Wishbone suspension analysis program by MCdermott

[junior]

Problem solved. Its all good!

[chetcpo]

Yup, for any other Miata spindle users faced with this quandry, just get the distance from your lower balljoint center to the chassis centerline to 26.3" and your front track will match your rear.

[dhempy]

Uh, yeah. I have 0.007" over 2" of bump and 0.020" over 2" of droop. And my numbers are kinda lousy because I am not shortening the Miata rack for my +4. I'd say the very most you could deal with would be 0.1" at 2" droop, and half of that at 2" bump. Even then it's probably going to be palpable.

I've got my rack apart now, ready for chopping. That won't happen for a week or two (AT LEAST) until I have the suspension designed.

But I've got to say, shortening the rack and lengthening the tie rods is a bit intimidating. I'm very interested in your design, Auto-X Fil. Could you post your dimensions? Better yet, how about attaching your .WSH file to a post? I'd be very interested in a design that didn't require cutting the rack, but had good bump steer qualities.


-dave

[dhempy]

The way Mazda does it (and I do also on my own Miata-based cars) is put the front pickup point for the lower control arm behind the steering rack, and make the rack the same width as the pickup points, and the tie rods at right angles to the direction of travel (that is, the tie rods are parallel to each other when viewed from above). Zero bump steer when going straight, minimal bump steer when bumping and turning.

Can you post some photos of this, Jack? Have you run the numbers through Wishbone?

-dave

[chetcpo]

The only way to achieve no bump steer is to shorten the length of your A arms to that of the stock Miata. I took nearly 6" out of my rack and I would've liked to have taken more, but that's all I could get without cutting into that big ol steel slug that goes in the end of the Miata housing.

What Jack and Mazda did was move the front lower suspension pickup back behind the steering rack. Imagine you are looking from above at the rack in place between the two uprights. Now imagine putting the front lower suspension pickup just behind the steering rack and the rear lower further back.

[bluej]

good morning fellow locosters.

does anyone have a complete set of measurements of a miata's suspension? i've done a bit of searching to no avail but it seems highly unlikely that this info isn't allready out there floating around somewhere.

[chetcpo]

good morning fellow locosters.

does anyone have a complete set of measurements of a miata's suspension? i've done a bit of searching to no avail but it seems highly unlikely that this info isn't allready out there floating around somewhere.

http://www.locostusa.com/forums/viewtopic.php?t=1409

[bluej]

good morning fellow locosters.

does anyone have a complete set of measurements of a miata's suspension? i've done a bit of searching to no avail but it seems highly unlikely that this info isn't allready out there floating around somewhere.

http://www.locostusa.com/forums/viewtopic.php?t=1409

thank you VERY much! that's exactly what i was hoping for! quick to the batsolidworks! (ok, that was a stretch.)

[Blackbird]

Yup, for any other Miata spindle users faced with this quandry, just get the distance from your lower balljoint center to the chassis centerline to 26.3" and your front track will match your rear.

I'm a little confused.
As I've read your message I was thinking to myself "wouldn't you want to have a wider front track than rear?", so I decided to check what Mazda did and found the specs of the 95 miata online -

FR track 1407 mm
RR track 1427 mm

And also the 99 miata -

FR track - 1405 mm
RR track 1430 mm

Hmmm

Moti

[chetcpo]

Yup, for any other Miata spindle users faced with this quandry, just get the distance from your lower balljoint center to the chassis centerline to 26.3" and your front track will match your rear.

I'm a little confused.
As I've read your message I was thinking to myself "wouldn't you want to have a wider front track than rear?", so I decided to check what Mazda did and found the specs of the 95 miata online -

FR track 1407 mm
RR track 1427 mm

And also the 99 miata -

FR track - 1405 mm
RR track 1430 mm

Hmmm

Moti

I think that it's pretty commonplace for people to have a wider front track than rear. Isn't the caterham csr 2" wider up front? I said what I did because many people want their front track to match the rear for aesthetics.

[chetcpo]

I edited the first post and added some pics to try and better explain how to use this program.

[davew]

If you Look at most track dims the front is almost narrower the the rear.

Most vehicle have a shorter front track, The shorter width front track leads to understeer which the auto makers design in to make it safer for the average Joe. But I guess an average Joe does not buy a sport car??

2nd Changing the front suspension geometry just so you do not have to shorten a steering rack would seem to require a lot more effect then the 2 or 3 hours to cut the rack and the $30 bucks to machine it.

Make the geometry right and mod the rack Dave.

[Pollux]

I don't know if it's flammable... but here it goes... Does anybody know a Mac (or cross-platform, say Java) suspension analysis program for us non-windows types? I haven't had a windows partition for ages!

Thank!

-S.

[RandyBMC]

I'm really trying hard to get this to work, but I have to admit I'm pretty incompetent with DOS stuff.

I have it downloaded, and when I open it, I don't know how to start a file - I tried putting in example file, but it says it is invalid. What am I doing wrong?

Thanks,
Randy

[RandyBMC]

Disregard - I figured it out. You don't want the extension, just EXAMPLE, nothing after that.

Once you do that, you can save the file under a new name and recall several set ups. The whole program is pretty cool.

Hope that helps,
Randy