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Thread: Maximum tire height (diameter) for '33

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    Senior Member rcotner's Avatar
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    Maximum tire height (diameter) for '33

    I have the 20x10 wheels but the tires I want only come in a fairly tall sidewall at the 20" wheel size. Does anyone know what the tallest tire height is that will still fit in the wheel well? I do not have fenders.

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    EFI Rules and Carbs Drool Arrowhead's Avatar
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    I am running 295/40/20 and they are 29" tall. Took quite a bit of modification to get them to fit and have any suspension travel. Your limited to how much you can raise the rear of the car by the lower frame rail and/or the three link support if you have one. I did a combination of things to gain more clearance - raise rear of body about 1/2", lower shock mounts 3/4", removed emergency brake cable mounts on frame and fish mouthed the lower frame tube so the driveshaft wouldn't hit, added spacers on the bump stops on the shocks. Raising the rear of the car also put the suspension arms in a weird angle and actually draws the axle forward so I've installed heim joints on one end of each control arm to lengthen them and also provide some adjustment. It was a lot of work, but was worth it to get the look and ride I wanted. Really didn't want skinny tires on the 20" rims.

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    Quote Originally Posted by Arrowhead View Post
    I am running 295/40/20 and they are 29" tall. Took quite a bit of modification to get them to fit and have any suspension travel. Your limited to how much you can raise the rear of the car by the lower frame rail and/or the three link support if you have one. I did a combination of things to gain more clearance - raise rear of body about 1/2", lower shock mounts 3/4", removed emergency brake cable mounts on frame and fish mouthed the lower frame tube so the driveshaft wouldn't hit, added spacers on the bump stops on the shocks. Raising the rear of the car also put the suspension arms in a weird angle and actually draws the axle forward so I've installed heim joints on one end of each control arm to lengthen them and also provide some adjustment. It was a lot of work, but was worth it to get the look and ride I wanted. Really didn't want skinny tires on the 20" rims.
    Well said;
    I did a lot of things to mine for the same reasons but I have one more obstacle, I run full fenders. These posts help the next guy so here's what I learned along the way. The longer your transmission the less issues you will have with driveshaft clearance. My 47RH Dodge is a long auto due to the rear OD case.
    If you run a stick tranny I would suggest looking at a gear vendors OD behind it IF you can make it all fit. After I moved/stretched my UCA frame tabs Jim S. told me
    about a bracket that bolts on the 8.8 housing ears where the UCA's attach. That bracket moves the pivot forward and has several holes to restore proper UCA angles. You would still want the heim joint upper and lowers to reduce bind but on a 4 link set-up that bracket also changes the length of UCA's required. It might even be the right length to correct the wheelbase and center the tire in the fender as well. If you make any changes do what I did and cut a 32" circle of cardboard and match it to the body lines/fender. Then pull a string through the middle and measure to a fixed point on the frame. This dimension will give you the proper center of axle no matter what type of changes you make. Even after changing my ride height I'm planning on a 28" tall rear tire due to fender issues.
    HTH
    Dale

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    Senior Member rcotner's Avatar
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    Thanks you guys. I appreciate all your help. The calculated tire height is 27.5". I do not plan on using fenders. I hope none of the modifications you guys did are needed but I know where to turn if I need help !

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    Senior Member esff32's Avatar
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    FYI Ray, my wheels are 19x11 with 305/35r19's and the tire height is 26". I have plenty of room all the way around.

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    33 Hot Rod #664 BrentM's Avatar
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    I am running a 305/30/19 on 19 x 10.5 wheels - 6 1/2" Backspace with 1" spacer





    I have the suspension as low as it can go and there is still about 3/4" between the top of the wheel well and the tire. I tried to flex the suspension and it wouldn't budge. Have not had it on the road so I don;t know if it will rub, but I can raise it up if needed. These pictures are with the jackstands under the axles.
    Last edited by BrentM; 02-23-2014 at 01:26 AM. Reason: Fixed picture

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    Senior Member rcotner's Avatar
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    Thanks Evan and Brent. At 27.5" I may have a problem to solve. Sounds like there are options. I got the kit in two stages. I am about a week out from getting my body. It will all be clear then. BTW, Nice looking wheels Brent.

    Ray

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    33 Hot Rod #664 BrentM's Avatar
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    Thanks Ray, I measured my tires and they are right at 26" in diameter. I have not played with the ride height much but you may be able to jack it up to clear.

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    I need some suggestions on a full fender build.

    I building a full fendered car with the desire to fill the rear fender as much as I can with 18" wheels. In understanding what was used on the FF5 red promo car, having a 59.25" rear end, the factory used a 305/30/19 tire, which is 26.3" diameter. Mounting this on an 11" rim with 6" back space gets you an estimated overall width of 71.250" (according to an online wheel calculator I used). In looking at the photos of that car, the fenders are filled in nicely. The only problem that I have, which is a personal preference, is I would like a little taller stance in the rear.

    FF5 recommends a 295/35/18 (26.1" diameter) tire with a 5.50” suggested back space wheel. Using these dimensions, I calculated an overall width (at the tire) of 70.850", which is close to the red car. I still have the problem with the lower stance, so I am considering a taller tire.

    For my car, I am using an adjustable 4 link rear set up that I purchased from Dan Ruth so I can get a better centerline on my rear axle. I'm also using a standard 8.8" rear axel measuring 59.25” hub to hub. From looking at photos of other cars, it seems that a 27" tire should fit (with the wheel being centered in the fender). I believe Dan Ruth found this out when he built his car and I believe he and a number of other builders have had success with the taller tire. I'm just not sure what modifications if any were required to get them to fit.

    That leaves me with a couple of options:

    Option 1: 285/40/18 (27” diameter)with a 5.50” back space I calculated overall width (at the tire) of 70.450” (I think would leave too much space between the side wall and fender)

    Option 2: 285/40/18 (27” diameter)with a 5.25” back space I calculated overall width (at the tire) of 71.050”

    Can anyone out there tell me if these are good assumptions or offer any suggestions? Any help would be greatly appreciated.

    Dave

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    Quote Originally Posted by DaveSL33 View Post
    I need some suggestions on a full fender build.
    I building a full fendered car with the desire to fill the rear fender as much as I can with 18" wheels. In understanding what was used on the FF5 red promo car used a 305/30/19 tire, which is 26.3" diameter. The only problem that I have, which is a personal preference, is I would like a little taller stance in the rear.
    FF5 recommends a 295/35/18 (26.1" diameter) I still have the problem with the lower stance, so I am considering a taller tire.
    For my car, I am using an adjustable 4 link rear set up that I purchased from Dan Ruth so I can get a better centerline on my rear axle. From looking at photos of other cars, it seems that a 27" tire should fit (with the wheel being centered in the fender). I believe Dan Ruth found this out when he built his car and I believe he and a number of other builders have had success with the taller tire. I'm just not sure what modifications if any were required to get them to fit.
    Can anyone out there tell me if these are good assumptions or offer any suggestions? Any help would be greatly appreciated.
    Dave
    Centering the axle/tire is the first step to allow taller tires, Then give yourself 2.5" inches for compression from ride height and 1" more to fenders and add bumpstops. Dan has taller softer springs too that would help a bit since the FF springs are pretty short and too harsh for most of us. The 33HR actually stands for Harsh Ride from the comments I see fairly often.
    IIRC they had 13" radius plus 2" travel plus the 1" clearance That gives the 32" dia of the glass fender. So you should drop 1" for the 27"s and softer springs with a bit more compression and then check the driveshaft clearance since that's your limiting factor.
    Dale
    Last edited by myjones; 03-04-2014 at 07:17 AM. Reason: correct dimensions

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    Quote Originally Posted by myjones View Post
    Centering the axle/tire is the first step to allow taller tires, Then give yourself 2.5" inches for compression from ride height and 1" more to fenders and add bumpstops. Dan has taller softer springs too that would help a bit since the FF springs are pretty short and too harsh for most of us. The 33HR actually stands for Harsh Ride from the comments I see fairly often.
    IIRC they had 13" radius plus 2" travel plus the 1" clearance That gives the 32" dia of the glass fender. So you should drop 1" for the 27"s and softer springs with a bit more compression and then check the driveshaft clearance since that's your limiting factor.
    Dale
    Thanks Dale. I forgot about the drive shaft.

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    tranny

    Quote Originally Posted by DaveSL33 View Post
    Thanks Dale. I forgot about the drive shaft.
    The other factor on the driveshaft clearance is the length of tranny you plan to use.
    My long auto with rear OD moved the front U-joint further back than most and that
    changes the arc the driveshaft travels through where it goes through the frame.
    HTH
    Dale

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    I just got mine on the ground for the first time yesterday running 285x35-18.now thinking of going with rear fenders.Just because i think again as everyone else, the tires look to short. Either FFRs rear fenders but Mcqueen said he would just sell the rears .I did a primitive measure with a tape and level Im right at 70.5 overall.It was a challenge because the car I bought has a 62.52 axle in it.Another reason I think the fenders might help.I ended up going with 7s on the front just so the reveal lip wasn't wider then the rear and to try to enhance the 10 inch wheel.I had to go to 7 inch BS on the rears to get the tire tucked in properly
    Attached Images Attached Images
    Last edited by bobbybuick; 08-23-2016 at 07:43 PM.

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    Bobby
    I'm running the same width 8.8 so I'll be watching how you wind this up with taller tires and different fenders.
    I agree it just looks wrong with those short tires on the back.
    DB Hemi33

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    from what Ive read if you go much past 26 " the rear moves forward to far in the opening .most tire combos are 25.9 to 26.3.I read and looked untill my head was spinning .Also to go the big little look you need some mods if you approach 27 inch tall.in the picture i have it up quite a bit it could be moved down,with all that said
    I ordered fenders today and found a roadster windshield
    305x30/19 26.3
    285x35/18 25.9
    Last edited by bobbybuick; 08-23-2016 at 07:41 PM.

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    You have to be willing to go with longer lower control arms with the front bracket dropped down. Then you get the rake with bigger rears. Not sure where your instant center lines up then or if it matters. At some point you gotta make the choice between Hoosier A7 or Mickey Thompson sportsmans. It's just fiberglass. Cut the rear fenders, add 2 inches and go wider! Have fun.

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    Quote Originally Posted by BrentM View Post
    I am running a 305/30/19 on 19 x 10.5 wheels - 6 1/2" Backspace with 1" spacer





    I have the suspension as low as it can go and there is still about 3/4" between the top of the wheel well and the tire. I tried to flex the suspension and it wouldn't budge. Have not had it on the road so I don;t know if it will rub, but I can raise it up if needed. These pictures are with the jackstands under the axles.
    Caution,
    I had 29" tall toyos with that sand 3/4 clearance. Jumped up and down and never hit the body (no fenders). Got it on the road and first time over a bump I hit the fenderwell big time. I think 27" is the true max diameter for these guys unless you go to the extremes noted above...

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    If you hit the fenders already then you will have to add bumpstops or risk a lot of fiberglass damage. Think about having 2 people, a full gas tank and a couple chairs maybe a small cooler, a bucket of detailing stuff etc for a car show. You will crack the fenders after a few bumps so it's time to raise the car for a bit more room for suspension travel and so it won't be hitting the bumpstops all the time. Remind me what your combo is on ride height and which rear coil overs you run.
    DB

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    Some of these posts point out why it's important to know the minimum length on your shocks and set up the car with mock-up bars that can either be adjusted to this length or have holes drilled to the minimum length, maximum length and 60% extended for normal ride height. If you can't easily switch back and forth between the mock-up bars and the coil-overs, then the coil-over mounts are poorly designed.

    When I built my '37 I used mock-up bars exclusively during the build. I even used them during front end alignment, to eliminate problems with the springs not compressing fully.

    I installed bump stops in the rear, so I could use reasonably soft 175 lb/inch springs and insure that my 30.5" tall tires didn't hit the fenders.

    http://www.energysuspensionparts.com/191306
    Last edited by DaveS53; 05-16-2017 at 05:34 PM.

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    Senior Member HVACMAN's Avatar
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    This is a web site some might find helpful.

    https://www.wheel-size.com

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    FFR only recommends tires that are about 26 inches tall with their 20" rear wheels (305/25/20 or 315/25/20). Even if you raise the lower shock mount and/or lower the upper mount by about 1.5 inches, to accommodate a 29" tire, you'll have a problem with the 4-bars no longer sitting level. The location of those mounts should be altered too. The 4-bars used on this car are shorter than those most often installed on hot rod frames. Just something to keep in mind if you don't want the low profile tires you'd get on a new high performance car these days.

    There should be at least 2" of travel available above the tire, without hitting the body, according to the folks who performance safety inspections for the NSRA. My car meets that requirement.

    Here's a little info on what happens when the control bar angles changes.

    http://www.motoiq.com/MagazineArticl...oll-Steer.aspx
    Last edited by DaveS53; 06-16-2017 at 01:33 PM.

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    Seasoned Citizen NAZ's Avatar
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    Just want to expand a bit on what DaveS53 mentioned above about the control arms (bars) setting level. It's important to handling that the lower control arms are level. If not you will experience roll steer and the more out of level or angle you have the worse it will get. If you're not familiar with the concept of "roll steer" Google it and look for a site that has a graphic. The original FFR chassis has very limited adjustment for this and with the variety of "ride height" figures I've seen tossed around with no regard to the tire diameter or the affect it has on the angle on these lower control arms I suspect there are many FFR vehicles on the road with varying degrees of roll steer. I set my 33HR up to run 30" diameter tires but there is nothing on the rear of my car that is FFR original. If you want to stray from the norm AND want your car to handle well, it's going to take a great deal of modification to "go big or go home". More than simply cutting fenders and jacking up the rear end for clearance. Remember, the rear suspension is a system and when you make a change in one area you affect another. And the car is made up of several systems that have to work in concert with each other.

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    Senior Member AJT '33's Avatar
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    Does anyone have experience with the IRS suspension an the sizing of the tires? I am going to receive my full kit in September and I am already looking at my options on tires as this can make or break the look of a car. Any input on adjustments and tire sizing is deeply appreciated. TY.

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    Ol Skool
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    With the rear fenders on I can go a lot wider than the 285/35/18 Hankooks on the FFR "bullit" wheels. Diameter maybe to 27" with low suspension and "softer ride". After that it is very chassis body dependent. I will have multiple sets of wheels and tires by the time I am done. Swapping between other toys will be a consideration for me. without the fenders I think Hoosier A7 345/18 will be on it. 28" is a stretch without compromises.

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    I would not expect the IRS to change the intended tire size. The car is made to use low profile tires, like the ones you'll find on a new Corvette. If you want a hot rod look with taller tires there are two problems. One problems is tall tires are getting harder to find all the time. With an IRS, the only way to accommodate a tall tire would be to lower all of the mounting points for the IRS, so the chassis and body sits higher. Someone also mentioned raising the body a little.

    I have 295/45/20 tires that at 30.5 inches tall, but those BFG tires are no longer made. For many years they were a hot rod standard.

    Today, the tallest tire I can find is a 295/40/20 with the same tread as the 225/45/17 that I use on the front. I can find 295/45/20 rear tires, intended for SUV use, but there is no matching front tire.

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    How much angle can you run on the axle, as in can you run the axle at a down angle to raise the car some?
    Ford 15 IRS.

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    All coil-over spring setups have a very limited range of adjustment. Ideally, you should have 60% of the travel in compression. If the spring mounts are set to provide 60% compression, jacking the car up with the springs immediately fouls up the rebound travel. The spring mounts need to be relocated to maintain the correct travel ratio. Angling the control arms and axles isn't wise either.

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    Quote Originally Posted by NAZ View Post
    Just want to expand a bit on what DaveS53 mentioned above about the control arms (bars) setting level. It's important to handling that the lower control arms are level. If not you will experience roll steer and the more out of level or angle you have the worse it will get. If you're not familiar with the concept of "roll steer" Google it and look for a site that has a graphic. The original FFR chassis has very limited adjustment for this and with the variety of "ride height" figures I've seen tossed around with no regard to the tire diameter or the affect it has on the angle on these lower control arms I suspect there are many FFR vehicles on the road with varying degrees of roll steer. I set my 33HR up to run 30" diameter tires but there is nothing on the rear of my car that is FFR original. If you want to stray from the norm AND want your car to handle well, it's going to take a great deal of modification to "go big or go home". More than simply cutting fenders and jacking up the rear end for clearance. Remember, the rear suspension is a system and when you make a change in one area you affect another. And the car is made up of several systems that have to work in concert with each other.
    NAZ, pardon for resurrecting an older thread but I just noticed this comment of yours. I understand bump steer completely, but this is my first experience with a solid rear - every other performance car has been mid-engine or IRS. So I'd love to read more about roll steer, and solid rear geometry. Unfortunately I haven't found a good explanation of roll steer yet... lots about bump steer

    I'll keep looking, but if you have a bookmark, send it over. Thanks
    James

    FFR33 #997 (Gen1 chassis, Gen2 body), license plate DRIVE IT says it all! build thread
    My build: 350SBC, TKO600, hardtop, no fenders/hood, 32 grill, 3 link, sway bars, 355/30r19
    Previous cars: GTD40, Cobra, tubeframe 55 Chevy, 66 Nova, 56 F100

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    Seasoned Citizen NAZ's Avatar
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    IMG_0752.JPG
    Having trouble adding a sketch so I took a photo of my cartoon to help explain roll steer.

    On a solid axle, the control arms travel in an arc. When parallel to the ground they hold the axle at the farthest point to the rear and the wheelbase is the longest at this point. When the axle is at the extreme ends of bump and rebound the axle is held closer to the front and the wheelbase is shorter. Roll steer is when a solid axle becomes skewed in the chassis when the body rolls such as when going around a corner. When weight is transferred to the outside during cornering the body & chassis rolls about the roll axis which typically lifts the chassis on the inside and lowers it on the outside (in reference to the turn). If the lower control arms are parallel to the ground they will travel in approximately the same arcs but in opposite directions and the wheelbase on each side will be approximately the same. If the lower control arms are angled up or down at the front when at static ride height then as the chassis rolls one arm will position the axle further back than the other side skewing the axel. See the attached sketch. Google roll steer again and try to find a site with graphics. It's different than bump steer but results in the same thing -- an un-commanded turn.

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    Ah yes, thanks. Makes total sense. Much appreciated NAZ.
    James

    FFR33 #997 (Gen1 chassis, Gen2 body), license plate DRIVE IT says it all! build thread
    My build: 350SBC, TKO600, hardtop, no fenders/hood, 32 grill, 3 link, sway bars, 355/30r19
    Previous cars: GTD40, Cobra, tubeframe 55 Chevy, 66 Nova, 56 F100

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    EFI Rules and Carbs Drool Arrowhead's Avatar
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    Quote Originally Posted by NAZ View Post
    More than simply cutting fenders and jacking up the rear end for clearance.
    When I did the initial modifications to make the large tires fit, I knew the control arm angles weren't the optimum. It was always in the back of my mind to revisit this and figure out a modification to bring everything back into alignment. So this past summer I had the car torn down for some major upgrades so I went all the way fabricated new upper control arm mounts. The lowers are usable as they are, the rear of the lower bars will use the original Mustang mounting holes. Basically the rear sits 3" higher than the FFR design so the bars will be parallel with the ground now.




    20170723_170710.jpg

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    Quote Originally Posted by Arrowhead View Post
    When I did the initial modifications to make the large tires fit, I knew the control arm angles weren't the optimum. It was always in the back of my mind to revisit this and figure out a modification to bring everything back into alignment. So this past summer I had the car torn down for some major upgrades so I went all the way fabricated new upper control arm mounts. The lowers are usable as they are, the rear of the lower bars will use the original Mustang mounting holes. Basically the rear sits 3" higher than the FFR design so the bars will be parallel with the ground now.



    20170723_170710.jpg
    I made new tabs for the front of my uppers as well but I didn't get quite that involved. Look at my gallery for the custom 4 link pics.
    Arrowhead;
    That looks like a very nice job of bracing and making room for fine tuning the instant center.
    Dale
    Last edited by myjones; 10-10-2017 at 06:01 PM.

  34. #33
    EFI Rules and Carbs Drool Arrowhead's Avatar
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    Quote Originally Posted by myjones View Post
    I made new tabs for the front of my uppers as well but I didn't get quite that involved. Look at my gallery for the custom 4 link pics.
    Arrowhead;
    That looks like a very nice job of bracing and making room for fine tuning the instant center.
    Dale
    Thanks, by dropping the mounting location 3" there wasn't any real estate nearby to grab on so I needed add the second tube. The single tube the original upper tabs are located on isn't the strongest either. I found some slight deformation of the tube where both tabs were attached. Not enough to warrant replacing the tube, but some reinforcement in that area would probably be a good idea even at stock ride height.


    20170820_144958.jpg
    Last edited by Arrowhead; 10-11-2017 at 07:51 AM.

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    IMG_0630.JPG
    Here's my idea of how FFR should have designed an adjustable rear suspension. I fabricated brackets for my UCA & LCA so that they have a wide range of adjustment for instant center, anti-squat, pinion angle, UCA offset, length of wheelbase, and can be configured as an offset three-link or parallel four link. And I used parallel links top and bottom instead of the inefficient triangulated links of the Mustang design. The LCA mounts on the axle also have several hole locations as do the shock mounts for ride height adjustment. The design includes a watts link with 10" of total roll center adjustment.

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    Does any of this info go to the 33 with IRS ?? Setup for IRS for best road race style car ?
    Last edited by 1932; 10-11-2017 at 12:11 PM.

  37. #36
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    Quote Originally Posted by NAZ View Post
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    Here's my idea of how FFR should have designed an adjustable rear suspension. I fabricated brackets for my UCA & LCA so that they have a wide range of adjustment for instant center, anti-squat, pinion angle, UCA offset, length of wheelbase, and can be configured as an offset three-link or parallel four link. And I used parallel links top and bottom instead of the inefficient triangulated links of the Mustang design. The LCA mounts on the axle also have several hole locations as do the shock mounts for ride height adjustment. The design includes a watts link with 10" of total roll center adjustment.
    That's some serious shtuff right there! Thanks for the explanation of Roll Steer NAZ!

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  39. #37
    EFI Rules and Carbs Drool Arrowhead's Avatar
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    Quote Originally Posted by NAZ View Post
    Here's my idea of how FFR should have designed an adjustable rear suspension.
    I guess I have to disagree with that. I think the design is fine for 99% of the builders out there. Frankly, most builders wouldn't know how to setup your suspension properly anyway and most alignment shops would just be left scratching their heads. As awesome a build you're creating, it's way more than the typical FFR customer will need or want.

    My guess as to why they kept it simple is it's more than just initial design and material cost, it's the support on the back end and fielding complaints about proper setup by the end users. Heck, there's plenty of questions posted about setting up the three link as it is, the four link has only one adjustment. The car was built to be a street car and maybe kill some cones on the weekends. If you want to build a track monster, have at it.

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