What does 'over tyred' actually mean?
Discussion
When people say that modern cars are 'over tyred', what does this actually mean? How do you judge whether a car is under or over tyred?
Surely it must relate to the weight of the vehicle? Let's for example consider the lowly MX5, it's got 'skinny' 185 section tyres which most people would probably consider 'under tyred'. But it only ways about 1000kg. If we put 225s on it, it would most definitely be 'over tyred', but 225s on a 2000kg car would definitely be 'under tyred'.
Is there an actual defined point where people/engineers would say "that's about perfect"?
As a simple comparison I worked out that the aforementioned MX5 would have about 250kg on each tyre, so 185/250 would give it a 'width to load' ratio of .74.
Compared to something like an E46 M3, which has closer to to 400kg on each wheel, and 225/255 tyres, that would be a WTL ratio of .56F and .64R.
Is the E46 is actually under-tyred compared to the MX5?
Are overweight modern cars actually still using relatively conservative tyre widths for the weight of the vehicles, despite peoples assumptions?
Surely it must relate to the weight of the vehicle? Let's for example consider the lowly MX5, it's got 'skinny' 185 section tyres which most people would probably consider 'under tyred'. But it only ways about 1000kg. If we put 225s on it, it would most definitely be 'over tyred', but 225s on a 2000kg car would definitely be 'under tyred'.
Is there an actual defined point where people/engineers would say "that's about perfect"?
As a simple comparison I worked out that the aforementioned MX5 would have about 250kg on each tyre, so 185/250 would give it a 'width to load' ratio of .74.
Compared to something like an E46 M3, which has closer to to 400kg on each wheel, and 225/255 tyres, that would be a WTL ratio of .56F and .64R.
Is the E46 is actually under-tyred compared to the MX5?
Are overweight modern cars actually still using relatively conservative tyre widths for the weight of the vehicles, despite peoples assumptions?
LeoSayer said:
Certain cars come with a massive range of tyres sizes as options.
My X5 30d can be had with 255s at the rear, or optional 315s! I would say the 315s are overtyred.
Thats a what, 2200kg car isn't it? Say 550kg on each wheel. 315/550 = .57. That's less rubber per kilo, and significantly so too, than the dinky MX5.My X5 30d can be had with 255s at the rear, or optional 315s! I would say the 315s are overtyred.
Is it really over tyred? Or is the 255 option just severely under tyred?
Who knows!
Edited by Kozy on Monday 3rd March 13:03
It's interesting to look back 20-30 years, when an acceptable family car tyre was 165 section and a Mercedes S-class rode on 205s...
I think the point at which the car rides badly, tramlines excessively and is affected by excessive road noise indicates if it is over-tyred. Cars are sold with ridiculously large wheels and rubber-band tyre profiles for styling, showroom appeal and possibly due to cheap OEM supply of large wheels by wheel manufacturers, possibly in colusion with tyre manufacturers, who realise such wheels are more vulnerable to damage and more expensive to replace.
I down-sized my Seat Leon from 17" with 225/45 tyres to 16" with 205/55. On the bigger wheels it rode like a skateboard and on bumpy roads the whole steering column shook sideways. Definitely over-tyred!
I think the point at which the car rides badly, tramlines excessively and is affected by excessive road noise indicates if it is over-tyred. Cars are sold with ridiculously large wheels and rubber-band tyre profiles for styling, showroom appeal and possibly due to cheap OEM supply of large wheels by wheel manufacturers, possibly in colusion with tyre manufacturers, who realise such wheels are more vulnerable to damage and more expensive to replace.
I down-sized my Seat Leon from 17" with 225/45 tyres to 16" with 205/55. On the bigger wheels it rode like a skateboard and on bumpy roads the whole steering column shook sideways. Definitely over-tyred!
mikeveal said:
On a trike like mine, the tyres should break adhesion and slide before you generate enough cornering forces to lift a wheel. Any trike that does not do this is over tyred.
Not sure that can really be used as a reference? Most FWD cars can cock a back wheel, even back in the 80s.I'm not sure how you would quantify it but I think most modern cars a over tyred. I don't really see the point of fitting hugely wide tyres to most things, they increase road noise, rolling resistance and the danger of aquaplaning for no real benefit at all. Absolute grip depends more on the compound and construction than the absolute width anyway so I suspect it is mostly fashion and marketing. My Golf rides on 225/40R18s which are frankly daft for a moderately powerful FWD hatchback, 16 or 17 inch rims with 205 width tyres would have been more than adequate.
Kozy said:
When people say that modern cars are 'over tyred', what does this actually mean? How do you judge whether a car is under or over tyred?
Surely it must relate to the weight of the vehicle? Let's for example consider the lowly MX5, it's got 'skinny' 185 section tyres which most people would probably consider 'under tyred'. But it only ways about 1000kg. If we put 225s on it, it would most definitely be 'over tyred', but 225s on a 2000kg car would definitely be 'under tyred'.
Is there an actual defined point where people/engineers would say "that's about perfect"?
As a simple comparison I worked out that the aforementioned MX5 would have about 250kg on each tyre, so 185/250 would give it a 'width to load' ratio of .74.
Compared to something like an E46 M3, which has closer to to 400kg on each wheel, and 225/255 tyres, that would be a WTL ratio of .56F and .64R.
Is the E46 is actually under-tyred compared to the MX5?
Are overweight modern cars actually still using relatively conservative tyre widths for the weight of the vehicles, despite peoples assumptions?
The contact patch depends in the diameter of the tyre, not just the width. Surely it must relate to the weight of the vehicle? Let's for example consider the lowly MX5, it's got 'skinny' 185 section tyres which most people would probably consider 'under tyred'. But it only ways about 1000kg. If we put 225s on it, it would most definitely be 'over tyred', but 225s on a 2000kg car would definitely be 'under tyred'.
Is there an actual defined point where people/engineers would say "that's about perfect"?
As a simple comparison I worked out that the aforementioned MX5 would have about 250kg on each tyre, so 185/250 would give it a 'width to load' ratio of .74.
Compared to something like an E46 M3, which has closer to to 400kg on each wheel, and 225/255 tyres, that would be a WTL ratio of .56F and .64R.
Is the E46 is actually under-tyred compared to the MX5?
Are overweight modern cars actually still using relatively conservative tyre widths for the weight of the vehicles, despite peoples assumptions?
If the tyres are big enough to have a negative effect on both ride and handling the car is over tyred (prioritising one over the other can be down to preference).
I don't think a simple linear relationship between tyre width and vehicle weight models it though.
I don't think a simple linear relationship between tyre width and vehicle weight models it though.
Edited by GravelBen on Wednesday 5th March 11:14
GravelBen said:
If the tyres are big enough to have a negative effect on both ride and handling the car is over tyred.
I don't think a simple linear relationship between tyre width and vehicle weight models it though.
This, as it's also related to the track width compared to the tyre width in terms of corrupting steering feel/feedback.I don't think a simple linear relationship between tyre width and vehicle weight models it though.
GravelBen said:
If the tyres are big enough to have a negative effect on both ride and handling the car is over tyred.
I don't think a simple linear relationship between tyre width and vehicle weight models it though.
My S1 Elise weighs nothing but has 225 rear tyres. Using the MX5 benchmark it is horribly over-tyred, yet handling seems to be lovely. So the model is definitely flawed.I don't think a simple linear relationship between tyre width and vehicle weight models it though.
Kozy said:
As a simple comparison I worked out that the aforementioned MX5 would have about 250kg on each tyre, so 185/250 would give it a 'width to load' ratio of .74.
Compared to something like an E46 M3, which has closer to to 400kg on each wheel, and 225/255 tyres, that would be a WTL ratio of .56F and .64R.
Is the E46 is actually under-tyred compared to the MX5?
Are overweight modern cars actually still using relatively conservative tyre widths for the weight of the vehicles, despite peoples assumptions?
If you want to go down the route of working it out scientifically, you'd have to get bhp (per driven wheel) in there and it certainly wouldn't use a linear scale on any variable.Compared to something like an E46 M3, which has closer to to 400kg on each wheel, and 225/255 tyres, that would be a WTL ratio of .56F and .64R.
Is the E46 is actually under-tyred compared to the MX5?
Are overweight modern cars actually still using relatively conservative tyre widths for the weight of the vehicles, despite peoples assumptions?
But I don't think there's any need for formulas and that - you should be able to work it out for yourself. In fact, I think different people have different wants and expectations, so the definition of 'over-tyred' is, ultimately, a personal one.
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