A few queries, any help appreciated.

cheeseontoast · Post by **cheeseontoast** » Tue Jul 29, 2008 9:16 am

I recently bought an '04 MX5 and I've got a few queries.
Is it possible to fit an aftermarket steering wheel, if so how do you get round the airbag issue?
Is there any consensus on the best engine oil to use?
Any thoughts on tyre choice (205/45/16's), something with a softer sidewall would be beneficial?
I heard that the South Island owners club was defunct, does anyone know?
Thankyou for any help you can offer.

poison · Post by **poison** » Tue Jul 29, 2008 9:50 am

I’m assuming you’re new to the MX5 world if so welcome. If not… err hello again J

You can get a steering wheel kit for almost every car there is. Legality?? who knows, I guess you’d need a Low Volume Vehicle inspection which is around $350 and then there is INSURANCE…. but IMHO you’d have to be crazy to ditch the air bag. Out of the 3 models NA, NB and NC (yours) I like the NA the most but the air bags in the NB were certainly a motivator for the change to an NB.

Oil, always something like tyres people will always disagree, but without going full synthetic, which is usually considered a waste of time on a standard engine. Magnatec used to get really good reviews in previous forum and email discussions, and I was very happy with it as it got rid of the tappet noise in my old NA, most important of all and even more important than the oil choice is regular oil changes.

Tyres, I have a NB (Model before yours) and have “215/40/17” tyres, and while they handle well they track like crazy and are heavier to steer and the ride is harsher, so IMHO I prefer the feel I had with 16’s. Again tyre choice is the key here. But I think your car came with bigger wheels stock, so I would still consider 17’s again someone else would have to confirm this.

The Bridgestone’s seem to be a popular choice (can’t remember the model).

I am pretty sure the South Island chapter of the MX5 club is alive and well, they have had some great turn out’s for their car runs shown in the club magazine. But I’m a JAFA so can’t be sure. None the less the MX5 club (NZ wide) is quite cheap to belong to and you get a great magazine every couple of months. I’m sure someone can post the contact details for this.

cheeseontoast · Post by **cheeseontoast** » Tue Jul 29, 2008 10:56 am

Thanks Poison, very thorough and insightful post.

The steering wheel change is more about ergonomics, the NB (MK2.5) seats are set high and lowering appears difficult, this, combined with a large diameter Nardi wheel conspire to create a less than ideal driving position. I thought that a smaller diameter, flat faced Momo or Sparco could improve this.

Oil: Your Magnatec suggestion is food for thought as my tappets are a litte noisy. I do prefer a quality fully synthetic oil but I am open to alternative suggestions.

Tyres: You're right, the MK2.5's run 205/45/16's as standard. What they gain in grip (which is very strong, even in the wet) they lose in delicacy, adjustability and composure. They love to tramline and the transition from oversteer back to grip is snatchy. I definitely don't want larger wheels as this won't help, I'd rather find a softer sidewall to offset the firmer MK2.5 suspension and create more progressive breakaway and recovery. Any thoughts?

South Island Owners Club: Thanks for your info I'll look into it.

Grant · Post by **Grant** » Tue Jul 29, 2008 12:13 pm

There's no South Island Owners Club as far as I know. There is a very active
club in Christchurch as well as clubs in many other areas such as
Marlborough, Nelson, Otago, Southland.
Where are you?

Grant in Blenheim.

cheeseontoast · Post by **cheeseontoast** » Tue Jul 29, 2008 1:43 pm

Thanks Grant, I'm in Christchurch and a quick squizz at the NZ MX5 club website (which I should have looked at first of all) shows the Christchurch arm to be healthy and active with a get together in 2 days and meetings at least once a month.

Ian · Post by **Ian** » Tue Jul 29, 2008 2:24 pm

Hi...and welcome.

You do not need to go up in tyre size, thats for sure.
Find out what is available in your size, and go for a 'performance tyre' with a good alignment.
I had old=hard Bridgestone Turanza 15" and was determined to wear them out, but got tired of waiting and went to one of the highly recommended tyres (for MX5s) - Toyo T1Rs...and have never regretted the choice. Your tyres could poss be oem? In which case they will be past their best simply because of their age....(I had intended to run Goodyear GSD3s but they were too pricy at the time, and while the Toyo T1Rs are not cheap by any means, their performance is worth it, in my book.
I race on Castrol Magnatec, but as stated, many MX5 enthusiasts do oil/filter changes at 5k intervals (self included), and this is often recognised as the best way to treat your MX5 engine.

Ian

Ian · Post by **Ian** » Tue Jul 29, 2008 2:32 pm

PS I run an aftermarket Momo with a flat bottom to aid entry/exit when using a race seat in the NA. Our NB has a Nardi airbag wheel and possibly it is like yours. Not sure that a smaller airbag wheel is available, so I might be inclined to seach the miata.net site to see what others have done in the US. I know that doing a 'foamectomy' is popular for tall drivers.......

cheeseontoast · Post by **cheeseontoast** » Tue Jul 29, 2008 5:16 pm

Thanks Ian, handy post. You may be right about the tyres, the cars done 44kms so I doubt the tyres are original but they are Bridgestone Turanza's and despite running them at 25psi the sidewalls are like Rimu and the ride is similarly 'wooden'.

As for oil......well if you're racing on Magnatec with no issues then it sounds like good stuff, is that just standard Castrol Magnatec?

I've read about the 'Foamectomy' but I'm not sure if people have carried this out on MK2.5 seats.........I'll get my bread knife and take a deep breath unless anyone suggests a less brutal fix.

Gordon Tucker · Post by **Gordon Tucker** » Tue Jul 29, 2008 5:38 pm

My previous car was a 2.5 with 17s. I tried other tyres first before I put Toyo T1Rs on. The T1Rs were streets (pun) ahead. I now have a NC and will replace the standard 17in Michelins (poor wet grip) with Toyos soon. I did the foamectomy with some success. I also put more foam in the front bolster area to give me more thigh support for my long legs which helped. I used Magnatec and found it very good. It pays to replace it at least every 10.000 kms as the 2.5 uses oil for the variable valve timing and works better if the oil is fresh

skams · Post by **skams** » Tue Jul 29, 2008 5:44 pm

Hi there,
I purchased My Mk 2.5 (02) Last year and it came with 205x45x16 Yokohama DNA S drives already fitted which seemed to perform really well and at about Xmass I bought a spare set of 16" wheels second hand (because my originals have been curb damaged) and they came fitted with well worn but warrantable 205x50x16 Goodyear Eagle F1s which I have been running untill recently when I changed back to the originals as it were, and have just done a trip to ChCh and back at the weekend with both wet and dry road conditions.
Now to give you a comparason, the Yokohamas gave a slightly harder ride as you would expect with the lower profile and seamed to be reasonably progressive when pushed to the limits on a wet road and yes they do tend to tram track. The Goodyears while slightly higher profile seem to hang on a bit longer in the wet (more efficient water removal?) even though they are obviously more worn, and do give a slightly softer ride, I can't comment on how well they regain their grip on a dry road as I don't recall detecting any loss of grip in the dry at any time, they do tend to Tram Track but not as bad as the Yokohamas. At this stage, when I need new tyres and given the choice I would go for the Goodyears.
Incidently, the speedo seems to be more acurate on the Goodyears when comparing readings with my GPS. At 100 kph on the GPS the speedo reads 103 with the goodyears and 108kph on the Yokohamas.
Now as far as oil is concerned I haven't done an oil change on the NB but when I changed to magnatech on my '91 NA, as already stated in a previous reply, the tappets very quickly shut up and behaved themselves and I had no more sticking or annoying tapping noises.
Hope this has been of some help, Cheers
Simon

cheeseontoast · Post by **cheeseontoast** » Tue Jul 29, 2008 7:31 pm

Gordon + Skam, thanks for your insightful posts. Gordon when you say that the Toyo's were streets ahead, in what way? Progressive breakaway? grip? ride? tramlining?
I'm not after the most grip, even my old Turanza's hang on gamely, which is more a product of the MK2.5's power to tyre size mismatch than anything.
I'd prefer a softer riding tyre with less grip if it means a more predictable transition between 'grip and slip'.

Skam, your foamectomy and Magnatech suggestions are noted and helpful. Thankyou.

Ian · Post by **Ian** » Tue Jul 29, 2008 7:34 pm

Gordon Tucker wrote:My previous car was a 2.5 with 17s. I tried other tyres first before I put Toyo T1Rs on. The T1Rs were streets (pun) ahead. I now have a NC and will replace the standard 17in Michelins (poor wet grip) with Toyos soon. I did the foamectomy with some success. I also put more foam in the front bolster area to give me more thigh support for my long legs which helped. I used Magnatec and found it very good. It pays to replace it at least every 10.000 kms as the 2.5 uses oil for the variable valve timing and works better if the oil is fresh

Not sure I would be running as low as 25psi......I think 28 might be recommended. I run 28, or 30 when touring.

cheeseontoast · Post by **cheeseontoast** » Tue Jul 29, 2008 7:58 pm

Ian, factory quoted tyre pressures for the MK2.5 16 inch 205/45/16 is only 26psi front and rear (seemed low to me too but you can't argue with the handbook and factory door shut sticker, the tyre profile is very low (it's a similar sidewall height to a 295/30 tyre, they don't get too much lower than that).
I only lowered the pressure 1 psi below recommended and there's no squish, no 'soft' feel to the tyre and no squirm during cornering and braking, on the contrary the primary ride is still a little harsh and wooden over give and take blacktop and I've got an inkling that a softer sidewall will relly help.

skams · Post by **skams** » Tue Jul 29, 2008 9:54 pm

Hi Again,
I usually run the tyres at the factory recommended pressures (26psi) but I have noticed that when traveling in the wet on a smooth surface at highway speeds that the tracks left behind appear rather dryer at the edges of the tyre track and obviously, significantly wetter in the middle of the track, suggesting to me that the pressures could be run a little higher to get more even contact across the tread.
Any way, as a sideline, some time ago I was given a copy of a magazine article (“Over Tyred”) which talked about tyre sizes (width) for a given vehicle. Essentially what it talked about was that regardless of how wide the tyre was, the area or size of the footprint remained essentially the same, that is, the wider the tyre the shorter the contact area and conversely the narrower the tyre the longer the contact area. The net effect of this is that the length of the contact area is directly related to the reaction time for the tyre, the shorter the footprint the quicker the reaction of the tyre to changes such as steering input and that there is no more grip to be had with a wider tyre, just that it will hang on longer but will let go quicker requiring quicker reactions on the part of the driver. In a some cases with tyres wider than standard the tyre will let go so quickly that the average person can’t react quick enough to be able to control the loss of traction. – Food for thought.
Cheers, Simon

cheeseontoast · Post by **cheeseontoast** » Wed Jul 30, 2008 8:57 am

Skams, I love the fact that you're anal enough to look at the tracks you leave behind on wet roads and determine tyre pressures based on what you see.
As for your 'Overtyred' post I'm afraid you lost me when you stated "There is no more grip to be had with a wider tyre, it'll just hang on longer".
That's one and the same isn't it?

Ian · Post by **Ian** » Wed Jul 30, 2008 9:49 am

cheeseontoast wrote:Ian, factory quoted tyre pressures for the MK2.5 16 inch 205/45/16 is only 26psi front and rear (seemed low to me too but you can't argue with the handbook and factory door shut sticker, the tyre profile is very low (it's a similar sidewall height to a 295/30 tyre, they don't get too much lower than that).
I only lowered the pressure 1 psi below recommended and there's no squish, no 'soft' feel to the tyre and no squirm during cornering and braking, on the contrary the primary ride is still a little harsh and wooden over give and take blacktop and I've got an inkling that a softer sidewall will relly help.

Oops...indeed 26lbs is the recommended pressure for an NA as well! Of course, having settled on 28lbs some three yrs ago when I first bought my car, 28 has become ingrained in my thought process, so I apologise. That being said, I personally would never run below the recommended pressure. I pump up at the service station (when tires are coldish) and recheck/adjust pressures at home with a Michelin guage.
Had another thought you might like to try...pop around to Chamberlains Suspension Ltd, 47 Sandyford St, Sydenham and drive onto their shock testing machine. The resulting print out may shed some light on things.
Re your tyres, with 44k I would not discount the possibility of them being the originals....Turanza E30s will go to the moon and back, for example.
Re breakaway/handling at the limit...I tend to drive conservatively (in the eyes of some) on the road...but apart from a moment in surface grit on the summit road above Akaroa, I can say that on the T1Rs (plus my suspension mods), I have never had my MX5 breakaway on me on a public road, despite some enthusiastic cornering on just about all of the South Islands challenging public roads.

Cheers, Ian

Gravelben · Post by **Gravelben** » Wed Jul 30, 2008 10:09 am

Ian wrote:...but apart from a moment in surface grit on the summit road above Akaroa, I can say that on the T1Rs (plus my suspension mods), I have never had my MX5 breakaway on me on a public road, despite some enthusiastic cornering on just about all of the South Islands challenging public roads.

You need to spend more time on gravel!

poison · Post by **poison** » Wed Jul 30, 2008 10:15 am

I’ve looked at my tyre trail too, and followed cars and wondered about the dry edge effect too, and have put that down to the fact the water can escape from the sides of the tyre thus causing a dry patch, but the middle section would not have time to push the water out the sides so it has to go underneath, which I’m guessing is why most of the modern tyres with wet performance in mind have a few straight deep grooves giving the water somewhere to go, then once the tyres rotates it would spread out again looking like it hadn’t been dry – all an uneducated assumption.

But I can’t believe that width doesn’t effect the footprint/contact area if the diameter stays the same. If anyone can post a link about this it would be great, I have had a quick look with no success.

Re- the oil, sorry Cheeseontoast (love that by the way) had assumed you had an NC.. doh… but yes many of us have had really good results from Castrol Magnatec on the lifter noise. My NA was quite noisy and other members swore by Magnatec, of course I thought ‘yeah right’ but holy crap it worked, I would never have believed it would work so well, it’s made a huge difference. Worth a try for sure, you have nothing to lose there. And do the oil filter too, there are lots of people here who swear you “Must use the genuine Mazda oil filter”, I’m not convinced, I think it’s OK to use aftermarket one’s as long as it’s a good brand , anyway check out this review as a starter and interesting read this well sorted article.

http://www.knizefamily.net/minimopar/oi ... index.html

Seats… I have heard the 2.5 has great seats. Mine are OK, but I’d love some aftermarket one’s, although I have not found any that sit low enough yet. I tired a couple and ended up looking at the sun visor and that was without the rails too. I would be cautious about trimming foam off the bottom. But if you did I guess you could always glue some more back in. I have not looked but would it be possible to modify the metal pan at the base of the seat to get an extra inch.

cheeseontoast · Post by **cheeseontoast** » Wed Jul 30, 2008 11:00 am

Ian, interesting stuff with your Toyo's although as I previously stated ultimate grip isn't my aim. The MK2.5's big tyres hang on so well that by the time they do give way you'd better be on the ball to get things back in line because you'll be carrying decent speed and generating pretty high g's.
Your suggestion for the suspension rig guys in Sydenham is one that I'll take up. Thankyou.

Poison, thorough answer and good reading (that oil filter link is extraordinary in its detailed analysis, I'm humbled by people that go to so much trouble). Great food for thought for a cynic like me.
As for the seat lowering I think that greatest gain would be to sit the seat in between the chassis rails as there is a around two inches of clearance under there, it would require fabrication of new rails though and realistically It'll probably remain in the inbox. For now the bread knife is staying in the kitchen drawer too!

And the tyre width/length/contact patch ratio.................well it just doesn't figure, as you say, only overall diameter could affect the front to rear contact patch and quite simply a wider tyre will have a greater surface area touching the road.
High powered cars have wide tyres primarily for extra grip, simple as that.

Thanks for all your help.

Ian · Post by **Ian** » Wed Jul 30, 2008 12:18 pm

cheeseontoast wrote:Ian, interesting stuff with your Toyo's although as I previously stated ultimate grip isn't my aim. The MK2.5's big tyres hang on so well that by the time they do give way you'd better be on the ball to get things back in line because you'll be carrying decent speed and generating pretty high g's.
Your suggestion for the suspension rig guys in Sydenham is one that I'll take up. Thankyou.

Poison, thorough answer and good reading (that oil filter link is extraordinary in its detailed analysis, I'm humbled by people that go to so much trouble). Great food for thought for a cynic like me.
As for the seat lowering I think that greatest gain would be to sit the seat in between the chassis rails as there is a around two inches of clearance under there, it would require fabrication of new rails though and realistically It'll probably remain in the inbox. For now the bread knife is staying in the kitchen drawer too!

And the tyre width/length/contact patch ratio.................well it just doesn't figure, as you say, only overall diameter could affect the front to rear contact patch and quite simply a wider tyre will have a greater surface area touching the road.
High powered cars have wide tyres primarily for extra grip, simple as that.

Thanks for all your help.

Re tyre contact patch: Al other things being equal...the tyre 'floats' the car. On a standard MX5, a 185/60 x 14 tyre has a contact patch is 19.64 square inches. Change to a 215/45 x 16 and you have a ...wait for it...contact patch of 19.64 square inches.The 'shape' of the two patches are very different.of course. It is the change in orientation of the patch which allows the wider tyre to generate more grip in a corner eg when racing.
On an MX5, esp on the road, increased width needs to be measured against the increased weight of the new wheel/tyre combo, as the suspension draws much of its ability from having a relatively light unsprng weight, and it is quite easy to upset that initial oem balance.

Ian

cheeseontoast · Post by **cheeseontoast** » Wed Jul 30, 2008 12:48 pm

Ian, I just don't get it.
As an extreme example are you saying that a 345 width tyre could have a similar contact patch to a 155 width tyre of the same diameter?
How so?

I do agree with your unsprung weight statement and the belief that the same car with smaller wheels can have subjectively better handling - even if outright grip is lower.
The Porsche Cayman 'S' is a good case in point.

As is the MX5.

Gordon Tucker · Post by **Gordon Tucker** » Wed Jul 30, 2008 12:49 pm

cheeseontoast wrote:Gordon + Skam, thanks for your insightful posts. Gordon when you say that the Toyo's were streets ahead, in what way? Progressive breakaway? grip? ride? tramlining?
I'm not after the most grip, even my old Turanza's hang on gamely, which is more a product of the MK2.5's power to tyre size mismatch than anything.
I'd prefer a softer riding tyre with less grip if it means a more predictable transition between 'grip and slip'.

Skam, your foamectomy and Magnatech suggestions are noted and helpful. Thankyou.

The Toyo's have extremely good grip in the dry and the wet, also progressive breakaway if you try too hard and they didnt tramline as much as other 17 inch tyres I have had. They were also softer riding. Because of all this the (only) downside is they wear quite quickly.
The best answer to the seat hight/legroom question is to get yourself into an NC

Gravelben · Post by **Gravelben** » Wed Jul 30, 2008 1:37 pm

cheeseontoast wrote:Ian, I just don't get it.
As an extreme example are you saying that a 345 width tyre could have a similar contact patch to a 155 width tyre of the same diameter?
How so?

Off the top of my head (and therefore potentially bollox)

I think its primarily a function of car weight which deforms the tyre to give a certain contact patch area (therefore same area = longer shape contact patch for a narrower tyre, presumably square might be optimal? but thats another question) - to take Ian's use of the word 'float', a boat of a certain mass will displace the same amount of water regardless of whether its wide and flat or narrower and deeper. Not a perfect example for this but gives the general idea. The difference is that tyre distortion is also dependent on pressure, and running wider tyres may also let you use lower pressure or a softer compound to increase grip without the same wear and temperature problems you'd get doing the same thing with a narrower tyre.

Ian · Post by **Ian** » Wed Jul 30, 2008 2:02 pm

cheeseontoast wrote:Ian, I just don't get it.
As an extreme example are you saying that a 345 width tyre could have a similar contact patch to a 155 width tyre of the same diameter?
How so?

I do agree with your unsprung weight statement and the belief that the same car with smaller wheels can have subjectively better handling - even if outright grip is lower.
The Porsche Cayman 'S' is a good case in point.

As is the MX5.

Yup....think of the four tyres 'floating' exactly the same weight. The 155 will have a log narrow footprint, and the 345 will have a short and wide footprint. The tyre deforms to present a footprint, but the area doesn't change.In a car with 50/50 weight distribution (which in theory the MX5 is) and with tyres at the same psi, the contact patch measurements I quoted are the ame on each corner. With wider tyres, cornering is enhanced usually as a result of one or more variables which will include changes to rim width, contact patch shape, aspect ratio, tread design, rubber compound etc....
It is generally accepted that an appropriately chosen high performance tyre is the single best (first?) mod anyone can do to their MX5 (of course, if you have a knackered shocks, they come first.)
Norman Garrett in his book 'Mazda Miata Performance Handbook' discusses the theory in Chapter 4. Although it was published before the introduction of your model, its still a good read.

Ian

Post by **jif** » Wed Jul 30, 2008 4:39 pm

2008/7/30 Gravelben <mx5talk@mx5forum.co.nz (mx5talk@mx5forum.co.nz)>

cheeseontoast wrote:Ian, I just don't get it.
As an extreme example are you saying that a 345 width tyre could have a similar contact patch to a 155 width tyre of the same diameter?
How so?

IIRC in theory the contact patch area can be worked out by dividing total weight (in lbs) by the tyre pressure (in psi) ... eg 2600 lbs / 26psi = 100 in.sq

Not sure how that works in metric world, with the newton-metres, and the kilo-pascals, and the road pushing against the tyres and everything tho

-j