275 tires on the rear of 84-87 suspension
Topic started by: Blowerwhine, Date: 05-14-2019 03:07 PM
Original thread: http://www.fiero.nl/forum/Forum2/HTML/142528.html


Blowerwhine MSG #1, 05-14-2019 03:07 PM
      Has anyone done 275 tires on the back of a non-88 suspension? I have 255/45/17s with coilovers in the back .... Wheels have +35 offset and with coilovers the tires are almost kissing the coilovers but has almost no poke. I know handful of 88s are running 275s and at this point every little bit will help

Will (william.lucke@gmail.com) MSG #2, 05-14-2019 03:49 PM
      An 84-87 car can fit 18x9.5 C5 Corvette rear wheels with 1" thick adapters and run 285/30-18 tires.

Of course those wheels will also fit the Corvette 275/40-18 size, but those are significantly taller. 275/35-18 would probably work pretty well, although those have been known to rub the wheel house liner on '88's when used on a race track that turns.

See these posts in my build thread:
http://www.fiero.nl/forum/F.../000121-21.html#p813

http://www.fiero.nl/forum/F.../000121-21.html#p817

[This message has been edited by Will (edited 05-24-2019).]

Blowerwhine MSG #3, 05-14-2019 05:26 PM
     
 
quote
Originally posted by Will:

An 84-87 car can fit 18x9.5 C5 Corvette rear wheels with 1" adapters and run 285/30-18 tires.

Of course those wheels will also fit the Corvette 275/40-18 size, but those are significantly taller. 275/35-18 would probably work pretty well, although those have been known to rub the wheel house liner on '88's when used on a race track that turns.

See these posts in my build thread:
http://www.fiero.nl/forum/F.../000121-21.html#p813

http://www.fiero.nl/forum/F.../000121-21.html#p817



Huh this is an interesting solution I haven't taken into account


mcguiver3 MSG #4, 05-14-2019 05:30 PM
      So my question would be what are the bearing loads incurred by running that offset and wheel tire width?
Also that means the front wheels and tires would be wider as well?
What would you run up front?
looks like major change to the scrub radius?


fieroguru MSG #5, 05-14-2019 10:22 PM
     
 
quote
Originally posted by mcguiver3:

So my question would be what are the bearing loads incurred by running that offset and wheel tire width?
Also that means the front wheels and tires would be wider as well?
What would you run up front?
looks like major change to the scrub radius?


Most of these extreme wheel fitments under the stock body are gaining width on the backside of the wheel/tire which better centers the wheel to the bearing and reduces scrub radius. I run 235/40/17 and 285/30/18 combo on my 88.


Blowerwhine MSG #6, 05-14-2019 10:37 PM
     
 
quote
Originally posted by fieroguru:


Most of these extreme wheel fitments under the stock body are gaining width on the backside of the wheel/tire which better centers the wheel to the bearing and reduces scrub radius. I run 235/40/17 and 285/30/18 combo on my 88.


That seems to be easy on the 88s, and they seem to be a lot more forgiving offset wise.... I'd be more than happy running 215/275 combo rather than the 225/255 I have right now


fieroguru MSG #7, 05-14-2019 11:30 PM
     
 
quote
Originally posted by Blowerwhine:

That seems to be easy on the 88s, and they seem to be a lot more forgiving offset wise.... I'd be more than happy running 215/275 combo rather than the 225/255 I have right now


The 84-87 can go wider with a 17" wheel than the 88 can. The 88's have to go to 18's to clear the strut mounting flange for additional width, so there are trade offs for both.

For my car, the first point of interference is the trailing link that the 84-87 doesn't have. The 84-87 struts are slightly more vertical, but you could mount your coilovers higher on the strut (like on the oem spring perch weld bead) to maximize wheel/tire clearance.


You can also move the top of the struts further inboard. Mine are 1" further inboard than stock 88 or close to 2" further inboard from the 84-87.




Another option is to do the Fog mod... He put 325s under his 84/87. He cut out the bolt pattern area of the strut tower and flipped it around to move it inboard 2 1/4". He also cut 1 7/8" out of the lower a-arm and pulled everything inboard to allow more wheel/tire on the outside. He did flare the top of the fenders some... but they were 325s!.





Spadesluck MSG #8, 05-15-2019 12:07 AM
      With my coilovers on my 87 I am running a 255/35 18 and have a lot of room. The rim is a +35 offset as well. I thought about going to a 275 at one point but ultimately went with the 255. It is still a 10" wide tire and fills the back nice. The tire tucks in just fine with not scrubbing.

Blowerwhine MSG #9, 05-15-2019 12:20 AM
     
 
quote
Originally posted by fieroguru:


The 84-87 can go wider with a 17" wheel than the 88 can. The 88's have to go to 18's to clear the strut mounting flange for additional width, so there are trade offs for both.

For my car, the first point of interference is the trailing link that the 84-87 doesn't have. The 84-87 struts are slightly more vertical, but you could mount your coilovers higher on the strut (like on the oem spring perch weld bead) to maximize wheel/tire clearance.


You can also move the top of the struts further inboard. Mine are 1" further inboard than stock 88 or close to 2" further inboard from the 84-87.




Another option is to do the Fog mod... He put 325s under his 84/87. He cut out the bolt pattern area of the strut tower and flipped it around to move it inboard 2 1/4". He also cut 1 7/8" out of the lower a-arm and pulled everything inboard to allow more wheel/tire on the outside. He did flare the top of the fenders some... but they were 325s!.




Good advice, I don't need a whole lot... I prefer 17s anyway.... Id be happy with 17x9 275 tires, shouldn't need too much more to safely tug along as we inch up the power scale
Edit: what did you exactly do to make the struts more inboard, do you have a write up on this?

[This message has been edited by Blowerwhine (edited 05-15-2019).]

Will (william.lucke@gmail.com) MSG #10, 05-15-2019 08:22 PM
     
 
quote
Originally posted by mcguiver3:

So my question would be what are the bearing loads incurred by running that offset and wheel tire width?
Also that means the front wheels and tires would be wider as well?
What would you run up front?
looks like major change to the scrub radius?


Bearing load has more to do with how much of the tire's grip you utilize when you drive. I also didn't mention the fronts... just the rears.

 
quote
Originally posted by Blowerwhine:


That seems to be easy on the 88s, and they seem to be a lot more forgiving offset wise.... I'd be more than happy running 215/275 combo rather than the 225/255 I have right now



A Fiero with 45/55 weight distribution should have front wheels and tires that are ~82% (45/55=0.82) as wide as the rear wheels tires. Thus a 7.5 is about the right front wheel to run with a 9.5 rear wheel, and a 225 about the right front tire with a 275 rear.

[This message has been edited by Will (edited 05-15-2019).]

Blowerwhine MSG #11, 05-15-2019 09:51 PM
     
 
quote
Originally posted by Will:
A Fiero with 45/55 weight distribution should have front wheels and tires that are ~82% (45/55=0.82) as wide as the rear wheels tires. Thus a 7.5 is about the right front wheel to run with a 9.5 rear wheel, and a 225 about the right front tire with a 275 rear.



With a 3800TC/4T65 I'm sure the weight balance is closer to 40/60... The front end feels very light!


Will (william.lucke@gmail.com) MSG #12, 05-24-2019 09:20 AM
     
 
quote
Originally posted by Blowerwhine:


With a 3800TC/4T65 I'm sure the weight balance is closer to 40/60... The front end feels very light!



Measure it and find out for sure.

[This message has been edited by Will (edited 05-24-2019).]