New Tyres then Oversteer
Discussion
I just replaced worn out SO2's on the back of my Chim with new SO3's. The front SO3's are less than half worn. Since then the car seems to oversteer a lot.
Is it because of the increased grip from the rears? I read the Bible which talks about under and oversteer and various angles etc but did not seem to make sense.
Anybody had similar problems?
Is it because of the increased grip from the rears? I read the Bible which talks about under and oversteer and various angles etc but did not seem to make sense.
Anybody had similar problems?
I'm confused. Do you mean oversteer? Oversteer is a result of rear wheels loosing grip thereby causing the car to turn deeper into a corner than you intended. If you are suffering from loss of front wheel grip then the car will tend to steer less, understeer, than you expect causing the car to move away from the inner curb.
I know this doesn't answer your question but it's important that we understand which tyres are loosing grip.
With SO3pp's you may need to reduce pressure by 2psi to mirror SO2pp cornering performance.
>> Edited by tvrbob on Wednesday 25th August 08:32
I know this doesn't answer your question but it's important that we understand which tyres are loosing grip.
With SO3pp's you may need to reduce pressure by 2psi to mirror SO2pp cornering performance.
>> Edited by tvrbob on Wednesday 25th August 08:32
clamdigger said:
I just replaced worn out SO2's on the back of my Chim with new SO3's. The front SO3's are less than half worn. Since then the car seems to oversteer a lot.
Is it because of the increased grip from the rears? I read the Bible which talks about under and oversteer and various angles etc but did not seem to make sense.
Anybody had similar problems?
The "Bible" also refers to "running-in" tyres. They have release agents which take time and mileage to remove.
It took about 500 plus miles before my Goodyear Eagles felt secure. Also having "more tread", the tyre will slightly oversteer more until 1/2K have scrubbed the blocks down a little. Doa track day and then see ???
Trev McM
Yep, was going to say they needed running in without even reading the original post and replies. Damn I'm good 
Also with new tyres the heating and cooling from accelerating and breaking gently in normal traffic will galvanize the tyres a little, which helps slow down premature wear. So I heard.
Also with new tyres the heating and cooling from accelerating and breaking gently in normal traffic will galvanize the tyres a little, which helps slow down premature wear. So I heard.
If its anything like the Proxes TX1-s I use, it'll take a good 250miles + to feel secure. I honestly felt like having the car checked over after my last new set it felt so horrible - anything over 70mph in a straight line was not at all comfortable, and commiting to a corner was a heart in mouth experience. Now, 500miles down the line they feel great!
clamdigger said:
I just replaced worn out SO2's on the back of my Chim with new SO3's. The front SO3's are less than half worn. Since then the car seems to oversteer a lot.
Is it because of the increased grip from the rears? I read the Bible which talks about under and oversteer and various angles etc but did not seem to make sense.
Anybody had similar problems?
I would have expected this configuration of tyres to cause mild understeer.
As others have posted: check your tyre pressures. I'd be surprised if new tyres needed that much running in.
Also - technique related - do you habitually get on the gas with lock on? Let the wheels straighten up before mashing the accelerator into the carpet...
I realy think i'm still learning about this handling stuff.
TVRBob - you were saying about oversteer being as a result of the back breaking away. Is it possible to have oversteer without the back losing grip?
I thought oversteer was when you turned the wheels into a corner and the car turns more than you think it would with nothing to do with losing the rear end.
Incidentally, whilst out yesterday I hit an uufortunate squirrel. I don't think I did him much good but he did knock off the splitter from the front. Driving without the splitter did seem to change the characteristics of the handling. Is this right or am I imagining it?
TVRBob - you were saying about oversteer being as a result of the back breaking away. Is it possible to have oversteer without the back losing grip?
I thought oversteer was when you turned the wheels into a corner and the car turns more than you think it would with nothing to do with losing the rear end.
Incidentally, whilst out yesterday I hit an uufortunate squirrel. I don't think I did him much good but he did knock off the splitter from the front. Driving without the splitter did seem to change the characteristics of the handling. Is this right or am I imagining it?
clamdigger said:Oversteer is rear wheel related. It would be wrong to say the rears need to break away but they do need to move sideways for oversteer to occur.
Is it possible to have oversteer without the back losing grip?
clamdigger said:I didn't notice anything. I've seen posts that suggest the engine cooling can be reduced. Most, probably 80% or more Chims drive without a splitter.
Driving without the splitter did seem to change the characteristics of the handling. Is this right or am I imagining it?
The lateral stiffness of tyres changes enormously during their life. It is also quite sensitive to tyre pressure, especially for brand new tyres.
Brand new tyres come covered in a slippery release agent that wears off after a few miles, and over the next hundred miles or so the tread wears slightly so that the contact patchy is flat, this is sometimes referred to as 'scrubbing in'. At this point the tyre is the right shape but the rubber in the tread is still relatively soft. This means the tread will distort relatively easily when you try to accelerate, corner or brake, and the fact that the tread blocks are very tall makes this even worse. The first thing to do at this point is cure the tyres by warming them up to about 50 deg and letting them cool down naturally. You can do this by a little energetic driving although you do need to be careful as the handling will be a little unusual at this point. The second thing is to lower the tyre pressure slightly when the tyres have a lot of tread. This increases the area of the contact patch, which shares the forces over more of the tread, so each tread block sees less load. Net result is the tyre deflects less under load. As the tread wears down you would gradually restore the normal pressure. We are not talking about a lot of pressure difference, probably no more than 1psi difference from brand new to completely worn out, but the effect is dramatic enough to make a noticeable difference to the handling.
If you have front/rear tyres in different condition the difference in lateral stiffness can make the handling quite unpleasant (or quite pleasant, if you have soft tyres on the rear and like long, gooey power slides). You can improve this a long way by curing the new tyres and adjusting the tyre pressures slightly.
Brand new tyres come covered in a slippery release agent that wears off after a few miles, and over the next hundred miles or so the tread wears slightly so that the contact patchy is flat, this is sometimes referred to as 'scrubbing in'. At this point the tyre is the right shape but the rubber in the tread is still relatively soft. This means the tread will distort relatively easily when you try to accelerate, corner or brake, and the fact that the tread blocks are very tall makes this even worse. The first thing to do at this point is cure the tyres by warming them up to about 50 deg and letting them cool down naturally. You can do this by a little energetic driving although you do need to be careful as the handling will be a little unusual at this point. The second thing is to lower the tyre pressure slightly when the tyres have a lot of tread. This increases the area of the contact patch, which shares the forces over more of the tread, so each tread block sees less load. Net result is the tyre deflects less under load. As the tread wears down you would gradually restore the normal pressure. We are not talking about a lot of pressure difference, probably no more than 1psi difference from brand new to completely worn out, but the effect is dramatic enough to make a noticeable difference to the handling.
If you have front/rear tyres in different condition the difference in lateral stiffness can make the handling quite unpleasant (or quite pleasant, if you have soft tyres on the rear and like long, gooey power slides
). You can improve this a long way by curing the new tyres and adjusting the tyre pressures slightly.Gassing Station | Chimaera | Top of Page | What's New | My Stuff