Yeah, I ended up getting this size because even on sites like Bofi racing, they sell them stating they are suitable for the NB with some light modification. It made sense to me that wider wheels would be a good idea now I’ve got that extra power
MattD like one of the earlier comments tyre pressure is massive when putting different wheels on a car or obviously on standard wheels I have to say in my experience of modifying cars placing wider wheels on a car or even on stretched tyres handling is better.
I find tyre pressures have a massive impact on the whole drive of a car from handling to even fuel consumption.
To me it sounds or appears your tyre pressures are too high. Especially as you drove as normal and nearly had a moment on the new wheel tyre set up.
I’ve experienced this myself where I have not checked the tyre pressure especially after a garage has fitted them as you normally expect a garage to know the correct pressures.
Be interesting to hear what the issue is.
Thanks Jeff. I’ll make sure to update the post when I get home in a couple of days 
Yes, but most of the new tyres I have had fitted are inflated to fully loaded pressures. That can be 5-6 psi too high.
I once inherited a 6-month-old Scirocco company car with a rock hard ride and bald tyres that were inflated to something like 62 psi all round. I do remember that it was the maximum inflated pressure indicated on the tyre wall.
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The reality is that, while most owners, obviously, want their tyres spot on pressure, in any form of busy tyre bay, especially the local independent that is cheaper than the rest, there is no time to know what the pressures are. You might well know what a common car like a Fiesta is because you see 10 a week, but the variance between a Fiat Dobblo van, a Range Rover Evoke and Honda Insight are vast. The tyre pressure labels are hidden all over the place and some cars don’t even have them. By the time you have got the keys from the customer, got it on a lift, found the hidden wheel nut key and got the wheels off, you are looking a easily 45 minutes if not an hour, even if everything goes without a problem. And there are plenty of problems on cars. When you have got two other customers waiting behind all getting upset because they don’t want to have to wait two hours then the time taken to blead air out of a tyre, through the valve is time you don’t have. And modern cars with ever increasing tyre size have increasingly large tyres which hold greater volumes of air and so take longer to inflate and deflate. Bleeding air through a TPM valve is yet another delay. It just does not get done, especially since most people buy tyres on price not on service. I doubt the guy even knew what pressures they were aiming for and I expect from what you say your pressures are going to be around 40psi
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The lesson I learnt many years ago which MattD will now is tell the fitter what tyre pressure you require.
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So, just checked the pressures and all tyres are good. 26psi from the garage
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Wheels are wrong offset. Tyres are too narrow for the wheels.
The wheel offset, by increasing the leverage on it, has probably highlighted the fact that your suspension, including the rubber bushes, is at least 17 years old. Rubber deteriorates with age.
Ok, I wish I had seen this earlier. There is a problem with this thread:
- You have not told us the full picture of why you want to change your tires/suspension and perhaps more importantly how/where you intend to drive the car once modified.
- The topic of suspension tires/wheels/offset/suspension is extremely rich/complex (and the mx5 allows for full suspension alignment, which increase the dimensionality further)
- (similar to 1) ) You have not provided full boundary/constraints information, such as do you still want the tires to last longer than 6 months? what is your budget range? What is your hierarchy of priorities in terms looks, handling, price, etc.
- Your own level of driving experience AND of driving knowledge AND of mechanical understanding (e.g. the word “understeer” can mean many different things to many people in the context of what you are trying to do)
This makes it very hard, if not impossible to make fully informed and safe recommendations.
In addition, this is the type of topic where it is easy to fool yourself in thinking that you know/understand more than you actually do, because it is a high-dimensionality problem: too many cases to just rely on trial and error, and not many ways to anticipate the result of a change/mods without installing it on the car.
For instance, some setups might appear to be safe/stable up to 50 mph and then become lethal above 65 mph (hence for instance why most rear-steer systems are speed dependent) and so testing your problematic setup in the manner that you have doesn’t even give you the full picture; you might solve the issues identified at low speed only for worse issues to crop at around 70mph, and only on certain road cambers, except that by then you will be going very fast, making the whole things very unsafe.
In fact, I know someone who had a serious accident for that exact reason: car was fine in almost conditions, except on slightly wet roads with rapidly changing cambers. The driver (who was relatively new to the car) didn’t anticipate the issue and once the issue manifested itself, the car electronics jerked the car sideways, the driver instinctively tried to fight the car electronics…and the car was totalled in a ditch with their passenger requiring spinal rehabilitation afterwards.
That is why others have simply asked you to go speak to a specialist.
But I am telling the same thing for a different reason:
You are asking about a non-standard setup and I am currently using a non-standard chassis/suspension/tires setup on my NC. So in a sense, we are similar.
Except that I know that my setup switches from lazy understeer to strong oversteer at the first sign of rain (even with v.good tires), but that’s how I like it and I have the discipline to slow down (a lot) or to avoid driving the car when it rains. Plus, oversteer is actually my natural car behaviour preference (which is very rare).
For that reason, I would never ask setup questions for my car on a forum. Instead I would go to a specialist, who could test drive the car, diagnose any potential suspension/chassis/tires fault, observe my driving style, and then make fully informed recommendations.
Similarly, because I don’t know ALL the quirks of your situation (including not having test-driven your car), I might inadvertently influence you to end with a setup with a non-linear behaviour like mine, even with the best of intentions, and that could put your life at risk.
So please, work more if you need to, sell a kidney if you have to, etc, but for the love of god, spend the money and go see a specialist.
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Thanks for the replies everyone. I fitted the coilovers yesterday and discovered what I think was the problem. One of the front drop links was knackered, the bushings on the control arms have about had it and the rebound on the old rear dampers wasn’t up to much either. I don’t know if the new wheels and tyres highlighted these problems more, or if it was the drop link just giving up on that drive. The other one looks quite new but it’s not something I’ve replaced, or had replaced. I’m sorting the link out tomorrow and then it’s booked in for a wheel alignment. I’ll have to save up for a set of bushings and sort that in the new year.
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Be sure to notify your alignment specialist of the worn bushings.
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