There are many 'characteristics' or driving impressions that one might place into the "Unstable at high speed" bucket.
You seem to have a solid grasp on primary influencers but maybe tuned into something thats not just at high speed, (i.e. chassis flex combined with under damped/old struts) but maybe just more noticeable @ SPEED with wind pushing you around. Or a combination of aero combined with a chassis flex characteristic, really hard to say.
What I am getting at is, the strut replacement should help, but it may be a combination of things to get the feel you are searching for. The combination could go past your list into tire flex (pressures are one component), chassis flex - probably want some underbody bracing so that other improvements will have maximum impact. (You didn't mention a hardtop, the MR2 may be relatively stiff for a conv, but it's still an open top car-so flexy.) Precise alignment (as you noted) can have big impact but so can road imperfections. Finally, the car is sort of darty.... sensitive at speed, it's light and wasn't built as a GT car. The folks that are on this site and drive often at high speed should chime in, many will have extra aero if high speed is their goal. 85 is usually faster than I drive for extended periods.

Good luck finding your settled feel, it may be a journey. (Following)

 

Thanks for all the comments.

Yes, I have hardtop and the following chassis reinforcements:

front strut bar, front under brace, breastplate, rear under braces and rear strut bar (stock).

Tires are Yokohama advan neova ad08rs.

Struts are the last on the "to do list" 🤷‍♂️

 

What model tires do you have?

 

yokohama advan neova ad08rs, on four corners, mounted at the same time...

 

When I first got the car I was surprised how floaty it was on the highway. I remember with my SW20 those little flaps under the car infront of the wheels made a huge difference.

On my spyder the TRD lip on my 2003 made a big difference, was actually very surprised how much of a difference that made on the highway.

Final big change for highway stability was my big ass GT wing lol.

Also removing spare tire did make it worse like you said.

 

Thank you so much for sharing your experience

I solved the floaty feeling in a 90% installing the front chin and front flaps.

What I still trying to solve is the erratic / unexpected lateral shaking when driving on high speed which becomes much worse on windy roads.

Honestly talking, I don't like at all how the TRD lips looks on the Spyder

 

It is really hard to put a feeling into numbers, but can you describe what you mean by "instability"?

I drive my 2001 pre-facelift MR-2 at high speeds many times and as luck would have it, I also ran Yokohama AD08R for a long time.
I actually hit the rev limiter once in 4th gear at 217 km/h.
But I never really felt is being unstable. I also drove a few laps on the Zandvoort track and Nürburgring track and it never felt unstable either.
I have also taken my NB Miata / MX-5 up to 200km/h a few times and that car felt much more sketchy at those speeds.
I am not sure if the pre-facelift 2001 already got the aerodynamic upgrades?

My front struts are pretty new, they are Sachs replacement dampers.
My rear dampers are the OEM KYB dampers which are 130.000 miles / 210.000 kilometers old.
The rear dampers need a replacement, but you only really feel that on the big bumps and dips. If you are familiar with the Nürburgring: that would be on compressions of Fuchsrorhe, Planzgarten and Stefan Bellof esses. So I do not expect your dampers to make a huge difference there.

Tyre pressure and toe are super important. I run only 1.8 bar in the front and 2.0 bar in the rear tyre.
I have the tiniest of toe in on both the front and the rear axle.
Do you have an alignment report of your car?

 

Thanks for the comments.

I define it as: erratic / unexpected lateral shaking when driving on high speed which becomes much worse on windy roads. I can feel it from 130km/h on straigh line and mid cornering.

Why are you running 2.0 bar on the rear? What's wrong with 2.2 bar? (factory recommendation).

Unfortunately I dont have any aligment report, I did it in a shop and I should have taken a picture

 

Just get the Flex Z and all of your issues with high speed stability will be solved. No need for any chins, splitters, wings or bandages, your problem is simple in that your OEM struts are gone.

 

I hope so, my faith is on Tein Flex Z lol. The wait to install them is taking forever for me as I want to wait until November to acquire them (Black Friday discounts = 200 bucks less)

 

IMO these cars are very bad aero wise above 90~ mph. I'd really love to see a good CFD and asked in a few various groups but was not able to get anything from the community.

I suspect the main issue (assuming top up obviously) is front air entering the area behind radiator and factory it is designed to exit under car the car (would be better if exited upward from hood), add in most people do not have/keep any rear undertrays and you are likely to have turbulent air underneath stacking up from the rear of the car forward interacting with the high pressure air exiting the front bay.

(Just speculation on my part would love someone more knowledgeable to bring actual data.)

Mine has gotten better with new suspension at high speeds but is still very sensitive to steering input, I plan to keep adjusting toe settings and see if can be improved.

I have some aero plans for mine but won't be for awhile.. Air dam, rear diffuser/floor (main goal being to cover engine bay and get air to flow smoother under car), small wing and hood vents.

 

Some people mention that this can be solved with hood vents (holes)... I have no idea.

Mine still preserves all the factory undertrays.

I think that steering input has to be treated as a different issue, perhaps it could be related too (alignment), but in my opinión it is more related due to having an excessively assisted steering system.

There are many different issues... can alignment solve all? Not in my opinion.

 

Thank you so much for sharing your experience

I solved the floaty feeling in a 90% installing the front chin and front flaps.

What I still

Struts are the last on the "to do list" 🤷‍♂️

My last comments. You have done much so don't leave doubt to the unknown. Get alignment rechecked, spend appropriately on struts, (not saying Tiens are a bad choice) and maybe the door latch shims.... Devs or TRD or similar (mine are China knock offs). I mention this because of your lateral shake comments.

Interesting thread

 

I agree... let's install the Teins plus new alignment and see what happen. I will keep you informed.

Hope that this thread reaches a happy ending and help more forum members

 

My '02 is stock ride height but chassis is braced and suspension is fresh, oem lip intact. Definitely floaty at 100+ mph, I believe due to aerodynamics making the front end even lighter, (I have experienced this on another car as well, my '74 Europa which also ran tall in US due to US bumper height laws).
At 50-80 mph my car is very stable (only after replacing worn out oem struts). Aerodynamics have much less effect at those speeds. Yet I would add my car feels darty because miniscule steering wheel input when driving straight, gives more lurch to that side than ideal. As @Labora said, I also plan to experiment with front toe. Maybe someone can mention here Toyota's front toe spec?
A law of physics says a MR2 Spyder, especially with spare removed, is going to change direction more in gusty crosswinds, compared to a car with more weight on front wheels, all else equal.

The good news is 99% of the time I'm not over 100 or in heavy crosswinds. If I was, I'd get a GT type car.

 

Maybe someone can mention here Toyota's front toe spec?

We moved from .15 deg toe in to .3 deg (still in tolerance) for a bit more straight-line stability

 

Get the Teins on and report back. I think you're going to find most if not all your problems go away.

Personally I don't like taking mine past 100mph for more than a few seconds, I don't feel that's what this car is about. I've been all the way across the country now... four times. Had plenty of time to feel this car out on the highway for extended periods of time. It lives its best life at 85mph and tears up mountain passes in 3rd and 4th gear without much need for brakes unless coming to a complete stop.

I've chased tornadoes across Kansas, plowed through crazy headwinds and skipped across puddles the size of small lakes. The precise control, positive traction in all conditions, and surprising off road capabilities of this car haven't ceased to amaze me. It literally takes everything I throw at it.

 

"off road" like fire trails/ Canadian stone packed roads? Perhaps a rally setup.

I Really liked rallying RWD Corollas in 80s.

 

Mine feels perfectly stable at 110+, about as fast as I've managed to get it on a track with stock power, but I'm curious about these flaps and the chin. When you say flaps, are they mud flaps or something else? The chin, I assume, is a sort of splitter for the front bumper?

Maybe this rubber flap?

OEM Front Spoiler, Part No. 7685117070 | MR2 SpyderChat https://share.google/GCaB75SerE87fzBYI

 

Maybe this rubber flap?

OEM Front Spoiler, Part No. 7685117070 | MR2 SpyderChat https://share.google/GCaB75SerE87fzBYI

That is the 'chin spoiler' being referenced. It wasn't on the early 2000 production cars.

FWIW I always have my spare tire in place in my 2001. The front end has never felt floaty at sustained high speeds (100 - 110mph). I've noticed this car is VERY sensitive to small changes such as alignment & tire pressure. Even a 2PSI difference between the front tires will impact driving straight vs slightly veering to one side IME.

If your suspension is causing the car to feel floaty due to movement, it's probably completely blown & you're riding on springs only.

 

What he said.

I use a digital tire gauge that measures in tenths of a pound. 27 front, 31 rear for the open road. Increase by 2 pounds if I'm spending the day in the mountains.

 

I use a digital tire gauge too. I always run with (or practically same) factory recommended preassures

 

Y'all make me feel old and slow. I couldn't tell you the last time I went over 90 mph in my car.

 

Lol, not gonna be making anyone happy driving under 90 on a race track. 😁 I've not been over 80 in it on a road, FWIW.

 

You can't slow down the pump electrically. It has to work within a specific range otherwise it will overheat.
This is why cars like BMW that have the handling package use an electric gear reduction to change the steering ratio so that the wheel tightens up and gives you feel.
The PS on our cars are way over boosted. Once you eliminate the pump or go the full way and convert it to a manual rack it is a night and day difference. The car feels rock solid and stable, gone is that twitchy front end and cheap filtered artificial steering feel. The same year Celica GTS that I have driven has a better steering feel than our car because it uses a mechanical PS pump.

 

You can't slow down the pump electrically. It has to work within a specific range otherwise it will overheat.
This is why cars like BMW that have the handling package use an electric gear reduction to change the steering ratio so that the wheel tightens up and gives you feel.
The PS on our cars are way over boosted. Once you eliminate the pump or go the full way and convert it to a manual rack it is a night and day difference. The car feels rock solid and stable, gone is that twitchy front end and cheap filtered artificial steering feel. The same year Celica GTS that I have driven has a better steering feel than our car because it uses a mechanical PS pump.

But since it works off of VSS signal could you not modify what signal it sees and have some adjustability to pressure modulation that way?

I'm speculating as I'm not sure how it "ramps" up/down in relation to speed, this seems to be why people where talking about a simple resistor. (Trick it into thinking you are going faster/slower?) I have some ideas how I could test it but need to get out my shop manuals and see how it is all wired up etc first..

Would be interested to hear if anyone has played with it any, other option could always be a different pump, pretty easy to get a Prius pump and several companies are already making variable controllers for those.

 

Let me describe my steering feel. Generally most adventurous drivers need to push their cars to feel it which is dangerous on the public roads. I drive to enjoy my car, not to be the fastest, in fact I would rather enjoy the car at a slower speed and get the same feeling.
With the PS pump out of the way and the lines looped I can go with force into a turn and feel the resistance from the wheel rather than a weird disconnected steering by wire sensation. It is hard to describe but you feel completely engaged like being one with the car but well below the limits of traction. The feedback you feel is not in your arms, it's in your brain especially when you are hyper focused. It's one of the modifications that is completely transformative giving the car a more old world European feel unlike that tin can Japanese refinement.

 

That's a pretty convincing argument. Although there's a principle that a chain is only as strong as it's weakest link, I should be fine compromising ease of parking for the greater good of why I'm driving the Spyder. So now my list of things to do on my car is growing, but should finally start getting knocked out now that summer's heat has dissipated from my garage. Maf mod, recover steering wheel, loop power steering lines. BTW, what fitting or adapter do I need to loop the steering lines?

 

Before replacing my struts and other major suspension parts, my car was unstable over 100 mph. After installing stock struts and other components, the car is more planted up to 110. Bumps at high speeds don't scare me anymore. I do have strut tower braces on the front and rear and bracing underneath the car. My extra 15 lbs also helps!

 

How is on windy roads?

 

It'll be next year before I can test the stuff on track to see how it helps, but I printed the side airflow directors in PETG-CF and got the center lip to try since it was pretty cheap from Toyota.

Have to get this lump sorted before I can put it on through. 😅

 

Side airflow directors?

 

Here's my high speed story: It was spring of 2008 and my aunt had passed and I was headed for her memorial service at the cemetery in Central Oregon near Bend. I had lived in that area for several years and thought I knew it well but I somehow managed to take a wrong turn. The landscape there is very similar: all flat sagebrush and juniper trees. At some point I realized my mistake and that I was headed in a completely wrong direction. I was driving my 2005 Spyder with the top down and I think I still had the OEM tires. After I got myself turned around it was pedal to the metal as the time was getting short. I know I passed 100 mph by a ways but I never saw my top speed. I was too busy watching for coyotes and antelope which are numerous in that area. It was exhilarating to say the least with the top down but I recall that the car was completely steady. I compared it to my 1969 BMW 1600 which I drove for hours on end in Montana at 90 mph (no daytime speed limit in the earl 70's).

 

Not sure if you fixed the issue or not, but I had a lot of the same issues with my 2003 and double checked alignment, all suspension nuts and bolts, and only fixed the issue by switching back to OEM wheels and OEM lug nuts.

I had been using Sparco FF1's and tuner lugnuts with extended threads but the tuner lugnuts just never seemed to clamp down as well as the OEM shank style on OEM wheels. All the highway shimmy and floaties went away with OEM wheels and lug nuts, which is a shame because the Sparcos are so lightweight.

I considered trying out extended ARP studs but decided it wasn't worth the hassle.

 

Not sure if you fixed the issue or not, but I had a lot of the same issues with my 2003 and double checked alignment, all suspension nuts and bolts, and only fixed the issue by switching back to OEM wheels and OEM lug nuts.

I had been using Sparco FF1's and tuner lugnuts with extended threads but the tuner lugnuts just never seemed to clamp down as well as the OEM shank style on OEM wheels. All the highway shimmy and floaties went away with OEM wheels and lug nuts, which is a shame because the Sparcos are so lightweight.

I considered trying out extended ARP studs but decided it wasn't worth the hassle.

Not fixed yet (pending to change the struts).

As mentioned in my first post:

I run oem wheels using Yokohama advan neova ad08rs (installed at the same time) with factory tire measures (185/55/R15 front and 205/50/R15 rear)