ReinCarNation

Visit our community sponsor

Thanks Thanks:  1
Likes Likes:  0
Results 1 to 14 of 14

Thread: Tires to body rear - IRS

  1. #1
    Senior Member
    Join Date
    May 2016
    Location
    North of sacramento Ca.
    Posts
    459
    Post Thanks / Like

    Tires to body rear - IRS

    How much room are you putting or is needed between tire and body with IRS - rear. Looked but didn't find , need to order wheels.

  2. #2
    Senior Member
    Join Date
    May 2016
    Location
    North of sacramento Ca.
    Posts
    459
    Post Thanks / Like
    Soo nobody knows how much tire clearance is needed on a 33 full fender with IRS--Tire inside to body? I am going to use 325/30/19 and will widen finder if needed.

  3. #3

    Ol Skool

    Join Date
    Oct 2013
    Location
    upstate NY
    Posts
    736
    Post Thanks / Like
    Nobody wants to commit a # so I'll suggest 325 is the limit with stiff vertical and lateral control on a full fender. Personally I would stay 305 to 315 without fender modification and here is why. The radius of the fender going towards the body (parallel to axle not the tire radius) is larger than the sidewall of a 30 series profile. If you have less than 2" vertical clearance between tire and fender at the flat area, then the outside of the tire hits the inside of the fender radius on compression. This also gets wadded up in the axle center. If you want to widen the fender then your fine. Calculate your offset so you have 3/4" or a little more inner clearance depending on your IRS upper arm travel and Arc. Once you widen the fenders the back of the car looks fat and you need to drive it like a dually. If I go to the trouble of widening the fender I want a 335 or 345. Go big or go home!! Or... consider a different fender style...

    I may do this in the spring, but I have solid axle, and I will still run 295/40/18 on street with one set of fenders and 345/35/18 hoosiers with something else. I have to have fenders of some sort. Check your trailer ramps before finalizing decision also.... mine don't slide quite as wide as I thought...

  4. #4

    Ol Skool

    Join Date
    Oct 2013
    Location
    upstate NY
    Posts
    736
    Post Thanks / Like
    IMG_20171222_150551_958 (361x640).jpg

    12" wide rim on narrow axle with 5.75" back space sets at the plane of outer edge. That's about where a 325 will be. I'll run 345 on those rims with a modified fender. Not sure how the IRS track and travel will work...

  5. #5
    Senior Member
    Join Date
    May 2016
    Location
    North of sacramento Ca.
    Posts
    459
    Post Thanks / Like
    Thanks erli I was going with 345 but didn't find tire i liked--this is going to be a driver and want to have tires that work all around.
    Michelin PS4S 265/35/19 front & 325/30/19 rear, mabe some autox. I am not into drag racing-like corners!
    The PSS is on the way out so don't want to set up for tire that is going out.
    Wheels that i go back to all the time are a lot$$$, that is the stress of it!

  6. #6
    Senior Member
    Join Date
    Aug 2013
    Location
    Gatineau, Quebec, canada
    Posts
    212
    Post Thanks / Like
    Very anxious to see what comes of this discussion stream as I have an IRS setup and looking to get the widest tires without modification of the fenders (don't need more work). The 5.75" backspace is a set number for me as well as I want to avoid any shimming as I would like to take it down the 1/8 mile every so often just for the fun of pissing off a few competitors!

  7. #7

    Join Date
    May 2014
    Location
    Simi Valley, CA
    Posts
    95
    Post Thanks / Like
    I consulted with Dan Ruth, who has built several '33s with various IRS configurations and full fenders / running boards. I wanted an all weather tire for daily driver use, and wanted to maintain the body rake with as large a diameter tire as would fit in the fenders. We ended up with BFG G-Force Comp 2 A/S tires: 245/45-18 front, 305/35-20 rear. I haven't figured out the backspace yet - still on the "to do" list. I plan to be buying the wheels and tires later this Spring.
    HTH,
    Keith

  8. #8
    Senior Member
    Join Date
    Aug 2013
    Location
    Gatineau, Quebec, canada
    Posts
    212
    Post Thanks / Like
    Quote Originally Posted by progmgr1 View Post
    I consulted with Dan Ruth, who has built several '33s with various IRS configurations and full fenders / running boards. I wanted an all weather tire for daily driver use, and wanted to maintain the body rake with as large a diameter tire as would fit in the fenders. We ended up with BFG G-Force Comp 2 A/S tires: 245/45-18 front, 305/35-20 rear. I haven't figured out the backspace yet - still on the "to do" list. I plan to be buying the wheels and tires later this Spring.
    HTH,
    Keith
    Do the full fenders allow for a larger wheel than just the front and rear fender kit with no running boards. I know the manual says a max 26" tire however I would not mind a larger tire if possible. If any of you find out I would appreciate knowing. TY!
    Last edited by AJT '33; 02-22-2018 at 08:18 AM.

  9. #9

    Ol Skool

    Join Date
    Oct 2013
    Location
    upstate NY
    Posts
    736
    Post Thanks / Like
    The rear FFR supplied fenders are the same for all kits. About 13" wide. Different fenders are available from other sources. 27" diameter on the rear is generally OK, but offsets and profiles vary. "Square" profiles with soft springs and wide tread get you into the fender sooner. My streets are 295/40 for that reason. I wanted more diameter and softer sidewall on the rear. With "squat" they are just under 27". Probably grow a little when warm and rolling.

  10. #10
    Senior Member
    Join Date
    May 2016
    Location
    North of sacramento Ca.
    Posts
    459
    Post Thanks / Like
    I am going with 19x12 BS 4.5 with 325/30x19
    19x9.5 BS 5 with 265/35x19
    That gives about 1.5 on front of rear fenders, don;t care on front space because will fit fenders to tire.
    If the car gets air the IRS will use an inch, that will give 1/2 clearance for front of rear fender at running board.
    Last edited by 1932; 02-22-2018 at 06:57 PM.

  11. #11
    Junior Member
    Join Date
    Feb 2018
    Posts
    21
    Post Thanks / Like
    Been working on calculating tire size as well

    For fenders FFR post 11" rims with 6" backspacing (315 tires) for backs. Wondering if IRS is wider than others.

    With IRS I calculate 5 1/4" backspace for 11" rims, the 315 tires would be just under 12 1/2" wide so this will be just under 6" of tire on the backside this would leave me with about 1/2" clearance on the inside and 1/2" on the outside at the narrowest part of the fender.

    Best I can measure is 6 1/2" of clearance to the body back from mounting point.

    I will be trimming fenders somewhat and with 17" rims 315/35 tires the outside diameter is 25 5/8 so tire actually wont be into fender at ride height.

    Anybody have backs on with IRS and able to confirm how much room for back space

  12. #12

    Join Date
    May 2014
    Location
    Simi Valley, CA
    Posts
    95
    Post Thanks / Like

    received new wheels yesterday

    I finally received my custom wheels yesterday - ordered them before this year's Cruise-In. I'm really happy with how they came out. Now I just need to go buy the tires and get them mounted...

    To answer the question about backspace, I specified 4" for both front and rear. I put one of the rear wheels on and tried to climb under the car to get a decent picture. I failed. However, here is the best I could do:

    The worst case was when the suspension (2015 IRS with Wilwoods) was at full droop. The clearance between the wheel and body was 1.75" in the back and (not pictured) about 1.5" in the front. I expect the tires to bulge out 1" past the wheel on both sides, so I've got at least 1/2" space between the tire and body. This gap grows to about 1.5" when I push the wheel up to approximate ride height, so I think that's good for street use. I am going to have to widen the fenders at the back a little though since the rubber will stick out past the edge of the fender otherwise.

    Keith
    Attached Images Attached Images

  13. Thanks Bgardner thanked for this post
  14. #13
    Junior Member
    Join Date
    Feb 2018
    Posts
    21
    Post Thanks / Like
    Keith, Looks great

    American racing with custom paint? From picture I gather its a flatter black and polished.

    I couldn't find in your post the width of your rims. 305 tires make me think 10 1/2 but I haven't seen many rim options with this size.

    From info you posted I gather that with suspension hanging you will have 1/2" from rubber to body and at ride height you will have about 1 1/2" from rubber to body. Appreciate your posting the info as I was not thinking about gap with suspension hanging and had my gap at ride height down to 1/2" but will make adjustment.

    Bob

  15. #14

    Join Date
    May 2014
    Location
    Simi Valley, CA
    Posts
    95
    Post Thanks / Like
    The wheels are from a small company called American Legend Wheels, which I bought through MotorActive USA Inc. in Long Beach, CA. Fronts are 18x8", rears are 20x10". These are 2 piece forged aluminum, polished with satin black powder coated segments. The forged blanks are made in China, while the final machining, assembly and finishing are done here. That's why it took 10 weeks between ordering and delivery. They were more expensive than American Racing, but much less than Billet Specialties. I felt that I got a fairly unique wheel design for a moderate price.

    Here is a photo of the wheel in the box as delivered. Note that there is protective plastic film covering the rim and I just pulled the plastic bag off to the side, but you can see it under the wheel. That's the reason for the strange reflections between the spokes.

    Keith
    Attached Images Attached Images

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Breeze

Visit our community sponsor