125" So take the difference, double it and you get the overall difference in diameter between the tires. If it's less than a few 32nds difference, it may not be an issue in the big picture. The trans-axle parts will experience higher stress loads due to rotational speed differences but the difference may not be enough to cause significant harm in the parts during the few months that you are driving on these tires.

Consider that even on AWD cars, the front tires will wear faster due to the added shear stress loads from steering, which is why manufacturers require tire rotations. That being said, the front and rear tires will have differences in their overall diameter at any point in time after the tires are commissioned.

Additionally, good engineers design parts with a safety factor in all mechanical parts in order to prevent failure and I doubt the added stress will push the parts into failure mode, assuming you are driving under intended conditions (i.e, no frequent and continuous abusive driving, launching, e-braking, or any actions in that category).


Offline
 Profile  
 
 Post subject: Re: Is it possible to run all same tires with different trea
Unread postPosted: Thu Nov 08, 2012 12:25 pm 
Major Trou
User avatar

Joined: Thu May 17, 2007 8:22 am
Posts: 8794
Location: Indypolis
I had a snow tire go flat once on the rear. I think rolling diameter was within 1/2 inch so I said "meh, whatever" and ran it just fine.



_________________
I couldn't open the door because it was locked, so I used a stick of dynamite to get in.
Offline
 Profile  
 
 Post subject: Re: Is it possible to run all same tires with different trea
Unread postPosted: Thu Nov 08, 2012 4:13 pm 
Subie Fanatic

Joined: Wed Apr 01, 2009 10:01 pm
Posts: 109
Rob, I would assume the tolerance for OD is +3% since tread depths can start at 12/32nds and I should hope that the engineers have considered people running on bald tires, plus and minus sizes for tire and wheel geometry.


Offline
 Profile  
 
 Post subject: Re: Is it possible to run all same tires with different trea
Unread postPosted: Thu Nov 08, 2012 4:49 pm 
Moar Dew.
User avatar

Joined: Wed May 16, 2007 6:17 am
Posts: 8301
Location: North Syracuse, NY
3% on a 205/55/16 is damn near 3/4 inch! That's a very extreme difference.

I can't dispute it because I have no idea, but that would contradict everything that's been said about having to replace four tires if you lose one to a puncture (or whatever). Naturally, as discussed above, with the potential for differences due to front/rear loading, uneven wear, and even varied tire pressure, there absolutely has to be some safe sway.

With a 205/55/16 size, at a mathematically correct 78.15" circumference, dropping 3% gives you 75.81". Those diameters at 60mph give you 811 and 836 rotations per minute, respectively. That's one rotation different every 2.4 seconds.

Would that activate a viscous diff? Probably not. Would an electronic diff act on it? No idea. Would a tooth count sample rate pick it up?

Someone somewhere knows the answer!!



_________________
Disclaimer: The above post is on the internet.
__________________________________

'00 Miata LS, Evolution Orange - Boosty!
'18 Crosstrek, Venetian Red Pearl - Lofty!
Image Image
Offline
 Profile  
 
 Post subject: Re: Is it possible to run all same tires with different trea
Unread postPosted: Thu Nov 08, 2012 5:05 pm 
Moar Dew.
User avatar

Joined: Wed May 16, 2007 6:17 am
Posts: 8301
Location: North Syracuse, NY
Found a post on NASIOC by North Ursalia (who I consider reliable) claiming that Subaru places the cap at 1/2" max difference. Asking me, if the tires on each axle (fronts or backs) match well, a half inch difference front to back probably wouldn't make yoar car asplode.

** Typical disclaimer: IMHO, YMMV, GLWT, TNFF, and TTFN. **



_________________
Disclaimer: The above post is on the internet.
__________________________________

'00 Miata LS, Evolution Orange - Boosty!
'18 Crosstrek, Venetian Red Pearl - Lofty!
Image Image
Offline
 Profile  
 
 Post subject: Re: Is it possible to run all same tires with different trea
Unread postPosted: Thu Nov 08, 2012 7:10 pm 
Major Trou
User avatar

Joined: Thu May 17, 2007 8:22 am
Posts: 8794
Location: Indypolis
You forgot Chris' favorite: PCS.



_________________
I couldn't open the door because it was locked, so I used a stick of dynamite to get in.
Offline
 Profile  
 
Display posts from previous:  Sort by  
 Page 1 of 1 [ 11 posts ] 

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  

cron