mx5cartalk.com

A few days ago, I decided to take the 5 to work and was in a rush to get going as I was running late.
I noticed that one of my rear tyres looked a bit flat, but as I was in so much of a hurry, I didn't pump it up, and there are no servos on my way into work, so I just drove on it thinking it would be OK for the 13k's to work.
Before I left work that day, I pumped the tyre up and thought nothing of it, when the next morning it was almost flat again.
I pumped it up and drove to work, and during the morning I took it to my favourite tyre dealer for him to fix it.

Being a performance tyre (Azenis RT 615), and as my tyre guy knows how I drive, he decided it would be best to take the tyre off the rim and put a patch on it from the inside.
So they took the tyre off and had a look inside, and it was full of rubber shavings and there were some obvious stress marks on the inside fo the tyre, so he recommended to me that I buy a new tyre to replace it, as he thought it might be unsafe during brisk cornering.
As the tyre was already more than half worn, I decided it best to replace the 2 rear tyres, rather than have one old tyre and one new on on the same axle.

It ended up costimg me $400 for the 2 new RT 615's in 215/40/17, so my laziness cost me dearly.

It can be very difficult to tell if your low profile tyres are under their normal pressures, so please take care, and if you suspect one of your tyres has a slight leak, check it and keep checking it as the cure could be very expensive!

I only check it because I want better milage.

I have same size wheel and usually aroud 32 psi for me.

Its generally good to check once a week, cold, with your own (quality) gauge- if you can see that a tyre looks soft, its very soft ie less than 20lbs- but Im sure you know that.

Good idea to change the tyre in pairs, but I wouldnt have replaced it because it looked \"stressed\". Mx5 is light and not very powerful, they arent hard on tyres. Tyre guys job is to sell tyres. Also, id move your two new tyres to the front, but Im sure you know that too.

regards Spaghetti

wun911 wrote:I only check it because I want better milage.

I have same size wheel and usually aroud 32 psi for me.

wow... I cant handle mine with more than 28.

I guess you don't have super hard bushes . But my size RT 615's are 50 profile

Spaghetti wrote:
Good idea to change the tyre in pairs, but I wouldnt have replaced it because it looked "stressed". Mx5 is light and not very powerful, they arent hard on tyres. Tyre guys job is to sell tyres. Also, id move your two new tyres to the front, but Im sure you know that too.

regards Spaghetti

Yes I agree....except in Bennys case. I'm not sure if you realise he drives spirited and he also drives an modded SP.
His better half drives even harer ROFLMHO.


Benny are you going this Sunday?

the guy at tyrepower told me to inflate my tyres at 39psi

my tyres are around 34psi.. with 205/45/16

Yours would be a normal street tyre. Not The RT 615 Benny & I are reffering to.

If its the Toyo T1R....or whatever.....I'd believe it. Thier sidewalls are softer than jelly compared to the RT615

RT 615 has very stiff re-enforced sidewalls. Much stiffer than your normal Performance road tyre. like C-drives, T1R, adrenalins & so on.
RT 615 are just short of a semi slick. Not quite R compound, a street compound with a Semi slik type pattern with stiff sidewalls. so a slightly different catergory tyre and not as much PSI required as your normanl street performance tyre.

on a 45 series road tyre I would expect at least 35psi

sliq wrote:the idiot at tyrepower told me to inflate my tyres at 39psi

my tyres are around 34psi.. with 205/45/16

fixed

sliq wrote:the guy at tyrepower told me to inflate my tyres at 39psi

my tyres are around 34psi.. with 205/45/16

When I did the driving course that came with buying the MX5, the instructor advise to pump the tyres at 35psi @ city driving and about 38psi highway driving. I've been doing it since.

The ride is rougher, but then again, I prefer better roadholding that compromise that for a smoother ride.

StanTheMan wrote:Yours would be a normal street tyre. Not The RT 615 Benny & I are reffering to.

If its the Toyo T1R....or whatever.....I'd believe it. Thier sidewalls are softer than jelly compared to the RT615

RT 615 has very stiff re-enforced sidewalls. Much stiffer than your normal Performance road tyre. like C-drives, T1R, adrenalins & so on.
RT 615 are just short of a semi slick. Not quite R compound, a street compound with a Semi slik type pattern with stiff sidewalls. so a slightly different catergory tyre and not as much PSI required as your normanl street performance tyre.

on a 45 series road tyre I would expect at least 35psi

Interesting. Years ago, the Azenis was actually an R compound tyre. Then they dropped the R desigantion, but they were still very good sport tyre. Is the RT615 actually R designated? (seems so by the name...)
You are correct about the Toyo TR1, btw. I have them on a Carrera, under the heavy arsed 911, they dont cope. Great road tyres in a straight line, great in the front, but the side wall deflection in the rear is very unsettling. The handbook tyre pressures on that car btw, are 36f/44r psi cold.

15in 32-34psi
16in 34-36psi
17in 36-38psi
18in 38-40psi

That was from yokohama during some tyre testing I was involved in a couple of years ago. Of course, these were for street tyres but they are pretty spot on - as you would expect being the guys that actually make tyres.

Hammer wrote:The ride is rougher, but then again, I prefer better roadholding that compromise that for a smoother ride.

I'm not really worried about either of those issues, I didn't see much of a change in actual roadholding ability when changing my pressures from 28-32, at least not road driving
what i'm more worried about is tyre wear, too low and the sides will wear faster, too high and the centre will wear quicker

if you have thicker profiles on your tyres, does that necessarily mean you have a smoother ride?

In general yes but it depends on a lot of things. The tread pattern & Compound has something to to with the amount of road noise. Sidewall stiffness relates to road holding

so if the sidewall profile is smaller then generally you would assume that there is less flex in the sidewall. So therefore it would become stiffer or give you better road holding. Also lower profiles require more air pressure to hold the weight of the car.

Mx5's also rely on a little bit of damping from the tyres especially those modded with a stiffer suspension.

now everything being equal (which it never is) this does not consider how different manufacurers manufacture the tyre sidewall.

We all know The TR1 has a pretty soft sidewall constuction. Most of us would agree that on the road with a standard MX5 (excepion of the SP) it is an OK Road Tyre. But take it to the track.....It stuggles a bit.

So then you look at a Tyre like the RT 615. which has pretty stiff sidewalls.

I found 28 psi very comfotable without having my filling rattled out of my teeth. 32psi is far to stiff for me. but then you need to consider the rest of the suspension for that reason. Mine is pretty stiff.

Then other factors are the tread pattern . Grip & so on

so overall My 45 series tyre with higher psi were more comfotable than my 50 series. But there is a compromise happening here because I just lusted after the Grip & handling of the RT 615

Hammer wrote:

sliq wrote:the guy at tyrepower told me to inflate my tyres at 39psi

my tyres are around 34psi.. with 205/45/16

When I did the driving course that came with buying the MX5, the instructor advise to pump the tyres at 35psi @ city driving and about 38psi highway driving. I've been doing it since.

The ride is rougher, but then again, I prefer better roadholding that compromise that for a smoother ride.

My car jumps all over the place and hangs the back out if I run more than 32psi. It makes it reallllly skittish