Everyone building a V8 miata on a budget is try to avoid the expensive custom axle and broched hub conversion. I think the factory 5 axles is the cheapest option for 8.8 ford axles but at $550 + broched hubs and A arm modification I am thinking there has to be a better way.
Stock Tbird Axles are 2 inches longer each than modified Miata axles. What if we used the stock Tbird axles, used stock Tbird hubs, and build longer custom control arms?
Positives: you would have cheap stock replacement axles. 5 lug wheels that open you up to the world of Mustang brakes. You have to modify the A arm anyways so why not make it the right way? You will have a wider stance giving you more rubber to the road.
Negatives: a lot of fab work. You have to 5 lug swap the front.
It seems to me that the positives out weigh the negatives. What do you guys think?

 

I don't see any real problems with that. If I was better at fabrication, I might attempt it.

There are a couple of small points (+ and -) that would also have to be considered:

- By making the upper and lower arms longer, you will change the spring ratio. Not a big deal, just put in higher rate springs.

- You would have to modify the upper and lower arms for both length and bushing fit. This could prove slightly difficult. And it might be easier to just build a set of tubular arms. Although tubular arms might be better for performance, that does increase cost and complexity.

- With longer arms and taller uprights, that will significantly change things like bump steer and camber change. Before doing that, I would want an expert suspension guy to calculate that all out for me. You might have to make custom pick up points on the sub frame.

- One of the Cobra companies makes a spherical bearing kit for the T-bird and Mustang uprights. That's a good thing.

- I'd love to see a 5 bolt rear hub. Which would allow a 17" or 18" wheel. And that leads to a greater tire selection, and a lower tire cost. The down side is weight. As I understand it, the miata does much better with very light weight wheels and tires. The extra weight on each corner could degrade handling.

- I don't see a relatively easy way to upgrade the front hubs to 5 lug.

- Brake options (I think) are fairly plentiful for the miata. T-bird or Mustang rear brakes
would be somewhere between stock Miata and Wilwoods, I would think.

 

A couple of points:

The FFR roadster axles are in the neighborhood of $250-$280 shipped. They do require machine work so the Tbird hubs fit in Miata uprights or broaching of the Miata hubs. I'm pretty sure the Tbird hubs can be modified cheaper than broaching the Miata hubs. But call it a wash. The deciding factor would be whether or not you want 5-lug wheels.

An additional track width of 4" (2" per side) will look a little strange without some extensive and expensive bodywork. And then you would probably want to do the front to match. More money.

A wider stance doesn't necessarily mean more rubber to the road. I'm not sure the longer arms are worth the effort, given that the delta between the expense of a reman stock Tbird axle and the FFR axle is in the neighborhood of $50-$75.

My approach was custom arms on the rear, using the Tbird uprights and, at the time, Cobra hubs to get the 5@4.5" pattern, 8.8" rear end, FFR axles, and late model Mustang rotors. Then the front has to be converted to the same 5@4.5" pattern.

Another approach is to redrill the Tbird hub, machine the diameter to fit in the Miata bearing, using the stock Miata arms with the shock moved rearward to clear the CV.

Some of this can be seen here:

MiataV8 Conversion: Five Lug Conversion

and on a couple of other blogs in this series.

Mike

 

I love it when guys think out of the box this way Rowen!

I paid $650 for my axles, broached hubs and shipping and another $140 for new CV joints. Brake and wheel advantages aside do you think you could build the A arms and put a decent set of flares on the car for 800 bucks?

Having just spent the last year in flare world I can tell you $1200 gets you epic, $750 gets you sweet and $300 gets you covered + shipping, paint and install supplies. But and this is a huge BUT none of them would give you the additional 50mm you need for this. Most flares give you about 30mm added width to the fender.

Adding 2" (50mm) per side would be the same as running -15 offset wheels and a few guys do that on Miatas but only the extreme tire stretch guys. For them 30mm flares work because they run skinny tires and leave the wheel stick out another inch.

No question 5 lugs open up a world of opportunities for better wheels and brakes. If anyone made a conversion kit at a decent price they would sell a lot of them.

Wider stance does not give you more rubber on the road because the limiting factor is not the width it's the height. In 16" tires there are no better options than 15s. 17s you pick up a few and probably the best is 285/30-18 at 24.7 tall. But that is a very tall tire for a Miata that will limit suspension travel, the ability to lower the car and add negative scrub radius to the geometry.

Bob is right wheel weight is a bigger deal in Miatas than a lot of other cars because the Miata is so light to begin with. It's all about percentage of unsprung to sprung weight so a 20 lb wheel on a 3800 lb Camaro is less of an issue than the same wheel on a 2500 lb Miata. I didn't weigh them but I would bet my 17s are a good 5 lbs heavier than my 15s were and no question I can feel it. I'm not sure it degrades handling but braking over bumps you can feel the mass in the steering wheel and in your butt.

Well that is my $.02 4am thoughts on the matter. Great discussion but I wish I could sleep!

 

The easiest thing may be to just bolt the entire T-bird rear subframe in. I know this was done in the past.

-Jason

 

LOL! ^^ Insert one large well duh! Never even dawned on my but mighty fine idea.

 

I didn't realize it was that easy... Guess Im off to the junkyard tomorrow!
But really, this does put things into perspective. Anything is possible when you are skilled/ crazy enough. But why when there are much simpler options?

 

"Easy" is sort of a relative term here.

The cast iron lower control arms were sort of a turn off for me. But the aluminum upright/hub carriers are really nice.

Maybe you could just split the Miata subframe and add 4" to the middle? For that matter, do the same to the front, then the body. The sawzall is your friend.

Mike

 

LOL ^ I haven't recovered from my last "yeah that should work" idea yet!

 

Let me get this straight, you want to save money by buying cheaper axles, then fab up tubular control arms and do body mods to make them fit? I applaud thinking outside the box, but in the end aren't you spending more in time and effort than just the money for the axles?
I went with the Boss Frog (Drive Shaft Shop) axles and they fit like a glove. NO broached hubs, no grinding or machining needed. At $650 they are plug and play provided you use coil over shocks OR use a shock like the Koni Yellow's adjustable perch/Monroe Sense-O-Trac with a removable perch and a spacer.
The hot set up to any of these options without moving the lower shock mount is to use a VW Passat outer boot (Beck Arnley PN 1032952) as it has only one small accordion wave between mounts. DSS will even install them for you if you request it with your order. Replacement boots from Rock Auto are less than $20 each shipped if you want to change out what you have now!

 

I have already had one of my machinist friends cut and re spline some used Thunderbird axles. The fear is that the cutting Un did the heat treatment and the axles will break. Only one way to find out.
I thought that Mustang brakes, 5 lug, and a wide body on a Miata are pretty epic. I have more experience with paint and body than most. The cheap axles are a plus. Also the custom axles could have camber adjustments for extreme camber on race day. The idea is sound if I could get an engineer to tell me what spring rate, angle, and placement of the struts.
For me, this would only be a back up plan for if my axles broke or if I became very bored.

 

hmmmm has this actually been looked into? Prolly a dumb question but if it's not super difficult why not just do that?

 

I don't think the T-bird subframe will match the width of the Miata nor meet up with the Miata body mounts. Grab a tape measure and let us know how it looks.