Old Man Jimbo

Wheels and offset confusion , where is Confucius ?

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How about that title ?.

Here's my dilemma.... I do not like the wheels on my Reatta nor do I like the gap so I want to tighten tire to wheel well at any cost ( not monetary so much as work involved ). Currently she is wearing 235/50/17 tires with Cadillac wheels and I do not know the offset as of yet. I believe the Reatta stock wheels are 40mm offset and the wheels that I am looking at are 18x8.5 with a 12mm offset.

My old and worn out brain has trouble understanding offset and I know that some of you do so where else would I go but here ?. I do realize that I will need to stiffen the suspension to do what I want to do and look into better bearings if I choose an extreme offset to achieve the look That I want . Not worried about fast cornering because I just don't have that desire in me anymore so can someone direct me as to how to push the envelope to the max ?.

Non the less this could be a good discussion for us old farts.

I'm attaching this photo so you can see the gap I'm not liking .

 

Reatta 3:8:18.jpg

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Update .... I see that I can get the same wheel with a 32mm offset I would have to get them powder coated satin black though , no biggie. 

Just a thought

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6 hours ago, Old Man Jimbo said:

I want to tighten tire to wheel well at any cost ( not monetary so much as work involved ).

 

I've been down that road and I didn't like the results. I've had some big 235/55-17 Mustang GT wheels on my Reatta. My Cadillac wheels had 235/60-16 tires on them when I bought them. Both of those looked good but they killed the acceleration and hurt the braking of the car to the point that I couldn't live with it. I sold the 235s and I now have 225/60-16 Cadillac wheels on my Reatta. They are a good compromise between the tall tires and the stock tire size which I think looks way too small.

 

When you put the tall tires on your car to fill the wheel well, it's like gearing the differential higher on a rear wheel drive car. Believe me. It really makes a difference.

 

If you want to continue with putting tall tires on your car the big factor is how close the tire will be to the spring perch on the strut. In the photo below I've marked with a red arrow the place you will need to worry about the tire hitting. As you can see, the 235/55-17 Mustang wheels were almost touching. The offset of the wheel determines how close the tire will be to that spring perch.

 

2007 mustang wheel-2.jpg

 

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The picture above posted by Ronnie tells the story.

A larger tire will hit/rub the part of the strut shown in the picture.....that part is the lower support for the spring.

A rim/wheel with less offset (that moves the wheel assembly out) would be needed....but you need to change the offset at least an inch.  so that a larger tire could be used to try and fill the opening.....but that brings its own problems (if you plan on driving the vehicle)

Moving the wheel assembly out changes the front steering geometry....affecting alignment and steering.....it also changes the load on the spring (lever arm) so the spring would be compressed more with the same weight.

Options ...... Rework the struts so that support is higher.....which means you would need to change or rework springs so the ride height would be normal or lower.

Another thought is to rework the upper strut support.......if you move that support UP it will lower the car.   Moving the support could be done in many ways but all require metal work....somehow cutting out the upper support and moving it up ....

whatever you move it UP the car will set lower the same amount .... but there are limits....at some point it hits the underside of the hood,  you could put holes or bumps in the hood and go as low as you want.

After, or hopefully during the process you need to consider the location of that upper mount....it controls half of the front geometry.....you could end up with bad caster and camber.........just some small things to consider.

 

The drawing below is not a Reatta but gives you some idea of the front suspension.

Image_002.png

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21 minutes ago, Barney Eaton said:

Moving the wheel assembly out changes the front steering geometry....affecting alignment and steering.....

 

You are exactly right. I had some 16" Mustang wheels on my Reatta that had a lot of offset to the outside. Even though the front end was aligned properly, I would get a bump steer that was quite noticeable, especially when going around a sweeping curve while accelerating and hitting dips in the road. When you hit a dip the car would kinda squirm around which made you feel like you need to correct the steering wheel to compensate. It just didn't feel stable like it does with the correct offset.

 

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I use this to model wheels and tires. Basically a 26.6" tall tire is about it without some radical offsets. For a 7" wheel the factory offset is 46mm and will vary if the wheel width changes. A 225x60x16 on a factory wheel has about 10mm clearance. A 235x60x16 is about 6mm taller but depends on manufacturer and inflation psi. Since the spring perch is angled, less offset will increase clearance but less than 40 mm with a 7" rim will begin to rub the wheelwells at full lock.

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Ron, you could ride that one west on the Oregon trail with those wagon wheels. I never did get the appeal of that look, and it rides and handles like crap.

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Thanks guys for taking the time to put out some very useful information that gives me a lot to consider. I ike what you said Barney and if I want to close the gap that is the most practical way  . I am going to take some different sponges with different thicknesses , pop some two face tape on them and set em on the front towers to see just how much space there is between the tower and the hood ( Macgyver process ).

Ronnie , reading what you said reminded me of when I put taller than stock tires on my 928 some years ago. It looked great although ........... when I took my Sunday drive heading up to the Cascades out of Mt Angel the first time with those new tires on , did my usual 70 into a 30 curve , I thought I was going to loose her. It threw everything off. The only good thing about those tires was they slowed me down big time. I miss that car . A nice 928 is a piece of work just like a Reatta.

Well , back to the drawing board .

Thanks guys.

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I did not mention cutting coils on the spring because that will affect front wheel travel......it will lower the front.  If someone had a parts car, that would be an ideal test vehicle.

I think there is a rubber stop at the top of the strut...cutting that in half or replacing with a polyurethane bump stop might help.

If you cut a coil and it lowers the front 1" then you loose 1" of travel.......maybe not a big deal for smooth road city driving.

Another possibility would be to use the springs from a Eldorado or Seville (they had a V8 that weighed more so the springs are probably stiffer)  Cut those springs.

Because they have a higher spring rate, it would take more force to bottom them out.

There was another recent post where the owner complained about a rough ride.....so some people already think the car rides too hard.

Unlike some other vehicles, not a lot of Reattas get modified so there is very little written about actual experience.

Edited by Barney Eaton (see edit history)
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Thanks Barney. When I put the Reatta on dolly's last night I took a good look at the strut/configuration /springs ect.I am wondering about a type of coil over shock and modifying the perch ( for lack of proper trem possibly ). Of course I haven't been able to find anything as of yet so that option will take a lot of cross referencing if that is a good way to go.

I believe that the Reatta body style was way ahead of it's time and my goal is to bring it up to date with the current high end coupes and they have very little gap at the wheel well.   I know this can be achieved it just takes an open mind and determination ( and some Barney brain ) to git er dun .

Keep in mind guys I do not want to degrade the Reatta in any way, I just want to make her hotter than a pepper sprout ;)

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Before spending any money on dropping the front of the Reatta you should consider how you would drop the rear to match. To my knowledge no one has been able to come up with a way to do that either. There has been a lot of discussion on ways to do it but I don't recall anyone actually doing it.

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Ronnie there has to be a way. Modified air bag system ?. way to much $ unless forget the kit and piece one together . I'm not good with saying it can't be done.

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1 minute ago, Old Man Jimbo said:

I'm not good with saying it can't be done.

 

I feel the same way. With enough time, enough people and enough money almost anything can be done.... all of which I am sorely lacking. :)

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For me , I'm not investing money in a Woman, I'm investing money in my passion. My Reatta won't cheat on me for a Lamborghini ! ..... Ha ha ........ ha

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I scrapped that for now. A guy from a race team in Northern Michigan offered me way to much money for the C4 suspension that I rebuilt so I took that money sold the 90 Reatta and bought a 75 Mach 1 to drive when I need a rush. And believe me , she's ridiculously fast and pretty.

 

Mach 1 9:5:16.jpg

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Hmmmmmm , would it be possible , possible  to select the perfect adjustable coilover modify the mounting points and be done with those humongous struts.?.

STRUT.jpg

SHOCK.jpg

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8 hours ago, Old Man Jimbo said:

Hmmmmmm , would it be possible , possible  to select the perfect adjustable coilover modify the mounting points and be done with those humongous struts.?.

 

The short answer would be no. Not without fabricating an upper control arm.

 

As you can see in the photo below the strut is not only the equivalent of a shock absorber and spring, it also serves as the upper control arm to maintain proper caster and camber in the front suspension. The coil-over shock you show in your photo isn't designed to do that. You would run into a similar problem if you tried to use the coil-over shock on the rear.

 

Front Struts 011.jpg

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Yes Ronnie I am aware of that. Doesn't the Riviera share the same configuration ?. And or is it possible to remove the bracket on the Reatta strut that bolts to the knuckle and use another style strut that has an OD of 2.125"

I probably sound crazy and I accept that. Maybe the humongous spring could be changed with a smaller diameter yet stronger spring then redesign the lower spring perch. I came across a place that produces cold rolled springs that would be better to shorten. 

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Update ; I think that I maybe onto something. I measured the diameter of the front coil springs on my Reatta and they are aprox 8". Then I measured the new coil spring I have for my Cherokee and they are 5".

So, I see no reason why I couldn't rethink the spring lower base to form to Eibach springs , put a bump stop on the ram and a boot. I would start with new front struts , find what the load rate is currently on the Reatta and call Eibach and discuss this with them.

Input please....

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I don't have details but there was a conversation I saw a long time ago about removing the welds where the actual strut tube inserted into the lower mount, remove the strut and drop in a different style strut with the concentric spring. A coilover shock won't work without an upper control arm.

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My tiny machinist brain tells me the best way to lower the front end is to modify the stock strut to move the mounting points for the knuckle up higher. That way you would retain the factory ride and you would still be able to adjust caster and camber normally. Below is how I think I would attempt to do it.  Moving the knuckle up would bring the tire closer to the spring on the strut so wheels with a different offset would be needed to move the wheel out to compensate. I have no idea if this would work. There are always numerous pitfalls to doing something like this. At least this way if you are going to start chopping up a Reatta to lower it a couple of inches, this procedure could be easily reversed by replacing the struts.

 

drop spindle-1.JPGdrop spindle-2.JPG

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Incredible participation Ronnie. Thank you. 

I am not at this point wanting to lower her nor " chop her up " , that would be an abomination . I want to put a larger wheel/ tire in there to not only fill the gap but to lay more tire on the road ( an example would be think back to the cartoon Fred Flintstones. If you remember his ride was full to the ground roller and his ride cornered like no other ! ) to handle better.

Correct me if I'm wrong , by moving the knuckle up would be very intense to the geometry . It would achieve what your suggesting although I think it would open up a can a worms. 

I'm thinking that as I said , new struts ( keep the knuckle intact ) get rid of that humongous 8" spring and go with an 5 maybe 6 inch spring with a modified base to set the lower part of the spring into. 

The top of the spring will remain the same as far as fastening it to( with minor mods ) the knuckle will remain the same and I will have up to 3" more to work with as far as wheel/tire selection.

The spring being the key, nothing else will matter.

Think about that.....

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