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Upgrading Everything -and keeping it Spitfire-ish

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dherr2 Avatar
dherr2 David Herr
Adamstown, MD, USA   USA
1972 Triumph Spitfire MkIV "Rat Rod"
I will send over dimensions for the R160 when I get a work break.

My opinion on the topic is that there is no "cheap" option, as you can't just swap out the differential, so a custom drive shaft, custom CV axles and then deciding on what to do about the bearing/hubs and upright, not to mention the leaf spring. Doing the R160 is "easy" since you can retain the basic suspension layout, but still expensive if you fix the rest of the issues, so it is easier if you go GT6 Rotoflex, it is a proven formula. I have to stress that just getting an R160 and the mounting kit from our friends in NZ is just the beginning.

If you are going a different direction, it really is new ground as many people have installed other solutions, but each solution is pretty much "one off". It would be fantastic if someone could find some off the shelf differential and suspension design that could be modified to work on our cars, as the supply of the parts to make the R160 work is getting harder to find.

I think the reason my drive line angle is not an issue with the longer R160 on my car is the difference in my engine/transmission mounting. Our engines are in the same location (front pulley just above the rack). But my engine/transmission is lower front to rear since my body was off the frame, it allowed me to lower the steering rack and I modified the frame to allow the transmission to be lower as well, so the drive line angle is ideal.

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Manana Avatar
Manana Steve Wten
Thornhill, ON, Canada   CAN
Hey Dave, I was hoping you'd chime in.

Yes, the fact that you lowered your steering rack is likely the biggest, maybe only difference in our basic set-ups.

I just went out to look at a MK3 frame I have and man that R200 will be a tight fit! I look forward to learning the dimensions of that R160, especially from front flange to the back of the housing not including the tangs for mounting. I figure all of the mounting hardware at the back will be inside a modified frame member in just about the same location as the current one much like you've done and shown earlier in this thread; also like Wolfcreek Steve did here....https://www.triumphexp.com/phorum/read.php?8,1402942,page=3.

Interestingly, last year I purchased from a great guy on this forum, (actually he pretty much gave the stuff to me) a Rotoflex set-up. I thought I might be able to use some of the parts with whatever I did annnnnd I'd at least have the stuff in hand to see and measure sizing.

I'd rather go with a double wishbone and coilovers.... the engineering is fascinating.... but I'm no dreamer; I may have to somehow make an R160 work or just be careful with my stock diff. I really want my first choice though smiling smiley.

Thanks for taking the time guys.



Steve
http://stevew10.wix.com/spit16

dherr2 Avatar
dherr2 David Herr
Adamstown, MD, USA   USA
1972 Triumph Spitfire MkIV "Rat Rod"
So here are the dimensions, (approximate) as I have everything clamped down for my emergency brake routing tubes ready for welding, so I did not want to remove it to make sure the dimensions were 100% but this is very close.

Front to back it's 18 1/2" long
Side to side, axle seal to axle seal 6 3/4" wide

8" high

So slightly longer than your R200, but much more narrow and not quite as tall (probably due to the larger crown wheel on the R200.

I agree with you on the double wishbone suspension. The UK guy that had the bolt-in solution was quite unique, but I think it shows some of the issues to package a suspension into the given space. I really wish this had gone beyond the two prototypes he built. Will be watching what you end up doing.

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Manana Avatar
Manana Steve Wten
Thornhill, ON, Canada   CAN
Maaaaaaaannnnnnnn, only 2" longer than the R200!. But wait, is that from the front of the input flange or the casing? and including the bolts coming out of the back of the casing?

So at the seals it's 6 1/2" wide and you don't have stub axles, just the CV joint goes into the diff and uses circlips inside right?

I love the narrow body of that diff, again, I think it would really help the CV Joints with bump, droop, and plunge.

Once I get the car out of storage and home I'll have to do some more math.

Thanks a bunch Dave.



Steve
http://stevew10.wix.com/spit16

dherr2 Avatar
dherr2 David Herr
Adamstown, MD, USA   USA
1972 Triumph Spitfire MkIV "Rat Rod"
Yes, that is from the front of the input flange. Does not include the rear casing so factor in 1/2 inch for the NZ casting and I had to notch the frame for one of the bolt heads. It is a tight fit length wise.

Yes, the rear is very narrow, cv axles just use the circlip inside the axle. Also keep in mind that the height of the cv axles as they almost touch the frame at full droop with a GT6 Rotoflex rear suspension. So another factor since the axles are mounted above the frame rails. My hybrid CV axles do appear to have plenty of ability bump, droop, and plunge, so no worries there.

Manana Avatar
Manana Steve Wten
Thornhill, ON, Canada   CAN
Ahhhhhh, okay, that sounds more like what I was expecting, but still not as long as I thought (I know, I know, that's what he said smiling smiley ). I'd also add the bulge in the back of the cover to get an accurate comparison. It must stick out another inch or so no?

So then we'd be adding about 1 1/2" to the length you mentioned earlier.

You didn't happen to weigh that thing did you? Frick, I bet it's under 65 pounds.

Thanks again, I'll start to compile a chart of this stuff.



Steve
http://stevew10.wix.com/spit16

clshore Carter Shore
Beverly Hills, FL, USA   USA
Some folks get fixated on 'double wishbone' solutions, as if they were the end-all and be-all of suspension design.
But analysis of successful racecar designs shows that lateral links combined with radius arms are more common at the rear.
Not only are the fore/aft and lateral forces resolved cleanly into separate load paths, eliminating high bending loads and variable load vectors,
but the packaging frees up valuable volume that is otherwise required to provide clearance for the wishbones throughout their entire range of motion.
Rear toe is controlled at the rear by a reversed lower wishone (a la GT6+) or pairs of parallel lower links.

The GT6+ forsakes an upper radius arm by making the rear leaf spring perform double duty, taking advantage of the tremendous lateral stiffness
to locate the upper end of the rear vertical link in the for/aft direction.
The price for this is the bespoke upper spring mount of the diff, leaving little space at the rear to fit alternate diff or suspension components.
There s nothing wrong with the Rotoflex vertical link or lower wishbone geometry.
The lower wishbone itself is a very heavy casting, bent in the middle to clear the rotoflex donut, which MUST be made of depleted Uranium.
But when CV axles are fitted, then the wishbones can instead be made of light strong welded steel tubing.
A coilover unit along an upper lateral link could replace the spring, but finding clearance for an upper radius arm is tough without cutting into the cabin.
A technically correct, but somewhat complex solution would employ a pair of small Watts linkages to locate each upper vertical link instead of a radius arm.

Another solution replaces the leaf spring with a lightweight tubular steel narrow based upper wishbone whose inner pivots are located about where the top
of the leaf spring bolts to the top of the diff. Bending forces would be high, but strong high quality bearings could be used rather than traditional rubber bushings.

A further refinement employs a 3D spaceframe structure that combines the functions of an upper wishbone as above and rocker arm.
The rocker arms would actuate coilover units, perhaps mounted side by side horizontally above the diff, or elsewhere via pushrod/pullrod links.

The rocker solution may sound needlessly complex, but pays performance dividends in that shock absorber stiction and hysteresis can be minimized,
it's one reason for the wide adoption in racecar design.
Best of all, little or no body or frame modification would be required to fit, and rocker fabrication requires only generic mild steel straight tubing, easily cut and welded.

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Manana Avatar
Manana Steve Wten
Thornhill, ON, Canada   CAN
Some good points Carter, thanks.

I think the lower wishbone will not be that challenging, and as I'm sure you've seen many times, there are a few designs out there that add an upper wishbone; they extend an edge forward longitudinally from end the aft lateral frame member and of course brace it accordingly. Like you, I've been thinking that a pushrod set-up would not only leave a little more room inside the wishbones for some of the extraneous things like half-shafts smiling smiley, but it would also reduce the unsprung weight.

If I go for this, I have no doubt that I'll have to massage the tub at least a little bit and modify the rear frame crossmembers, but if it works out I think it'll be a better geometry suspension. One thing I really like is getting that upper control arm shorter than the lower, contrary to the Spit / GT6 set-up. Unless I've misunderstood everything I've read and have no concept of geometry, shorter on top is much better for camber when roll is induced.

When I get closer to the actual design, I hope I can count on some of you smarter guys for input. For now though, (head hanging emoticon) I need to get back to our house renos.

Thanks again.



Steve
http://stevew10.wix.com/spit16

clshore Carter Shore
Beverly Hills, FL, USA   USA
In reply to # 1533626 by Manana Some good points Carter, thanks.

I think the lower wishbone will not be that challenging, and as I'm sure you've seen many times, there are a few designs out there that add an upper wishbone; they extend an edge forward longitudinally from end the aft lateral frame member and of course brace it accordingly. Like you, I've been thinking that a pushrod set-up would not only leave a little more room inside the wishbones for some of the extraneous things like half-shafts smiling smiley, but it would also reduce the unsprung weight.

If I go for this, I have no doubt that I'll have to massage the tub at least a little bit and modify the rear frame crossmembers, but if it works out I think it'll be a better geometry suspension. One thing I really like is getting that upper control arm shorter than the lower, contrary to the Spit / GT6 set-up. Unless I've misunderstood everything I've read and have no concept of geometry, shorter on top is much better for camber when roll is induced.

When I get closer to the actual design, I hope I can count on some of you smarter guys for input. For now though, (head hanging emoticon) I need to get back to our house renos.

Thanks again.

SLA (short - long arm) is a term often applied to independent suspensions having a vertical link with an upper and lower control arm.
Refine that term further as STLBA, sort top long bottom arm, and LTSBA, long top short bottom arm.

But consider this:
An SLA having zero camber at rest typically exhibits about the same camber change per inch of compression as per inch of extension.

So STLBA behaves the same as LTSBA when turned upside down, yes?

There are some advantages to having the lower arm as long as is practical:
1) Less track change, ie and disadvantages sideways wheel scrub with suspension deflection.
2) Less roll effect of roll center movement with suspension deflection.

But those effects, particularly #2, are shared by having both upper and lower arms as long as is practical.

Longer links have disadvantages of their own:
1) The longer the link, the weaker it is in compression loading for the same cross sectional form and area, so they must be heavier to prevent flexure & buckling
2) Requires larger packaging volume for the range of movement of the arm.
3) May result in a larger effective bending load between the upper and lower pivots.

You can see the evolution of SLA technology in F1 car suspension, particularly the front.
Lower and upper arms as long as is practical, and inner pivots located high and close together.

Now consider the Spitfire/GT6 rear chassis.
No big lump of a motor, but a wide ladder chassis that limits the placement of the lower wishbone pivot, and thus it's length.
If we go with a STLBA solution, the upper link inner pivot mounts … where?
There's no chassis, so we have to fabricate some structure to carry the loads to the chassis.
And given the already rather short lower arm, our upper arm cannot be too short, else the roll center will move all over the place.
We don't have room for a standard wishbone, and we can't use a single lateral link, because we don't want to cut holes in the cabin for a radius arm.
Speaking of the roll center, where do we want it?
Our existing front suspension is optimized to work with a swing axle, having a high rear roll center that that stays fairly still.about 10-12" above the road.
How can we stabilize the roll center, avoid costly changes to the chassis, to the diff, to the front suspension?

Triumph's answer: Design a LTSBA that utilizes the spring leaf as the long top suspension link.
Addresses the issue of track change and scrub.
Although roll center is lowered vs swing axle, it minimizes the issues of roll center movement compared to STLBA.
Retains the existing chassis and front suspension, requiring only anti-rollbar changes.
Eliminates the need for a short upper wishbone and custom structure to carry the loads to the chassis.
Eliminates the need for a radius arm, and attachment in the cabin.

For those of us scheming to replace the rear suspension, there are a wide variety of approaches we could take.

For example, to get around the limitations on lower arm length posed by the chassis rail locations, consider this:
Holes all the way through the chassis rail, with the pivot bracket ears located on the inside face of the rail instead of the outside.
The holes would be like a flattened megaphone with square corners, wider on the outside, tapering towards the inside,
a steel box welded into the frame, reinforced at the edges to prevent flexure. shaped to allow the lower arm to pass
through to the pivot, but able to articulate through it's full range of motion without touching.
Rather than a lower wishbone, two parallel lateral links attaching to the lower ends of the rotoflex vertical link
The longer lower arms would allow for a longer upper arm, minimizing the roll center movement and track/scrub effects.

OK, I'll put the crack pipe down now, time for dinner.

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Manana Avatar
Manana Steve Wten
Thornhill, ON, Canada   CAN
smiling smiley

I think Marcus Brewley (sorry for butchering your name Marcus, I don't have time to look it up right now) did something along those lines by attaching his lower wishbone beneath the frame rail. Very clever, I'm just not sure I'm okay with the lower ground clearance, and in the end also (haven't done the math) not sure it will end up with the best geometry.



Steve
http://stevew10.wix.com/spit16

SpitfireBGT Avatar
SpitfireBGT Mike Soltez
Irwin, PA, USA   USA
Someone has Carroll Smith's book Tune to win



Aspiring Know It All

clshore Carter Shore
Beverly Hills, FL, USA   USA
Here's a sectional view of the R160 diff that some may find helpful.

This one is from a Datsun 510 that used stub axles for U Joints retained with a center bolt, but the basic configuration remains.


Attachments:
Datsun510.R160.diff.pdf    1.63 MB

Spitfired Xtreme Michael Perry
Pinson, AL, USA   USA
i feel like my build thread has been seriously hijacked. I have never considered a R180 or R200 differential. This thread is beginning to get all over the place - which is not what I want for the build.

Wouldn't it be better to start an entirely new thread about the R180 v.s. R200 or other differential comparisons?

I am not trying to be a dick -but I already have too many choices on my plate at 4. I actually need to narrow this list.

And I think I am going to choose between the Miata Torsen and the Ford 8.8. so now my goal is to mock up the two with arms, axles, knuckles etc. And see what size cage will be required for either.



Success is a measure of determination!

Manana Avatar
Manana Steve Wten
Thornhill, ON, Canada   CAN
Totally sorry about that Michael.

We've tried to share info on the options, pros and cons, and quite honestly I was hoping to hear back on some dimensions and weights of those 8.8"ers.
In the words of Red Green, "Remember, I'm pulling for ya. We're all in this together!"

I figured you were still considering other options in pursuit of the best one, and thought this relevant, but I will now cease and desist. Again, apologies.


PS; No excuse for sure, but this is a good example of how build threads are just about the worst way to pass this kind of information (especially if you want it to be easily accessible at any point down the road).



Steve
http://stevew10.wix.com/spit16

clshore Carter Shore
Beverly Hills, FL, USA   USA
In reply to # 1533727 by Spitfired Xtreme i feel like my build thread has been seriously hijacked. I have never considered a R180 or R200 differential. This thread is beginning to get all over the place - which is not what I want for the build.

Wouldn't it be better to start an entirely new thread about the R180 v.s. R200 or other differential comparisons?

I am not trying to be a dick -but I already have too many choices on my plate at 4. I actually need to narrow this list.

And I think I am going to choose between the Miata Torsen and the Ford 8.8. so now my goal is to mock up the two with arms, axles, knuckles etc. And see what size cage will be required for either.

Hate to break it to you, but this is not a 'Build Thread', it's a Forums posting.
Any member is free to make any post that meets the site guidelines.
You are likewise free to simply ignore those postings and post whatever you wish.
It's as much for us as it is for you. Doesn't 'belong' to you, belongs to the group, all you did was start it off.
Think of it like a soccer ball, we all have a chance to participate and get in some kicks if we want to.
If you want exclusive control of the content (but not the comments), I suggest a build thread in the 'Journals' section.
But be prepared for reduced visibility and participation, since they require active interest by members to see what is in your Journal.
Many folks do both, posting Journal related milestones, challenges, and questions in the Forums as updates to existing or new topics that will
rise to the top of the list and be seen.

I hope that you are not offended, and will continue to post in the Forum, but to expect us to simply sit back and passively listen is unrealistic.

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