[Epic]

Hi all,

I have searched Team BHP for answers with regards to the title of this thread and also on many ocassions posted this question but never got an answer for the same.

I have also noticed that in many threads regarding wheel upgrades, there are alot mentioning about the right size of rim for the car, right tyre size for that rim/car and also a seperate thread with regards to the right PCD for particular cars and many links to the 'Wheel & Tyre Bible' to help us with the same. Even though I agree that these are all important factors to be considered while upgrading your wheels, I have rarely seen the 'recommended offset' mentioned while doing so.

I have read on the internet that the 'recommended offset' is equally important as the other factors but rarely mentioned on this forum; so my questions are -

1. Does one stick to the original offset of the stock rim at the time of wheel upgrade?
2. How does one calculate the 'recommended offset' during a wheel upgrade.
3. How important is this figure?
4. What are the issues one can face if 'recommended offset' is not adhered to?
5. Stock offsets & recommended offset based on the best/recommended wheel upgrades for various cars.

[rjstyles69]

The most common definition that I can think of offset of a car's wheel is the distance between the center-line of the wheel and the plane of the hub-mounting surface of the wheel where you would bolt the wheel.

These include Positive Offset, Zero Offset and Negative offset. Just adding a random image for reference.

1. Does one stick to the original offset of the stock rim at the time of wheel upgrade?

2. How does one calculate the 'recommended offset' during a wheel upgrade.

Recommended that you stick to an offset which is zero or positive. You can use this calculator Wheel Offset Calculator .

Deep dish models are mostly negative offset. Typical SUV type alloys.

3. How important is this figure?

If the offset aint right then this can adversely affect the handling of the car. Take a tight corner flat out and you will remember every verse in the bible.

5. Stock offsets & recommended offset based on the best/recommended wheel upgrades for various cars.

You only need to calculate and demand for the same offset when you go in for an upgrade. I think most alloy manufacturers have offset info displayed with the brochure.

[Epic]

Hi RJ,

A very detailed explanation with pics & ofcourse the Wheel Offset Calculator has helped but this only tells you as to how far out/in your wheel will protrude/intrude but it does not tell you what should be the right offset figure during an upgrade.

For example - A Swift Vxi come with 5.5 X 14" rims with an offset of 38 (not sure of offset, kindly correct me if I am wrong) with 165/80/R14 tires as stock and we would like to upgrade the wheels to 15".

The right upgrade would be - 6.5 X 15" with a tire size of 195/60/R15 OR 205/55/R15. But what would be the correct offset figure that we would require for both these upgrades based on the size of the rims and tires??

[Davis.K]

Originally Posted by rjstyles69

You only need to calculate and demand for the same offset when you go in for an upgrade. I think most alloy manufacturers have offset info displayed with the brochure.

Not always., in india yes its the case, but stags have different concept

Originally Posted by Epic

Hi RJ,


The right upgrade would be - 6.5 X 15" with a tire size of 195/60/R15 OR 205/55/R15. But what would be the correct offset figure that we would require for both these upgrades based on the size of the rims and tires??

Stick to wheels with offset in range from +38 to +43... blindly. Not less or more.

[Epic]

Originally Posted by Davis.K

Stick to wheels with offset in range from +38 to +43... blindly. Not less or more.

Hi Davis,

How did you come to this conclusion? Is there any formula or calculator to achieve a recommended offset value?

Also, do you mean to say stick to +38 to +43 based on the wheel upgrade to 15" with the mentioned tire options OR would the offset value change with an upgraded tire on a 14" rim or 16" rim?

[PJSPEED]

The best offset are tested by the Wheel manufacturer and they give certificate for each cars.

Check this TUV certificate for you ref.

[Epic]

Originally Posted by PJSPEED

The best offset are tested by the Wheel manufacturer and they give certificate for each cars.

Check this TUV certificate for you ref.

Hi PJ Speed,

Agreed. But the TUV certificate that you have posted is of the International wheel maker BBS and in German so I dont understand anything of it and I am sure, a Swift sold abroad & the Swifts sold here in India have a totally different set up in terms of suspension settings & even wheel & tire size. So if I purchase BBS rims for my Swift, I am sure they will be aware of the Indian Swift specifications & suggest accordingly and not give a ball park figure based on the Swifts sold abroad? I myself are using a set of OZs for my Swift with an offset of 43 as suggested by the dealer abroad after me giving them the specifications of the stock rims.Also, again we are talking about professional & reputed companies like BBS & OZ here who manufacture high quality rims which have an equally high price so I am sure they cannot afford to get such specifications wrong.

However, what about a wheel and tire shop say at Milan Subway who sells rims, are they technically equiped to sell an upsized rim with the right specifications? What if they are not? I have hence opened this thread to find out a solution or way on how to find out the right 'recommended offset' & not depend some dealers or manufacturers who may not be technically versed & may just want to sell their wheels to customers who may not have this information.

[Nikhilb2008]

Epic, it's very simple. The offset of most vehicles is a standard value. So, offset for i10, i20, Santro, Swift, Getz, OHC, NHC, ANHC, Corolla are the same. You can use the same alloys on all these cars. But Corsa, which also has a 100 PCD setup has a wierd offset. So, you cannot fit the steel wheels which you can on the above cars on a Corsa safely.

Now, take the case of 114.3 PCD cars. Esteem and Zen have 114.3 PCD and you can exchange the rims between these cars. These are 4 hole 114.3PCD. Now, the Matiz and spark is also 4 hole 114.3 PCD. But the offset is different. You CANNOT use Esteem/Zen rims on the Spark.

Basically, it boils down to the knowledge of your tyre guy(if you are not a tbhpian) and your ability to read the user's manual where all the specs are given.

So, read the user's manual of the Swift. I'm not sure what the exact offset is though. Make a note of the offset and then go to the alloy wheels dealer and ask him the offset of the alloy wheels. Then you take a call.

[lancer_rit]

ET is very important! I did also a lot of searching and reading on this topic on tbhp and elsewhere when upgrading my car's wheels & tyres. ET is especially important where you change your wheels as well as upsize to fatter tyres!

Firstly, all cars DO NOT have same ET. Anybody who says otherwise does not understand ET.

Car and tyre bible is the best bet to understand the impact of offset. Car Bibles : The Wheel and Tyre Bible Page 3 of 4

Now, here's an example from my Lancer upgrade.
Stock ET = 46mm
Tyre width = 175mm

Upgraded to alloys with ET=40mm
Tyre width = 195mm

So, the inside of the tyre is closer to suspension arm/wheel well by = (195-175) / 2 - (46 - 40) = 4mm

The outside of the tyre is closer to wheel well outside by
= (195 - 175) / 2 + (46 - 40) = 16mm

So, if the tyre width remains same, you should go for original ET or within a few mm of it for best fit, proper steering handling and no suspension worries. If your tyre width goes up, you need to choose an ET, which allows your tyre inner and outer wall to have reasonable clearance for your car's wheel well and suspension. However, the delta between original and new ET should be less than 5-7mm.

Hope the above helps.

BTW, upsizing also means that OD of wheel+tyre combo must remain within +/- 2% as rule of thumb!

[Epic]

Dear Nikhil & Lancer,

I do not think you are getting my question or probably I am not asking it right. I have throughly understood the concept of 'Offset' of a wheel through 'The Wheel & Tire Bible' & various other threads & articles on the net. But my question is - How does one calculate the same?

@Lancer - Lets take your example itself. You upgraded from a stock ET of 46 to an ET of 40. How did you get to know that the right ET is 40 & not any other figure. Is the ET of 40 actually the 'recommended offset' for that upgrade? Was this technically calculated or was this figure given by the tire dealer? If technically calculated, how was this done?

You have also mentioned that - "The delta between original and new ET should be less than 5-7mm". Now, are you saying this is a standard figure? I believe ET will depend on the width of rim & tire.

I hope you all are getting what I am saying or asking here & I hope I am not creating any confusion :-)

[nitrous]

Negative offset = Wider Track = better traction for corners.
Positive offset = Narrow Track = Puts down the power better.

[lancer_rit]

Originally Posted by Epic

Dear Nikhil & Lancer,

I do not think you are getting my question or probably I am not asking it right.

I got your question, I just wanted to emphasize about what ET is since some other posts were confusing in this thread :-)

But my question is - How does one calculate the same?

There is no specific formula. Ideally, your ET must be same as original. 5-7mm tolerance is a rule of thumb that for example, is mentioned in the tyre bible ...
They key thing is your new wheels + new tyres combo cannot hit the wheel well (inside or outside) or foul up the suspension. So, you can only go for such a upgrade which minimzes this possibility.
For the clearance in the wheel well and the suspension arms, you need to look at your vehicle and estimate what if wider wheels/tyres ?
It also means that one shouldn't choose alloys with an ET with vast difference (not one alloy wheel dealer has a clue) just by looking at the style and bolt pattern !!

@Lancer - Lets take your example itself. You upgraded from a stock ET of 46 to an ET of 40. How did you get to know that the right ET is 40 & not any other figure. Is the ET of 40 actually the 'recommended offset' for that upgrade? Was this technically calculated or was this figure given by the tire dealer? If technically calculated, how was this done?

That is easily explained. First, one won't find alloys with all possible ET values. Second, wheel and tyre dealers I met knew nothing about ET. And when you set an ET range (acceptable), your choices of alloy wheel models will narrow down significantly.
Why did I chose 40 ?
a) I couldn't find an alloy wheel with 46 in my search
b) More importantly, My tyre width (as I explained) went up by 20mm (10mm on each side), so I wanted to have more clearance towards the suspension/hub side, and I knew my car has reasonable clearance in the wheel well on the outside.
So +40 was good choice for me keeping a safety margin against fouling up the suspension ...
Hope that explains it.

You have also mentioned that - "The delta between original and new ET should be less than 5-7mm". Now, are you saying this is a standard figure? I believe ET will depend on the width of rim & tire.

Rule of thumb figure from tyre bible. Wrt ET figure itself
a) ET has nothing do with tyre.
b) ET has to do with offset between central axis of wheel (vertical), and hub plane...
Same width wheel can have +ve ET, -ve ET etc depending on car's design requirement.

Hope I could clear up your doubts a bit ...

[Epic]

Hi all,

I have come back to this thread as I have either not understood the concept of calculating the offset of the wheel during a wheel upgrade or not satisfied with the above posts. What I have understood with the above posts is the the offset is recommended based on the size and width of the upgraded rim and the profile of upgraded tire. Say if I have to upgrade my Swift stock rims to 16" X 7" rims of PCD 100 with 205/50/R16 tires, the rims of this size should have a fixed offset value right?

Now, I went to the OZ Racing website and looked for 16" rims, I came across rims having the same design and of the exact same specifications but with different offset values and that too of +37 & +42 only! Why is this the case?

Here's the link for the same http://www.ozracing.com/at-team/whee...05.2005/-16/en

[sunnysdome]

WOW... I didnt know that one needs to consider so many factors before switching from his or her stock set.
I had made up my mind to upgrade my stocks on my OHC 1.5 with alloys and upsize them this weekend.
Now.. I think i should hold my horses do my home work and then go in for one.
My oh my all the hard work we car lovers have to go through..

[lancer_rit]

Originally Posted by Epic

Hi all,

I have come back to this thread as I have either not understood the concept of calculating the offset of the wheel during a wheel upgrade or not satisfied with the above posts. What I have understood with the above posts is the the offset is recommended based on the size and width of the upgraded rim and the profile of upgraded tire. Say if I have to upgrade my Swift stock rims to 16" X 7" rims of PCD 100 with 205/50/R16 tires, the rims of this size should have a fixed offset value right?

Now, I went to the OZ Racing website and looked for 16" rims, I came across rims having the same design and of the exact same specifications but with different offset values and that too of +37 & +42 only! Why is this the case?

Here's the link for the same Choose a wheel - OZ - Inside the excellence since 1971

As I posted above, a wheel of a given size (say 16" from your example above) can have any ET - i.e. ET is not a function of wheel rim size. It can have +ET, -ET etc making it suitable for different cars and their suspension/wheel setup design. So, for OZ racing case,
* Same wheel spec (w/o considering ET) can have ET of +37 and +42. These wheels are suitable for different vehicle/wheel/suspension setups. For eg. for my Lancer, +42 is probably better than +37.
* ET of a wheel by itself does not become a factor. You have to consider ET of a replacement wheel wrt
a) ET of original wheels in your car
b) Width difference of original tyres in your car vs the replacement one which you put on the replacement wheel
c) Space inside your wheel well on the outside and inside of your existing wheel/tyre combo
d) Clearance with the suspension arm for your existing wheel/tyre combo
Hope this clears up your doubt.

@sunnysdome, yes, there are a good many factors to doing the wheel/tyre upgrade. Please take your time and do the math! Of course, you can post on tbhp and get opinions from members here to help :-)

Cheers,