Pulls Right on Acceleration and Left on Deceleration

When I accelerate my 1999 NB is pulling to the right, when I lift my foot it pulls to the left.
When breaking there is on obvious pull one way or the next.

If I center the car on a flat straight road it drives true. Accelerate and it pulls right, foot off and it pulls to the left.
Straighten up and it again drives straight.

I found some useful information on another MX5 forum (from 8 years ago) but think it worth asking here for suggestions on what to check.
The other forum gave lots of suggestions but nothing conclusive and no closure by the original poster.

As far as I know the rear tires are of the same age and I recently checked the pressure and added air.

Thanks
Nathan

My 2011 Mk3.5 did exactly as you describe. Tried tyre pressures, laser alignment all to no avail. It did seem to be worse after my OH very lightly damaged a rear tyre and I purchased a new one of the same make ( Bridgestone Potenza ) but made in a different country.

Four new same brand(Khumo)tyres fixed the problem. Now it is back to it’s former self and a pleasure to drive.

Do you have uni directional tyres fitted? I have Toyos fitted which are.
If so are they rotating in the correct direction? Ie have lefts and rights been swapped.
Good luck

I would start with wheel alignment and checking the if the tyres are directional if they are on the right sides.

Mine did the same and it was just air pressure was different on the fronts.

When first acquired, my Mk1 had 3 different brand budget tyres, and a Hankook.

It behaved similarly to OP’s car.

4 new Uniroyal Rainexperts later, it behaves fine.

I had a similar problem on a Fiesta many years ago.  Although both front tyres were the same make and type the car pulled one way on acceleration.  The problem went away when the front tyres were replaced.  Maybe you could try swapping wheels front to rear to see if the problem persists.  It could help identify if it is a suspension or tyre problem.  

JS

There is a phenomenon known as ‘torque steering’, and is common (one could almost say ‘normal’ !) on front-wheel-drive cars, caused by the action of the power from the engine through the drive shafts affecting the steering.  However, I have never experienced this on a car with rear-wheel-drive such as an MX-5 - curious !

 

Thanks all. I hope it is as simple at tire pressure/issues! I’ll check again there first. Still interested in any other replies/ideas.
The car has recently new rear tires, of the same make. Fronts are likely near the legal limit however and not the same as the rear. Moving the wheels around to see if the direction of the pull changes sounds like a good and easy check.

Torque steering is common on FWD absolutely but should not affect RWD cars the same way.
Some details here (was one of the first things I looked up as, like you, I was not sure about this on RWD cars).
https://en.wikipedia.org/wiki/Torque_steering

Does it have a limited slip diff? If so, wear in this can cause this as the drive can be different to each wheel.

Other than that I have know for tread to be separating from the carcass causing the issue.  

First thing, swap the front tyres to the rear to check if it is the car or tyre. 

Somewhat good news considering the alternative; I likely have a puncher.
The driver rear right was 7 PSI down, only checked 10 days ago.
Once all set to 26 PSI the car drives as would be expected.
Amazed at how much impact this had on the driving; is this due to it being RWD or being so light?

Anyway, thanks all for the advice.

Nathan

Had the same situation with a 2 litre Mk 3.5. Had the Mismatched o/s rear replaced with a matching tyre. Alignment done and its now pleasure to drive. Previously wanted to move to the right on acceleration.

Cheers

Keith