AWD diff tuning
03-25-2021, 04:37 AM
#1
AWD diff tuning
I have found some useful info on how to set up a ball diff. Essentially push the car backwards, goose the throttle and see if it slips. If it does, tighten it a bit until it doesn’t.
This seems to be recommended for pan cars and 2 wheel drive cars - but this could get complex for an awd car I think.. is the process the same or is there another way to go about this?
And for the next layer of complexity... can someone provide a link to or copy/paste some discussion about the interplay of front and rear diff tightness and how that would affect entrance steering, exit steering and over/under steer (and other factors I’m not thinking about? I plan to play around with different settings when I get my cars built just to compare theory to practice...
I am about to start building a BZ3 and also an AMZ (couldn’t decide, bought both...) to run in my garage. I would call the surface low-medium traction as I mop the concrete and keep most of the dust off. I have on order a bunch of different tires/wheels varying in offsets, widths, tread pattern, brand, compound, etc...
as well as a lap timer/transponder setup.
so while there is no 1/28th scale race community in my area that I know of - I think I can still have fun racing myself - I just just have some gaps in my understanding of car setup that I am eager to fill in - namely diff tuning right now.
This seems to be recommended for pan cars and 2 wheel drive cars - but this could get complex for an awd car I think.. is the process the same or is there another way to go about this?
And for the next layer of complexity... can someone provide a link to or copy/paste some discussion about the interplay of front and rear diff tightness and how that would affect entrance steering, exit steering and over/under steer (and other factors I’m not thinking about? I plan to play around with different settings when I get my cars built just to compare theory to practice...
I am about to start building a BZ3 and also an AMZ (couldn’t decide, bought both...) to run in my garage. I would call the surface low-medium traction as I mop the concrete and keep most of the dust off. I have on order a bunch of different tires/wheels varying in offsets, widths, tread pattern, brand, compound, etc...
as well as a lap timer/transponder setup.
so while there is no 1/28th scale race community in my area that I know of - I think I can still have fun racing myself - I just just have some gaps in my understanding of car setup that I am eager to fill in - namely diff tuning right now.
03-25-2021, 06:20 AM
#2
Track Pictures
For context - Here is my current track setup. It is just some PVC casing setup on hinges so I can rapidly set-up/take-down/rearrange (takes me about 1-2 minutes either way and the sections stack nicely in the corner of the garage). The track is about 15’ x 15’ and I am working on a way to secure the middle sections better so I don’t have to reset them when I take a corner too early and hit the wall...
maybe down the road I will find some kind of material to roll out before I set up the track to increase traction - but right now I’m somewhat enjoying the challenge of the low-medium grip concrete surface. That and it forces me to go slower which is more on par with my reaction time and hand/eye coordination level...
maybe down the road I will find some kind of material to roll out before I set up the track to increase traction - but right now I’m somewhat enjoying the challenge of the low-medium grip concrete surface. That and it forces me to go slower which is more on par with my reaction time and hand/eye coordination level...
03-27-2021, 04:46 AM
#3
Typically, I start with both differentials set a bit loose. In that I can slip outer wheel when holding the inner wheel and diff gear in hand while testing.
I focus on setting the rear diff first. Tightening as I test in a similar fashion to what you described. Once I feel that there is no more slip coming from the rear, I bring the front to a similar tension.
I personally, tend to prefer slightly less tension in the front than the rear on the AWD platform. However, I do not brake much on the cars. Higher traction surfaces with heavy brake zones, the front needs to be tighter to handle the braking.
10+ years ago, I was driving the Mini-Z AWD car a lot, and when both differentials were equal in tension, I would see a lot of chatter mid corner. Leaving the front diff slightly loose, to the point that it could slip eliminated that chatter. After some development, I noticed that the rollout/diameter of the wheels was different front to rear. Fronts were usually around 23mm, and rear almost 25mm. Attached to the same driveshaft, a game of tug of war was being played on the drivetrain, and keeping that front diff loose and driving it like a 2wd car with "traction control" was sort of the band-aid which we were putting on it to make it work. I started testing smaller front differential gears, and matching the rollout of the front and rear of the car, which essentially eliminated the chatter and need to use a loose front differential.
So now, I run my differentials very close in tension, still have the front slightly looser than rear, but neither diff slips. A looser front differential will generate more steering into the corner, but less off the corner. A tighter front diff will have less steering into the corner and mid corner, but more steering off the corner on throttle application. It will also tend to track straighter, and be driven more aggressive. The difference between loose and tight, is often less than half a turn of tension on the adjustment collar. Even a quarter difference may be the limit of the tuning window.
I focus on setting the rear diff first. Tightening as I test in a similar fashion to what you described. Once I feel that there is no more slip coming from the rear, I bring the front to a similar tension.
I personally, tend to prefer slightly less tension in the front than the rear on the AWD platform. However, I do not brake much on the cars. Higher traction surfaces with heavy brake zones, the front needs to be tighter to handle the braking.
10+ years ago, I was driving the Mini-Z AWD car a lot, and when both differentials were equal in tension, I would see a lot of chatter mid corner. Leaving the front diff slightly loose, to the point that it could slip eliminated that chatter. After some development, I noticed that the rollout/diameter of the wheels was different front to rear. Fronts were usually around 23mm, and rear almost 25mm. Attached to the same driveshaft, a game of tug of war was being played on the drivetrain, and keeping that front diff loose and driving it like a 2wd car with "traction control" was sort of the band-aid which we were putting on it to make it work. I started testing smaller front differential gears, and matching the rollout of the front and rear of the car, which essentially eliminated the chatter and need to use a loose front differential.
So now, I run my differentials very close in tension, still have the front slightly looser than rear, but neither diff slips. A looser front differential will generate more steering into the corner, but less off the corner. A tighter front diff will have less steering into the corner and mid corner, but more steering off the corner on throttle application. It will also tend to track straighter, and be driven more aggressive. The difference between loose and tight, is often less than half a turn of tension on the adjustment collar. Even a quarter difference may be the limit of the tuning window.
03-27-2021, 05:04 AM
#4
Would it be possible to equalize wheel diameter by truing the rear tires to be the same diameter as the fronts?
Also - most of the info I’m finding about AWD diff tuning is coming from 1/10th TC scene. A lot of people seem to run very tight front diffs or even spools, and relatively loose rear diffs.
It seems like that setup would sacrifice entrance cornering for mid and exit.
Also - most of the info I’m finding about AWD diff tuning is coming from 1/10th TC scene. A lot of people seem to run very tight front diffs or even spools, and relatively loose rear diffs.
It seems like that setup would sacrifice entrance cornering for mid and exit.
03-27-2021, 05:37 AM
#5
The larger TC cars have much more mass, and make much more time up on the brakes than the micro cars do. This is why I feel that they run much tighter front diffs than micro. In addition, in micro scale, we do not run the same tires front and rear. So we can adjust the car considerably on the tire with compound and width where 1/10 most classes use the same tire on all 4 corners. So the tendency in 1/10 may not scale directly to micro due to the differences in options which are available in this scale. Essentially, removing some front end traction, maximizing braking, and increasing drive off the corners seems to be the focus of setup on 1/10 based on the setup choices.
As for adjusting rollout by truing rear tires, it would really depend on the tire used. Some tires which come as a radial, are best used with the full diameter. On smooth concrete, the radial tires tend to deal better with the dust than a slick would. I would run a smaller front spur and radial rear tire on a concrete, or low traction surface.
As for adjusting rollout by truing rear tires, it would really depend on the tire used. Some tires which come as a radial, are best used with the full diameter. On smooth concrete, the radial tires tend to deal better with the dust than a slick would. I would run a smaller front spur and radial rear tire on a concrete, or low traction surface.
03-27-2021, 10:35 AM
#6
This all makes a lot of sense. I appreciate the info and help understanding some of the reasons behind your tuning decisions.
something tells me that I will be buying a proper RCP track in the near future. I have space in my finished basement to do it.
something tells me that I will be buying a proper RCP track in the near future. I have space in my finished basement to do it.
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