howardb

One of the guys at work has had a new tyre fitted on his Lexus. Before, he had the standard oem potenzas (SO1's?) all around, but his new tyre is an SO2 on the rear axle (driven wheels). Personally I dont think this is safe. Any comments??

AlexM

Hi,

It won't do any favours to the handling balance (promote understeer by increasing grip at the rear), but this probably isn't unsafe in a RWD saloon.

Cheers,

Alex

howardb

Alex,
Thanks for that.

Can I just make it clear that currently his rears are a SO1 and a SO2. I dont like the fact that he has two diffent tyres on the same axle, one technically being leaps and bounds better than the other.

Neil Smalley

If it's two tyres at the back, then it should be OK. If it's just a single tyre I.e 1 SO2 and 3 standards then he could be asking for trouble. The SO2 will have more grip than the other tyres and so make the car potentially very twitchy in wet and slippery conditions.

Sadman

It's OK having different tyres front to back but you should never mix tyres on the same axle....end of story!

howardb

Neil: 2x SO1's at the front, 1x SO1 and 1x SO2 at the rear.


All:
Thanks very much for your replies. I'll tell him to get it sorted (ie SO2 on other side) asap.

SDB

IMHO this is potentially lethal.

Mixing tyres at all is dangerous (even if you the same across axles) as the car will no longer bhave on the limit as it was supposed to as the tyres do not resist the suspension at even rates anymore.

Sticking 1 S02 on the car is a disaster waiting to happen. The worst part is that the time when those two tyres are *most* different is in the wet.

I've done too much tyre testing and seen the disasterous effects to allow me to ever have mis-matched tyres on my road car again.

Cheers

Simon

alistair

NO NO NO NO NO !!!!!!!!!!!

NEVER mix tyres - even on different axles it's just not worth it ! I was running for a while with SO2's front and SO1's rear and it seemed fine for months until I span it in the wet one day ...... but I just put that down to oil on the road.

I then went on Wetter The Better and thankfully Don Palmer used my car for the demo lap - at the end he asked if I had any tread on the rear tyres - it was that bad - I actually had about 6mm left on S01's - the difference is that much - the SO2's have a much higher grip level in the wet - it's just that you don't find out until you're on the limit.

I put SO2's all round that week and then went back to MIRA - the difference was stunning. IMHO it's just a false economy to mess around with tyres and now I will only ever replace all 4 together - lesson learnt !

pat

Just one thing to add... it is sometimes advantageous to mix tyres between axles, if there is a fundamental problem with the car to start with (ie the manufacturer got it "wrong")... or if you're a big wuss like me That still leaves the problem of different characterstics on the limit, but it can push the limit up a bit...

I deliberately put stickier rubber on the back of the MR-2 Turbo as I have the MkII Phase I car which has "interesting" geometry at the back.... you just cannot put down the power coming out of bends, sure you can hold it in a power slide, BUT you just can't get enough to keep up with a Scoob (if you tried, it would swap ends on you or if you're skilled enough to hold it, you'de basically be doing a burn-out ).... after a slight "tweak" I could stay with an un-modded MY01 on most surfaces. The ride is quite entertaining as the tyres still have difficulty putting the power down... but it's more a case of booting it and making minor corrections with the steering (pretty much like my Scoob, it also likes to break traction at the back, and that's with 225 section Bridgestone rubber), rather than having to balance it on the throttle.... my Scooby would eat it for breakfast though (but then you'de have difficulty spotting the original part in that! )

Cheers,

Pat.

davyboy

its a lexus, I doubt he would ever drive it on the limit! In fact I doubt he would ever notice. Not every drives on the limit! It will not suddenly turn in to a death trap!

DavidBrown

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by davyboy:
<B>its a lexus, I doubt he would ever drive it on the limit! In fact I doubt he would ever notice. Not every drives on the limit! It will not suddenly turn in to a death trap! [/quote]

Consider going around a roundabout in the wet and having to slam your brakes on because someone pulled out in front of you.. suddenly the car is <B>on the limit</B>.

Lexus aren't cheap cars, I'm surprised he's risking his safety for the sake of £1-200

SDB

pat

I strongly disagree with the idea of altering handling by mixing tyres.

If you were to do what you suggested with the MR2, so that you could put enough power down to keep up with a scoob, etc.. you would be losing the potential cornering speed you would have by having S02s on the front as well.

Tyres aren't all exactly the same appart from the grip levels.. it's not as though they have a grip value and that's the only difference.. they have different characteristics in hundreds of different areas.

Some may have a higher spring rate, so even though the compound is grippier in a certian situation, they might cause unwanted skipping at that end of the car compared to the front on certian surfaces / over bumps of just the right frequency..

some tyres exhibit more mechanical locking but less chemical adhesion than ohers, so they will be better in some situations and worse in others.

The whole idea of the chassis working well is that the designers know that there is going to be roughly the same resistance at each corner of the car.

-----------

And DavidBrown is right. The limit can arrive in strange places. Just becuase you don't drive "fast" doesn't mean that you won't be thrown into the limit one night on blind bend on a dark country road.

Mixing tyres is very dangerous, even if you are doing it for a specific reason.

Best regards

Simon

AlexM

Hi,

I misread the original question, and would echo what people have said about mixing different tyres on the same axle. This would obviously create inconsistent handling in left/right corners..

What alastair said about new S02s on the front of his scooby with worn S01s on the rear.. yes you can expect fairly lairy oversteer pretty much everywhere .

Understeer is a bit easier to manage for most drivers, so if you must mix tyres put the grippiest pair on the rear.

Cheers,

Alex

jon hill

Though i agree with this generally, i've had yoko a539's on the front and bridgestones re94's on the back of my integra for some time (wasnt planned - the dealer screwed up). It all works stunningly well - wet, dry, road and track (i've got the same mix on some track day rims, albeit with about 1mm of tread on each - dont ask, its all too complicated). The yoko's are supposedly a bit grippier the the re94's too.

Simon - this is the black integra you did a few laps in at bruntingthorpe on one of Don Palmers days.

So - yep, definatly not recommended, and i'll be going to 539's all round if the bridgestones ever wear out... but from experiance it can work.

jon