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[davislau]

I know this has been discussed many times, but please hear me out.

I'm wondering how (specifically) putting summer tires in front and all-seasons in the rear of an RWD car (M3) negatively impacts handling or safety when compared to all-seasons all around. And I wonder if anybody has specific experiences they can share (racing or low-grip scenario) and can describe the nuances of handling/feel impacts, and compare their experience with all-seasons all around.

Most discussions online:

• only cover the theory at surface level
• say the "engineers designed it that way so don't mess with it"
• compare 2 performance tires as worse than 4 performance tires (of course it is), rather than 2 performance tires against 4 budget (all-season) tires.
• compare 4 winter tires to winters mixed with summer/all-season (of course 4 winter tires is better in the snow)

About myself:

• I currently have all-seasons all around, but need to replace my front tires
• I'm only concerned with driving on the street in the dry and rain (including road debris), not snow.
• I've done a lot of research online on this topic already
• I've lost traction, spun out, and drifted on dry pavement, rain, and snow either on the street, on a track, or on a skidpad. Not an expert by any means, but familiar with driving past the limit in various conditions.
• I'm a mechanical engineer with 7+ years experience in high-caliber automotive, aerospace, and tech companies.
• I've also studied suspension geometry and vehicle dynamics a little during my days on the formula racing team in college, but I only remember the high-level concepts.
• Yes, I admit I'm asking because I'm being cheap I know it's best to have consistent tires all around, but I want to understand the true, real-world impact at a deeper level.

So I'm no stranger to the physics, theories, and concepts around this topic, but that doesn't mean I'm an expert. That's why I'm looking for someone with actual experience on this (especially people who've tracked their car, practiced on a skidpad, or got into a tricky street situation with mixed tires).

Much appreciation to anyone who can provide a detailed, nuanced, specific answer backed by experience! I've ran into many people that take it personally when I ask for more specifics or challenge their assumptions. Just trying to learn, please don't take it personally!

[tbuck]

In general terms, not specific to your parameters set forth above, running non-matched tires is not advisable due to the very different level of grip the front and the rear will have. In the scenario you state above I would be concerned that the rear would break traction well ahead of the fronts which is very dangerous in all cases. Also the car is designed for a bit of understeer and you will now be having an almost forced case of oversteer. If you are just driving back and forth to work and never pushing the car it is unlikely to ever be an issue, but still no an optimal situation.

I would be somewhat shocked if many people did what you are asking about, but who knows....

[davislau]

Thanks tbuck. Are there any scenarios where I want the front to break traction before the rear, or at the same time as the rear?

One scenario I can think of where the dynamics would be different is emergency breaking mid-turn:

• weight transfers to the front
• rear wheels with all-seasons swing out
• front wheels with summer tires stay pointed and grippy, less likely to lock
• car might steer into a curb or hit something side-on, but the driver still has some option to counter-steer / control it

Compare that to having all-seasons all around, in the same scenario:

• weight transfers to the front
• rear wheels with all-seasons swing out
• front wheels with all-season tires lock-up or plows due to lower grip
• the whole car plows forward/sideways (but less sideways than with front summer tires) because all tires have lost traction, hits something more head on. The driver doesn't have many options other than release the break a little to regain grip (unlikely in an emergency scenario that happens in the blink of an eye)

Wouldn't a car with imbalanced but more traction up front, rather than less traction on budget (all-season) tires all around be okay, if not slightly better? I suppose it's better to increase your chances of hitting something head on, rather than side-on, hence many street cars are designed to understeer, especially to protect the average driver who has no idea what to do when their car loses traction?

[tbuck]

For safety reasons cars are generally designed to understeer as, regardless of the experience of the driver, it is much easier to control than oversteer. I would always go with the same tires, no matter the type, simply to have a much more predictable handling profile in all cases and in all situations. Personally I can not see any advantage, other than money wise, nor a scenario where running mismatched tires would be a good thing.

[davislau]

Yep, I agree that understeer is often safer, regardless of driver experience. Things happen too quickly in emergency situations.

I do think oversteer is "easier" to control though. The bad thing about it is that it can get out of hand, but at least the driver has some options. If your car is understeering heavily and plowing into an accident, there's almost nothing you can do other than ride it out and hope for the best.

To your point though, an accident where you've lost all control but the car's trajectory remains tidy is likely safer than an accident were you have a little control, but the car is spinning wildly. Anyone who thinks they can control the oversteer are likely overestimating their reaction time and ability and underestimating the suddenness and severity of accidents.

I think the the rule for having matched tires holds true for optimal safety. But I think the question becomes: how much does having mismatched tires actually affect the handling? Is the effect so small that only a professional driver can notice, or so large that your mom will comment on the strange handling? Probably somewhere in between, but I think only people with experience will be able to answer.

If it's very hard to notice, or only has an effect in the most extreme scenarios, then I would argue it's no big deal to mix.

[DRLane]

Originally Posted by davislau

Yep, I agree that understeer is often safer, regardless of driver experience. Things happen too quickly in emergency situations.

I do think oversteer is "easier" to control though. The bad thing about it is that it can get out of hand, but at least the driver has some options. If your car is understeering heavily and plowing into an accident, there's almost nothing you can do other than ride it out and hope for the best.

To your point though, an accident where you've lost all control but the car's trajectory remains tidy is likely safer than an accident were you have a little control, but the car is spinning wildly. Anyone who thinks they can control the oversteer are likely overestimating their reaction time and ability and underestimating the suddenness and severity of accidents.

I think the the rule for having matched tires holds true for optimal safety. But I think the question becomes: how much does having mismatched tires actually affect the handling? Is the effect so small that only a professional driver can notice, or so large that your mom will comment on the strange handling? Probably somewhere in between, but I think only people with experience will be able to answer.

If it's very hard to notice, or only has an effect in the most extreme scenarios, then I would argue it's no big deal to mix.

If you have understeer, you're simply asking the tires to do more things simultaneously than they're capable of. Less inputs return grip almost immediately. That's not the case with oversteer as weight shift can also play a larger role in the disruption and therein lies more skills.

Regarding tires, If you're novice you're not likely like running the tires to their limit but instead to a limit you're imposing on them through poor technique and awareness.

I think the evidence is overwhelming that mismatched tires won't yield faster lap times or improved control. Sure You can run mismatched tires. Reach out to Rhary s he's been conducting this test for a couple years now. I wouldn't say he's inherently striving for absolute speed and lap times but instead economic reasons and because he likes the data challenge.

[davislau]

Regarding tires, If you're novice you're not likely like running the tires to their limit but instead to a limit you're imposing on them through poor technique and awareness.

I think the evidence is overwhelming that mismatched tires won't yield faster lap times or improved control. Sure You can run mismatched tires. Reach out to Rhary s he's been conducting this test for a couple years now. I wouldn't say he's inherently striving for absolute speed and lap times but instead economic reasons and because he likes the data challenge.

Yeah, absolutely agree that mismatched tires will not improve handling (and lap times). I'm asking for economic reasons for sure (and for science ). I'll likely upgrade my rear tires to match eventually, but wanted to understand if it's really all that bad to mix tires in every day street driving (and occasional emergency) scenarios, or if my car will start showing some crazy behaviors.

I think the worst part about having mismatched tires will probably be other people judging you lol.

[davislau]

Originally Posted by DRLane

Reach out to Rhary s he's been conducting this test for a couple years now. I wouldn't say he's inherently striving for absolute speed and lap times but instead economic reasons and because he likes the data challenge.

Where can I find his contact information / profile?

[DRLane]

Originally Posted by davislau

Yeah, absolutely agree that mismatched tires will not improve handling (and lap times). I'm asking for economic reasons for sure (and for science ). I'll likely upgrade my rear tires to match eventually, but wanted to understand if it's really all that bad to mix tires in every day street driving (and occasional emergency) scenarios, or if my car will start showing some crazy behaviors.

I think the worst part about having mismatched tires will probably be other people judging you lol.

If it's on the street? Just get matching tires man. All Season tires will reduce the tendency for driving like an asshole. You're not going to notice any improvement in driving from grippier fronts, but you could open yourself up to questions from insurance companies if in an accident as to fault…

[davislau]

All Season tires will reduce the tendency for driving like an asshole. You're not going to notice any improvement in driving from grippier fronts

That's true, I likely won't be pushing the car hard enough to take advantage of summer tire performance, especially on the fronts, on the street. I'm skeptical of my current front tires because they are old and one of them has sidewall damage, but multiple mechanics have said the damage is not concerning.

Guess I'll just do new all-seasons for now, and wait until it makes more sense for me to do a full set of summer tires.

[DRLane]

Originally Posted by davislau

That's true, I likely won't be pushing the car hard enough to take advantage of summer tire performance, especially on the fronts, on the street. I'm skeptical of my current front tires because they are old and one of them has sidewall damage, but multiple mechanics have said the damage is not concerning.

Guess I'll just do new all-seasons for now, and wait until it makes more sense for me to do a full set of summer tires.

That's the smart move! You don't want the ultra summer tires in the cold anyhow. Pick up a set for next summer and let the car rip. You'll love the update coming off A/S

[DRLane]

Originally Posted by davislau

Where can I find his contact information / profile?

Rhyary is his username.

[davislau]

Thank you!

[rhyary]

I have been running any combination tires you can imagine. But I just bought my first set of UHP All season to run in the north east cold weather and also to be used as my rain tires.

Cooper 305/30/19 for the rear
DWS+ 285/30/19 for the front.

My goal is $200/tire

The one thing I always made sure is that at least on paper my rear are always more sticky than the front.

[rhyary]

>> I'm wondering how (specifically) putting summer tires in front and all-seasons in the rear of an RWD car (M3) negatively impacts handling or safety when compared to all-seasons all around.

I would do that in the rain and snow. But not on a dry track.

[rhyary]

This can be very helpful when discussing tires:

Tire Grip by Michelin Tires

https://www.paradigmshiftracing.com/...p-michelin.pdf

[DRLane]

Originally Posted by rhyary

This can be very helpful when discussing tires:

Tire Grip by Michelin Tires

https://www.paradigmshiftracing.com/...p-michelin.pdf

FYI, He's inquiring specifically about street driving not on track.