As many people know (some just by looking at one), the DMC uses different-sized wheels & tires in the front and rear. This was done because of the rear-engined nature of the car and how tail-heavy it made it (the original weight balance was 35/65 front/rear). People have put matching-sized wheels on all 4 corners, but it just doesn't quite look right.
Which brings me to what I'm trying to figure out- I'm going to be trying to keep as much of the functionality of the iD.4 that will be serving as the drivetrain/battery donor for the the DMC's EV conversion, and keeping the computers happy will probably mean needing to keep the wheel speed sensors. The conversion that I'm using as the template for mine- Bill Carson's 'Project Lightning'- which used a Bolt as the donor vehicle 'solved' this problem I believe by putting all of the sensors around one of the driveshafts with a sensor ring so they all think they're spinning at the same speed and the computer thinks everything is perfect.
The downside to this is that it loses the ABS and traction control capabilities of the donor vehicle. On a more normal vehicle, you could (hand-waving a lot of mechanical work aside) mount the ABS rings and sensors on the hubs of each of the wheels and go from there (interestingly, the iD.4 apparently also uses the wheel speed sensors in place of TPMS sensors in the wheels to monitor the tire air pressure...). But- as noted earlier- the DMC has different-sized wheels & tires between the front and back- so at a constant speed with no slippage the front wheels are going to be turning faster than the rear.
So- I'm thinking that if I wanted have a shot at getting the wheel speed sensors to work properly, I would have to have proportionally different rings on the front and rear wheels, right? Actually I'll probably need different ones on ALL of them vs. the stock iD.4 since it's base wheels & tires have an OD larger than I believe will fit even on the rear of the car (no way they'll fit up front without it looking even more high-nosed than the time machine with whitewalls on it in BTTF3) and the computer would be figuring the speed wrong. I'm guessing that there's not a way to simply tell the computer that, "Hey, you've got different-sized wheels than usual, here's the new sizes." so it's going to have to be done purely with hardware.
Anyone ever done anything like this?
If you wanted to be really brave, you could setup a digital reader/writer that would do the proportional scaling for one or both ends of the car to get the control system to think everything is still happy. It would also indicate if anything unusual happened like slip/low pressure/etc. The basic functionality is simple. The actual application may not be so easy.
- Capture the wheel speed output signal from the existing hardware
- Apply whatever scaling factor to that signal based on the size differences between the ID4 and deLorean tires
- Send the matching signal type (square, saw tooth, triangle, sine wave, etc) at the adjusted rate
- Profit...
Mechanical is where my head went first, but you will likely need a non-integer correction and a partial tooth is going to be difficult.
In reply to stafford1500 :
This is something that a MSGPIO could probably do, to be honest.
Assuming that they are VR sensors and not active sensors, anyway.
We once put larger diameter tires on one end of a 2004 Miata. It didn't complain, it it did trigger ABS early.
I wouldn't worry about making all the tires larger diameter. Takes some real voodoo for the car to detect that - the ND Miata does it with sidewall resonance or something but it doesn't really care all that much.
If the tone rings can be removed, you could maybe machine/cut some with an appropriate number of teeth so the pulses per mile are the same front and rear.
In reply to stafford1500 :
Hmm, I hadn't thought of trying to modify the signal itself. I'm an engineer so tend to think physical/mechanical before software, but assuming it would be possible to figure out and replicate the signal it would probably be trivial to ratio it appropriately for the respective tire diameters vs. what it's expecting.
I don't have any real answers, just wondering some stuff.
What does the car use for vehicle speed ? Is it the tone rings?
Also, does the wheel speed sensor care how fast the teeth are going, or is it just comparative?
Trying to work it out in my head, correcting an arbitrary 7% discrepancy over a 32 tooth tone wheel would likely require a significant change in the number of teeth to find a common denominator.
And how much would tire wear effect it?
Like I said, I don't have any answers, it's just a fun problem to think about.
In reply to Crackers (Forum Supporter) :
Wheel speed sensors detect wheel speed, not just comparative. You can read wheel speed from each sensor on a scan tool even from ABS in the 80s. In many/most newer cars that speed information is also THE speed information used by the rest of the car and is transmitted over high speed CAN, to the point that some cars without ABS will have one wheel that will have a wheel speed sensor, because there isn't a way to measure wheel speed directly from powertrain sensors. (Hyundai is the main one I think of)
Many newer cars have directional sensors, too. That is, they will know if the wheel is traveling forward or backward. I don't know the wizardry of how they do this with a sensor that only has two wires, but they do.
Forward backward is easy, just use three teeth with a different spacing bettwen them, make all the other teeth the same. Big gap then small gap? forward. Small gap then big gap? backward. If the computer knows to expect gaps in the tone ring, the computer wont care or think the signal is missing.
I would start with mechanical option ASSuming you get something reasonably close.
Some quick googling and excel work...
Long story short, count the pulses on the tone rings front and back, build new tone rings that are proportionally correct. The percent error is pretty insignificant and less than what putting one worn out tire on the car would have. Thats the easy button I would think.
dps214
SuperDork
4/29/25 12:36 a.m.
How much of a difference in tire diameter is there? I'm not well versed in EV control systems - I could see them operating on tighter tolerancves - but the standard ABS/TC systems for ICE cars generally have a surprisingly high tolerance for changes in diameter stagger. For example my cayman has an inch of diameter stagger stock, and people have run slightly negative stagger without issues.
In reply to dps214 :
The tires on the donor iD.4 should be 235/50 R20's. 93gsxturbo's spreadsheet excerpt above shows the stock DMC tire/wheel sizes: 195/60 R14 in the front and 235/60 R15 in the rear.
It's easier sometimes to just see things visually, so here are the stock DMC Front & Rear tires vs. the iD.4's (including the data on the diameter):
Rear:
For S&G's, here's the DMC's front vs. rear to see how the difference in what identical tone rings on all corners would be seeing:
'Internally' (i.e. between the DMC tires) it wouldn't be that bad since there's just a 4.5% difference in the circumference- it's possible that having that difference wouldn't cause problems with the ABS/traction control, there's not a good way of knowing without testing as I'm going to guess that the technical data regarding how much of a difference triggers the computer isn't remotely readily available.
However, looking at the differences between the iD.4's tires and both of the DMC's is much more obvious- the front will be off by more than 20% and the rear by about 17%, so the speedo will clearly not read properly without either different tone rings or processing the signal to ratio it to the tire sizes.
Honestly, I'm kind of more inclined toward trying to work it out processing the signal because it seems (from the Dakota Digital box I posted the link to) it is something that has been done already, so it should be possible to do it again (hopefully less expensively). That would also be more flexible in that if it were set up to be adjustable if I used different tires/wheels I could just modify the ratio in the software vs. having to find/build another tone ring.
Which is the other reason- I'm not particularly certain how to build a custom tone ring. I've not really found much of anything in searching regarding people having done so. Granted there are plenty of rings from other cars and there are probably even ones from other VAG vehicles that use smaller wheels & tires that would work. And in fairness- there's a decent chance that I won't be able to use the iD.4's actual original tone rings since they look to be integrated into the wheel hub/bearing assemblies (though the shop manual does make it look like it might be a separate part though it's not listed on the parts page separately):
Adding complication is that I won't know until I actually get into trying to merge everything together whether I'll be retaining and using the original DMC (4x100) hubs or trying to modify things to use the iD.4's (5x112) hubs. Odds are (especially in the front) that I'll be sticking with the DMC's since it will require the least amount of modification to the suspension- but being able to use the VW's hubs would likely open up a lot wider range of wheels that I'd be able to use since I'm not 100% on keeping the DMC's original wheels on the car. Using more modern lower-profile tires on it would be nice (and easier to find).
Keith Tanner said:
We once put larger diameter tires on one end of a 2004 Miata. It didn't complain, it it did trigger ABS early.
I wouldn't worry about making all the tires larger diameter. Takes some real voodoo for the car to detect that - the ND Miata does it with sidewall resonance or something but it doesn't really care all that much.
If the tone rings can be removed, you could maybe machine/cut some with an appropriate number of teeth so the pulses per mile are the same front and rear.
Sorry that's kind of a funny statement, "It didn't complain, but it triggered ABS early."
That kind of seems like the definition of the car complaining.
Hub choice will determine your next move. If you use ID4 hubs and they are unitized you are going to have to use the digital option. If you use DeLorean hub that dont have a tone ring from the jump, you will have to engineer a solution that attaches to a spinny bit and uses ID4 sensors. Then its just a matter of cracking an ID4 hub open, figuring out what the sensor was made of (material, tooth profile), and then making your new tone ring fit the Delorean hub and the ID4 sensor, while having the correct number of pulses to keep the stock computer happy.
I saw 19s and 20s as options for the ID4. Not sure if a wheel choice requires an ECU change or not. Are you using the gauge cluster from the ID4?
In reply to 93gsxturbo :
I'm planning on using the gauge cluster (and infotainment center... and pretty much everything that I can get to work...) from the iD.4. I've not looked into whether there's a way to tell the car what wheel/tire size you're using. But the different choices of wheel between the models don't change the diameter of the tires:
The 20's use slightly less tell sidewalls than the 19's (45 vs 50- 10% difference) so the computer wouldn't need to be adjusted between the two. The front tires differ slightly from the rears (~1% for the 20's), so the computer must either not care about the difference or be programmed to account for the difference between front & rear.
Makes sense. Figure out the hub sitch and go from there.
z31maniac said:
Keith Tanner said:
We once put larger diameter tires on one end of a 2004 Miata. It didn't complain, it it did trigger ABS early.
I wouldn't worry about making all the tires larger diameter. Takes some real voodoo for the car to detect that - the ND Miata does it with sidewall resonance or something but it doesn't really care all that much.
If the tone rings can be removed, you could maybe machine/cut some with an appropriate number of teeth so the pulses per mile are the same front and rear.
Sorry that's kind of a funny statement, "It didn't complain, but it triggered ABS early."
That kind of seems like the definition of the car complaining.
There were no warning lights (ie, complaining), the system just didn't perform as well as it should (ie, triggered earlier than ideal). It's been a long time so I don't recall the specific diameter difference, but it wasn't enormous.
Miata tone rings could be manufactured by Send Cut Send, I think.
I wouldn't be as worried about changing total tire OD. I know an ND Miata with indirect TPMS can sense the difference but it didn't affect the way the DSC/ABS worked. But if you're doing new tone rings or modiying the signal anyhow, you can correct for that.
FYI, NA Miata uses 44 teeth, equally spaced. That's about one pulse per 41mm or about 650 Hz at 60 mph. I know from messing with ND Miatas that the ABS system is very sensitive to delayed signals - even just passing the CAN data through a gateway without modification was enough to trigger an ABS failure occasionally. We had to move the gateway so that it wasn't in the path between the PCM and the DSC. That's why I'd prefer to modify the signal by messing with the tone ring as a first choice.
In reply to Keith Tanner :
Interesting, but that makes sense- the system needs to react very quickly so it stands to reason that it would be sensitive to signal delays.
Looking at the VW parts site it looks like the iD.4, Atlas, and Tiguan all share the same wheel bearing/hub assembly so I'm keeping an eye out for the latter two (not figuring on finding an iD.4) in the nearby junkyards- it would be useful to grab the bearing/hub, housing/knuckle, and wheel speed sensor to do some testing with it. That and having the bearing assembly would give me a chance to see how difficult it might be to use them on the DMC.
