18 Inch Wheels 78 Trans Am

[zzbellazz]

I am in desperate need of some clarification on Wheel Fitment for a 78 Trans Am. I have read all through this forum and found many different suggestions but always seemed like application was different than mine. I am currently ordering custom 18" wheels for my car. The problem I am having is the proper backspacing and allowable width. The car has 550 HP and 600 FT. I need as much meat on the back-end as I can. I didn't want to cut the car up and do mini tubs. My car has the seat belt humps massaged so I should have more room. My shop that is finishing the resto is recommending 18 x 9" all around. I'm fine with the fronts at 9 inches. Can I fit larger than 9 inch out back without rolling fender lips? Any facts on what will work with a leaf-spring car with the seat belt humps removed would be greatly appreciated.
Thanks

Hoskins Suspension
Moser 9 inch
Caltracs
Wilwood Brakes
Welded Box Frame Connectors

[mc84_zz4]

Here’s a good thread on that topic:
https://www.pro-touring.com/threads/67849-Tires-for-2nd-Gen-Firebird
HTH

[zzbellazz]

Thanks.. The only problem is the early second gens have more room in the well. I was hoping for someone with a late second gens experience.

[mc84_zz4]

Here’s one for later 2nd gens:

https://www.pro-touring.com/threads/103522-How-wide-can-I-go-on-a-77-Firebird
And here is a thread with 30+ pages, I hope there may be something of use..
http://transamcountry.com/community/index.php?topic=23970.0
HTH

[Tuomas]

I’m working with same issue right now.
1978 TA restored try to hit 10x18 with 295/40R18 with Ridetech Streetgrip leaf springs.

Current wheels are Year One 9x17 with 275/40R17 BS 5.125 and plenty of room in wheel well, factory height now.
Same size in front, sits nicely to ”corners” no rubbing.

Regarding rears, first problem noticed, looks axle is almost 1/2” more on passenger side so needs centering.

measured/compared with current wheel tire combo, 10x18 offset 0 BS 5.5 should fit to my car with 295/40 and 2” lowering, may require light hammering inner wheel well where’s seatbelt mounts.

fronts will go to 8.5 offset 0 and 245/40R18.


Got measuring tool and correct tire today confirm fitment, will do this asap.

177158

[68Formula]

I’m working with same issue right now.
1978 TA restored try to hit 10x18 with 295/40R18 with Ridetech Streetgrip leaf springs.

Current wheels are Year One 9x17 with 275/40R17 BS 5.125 and plenty of room in wheel well, factory height now.
Same size in front, sits nicely to ”corners” no rubbing.

Regarding rears, first problem noticed, looks axle is almost 1/2” more on passenger side so needs centering.

measured/compared with current wheel tire combo, 10x18 offset 0 BS 5.5 should fit to my car with 295/40 and 2” lowering, may require light hammering inner wheel well where’s seatbelt mounts.

fronts will go to 8.5 offset 0 and 245/40R18.



If you can fit a 275 on the front, why downsize to a 245?

[zzbellazz]

Let me know what you find out... Thats a great tool... I havent ordered tires yet..

[Tuomas]

Looks ~1/4” axle centering needed, sits outer on Passenger side. Test tire 295/30R20 but OD close enough compared to 295/40R18. Think 285 definitely better tire but looks 10x18 BS 5.70 offset 5 sits best and room for 2” lowering. Maybe minimal hammering needed,will see.


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[Tuomas]

If you can fit a 275 on the front, why downsize to a 245?

Well youre right. Dont even know why thought down size.

[1965gp]

I have 275/40 17’s all the way around on our stock 79 with no issues

[Tuomas]

I have 275/40 17’s all the way around on our stock 79 with no issues

Same. Just looking for little bigger tire/small lowering with Forgeline TA3’s.
And wanna get rid of Chinese stuff.

177212

[Tuomas]

Let me know what you find out... Thats a great tool... I havent ordered tires yet..

So, sent email late last night and final specs/ tires combo will go is


fronts 9x18 offset +5 BS 5.20 tire 265/40R18
rears 10x18 offset +5 BS 5.70 tire 295/40R18

Forgeline TA3 polished outer rim, gloss black/HTM center. Hankook Ventus R-S4 tires. Ridetech Streetgrip for lowering. I’m overseas, so lets see when get them all here.

[zzbellazz]

Sounds good. I have my order in for BOZE snowflakes. Just waiting on specs for width and backspace.

[Tuomas]

Came two weeks ago. Beutiful!

[T/A Addict]

Wow..... Very nice! That will add some meat, can't wait to see them on the T/A. Gonna be selling your current wheels and tires then?

[Alwhite00]

Very nice. Great looking wheel.