Slippy moment

[Chas]

I recently fitted KM2's 255/85/16. The other day I was going down some twisty country lanes, in the dry, and going round a bend at a speed I would have comfortably have done with the Cooper STT's, I touched the brakes and the back end started to break away , this happened again on my return journey, different bend, I checked the pressures at home, all OK at 32psi so I can only assume KM2's don't give the same grip, on tarmac at least.

 

[stumog]

Driver error there chas. you never touch the brakes in a bend you get all your braking down on the approch to the bend then throttle around the corner.
I chuck mine about some time and never had any issues any diesel on the road?

i run mine at 40psi on the road they are a bit squirmy lower pressures to be fair.

stu

 

[Chas]

It was just on the approach to said bend and just touching the brakes not severe at all, and anyway if you find yourself a tad too fast what's the alternative? through the hedge maybe. I've been driving over 55 years now, I think I've learnt enough not to brake IN a bend.
So Stu are you saying increase the pressures for better grip, or am I reading that wrong?

 

[clivehorridge]

It was just on the approach to said bend and just touching the brakes not severe at all, and anyway if you find yourself a tad too fast what's the alternative? through the hedge maybe. I've been driving over 55 years now, I think I've learnt enough not to brake IN a bend.
So Stu are you saying increase the pressures for better grip, or am I reading that wrong?

I'd go along with that Chas, I find them a bit "blocky" for asphalt and they take a bit of getting used to, and even moreso when it's wet. They are not a good asphaly tyre IMO, but they will outstrip most on performance on tracks, rock and of course MUD.

It's easy to make them howl on asphalt and I've found that 40 psi works better than anything less, on the black stuff.

Who says driver error to a veteran anyway Stu? Where's your diplomacy. Kids these days, no respect at all!

Practice Chas, that's all they need, a bit of time for them to get to know you .

 

[Chas]

Thank you for those few kind word Clive, I'll try upping the pressure and see. Oh! and by the way, on my way home from my archery shooting there is a corner turning right off the Ewell bypass at The Organ Inn where I could always boot it away from the lights and turn, not so with the KM2's they squeal like mad they obviously need to be treated with a bit of respect.

 

[clivehorridge]

That's it Chas, they need some respect on asphalt, but you'll just love 'em at Lincomb!!

I'm green with envy that I can't be there and a bit peed that you guys get all the action

Tantrum over...

 

[Towpack]

Lowering the pressures will increase the tyres grip on the road surface as the contact patch will increase but the there will be more flex in the sidewall meaning the rim will move about more laterally in the tyre giving a loose squirmy feeling to the handling. Increasing the pressures will tighten things up but grip will be less. Exactly the same thing happens with dirt bike tyres on tarmac but it's much more exaggerated. I run 20 psi F&R on the Husaberg which I find is a good compromise between off road grip and on road manners and also gives reasonable protection against snake bite punctures. Dropping to around 10-12psi gives a noticeable increase in wet mud grip but on-road cornering can be 'eventful' to say the least.

 

[clivehorridge]

Lowering the pressures will increase the tyres grip on the road surface as the contact patch will increase but the there will be more flex in the sidewall meaning the tyre will move about more laterally in the tyre giving a loose squirmy feeling to the handling. Increasing the pressures will tighten things up but grip will be less. Exactly the same thing happens with dirt bike tyres on tarmac but it's much more exaggerated. I run 20 psi F&R on the Husaberg which I find is a good compromise between off road grip and on road manners and also gives reasonable protection against snake bite punctures. Dropping to around 10-12psi gives a noticeable increase in wet mud grip but on-road cornering can be 'eventful' to say the least.

Thanks TP, I may try experimenting more, but generally (particularly through the summer) I'm on ATs on the asphalt and I keep the KM2s for the weekends when offroading.

I think there may be some performance variances with tyre sizes too.

I'm running 305/70/16s on 16x10 rims, but I'm guessing that Chas' 255/85/16s are on 16x8" rims. The difference could be considerable, with Chas' relatively high rim to road measure (85 ratio) compared with mine (70 ratio) and the tyre and rim width differences, the performance characteristics could differ a lot.

I'll do a bit of experimenting

 

[Gary820]

Are they the same size as your old tyres?
I find the opposite problem, my cooper st 255/85 will loose grip with relative ease. The bfgs (the older km) are ok but obviously much wider so more rubber.

 

[SpinDrift]

I don't know Clive, quite a few of us would like to be where you are with mountains, forests and track that you are allowed to drive the grass is always greener ...

I'm green with envy that I can't be there and a bit peed that you guys get all the action

Tantrum over...

 

[AndycruiserguyLomas]

Are they the same size as your old tyres?
I find the opposite problem, my cooper st 255/85 will loose grip with relative ease. The bfgs (the older km) are ok but obviously much wider so more rubber.

On the subject of 255vs285 KM2's I've had both fitted to 80's. both sets were like new and I must admit I didn't have a lot of confidence in the 255's especially in the wet, although I never had one step out. The 285's were a lot better to drive on in all conditions. I suppose the 255's dont have a lot of rubber on the contact patch and have quite a hard compound.

Andy

 

[Chas]

Are they the same size as your old tyres?

No, my Coopers were 285/75/16, BFG's are 255/85/16 so a bit higher than tread width in comparison. Seeing as how 90% of my driving is on road I might have to think about some AT's.

 

[Beau]

I wouldn't say it's down to driver error or the presssures in the tyres, as what you're running at sounds fairlu reasonable on a tyre with that size sidewall.

It will probably go down to the tyre compound used. At the side of the tyre it should have a ratting for Temp, traction and also a tread wear. Have a look and see what it says. I bet the traction is probably a step down from what you previously had.

On my road tyres I run for example which are coopers, they have a ratting for the following. Temp - A, Traction - A, treadwear - 620

 

[Chas]

I wouldn't say it's down to driver error or the presssures in the tyres, as what you're running at sounds fairlu reasonable on a tyre with that size sidewall.

It will probably go down to the tyre compound used. At the side of the tyre it should have a ratting for Temp, traction and also a tread wear. Have a look and see what it says. I bet the traction is probably a step down from what you previously had.

On my road tyres I run for example which are coopers, they have a ratting for the following. Temp - A, Traction - A, treadwear - 620

I'll check in the morning, thanks Beau

 

[grantw]

Chas - one other thought may be the load balancing valve or the adjustment of it. If it's adjusted too far you're rear brakes may be locking up pre maturely.

 

[Bodhi]

All of the above and how many miles have you done on the new tyres, were they scrubbed in?

 

[Chas]

All of the above and how many miles have you done on the new tyres, were they scrubbed in?

They've not been on my 80 long, about a month, I bought them used from a fellow member, plenty of tread left (hardly worn) but they were definitely scrubbed in.

 

[Bodhi]

They've not been on my 80 long, about a month, I bought them used from a fellow member, plenty of tread left (hardly worn) but they were definitely scrubbed in.

Guess you can rule that one out then Chas

 

[clivehorridge]

I shouldn't comment more either 'cos I've just realized that Chas' tyres are literally almost half the width of mine, making the feel completely different, I'd imagine.

 

[Gary820]

As said above is the load valve ok.
Otherwise they are quite a narrow tyre, I've not had issues under braking but cornering under power can break traction, wet roundabouts can be fun if you prod the loud pedal
that's cooper st's not bfgs so different tyre.