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Discussion Starter · #1 ·
Why doesn't the 156 GTA have 215/45/17 as standard instead of 225?

I'm considering potentially getting some Silverstone Type RR tyres for track days, and these only come with a 215 width:
http://www.silverstone.com.my/tyre_ftzTypeRR_spec.asp
They seem pretty keenly priced, apparently only £85 stg a tyre and are used as the control tyre in some Malaysian FWD Saloon series.

Just wondering if anyboy has any "no don't do it!" insights :)

This would probably mean I would switch to using my current original GTA alloys as my track wheels, and keep my 8x18" multi spokes for the road.

I'm looking at this rather superb tyre bible link below and have confirmed that
215/45/17 is within the acceptable range for the GTA's 17x7.5" rims, almost in the exact middle.

http://www.carbibles.com/tyre_bible.html

So if anything 215 looks much closer to the middle of the allowed range than 225 according to the ideal rim width calculator on that page.
7.5" rims are at the narrow limit for 225 width tyres, 9" being the highest.

AFAICS 215 width should mean less tyre wall deformation which would be more suitable for track use, at the expense of a slightly less comfortable ride for road use which wouldn't be relevent, at leats in my specific circumstances.

Did the 147 GTA come with 215 width?

Cheers,
TB
 

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i guess there are many reasons for 'why', but there would be no great reason why you cannot use a 215, especially for track purposes.

issues:
*availability and cost: presumably, alfa created a tyre deal to fit 225s to their cars, so would have bought in bulk or have a contract in place for bulk-pricing
*handling and comfort: presumably, 225s were considered the best compromise for cornering grip, comfort (profile height), straightline stability, etc

changing to 215s will alter the grip/comfort/stability balance slightly, but if the compound is actually stickier, no probs. more significant would be speedo error; but again, on the track this is not a major issue.

overall, 225/45/17 is a fairly common size, for not only alfa, but other cars. so there's plenty of choice for non-OEM tyres when replacement is required. that's a good thing for drivers (more choice).

:)
 

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215/45 => 7.0 to 8.0 rim width
225/45 => 7.0 to 8.5 rim width

My thoughts as to why the GTA comes with 225/45 tyres.

1. Looks and acceptability - 225/45 is the standard fit for many high performance saloons and 215/45 is already fitted to lesser 156 / 147 so the GTA needed something bigger and better. Also the wider tyre will give more rim protection on a 7.5" rim.

2. Extra grip to contain 250bhp

3. Comfort - the 225/45 tyre has bigger side wall than the 215/45 tyre giving a slightly more complient ride.

If you fit a 215/45 tyre on a 7.5" rim you will stretch the tyre over the rim more than on a 7" rim and IMO this will give less side wall flex and a harsher ride - not a problem if you are using the tyres on the track.
 

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Discussion Starter · #4 ·
Thanks for the informational posts guys :)
If I get them I'll report back on how it worked out.

I think I need to have a few cups of coffee before I get the full "Zen" of tyre contact patches discussed in the tyre guide bible :lol:
Apparently the size of the contact area stays the same with narrower width tyres, its just the shape of the contact area that changes.
I get that much, but would like to unstand the effective difference when cornering hard.

With some courage I will attempt to undertand the fancy friction graph (deflection, penetration, deformation) when I feel a bit more energetic!

Cheers,
TB
 

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I gave up reading that tyre bible - couldnt get my head around the contact patch thing and wasnt too interested at the time to continue reading it - probably need to read it again :rolleyes:
 

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Discussion Starter · #7 ·
I guess 235 might give more traction, but suspect not more cornering forcefor a 7.5" rim, and maybe would feel very squirmey.
 

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Nothing like testing it out in practice :D

You have the rims, the tyres are only 85 quid per corner, go ahead and see how they go. They certainly look good. I would try the 215's though.

I guess 235 might give more traction, but suspect not more cornering forcefor a 7.5" rim, and maybe would feel very squirmey.
 

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i'm no tyre guru, but tyre size is only one factor in the overall equation.

sure, if you compare the exact same model of tyre, but in different sizes, you may be able to draw some conclusions about what works best after doing the testing.

but if you end up comparing not only different sizes, but also different model tyres, then such things as compound, sidewall stiffness, tread pattern, etc, all have an impact. and unless you are able to consistently repeat the 'conditions' you place each tyre under (ie: do racetrack laps at a consistent pace), and do enough testing, you probably can't draw any real conclusion.

however, i can only presume you will still have an idea of 'how a tyre feels' and whether it's really good or really bad (for your needs). it's the small differences you may not detect; and arguably, 'so what'.

:)
 

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Discussion Starter · #10 ·
All sensible points, I have telemetry for track use to help with comparing performance under brakine/accel/cornering.

Of course as you say these will be a different brand of track tyre to what I am currently using, but since don't come in 225 anyway I thought it might be worth giving 215 a go.
 

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Why doesn't the 156 GTA have 215/45/17 as standard instead of 225?
On the std 156, the 17" was, at least originally, a dealer fit option rather than a factory fit.

I read that there is a TUV reg that requires optional tyres to be no bigger in dia than the std tyres. 225/45R17 is slightly larger dia than 205/55R16 so 215/45R17 were used.

However, 17" was the std GTA size (with a smaller 16" option) so 225/45R17 was fine and also comes with a higher load index.

For track use there is no reason not to use the 215/45R17. You are very unlikely to max it in 6th gear so the lower top speed will not be an issue.
Wider tyres will also take longer to warm up.
 

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Discussion Starter · #12 · (Edited)
Thanks David, didn't know about the longer time to warm up business.
I guess it would follow from that that they overheat more slowly?
Probably a good consideration for road tyres used at track days?

My car is equipped with pretty good front tyre warming facilities :lol:
I don't mind the rear being a little cold, at least on road tyres, I have learned to respect cold pilot sport cups on the back though!
Anyway it sounds like Silverstones I am looking at should do the business. I'll report back if they any good, they seem to be way cheaper than the big brand competition.

Cheers,
TB
 

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My car is equipped with pretty good front tyre warming facilities :lol:
I don't mind the rear being a little cold, at least on road tyres, I have learned to respect cold pilot sport cups on the back though :lol:
Some people with powerful FWD cars use different tyres at front and rear wheels. Harder for front and softer for rear. This will even out the difference in warmup time and treadwear but may slightly inbalance the car's behaviour.

It is not uncommon to use semislicks at the front and normal tyres at the rear wheels for people that go to racetracks regularly.
 

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Discussion Starter · #14 ·
On a dry day I would consider trying different compound front and back at some point, the effect would be quite extreme though I think.
I would have 20% less grip on the rear than the front, it could be quite enjoyable on a slowish technical circuit like Mondello but I would probably wet my pants at the Ring or Donnington!

Since the brake bias isn't adjustable I suspect the rears would tend to be at the limit of locking all the time under hard braking which could make things tricky.

Its not an option for me currently since I just have one set of 18" rims and one set of 17" rims, so mixing different rim sizes (not to mention radically different styles :lol:) probably also would screw up the EBD distribution.

Right now I just whack up my rear dampers to max, but it looks like an adjustable anti-roll bar for the rear (planning to get over the summer) will do wonders for the balance and I still have the option of much much stiffer rear springs.

Cheers,
TB
 

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Discussion Starter · #15 ·
A mate just told me that it is usual enough for track oriented tyres to have a larger contactpatch for any given size compared to road tyres. He has 205 Totyo R888's that are as wide
as his 215 road tyres.

Anyway just ordered the Silverstones earlier today :)
Will use them at a track day on St. Patricks weekend (19th March)

Thanks to all,
TB
 

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@TB: 215 works just fine. (drive on them too ;) ) advantage: less resistance, disadvatage: little less on the brakes.

235's: handling like a VolksWagon ;)

(track tested :cool: )
 

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A mate just told me that it is usual enough for track oriented tyres to have a larger contactpatch for any given size compared to road tyres. He has 205 Totyo R888's that are as wide
as his 215 road tyres....
Semi's are usually a bit wider; slicks even more so. 888's are nice for the Ring when it's dry :) The better, but much more expsive tyres: Yokohama advan, Michelin pilot sport Cup (terribly expensive...)
 

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Discussion Starter · #18 ·
I am using the cups at the moment, they handle great, don't overheat, and wear very well ..but are over twice as dear as the Silverstone type RR tyres I just purchased so I am happy to try these as alternatives.
I haven't tried the Toyos on my car but I suspect they are softer and grippier until they overheat sooner which seems to be a characteristic.
They really should be quicker for a single timed lap since they are such a soft compound that they would only last one or two track days with my car. The cups would last 4 full days.
 

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Depends a lot on what circuit you drive on, and how many consecutive laps ;) From my experience the 888 is not better gripping then the Cups; but they are so much cheaper :)

If you run them on the Ring, don't run more then 2 to 3 laps behind each other on full throttle, otherwise you will not make it to the end of the week-end ;)
 

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Discussion Starter · #20 ·
I probably won't bother with track tyres for the ring, I would have to bring road tyres as well in case it rained, most likely will just be PS2's for me .

No doubt a moments insanity before departure will cause me to recant and pack the car up with them.
 
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