Here's a wheel conundrum.

 

"Everyone says" you should replace the J spec rears with UK spec rears.

Both are 16". J spec are 7.5" wide and take a 225/50. UK are 8.5" wide and take a 245/45.

 

The UK wheel is 1" wider than the J spec. The UK tyre should be 20mm wider (0.78").

 

That's the theory!

 

In this picture, there is a UK wheel/tyre and a J spec wheel/tyre. Can you tell the difference?

No, neither could I and neither could the guys at Protyre.

 

So I took some close-ups:

 

Tyre A is 221mm wide at the sidewall and has wear-to-wear tread of 197mm

 

Tyre B is 218mm wide at the sidewall and has wear-to-wear tread of 199mm

 

Which one is the 225 and which the 245? Both are Bridgestone S-03s.

 

Actually Tyre A is 245 and Tyre B is 225. Which means the theoretically 20mm wider tyre is in reality 2mm narrower!

 

Also, according to Protyre, the J spec profile of 50 should give you a marginally smoother ride as this is not quite so low profile as the UK 45.

 

Now, given the 245 tyre has no more tread than the 225, has a slightly harsher ride and costs £30 more, tell me again why I should want to get rid of my J spec rears and replace them with UKs?

 

From the evidence so far, it seems that J spec owners can stop worrying about having 225s all round - there's no tread difference, you get a slightly better ride (I can't tell the difference but that's the theory) and they're cheaper.

 

Any tyre gurus here who know any different? Be interested to hear...

 

Cheers - Gio

what about

 

245x45-(225x45)-bhp+no of seatsxhow old you are+about99+a69+(havnt a clue)??

:rofl: :dance: :rofl: :dance:

 

 

I would say the one on the left is UK;)

 

 

Gio there is only 1 simple reason for fitting a wider rear tyre on your car.

 

 

It will handle much better;)

Now do the test with a ton of weight on the wheel flattening the tyre out.

 

As we know the more weight on a wheel the more pressure is needed to make it flat to the round. You have no weight on them and they will bulg out.

MAC 1, yes mate, I accept that usually a wider tyre means better grip (all things being equal) but as you can see from the pics, the 245 tyre isn't wider!

 

Stu - yes absolutely, but the measurements of the tread were taken from wear edge to wear edge (the tyres have been on the car for miles) so this is actually the width of the tyre tread in use on the car.

dunno about you but i can see an obvious difference in the size there.

Originally posted by SRRAE

As we know the more weight on a wheel the more pressure is needed to make it flat to the round. You have no weight on them and they will bulg out.

 

 

:rofl: :rofl: :rofl: HUH????? :rofl:

I have 225 J'Spec all round and have never felt the necessity to change to the wider rears, admittedly I have thought about it but mainly for cosmetic reasons.

 

I have to drive like a hooligan to get the rears to let go, so why would I change to a wider tyre and spend more money doing so? As far as I can see there is actually a dowside to changing to wider tyres and that is grip in the wet, but I guess that's another story.

 

I would happily go head to head with someone on track UK vs JDM and I would guess that driver skill would show through before any tyre benefits.

 

For now I'll stick with my 225s. :D

 

Tim

If there is no difference between them (!) why would they make two different types (?)

 

and

 

Why did uk car have 'wider' rears anyway? What was the point if the Jap cars had always had hte same boot at all four corners?

Clarkey - we measured the friggin things with the results posted above - tread width is smaller on the 245 than on the 225.

 

TT Tim - I agree with you but why do you think UK tyres are wider? The ones I photographed certainly weren't.

 

NigelBoyd - yes that's exactly why I asked the question.

 

So we have the summary at the moment that no-one can suggest a logical reason why the 245 tyres on the UK wheels in the photos are better than the 225 tyres on the J wheels.

 

Noone can say why the UK rims are 8.5" vs the J 7.5".

 

And noone can say why the 245s are a narrower tyre than the 225s.

 

Yours ever - Gio

Iirc the rubber is different.

 

In any case, if your tyres are over 6 years old

then change them.

Even if the tread looks ok.

 

If you do not then you may well wish that you had.

Worse, someone else may wish that you had.

Uk wheels do seem to fill out the arches slightly more than JDM. So I'd say asthetics were probably the driving force behind the difference.

 

I have 225's all round but still have to work really hard to get the tail out.

 

Jon

maybe theyve marked them wrong :confused: mine are obviously wider on the rears

Originally posted by JonJon

I have 225's all round but still have to work really hard to get the tail out.

 

I used to have that problem (i.e. getting the arse out) I was running on Stock Jap Spec's with F1's all round and they really stick, I then changed to 285's x 18's on the back and 245 x 18's on the front (still F1's) and that made it even more difficult.

 

However I have now upped the boost to 15ish psi and I have no problem getting my arse out at all :D

I've got 255/40/17 on the rear and 235/45/17 on the front and it is the jap spec Bridgestone g'grid all round and i have no problem getting my arse out under acceleration. (no cluth of coarse) in pervect good dry hot weather.

Hmmm, well I just took the opportunity to measure my Poxy T1's and as far as the width of the tread touching the road goes then I have to agree with Gio !

Tyres from different manufacturers would also show different results. On a tyre with a more "square" cross-section (like a Michelin Pilot Sport) where the tread runs right to the sidewall you would see a more pronounced difference.

 

I have 255/40/17 rears and 235/45/17 fronts (Goodyear GDS3), so they are still only 20mm apart and the tread width of the rears looks noticeably wider.

 

I'm sure it's been proven that wider tyres don't necessarily mean more road contact as generally the weight is spread more over the width making a smaller contact area from front to back of this rectangle. Wider tyres aren't necessarily as good in the wet either.

 

However wider tyres give better lateral stability (less sideways movement) during cornering, in the dry of course. Which is why the UK spec car has wider rears. Jap roads are long and straight like those in the USA, whereas in Europe/UK we have to contend with more corners, often at higher speeds.

 

Richard;)

Mines ajspec NA so of course never frlt the need to change.

 

I have noticed though that tyres do wear edge to edge so getting full tread on the road, so would pressume wider tyres would give even more tread on the road!

 

However do things change as soon as you put larger dia. wheels on?

hehehe - well this appears to be one of those Z myths!

 

I have sent the photos to Bridgestone to see what they say and if there is a reply, will post it.

 

In the mean time, if you have J spec wheels all round, IMO don't bother to change the rears for UK spec!

 

Cheers - Gio

 

PS if anyone wanted to post the real tread width of their 225 or 245 tyres, I'd keep a summary list. Ideally post 225 or 245, tyre name, width at widest point, wear-to-wear tread width.

Heres a possiblity, i know sod all about this but its just a guess theory.

 

Is it possible that if the tyre is bigger, the pressure increase caused by running at very high speed may have been found to be safe running 245's at 120mph and over but not quite so clever running at that speed on a 225 tyre used in Japan, thus they used the 245's as a safetey concern in the uk, but as the jap ones werent made to exceed 112mph so they werent needed over there?:confused:

 

Having said that, the fronts are 225's so that cant be the theory then!!!

 

May as well delete this post but it all adds to the post count!!!;)

Just thought i'd chip in and throw a spanner into the whole tyre works thing.

When a tyre size is written, i.e. 225/45x17 this means

225- is, or should be, the width of the tread

45- this is the tyre side wall hight, as a percentage of the tyre width

And 17- is obviously the wheel size.

Now i do know that if the tyre is fitted to a wheel with the incorrect J rating, this will throw the whole measurement thing out the window

incedently, 225 tyres should be fitted on a 7J wheel, where as a 245 tyre should be idealy fitted on an 8J wheel

have fun with that one

Also, the reason for changing Jap tyres for British ones is quite simple, basicly, they dont come up to British safty standards, which will effect your insurence should the nasty occur:slap:

:dance:

So, working on sraaee theory, dont fit bigger tyres just let the air out, this lets them bulge more and you can use the side wall for grip?????????????????????????LOL

I must say when i compared my front's to my rear's, the rears looked much bigger. Also i now have Toyo Proxies and they are much rounder profile wise, they're nowhere near as wide looking as my previous tyres -It's like having 195's in comparison.

Following Robtor's above post, it looks like my theory regarding different manufacturers was right:)

 

As the profile of Toyos is more rounded, they obviously appear narrower over the tread width.

 

Lets wait to see what Bridgstone reply to Gio....

 

Richard

I changed from Jspec to uk rear wheels with bridgestone s02's.

The tread in contact with the road is no greater on the new 245's than it was on the old 225's exactly as gio says.

But the wheel sticks out an inch wider each side of the car and handling does feel even stabler now. Plus IMO they look better filling out the wheelarch.