Menu toggle

Tyre Loadings - Help Please!

K

kasbridge

PCGB Member
Member
All,
So my new 888s have arrived today and I have a question.

The ones currently on the car are

225/40/18 92Y
265/35/18 97Y

Toyo have supplied the same sizes but with the 265/35/18 in a 93Y loading instead - not sure whether this is an issue or whether i will feel the difference?

The other two sets of wheels I have are the CS Mags 7.5/9" width which have Michelin PS3 with 205/50/17 89Y N3 (front) and 255/40/17 94Y N3 (rear) and just to confuse matters the 17" Cups currently on the CS which did the Spa trip last year are 8/9.5" width and have 225/45/17 94W front and 255/40/17 94W rears.

So, the question I have is - do I need to send the 265/35 93Y tyres back and get 97Y instead?

Thanks for any advice,
Kevin
 

ORIGINAL: kasbridge



So, the question I have is - do I need to send the 93Y tyres back and get 97Y instead?

Thanks for any advice,
Kevin
Click to expand...

No [;)]....not at the vmax we enjoy on track days......
 
John,
I think its more a question of sidewall loading vs speed as both tyres have the same speed rating of Y, my understanding is that the higher the number - the stiffer the sidewall. I recall 888s delaminating internally on GT3s in the early days dues to them exceeding the allowed load rating IIRC.

Or have i missed the point and do you mean that we don't go fast enough to generate enough lateral load to get to the tyres sidewall limit with our relatively light/slow cars?

Cheers,
Kevin
 

ORIGINAL: kasbridge

John,
I think its more a question of sidewall loading vs speed as both tyres have the same speed rating of Y, my understanding is that the higher the number - the stiffer the sidewall. I recall 888s delaminating internally on GT3s in the early days dues to them exceeding the allowed load rating IIRC.

Or have i missed the point and do you mean that we don't go fast enough to generate enough lateral load to get to the tyres sidewall limit with our relatively light/slow cars?

Cheers,
Kevin
Click to expand...
Kevin, I think I would go with slightly harder sidewalls rather than softer.
 
My 17s are also 94W like those on your NGT. These are the 'medium' compound 888 tyre for 17s. Therefore I have mediums on front and rear.

The demon tweeks website shows that for the 18s they only supply the medium too but in the case of the 18 265/35 it is a 97Y load. Therefore my guess is that you have been supplied with the 'soft' tyre for the rear. So personally I would want to swap those rears for the mediums so that they match your front tyres which are also mediums (225 40 92Y is a medium).
 

ORIGINAL: kasbridge


Or have i missed the point and do you mean that we don't go fast enough to generate enough lateral load to get to the tyres sidewall limit with our relatively light/slow cars?
Click to expand...

Sort of !

Our cars are not heavy , compared to a standard 964 or a GT3 . So the static load per tyre nowhere near the tyre ratings we are talking about - however we need to consider the dynamic load as well , see below .

As for dynamic load , the most lateral G I have seen on my datalogger is 1.1 and the most longitudinal G under braking is 1.2
...so if we take a RMS value for max static load + max dynamic load we get a multiplier of x 1.56 to be applied to the static loads .

My stripped C2 weighs about 1336 kg with driver , half tank spare wheel tools in the spec I take on tracks , and your RSL will weigh about the same . Here is the breakdown of that weight -

Wheel load on fronts , static 243 kg , 273 kg

So multiply these static loads up by 1.56 for max loading , biggest load for fronts = 1.56x 273 = 426 kg

This is nearest equivalent to a tyre load rating of 78


Compare with
Tyre load rating of 87 = 545 kg ( this is the rating on my Dunlop DZ03G 17x215x45 front tyres )
Tyre load rating 91 = 615 kg ( this is the rating on my old Toyo R888 17x215x45 front tyres )


Wheel load on rears , static 395 kg , 425 kg

Again , multiply up by 1.56 for max loading , biggest load for rears = 1.56x 425 = 663 kg

This is nearest equivalent to a tyre load rating of 94


Compare with
Tyre load rating of 94 = 670 kg ( this is the rating on my Dunlop DZ03G 17x255x40 rear tyres )
Tyre load rating of 94 = 670 kg ( this is the rating on my old Toyo R888 17x255x40 rear tyres )

So I guess I'm OK with 94 but you will feel safer with a 97 rating rather than a 93 after all !
 
I'm very impressed with the maths John.

FWIW I would add another 120kg for a passenger and use a full tank and add a 15% error margin. Presumably there are differences depending on temperature.

Also static weight distribution is 60% - 40% rear to front. When breaking it's probably the other way around.
 
So, did to swap to the different/correct tyres Kevin - are they available from the supplier at similar money, please?

As you know, I also need a set.

Ian
 
Ian,
Sorry for the delay in reply.....

I think that you will be buying a set of 17s so these are available in the same load ratings as per the details above, South Shore Tyres should be able to get these for you I think.

In terms of the 18s the 93Y and 97Y are physically the same tyre - literally there is no difference - what has happened is a re-classification of the tyre which is to comply with noise regulations and is nothing to do with the sidewall stiffness or load carrying capability of that particular size (265/35 x 18).

It has led to some confusion as you might expect, I did ask Toyo to give me some words a week ago but just to clear things up this is the situation as i understand it - my source was the Technical Motorsport rep at Toyo UK so it is definitely true. They also confirmed that their 93Y is fine to use on a 911 as it should be given that it is actually a 97Y tyre.

Hope this makes sense, as I say it doesn't impact the 17s....


Cheers,
Kevin
 

ORIGINAL: kasbridge

In terms of the 18s the 93Y and 97Y are physically the same tyre - literally there is no difference - what has happened is a re-classification of the tyre which is to comply with noise regulations and is nothing to do with the sidewall stiffness or load carrying capability of that particular size (265/35 x 18).

It has led to some confusion as you might expect, I did ask Toyo to give me some words a week ago but just to clear things up this is the situation as i understand it - my source was the Technical Motorsport rep at Toyo UK so it is definitely true. They also confirmed that their 93Y is fine to use on a 911 as it should be given that it is actually a 97Y tyre.
Click to expand...

I must say Kevin I find this hard to believe. The load rating is a measure of the wall stiffness and nothing to do with the noise rating which all tyres need classifying, as part of the EU directive, along with performance data rating of the wet/dry handling and more.
Yes the tyres are physically the same to look at but that's all.
I would think that the rep has got confused and would wait to see it in print from a tyre manufacturer before changing my mind.
 
David,
According to the Toyo employee I spoke to at UK HQ the tyres now stamped 93Y are physically the same as those previously stamped 97Y - this is information direct from the factory.

As Toyo no longer provide a 265/35 stamped 97Y it is Hobson's choice - the 97Y left in the supply chain are old stock.

I agree with your comment, it does seem strange.....

Cheers,
Kevin
 
I now have it in writing from their Technical Director in Germany.

If anyone needs/wants a copy of the letter please let me know by PM.
 
Hi Kevin

Your mail-box is full.

All I really need to know is exactly which spec to ask for, the new designations have been around for a while so I guess I'll be able to locate a set (West Coast?) easily enough.

All the best, mate.

Ian
 
Ian, presuming that you're still running 17s I don't think anything has changed spec wise for the tyres. It was the change in spec of the 18 inch rears that Kev needed clarifying. The specs for the 17s are in his first post.
 
Ian,
You are on 17s, so there is no change to the load ratings....

My 17s on the N/GT are on 8/9.5 rims and are 255/40 and 225/45 both 94W load ratings.

Give me a ring if I can help confuse matters further :)

Cheers,
Kevin
 
You must log in or register to reply here.

Posts made and opinions expressed are those of the individual forum members

Use of the Forum is subject to the Terms and Conditions

Disclaimer

The opinions expressed on this site are not necessarily those of the Club, who shall have no liability in respect of them or the accuracy of the content. The Club assumes no responsibility for any effects arising from errors or omissions.

Porsche Club Great Britain gives no warranties, guarantees or assurances and makes no representations or recommendations regarding any goods or services advertised on this site. It is the responsibility of visitors to satisfy themselves that goods and/or services supplied by any advertiser are bona fide and in no instance can the Porsche Club Great Britain be held responsible.

When responding to advertisements please ensure that you satisfy yourself of any applicable call charges on numbers not prefixed by usual "landline" STD Codes. Information can be obtained from the operator or the white pages. Before giving out ANY information regarding cars, or any other items for sale, please satisfy yourself that any potential purchaser is bona fide.

Directors of the Board of Porsche Club GB, Club Office Staff, Register Secretaries and Regional Organisers are often requested by Club members to provide information on matters connected with their cars and other matters referred to in the Club Rules. Such information, advice and assistance provided by such persons is given in good faith and is based on the personal experience and knowledge of the individual concerned.

Neither Porsche Club GB, nor any of the aforementioned, shall be under any liability in respect of any such information, advice or assistance given to members. Members are advised to consult qualified specialists for information, advice and assistance on matters connected with their cars at all times.

Porsche
Lockton
Pirelli
Officially approved
Oracle Finance
WEX Esso
Collecting Cars
Archant Dialogue
Back
Top