ProfessorMetal
ProfessorMetal None
4/5/12 3:11 a.m.

Hi, All

I recently purchased a '95 MX-5 from a friend's stepdaughter. Her fiance 360'd into a bush but the only detectable evidence is some very minor crinkles in the passenger panels. My quandry is this: I had to have some work done on it(replaced the rear rotors, brake stuff etc.) and all seemed well.

The problem is this now and it doesn't make sense to me(I'm not inexperienced when it comes to performance machines). The steering seemed sluggish and a bit stiff so I immediately suspected tire pressures as being a potential culprit.

I checked the the pressures and they were a bit low according to specs. All four tires ran from 18 - 20 psi when the specs called for(according to Mazda specs the optimal is 26 psi). At the off-spec pressures the driveability was good. When I increased the pressures to spec, the thing nearly beat my teeth out of my mouth at freeway speeds(65-70 mph). The front end vibrated like a - well, I leave that up to your imagination. Up to that speed the driveability was excellent after increasing the pressures.

I checked the tires over - did a visual inspection as well as running my hands over the tires to see if there were blisters or other abnormalities and found nothing. The wheels aren't bent - they're not even nicked, and I also did a visual inspection of the fronts to see if there was any obvious misalignment. Again, negative.

The whole situation is totally funky. I'm running Kumho 185/60 R14 82T's. I don't know how long they've been on the car or if that would even be a factor. I do know that the car had been sitting for about 5 months before I bought it. Maybe there's some dry rot or flat spot issues because of that. I don't know. If anybody has any ideas or advice, I'd greatly appreciate it.

Oh, and glad to be here,

Jeff

petegossett
petegossett UltraDork
4/5/12 5:17 a.m.

Welcome Jeff!

Miata are notorious for 60-65mph shakes. A re-balance of the tires might help, might not. Sometimes the tires need replaced to cure it, sometimes it takes a different set of wheels. Some cars just seem to be more sensitive to slight imbalances than others.

My advice? Make the 50-70 sprint as quickly as possible.

914Driver
914Driver MegaDork
4/5/12 5:50 a.m.

Welcome! Have the tires rebalanced, a weight could have been knocked off in the 360 bush.

Dan

jstein77
jstein77 Dork
4/5/12 7:16 a.m.

Also try switching the tires front to rear and see if the problem follows the tires or stays in the front end. That should help narrow things down.

DrBoost
DrBoost UberDork
4/5/12 7:52 a.m.

These three posts really hit it on the head. I just wanted to say you'll fit in here quite nicely. You already have a miata (there are posting restrictions on here for those not 'in the fold') and you did all the intelligent things before looking for help.
I

iceracer
iceracer SuperDork
4/5/12 8:29 a.m.

Was there anything in the "bush" that might have bent a wheel ? Just something else to check.

Dashpot
Dashpot Reader
4/5/12 8:35 a.m.

Welcome!

Try to find a shop with a road force balancing machine so you can eliminate that variable. That machine will measure tread & rim runout as well, so you'll know if something's way out of wack.

Pulled my '01 out of 4 month storage and had the same experience as you. The tires had "gone square" despite sitting in a nice heated space @ 40 PSI. They did work themselves back into shape over the the next few miles.

curtis73
curtis73 SuperDork
4/5/12 8:46 a.m.

I would also check the suspension bushings. The strong lateral forces that were put on them during the 360 (and any bushes that may have added to it) could have ripped or damaged a suspension bushing. If that's the case, a small vibration can become a huge vibration. The damping that was there before with a good bushing is now not damped by the damaged bushing.

AND WELCOME TO THE FORUM! We're kind of a big deal.

curtis73
curtis73 SuperDork
4/5/12 8:50 a.m.
DrBoost wrote: You already have a miata (there are posting restrictions on here for those not 'in the fold')

Tell me about it... I have a van and a bunch of classic american iron, and all these folks tease me about is my hair. (they're just jealous)

N Sperlo
N Sperlo UberDork
4/5/12 9:47 a.m.
curtis73 wrote:
DrBoost wrote: You already have a miata (there are posting restrictions on here for those not 'in the fold')

Tell me about it... I have a van and a bunch of classic american iron, and all these folks tease me about is my hair. (they're just jealous)

How's it taste? Btw, the last picture i saw, I believe it was quitea bit shorter.

Btw, welcome new guy. Just stepped in to threadjack.

curtis73
curtis73 SuperDork
4/5/12 10:45 a.m.
N Sperlo wrote: the last picture i saw, I believe it was quitea bit shorter.

I've really been letting myself go

I guess (back to the topic) I'm interested to see what the bushings look like.

Cone_Junky
Cone_Junky Dork
4/5/12 11:05 a.m.

Four flat-spotted tires from the spin. Would definitely be more noticeable with inflated tires.

mtn
mtn PowerDork
4/5/12 3:43 p.m.

Does 26 sound pretty low for daily driving to anyone else?

Apexcarver
Apexcarver UberDork
4/5/12 4:05 p.m.

I run 30ish on mine (205 RE11's) and 35ish on my snowtires (175's very narrow and probably on the high side)

That said, I could get away with pressures that low as far as wear on the A-X course, it was just slow. (30-32 is where it lives for A-X)

92CelicaHalfTrac
92CelicaHalfTrac MegaDork
4/5/12 4:07 p.m.
mtn wrote: Does 26 sound pretty low for daily driving to anyone else?

Yes, especially depending what kind of tires.

iceracer
iceracer SuperDork
4/5/12 5:29 p.m.

what pressure does Maxda reccomend ?

DeadSkunk
DeadSkunk Dork
4/5/12 6:24 p.m.

I run mine at 26 with no issues. That's what's recommended.

mtn
mtn PowerDork
4/5/12 6:29 p.m.
iceracer wrote: what pressure does Maxda reccomend ?

Are they OEM tires? If not, why would it matter what Mazda recommends? I've always gone by what the tire manufacturer runs, and if I am not mistaken, that is what the owners manual says to do as well.

Apexcarver
Apexcarver UberDork
4/5/12 6:40 p.m.

Meh, if mine are a touch overinflated I will see how they wear. If they wear alright, higher pressure = better fuel economy.

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