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The mkiv Supra Owners Club

Wheel size options


supna

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Originally posted by supna

What problems would a 71.5 centre cause?

 

They won't centre on the hub spigot, wheels are supposed to be located fully and tightly on the centre hole, over the male spigot, wheel nuts / bolts are NOT NOT NOT for this purpose :-) You risk wheel wobble, imbalance and safety. Do not go swapping wheels willy nilly, it's an exact science and the offsets wrong anyway.

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Originally posted by Chris Wilson

They won't centre on the hub spigot, wheels are supposed to be located fully and tightly on the centre hole, over the male spigot, wheel nuts / bolts are NOT NOT NOT for this purpose :-) You risk wheel wobble, imbalance and safety. Do not go swapping wheels willy nilly, it's an exact science and the offsets wrong anyway.

 

What is the correct offset? do you need a different offset if you change to 19" rather than 16"s for example? or wider wheels?

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Been working on a couple of rim upgrades on other cars recently, so I may be wrong, but I am 90% sure the MKIV has 50mm offset rims. I would NOT recommend anything more than 17 inch rims on the MKIV, maybe 18 if you value looks rather than handling. If you try and go wider than stock you may have to compromise offset to get things to clear, or if you want off the shelf el cheapo rims form a wheel palace, then you may find only 2 or 3 offsets are available and the wheel salesman will fob you off with "they'll fit fine mate". Sadly he won't be interested when the car tramlines and the handling goes to pot.

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Originally posted by springbok

Chris W,

 

I have been saving my pocket money for some 18" version of this rather well known wheel. What you said about sizes was interesting.?

 

Would you not recommend these in 18" for my IV then?

 

Hmm, this will be controversial, but here goes. Most road cars haven't got good enough camber control to truly make good usage of ultra low profile tyres, so if you go up more than say 1 size in diameter on stock rims, and have to come DOWN on aspect ratio (sidewall height) handling suffers. Supras have already gone from 16 to 17 inch rims, to accomodate bigger UK / US brakes.

 

Why do makers fit big diameter rims? Style. Ask any handling engineer, and if he is truthful he will say the cars are generally better on a higher profile tyre. If camber control is poor (and 90% of road cars roll too much to have good camber control) then they pick up the edges of ultra low profile tyres. However, when fitted from new, factory stock, the suspension engineers have hopefully tuned the whole of the suspensions kinematics and compliance to use said larger rims. It's a VERY different kettle of fish when the end user decides to bolt on some larger diameter rims, and leaves the rest of the suspension alone....The stock suspension bushings hysterisis is also too soft to effectively control the loadings from ultra low profile tyres, this is why a car designed to run on 50 or 55 profiles feels edgey and follows tyre ruts, surface breaks and camber changes so much when fitted with say 35 profile tyres. Until you start to radically modify a cars suspension to utilize ultra low profile tyres it's better, IMO, to stay with near stock wheel and tyre sizes.

 

Reality check :- With respect a lot of drivers neither know nor care whether the handling is the same, better, or worse, so the above doesn't apply, they merely like the looks of certain style and size of wheels and tyres, and that's fine by me, but as you asked....:flame Dev

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Thanks Chris, I had been wondering about this very subject for a long time - and I am glad a valued tech resource such as yourself has posted this precise reckoning of the situation.

 

I am sure it will make some of the big rim boys perk up a bit - and in general real road usage conditions may not make a huge difference anyway - but coming from a motorcycling background where tyre and rim choice make a world of difference I believe I could be sensitive to the changes you suggest - difficult to measure in a person I know - can only try I guess!

 

I was thinking about stepping up my stock rims to 18in in the spring - and I think I'd get a specialist such as yourself to set up the suspension if I chose to do this.

 

Now I am having a rethink!

 

Thanks chap! Honestly!

 

R

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Rob: To be frank I am too busy to get into a flame war :)

However, if anyone wants my opinion on what to do to BEST make use of an 18 inch rim, then i would say get a rim with the EXACTLY correct offset, choose one that is as LIGHT as possible, and choose a quality, LIGHT tyre. Gyroscopic precession, where the gyroscopic effect of a large diameter heavy wheel and tyre overcomes the designed steering response and makes the car feel dead to steering inputs, but very alive to road disturbances, can turn a lovely handling car nto a dog, very easily. So think offset, think weight, think quality tyre. On some forums i see tyres discussed solely on price, and yet the poster has just spent hundreds on fancy bits to get the car to handle better...

 

As a race engineer I, and others like me, assess a car at the design stage by deciding first what TYRES it will run, and EVERYTHING, chassis wise, is designed to make maximum use of those particular size, make and compound of tyre, with minimum weight and maximum chassis rigidity. Believe it or not, modern car makers do a similar process of evaluation, only offsetting some of the ultimate handling and weight saving goals with the need to consider NVH (noise, vibration and harshness), and to make a generally benign handling car suitable for the average driver, on average roads. their skill is immense, their resources stupendous. Make no mistake, to improve, alter or generally *iss about with their work is not trivial, and to better it in pursuit of a particular handling trait is tricky, and often unsuccessful. As they say, "Beware, here lie dragons" ;)

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Chris,

 

I already have a set of 18"s on my car and yes, these were chosen purely for style reasons initially - but I have since had the Whiteline "the works" suspension kit fitted and have taken to doing track days, so I'm wondering whether I am suffering from some of the issues you describe...? (more than likely)

 

I'm just wondering whether there's anything I can do with my existing set up to make sure its at least the best it can be with what I've got? Obviously its not something I can do myself, but I just wondered if you have any pointers?

 

TIA,

 

Mark.

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Totally understand and you posting at this hour is much appreciated!

 

What I would like to know is there a huge difference in these factors between the JSpec smaller rims and the UK Spec bigger rims.

 

I wonder what tweaks may have been done to geometries between the two etc. Or if its just the case different rubber was recommended etc.

 

I love the may my JSpec turns in and bites the bends (long and short) and the power just prickles along the driving axes nicely.

 

Difficult to say if it's perfect without lots of buggering around I guess - but I am loathed to spend 2-3K on alloys and rubber to find I need to backtrack and make a host of other patch up changes just to look a bit shinier.

 

Hmm - its a tough call.

 

R

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Chris,

 

Full marks for those comments, to be honest that was what I expected you to say. I am not an engineer by trade but I do like things done correctly, which is why I have not started any mods yet. I have spent a year looking around making notes on many different aspects.

 

I already knew i would have to change the suspension setup when I change the wheels. Do you know if this particular wheel can run correctly, or should I say well, on a IV. Correctly would mean a complete track setting in my book. As its a road car compromise will have to be the result on the day. Otherwise I fear it would be very un driveable on a A+B roads etc,,

 

Although you didn't know it. I was going to ask you to do my suspension tuning anyhow. I picked up on what you said a while back about ride height, folk often like to take it really low. But this is for looks again. It does not do the car any good on a public road.

 

rgds,

 

Alan

 

 

:cool:

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Originally posted by springbok

Chris,

 

Full marks for those comments, to be honest that was what I expected you to say. I am not an engineer by trade but I do like things done correctly, which is why I have not started any mods yet. I have spent a year looking around making notes on many different aspects.

 

I already knew i would have to change the suspension setup when I change the wheels. Do you know if this particular wheel can run correctly, or should I say well, on a IV. Correctly would mean a complete track setting in my book. As its a road car compromise will have to be the result on the day. Otherwise I fear it would be very un driveable on a A+B roads etc,,

 

Although you didn't know it. I was going to ask you to do my suspension tuning anyhow. I picked up on what you said a while back about ride height, folk often like to take it really low. But this is for looks again. It does not do the car any good on a public road.

 

rgds,

 

Alan

 

 

:cool:

 

These are the Blitz ones? I have driven 2 MKIV TT's on these. One was iffy, but turned out had similar style rims, but of the wrong offset, purchased from someone wha had them on some other type of car. the other, someone on, or who was on, this list, was fine. The car was a bit edgey, due to the very low profiles, but drove OK. I later fitted my custom suspension set up, and the car was beautiful. His name is Nick Martin, his car was one of the first to have my kit, at the time he was very vociferous in its praise. If you want an independent opinion he was at:

[email protected]

The car was a 1998 VVti

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Guest Terry S

Rob if you are serious about " proper 18's" then I am selling mine. I had these made spcifically for the car using 50mm offsets front & rear. They are 3 piece, much lighter than Blitz wheels, but not as *pretty*. They are 8" front & 10" rear ( yes they are 1/2" nearer the bodywork but don't rub & the fronts were made to fit UK brakes. I had these made after a similar discussion with Chris 2 years ago. I am in the process of getting the outer rims repolished to sell them but PM me if you are interested. I am going to get another set made up to accomodate a wider rear tyre.

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FWIW, The latest edition of Racecar Engineering ( http://www.racecar-engineering.com ) has a whole section (start of a series) on suspension and steering. The first part is all about steering and how its affected by the location of the steering "knuckle" in relation to the centre point of the hub/wheel.

 

From what I can gather from it I believe the ~50mm offset version of the BBS LM to be the best for the Supra. The wheels look a bit odd with the spokes/face on the front wheel sticking out a little bit, but it places the steering point closer to dead centre than some +50mm offset wheels.

 

There is also a fantastic diagram in the mag detailing offset, castor, camber, etc etc Well worth a read if you're serious.

 

Copies can be found at WHSmiths.

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Folks,

 

It seems like there are a good few of you that know exactly what you are talking about and I have a problem that I hope someone can help me with.

 

I bought a Japanese spec. 94 MKIV TT Manual that had been lowered and fitted with 18" alloys before it was imported to the UK (Not sure whether this was factory fit or after). The problem I have is that it just failed it's MOT due to excessive wear on the inside of both front tyres. When I say excessive I mean excessive - there is a good 10mm of tread on the rest of the tyre and the fibres are showing on the inside 15mm of the tyres. The tyres are 225/40 RZ 18's on both front and back.

 

I had originally thought it was maybe just a problem with the camber on the fronts and was on here to look for recommended camber settings but now I'm not so sure. Any suggestions? And does anyone know of a decent place to get the work done in Edinburgh? Additionally, any recomendations for tyres? :)

 

I know it's a lot to ask but I'm a complete novice and the last thing I want to do is take it into Kwik Fit and them feck it up completely ;)

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