Another question about 18s
Thread Starter
Instructor
Joined: Jan 2008
Posts: 241
Likes: 41
From: Skaelskoer, Denmark
Another question about 18s
Hi CF
I´ve decided to buy 18s for my 69 BB, and at the same time install my new suspension (QA1 single adjust and 550 lbs spring in front and van steel rear coil over kit with off set t-arms). But I´m not sure which BS to choose?
Front will be 8x18 with 4"BS and 245/45
Rear will be 9,5x18
But which BS rear?
I would prefer to mount as wide rear tires as possible - but which? I´m affraid that 285/40-tires will be too wide for the rim, and the difference between the cross section and the rim will make too much "shoulder", and be too close to the fender (if BS is 5,0) or too close to the frame/t-arm (if BS is 5,5).
So the question is:
which BS to choose with 9,5x18 and 285/40 rear (if possible)
or should I go for 5,5"BS and 275/40 (though thats not 27" O.D.)
I´ve decided to buy 18s for my 69 BB, and at the same time install my new suspension (QA1 single adjust and 550 lbs spring in front and van steel rear coil over kit with off set t-arms). But I´m not sure which BS to choose?
Front will be 8x18 with 4"BS and 245/45
Rear will be 9,5x18
But which BS rear?
I would prefer to mount as wide rear tires as possible - but which? I´m affraid that 285/40-tires will be too wide for the rim, and the difference between the cross section and the rim will make too much "shoulder", and be too close to the fender (if BS is 5,0) or too close to the frame/t-arm (if BS is 5,5).
So the question is:
which BS to choose with 9,5x18 and 285/40 rear (if possible)
or should I go for 5,5"BS and 275/40 (though thats not 27" O.D.)
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
I run a 18X10 with a 5.5 backspace and a 275 40 18 tire. The tire selection is much greater at the 275 40 18. The difference between the 275 and 285 is minimal. I have a slight rub at full wheel travel with my setup. It just grazes the inner wheel house, buffing the inside slightly in one tiny area. I would not want to go out any further either. You risk hitting the fender. Some will argue the 285 fits and some have had success but the minimal tire width advantage is not worth the risk for me. 
Melting Slicks
Joined: Jul 2006
Posts: 2,373
Likes: 6
From: Baltimore MD
I have boss motorsport rims and they are 18x8 front and 18x9.5 rear and the rear is 5.0 b.s and fits perfect and the front is 4.0 b.s ,and i used a 3/8 spacer to bring it out a little.
Last edited by Billysvette; Dec 15, 2009 at 08:17 PM.
Race Director
Joined: Jan 2007
Posts: 14,928
Likes: 3,334
From: NYC NY
I'll 2nd what Gordonm advised. If you're going with a 9.5" rear wheel a 5" backspace with a 275/40 tire has proven to work with NO drama. I don't think the 285 tire is worth taking the chance of hitting a fender. One thing you always have to keep in mind with older cars when you get to max sizes they are all a little different. Production tolerances and 40+ years of wear and tear will do that to them.
Drifting
Joined: Oct 2008
Posts: 1,496
Likes: 6
From: springfield ohio
18x10 with a 5.5 back space on 285/40/18 with the car lowered 2''.Yes it has
rubbed on the inside driver side when hitting a big dip, but it not enough for
me to worry about. If the back spacing is to much, it can be corrected with
a spacer, last resort though. I have not had it rub on the outer fender.
Here's what it looks like.
Riggs.
rubbed on the inside driver side when hitting a big dip, but it not enough for
me to worry about. If the back spacing is to much, it can be corrected with
a spacer, last resort though. I have not had it rub on the outer fender.
Here's what it looks like.
Riggs.
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Race Director
Joined: May 2003
Posts: 10,956
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From: California
not my thread but relevant question.....What about hight also...... smaller hight tire and or rim (17") in the front to try and get the nose down a little more.... is there any problem with this situation or idea?
Race Director
Joined: Jan 2007
Posts: 14,928
Likes: 3,334
From: NYC NY
) cut the springs or replace the front springs.
Drifting
Joined: Oct 2005
Posts: 1,527
Likes: 148
From: East London/SW Essex UK
I have 18 x 9 on 5" backspace on rear with 285/40/18's - no contact anywhere and the rear track matches the front (8 x 18 on 4" backspace with 255/45/18's) although I do have a little fenderwell contact on front.
Race Director
Joined: May 2003
Posts: 10,956
Likes: 409
From: California
Usually when upgrading the rolling stock on a C3 it's best to try to stay near the original tire height of 27" tall. The problem with trying to lower the front by using shorter tires is for every inch you lower the tire height you only lower the ride height a 1/2". On top of that you are increasing the gap between the top of the tire and the fender opening which is not very becoming to the overall appearence of the car. The bottom line if you want to lower the front end lower the ride height not shorten the tire height. Either (dare I say this ) cut the springs or replace the front springs.
) cut the springs or replace the front springs.But thank you... it seems an important side not on this topic.
Thread Starter
Instructor
Joined: Jan 2008
Posts: 241
Likes: 41
From: Skaelskoer, Denmark
Thanks for advising and sharing out all your experience
As some of you point out, its not worth taking the risk with 285´s, so I´ll settle with 5,0BS on 9,5" rears and mount 275/40´s
As some of you point out, its not worth taking the risk with 285´s, so I´ll settle with 5,0BS on 9,5" rears and mount 275/40´s
Drifting
Joined: Sep 2006
Posts: 1,986
Likes: 21
From: Columbus MN
I have 255/40s instead of 255/45s on 18x8 wheels in the front and don't have any fenderwell contact. The 5% lower profile of the 40s compared to 45s have the same outside dimensions as my stock 255/65-15s.
Drifting
Joined: Oct 2008
Posts: 1,496
Likes: 6
From: springfield ohio
Race Director
Joined: May 2003
Posts: 10,956
Likes: 409
From: California
18x10 with a 5.5 back space on 285/40/18 with the car lowered 2''.Yes it has
rubbed on the inside driver side when hitting a big dip, but it not enough for
me to worry about. If the back spacing is to much, it can be corrected with
a spacer, last resort though. I have not had it rub on the outer fender.
Here's what it looks like.
Riggs.
rubbed on the inside driver side when hitting a big dip, but it not enough for
me to worry about. If the back spacing is to much, it can be corrected with
a spacer, last resort though. I have not had it rub on the outer fender.
Here's what it looks like.
Riggs.
Gosh I'm jealous, I want to do that first quarter 2010... getting mine painted right now...Beautiful cars and stances
p
Drifting
Joined: Oct 2008
Posts: 1,496
Likes: 6
From: springfield ohio
