Woodstock Posted March 14, 2009 Share Posted March 14, 2009 if I get 18x7.5 rims for summer and use my stock 17" rim for winter, what are the things I need to consider? do I need to re-balance the wheels everytime I switch 18" and 17"? Do I need to adjust anything? will 18" mess up my speedo? if it will what are the closest set up to prevent messing up my speedo with good protection from bent and curbage for my wheels and good for DD? pointers please. thanks! appreciate it! I apologize if this has been already discussed, and can you please lead me to the topic. Link to comment Share on other sites More sharing options...
mwiener2 Posted March 14, 2009 Share Posted March 14, 2009 search. then post. mount stock sized tires onthe stock sized rims. balance them when they are mounted. Don't need to rebalance them untill you change the tires or feel that they need re-balancing. For the 18's, use a tire size calculator (search 'tire size calculator') to match a tire size to the 18" rim so that it has the same overall diameter as the stock wheels. then balance them as descrived above. My Mods List (Updated 8/22/17) 2005 Outback FMT Running on Electrons Link to comment Share on other sites More sharing options...
Mr. Sinister Posted March 14, 2009 Share Posted March 14, 2009 Did you read the sticky wheel FAQ at the top of this section? Also, look at this site: http://www.discounttiredirect.com/direct/brochure/info/tmpInfoTireMath.jsp It's what I used when figuring out wheel sizes for my Spec. B. 18" stock for summer, 17" for winter. I had to pick up a GT spare for my winter setup, otherwise my stock spare would have been too large. Your speedo will be off. How much depends on what tire size you get. You can use the calculator to try and get one close to your stock diameter to avoid having to get a different spare and the speedo won't be off as much. The numbers below (according to the calculator) are what I used for comparing the GT/Spec. B spare and tire sizes. T135/70 D17 Sidewall Height: 3.72 Section Width: 5.31 Overall Diameter: 24.44 Circumference: 76.78 Revs per mile: 825.18 T155/70 D17 Sidewall Height: 4.27 Section Width: 6.1 Overall Diameter: 25.54 Circumference: 80.25 Revs per mile: 789.57 215/45/R17 Sidewall Height: 3.81 Section Width: 8.46 Overall Diameter: 24.62 Circumference: 77.34 Revs per mile: 819.24 215/45/R18 Sidewall Height: 3.81 Section Width: 8.46 Overall Diameter: 25.62 Circumference: 80.48 Revs per mile: 787.26 Link to comment Share on other sites More sharing options...
Woodstock Posted March 14, 2009 Author Share Posted March 14, 2009 Thanks! I have read the stickies before I posted. When running 18" do I need to switch my spare tire aswell? Link to comment Share on other sites More sharing options...
Mr. Sinister Posted March 14, 2009 Share Posted March 14, 2009 Thanks! I have read the stickies before I posted. When running 18" do I need to switch my spare tire aswell? Depends on your tire size. Use the calculator to see if your spare is within .25" in diameter. If it's not, you'll need a different spare. Or just get a AAA membership. Link to comment Share on other sites More sharing options...
TRS Posted March 14, 2009 Share Posted March 14, 2009 I run 225/45R-17 winter tires on the stock 17x7 wheels and 225/40R-18 summer rubber on 18x7.5 aftermarket wheels. The summer setup is only 3mm or 0.1" larger in diameter and the speedo error is only 0.5% low (indicated 60 mph would actually be 60.3 mph). There is a really good tire/wheel size comparison calculator here: http://www.rimsntires.com/specs.jsp Link to comment Share on other sites More sharing options...
Woodstock Posted March 15, 2009 Author Share Posted March 15, 2009 Depends on your tire size. Use the calculator to see if your spare is within .25" in diameter. If it's not, you'll need a different spare. Or just get a AAA membership. I have another stupid question. What is the size of the spare tires on a 08 LGT? would it be same as the stock tires? 637 mm (25.1'') 11 mm (1.8%) taller. tire diameter for the 225/40/18 on a 18x7.5 5x100 48+ Link to comment Share on other sites More sharing options...
c-lo Posted March 15, 2009 Share Posted March 15, 2009 ummm.......have you looked at your spare?? that usually will tell you;) I have another stupid question. What is the size of the spare tires on a 08 LGT? would it be same as the stock tires? 258k miles - Stock engine/minor suspension upgrades/original shocks/rear struts replaced at 222k/4 passenger side wheel bearings/3 clutches/1 radiator/3 turbos Link to comment Share on other sites More sharing options...
Woodstock Posted March 15, 2009 Author Share Posted March 15, 2009 ummm.......have you looked at your spare?? that usually will tell you;) no, LOL! I just check if they have enough air when going on a long drive. This is the first time I am into cars. Before, I don't even know to read those 225/32/15 stuff on the tire. I have purchased a 18x7.5 rims, so I kinda need to educate myself before I put it on the car. I rarely go to wheel and tires section. I thought that I would be keeping the stock rims forever. oh well.... is all your fault! LOL! Link to comment Share on other sites More sharing options...
c-lo Posted March 15, 2009 Share Posted March 15, 2009 open on the trunk and look at the spare you tool! you'll answer your own question and feel silly for asking:lol: oh, the spare is in the trunk!!! 258k miles - Stock engine/minor suspension upgrades/original shocks/rear struts replaced at 222k/4 passenger side wheel bearings/3 clutches/1 radiator/3 turbos Link to comment Share on other sites More sharing options...
Mr. Sinister Posted March 15, 2009 Share Posted March 15, 2009 I have another stupid question. What is the size of the spare tires on a 08 LGT? would it be same as the stock tires? 637 mm (25.1'') 11 mm (1.8%) taller. tire diameter for the 225/40/18 on a 18x7.5 5x100 48+ Spare sizes for a GT and Spec. B are both listed in my original post. The smaller would be for the GT of course. At 25.1", both spares have more than a .25" difference. Link to comment Share on other sites More sharing options...
Woodstock Posted March 15, 2009 Author Share Posted March 15, 2009 I used the tire size calculator on your first post and it has .47 overall diameter difference with stock GT rims vs 225/40/18. Link to comment Share on other sites More sharing options...
Mr. Sinister Posted March 15, 2009 Share Posted March 15, 2009 I used the tire size calculator on your first post and it has .47 overall diameter difference with stock GT rims vs 225/40/18. And that puts you pretty much right in between both spare sizes; not the best place to be. If you're dead set on that size, either get a 5th wheel and use that for a spare or ditch the spare altogether and go AAA. Link to comment Share on other sites More sharing options...
mwiener2 Posted March 15, 2009 Share Posted March 15, 2009 the spare is a donut. It's ok to use AS A SPARE no matter what size tires you put on the car. My Mods List (Updated 8/22/17) 2005 Outback FMT Running on Electrons Link to comment Share on other sites More sharing options...
Mr. Sinister Posted March 15, 2009 Share Posted March 15, 2009 the spare is a donut. It's ok to use AS A SPARE no matter what size tires you put on the car. For a few miles, sure. I wouldn't take the risk of getting stuck in the middle of nowhere and driving on a spare that's considerably different in size for a few hundred miles though. Link to comment Share on other sites More sharing options...
mwiener2 Posted March 15, 2009 Share Posted March 15, 2009 By the book, it's good for 55miles at 55mph. Even with that marginal rating, I can't imagine too many places where you'd be farther than 55 miles from ANY help And the stock spare fits over Brembos. My Mods List (Updated 8/22/17) 2005 Outback FMT Running on Electrons Link to comment Share on other sites More sharing options...
Mr. Sinister Posted March 15, 2009 Share Posted March 15, 2009 By the book, it's good for 55miles at 55mph. Even with that marginal rating, I can't imagine too many places where you'd be farther than 55 miles from ANY help And the stock spare fits over Brembos. Yeah, but the stock spare is within .25" of the stock wheel. If you go from a 17" to an 18" or vice-versa, the difference can be up to an inch depending on your tire size. You probably would be fine either way, but I'm paranoid when it comes to stuff like this. Link to comment Share on other sites More sharing options...
mwiener2 Posted March 15, 2009 Share Posted March 15, 2009 it's not .25" on an outback My Mods List (Updated 8/22/17) 2005 Outback FMT Running on Electrons Link to comment Share on other sites More sharing options...
Mr. Sinister Posted March 15, 2009 Share Posted March 15, 2009 it's not .25" on an outback That's fine and dandy, but we don't drive Outbacks. I've said what I have to say and the OP can decide for himself if it's an acceptable risk. For me, it was not. In a pinch, I know I'll be able to drive with the spare on for a couple hundred miles and not worry about whether or not I damaged my drivetrain. Not bad for the $50 or so dollars that I paid for a GT spare. Link to comment Share on other sites More sharing options...
mwiener2 Posted March 16, 2009 Share Posted March 16, 2009 Yeah, you're not driving an OB... but if it wasn't ok for the drivetrain, then Subaru would have given the OB's a larger spare..... since they have the same drivetrain as the Legacy's but since they didn't, it's perfectly acceptable. My Mods List (Updated 8/22/17) 2005 Outback FMT Running on Electrons Link to comment Share on other sites More sharing options...
Woodstock Posted March 16, 2009 Author Share Posted March 16, 2009 so, it wouldn't mess up my transmission or anything if i use the LGT spare while using the 18"? Link to comment Share on other sites More sharing options...
mwiener2 Posted March 16, 2009 Share Posted March 16, 2009 if you use it properly, no My Mods List (Updated 8/22/17) 2005 Outback FMT Running on Electrons Link to comment Share on other sites More sharing options...
sooberoo Posted March 16, 2009 Share Posted March 16, 2009 The spare tire is an exception to the golden rule which is to keep the overall diameter of the tire (whether it be a 17, 19 or 19 inch rim) as close as possible to the overall diameter of the stock tire. My understanding is that +/-3% of the overall diameter is acceptable. I like using this calculator. http://www.miata.net/garage/tirecalc.html By playing with the tread width and profile you can see how it changes the overall diameter of the tire. It also updates you as to the % difference in diameter and how much it will affect your speedo. Hope this helps! Link to comment Share on other sites More sharing options...
Woodstock Posted March 16, 2009 Author Share Posted March 16, 2009 cool! so I won't have to worry about the spare tire. should I get 225/40/18 or 235/40/18? will 235/40/18 have rubbing issue? I don't want fender rolling because I am not familiar with the procedures. I have a '08 LGT. I read that 235/40 is good for pot-hole city driving though you need fender rolling. I want good protection for my rims. Will 225/40 do this job since its only 7.5". The rims are 18x7.5 5x100 48+ offset. Any 08' that has this tire size on 18s? do 05-09 model has the same fender size? thanks! Link to comment Share on other sites More sharing options...
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