Small tyre size difference seems big grip difference

corkgsxr

Had Goodyear 215/65/16 on the van. Needed 4 new tires

He had Goodyear in 205/65/16 which is also a recommended size thought ya no bother.

Have them on a few days maybe 300kms.

But they don't seem to grip as well at all. Could this just be my imagination or what

Same brand and type. At the recommended psi

Andrewf20

Hmm, I find new tyres can take a good while to bed in sometimes. The roads are noticeably greasier in the last 2 weeks in places also. There's like a muddy sludge building up slowly in places. The outer ring road from the n7 to Lucan is very slippy on the roundabouts for example.

I'm not sure what the physics of thinner tyres are. Smaller contact patch but more pressure per unit area to compensate as the vehicle is the same weight...

listermint

corkgsxr wrote: »

Had Goodyear 215/65/16 on the van. Needed 4 new tires

He had Goodyear in 205/65/16 which is also a recommended size thought ya no bother.

Have them on a few days maybe 300kms.

But they don't seem to grip as well at all. Could this just be my imagination or what

Same brand and type. At the recommended psi

They need to bed in. This is normal.

CJhaughey

What pressures are you running in them?

ARGINITE

It's also a narrower tire.

Alun

CJhaughey wrote: »

What pressures are you running in them?

This ^^^ Double check the tyre pressures.

Many garages and tyre places pump new tyres up to some arbitrary "sure that'll be grand" pressure they have in their heads that often bears no resemblance to the manufacturer recommended pressures, more than often erring on the high side. Overinflated tyres will generally make the car more skittish.

Atlantic Dawn

That's about a 5% difference in surface area of the tyres on the road, should not be noticeable, I'd say as was said they are bedding in. If not resolved by 500km I'd worry about it.

H3llR4iser

I had similar experiences in the past, the first few hundred KMs the grip wasn't ideal, then it "comes" to them. Some say new tires come with some sort of protective stuff on, I can't find any info about it.

Also, the last few days temperatures dropped fairly low - normal tires don't work at an optimal level sub 5 degrees. I'd also check the pressures, I had situations where newly installed ones turned out to have 4 different, completely arbitrary values!

Last...maybe it's pointless, but...check for direction. Tyre places/fitters should know about it, but it's a mistake that can happen; maybe there are two or three guys doing the job, they pass the wheels to each other and a left wheel ends up on the right side and vice versa...

Stephenc66

OP even though the new tires were Goodyear the same brand as your old ones are your sure that they were the same type/model tire as the ones they replaced. Manufactures do make tires in different compounds and thread patterns which will effect grip in different situations. And as others here have said new tires sometimes need to bed in

pa990

Stephenc66 wrote: »

OP even though the new tires were Goodyearn the same brand as your old ones are your sure that they were the same type/model tire as the ones they replaced. Manufactures do make tires in different compounds and thread patterns which will effect grip in different situations. And as others here have said new tires sometimes need to bed in

that might be your problem

http://tinyurl.com/zv7da3l

are these batteries any good ?

CJhaughey

All tyres need to be scrubbed in, same with Motorcycle tyres they have mould release in the top layer of rubber that needs to be worn away before the grippy rubber is exposed.
I'd say its a combination of the new tyres, cold roads and possibly tyre pressures as well causing the skittishness.

fryup

wider the tyre the better the grip.. seems obvious..no?

CiniO

fryup wrote: »

wider the tyre the better the grip.. seems obvious..no?

Not really.
We all learnt in school on physics, that grip doesn't depend on contact surface area.

Cheensbo

fryup wrote: »

wider the tyre the better the grip.. seems obvious..no?

Exactly. That's why snow tyres are so wide

mickdw

Id be confident id feel a difference between a 205 55 16 and a 215 55 16 driven back to back on same car. Shouldn't be a major lack of grip though.

fryup

CiniO wrote: »

Not really.
We all learnt in school on physics, that grip doesn't depend on contact surface area.

i must have missed that class

...so what does it depend on then??

blackbox

Andrewf20 wrote: »

Hmm, The roads are noticeably greasier in the last 2 weeks in places also. There's like a muddy sludge building up slowly in places.

Definitely roads have been much more slippery over last few days - lower surface (and rubber) temperatures and damp salty coating.

.

CiniO

fryup wrote: »

i must have missed that class

...so what does it depend on then??

Static friction (as this is what keeps tyres gripped to the road surface) depends on coefficient of friction between those two surfaces (tyre and tarmac), and a normal force exerted by each surface on the other.

I'd say it's either your imagination or the tyres scrubbing in or the weather.
Couldn't imagine it being attributed to the size. A worn 215/65/16 would have approximately the same overall diameter as a new 205/65/16 as there'd be 5/6mm worn off the old tyre thread when you changed them. So there shouldn't be any leaning differences etc.

GerryDerpy

Surface area in contact with road does not affect traction. Traction is a function of downforce and coefficient of friction.

VeVeX

GerryDerpy wrote: »

Surface area in contact with road does not affect traction. Traction is a function of downforce and coefficient of friction.

Yes. Fitting a larger tyre doesnt give you more grip unless the force acting on the surface of the tyre is also increased. The additional friction from the increase in width is directly offset by the reduction in pressure across the face of the tyre.

<not helping...>

king_of_inismac

In theory, tyre width shouldn't affect braking but in reality it is more complex than that:

https://www.physicsforums.com/threads/tyre-width-grip-friction.24374/

corkgsxr

Sorry late reply.

55 front 60 rear.

Same brand and model.

Id be fairly up on it but maybe it is just cold Temps on new tires

corkgsxr

Or does anyone no what money you'd get for new tires after fitting

CJhaughey

corkgsxr wrote: »

Or does anyone no what money you'd get for new tires after fitting

You mean partworns:pac:

corkgsxr

CJhaughey wrote: »

You mean partworns:pac:

Yep I know the way

9935452

corkgsxr wrote: »

Had Goodyear 215/65/16 on the van. Needed 4 new tires

He had Goodyear in 205/65/16 which is also a recommended size thought ya no bother.

Have them on a few days maybe 300kms.

But they don't seem to grip as well at all. Could this just be my imagination or what

Same brand and type. At the recommended psi

I went the opposite way a few years back from 175/80/14 to 195/65/15.
I found a lot more grip on accelerating and braking , the car was less likely to spin the wheels or skid when braking hard
People will say its because i went from worn out tyres to new tyres but 3 sets later i found no difference from worn out tyres to new within the same size.

corkgsxr wrote: »

Or does anyone no what money you'd get for new tires after fitting

At a guess half.
The next guy will have to pay 10 ish for fitting and balancing as well.
For a few quid more he will have a new tyre.