Track day, 18" 108's or 19" wheels?

[Z43.0Si]

I'm planning on a track day in the coming months.

I currently run the car with 19" alloys with continental tyres all round (non run flat).
I have the original 18" BBS 108's which I'm about to put Michelin Supersport tyres on them.

My question is, what should I use for the track day? I'm thinking the 18" 108's may be the better option in terms of handling.

Your thoughts please......

 

[ga41]

Well, generally speaking the smaller diameter the better, for less weight. I'm even pondering about 17" for my car when I eventually start tracking it again.

 

[ga41]

Plus tires will usually be cheaper!

 

[Number5]

Well, generally speaking the smaller diameter the better, for less weight. I'm even pondering about 17" for my car when I eventually start tracking it again.

..and the larger the diameter, the quicker you will be as one revolution will have a bigger circumference.
1" Dia x Py ( 3.14) = 3.14 inches further down the track, assuming the tyre profile is the same.
(...or is that just my man maths ? )

 

[ga41]

I guess so but wont it take more power to spin the bigger wheel at the same revolutions? Why don't race cars run with 20" or more then?

Some of the weight advantage of a smaller wheel is reneged by the bigger weight of a "fatter" tire to maintain the same overall diameter as stock but i would still think the net result is less overall weight. Don't quote me on that though as I've never tried putting down figures...

 

[mmm-five]

..and the larger the diameter, the quicker you will be as one revolution will have a bigger circumference.
1" Dia x Py ( 3.14) = 3.14 inches further down the track, assuming the tyre profile is the same.
(...or is that just my man maths ? )

Just man maths I'm afraid, as you tend to reduce the tyre wall by 1" when you increase the wheel diameter by 1".

So you'd have, for example, a 255/40r18 and change to a 255/35r19 would give you a 5% smaller sidewall. 5% of a 255mm width tyre is 12.75mm x 2 sides = 25.5mm or about 1".

It's also why the rear tyre size on a staggered set up is at the size it is - to approximately match the rolling radius of the front tyre.

Personally, I've always gone for the smallest wheel option I could that would fit over the brakes. The benefits to me where lighter weight (for the same model wheel) and cheaper/more available tyre options (especially in part-worn, ex-race/qualifying tyres).

 

[Number5]

..and the larger the diameter, the quicker you will be as one revolution will have a bigger circumference.
1" Dia x Py ( 3.14) = 3.14 inches further down the track, assuming the tyre profile is the same.
(...or is that just my man maths ? )

Just man maths I'm afraid, as you tend to reduce the tyre wall by 1" when you increase the wheel diameter by 1".

So you'd have, for example, a 255/40r18 and change to a 255/35r19 would give you a 5% smaller sidewall. 5% of a 255mm width tyre is 12.75mm x 2 sides = 25.5mm or about 1".

It's also why the rear tyre size on a staggered set up is at the size it is - to approximately match the rolling radius of the front tyre.

Personally, I've always gone for the smallest wheel option I could that would fit over the brakes. The benefits to me where lighter weight (for the same model wheel) and cheaper/more available tyre options (especially in part-worn, ex-race/qualifying tyres).

That's interesting. So the profile of /35/ or /40/ is a percentage of the tyre width ? I'd just always assumed it was the wall height in millimeters.

 

[patriot66]

..and the larger the diameter, the quicker you will be as one revolution will have a bigger circumference.
1" Dia x Py ( 3.14) = 3.14 inches further down the track, assuming the tyre profile is the same.
(...or is that just my man maths ? )

Just man maths I'm afraid, as you tend to reduce the tyre wall by 1" when you increase the wheel diameter by 1".

So you'd have, for example, a 255/40r18 and change to a 255/35r19 would give you a 5% smaller sidewall. 5% of a 255mm width tyre is 12.75mm x 2 sides = 25.5mm or about 1".

It's also why the rear tyre size on a staggered set up is at the size it is - to approximately match the rolling radius of the front tyre.

Personally, I've always gone for the smallest wheel option I could that would fit over the brakes. The benefits to me where lighter weight (for the same model wheel) and cheaper/more available tyre options (especially in part-worn, ex-race/qualifying tyres).

That's interesting. So the profile of /35/ or /40/ is a percentage of the tyre width ? I'd just always assumed it was the wall height in millimeters.

Yes it is a percentage of the tyre width. It's referred to as the Aspect Ratio.

 

[Z43.0Si]

The 19" wheels I've got have exactly the same diameter as the 18" wheels for your info. I guess the 19" wheels have a larger mass though. A good point you raise about the tyre size, smaller being cheaper. This could be the deciding factor!

 

[mmm-five]

The 19" wheels I've got have exactly the same diameter as the 18" wheels for your info. I guess the 19" wheels have a larger mass though. A good point you raise about the tyre size, smaller being cheaper. This could be the deciding factor!

How can a 19" wheel have the same diameter as an 18" wheel - or are you including the tyre? :?

 

[Z43.0Si]

The 19" wheels I've got have exactly the same diameter as the 18" wheels for your info. I guess the 19" wheels have a larger mass though. A good point you raise about the tyre size, smaller being cheaper. This could be the deciding factor!

How can a 19" wheel have the same diameter as an 18" wheel - or are you including the tyre? :?

Yes, this is including the tyre. Less rubber so equates to the same diameter.

 

[StigJ]

I use my 19" with Michelin PSS for track days. Very happy with them. Very good grip.

So if I should choose between your wheels I would go for the 18s with PSS just because its a great tire for track days

 

[Z43.0Si]

Very keen to put 4 Michelin pilot supersports on the 18" 108's now, apparently they don't make the standard rear tyre size though

 

[sars]

Well, generally speaking the smaller diameter the better, for less weight. I'm even pondering about 17" for my car when I eventually start tracking it again.

..and the larger the diameter, the quicker you will be as one revolution will have a bigger circumference.
1" Dia x Py ( 3.14) = 3.14 inches further down the track, assuming the tyre profile is the same.
(...or is that just my man maths ? )

Larger diameter wheels reduce the amount of force available to accelerate the vehicle (when fitted to the same vehicle) as it's a function of torque, Newton's second law is acceleration = Force/mass

Torque = Force * radial distance, re-arranging to Force = Torque/Radial distance so if the torque is the same at the diff and the wheel diameter (radii) increase we get less force and ergo less acceleration

How fast you can go is governed by power, wheel diameter is not so important and is completely irrelevant when the car is fitted with a speed limiter and not restrained by power

.....so if you want to accelerate better out of a corner, you want 17" wheels with tyres that have about 3.0 mm of tread or less if it's dry

 

[patriot66]

If your going to exploit the cars capabilities fully and intend to really 'give it some beans' then fit an old set of Style 103s 17" with proper trackday tyres like Yokohama A032, A048, A008, Toyo
R888s etc (loads of new/part worn on Ebay). You will be amazed at the grip which makes it all much safer and inspires more confidence and ultimately makes it all the more enjoyable.

 

[Z43.0Si]

If your going to exploit the cars capabilities fully and intend to really 'give it some beans' then fit an old set of Style 103s 17" with proper trackday tyres like Yokohama A032, A048, A008, Toyo
R888s etc (loads of new/part worn on Ebay). You will be amazed at the grip which makes it all much safer and inspires more confidence and ultimately makes it all the more enjoyable.

I would def go for some full blown track tyres, however I have an almost 300 mile journey to get there and I wouldn't fancy my luck if it rained which we all know is most likely to happen!

 

[patriot66]

If your going to exploit the cars capabilities fully and intend to really 'give it some beans' then fit an old set of Style 103s 17" with proper trackday tyres like Yokohama A032, A048, A008, Toyo
R888s etc (loads of new/part worn on Ebay). You will be amazed at the grip which makes it all much safer and inspires more confidence and ultimately makes it all the more enjoyable.

I would def go for some full blown track tyres, however I have an almost 300 mile journey to get there and I wouldn't fancy my luck if it rained which we all know is most likely to happen!

I did many trackdays several years ago in my kit car and speaking from experience I would suggest that you could do with a mate/wife/girlfriend in a 'support' car with your track wheels, trolley jack, fuel, spares and tools on board. Trailering your Zed behind the 'support' car is also a good idea just in case you break something or god forbid you prang it.