17\" Wheels - jumpy ride

[bark]

Hi All,

I recently purchased some 17\" wheels, charcoal grey with a nice polished lip. Since installing them I have not liked the ride, as the car feels to be jumping over bumps rather than riding over them. Tyre pressure was 40 but I have recently lowered them down to 35, which has made a difference.

What other changes can or should I make to the car to get a better ride?

[Gilly71]

The extra weight in the wheel and tyre combo may well be upsetting your damper rates. The standard MX5 wheels were quite light, so aftermarket upgrades are often quite heavy unless you know what your looking for.

The lower profile tends to increase harshness as well. Your only option to improve things if you intend to hold on to these wheels is to upgade the springs and get adjustable dampers such as the Koni yellows. The extra spring rate and adjustable rebound can help you dial in the new wheels.

If you have the money and intended to upgrade anyway, you could always go for tein SS or bilstein PSS-9 setups.

I would weight your wheels just to know what you are working with if they are anymore than 7-8 kg rim only or about 12-13 kg all up? You may need to consider searching for alternative wheels.

If you post the type of rim, there are a number wheel weights lists that might be able to identify your rim only weight.

[roddclarke]

What modle MX do oyu have?? i have 17\" on mine, and yes it is a lot harsher than the standard 16\"
i run my tyres at 36PSI .. but if you go to about 32-34 it will be a lot softer ride... but i like the feel and handleing at 36..

allso i have PSS9's on mine and that did change the way it felt..

[bark]

I have a 89 MX5 (import). The wheels are Osaka brand and from memory they were heavier than the standard wheels. I will try to weigh one tomorrow.

I do intend to hold onto the wheels. Anyone know where I can source cheap koni yellows from? What sort of springs should I be looking for? If I change the springs and shocks will this most likely cure my problem?

I will try to post a pic of the rims later today.

[Gilly71]

It will definitely help to add higher spring rates and adjustable shocks. The standard combo is koni and king springs, but I'm thinking (see my other thread) there there are probably better combinations out there..

The other thing you can do is replace your brake rotors with some higher spec lightweight DBAs, since it's all sprung weight it will at least offset some of the weight you have added. You can alos get lightweight alloy wheel nuts.

[JBT]

I have a 89 MX5 (import).

The car (NA) was never designed around 17" wheels and 40/45 series tyres. It's any one's guess what appropriate spring/damper combination would suit.

[bark]

An update...

I ended up purchasing some D2 street adjustable suspension from NZ - however they never arrived as NZ Post lost them!!! So now I begin the fun task of being reimbursed for their stuff up...

On a better note, I ended up purchasing some HKS Hipermax 2 suspension from Forced Fives (thanks) and have just finished installing them and WOW what a difference they have made. I feel much more comfortable in the car and the steering feels much more direct. The ride quality is absolutely superb.

So thanks to everyone who posted a reply above, I am really happy that I invested in some suspension. Next up will be beefing up the brakes...

[zoomzoom]

When I was looking at adjustable shocks I couldnt go past kyb. At the time I was looking at getting koni, but Boags put me onto these. For half the price it made the choice easy. They feel great but the only drawback is they are noisyer than std and many others, which doesn't bother me at all, but that may be a personal thing.

[kev.yan]

what size tyres are you running on the Osaka Rims?

[MasterZ]

i have 17's on my car and i don't think its bumpy at all

[bark]

I am running 205/40/17 on the Osaka rims. Tyre pressure was 40 psi when fitted but I reduced this down to 35 psi.

[kev.yan]

I advise you to check with your local RTA as the tyres you are running are approx 17mm over th original diametre fitted to your car and if it were here in Queensland your car would be un-roadworthy and technically un-insured. This is a common size for tyre shops to fit, but is illegal in most states. Many tyre shops don't do their home work on rolling diametre's and load ratings and end up fitting illegal either under loadrated or over diametre tyres on the un-suspecting customers car. I come across it daily at my shop.
The rules here in queensland are basically as follows, you may fit larger wheels to your vehicle but must not increase the overall rolling diametre of the placarded original tyre size by more than 15mm or decrease by more than 25mm. Also the wheels and tyres must at least match the original load rating.
As the owner of the car you could be liable for 2 points per wheel and or tyre and up too $200 fine each, it rarely happens but beware.
The company that fits them may also be fined $5000 by the RTA
Many tyre shops are unaware of the rules.
I have not put this up as a stir I am just sick of others playing with others liability and possibly money due to lack of dilligence.