Where is this magic place where you can get downhills without uphills yet get back to your house?
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The quest for wider wheels and tires, 295, 305 and beyond...
- Thread starter Davidss2
- Start date
drpheta
Member
In an alternate universe from the old guys that went to school uphill both ways.
Not joking, but trying to figure out what you mean.
"Killing your momentum" means changing speed. But in an EV, this means regen. If regen was 100%, it would make no difference if you changed speed, you'd get it all back. As it is, you get about 85% back.
In a given EV, the primary driver of efficiency is your average speed due to air drag.
Next is HVAC usage. EV delivery vans use more energy in HVAC than motion. People that quote <300 wh/mi at any speed almost always live in SoCal
Next is how much friction braking you use, as this is all wasted energy. This is where your energy goes to when racing.
Probably last is how much you change speed, given regen is pretty efficient at getting this back.
There's no magic energy recovery as you go downhill, there's a hill on the other side you'll need to go up. Is what you mean by "take advantage of the downhills" just "don't let the car speed up on downhills"? I agree that using cruise at a fixed speed is likely the best for range since it minimizes time spent at higher air drag velocities, but note that this does technically involve "accelerating" up hills as you need way more power to go uphill, and your longitudinal acceleration is non-zero since the car is not level.
drpheta
Member
So, this is my current setup.
20x9 ET30 with 255/35/20 Conti DSW06 with P3D rotors.
If I went 19x10 ET30 for a track setup, would it clear the knuckle on 275/35/19 tires? If looking at this properly, I'll have 2-3mm of clearance on this track set.
Sorry for the blurry second photo, but it looks like I have about 15mm of clearance on the 20x9 at the moment.
20x9 ET30 with 255/35/20 Conti DSW06 with P3D rotors.
If I went 19x10 ET30 for a track setup, would it clear the knuckle on 275/35/19 tires? If looking at this properly, I'll have 2-3mm of clearance on this track set.
Sorry for the blurry second photo, but it looks like I have about 15mm of clearance on the 20x9 at the moment.
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Ok this only works for people who drive above speed limit.
I try to carry my car's momentum up hills to reduce the amount of juice used to get up that hill. from 85 to 75 for example.
Then i gently get back up to speed and do the same thing downhill but while keeping a bit of regen green bar.
There are times during my 'efficient' commutes where my wh/mi sinks as low as 240's while on the OEM 235 pzero's, by the time i get home its back up to 270's. during these trips most of the braking is done by regen.
During my 'not so efficient' commutes i get home with about 280-305 wh/mi.
im not encouraging speeding but tbh the average speed out there these days is 10-15mph above posted.
I try to carry my car's momentum up hills to reduce the amount of juice used to get up that hill. from 85 to 75 for example.
Then i gently get back up to speed and do the same thing downhill but while keeping a bit of regen green bar.
There are times during my 'efficient' commutes where my wh/mi sinks as low as 240's while on the OEM 235 pzero's, by the time i get home its back up to 270's. during these trips most of the braking is done by regen.
During my 'not so efficient' commutes i get home with about 280-305 wh/mi.
im not encouraging speeding but tbh the average speed out there these days is 10-15mph above posted.
Why is efficiency being mentioned in this thread!? Please take that crap elsewhere
Physics doesn't work this way. "Momentum" is kinetic energy, which by definition came from the battery at some point. You flat out cannot reduce the amount of energy required to go up a hill, that would violate conservation of energy. All you can do is speed up before the hill and move some energy to kinetic energy and then convert that into potential energy as you go up the hill. Or you can just directly go from battery to potential if you don't change speed.
Going faster (kinetic) is less efficient however, because any speed addition also adds air drag. The reason what you do has any chance of working is that you actually spend some time below 85. Your average is probably about 80 MPH. If you just drove the whole thing at 80 you'd save even more energy than varying from 85 to 75 to 85. Drag is square of velocity so you use less energy just driving at 80 than half your time at 85 and half at 75 even though the average speeds are the same.
Note that going 80 up the hill vs on level ground has no impact. You'll get much better efficiency at 80 than 85 no matter where you are.
If you want to maximize efficiency and you were doing 85 on the flats and 75 up the hills, just go 83 all the time. Your drive time will be identical and your energy use lower.
The only thing you really want to avoid is ever having to use the friction brakes downhill. Somewhat paradoxically you want to avoid regen too as it's less than 100% efficient. Given the reality of speed limits, Regen is much better than friction brakes though, and if you are going downhill, it's better to use regen to capture that energy than it is to allow the car to speed up significantly (due to the square drag thing again).
And then use all this energy savings to run massively wide tires and track the car. My average wh/mi over the last 6K miles is >500
MasterC17
Active Member
Got the 305/30/19 Falken RT660's installed on the 10.5x19 ET25 MW03's! I believe they call this - snug.
drpheta
Member
Clearance 0.0005mm
I'm impressed.
Question. How much clearance is the minimum w/o rubbing too much? I suppose a small bit of rub isn't a catasrophe, but JFC that's the the best "annoying-sibling-I'm-not-touching-you" clearance ever.
Also, what brake rotors are these mounted with... AP?
MasterC17
Active Member
I've previously run similar clearances on two other cars with different setups, and thus far it doesn't seem to be an issue. Basically if it doesn't rub up in the air it won't rub out on the track. You would think there's some play in the hub, but if there is it's not measurable.
drpheta
Member
That's really comforting to know. So, I can basically have the tire just barely breathing on the knuckle at rest, and it'll be fine on the track.
MasterC17
Active Member
I've yet to damage any tires. Just make double, triple sure the wheel speed sensor is safely secured BEHIND the knuckle. I actually just added a second zip tie. You can also see I wrapped it in extra tape.
SK360
Member
Just tape some sandpaper to the sidewall and let it self clearance.
MasterC17
Active Member
Yeah - sadly it looks like the rear is going to be an issue. I was concerned about that. Sticking out about ~5-10mm too far. This is why I think somewhere between an ET30 and ET35 would be the perfect square setup for our cars. ET40 requires a huge front spacer and ET25 sticks out too far in the rear. Oh well, try again lol.
Already done after I took the previous knuckle photo. Shaving a few mm off the knuckles is easy!
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