Tyre Size Choice

[LotsOfLaughs]

Hi, Im after some advice - I'll try to be as concise as possible without missing anything out.

Car - Subaru Legacy Spec.b, 260hp, 1700kg inc fuel and driver.
Use - Road only, no track days, no snow. Road conditions varying from bitterly cold and soaking wet to lovely baking hot summers day.

I'm not sure which tyre to go for, Im torm between a Bridgestone Potenza, Michelin PS5, and the Uniroyal Rainsport 5. Not all of these are available in all the sizes Im considering, I know that for example the PS5 doesnt come in an aspect ratio higher than 45, I dont think. Im open to any other suggestions, but tyres are expensive.

The size dilema - So the Subaru Ive got came with many different wheel and tyre sizes, the smallest being a 15" or 16", and the biggest being an 18", which is what mine has currently, with 215/45R18s. 17" wheels are the smallest that will clear my current brake callipers. If I upgrade my callipers, none of my current wheels will fit.

I have a number of things Id like to change, and Im hoping that tyres will do them all.
1.) Ground clearance is poor, the car scrapes on some speedbumps. The speedo already over-reads, so I can afford to go for a larger overall size, I think up to 700mm overall diameter (currently at 650ish, iirc)
2.) The steering is very light and a bit lacking in "feel" - this is becuase the power steering is over-assisted, but Im hoping a different and/or wider tyre will help.
3.) Id like the car to stop a bit better - its already very good, but it could be better. Not much point upgrading the brakes until Ive got tyres that can use the extra stopping power. Currently, I only ever get brake fade if Im driving like a clot. Stopping distance is good, but its not great, its an almost 20 year old car and the world has moved on, even Skodas come with bigger brakes these days.
4.) The ride isnt great, so some extra sidewall would be nice.
Wheel choice - I currently have 2 sets of wheels, both OE alloy wheels, one set of 17x7 and one set of 18x7. I'm contemplating picking up a set of 18x8 Prodrive wheels, which will allow me to fit wider tyres. Im told theyre also lighter than the standard 18s. Im not aware of any subaru-specific 17x8 wheels, but 17x7.5 wheels are common. Once Ive selected a wheel and tyre, Ill be getting rid of the others, because I havnt got room to keep them.

So - what should I do? Which tyre, and in which size?
Thanks!
Edit: I know the easy answer is "buy quality tyres in the standard size", but thats not an upgrade. I want to upgrade, but I want to make an informed decision, rather than guess and hope I dont ruin the car by changing the geometry of the steering/suspension.
I should also mention that Ive gone through a set on Uniroyal Rainsport 5s in about 8000 miles, I think they didnt like being pushed hard on hot days.

Edited by LotsOfLaughs on Sunday 3rd November 23:59

[MustangGT]

First choices for me would be Michelin Cross Climate or Goodyear Vector 4 season if available in that size.

[Scrump]

You have thrown in so many variables that I am not sure where to begin.

If you want more ground clearance and a bit better ride then go for tyres with an increased sidewall height, 17 inch wheels will be better for this than the 18.
My cars have PS4 and GY eagle Assy5, the GY eagle were a lot cheaper than the PS4, yet seem be a close match.

[mmm-five]

An all-season will generally give you a softer ride than a touring/summer tyre, and if there's no snow use then the Michelin Cross-Climate loses some of it's advantage, and for an all-season the Goodyear is a very good option.

There's also the new Continental AllSeasonContact 2 which has better cold & wet performance than both previously mentioned, but availability is a bit poor at the moment (I got sent ASC1 three times before three different online tyre places admitted they couldn't get them - despite them being shown as in stock on their websites).

Finally, the Vredestein Quatrac Pro Plus is good value for money.

https://www.tyrereviews.com/Article/Best-All-Seaso...

For summer tyres, I've always gone for the latest version of whichever of Continental SportContact, Michelin Pilot Sport, or Goodyear F1 Eagle is available in my size at the time.

Edited by mmm-five on Monday 4th November 13:11

[InitialDave]

I fitted CrossClimate 2s to my car, with the intention of getting some performance summer tyres in the summer (Conti Sport 7s were my prime candidate).

But I got on well enough with the CC2s that I didn't feel the need to in the end.

[Smint]

Vred Quatrac Pros have made the Forester a real pleasure once again to drive, can scarcely believe the improvement in ride quality and near silent running in comparison to the Falken set they replaced, even better ride now than the full winter set that are now redundant, Vreds 55 aspect where the winters were 60 aspect along with 1" smaller wheel diameter.

[E-bmw]

Scrump said:

You have thrown in so many variables that I am not sure where to begin.

^^^^ Wot 'e said.

Start (on your own) by deciding what size wheels you want and then ask about tyres as the wheel size WILL limit your options.

[Pica-Pica]

Start by working out the minimum size wheel that will fit over your existing brake set up.
Use this for determining the (comparable) rolling circumference of tyres available (diameter is never used).
http://www.wheelcalc.com

You won’t get much ground clearance change by changing tyre sizes, unless you send your speedometer into the illegal zone. For increased ground clearance you will need a suspension change.

[stevieturbo]

No point upgrading brakes, when the standard brakes would be able to lock up the wheels anyway ( ABS aside ).

And as you say you do not track the car....seems odd you think the OE brakes would not be perfectly fine.

But tyres, and same response for pretty much all queries.....there are just so many reviews on Tyre Reviews on Youtube, it's a wonder the decision is really that hard.

Whilst there is a bit of a fantasy about all season tyres ( and I did put CC2's on my dads...but then never really got the winters i though we might )....I think the reality is that a good normal tyre, will still be better 90% of the time for cold and wet. At least this is what the tests show.
Even CC2's, probably the best all season, do not brake as well as normal tyres even in cold/wet conditions

Perhaps a more average "touring" type tyre might be better suited ?

https://www.youtube.com/watch?v=3ZsWD4N0yds

all season ?

https://www.youtube.com/watch?v=cTxxiYcDvQU

etc etc etc

[LotsOfLaughs]

MustangGT said:

First choices for me would be Michelin Cross Climate or Goodyear Vector 4 season if available in that size.

I dont see why I need all seasons, I think Ive driven on snow twice in my life, both times in 2wd cars on summer tyres. Obviously its not ideal and if I were planning on driving somewhere snowy for a winter holiday, Id get winter tyres.

Scrump said:

You have thrown in so many variables that I am not sure where to begin.

If you want more ground clearance and a bit better ride then go for tyres with an increased sidewall height, 17 inch wheels will be better for this than the 18.
My cars have PS4 and GY eagle Assy5, the GY eagle were a lot cheaper than the PS4, yet seem be a close match.

Yep, wider tyres means more grip (on dry tarmac at least), but I also think its easy to make a mess of it by going too wide or getting the offset wrong or fitting a tyre thats the wrong size for the wheel etc.
A for a 17" tyre, I think Id be looking at a 215/60R17, or possibly a 225. Thats quite a tall skinny tyre, so should I look at a wider wheel, so that I can fit a wider tyre, of a lower aspect ratio, but have a similar sidewall thickness? (Say a 235/55r17)

E-bmw said:

Start (on your own) by deciding what size wheels you want and then ask about tyres as the wheel size WILL limit your options.

Its the wheel size Im not too sure about. Tyres are only really part of the question in a "are Pilot Sports so good that Ive got to stick with an 18" wheel?" sence.
Ive not got much choice on wheel size, its 17" or 18", and then either 7j, 7.5j or 8j in either.

Pica-Pica said:

Start by working out the minimum size wheel that will fit over your existing brake set up.
Use this for determining the (comparable) rolling circumference of tyres available (diameter is never used).
http://www.wheelcalc.com

You won’t get much ground clearance change by changing tyre sizes, unless you send your speedometer into the illegal zone. For increased ground clearance you will need a suspension change.

The minimum wheel size that will fit over my current, 2-pot brake setup is 17", 7j, the wheels that will fit over bigger, 4-pot brakes are also 17", but they arent the same 17" wheels that I currently have, and they are 7.5j.
My speedo is already in the barely legal zone in that its 7-10% under, so I can go quite a bit bigger. Its also not that difficult to recalibrate the speedo I dont think.
Changing the suspension isnt something Im too keen on, I cant find any coilovers that go taller than standard, and the current suspension handles so well I dont want to much it up.

stevieturbo said:

No point upgrading brakes, when the standard brakes would be able to lock up the wheels anyway ( ABS aside ).

And as you say you do not track the car....seems odd you think the OE brakes would not be perfectly fine.

But tyres, and same response for pretty much all queries.....there are just so many reviews on Tyre Reviews on Youtube, it's a wonder the decision is really that hard.

Whilst there is a bit of a fantasy about all season tyres ( and I did put CC2's on my dads...but then never really got the winters i though we might )....I think the reality is that a good normal tyre, will still be better 90% of the time for cold and wet. At least this is what the tests show.
Even CC2's, probably the best all season, do not brake as well as normal tyres even in cold/wet conditions

Perhaps a more average "touring" type tyre might be better suited ?

https://www.youtube.com/watch?v=3ZsWD4N0yds

all season ?

https://www.youtube.com/watch?v=cTxxiYcDvQU

etc etc etc

If I go for wider tyres, I might then benefit from a brake upgrade, although I doubt Ill be going that much wider.
Ive managed to get the brakes very warm on a spirited drive, keeping up with a much newer WRX STI, which has much bigger brembo brakes, and there was a noticable difference in stopping power once my brakes were hot. If EBC discs and pads will do, then I wont spend 4-figures on brembo callipers...
I do like a sporty tyre, they just dont seem to make them, well, PS5s at east, in a tall aspect ratio. Rainsports come in a slightly taller size, but theyve not lasted very long and they arent that much cheaper anymore.
Ive noticed that 225/40R18s are about £100 a set cheaper than 215/45R18s, which is the standard size for my car. The price difference grows when you start to look at premium tyres, so Im wodering if theres another size in a taller aspect ratio that I should look for, if anyone else knows of such price differences, without me manually going through every size between 215-235 and 40-65 in 17" and 18", thats 36 sizes, although there are probably a dozen sizes that would do.

[wyson]

Why not just stick to standard Subaru sizes, one size down and then get decent tyres? A comfort orientated summer tourer. Tyrereviews is a good resource, pick a tyre that reviews well for comfort.

If you are worried about your car grounding, buy a lift kit, but this will negatively affect your handling. I found it weird that a boggo car like a Legacy will ground on a speed bump though. Have you lowered it? You could also approach speed bumps supercar style, one corner first. Videos of this technique are up on youtube.

Buy a brake kit that will fit into the above choices. If you want massive brakes requiring bigger wheels, accept ride quality is going to suffer. How often do you drive so spiritedly that brake fade becomes a problem, vs everyday ride comfort?

Like others have said, I find some of the OPs logic a bit baffling.

I’ll also add, I ONCE fiddled with non standard tyre sizes, it upset the handling of the car. I don’t know enough about suspension geo set up, nor do I want to spend hundreds extra going to a specialist to sort that out. It’s much safer to stick to standard wheel and tyre sizes the manufacturer has already tested and recommended.

Edited by wyson on Wednesday 6th November 06:44

[E-bmw]

OK, you are just rambling and seem to be arguing your way down one direction without actually admitting what direction you want to go in, so lets see if we can help you out, answer the following questions.

Ultimately, you need to start somewhere not everywhere at the same time.

1. Why do you want a brake upgrade? If it is because they aren't very good, have you actually done a brake service/refresh to get them as good as they can be? If not, that is your first step as then you may forget the big brake kit & that will help the next steps.


2. What is the full tyre/wheel size you currently have and (precisely) how accurate/un-accurate is the speedo referenced to GPS?


3. What type of driving will the car be used for, in what weather conditions, and in what area of the country are you?


4. Do you want to achieve any particular look wrt wheel size etc?

[wyson]

For me its not the rambling, I can somewhat see through that, it’s the lack of awareness surrounding the trade offs.

Op wants higher ground clearance, a better ride and massive wheels to fit a huge brake kit so they can resist fade and stop the car in a shorter distance. He would also like more steering feel.

He thinks that fiddling with tyre sizes is going to achieve all this. It won’t.

Really, that is quite a complex set of requirements requiring 3 sets of modifications:

Wheel and tyres.
Suspension.
Brake kit.

It’s going to cost thousands, to be done properly. It will likely affect his insurance as well.

Can’t help feeling it would be easier for him to chop in his car for a Porsche Macan or Cayenne on air suspension with PCCB brakes.

Edited by wyson on Wednesday 6th November 11:36

[MustangGT]

LotsOfLaughs said:

MustangGT said:

First choices for me would be Michelin Cross Climate or Goodyear Vector 4 season if available in that size.

I dont see why I need all seasons, I think Ive driven on snow twice in my life, both times in 2wd cars on summer tyres. Obviously its not ideal and if I were planning on driving somewhere snowy for a winter holiday, Id get winter tyres.

The point about all seasons is that they are an excellent compromise for 12 months of the year. They are not anything to do with snow per se. If wanting just one set of wheels and tyres this is my preferred option.

[stevieturbo]

sporty and tall ratio, would be quite the contradiction.

[LotsOfLaughs]

wyson said:

Why not just stick to standard Subaru sizes, one size down and then get decent tyres? A comfort orientated summer tourer. Tyrereviews is a good resource, pick a tyre that reviews well for comfort.

If you are worried about your car grounding, buy a lift kit, but this will negatively affect your handling. I found it weird that a boggo car like a Legacy will ground on a speed bump though. Have you lowered it? You could also approach speed bumps supercar style, one corner first. Videos of this technique are up on youtube.

Buy a brake kit that will fit into the above choices. If you want massive brakes requiring bigger wheels, accept ride quality is going to suffer. How often do you drive so spiritedly that brake fade becomes a problem, vs everyday ride comfort?

Like others have said, I find some of the OPs logic a bit baffling.

I’ll also add, I ONCE fiddled with non standard tyre sizes, it upset the handling of the car. I don’t know enough about suspension geo set up, nor do I want to spend hundreds extra going to a specialist to sort that out. It’s much safer to stick to standard wheel and tyre sizes the manufacturer has already tested and recommended.

Edited by wyson on Wednesday 6th November 06:44

No, its not lowered, its a spec.b, so its on lower, stiffer suspension than the "boggo" legacy, and its got a 2.5" stainless exhaust, which hangs a bit lower than standard, and thats the bit which catches.
The bigger brakes needing different wheels is more to do with the shape of the calliper, the standard brakes only have pots on one side, whereas the big brakes have pots on both sides, and so the standard wheel spokes dont clear them. There are 17" wheels available which clear the big brakes.

E-bmw said:

OK, you are just rambling and seem to be arguing your way down one direction without actually admitting what direction you want to go in, so lets see if we can help you out, answer the following questions.

Ultimately, you need to start somewhere not everywhere at the same time.

1. Why do you want a brake upgrade? If it is because they aren't very good, have you actually done a brake service/refresh to get them as good as they can be? If not, that is your first step as then you may forget the big brake kit & that will help the next steps.


2. What is the full tyre/wheel size you currently have and (precisely) how accurate/un-accurate is the speedo referenced to GPS?


3. What type of driving will the car be used for, in what weather conditions, and in what area of the country are you?


4. Do you want to achieve any particular look wrt wheel size etc?

So - as to the question of bigger brakes - I changed the pads, just to standard ones. I can either upgrade the discs and pads, and keep the standard callipers, or get bigger callipers too. Ive not tried upgraded pads, but Id rather just spend the money once, rather than upgrade the discs and pads, find out that they still fade, then have to throw them away because the bigger callipers need a different disc and pad.
The tyres are currently 215/45R18, and the speedo is out by at least 7%, any more than 10% is an MoT fail. (It may not under-read at all, so max diameter is 700mm to be safe)
The car is driven daily, A-roads, dual carridgeways, through the village with potholes and speedbumps, and then thrashed on the best mountain roads when the opportunity presents its self. Im in Wales, not far from Snowdonia, so plenty of great roads, but lots of rain. No snow, and when there is its cleared very quickly.
Not bothered by how the wheels look, although I dont want the wheels poking outside the arches because thats illegal.

wyson said:

For me its not the rambling, I can somewhat see through that, it’s the lack of awareness surrounding the trade offs.

Op wants higher ground clearance, a better ride and massive wheels to fit a huge brake kit so they can resist fade and stop the car in a shorter distance. He would also like more steering feel.

He thinks that fiddling with tyre sizes is going to achieve all this. It won’t.

Really, that is quite a complex set of requirements requiring 3 sets of modifications:

Wheel and tyres.
Suspension.
Brake kit.

It’s going to cost thousands, to be done properly. It will likely affect his insurance as well.

Can’t help feeling it would be easier for him to chop in his car for a Porsche Macan or Cayenne on air suspension with PCCB brakes.

Edited by wyson on Wednesday 6th November 11:36

No, selling my 3-4k Subaru for a Macan wont get me anywhere. Even if I could afford one, I dont want one. They cant be had with a manual gearbox, and as far as I can tell theyre just a poncy Tiguan.
Theres no reason to fiddle with the suspension - changing the tyre size will change both the groundclearance and comfort to some degree.

MustangGT said:

The point about all seasons is that they are an excellent compromise for 12 months of the year. They are not anything to do with snow per se. If wanting just one set of wheels and tyres this is my preferred option.

The most "wintery" it gets is rain. Most of the summer, it rains. Sometimes in the summer its hot and dry. All the tyres that score best in wet braking are the sporty summer tyres - not the extra sporty ones (e.g. PS4 did better than PS4S)

stevieturbo said:

sporty and tall ratio, would be quite the contradiction.

Thats the problem Im finding.


Okay, lets go back to the start - forget comfort, and bigger brakes, I want more groundclerance and more steering feel, and I want the best grip, for safety.
Is a 235/50R18 going to be better than a 215/60R17, in terms of steering feel and grip?

[E-bmw]

LotsOfLaughs said:

E-bmw said:

OK, you are just rambling and seem to be arguing your way down one direction without actually admitting what direction you want to go in, so lets see if we can help you out, answer the following questions.

Ultimately, you need to start somewhere not everywhere at the same time.

1. Why do you want a brake upgrade? If it is because they aren't very good, have you actually done a brake service/refresh to get them as good as they can be? If not, that is your first step as then you may forget the big brake kit & that will help the next steps.


2. What is the full tyre/wheel size you currently have and (precisely) how accurate/un-accurate is the speedo referenced to GPS?


3. What type of driving will the car be used for, in what weather conditions, and in what area of the country are you?


4. Do you want to achieve any particular look wrt wheel size etc?

So - as to the question of bigger brakes - I changed the pads, just to standard ones. I can either upgrade the discs and pads, and keep the standard callipers, or get bigger callipers too. Ive not tried upgraded pads, but Id rather just spend the money once, rather than upgrade the discs and pads, find out that they still fade, then have to throw them away because the bigger callipers need a different disc and pad.

As I have not heard another owner of the same car suggest they are under-braked & you aren't using it for anything that would want bigger brakes, I would suggest you may well be wrong, buy hey-ho, it is up to you.

LotsOfLaughs said:

The tyres are currently 215/45R18, and the speedo is out by at least 7%, any more than 10% is an MoT fail.

No it isn't, speedo accuracy isn't even tested.

LotsOfLaughs said:

The car is driven daily, A-roads, dual carridgeways, through the village with potholes and speedbumps, and then thrashed on the best mountain roads when the opportunity presents its self. Im in Wales, not far from Snowdonia, so plenty of great roads, but lots of rain. No snow, and when there is its cleared very quickly.

In that case, I would definitely be sticking with standard everything & just going up a bit on the sidewall to get the speedo closer after a full brake refresh.

[stevieturbo]

LotsOfLaughs said:

Thats the problem Im finding.


Okay, lets go back to the start - forget comfort, and bigger brakes, I want more groundclerance and more steering feel, and I want the best grip, for safety.
Is a 235/50R18 going to be better than a 215/60R17, in terms of steering feel and grip?

Depends on tyre choice, environment you are driving, wheel width.

Best grip under what conditions ? Wet ? dry ? snow ? rough terrain ? etc etc ? Braking ? cornering ? There are always compromises everywhere.

And "best grip", may not always be the most progressive, best handling etc, and could break away more suddenly leading to a more dangerous tyre and poor handling. Something with a more progressive might break away earlier, but in a more controlled manner, making it much safer. So you could perceive that as less grip, but in reality it is a better choice.
And wheel width relative to a tyre can also affect this. Narrower tyres on a wide rim seem to break away in a more progressive manner vs wider tyres on the same rim.

So really....just buy good tyres for your driving environment. But potentially yes, a stiffer sidewall should give more feel. Even two tyres brands the same size, can give different feel anyway

[MustangGT]

LotsOfLaughs said:

Thats the problem Im finding.


Okay, lets go back to the start - forget comfort, and bigger brakes, I want more groundclerance and more steering feel, and I want the best grip, for safety.
Is a 235/50R18 going to be better than a 215/60R17, in terms of steering feel and grip?

Change the suspension, not the tyres.

[LotsOfLaughs]

E-bmw said:

As I have not heard another owner of the same car suggest they are under-braked & you aren't using it for anything that would want bigger brakes, I would suggest you may well be wrong, buy hey-ho, it is up to you.

Its a common complaint and upgrade on most non-STI Subarus. Im not going to be doing any trackdays though so I think Ill get away with just a pad and disk upgrade.

stevieturbo said:

Depends on tyre choice, environment you are driving, wheel width.

Best grip under what conditions ? Wet ? dry ? snow ? rough terrain ? etc etc ? Braking ? cornering ? There are always compromises everywhere.

And "best grip", may not always be the most progressive, best handling etc, and could break away more suddenly leading to a more dangerous tyre and poor handling. Something with a more progressive might break away earlier, but in a more controlled manner, making it much safer. So you could perceive that as less grip, but in reality it is a better choice.
And wheel width relative to a tyre can also affect this. Narrower tyres on a wide rim seem to break away in a more progressive manner vs wider tyres on the same rim.

So really....just buy good tyres for your driving environment. But potentially yes, a stiffer sidewall should give more feel. Even two tyres brands the same size, can give different feel anyway

Right, so it sounds like a slightly wider wheel with a standard tyre, or a significantly wider wheel with a slightly wider tyre, will be an upgrade in every way?
(Irrelevant sidenote, this is a big no-no for offroad applications because it leaves the sidewall very exposed to punctures/damage/etc, especially at lower pressures)
So based on what youve said, going from a 215/45r18 on an 18x7j wheel to a 235/45r18 on an 18x8j wheel will do everything, because the tyre width increase (20mm) is less than the wheel width increase (25.4mm, 1") so it gives both more grip and a more progressive breakaway characteristics?
Is there any way I can find the specs for sidewall stiffness? Say if I wanted to know which, between a Pilot Sport 5, a Potenza Sport, or a Rainsport 5, had the stiffest sidewall?