PSS is 255 on backorder - what is next size?
04-28-2014, 11:43 AM
#26
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Mercedes c63 amg
This thread is way more in depth than it needs to be. We are talking about C63's here that see the road daily for the most part. MOST people who have modded suspensions stop at coilovers/springs and MOST people stop the performance bar at a tune/headers. Yes, some S/C's are out there, but it still doesn't matter. Correct me if I'm wrong, but people here are looking to get off the line a few times on their drive, maybe get in a highway pull or two, and take a few turns with some enthusiasm. Nobody here is going to Leguna Seca with a completely stripped car that weighs 2000lbs worrying about mm's off a tire.
That being said, while I agree with much of what has been posted here it just doesn't matter for the C. I think tirerack has their max difference at something like 4%. Yes, 4% is high, but 1%? You go through that on every set of tires you've ever put on a car unless you change tires like you do underwear.
On OEM wheels just put 265's on the back and 245's on the front and call it a day. On aftermarket wider wheels definitely put 245's if not 255's on the fronts and you can get crazy with 275 or even 285 on the rear. It won't hurt anything for 99.9% of people who are on here. I leave the .1% for anyone that comes along and drops an insane amount of money on the car in terms of making it just off the charts crazy becauseracecar.
Whoover - I understand your logic and good on you for posting up some seriously valuable information... However, it is way more detailed and strict than it needs to be for the people on this board. I'm sure it is useful for some cars on the road.
That being said, while I agree with much of what has been posted here it just doesn't matter for the C. I think tirerack has their max difference at something like 4%. Yes, 4% is high, but 1%? You go through that on every set of tires you've ever put on a car unless you change tires like you do underwear.
On OEM wheels just put 265's on the back and 245's on the front and call it a day. On aftermarket wider wheels definitely put 245's if not 255's on the fronts and you can get crazy with 275 or even 285 on the rear. It won't hurt anything for 99.9% of people who are on here. I leave the .1% for anyone that comes along and drops an insane amount of money on the car in terms of making it just off the charts crazy becauseracecar.
Whoover - I understand your logic and good on you for posting up some seriously valuable information... However, it is way more detailed and strict than it needs to be for the people on this board. I'm sure it is useful for some cars on the road.
04-28-2014, 11:57 AM
#27
That tire will be a little over 1% off in terms of rolling radius:
http://www.tacomaworld.com/forum/tir...5r18-265-35r18
Personally, I wouldn't use a tire that's any more than .5% off. Of course, it's your car and a lot of people go with tire fitments that are off this much, but you should know exactly what it means.
The car's axle plane will be off by 3.5 mm from the engineered height from ground (half the difference in the two tires' diameters). So you have to ask yourself how you'd feel about a shop getting your rear alignment wrong by 3.5 mm. Race cars (and even race suspensions for our cars) are much more adjustable both front and back so that alignment can be dialed in with different tire diameters, offsets, etc., but a stock rear end will just be out of alignment, if only slightly. With a suspension as carefully engineered as ours, it's asking for handling differences and accelerated tire wear.
The other issue to think about is ESP/ABS. A 2% difference between expected and actual revolutions per mile tells it the car is skidding. You're using half of that "normally," so you can expect the ESP to cut in sooner than it should. Again, at 1% variance you'll be in the "probably ok" area most of the time, but you shouldn't be surprised if the car notices.
Once again, for a car like this I'd keep it within .5%. The bad news is that there isn't an 18" size that will do that. But as an example, notice how close a circumference match the stock 507 19" tire is to the stock 18":
http://www.tacomaworld.com/forum/tir...5r18-255-30r19
http://www.tacomaworld.com/forum/tir...5r18-265-35r18
Personally, I wouldn't use a tire that's any more than .5% off. Of course, it's your car and a lot of people go with tire fitments that are off this much, but you should know exactly what it means.
The car's axle plane will be off by 3.5 mm from the engineered height from ground (half the difference in the two tires' diameters). So you have to ask yourself how you'd feel about a shop getting your rear alignment wrong by 3.5 mm. Race cars (and even race suspensions for our cars) are much more adjustable both front and back so that alignment can be dialed in with different tire diameters, offsets, etc., but a stock rear end will just be out of alignment, if only slightly. With a suspension as carefully engineered as ours, it's asking for handling differences and accelerated tire wear.
The other issue to think about is ESP/ABS. A 2% difference between expected and actual revolutions per mile tells it the car is skidding. You're using half of that "normally," so you can expect the ESP to cut in sooner than it should. Again, at 1% variance you'll be in the "probably ok" area most of the time, but you shouldn't be surprised if the car notices.
Once again, for a car like this I'd keep it within .5%. The bad news is that there isn't an 18" size that will do that. But as an example, notice how close a circumference match the stock 507 19" tire is to the stock 18":
http://www.tacomaworld.com/forum/tir...5r18-255-30r19
new 2 x 10/32 or 0.62" diameter
so does loading, going from 1 driver to driver + 3 passengers
so does velocity, it will 'sling' the tire into a larger diameter
so will tire pressure variation, due to setting or temperature
the control systems look for a delta in rpm (actually w or angular velocity and alpha or angular acceleration) not absolute rpm
there will be absolutely no difference in control system response going from a 255/35 to a 265/35...none
Last edited by Ingenieur; 04-28-2014 at 11:59 AM.
04-28-2014, 07:40 PM
#28
MBWorld Fanatic!
Sounds like you're saying you had a set of 275's on the car that ended up rubbing and scratching a wheel? I'm just trying to figure out what is going on here so bear with me.
Your tire isn't going to end up scratching your wheel. Maybe you curbed the wheel and just didn't realize it? Also, hopefully the 275's weren't on OEM wheels because those would actually be a little too wide for the OEM wheels. I bet it could be done but just isn't the right thing and would lead to a mushy feel and a tire that bulges.
Next, while many will claim that 275's have rubbed so much goes into it. The wheel width and offset play the biggest role here.
Help me out here and just try to clean up what you're saying/asking and hopefully I can answer your questions.
04-28-2014, 07:49 PM
#29
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2017 Dodge Viper GTC, 2014 C63 AMG (gone), 2014 GL450
IIRC. OEM wheels fall within Michelin specs for 275/35. So it should be fine according to manufacturer. As long as it doesn't rub of course. Which it doesn't according to what I've seen.
04-28-2014, 09:04 PM
#31
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https://mbworld.org/forums/c63-amg-w...ger-tires.html
04-28-2014, 09:40 PM
#32
MBWorld Fanatic!
Before going to that size, it would be a good idea to PM this guy and see if he sorted out his problem.
https://mbworld.org/forums/c63-amg-w...ger-tires.html
https://mbworld.org/forums/c63-amg-w...ger-tires.html
04-28-2014, 10:01 PM
#33
MBWorld Fanatic!
Here's an article that discusses the issue a bit. It also suggests keeping the circumference change below 1%, preferably .5%. The 275's are off by more than 2%.
http://tires.about.com/od/understand...nus-Sizing.htm
Last edited by whoover; 04-28-2014 at 10:11 PM.
04-28-2014, 10:19 PM
#34
MBWorld Fanatic!
I kept telling myself I had 235's on the front when I had my c63. I actually had 275/30 and 245/35 which turns out to be exactly 1% difference. No issues at that spec
04-29-2014, 03:39 PM
#35
The traction control is doing exactly what it's supposed to do when the rear wheels seem to be traveling 2% faster than the fronts, per its calibration. I suggest you google "larger tires traction control" (no quotes) and see what others have found. Or pm the dude.
Here's an article that discusses the issue a bit. It also suggests keeping the circumference change below 1%, preferably .5%. The 275's are off by more than 2%.
http://tires.about.com/od/understand...nus-Sizing.htm
Here's an article that discusses the issue a bit. It also suggests keeping the circumference change below 1%, preferably .5%. The 275's are off by more than 2%.
http://tires.about.com/od/understand...nus-Sizing.htm
the rear wheels are smaller: 25" vs 25.4"
and they slip 3% (look at Tire rack rolling rpm at 60 mph vs 5280/static diameter)
the front don't slip since they are not delivering thrust/force
2% will not make a difference, if it did the controls would be intervening continuously
a primer: http://www.motortrend.com/features/p...ction_control/
typically on a performance car mu or slip is 15-20% before intervention (5 to 20 range for all cars)
2% is nothing, 3% is normal crusing
Last edited by Ingenieur; 04-29-2014 at 03:46 PM.
04-29-2014, 03:46 PM
#36
Member
Is the sidewall height 35 or 40 on the front? I want to make sure I use the correct size. Thanks.
04-29-2014, 04:10 PM
#38
MBWorld Fanatic!
the rear wheels are smaller: 25" vs 25.4"
and they slip 3% (look at Tire rack rolling rpm at 60 mph vs 5280/static diameter)
the front don't slip since they are not delivering thrust/force
2% will not make a difference, if it did the controls would be intervening continuously
a primer: http://www.motortrend.com/features/p...ction_control/
typically on a performance car mu or slip is 15-20% before intervention (5 to 20 range for all cars)
2% is nothing, 3% is normal crusing
and they slip 3% (look at Tire rack rolling rpm at 60 mph vs 5280/static diameter)
the front don't slip since they are not delivering thrust/force
2% will not make a difference, if it did the controls would be intervening continuously
a primer: http://www.motortrend.com/features/p...ction_control/
typically on a performance car mu or slip is 15-20% before intervention (5 to 20 range for all cars)
2% is nothing, 3% is normal crusing
In straight-line travel on a good surface, a 2% disparity between rear and front wheel speed is not normal. Don't forget that the ESP knows you're not accelerating or turning. It will absolutely see this as a problem. That's why a good tire shop will always keep you within 1%, and preferably within .5% of stock circumference. Ask them.
04-29-2014, 04:19 PM
#39
Circumference difference (front-to-rear) is not mu (coefficient of friction). The ESP computes mu from many variables. Ratio of driving to driven (rear to front) wheel speed is only one. Intended versus actual path (steering angle versus yaw sensor) and two-dimensional direction vector (accelerometer readings) are used as well.
In straight-line travel on a good surface, a 2% disparity between rear and front wheel speed is not normal. Don't forget that the ESP knows you're not accelerating or turning. It will absolutely see this as a problem. That's why a good tire shop will always keep you within 1%, and preferably within .5% of stock circumference. Ask them.
In straight-line travel on a good surface, a 2% disparity between rear and front wheel speed is not normal. Don't forget that the ESP knows you're not accelerating or turning. It will absolutely see this as a problem. That's why a good tire shop will always keep you within 1%, and preferably within .5% of stock circumference. Ask them.
Straight line constant highway speed 2wd
Rear wheels slip 3%
Front 0
The systems in even the most sensitve allow close to 10% slip
And they look for the rate of change of the delta
The control has P. I and D components
Proportional the difference
Integral error summed over time or revolution
Derivtve rate of change
The car would be undrivable at the 0.5 or 1% limit you claim
Are you an engineer?
Last edited by Ingenieur; 04-29-2014 at 04:21 PM.
04-29-2014, 05:33 PM
#41
MBWorld Fanatic!
04-29-2014, 05:46 PM
#42
MBWorld Fanatic!
Circumference difference (front-to-rear) is not mu (coefficient of friction). The ESP computes mu from many variables. Ratio of driving to driven (rear to front) wheel speed is only one. Intended versus actual path (steering angle versus yaw sensor) and two-dimensional direction vector (accelerometer readings) are used as well.
In straight-line travel on a good surface, a 2% disparity between rear and front wheel speed is not normal. Don't forget that the ESP knows you're not accelerating or turning. It will absolutely see this as a problem. That's why a good tire shop will always keep you within 1%, and preferably within .5% of stock circumference. Ask them.
In straight-line travel on a good surface, a 2% disparity between rear and front wheel speed is not normal. Don't forget that the ESP knows you're not accelerating or turning. It will absolutely see this as a problem. That's why a good tire shop will always keep you within 1%, and preferably within .5% of stock circumference. Ask them.
Ok, sooooo when you buy a set of tires and they are all brandy spankin new to MB OEM specs (235/40/18 and 255/35/18) There is already a 1.5% difference in size between front and rear. Now, you use your C63 as MB AMG intended and you find yourself squealing with joy engaged in making bugs splatter on your side windows instead of windshield (drifting) and you do some lovely burnouts chewing up your rear tires you are making that difference even bigger.
Now you're driving home, cruising and OMG everything just fails because it is greater than .5% difference? Um no.
I agree with what has been said that it is more like 10-15% difference. Seriously, take a step back and ask yourself would anyone engineer an essentially off the shelf product and design it to fail with such minor differences? No.
Again, over complicating such a simple topic.
People, it has been said more times than I can count. On STOCK wheels run 245/40/18 on the front and 265/35/18 on the rear.
/end all OEM tire talk.
Last edited by CarHopper; 04-29-2014 at 05:50 PM.
04-29-2014, 06:21 PM
#43
MBWorld Fanatic!
I have no desire to convince anyone. We all approach our cars differently. But I'll refer anyone interested to another article:
http://www.f1technical.net/features/10698
An interesting excerpt is:
The methodology itself was initially based on a realisation that the optimum 4-6% slip goal was too simplistic. A range of 12-15% at low speeds, and less than 2% at high speeds was more accurate. Further it was found that percentage slip was not the best way to characterise slip. The 4% ‘optimum’ was only optimum at a nominal corner velocity of 90-100kph.
A slip percentage of 4% at 90kph was best understood as describing the actual delta speed (4-5kph) between the front and rear wheels. The relative difference in rotational speeds gave the car it’s characteristic feel in yaw and what the driver was actually experiencing.
Keep in mind that we're talking about introducing a 2% error in some very sophisticated algorithms. Of course it considers the physics of the contact patch of driving vs. driven wheel. That's all part of its calibration. When you throw that off by 2%, when it's likely that it's using a small slip target at high speed, straight-ahead travel, it's not surprising that people report spurious ESP intervention at speed. I linked such an owner's post. If you want to insist it's unrelated to the tire change that initiated it, be my guest.
A 2% difference in tire circumference for our car is almost 2" per revolution. That is not minor to an AMG engineer.
http://www.tacomaworld.com/forum/tir...5r18-275-35r18
But please, let's just agree to disagree.
http://www.f1technical.net/features/10698
An interesting excerpt is:
The methodology itself was initially based on a realisation that the optimum 4-6% slip goal was too simplistic. A range of 12-15% at low speeds, and less than 2% at high speeds was more accurate. Further it was found that percentage slip was not the best way to characterise slip. The 4% ‘optimum’ was only optimum at a nominal corner velocity of 90-100kph.
A slip percentage of 4% at 90kph was best understood as describing the actual delta speed (4-5kph) between the front and rear wheels. The relative difference in rotational speeds gave the car it’s characteristic feel in yaw and what the driver was actually experiencing.
Keep in mind that we're talking about introducing a 2% error in some very sophisticated algorithms. Of course it considers the physics of the contact patch of driving vs. driven wheel. That's all part of its calibration. When you throw that off by 2%, when it's likely that it's using a small slip target at high speed, straight-ahead travel, it's not surprising that people report spurious ESP intervention at speed. I linked such an owner's post. If you want to insist it's unrelated to the tire change that initiated it, be my guest.
A 2% difference in tire circumference for our car is almost 2" per revolution. That is not minor to an AMG engineer.
http://www.tacomaworld.com/forum/tir...5r18-275-35r18
But please, let's just agree to disagree.
04-29-2014, 06:29 PM
#44
MBWorld Fanatic!
Agree to disagree it is
04-29-2014, 07:47 PM
#46
MBWorld Fanatic!
04-29-2014, 08:38 PM
#47
I have no desire to convince anyone. We all approach our cars differently. But I'll refer anyone interested to another article:
http://www.f1technical.net/features/10698
An interesting excerpt is:
The methodology itself was initially based on a realisation that the optimum 4-6% slip goal was too simplistic. A range of 12-15% at low speeds, and less than 2% at high speeds was more accurate. Further it was found that percentage slip was not the best way to characterise slip. The 4% ‘optimum’ was only optimum at a nominal corner velocity of 90-100kph.
A slip percentage of 4% at 90kph was best understood as describing the actual delta speed (4-5kph) between the front and rear wheels. The relative difference in rotational speeds gave the car it’s characteristic feel in yaw and what the driver was actually experiencing.
Keep in mind that we're talking about introducing a 2% error in some very sophisticated algorithms. Of course it considers the physics of the contact patch of driving vs. driven wheel. That's all part of its calibration. When you throw that off by 2%, when it's likely that it's using a small slip target at high speed, straight-ahead travel, it's not surprising that people report spurious ESP intervention at speed. I linked such an owner's post. If you want to insist it's unrelated to the tire change that initiated it, be my guest.
A 2% difference in tire circumference for our car is almost 2" per revolution. That is not minor to an AMG engineer.
http://www.tacomaworld.com/forum/tir...5r18-275-35r18
But please, let's just agree to disagree.
http://www.f1technical.net/features/10698
An interesting excerpt is:
The methodology itself was initially based on a realisation that the optimum 4-6% slip goal was too simplistic. A range of 12-15% at low speeds, and less than 2% at high speeds was more accurate. Further it was found that percentage slip was not the best way to characterise slip. The 4% ‘optimum’ was only optimum at a nominal corner velocity of 90-100kph.
A slip percentage of 4% at 90kph was best understood as describing the actual delta speed (4-5kph) between the front and rear wheels. The relative difference in rotational speeds gave the car it’s characteristic feel in yaw and what the driver was actually experiencing.
Keep in mind that we're talking about introducing a 2% error in some very sophisticated algorithms. Of course it considers the physics of the contact patch of driving vs. driven wheel. That's all part of its calibration. When you throw that off by 2%, when it's likely that it's using a small slip target at high speed, straight-ahead travel, it's not surprising that people report spurious ESP intervention at speed. I linked such an owner's post. If you want to insist it's unrelated to the tire change that initiated it, be my guest.
A 2% difference in tire circumference for our car is almost 2" per revolution. That is not minor to an AMG engineer.
http://www.tacomaworld.com/forum/tir...5r18-275-35r18
But please, let's just agree to disagree.
By your logic
New tires in the front
Wear bars in the rear
>2% difference
Traction control engages
It takes a rate of change and at least 10% to begin to engage
Lower your rear tire pressure to 36
C is reduced by 2%
See if your traction control engages
It won 't
2% tire difference means nothing
Manufacturing tolerance is about that
I read the same article they talk about pid's
They are discussing cornering, ie, yaw
Also traction control and slip, not circumferential delta
In an F1 car NOT a street car! Lol
On slicks to boot, less slip but still some
Again when applying power, NOT due to tire c
When slip is accomanied by a drop in torque deliveref
A street car at 60 has 3% slip
Again are you an engineer?
Get a copy of the Bosch automotive engineering handbook
Mine's at wotk
I'll scan the traction control limits and allowable tire delta
Agree to disagree means let me be wrong
There is only one correct position in this case
A 2% tire C difference means zilch
It will not have any effect on any dynamic control system
In awd it may stress the center diff
Last edited by Ingenieur; 04-29-2014 at 09:04 PM.
04-30-2014, 01:56 AM
#49
MBWorld Fanatic!
Absurd
By your logic
New tires in the front
Wear bars in the rear
>2% difference
Traction control engages
It takes a rate of change and at least 10% to begin to engage
Lower your rear tire pressure to 36
C is reduced by 2%
See if your traction control engages
It won 't
2% tire difference means nothing
Manufacturing tolerance is about that
I read the same article they talk about pid's
They are discussing cornering, ie, yaw
Also traction control and slip, not circumferential delta
In an F1 car NOT a street car! Lol
On slicks to boot, less slip but still some
Again when applying power, NOT due to tire c
When slip is accomanied by a drop in torque deliveref
A street car at 60 has 3% slip
Again are you an engineer?
Get a copy of the Bosch automotive engineering handbook
Mine's at wotk
I'll scan the traction control limits and allowable tire delta
Agree to disagree means let me be wrong
There is only one correct position in this case
A 2% tire C difference means zilch
It will not have any effect on any dynamic control system
In awd it may stress the center diff
By your logic
New tires in the front
Wear bars in the rear
>2% difference
Traction control engages
It takes a rate of change and at least 10% to begin to engage
Lower your rear tire pressure to 36
C is reduced by 2%
See if your traction control engages
It won 't
2% tire difference means nothing
Manufacturing tolerance is about that
I read the same article they talk about pid's
They are discussing cornering, ie, yaw
Also traction control and slip, not circumferential delta
In an F1 car NOT a street car! Lol
On slicks to boot, less slip but still some
Again when applying power, NOT due to tire c
When slip is accomanied by a drop in torque deliveref
A street car at 60 has 3% slip
Again are you an engineer?
Get a copy of the Bosch automotive engineering handbook
Mine's at wotk
I'll scan the traction control limits and allowable tire delta
Agree to disagree means let me be wrong
There is only one correct position in this case
A 2% tire C difference means zilch
It will not have any effect on any dynamic control system
In awd it may stress the center diff
BTW, tire circumference is determined mostly by steel, not air. Here's a clever experiment showing that lowering inflation pressure has practically no effect on circumference:
Last edited by whoover; 04-30-2014 at 02:08 AM.
04-30-2014, 09:22 AM
#50
Some curves from the Bosch manual would be very helpful.
BTW, tire circumference is determined mostly by steel, not air. Here's a clever experiment showing that lowering inflation pressure has practically no effect on circumference:
Does tire pressure affect the rolling circumference of a wheel? - YouTube
BTW, tire circumference is determined mostly by steel, not air. Here's a clever experiment showing that lowering inflation pressure has practically no effect on circumference:
Does tire pressure affect the rolling circumference of a wheel? - YouTube
old TPMS used the wheel speed sensors (ABS sensors) to detect air loss (ie C got smaller)
I've uploaded the chapter on TCS/vehicle stability controls
they don't give 'curves' they give the mathematical expressions, and if you study them you will see rolling diameter (as relates to wheel speed) is inconsequential
2% will not be detected
Last edited by Ingenieur; 07-16-2014 at 05:23 PM.
