Do you get an ABS fault by running a 150/70/r17 rear tire?

[wheel_of_steel]

It's 3% taller than stock - the ABS has to tolerate a certain amount of speed differences between front and rear tires due to tire wear anyway.

The worse case scenario would be a front tire worn down to the cords, and a brand new 150/70 on the back - you might have a wheel speed differential of say 10% which could cause a fault code to trip?

 

[CapeMan]

I've been running TKC-80s for over a year now - IIRC front is 120/70/17 and rear is 150/70/17 - and no problems w/ ABS or DCT. So if my notoriously leaky memory is OK, you should be good to go.

 

[Deleted member 1183]

A friend recently changed tyre size on the rear of his CB500X. No issues with the ABS and one good side affect. His speedo is now reading dead accurate per his GPS.

 

[hulkss]

The effective rolling radius of a tire is at the neutral axis of the tire assembly. The plies of the tire carcass are responsible for the strength of the tire and as such are close to the neutral axis. The rolling radius is largely unaffected by tread wear or tire pressure.

Measure the tire roll-out under load to determine the effective diameter of the tire.

 

[Lee Dodge]

I've been running TKC-80s for over a year now - IIRC front is 120/70/17 and rear is 150/70/17 - and no problems w/ ABS or DCT. So if my notoriously leaky memory is OK, you should be good to go.

I've been running that exact combo for multiple sets of tires. Never any issues with ABS or DCT either.

 

[TheIronWarrior]

The rolling radius is largely unaffected by tread wear or tire pressure.

Not strictly true. Small variances in tire pressure will be negligible, but consider a completely flat tire, supported only by the carcass. The rolling radius is significantly smaller than a properly inflated tire.
Rolling radius IS affected by the vertical stiffness and pressure absolutely has an effect. As an approximation, you can estimate the effective rolling radius by considering a point halfway between the "bottom" of the tire and the edge of the contact patch (1/4 of the total contact patch). A flatter tire has a larger contact patch.


A more accurate approximation:




Considering the weight of the loaded bike also has an impact (and varies with riders/passengers/cargo/fuel quantity/etc.) as well as the forces in the forward/aft direction too (acceleration, braking, hills, etc.) I would suggest that rather than try and determine mathematically a tolerance range for the ABS, they picked a number they thought made sense, tried it out on a track or in a lab with varying conditions (pressures, loads, etc.) and adjusted the tolerance up or down until they had the outcome they wanted.

Or, just designed the system to respond to "one wheel rolling, one wheel stopped (+/- % tolerance)" since ABS is mostly concerned with a locked wheel (in my best Homer Simpson voice, the A stands for Antilock).May not be the most elegant of solutions, but a simple one.
IE, if one wheel is above 10km/h equivalent RPM and one wheel is below 2km/h equivalent RPM, fire ABS. If wheel slip not resolved, throw fault code.

In either case, I imagine you'd need a pretty extreme departure from OEM wheel sizes and pressures to cause problems.

 

[hulkss]

I should have said rolling radius is largely unaffected by tire pressures within the design operating range of the tire.

Be careful not to confuse "ride height" with "rolling radius".

 

[TheIronWarrior]

I should have said rolling radius is largely unaffected by tire pressures within the design operating range of the tire.

Be careful not to confuse "ride height" with "rolling radius".

Don't worry, I'm not confusing them.
The amount of deflection of the tire directly influences Reff.
Though, within design/operating parameters, yes, there shouldn't be a significant difference. You have to take an awful lot of air out of the tire before it deflects significantly.
The tires on my NC right now though? After winter storage are only about half the required pressure, and you better believe the tire deflection (and therefore Reff) is affected.
To be clear, I haven't ridden on the half-flat tires, and will be inflating to the required spec before riding. Maybe I'll measure "tire squish" at varying pressures and plot out how approximated Reff changes with pressure.

Where are you getting the rolling radius lies on the neutral axis? I'm only curious because based on the approximations I've found, it seems to depend mostly on the overall (unloaded) radius and the deflection. While the deflection is unlikely to change with treadwear, the overall radius will. These are, however approximations and maybe you have some better information (which I'd be very interested in reading).

 

[hulkss]

Where are you getting the rolling radius lies on the neutral axis? I'm only curious because based on the approximations I've found, it seems to depend mostly on the overall (unloaded) radius and the deflection. While the deflection is unlikely to change with treadwear, the overall radius will. These are, however approximations and maybe you have some better information (which I'd be very interested in reading).

See the paper linked here: https://vtechworks.lib.vt.edu/bitstream/handle/10919/88829/Lee_H_D_2017.pdf?isAllowed=y&sequence=1

I worked with the team that designed this machine:

 

[TheIronWarrior]

See the paper linked here: https://vtechworks.lib.vt.edu/bitstream/handle/10919/88829/Lee_H_D_2017.pdf?isAllowed=y&sequence=1

I worked with the team that designed this machine:

That's a very cool test rig!

I'm not seeing in the paper where they equate the rolling radius to the neutral axis. I'm seeing where their modeled thin flexible ring uses the neutral axis as the unloaded radius (which makes sense as the circumferential deformation along the neutral axis should be effectively zero), but the loaded rolling radius of the model is different from the unloaded radius. You can even see in Fig 5-10 how the radial deformation (therefore rolling radius) is affected by load. The model is also dependent on stiffness, which is affected by tire pressure. The test results are shown to agree with measurements in Fig 5-11. Maybe I'm missing something (please help me understand if I am) but that paper seems to confirm that rolling radius is impacted by tire pressure and treadwear.

Please don't feel like I'm trying to prove you wrong or anything, I just enjoy learning and that won't happen without discussions and challenging the statements of others.
Plus, if I'm right all the time, I'm not learning anything new, so I don't get offended if I'm proven wrong.
I can get a little frustrating to others though, because until I DO understand, I can be tenacious. Occupational hazard (engineer, we're lots of fun at parties).

 

[hulkss]

To the question of tire size and the effect on vehicle speed:

The tire roll-out distance, as I pointed out earlier, is what matters as far as having an effect on rpm based vehicle speed. So I'm just saying that the tire neutral axis circumference can be used to estimate roll-out (more accurately than the tread face circumference). Also, the stiff plies and belts in the carcass basically establish the neutral axis location. For deformations within the rated vehicle loads and specified tire pressures, or tread wear, there is insignificant change in the neutral axis circumference.

On P98 of the linked article they apply the "inextensibility assumption": "the length of the neutral plane of the ring is constant during deformation."

 

[TheIronWarrior]

To the question of tire size and the effect on vehicle speed:

The tire roll-out distance, as I pointed out earlier, is what matters as far as having an effect on rpm based vehicle speed. So I'm just saying that the tire neutral axis circumference can be used to estimate roll-out (more accurately than the tread face circumference). Also, the stiff plies and belts in the carcass basically establish the neutral axis location. For deformations within the rated vehicle loads and specified tire pressures, or tread wear, there is insignificant change in the neutral axis circumference.

On P98 of the linked article they apply the "inextensibility assumption": "the length of the neutral plane of the ring is constant during deformation."

Yes, the length of the neutral plane remains effectively constant even during deformation because tangential stresses are negligible. That does not mean the rolling radius of the tire lies on the neutral plane though.
A very stiff tire is going to have less deformation than a very flexible tire, but in both cases the neutral axis is relatively unstressed in the tangential direction. This is the same reason that I-Beams exist, you put the material where the stresses are high and cut material out of where stresses are low. However, the stiffer tire will deform less than the flexible tire, and will therefore have a larger rolling radius EVEN IF the neutral axis is at the same location (in the unloaded tire).

Edit A: I can draw infinite shapes based on a deformed ring that have the same perimeter (length of neutral axis) and all having different effective rolling radii. Take a circle of string, any shape you can make it into will have a constant perimeter.

 

[hulkss]

Just to be clear, I probably should have been using the term "effective rolling radius". The radius that can be used to calculate the linear speed of a tire from rpm. I'm just sayin' that the neutral axis is a good estimate, not a perfect answer.

Here's another paper:

 

[TheIronWarrior]

The linked paper states in multiple places the effective rolling radius is affected by many factors and is constantly changing. They even make clear statements that tire pressures affect the rolling radius. Fig 6 even gives the experimental data at different pressures, and you can extrapolate that rw0 is significantly different at the different pressures (27 PSI and 31 PSI) for the exact same tire.
As for estimating an average or nominal value for a tire even neglecting the effects of pressures and loads, I don't think neutral axis would be the best value either. If I make a tire with 1" thick treads, the rolling radius is going to be larger than the exact same tire with only 3/32" treads all else being equal.

 

[hulkss]

Keep in mind I am suggest a way to estimate the effect of tire selection on vehicle speed or gear ratios. Comparing the diameter of the belts in the tire carcass is a better estimator than comparing the tire outside diameters. More info attached:

 

[TheIronWarrior]

Your most recent attachment isn't showing the formulae for me.

The effective rolling radius of a tire is at the neutral axis of the tire assembly. The plies of the tire carcass are responsible for the strength of the tire and as such are close to the neutral axis. The rolling radius is largely unaffected by tread wear or tire pressure.

Keep in mind I am suggest a way to estimate the effect of tire selection on vehicle speed or gear ratios. Comparing the diameter of the belts in the tire carcass is a better estimator than comparing the tire outside diameters.:

These two statements are not the same.
You start off by saying that tread wear and tire pressure have negligible effects.
Treadwear may be negligible, especially given that the change in radius from "new" to "bald" is probably somewhere around 1/4" for a tire with a "new" radius of 12" or so.
However, air pressure has a significant impact on deflection, and the effective rolling radius changes with deflection. As shown above, even a few PSI difference (27 vs 31) there is significant difference in deflection. I'm eyeballing maybe 8-10% when no wheel torque is applied, and only reaching no difference in deflection at 295ft-lbs of wheel torque which you can only get at the rear wheel of an NC700 in 1st gear (peak torque at the wheel in 2nd is 255 ignoring any losses).
You then seem to change your claims that you're just trying to find a comparison between two different tires, for which you would have to ignore the effects of loading, treadwear, pressure, etc. Choosing to ignore for ease of comparison is not the same as saying it has no effect. If I choose to ignore the effect of wind speed and direction on fuel economy to simplify a comparison between two bikes (which makes sense seeing as you can assume both machines would be subject to similar conditions, and two similar bikes should have similar coefficients of friction) that's valid. I cannot then turn around and say that wind speed and direction has no impact on fuel economy because I chose to ignore Cf for my comparison.
If all your saying is that the beltline is a better comparison that OD, I'll buy that, however I'd expect the difference ratio in beltline diameter and OD would be awful close. IE, the belts are likely at a similar position in the stack-up, like maybe at 80% of the thickness or something. There may be some tires that don't follow some typical values, but I'd imagine nearly all road oriented tires will have approximately the same radius ratios whether you use OD or beltline.

Back to OPs question whether a 3% difference in tire OD will trip a fault code. A new tire that's overinflated by 1PSI compared to a mostly worn tire that's underinflated by 1PSI might have a 5-10% difference in rolling radius under the same conditions (rough estimates based on the papers you have linked). I imagine the ABS system would be designed that a few PSI and a few 32nds treadwear won't cause faults, but that's just a gut feeling.

 

[hulkss]

A new tire that's overinflated by 1PSI compared to a mostly worn tire that's underinflated by 1PSI might have a 5-10% difference in rolling radius under the same conditions (rough estimates based on the papers you have linked). I imagine the ABS system would be designed that a few PSI and a few 32nds treadwear won't cause faults, but that's just a gut feeling.

I have never experienced speedometer errors anywhere near that magnitude with changes in tire pressure or tread wear over the life of a tire. I see about a six psi change just from tires warming up on the road with no noticeable effect on the speedometer (I use tire pressure monitors and a gps when I ride or drive a car).

 

[TacomaJD]

Fwiw, back in my younger days, I had an 07 Kawi ZX10R. upon topping it out on the freeway, oem size rear tire and same model tire compared (Michelin Pilot Power 190/50/17), it would register 189 on the speedo on a fresh rear tire, and 191 with a nearly worn out rear tire. So if the absence of tread depth at those speeds only offsets the speedo by 2mph, it's of fractional significance at normal highway speeds.

 

[TheIronWarrior]

I have never experienced speedometer errors anywhere near that magnitude with changes in tire pressure or tread wear over the life of a tire. I see about a six psi change just from tires warming up on the road with no noticeable effect on the speedometer (I use tire pressure monitors and a gps when I ride or drive a car).

Without a change in volume, that would give an increase in temperature of about 55C (167F). It appears to be generally accepted that tire temperature increases 50F (29C) when "warm" at highway speeds, which means there is about an 8% change in volume. It is clear we cannot assign the entire 8% to radial changes as the sidewall will deflect more, but I suspect some of the volume change will impact the rolling radius. The increased pressure also affects the stiffness of the tire assembly, therefore the deflection, therefore the rolling radius. How fast are you driving when you're seeing no noticeable effect, and what is the accuracy/resolution on the measuring devices? If you're driving 60mph, a 3% change in speed read will be 1.8mph. That's what the initial question is about, is 3% enough of a change in tire OD (all else being equal) to confuse the ABS. I imagine that tire wear and pressure drop (in a normal "few PSI" range) would cause a greater impact than this small of a change in tire OD.

Fwiw, back in my younger days, I had an 07 Kawi ZX10R. upon topping it out on the freeway, oem size rear tire and same model tire compared (Michelin Pilot Power 190/50/17), it would register 189 on the speedo on a fresh rear tire, and 191 with a nearly worn out rear tire. So if the absence of tread depth at those speeds only offsets the speedo by 2mph, it's of fractional significance at normal highway speeds.

Based on this one data point, the impact of tread wear could be about 1%, which is more than 1/3 the impact of the initial tire change proposed. Is it going to affect your speedometer to an appreciable amount? No, going +/-1% of your indicated speed isn't a problem. Is it going to make a significant difference when assessed next to the proposed tire change? 1/3 is not nothing.

The data is coming from the same sensors, but used in very different ways, so saying tire wear has a negligible impact on speedometer reading is different than saying tire wear has a negligible impact on ABS. I'm not saying it does at all, in fact I'm stating it doesn't. I'm stating the impact of tire wear and pressure is likely to exceed the impact of the proposed tire size change.

 

[TacomaJD]

I'm not 100% sure how the sensors work that relate to ABS and then to the DCT, but I imagined that the 150/70 being approximately 3/4" taller than a 160/60 would be significant enough to throw off sensors. Or are we talking about an ABS manual version since the OP is not from the U.S.?