Offset for 9-10” rims

[JacobM03]

I am planning on getting better and wider tires to get more traction for my project 92 tbird and I am wondering what would be the best rim setup.

I am switching to the 5x4.5 mustang bolt pattern and 1993+ front spindles for my brake upgrade.

I was thinking of getting 17 or 18” rims, 255 in the front and 295 or 305 in the rear.

Now what kind of offset would I need for 10” rear rims and 9” front rims to fit well and clear?

 

[XR7-4.6]

Front ideally 36-39(my front 17x9s are +30 and kind of pushing it)

My 18x10 rears are +45, they fit great between the fender lip and sway bar but I'd recommend rolling the fenders if you're low, I scuffed my 295s a few times before I did

 

[Zep5.0]

Front ideally 36-39(my front 17x9s are +30 and kind of pushing it)

My 18x10 rears are +45, they fit great between the fender lip and sway bar but I'd recommend rolling the fenders if you're low, I scuffed my 295s a few times before I did

View attachment 4632

You're on 1.6" drop vogtlands? Or 1.5" Eibachs?

 

[XR7-4.6]

You're on 1.6" drop vogtlands? Or 1.5" Eibachs?

Neither, those are 1” drop vogtlands. However the rear tires are 295-45-18, so over an inch taller than most people run and the rear gap is in effect more typical of a 1.6” drop

 

[Ericv8thunderbird]

I’m running 18x9 with 245/45 and 18x10 with 275/40 with a +30mm backspace

 

[MarkM TCCoA VP Emeritus]

Damn and I thought my 255/50/17s were wide.

 

[Stanley]

I have 2011-2014 Mustang GT wheels (19x9) on a 97 Sport, and 245/45r19 tires. After a hub swap to mount the wheels properly, am I going to need spacers? If so, how would I determine the size that I'll need? I'm finding offset quite confusing.

EDIT: I might as well ask for 245/40r19 tires as well, since I'm going to switch to those soon.

 

[XR7-4.6]

I have 2011-2014 Mustang GT wheels (19x9) on a 97 Sport, and 245/45r19 tires. After a hub swap to mount the wheels properly, am I going to need spacers? If so, how would I determine the size that I'll need? I'm finding offset quite confusing.

EDIT: I might as well ask for 245/40r19 tires as well, since I'm going to switch to those soon.

These wheels by chance?



I used 1/4” spacers on mine but 1/8” would have done what I needed, the biggest issue that necessitated them is the wheel weights would hit the spindle in front without them at all. If you use stick on weights on the inside when you get new tires you might not need spacers at all.

Offset is just that; the relationship from where the hub mounting surface is relative to the direct center of the wheel. 2011-2014 mustang wheels are +42, adding a spacer effectively shortens that offset by adding a to the hub mounting surface, so of using a .25” spacer you’re effectively subtracting roughly 6mm offset from the wheel, making the wheel+spacer combination a +36mm offset

 

[Stanley]

Yeah, those are the ones: I came across pictures of your machine while trying to do research on this (looks beautiful). My problem is that I'm completely new to all this and most of the posts on the subject are assuming a certain base-level of knowledge I don't have.

For example, I'd never heard of wheel weights until your post. Is this something I need to buy, or are they already on those wheels?

Also, I take it from your post that the small difference in planned tire sizes I have doesn't matter here?

Currently these wheels are eating bearings like they're goddamn tic tacs, because of the way the original owner Frankensteined them onto the car's stock hubs. As such, I'm reflexively hoping to avoid spacers if at all possible. At the same time, I have no idea how 1/4 or 1/8 spacers compares to what's on them now (the impression the mechanic gave me last time I was in to replace the bearings was that the current setup was enormous). I won't know that until I get in there with a friend next month to switch to Mustang hubs.

If I can ask a stupid question, how do I know ahead of time what offset is desirable in the first place?

 

[XR7-4.6]

Yeah, those are the ones: I came across pictures of your machine while trying to do research on this (looks beautiful). My problem is that I'm completely new to all this and most of the posts on the subject are assuming a certain base-level of knowledge I don't have.

For example, I'd never heard of wheel weights until your post. Is this something I need to buy, or are they already on those wheels?

Also, I take it from your post that the small difference in planned tire sizes I have doesn't matter here?

Currently these wheels are eating bearings like they're goddamn tic tacs, because of the way the original owner Frankensteined them onto the car's stock hubs. As such, I'm reflexively hoping to avoid spacers if at all possible. At the same time, I have no idea how 1/4 or 1/8 spacers compares to what's on them now (the impression the mechanic gave me last time I was in to replace the bearings was that the current setup was enormous): I won't know that until I get in there with a friend next month to replace the hubs.

If I can ask a stupid question, how do I know ahead of time what offset is desirable in the first place?

The ideal offset is dependent on the car, and in our case the factory offset on the original 15-16” wheels is +39mm. It’s not hard and fast that you adhere to that but just as you saw going to extremes like the amount of space added with bolt circle adapters can be an inch or more and can put stress on the hub bearings. Personally I think the absolute minimum offset is use is +24 as that’s the typical SN95 9” wheel Mustang offset and our hub designs are for all intents and purposes the same (literally the same with the hub swap). Max is +40ish since you’ll run into inboard clearance issues at that point. Remember this; high numerical positive offset will tuck the wheels in, low numerical positive offset they’ll stick out of the fender, which is what you’re seeing on yours with adapters. Spacers and adapters effectively lower offset.

1/8” spacers are very safe to use, 1/4” ones you’re still good in terms of stud length however the hub bore will no longer engage the wheel making the lugnuts being the sole means of centering the wheel on the hub - which is fine for those wheels and normal tapered lugnuts but not ideal.

Wheel weights is not something you have to personally worry about, they are supplied and installed by the tire shop during the balancing process. There’s two types, conventional clamp on and stick on, from Ford those wheels will actually have both since there is no outer lip for clamp ons while there is an inner lip for the clamp on style. When you go to get new tires just simply specify you want stick on wheel weights only.

The factory tire size for those actually is the size you’re moving to; 255/40/19, those were what were on mine and those were low mile factory installed pirelli P zeros. Size wise at 27” they’re perfect for the Thunderbird. 255/45/19 is very tall at 28” I’m surprised it has them, in front without spacers they’d be likely to rub the upper ball joint, so going down to the 40 as you plan not only is a good idea but essential. The 45s work fine in the back though.

 

[Stanley]

Excellent: this clears up a great deal.

The wheels I have and are thinking of are both 245s rather than 255s, but yeah, I figured the 45 height is part of my trouble. Any time I hit a substantial bump I'm getting loud fender rub and I want to kill that: I'm hoping the proper hubs and mounts and a proper tire size will combine to solve the issue. I'm not sure why the guy originally used 45s: maybe that's what he had lying around with the Mustang wheels and just said screw it when moving them over to the Bird.

I've ordered a set of 3mm spacers. Thanks for the assist on all this.

 

[Chingon1]

Dang those trackpack wheels look really good on your cougar! I doubt them bitches would clear the ATS brembo’s tho sucks

 

[XR7-4.6]

Dang those trackpack wheels look really good on your cougar! I doubt them bitches would clear the ATS brembo’s tho sucks

Yes they would, the other nickname for these wheels were Brembo wheels as the track pack came with the 14” brembos



Biggest con with these wheels is they were very heavy