That explains everything – ZERO suspension travel

[Christos Adam]

Hey guys, I don't know if I missing something but it's pretty obvious to me that if I reverse the mounts the whole weight will be suspended from 4 little bolts on each corner.

In the image below you can see the mount:


As you can see the spring rests where the green arrow shows and all the weight goes to the top of the shaft.

The top of the shaft is supported by a bearing - in my set up the bearing can not go up since the upper hole in the mount is too small to let it go through (see image below).



If I install the mount upside down the only support to the top half of the mount will be coming from the 4 little bolts that connect the two pieces of the mount and the mount will collapse at the red line (two images up).

Is this clear?


[off topic]Btw I just completed 12 hours of work today - things have been crazy at the office... time to go home and work on the car...[/off topic]

[Walter Wong]

Nice diagrams. I understand now. You're correct, you can't invert the mount or the four little bolts will eventually fail. Doh!!! I see that George had a much better understanding of the issues with the top mounts from the start. Kudos to George and others. You're options are: 1 - shorten the shocks, 2 - get new upper mounts. For the rears, I'd go with new upper mounts and you might consider shortening the shocks anyways to gain even more compression travel. For the fronts, you might be able to get away with just shorter shocks. If you get rear top mounts like the FM ones, you could imitate the function of the bearing with Hypercoil hydraulic perches. Ask Jason R about the hydraulic perches as he used to run them on his 240.

[Thomas Smith]

You're correct, you can't invert the mount or the four little bolts will eventually fail. Doh!!!

Based on what? What size are the bolts? If you replace them with a high quality bolt of known tensile strength I see no reason why flipping the perches shouldn't work. A 3/16" NAS bolt is good for 1800# in tension for example. That times 4 is way more capacity then you need. Take your time and do the engineering or find someone to do it for you.

They probably won't give you the travel you need however. I suggest talking to ISC as Jason suggested and see if their perch will work. I think they even custom build them to your specs for very little money.

[Walter Wong]

My comment about flipping the mounts is based on not replacing the current bolts. I don't doubt that you could replace the bolts.

[Marshall Grice]

I recommend you listen to Jeff Wong not all of us forum jockey's.

[Steve Ekstrand]

Jeff's da Man!

[Jonathan Lugod]

Jeff's da Man!

:gpower: :gpower: :gpower:

now send your shocks in too and get that car working!

[Bill Martin]

Reading through your posts it appears your total front travel is maybe 3.5", minus the amount of bumpstop you want to run. So what...maybe 2.5" of travel before hitting BS? And if you're lucky enough to be able to center your stroke, you'll have a little over an inch up and down? Is that something you really want to live with? The other methods with custom tophats would seem to give a serious percentage increase to your overall stroke, no?

[Marshall Grice]

The other methods with custom tophats would seem to give a serious percentage increase to your overall stroke, no?

the shock bodies are too long. Jeff already said he'd fix it. end of story, no?

[Bill Martin]

the shock bodies are too long. Jeff already said he'd fix it. end of story, no?

Not sure. You don't get more stroke by shortening the shock body...but you can center it up that way, which is a good thing. Maybe good enough. Even Jeff said it was only a little over two inches total travel to the bump stop. And you have to split that between bump and rebound. Shorter bump stops would give a little more travel, but I'm guessing he's going to need a lot of bump stop.

So Marshall, are you saying that plus/minus 1" travel or so is okay for a dual purpose car? I honestly don't know, but it seems slim to me. And since there are other options...Just sayin'

[Jeff Wong]

If I calculated the measurements right based on the pictures, Chris will have approximately .25" - .5" of wheel travel left before his wheel hits the frame rail without a bumpstop, the shock would need to be shortened 3/8" on the body to have his wheel contact the frame rail, assuming he had .5" of wheel travel left. When I originally talked with Chris I was unaware of how he was going to tune his shocks and I would agree the shocks are too long for how he wants to tune it. We are going to shorten the shocks based on what he wants and anything after that will be up to him and when he wants the bumpstop to contact, lets just hope he tunes it right so his tires don't get ruined. I will admit that our drawings are universal for the many classes/tire combination that it can be used for and to get something as precise as what Chris wants, we would have needed specific measurements from him. The shocks that I have on the civic, the shocks and upper control arm bottom out at the same time without a bumpstop, it took me hours of measuring/double checking the mounts, wheel travel and shock travel to get this right but then again, how I tune my shocks might not be how you or anyone would do it.

In the end, we are here to make the shocks right for how he wants it.

[Jeff Wong]

the shock bodies are too long. Jeff already said he'd fix it. end of story, no?

Not sure. You don't get more stroke by shortening the shock body...but you can center it up that way, which is a good thing. Maybe good enough. Even Jeff said it was only a little over two inches total travel to the bump stop. And you have to split that between bump and rebound. Shorter bump stops would give a little more travel, but I'm guessing he's going to need a lot of bump stop.

So Marshall, are you saying that plus/minus 1" travel or so is okay for a dual purpose car? I honestly don't know, but it seems slim to me. And since there are other options...Just sayin'

Based on where his car was sitting, he would have had less then 1.1 - 1.2" of compresion wheel travel at static ride height without the bumpstop (assuming he already preloaded the bumpstop some already).

[Dan Shaw]

Kinda random, but could loosening up the rebound help with the car load jacking? i.e. is the shock decompressing too slowly in daily commute to allow the correct level of travel?

[Jeff Wong]

Kinda random, but could loosening up the rebound help with the car load jacking? i.e. is the shock decompressing too slowly in daily commute to allow the correct level of travel?

In his case, no, he is worried about compression travel, he did not to cut the bumpstop down, so his car is low enough that he is riding on the 1.5" bumpstop majority of the time. The idea that Chris had was to have the shock shorter so the wheel would hit the frame plus more but he would add spacers to ultilize the 1.5" bumpstop to tune it. RX-8's stock use the bumpstop as a tuning tool but we are talking stock class. The bumpstop is to add additional spring rate without acutally changing the main spring.

[Dan Shaw]

Kinda random, but could loosening up the rebound help with the car load jacking? i.e. is the shock decompressing too slowly in daily commute to allow the correct level of travel?

In his case, no, he is worried about compression travel, he did not to cut the bumpstop down, so his car is low enough that he is riding on the 1.5" bumpstop majority of the time. The idea that Chris had was to have the shock shorter so the wheel would hit the frame plus more but he would add spacers to ultilize the 1.5" bumpstop to tune it. RX-8's stock use the bumpstop as a tuning tool but we are talking stock class. The bumpstop is to add additional spring rate without acutally changing the main spring.

Cool cool. Good thread, actually. Thanks for the insight. Lots of parameters to consider that I hadn't expected.

[Adam Richter]

It looks like those shock mounts just aren't very well suited for use on a miata. If you plan to keep them you'll need to have the shocks shortened as others have mentioned. Just make sure you still have a long enough stroke for the spring rates you're using. My mounts are fairly similar to yours upside down, except the load from the spring is going into the mount on my instead of the bearing.

[Christos Adam]

Thank you so much for all the helpful comments guys, I've been in communication with Jeff since day 1 and he is helping me to set the shocks right.

I did most of the measurements required and right now the situation is pretty straight forward for the fronts.

FRONT
Total shock travel = 85mm-> 123mm wheel travel
(basically measurement w/o spring but with the bumpstop (which at that point was fully compressed to 1/4" or less-)
Spring motion ratio for the front 0.69
Wheel to the body gap - 42mm on stock tires and 45 on race tires. 45mm-> 31mm shock/spring
(so basically the the fronts need to be shortened by 31mm~1 1/4")

That will give me at the height that I am
45mm compression
78mm drop

Rear
Total shock travel ~ 88mm-> 122mm wheel travel
Spring motion ratio for the rear 0.72
Wheel to body gap ~56mm -> 40 mm shock/spring

At the rear the miata has plenty of space until the wheel hits that frame and I'm a bit confused:

OPTION 1 - Utilize all the available wheel compression I can get (56mm)
Shortened the rear shocks by 40 mm
The problem with this option might be the shock size - which is pretty small at the rear and I'm not sure if
(i) they can shortened by 40mm
(ii) the reduced oil capacity might have ill effects

Anyways that will give me at the height that I am
56 mm compression
66 mm drop

OPTION 2 - Provide compression equal to the front wheels(45mm)
To do that the shocks will need to be shortened by 32mm

That will give me at the height that I am
45 mm compression
77 mm drop
Almost identical number with the fronts

Even though option 2 seems more balanced with same compression/drop at the front and the rear wheels, the real question though is what do I need the most?
For example if the 77 drop is too much and the 66mm drop is good enough it might be better to go with option 1 and get 56 compression/66 drop at the rear.

I'm also not sure if I should be mentioning 78mm drop for the fronts since that's not correct when the sway bar is connected - so in real life option 1 for the rear might be more balanced.

[Dan Shaw]

One thing to keep in mind is how the car was originally engineered. The stock shocks are shorter in the back from the factory which does fall in line with how your measurements come out. Might be worth taking a look into that. Gotta say Mazda did do some pretty good engineerig on the car OEM.