Chevy Cobalt Forum banner

Status
Not open for further replies.
1 - 20 of 26 Posts

·
Registered
Joined
·
429 Posts
Discussion Starter #1 (Edited)
i have a set of 18" wheels that i want to put on my LT,the stock wheels are only 15s and some people are saying that i would have to calibrate the speedometer for those,but ive been reading a few posts on here and havnt seen where anyone has calibrated their cars for 18s and i was wondering if i would have to and if i did how would i do it? i was kinda thinking u wouldnt have to because the ABS wheel speed sencors would still read the same beacause the axel would still go the same,but then again those are for the ABS witch are breaks. but i also know that the engine will have to work alittle harder because of the little extra weght,so im confused,plz let me know

---------- Post added at 12:22 PM ---------- Previous post was at 12:10 PM ----------

bump
 

·
Registered
Joined
·
429 Posts
Discussion Starter #3
ok,thanks,i just wanted to make sure,and would u know where i could get a spare to match the 18s,cause id hate to b somewhere and have a flat and end up having 3 18" wheels with a little 15" doughnut on,lol

---------- Post added at 12:42 PM ---------- Previous post was at 12:30 PM ----------

bump
 

·
Registered
Joined
·
1,969 Posts
i wouldnt worry about getting a spare. unless you really think your going to pop a tire
 

·
Registered
Joined
·
1,969 Posts
yea and even if you do get a flat put a spare on til u get the tire fixed.
my sister had to do that. looked pretty funny because all the other rims were 18 and a little donut was on the one side
 

·
Registered
Joined
·
77 Posts
The outside diameter is what has to stay the same, as long as that is within a reasonable limits, your speedo should be fine. But if you put over sized tires, like I did to my ranger, your speedo will need to be recalibrate to be accurate.

I don't see it causing any issues as long as you maintain your outer diameter.
 

·
Registered
Joined
·
77 Posts
would 224/40 work then?
Visit this page Tire size calculator

Put in your stock tire size, and it tells you the radius and diameter. Then use the other slot to adjust your rim to 18"s and your tire size to maintain the same diameter.

From there you can adjust the new tire ( for your 18's) to the height and width you want, and keeping the outer diameter the same. It might be a good idea to open up a tire site to make sure your size is a real size and is available.

From my quick looks early I wrote down 225/40 r18, which is what you were asking and I would lean towards yes, but always double check. I could be wrong!
 

·
Premium Member
Joined
·
745 Posts
225/40 is very close to the stock size. Well, as close as you are going to get with that width.

And Adamseye is right, as long as the overall diameter is close to the stock size, you should be fine.
 

·
Registered
Joined
·
821 Posts
hmmm so if I put hankooks @ $200 bucks a tire... Replacing my 225/40s with 225/50's then what? I figure that's the best way to take even more gap out of the wheel well.... Whatcha think?
 

·
Registered
Joined
·
77 Posts
hmmm so if I put hankooks @ $200 bucks a tire... Replacing my 225/40s with 225/50's then what? I figure that's the best way to take even more gap out of the wheel well.... Whatcha think?
I am not sure how much but that might send your speedo off. It is only 1 inch larger, but there are 63k inches in a mile. That means every time your tire goes around 12 times, it travels 1 foot further then the speedo will read. I could probably do the math if I wanted to but I think the end result would be minor, however inaccurate. Most speedos are allowed 0-3 mph +/- from factory any how.

In short it will be off, how much I don't know, could be 1mph. Anyone running 225/50's?
 

·
Registered
Joined
·
992 Posts
hmmm so if I put hankooks @ $200 bucks a tire... Replacing my 225/40s with 225/50's then what? I figure that's the best way to take even more gap out of the wheel well.... Whatcha think?
Use this (Thats an example of when I went from stock to my 19's)
Just put in all the nessecary information and it tells your everything.
You'll notice my speedo is off 0.8 mph because of the diameter difference

Tire Size Calculator - tire & wheel plus sizing
 

·
Registered
Joined
·
429 Posts
Discussion Starter #14
I used that calender and it said 225/40 would spedometer would be 1.8 miles off,i startedfiddling around with it and found that 235/45 would only be 0.3 miles off,im not really into tire stuff im more into engine mods/body work and accessories so would that work on every 18" rim?because i have a set of 18s and right now they have 225/40 on them but they are torn up to hell from the kid that had them b4 me (i got them off him for $80 and they arent bad looking at all)so whn i get new tires i just wanna make sure everything(the 235/45s) would work

---------- Post added at 07:31 PM ---------- Previous post was at 07:06 PM ----------

bump

---------- Post added at 08:09 PM ---------- Previous post was at 07:31 PM ----------

bump

---------- Post added at 08:41 PM ---------- Previous post was at 08:09 PM ----------

bump
 

·
Registered
Joined
·
821 Posts
I'm mobile... Training... And in the desert. Someone please hit up that calculator link and give me a heads up on the 225/50's? I'm trying the link... It sucks being stuck here lol

---------- Post added at 09:47 AM ---------- Previous post was at 09:08 AM ----------

ok, finally loaded it.... I guess my 09 stock size is 225/40... Comparing stock size and 225/40 and the numbers match up....

so I then compared 225/40 to the 50's..... 6% difference in wheel diameter.... Other than that I'm fairly clueless about what this calculator is telling me. So I'm not under the 3% they say is optimal... So what? So my speedo might be off what--maybe 1 or 2 mph? Big deal. Wht I DO notice in the calc is if I'm running 50's my engine will go same speed at a lower rev limit..... This is saying that my engine is running safe in the "green" and not at a more higher or hotter rev limit per mph.... Is this correct?

*if all that I said is in fact correct and true, how does this change my romping, redline, or etc.... Either from a dig or roll? My guess is from a dig it will be a lot harder to get up to speed? Thanks for any help.

---------- Post added at 09:52 AM ---------- Previous post was at 09:47 AM ----------

speedometer difference-7% too slow??? That means when I'm driving and I think I'm doing 100mph I'm really doing 93mph?

50mph really = 46.5mph?
etc... Etc....?

---------- Post added at 09:53 AM ---------- Previous post was at 09:52 AM ----------

this might actually be a good thing for me to do... Speed and ticket wise.... And saving my engine from running so fast/hot... Right?
 

·
Premium Member
Joined
·
745 Posts
225 50?????

Do you guys realize how much sidewall flex you are experiencing on turn in???

50 is a HUGE sidewall.

Can i be a moderator for the suspension forum?

I need to be able to control this madness... lol
 
1 - 20 of 26 Posts
Status
Not open for further replies.
Top