 What exactly IS offset, and how do I find it??, Buying Tenzo RS5s- need info on tires 2 |
 Jun 2, 2004 - 12:23 AM
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 Enthusiast  Joined Jan 8, '04 From LA Currently Offline Reputation: 0 (0%)  |
Ok, offset determines how far your tires stick out from the car. Right? good.
Whats the stock offset measurement on our cars? What does that mean? I'm getting Tenzo RS5s 17x7s- whats the offset? Does it even matter on the rim? or is it all in the tire size? and what tire size is right for our cars when upgrading to 17 inchers? Because I've heard that if you increase the wheel size, but don't decrease the tire size, things like your speedo will be off. Is the speedometer problem fixable? or is the only way to go with lower profile tires (and get much lower ride quality). Does upgrading to 17s and decreasing tire size even increase handling? or is it the same? As for offset recommendations- what do they mean and how do I implant them? I'd like to have the new rims to stick out from the car a LITTLE (I think it looks very rallyish and cool  but will that cause rubbing problems?And whats this about checking break clearance? Is that only needed when going the other direction (more IN to the car) is going out to less flush with the car a stupid idea? Feel free to tell me so. I did a search, but all I got was a lot of garbled results. A couple were decent. "Use this and this offset" but I still didn't UNDERSTAND the reasoning behind it. and whats this about a higher number offset being in closer towards the vehicle? So confused! Help!~!! |
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Replies
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Jun 2, 2004 - 10:21 AM
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Enthusiast Joined Jan 17, '04 From Illinois Currently Offline Reputation: 0 (0%) |
The offset of a wheel is the distance from its hub mounting surface to the centerline of the wheel. For our cars, offset is always a positive number. I have read that stock wheels on a GT have a 38 offset. However, this needs to be confirmed. I bought 17" wheels a few weeks ago with a 40 offset and I swear they stick out further than my stock wheels. Assuming a 38mm offset, the mounting surface is 38 mm further out toward the outside of the car than the centerline of the wheel. Increasing offset means the centerline is further out which, in effect, sucks the wheel into the car and closer to the suspension components. Using a lower offset does the opposite - it pushes the wheel out away from the suspension components. When you change wheel widths (to for example a 7.5" or 8" wheel), the offset numbers change. I suggest you use this website if you are changing the width of your wheels. wheel offset calculator
I have no idea. Call the vendor. A good one should know.
215/45/17 is what most of us with 17's are running. The 45 sidewall is better than something lower for purposes of ride comfort and protecting your rims from damage from a large pot hole. The tire is about 3% bigger in diameter than our stock wheels so your speedometer will be a little off. When the speedometer says 60, you will actually be traveling about 62. You can use this website to help pick out tire size to keep the speedometer deviation as close to zero as possible: Tire Size Calculator 205/45/17 are probably closest to stock size without sacraficing sidewall width but unfortunately there are not alot of tires out there in this size. 215/40/17 are also a good choice if you have very good roads in your area.
You can get new guages with a renumbered speedometer. Speedhut will custom make guages for this purpose. I checked into this when I was considering 225/45/17 because they are about 4.1% bigger. I was quoted a price of about $140 for reverse glow guages with the speedo markings moved and a 160 m.p.h. mark actually added to the guage. You also need to remember that changing overall tire size will also change your gear ratio which will affect performance. Hope it helps. - Jay This post has been edited by jgreening: Jun 2, 2004 - 10:38 AM -------------------- QUOTE(lagos @ Jul 10, 2006 - 1:55 PM) [snapback]454118[/snapback] i know your trying to do the right thing for your motor, but this is one of those times where you should just trust the guys who have had their swaps for a while and have done a ton of research into this. |
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Jun 2, 2004 - 10:53 AM
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Enthusiast Joined Jan 8, '04 From LA Currently Offline Reputation: 0 (0%) |
Thank you so much jay!
changing overall tire size will change gear ratio which will affect performance.. adversly? |
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Jun 2, 2004 - 11:22 AM
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Enthusiast Joined Jan 17, '04 From Illinois Currently Offline Reputation: 0 (0%) |
I am not sure about this. I have read that increasing overall tire circumfrance will decrease acceleration but increase top speed. By logic alone, I can tell you the second part is true but I am not sure about the first. This post has been edited by jgreening: Jun 2, 2004 - 12:06 PM -------------------- QUOTE(lagos @ Jul 10, 2006 - 1:55 PM) [snapback]454118[/snapback] i know your trying to do the right thing for your motor, but this is one of those times where you should just trust the guys who have had their swaps for a while and have done a ton of research into this. |
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Jun 2, 2004 - 11:48 AM
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Enthusiast Joined Nov 25, '03 From Mizzeri Currently Offline Reputation: 0 (0%) |
Upping you wheel and tire size will probably adversely affect performance. The reason being is that you are putting more rotational mass farther out from the center fo the wheel. Given the same amount of weight, a 15" wheel/tire will be quicker than a 17" wheel/tire, since even though they are the same weight, the mass is actually distributed farther out from the center. You can offset this performance detrement by going with lighter wheels than the stock ones. Basically, the gains/losses are going to be negligable unless you are racing... unless you are going with some 50 pound wheels or something
 I wouldn't sweat it too much.
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Jun 2, 2004 - 12:06 PM
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 Enthusiast Joined Jun 26, '03 From Wisconsin Currently Offline Reputation: 0 (0%) |
i have 215/35/18 and my speedo is the same
-------------------- i am awesome
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Jun 2, 2004 - 1:54 PM
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Enthusiast Joined Jan 8, '04 From LA Currently Offline Reputation: 0 (0%) |
Shawn, you're going faster than you think you are....
as for the rotational mass thing, you're right on both counts. Smaller size overall increases acceleration from a stop, while a larger tire size actually helps acceleration and top speed. So it's a give and take Will this also affect the odometer? |
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Jun 2, 2004 - 2:06 PM
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Enthusiast Joined Jan 17, '04 From Illinois Currently Offline Reputation: 0 (0%) |
Yes. -------------------- QUOTE(lagos @ Jul 10, 2006 - 1:55 PM) [snapback]454118[/snapback] i know your trying to do the right thing for your motor, but this is one of those times where you should just trust the guys who have had their swaps for a while and have done a ton of research into this. |
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Jun 2, 2004 - 2:40 PM
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Enthusiast Joined Jan 8, '04 From LA Currently Offline Reputation: 0 (0%) |
Nooooo
 but it'll show as less miles than is really on the car, right? hahahahaH! |
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Jun 2, 2004 - 3:43 PM
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 Enthusiast Joined Feb 25, '04 From Wisconsin Currently Offline Reputation: 0 (0%) |
thats a good question.... |
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Jun 2, 2004 - 4:57 PM
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Enthusiast Joined Jan 17, '04 From Illinois Currently Offline Reputation: 0 (0%) |
You are correct. If the tires are larger, the car will travel further per rotation than stock and the odometer will show fewer miles than actually travelled. -------------------- QUOTE(lagos @ Jul 10, 2006 - 1:55 PM) [snapback]454118[/snapback] i know your trying to do the right thing for your motor, but this is one of those times where you should just trust the guys who have had their swaps for a while and have done a ton of research into this. |
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Jun 2, 2004 - 6:20 PM
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Enthusiast Joined Jan 8, '04 From LA Currently Offline Reputation: 0 (0%) |
Excellent
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Jun 5, 2004 - 2:21 PM
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Enthusiast Joined Apr 3, '04 From Allen, TX Currently Offline Reputation: 0 (0%) |
Alright, so what if you were wanting to go with 18x7.5's or 18x8's instead...what offset would match the tires with the EDGE of the fenders? I need to get some rims that will fill the wheel well and come to the egde of the fenders.....much better than the stock ones hopefully?
And if anyone knows of any suggestions I am open to that as well. I am a newb....just got the celi, still checking things out....but I want some black or gmg rims with a polished or chrome lip....any suggestions? |
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Jun 5, 2004 - 2:35 PM
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Enthusiast Joined Jan 8, '04 From LA Currently Offline Reputation: 0 (0%) |
Its like they said, the correct offset differs from rim to rim
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Jun 8, 2004 - 5:05 AM
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Enthusiast Joined Mar 4, '03 Currently Offline Reputation: 0 (0%) |
Talk to a good tire/wheel store and they should be able to hook you up with a speedo workshop. You can have your speedo and odometer recalibrated for maybe $100. |
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Jun 8, 2004 - 9:26 AM
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 Enthusiast Joined Apr 16, '04 From Worcestershire, UK Currently Offline Reputation: 0 (0%) |
Just remember that changing the rolling radius will have an impact on your speedometer. The difference between a 225 and 215 tyre on an 18" rim can throw your speedo out by about 3mph at 30mph but about 7mph at 70.
Check out this tyre fitment calculator to see how your new rims and tyres will affect your speedo. |
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