Unstable car over 70mph

[nm36.hw]

Hi All,

I recently got an MG M4 SE Long Range (66kw), which I have used predominantly for very short trips at low speed and I have been generally quite happy with it.

However, over Easter, I went for a road trip in the countryside, and I noticed the car felt quite unstable every time I was going faster than 70mph. The feeling was the same as when there is strong wind, with the car moving left and right randomly... the problem is there was absolutely no wind.
My previous car was an Alfa Romeo Giulietta, which is a similar size, and I never felt this unless with strong wind.

For additional context, we were 4 in the car, with a couple of bags in the trunk. Tires pressure was 2.5bar on the front wheels and 2.6 on the rear ones.

Any clue on potential reasons? or is this normal for a car like this one?

[nm36.hw]

Hi All,

I recently got an MG M4 SE Long Range (66kw), which I have used predominantly for very short trips at low speed and I have been generally quite happy with it.

However, over Easter, I went for a road trip in the countryside, and I noticed the car felt quite unstable every time I was going faster than 70mph. The feeling was the same as when there is strong wind, with the car moving left and right randomly... the problem is there was absolutely no wind.
My previous car was an Alfa Romeo Giulietta, which is a similar size, and I never felt this unless with strong wind.

For additional context, we were 4 in the car, with a couple of bags in the trunk. Tires pressure was 2.5bar on the front wheels and 2.6 on the rear ones.

Any clue on potential reasons? or is this normal for a car like this one?

[Caddyshack]

Does the car have any form of torque vectoring with the motors? I wonder if something is out of sync.

[nm36.hw]

no clue actually - how can I check?

[TheDeuce]

nm36.hw said:

Hi All,

I recently got an MG M4 SE Long Range (66kw), which I have used predominantly for very short trips at low speed and I have been generally quite happy with it.

However, over Easter, I went for a road trip in the countryside, and I noticed the car felt quite unstable every time I was going faster than 70mph. The feeling was the same as when there is strong wind, with the car moving left and right randomly... the problem is there was absolutely no wind.
My previous car was an Alfa Romeo Giulietta, which is a similar size, and I never felt this unless with strong wind.

For additional context, we were 4 in the car, with a couple of bags in the trunk. Tires pressure was 2.5bar on the front wheels and 2.6 on the rear ones.

Any clue on potential reasons? or is this normal for a car like this one?

I suppose it's possible that what you're sensing is just a result of heavier car then you're used too... But if you're actually having to correctively steer to keep the car straight and in the centre of the lane, I would say that needs looking at asap. A damaged bush or suspension element could be the cause.

It's definitely not 'normal'.

[FarmyardPants]

Make sure there are no "lane assist" features enabled, these are sometimes on by default.

[Caddyshack]

I just googled it and it says it does have it.

I think it’s worth googling to see if any other people have had that issue and speak to a dealer

[Caddyshack]

Have a read on here:

https://www.mgevs.com/forums/mg4-ev-forum.38/

[GT9]

Was the wandering like having somebody else turning the steering in your hands or just the car moving off line?
Lane assist feel like someone else is steering the car, are you familiar with that feature?

[vetrof]

Tyre pressures seem a bit low for a loaded up car.

[FMOB]

I would suggest checking the basics, are the tyre pressures correct, could the wheel alignment be out, etc before delving into the world of electronics..

[Pica-Pica]

FarmyardPants said:

Make sure there are no "lane assist" features enabled, these are sometimes on by default.

They are ALWAYS on by default. A mandatory requirement since 2022.

[WilliamWoollard]

Yes, check tyre pressures. I had the same on a car I'd just purchased, drove fine until at motorway speeds then it was wondering all over the place, stopped and topped up the pressures and it was like a different car.

[Wilmslowboy]

Wheel bolts all torqued up ?

[FMOB]

A quick Google showed the fully laden tyre pressures for the EV 4 are 38 and 42 psi front and rear respectively, your 2.5/2.6 bar (35 and 36.4 psi) is a little low, some vehicles can be very sensitive to tyre pressures.

[Cobnapint]

I think this might be a result of the design of the EPS system. They're not as gradual as hydraulic systems are and the issue doesn't show up until the car is travelling at speed. My missus's Fiesta does it a little bit. They're a bit on/off.
You feel like you're having to correct all the time as the car takes a zigzag course down the carriageway.

[samoht]

FMOB said:

A quick Google showed the fully laden tyre pressures for the EV 4 are 38 and 42 psi front and rear respectively, your 2.5/2.6 bar (35 and 36.4 psi) is a little low, some vehicles can be very sensitive to tyre pressures.

+1

Specifically, it's the recommendation to have the rear tyres ~10% higher pressure than the fronts which I think would provide the missing stability.

Relevant factors:
- the MG4 has roughly 50/50 weight distribution, whereas most normal petrol family cars like the Alfa are front heavy
- you had rear passengers and luggage in the car, adding more weight to the rear axle
- lateral (yaw) instability increases with speed

the higher rear tyre pressures mean that for a given sideways deviation, the front tyres will 'give' more than the rears, pointing the car into the deviation and killing it. Without that (ie with similar pressures), the rear tyres can give more than the fronts (as they have more weight on them), amplifying the yaw instability to the point you have to consciously correct with the steering.

With mid or rear engined cars you will see they actually have wider tyres on the rear wheels than the fronts to provide this extra lateral 'stiffness' and hence stability, since the MG4 is about 50/50 and it's simpler to just have one kind of tyre, so they do it with the tyre pressures I think.

[nm36.hw]

Thanks all - very helpful!

I don't think it's the lane assistance as when that kicks in, it beeps and turns the car (quite abruptly) back to the centre of the lane.

Instead, this feels exactly as when there is wind and the car gets "light" and starts to zig-zag. It only happens at speed (e.g. above 65-70 mph). I also had a few instances of aquaplaning/hydroplaning during the weekend, which seemed excessive for the amount of water on the ground.. and I am wondering if that could be also related.

Can it really be the tyre pressure? I agree 2.5/2.6 might be slightly low when the car is fully loaded but still within the range.. With my previous cars I never adjusted the pressure that often (definitely not if I was driving alone or with other 3 people)..

Thanks again!!

[Caddyshack]

Try doing the same driving but without passengers.

Easy enough to experiment with the tyre pressures

[740EVTORQUES]

samoht said:

FMOB said:

A quick Google showed the fully laden tyre pressures for the EV 4 are 38 and 42 psi front and rear respectively, your 2.5/2.6 bar (35 and 36.4 psi) is a little low, some vehicles can be very sensitive to tyre pressures.

+1

Specifically, it's the recommendation to have the rear tyres ~10% higher pressure than the fronts which I think would provide the missing stability.

Relevant factors:
- the MG4 has roughly 50/50 weight distribution, whereas most normal petrol family cars like the Alfa are front heavy
- you had rear passengers and luggage in the car, adding more weight to the rear axle
- lateral (yaw) instability increases with speed

the higher rear tyre pressures mean that for a given sideways deviation, the front tyres will 'give' more than the rears, pointing the car into the deviation and killing it. Without that (ie with similar pressures), the rear tyres can give more than the fronts (as they have more weight on them), amplifying the yaw instability to the point you have to consciously correct with the steering.

With mid or rear engined cars you will see they actually have wider tyres on the rear wheels than the fronts to provide this extra lateral 'stiffness' and hence stability, since the MG4 is about 50/50 and it's simpler to just have one kind of tyre, so they do it with the tyre pressures I think.

That's really useful info. My EV has recommended tyre pressure of 34 front, 39 rear I'm sure for the same reason. It feels very stable, but I bet if you increased the front pressures to near to the rear it would suffer from the same effect, really interesting to understand why. (same size tyres all round, 49:51 weight distribution)

I bet more EV's have this issue with more of the weight in the centre from the battery and a 50:50 weight balance, and I'd also bet that a lot of people will naturally just inflate all four tyres to the same pressure as is often the case with ICE vehicles. My wife's Mini actually has higher recommended front than rear pressures by contrast due to the weight of the engine 62:38 weight distribution.

Edited by 740EVTORQUES on Wednesday 3rd April 09:55