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Thread: Rear tire to body clearance

  1. #1
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    Rear tire to body clearance

    I’m finishing some final touches on the car and I’m aware as I drive that things settle in. I’m looking at the rear wheel to fender clearance and I noticed that with the chassis set at 4.75” in the rear that the drivers side is closer then I expected. Measuring from the bottom of the fender lip to the tire I get a minimum clearance of 40 mm or 1.57”. Does any one know how much a solid axle cars rear suspension travels?

    B917025C-297C-43BB-8D1F-3B1FFC6A231B.jpeg062D3B5D-98DF-4E4B-85E9-327D709653DC.jpeg
    Last edited by GFX2043mtu; 09-19-2018 at 10:51 AM.
    Mk4, Moser M88 rear end, Eaton truetrak, Craft Racing 461 Windsor, MMR pro trans, Glennís 1,000 hp cobra fuel system and lots of other parts.

  2. #2
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    It will travel until it hits the bump stops on the shocks. From your ride height I’d say3” travel up, definitely inside the wheel wells.
    Put the frame on jack stands, take the snap rings off the shocks that the adjustable spring collars sit on. Not you can use your jack to jack the rear end up until it bottoms out or the tires hit the body.

  3. #3
    Senior Member CraigS's Avatar
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    Looks to me like you should be OK. Drive it w/ a passenger and full tank to check. Usually, if it does hit, it contacts inside the fender right over the center of the tire(looking from the side). And it is usually just a quick zing sound that puts a black mark on the underside of the fiberglass but doesn't hurt anything. BTW the solid axle goes straight up when you go over a bump. But when cornering the top of the tire actually moves inward towards the center of the car. So, if you get a zing going over a bump you will usually be fine in a corner.
    FFR MkII, 408W, Tremec TKO 500, 2015 IRS, DA QA1s, Forte front bar, APE hardtop.

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    Thanks guys. The 3” of travel concerns me and I measured the travel to the bump stop at the ride height and Murd is correct as it about 3”. The 18” wheels are about 1/16” in from the fender lip on top of the tire and it defiantly sticks past them on the back side. One thing I did was loosen the coil over coller as far as I could and I raised the rear end to just before it hits the body. Mine will hit on the fender lip at the 2:00 position on the drivers side. This is a full 1.5” before it hits the bump stop. Since I want to track the car I see this as a problem as smashing the tire into the fender lip when driving in anger does’t sound good. I’m thinking I may just add another bump stop so that it bottoms out on that before the body and up up the spring rates to 750 front 500 rear to help keep it off the body. I am a little bit bummed that Factory five didn’t set up the wheel offset or body for complete suspension travel clearance.
    Mk4, Moser M88 rear end, Eaton truetrak, Craft Racing 461 Windsor, MMR pro trans, Glennís 1,000 hp cobra fuel system and lots of other parts.

  5. #5


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    Jeff Kleiner's Avatar
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    What is your overall rear end width from the mounting surfaces?

    Jeff

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    Best I could measure with the rotors on it’s about 60-60.25”. So axle to axle it should be around 59.5”- 59.75”. The rear end came from Moser with the FFR width of that helps. Kinda wish I knew this before I had the rear end built as I would have had it narrowed 1/2”.
    Mk4, Moser M88 rear end, Eaton truetrak, Craft Racing 461 Windsor, MMR pro trans, Glennís 1,000 hp cobra fuel system and lots of other parts.

  7. #7
    Senior Member rich grsc's Avatar
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    Unless you're doing stadium jumps, you'll never have 3" of suspension movement.

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    I've been talking with Gordon at Levy racing about this and I sent him a bunch of pictures and I got some initial feed back about how to set the car up including how to correctly adjust the red Koni shocks. I may get some new springs from him to to complete the package. I'll let you guys know what he tells me I should do to ensure clearance once he gets back with me. He also told me that if you get a FFR Moser rear end or order one from them that the axle is S95 width and the Fox width fits better since is a little narrower. With the FFR 18" wheels 315 R888R tires I have they are about flush with fender flairs at the top and obviously wider as you go towards the rear of the car so I'm a bit concerned with clearance. I don't plan on doing stadium jumps with the car but I do intend to run it at Grattan raceway along with several other tacks in the area. My concern is mainly for two sections of the track at Grattan, first being the jump as I have had many vehicles with all four or two wheels off the ground on that section of track racing (not that I intend to launch the FFR but you never know). The other is turn 10 which has a nasty divot that you hit at some where around 80-90 mph.
    Mk4, Moser M88 rear end, Eaton truetrak, Craft Racing 461 Windsor, MMR pro trans, Glennís 1,000 hp cobra fuel system and lots of other parts.

  9. #9
    Steve >> aka: GoDadGo GoDadGo's Avatar
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    GFX,

    Please make sure that your U-Joints don't bind when the suspension is in full droop if you're going to be Flying Your Factory Five .
    The reason why I'm making this point is because some F5's have this issue and if you do please consider installing limiting straps.

    Steve
    Last edited by GoDadGo; 09-20-2018 at 06:47 PM.

  10. #10
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    Yep, I had a set of straps made. I just won’t install them till I figure these other issues out. Plus they will help prevent my BMR sway bar mounts from hitting the panhard mount.
    Mk4, Moser M88 rear end, Eaton truetrak, Craft Racing 461 Windsor, MMR pro trans, Glennís 1,000 hp cobra fuel system and lots of other parts.

  11. #11
    Senior Member CraigS's Avatar
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    More research needed here. MkIVs have been out for maybe 5-6 years and and 315s are the most common rear tire size. I haven't seen anyone else w/ this problem. Can you measure the backspace on your rear wheels? Running 500# springs to 'fix' this problem shouldn't be required.
    FFR MkII, 408W, Tremec TKO 500, 2015 IRS, DA QA1s, Forte front bar, APE hardtop.

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    That was my thought too Craig. But I can’t find any thing where other people are worried about this. Perhaps people don’t pay to much attention to this, or perhaps somethig is incorrect on my car. I’ll check the wheels this evening and let you know what I find.
    Mk4, Moser M88 rear end, Eaton truetrak, Craft Racing 461 Windsor, MMR pro trans, Glennís 1,000 hp cobra fuel system and lots of other parts.

  13. #13
    Steve >> aka: GoDadGo GoDadGo's Avatar
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    GFX,

    The 18 X 11.0" inch wheels have a back spacing of 6.46".
    This means you have 4.54" as the outer offset.

    The 17 x 10.5" inch wheels have a back spacing of 6.70".
    This means that those wheels have 3.80" as the outer offset.

    Your 18" wheels stick out .74" more than they would have had you gone with the 17's.
    That puts your overall track at 1.48" wider with the 18's then they would have been with the 17's.

    Hope This Helps!

    Steve
    Last edited by GoDadGo; 09-21-2018 at 09:50 AM.

  14. #14
    Senior Member CraigS's Avatar
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    Well dang Steve, if all your numbers are correct, what is FFR doing? An extra 3/4 inch is not good.
    FFR MkII, 408W, Tremec TKO 500, 2015 IRS, DA QA1s, Forte front bar, APE hardtop.

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    Ya that’s the issue that I think I’m seeing compounded by the s95 width axle. I’m looking at 1“ per side more the the 17” wheel IRS cars. I’m just wondering how the solid axle guys with 18” wheels are pulling this off. I can tell you at 12 o-clock from the center of the wheel, the tire is under the fender lip by about .125” and by the 1 O’clock position it sticks past it and that is where the fender is closest to the wheel. To me there is no way to tuck it under unless I either shorten the new $4500 moser M88 axle (don’t want to have a new powder coated axle cut and re-coated) or machine the back face of the rear wheels and remove .5” -.75”. Which may be an option since I have a inch of caliper clearance. I did some corner adjusting and I can get 1.5” of clearance to both fenders with the chassis at 5” in the rear. Kinda starts to kill the low Cg but my track width is wider. If your numbers are right Godad I hope FFR realizes it and starts to make the 18” wheels with the same outer offset as the 17’s. If they did I would ask to send mine back to be done with this.
    Last edited by GFX2043mtu; 09-21-2018 at 03:28 PM.
    Mk4, Moser M88 rear end, Eaton truetrak, Craft Racing 461 Windsor, MMR pro trans, Glennís 1,000 hp cobra fuel system and lots of other parts.

  16. #16
    Steve >> aka: GoDadGo GoDadGo's Avatar
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    GFX,

    I've got the Moser TSD-500 (Dana 44) and am running 285/40-17's.
    My rear wheels have an offset of 6.10" and fit fine.

    https://youtu.be/IGYtX-3p7xk

    Could you possibly drop down from a 315 to a 295?
    Would that help and/or solve the problem?

    Steve

  17. #17
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    Somebody feel free to correct me if I’m wrong but fox width axle is 59.25”. Sn95 .75” per side wider so 60.75”. Sounds like you measured right about fox width.
    Not sure about the 18” wheels but lots of guys seem to run them, how much clearance from the inside of the rim to the brackets that bolt to the axle for shocks and Panhard bar? Usually this is really tight, if you have .75 - 1” then backspace must be way off.

  18. #18


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    Jeff Kleiner's Avatar
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    I have cars in the shop right now with both FFR 17s and 18s. I measured from wheel mount surface to the outermost edge of the wheel lips. The 17 is 4 3/4"; the 18 is just under 5 1/4" meaning that the 18s will be approximately 1/2" farther outward. I suspect that the extra width of the 18 vs 17 rim was pushed outward because of the tight clearance on the inside that Murd mentioned.

    Jeff

  19. #19
    Steve >> aka: GoDadGo GoDadGo's Avatar
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    Quote Originally Posted by GoDadGo View Post
    GFX,

    The 18 X 11.0" inch wheels have a back spacing of 6.46".
    This means you have 4.54" as the outer offset.

    The 17 x 10.5" inch wheels have a back spacing of 6.70".
    This means that those wheels have 3.80" as the outer offset.

    Your 18" wheels stick out .74" more than they would have had you gone with the 17's.
    That puts your overall track at 1.48" wider with the 18's then they would have been with the 17's.

    Hope This Helps!

    Steve

    NOTE
    : The backspacing information was pulled from Factory Five's website so Jeff's Measurements prove the point in the Real World.
    Last edited by GoDadGo; 09-23-2018 at 08:35 AM.

  20. #20
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    A wheel with 6.46in. Backspacing and 4.54in. Front spacing is 10 in. Wheel and the 6.70in and 3.80in. Back and front spacing numbers would be referring to a 9.5 in. Wheel. Kind of a detail mentioned just for technical correctness.
    358 SBC, Winters QC, Sweet mfg, Coleman, AP Racing, ARS, TKO 600, Fuel Safe

  21. #21
    Steve >> aka: GoDadGo GoDadGo's Avatar
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    Quote Originally Posted by stevehsr View Post
    a wheel with 6.46in. Backspacing and 4.54in. Front spacing is 10 in. Wheel and the 6.70in and 3.80in. Back and front spacing numbers would be referring to a 9.5 in. Wheel. Kind of a detail mentioned just for technical correctness.

    18 x 11.0"

    ...6.46
    .+4.54
    ====
    .11.00

    17 x 10.5"
    ...6.70
    .+3.80
    ====
    .10.50

    Sorry, It's The Banker In Me!
    Last edited by GoDadGo; 09-23-2018 at 06:46 PM.

  22. #22
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    Wheel width is measured to the inside surface of the tire bead flange, whereas back spacing is measured to the outer edge of the wheel (about 1/2 in. difference on each side) so a 10in. wheel is actually about 11 inches overall edge to edge. For instance a zero offset 10 in. wheel will have a 5.5 in Backspacing. Kinda odd, but that's how the wheel people do it.
    358 SBC, Winters QC, Sweet mfg, Coleman, AP Racing, ARS, TKO 600, Fuel Safe

  23. #23
    Richard Oben's Avatar
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    Sounds like the right suspension and the incorrect wheels. The 18 were created for the hot rod not the Roadster I believe. The extra 3/4 of an inch per side can kill a tire in a very short time. JMHO. Richard.
    Richard Oben FFR builder www.northracecars.com

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  24. #24
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    I remember when the 18” wherls where released, and FFR advertised them for the roadster and coupe. I even told them when ordering the car I wanted the 3 link and 18” wheels. I called them the other day and told me the max compression I would see on the 3 link is 1” and some change which matches what Gordon Levy told me. FFR knows about the width and I was told set the suspension to 1.5” clearance and I would be good. I just wish that they revise the shock brackets on the 3 link and moved them in the .75” each side so that you can run a narrower axle to fit the 18’s better in the quarters. But perhaps there is a design issue by doing this that we just don’t see. Eitherway I’m running 4.25” ride height in the front and 5” in the rear and it looks ok to me as I have just over 1.5” clearance at the narrowest point. So I’m going to see how it works. I figure if I can drive on our Michigan roads with out bottoming a wheel in the fender then I should be good. Also I don’t get how the extra .75” would kill tires. Wheel bearings with heavy offsets sure but tires? Plus I need all the grip I can get with the 655 ft-lb of torque I have.
    Last edited by GFX2043mtu; 09-24-2018 at 07:57 PM.
    Mk4, Moser M88 rear end, Eaton truetrak, Craft Racing 461 Windsor, MMR pro trans, Glennís 1,000 hp cobra fuel system and lots of other parts.

  25. #25
    Senior Member CraigS's Avatar
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    That is a very disappointing response. Looks like they made one set of wheels that kind half a$$ fit two applications. IMHO there should be no restrictions on ride height because of tire interference. $1899 for wheels that don't fit??? If it were me I'd be pushing for a refund so I could then buy correct fitting wheels.
    FFR MkII, 408W, Tremec TKO 500, 2015 IRS, DA QA1s, Forte front bar, APE hardtop.

  26. #26
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    This is my concern too, at the 2 o’clock position where the width of the tire starts to protrude beyond the wheel well. Looks like with suspension travel going up it’s going to hit. I have 15”s all around, 275 in the back with the IRS. I attached a few pics. My ride height is set to 5”. Have not officially aligned the car but not sure if that’s going to help.

    B58CE679-1053-4C39-9D2D-9005366FCC94.jpg6CE7A19B-BC1F-4FB6-914D-AE05FA50714D.jpgDF2269EC-8625-44C8-846C-7A640CFE1865.jpg5E46F79B-C5BB-46D4-BEC1-307D4E050DB2.jpgCA8F9FE8-CF21-442F-9503-05EB2FE6C215.jpeg
    Last edited by stevant; 11-08-2018 at 09:08 AM.
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  27. #27
    Senior Member Just puttering's Avatar
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    Just a note: be sure to measure perpendicular to the floor ( like the first picture ) not to the center of the wheel, this should measure more travel than you might think is available!
    Mk3.1 347 AFR 205cc Race Heads EFI siemens deca 60lb injectors MSD 6AL ignition Vortech V-3 3 Link PS/PB

  28. #28
    Senior Member Avalanche325's Avatar
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    Stevant,

    Do some bodywork or something. That garage is WAY too clean.

  29. #29
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    Stevant,
    I have 295 15s and they stick out wider than yours but still can tuck right up inside at full compression, it’s tight though and a had to adjust panhard bar just a bit to stop a slight rub if you bottomed the suspension on a big dip.
    One key thing that will give you more clearance is grinding down the extra 1/2” or so of fibreglass from the wheel well lips. That extra space is needed at the 2 o’clock position you’re concerned about.

  30. #30
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    After talking with Gordon Levy, FFR, and others I set my car with 1.75” of vertical clearance. Verticals is the key as the tire moves up and down. Which means you have more clearance then it appears. I put 180 miles on my car so far and with the read Koni shocks on full stiff I haven’t bottomed out. I was told that even if I track the car and do bad stuff to it the rear tires won’t move much more then 1” up from there normal position. I would also recommend for you to trim the fender edges to remove the excess material. That will defiantly gain you room on your car.
    Mk4, Moser M88 rear end, Eaton truetrak, Craft Racing 461 Windsor, MMR pro trans, Glennís 1,000 hp cobra fuel system and lots of other parts.

  31. #31
    Senior Member CraigS's Avatar
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    Stevant's center pic illustrates another FFR short coming. The wheel is too far to the rear in relation to the wheel opening in the body. A couple of years ago someone had that problem but it seemed even worse. It was acceptable once he got the pinion angle of his 3 link correct. Shortening the 3rd link helps pull the axle forward.
    FFR MkII, 408W, Tremec TKO 500, 2015 IRS, DA QA1s, Forte front bar, APE hardtop.

  32. #32
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    I have not aligned my car yet, but I have an IRS. Other than my alignment I don’t have any other adjustments to center it. I’m thinking the alignment will do it justice. My body is mounted correctly. I did notice it sits back a little and wanting to be centered. Trimming the inner lip is a definite!!
    Last edited by stevant; 11-11-2018 at 09:27 PM.
    Build#1: MKIV Roadster #9320

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