Infraction 1/7 scale road racing thread. (T/C,G/T, F1, and Indy)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, and others.
I've finished with the layout changes (still need to modify battery securing, but here it is.

5F5542EC-285F-46AE-BAD3-7B644E89C179.jpeg


The weight balance across all 4 wheels seems good. They are each 1250 grams give or take 20 or 30 grams. I think that's good enough.

It's 5kg ready to run, without the body shell. I don't know what a stock infraction weighs.

The car seems to handle well and is balanced, at least as far as I can feel. On 4S it still has more power than traction :).

I haven't done the front shock stiffening yet, but have both harder springs and oul ready to go.

I might do it when I next go to the track, and will do some timed laps to get a baseline, then stiffen the front and see if it makes a difference, in feel and lap times.
Didn't mention i did as some 'balast' into the radio box to add a little more weight to the front wheel on that side to make it more evenly distributed. I think I added was about 75g, but I'll have to double check that.
 
Last edited:
Does anyone know what the weight bias front to back would ideally be for a circuit racing 4wd car? 50/50?

I'll do some googling as well.
 
Does anyone know what the weight bias front to back would ideally be for a circuit racing 4wd car? 50/50?

I'll do some googling as well.

I think it is often 50/50; if I understand correctly that its for "feel" of the car; of course a bit diff for RC with respect to feel of traction breaking and how car does break traction.

imo is something worth "playing with" yourself.

I try out weight bias towards front first, working weight toward back. I feel like my lim has too little traction at front, maybe because of wheelbase but the rear is never even close to breaking traction from turning. meaning the traction breaking between front / rear is not even on "same page" lol (of course can easily break rear traction with accelerator. meaning here is breaking lateral traction from turning.

imo ideally i would need to balance turn speed with rear breaking traction for most of turn. as it is now I need to slow so much to get turn in, the rear is FAR from breaking traction, even with coming out of turn, kicking out rear is not really an issue, it's still understeer.

have not checked myself but am curious about the steering angles / ackermann seems to be HUGE give the track of a lim is like 8"-10". maybe the two front tires are are too much of different angles and are actually "fighting" each other.

Is still not warm where am at to get into "testing"; currently just parkinglot lapping the stock hoons until they're toast. by then it'll be warmer and will get GRPs.

Here is a quote from a MT article "Remember, no amount of chassis setup adjustment will overcome excess Ackermann effect and the loss of front grip associated with it."
 
Last edited:
Gents!

Been super busy, and wasn’t getting any notifs on new posts, but stoked to see all the action here! Some awesome setup tips, tyres, aero…love it.

I’ve made some changes to my setup, started running the same weight diff oil in the center and front, (1M), and went to 100k in the rear. Eliminated Ackerman with the Losi Typhon Ackerman plate, did some sealing up on the splitter with 3M wrap, new limitless body, (have the biddy waiting for paint on the other car), added a Biddy rear wing and made it adjustable. Also Pennie’s up for the new Sanwa M17…yea, it’s that good.

One brainwave I had was to put softer rear and front springs on, and heavier sway bars. Front just hard enough to support the car, and used some Tekno orange springs on the rear that I cut down. Then, a Tekno “C” block, and was able to adjust the anti-squat so the nose wasn’t lifting under acceleration. Car DIGS on power in the turns, and does not want to drift. Having so much fun with these now, and really would like to find a track…

One note on shock oil/diff oil, you can use the following formula to make your own/

X(A) + Y(B) = Z/(A+B) = final weight/cst

X = weight or cst of oil 1
Y = weight or cst of oil 2
A = fl oz or grams
B = fluid oz or grams

I use this to make diff oil and shock oil when I cannot find or don't have the weight I want. Have to blend it really well, but I can make the heavier weight shock oils now. Drilling my own pistons has helped as well.

Pic of the latest:

255065D7-C4A1-4F3C-BCBC-4636ACED99AA.jpeg


Going to take a closer read through tonight, and probably will have some questions for y’all:)

Wade
 
Had my first real race track run today. It was a blast, even though the track was a little slippery due to light rain, but I tried out the GRP rain tyres and they worked ok.

View attachment 213510

Had one minor crash after cutting across a curb too much and it flipped the car, luckily at low speed.
View attachment 213511
Now I'm hooked big time!

I got some advice from someone there who raced 1/8 GT cars.

He suggested that to improve my infractions handling, I need to:

1- stiffen up the springs, and increase the oil weight. The front should be stiffer/heavier oil weight than the rear.

2 - lower the ride height to about 6mm.

FYI the stock springs are...

Front

ARA330600 | 35mm 4.7N/mm (27lb/in)​

Rear

ARA330599 | 40mm 6.6N/mm (38lb/in)​


Arrma does two stiffer front 35mm springs...

View attachment 213507

I'll probably get both to try out.

For the rear, I can't see any stiffer springs from Arrma. Do I just search for 40mm springs, maybe from Tekno or similar race brands?

What about oil weight suggestions? The manual shows the stock weight is 2000 on both ends, which seems high to me...
View attachment 213509

So I thinking of trying 2500-3000 or thereabouts on the front, and 2000-2500 on the rear. Any suggestions, thoughts?

I've also got a good selection of different GRP compounds now, so starting to try them out in different situations to see what works.

Still have to do my weight balance measuring. I have the scales now.

Cheers!
SAGA R/C sells super stiff springs for the Arrmas, but I’ve had better luck, FWIW, using softer springs, heavy oil, and stiffer sway bars…my cars really have some noticeable on power steering improvement…
 
SAGA R/C sells super stiff springs for the Arrmas, but I’ve had better luck, FWIW, using softer springs, heavy oil, and stiffer sway bars…my cars really have some noticeable on power steering improvement…
Intetesting. I'll try the stiffer front end first and see what happens.
Gents!

Been super busy, and wasn’t getting any notifs on new posts, but stoked to see all the action here! Some awesome setup tips, tyres, aero…love it.

I’ve made some changes to my setup, started running the same weight diff oil in the center and front, (1M), and went to 100k in the rear. Eliminated Ackerman with the Losi Typhon Ackerman plate, did some sealing up on the splitter with 3M wrap, new limitless body, (have the biddy waiting for paint on the other car), added a Biddy rear wing and made it adjustable. Also Pennie’s up for the new Sanwa M17…yea, it’s that good.

One brainwave I had was to put softer rear and front springs on, and heavier sway bars. Front just hard enough to support the car, and used some Tekno orange springs on the rear that I cut down. Then, a Tekno “C” block, and was able to adjust the anti-squat so the nose wasn’t lifting under acceleration. Car DIGS on power in the turns, and does not want to drift. Having so much fun with these now, and really would like to find a track…

One note on shock oil/diff oil, you can use the following formula to make your own/

X(A) + Y(B) = Z/(A+B) = final weight/cst

X = weight or cst of oil 1
Y = weight or cst of oil 2
A = fl oz or grams
B = fluid oz or grams

I use this to make diff oil and shock oil when I cannot find or don't have the weight I want. Have to blend it really well, but I can make the heavier weight shock oils now. Drilling my own pistons has helped as well.

Pic of the latest:

View attachment 215748

Going to take a closer read through tonight, and probably will have some questions for y’all:)

Wade
I think local tracks having a limitless class would be awesome! The cars have that cool F1 ish factor, but good parts support and local hobby shops sell them.

When I get more involved with my local club, I'll try to raise the idea of a limitless class. Could even try to get the local hobby shop that sponsors the track to sell 'packs' of the roller, electronics, clear body GRP tyres etc. would be a super cool class to have.

Could also be infractions, but imitless has a more race look that I think people would be attracted to running.
 
Last edited:
SAGA R/C sells super stiff springs for the Arrmas, but I’ve had better luck, FWIW, using softer springs, heavy oil, and stiffer sway bars…my cars really have some noticeable on power steering improvement…
Wade, the interesting thing about those stiffer springs from SAGA is that the recommend 60-80wt shock oil, which is lighter than the stock oil.

It's making me question of stiffer springs would also have 'thicker' shock oil?
 
Wade, the interesting thing about those stiffer springs from SAGA is that the recommend 60-80wt shock oil, which is lighter than the stock oil.

It's making me question of stiffer springs would also have 'thicker' shock oil?
Yea, traditionally, stiffer springs means heavier oil.

Here’s my thinking behind modding these specific cars for track use, rather than speed runs or drifting, vs a proper 1/8 scale touring car. I’m not saying I’m the expert at all, just what I’ve changed to make my cars turn:)

These cars are looong off-road buggies, with short shocks, and absolutely terrible tires out of the box. They have a laggy radio, with a gyro, ancient pillow ball front suspension, super flexy rear suspension arms, awful endlinks, an 18 degree caster angle, SLOW servo, an aluminum tower to tower brace, and bushing loaded steering components. Bashing buggies. Not race bred platforms. The rear ends are sooo stiff and don’t articulate at all in a turn, the only way to get them around a corner is to drift it.

Any 1/8 scale touring car platform will smoke these cars around a track. The challenge as I see it, is to find the changes in setup and components to have fast comer entry, a consistent, smooth transition to on power out of the apex, and creating grip through chassis dynamics in order not to trash your tyres in one pack. IMHO, caster angle needs to be changed from 18 deg to about 10-12deg, roll center raised at the rear, shocks need to be stood up, and the rear springs softened, we have to figure out how to create better geometry with sways and links, ackermann needs to be eliminated, anti-squat must be increased at the rear, rear toe has to be changed from -3 deg, rear arms need to be stiffer, weight needs to be reduced, and functional aero must be added.

When was the last time someone was like, holy poop bro, that (off-road) Arrma turns like crazy?

Never, lol…any Tekno will smoke an Arrma on a track. We have to re-think the engineering and goals of this platform to a certain extent:) Take some ideas/setups from 1/8 touring, but not all, as touring car platforms are vastly different than these cars.

After seeing the lightweight 4S ideas, that’s gotta be my next build. A Scorched R\C carbon fiber chassis is on the way:)
 
Thanks Wade. Lots of good info to think over there.

I started at reducing power to 4S, and reducing weight, mainly by removing unnecessary stuff. The only thing I've replaced is the servo mount, as i wanted to remove all that unnecessary plastic.

I still have to weigh all the things I took off the car, but full running weight with the seven65 body is about 5.4kg (11.905 pounds).

I don't think I'll go into full weight reduction mode by replacing things with carbon fibre and other lighter materials. for me, this will be a fun track and carpark race car, not a 'real' competitive race car. There's no class to really race it in anyway.

I'll post some better close up pictures later today of my car.
 
Thanks Wade. Lots of good info to think over there.

I started at reducing power to 4S, and reducing weight, mainly by removing unnecessary stuff. The only thing I've replaced is the servo mount, as i wanted to remove all that unnecessary plastic.

I still have to weigh all the things I took off the car, but full running weight with the seven65 body is about 5.4kg (11.905 pounds).

I don't think I'll go into full weight reduction mode by replacing things with carbon fibre and other lighter materials. for me, this will be a fun track and carpark race car, not a 'real' competitive race car. There's no class to really race it in anyway.

I'll post some better close up pictures later today of my car.
Maybe if enough of the tik-toks, (us), keep doing this, there maybe be a class for these someday! I’m trying here in Colorado to get something going…

Anyway, love the 4S idea, I have a XeRun Gen 2 and 4268 2000kv setup on one of my cars running 6S, and am def going to try the 4S rig, and will be moving some of the components around the chassis like you have. Thinking about a 2WD F1 style car too, with a revised front end to get a better splitter and front wing design prototyped.

When you go run some laps, would you mind removing the center brace, and seeing if you have any improvement grip wise? I also added a buggy wing mount to 2 of my cars, with a Tekno high downforce wing to get the downforce on the chassis instead of the body. Seemed to help. Last but not least, (as I am obsessive as they come), I removed the second and fifth vanes in my diffusers, as these are the areas of low pressure air escaping, and this made an improvement in rear grip as well. Will post some pics later.”

Loving this…

Wade
 
Here's a few better pictures of details of my 4S focused (but 6S capable) infraction GT car.

My lightweight battery 'tray', that's not really a tray. Its 3M dual lock, with a single original velcro strap. So far so good. Haven't had a major crash to test it to its limits however, but I 'think' it'll be ok. I had to drill one hole in the chassis for this. This dual lock stuff is very strong, and the strap should hold down the battery in a crash, and the dual lock will stop the battery from being able to slid in any direction.

IMG_6958.jpg



I cut up the ESC mount, to keep the receiver box. I wasn't going to have a receiver box at all, but I needed some more weight to balance the car, so I kept it, and actually added about 75G of ballast in here. Its also helpful to keep all the wires that are longer than necessary.

I bought a GPM servo mount, and drilled 4 holes in the chassis for it. I chose that position, as it helped to best balance the weight across all 4 wheels. Seems to work great. Its very solid.

I still have to get around to replacing the steering bushings with bearings.
IMG_6960.jpg



The ESC is a hobbywing max6. I took off the plastic cover and mounted a much better fan. The plastic cover didn't seem to have any real function, so its wasted grams.

In hindsight, I think I should have got the xr8 pro, which is a fair bit lighter, smaller, and 4s dedicated. Oh well.
IMG_6959.jpg


The motor is the HW 1650kv. Its fast on 4S with a 23 tooth pinion. More than fast enough for track work. It is a bit heavy though, so also with hindsight, I'd probably pick something lighter that is 4S focused. I'll try different pinions as I get more track time.

At least with this ESC motor combo, I can still chuck in a 6S pack and remind myself what insane straight line speed is. OMG its fast!!

I made a dual fan mount from some L profile alu and Rocket 40mm fans. Works well and looks ok I think. Its secured with 'dual lock' hook and loop. I've since added that last bolt on the left fan.
IMG_6961.jpg


IMG_6962.jpg



This is all the leftover stuff that I took off. There's a lot of screws etc also in here. There's a couple of little things missing, so it's saved probably about 400 grams.
IMG_6963.jpg



I was previously putting 2 of these 6S batteries in the car to keep in balanced, but that was 1.5KG of weight!!
IMG_6965.jpg


Now I just run a single 4S at almost 1/3 the weight. This one change alone makes a just difference. If you're usually running 2x 3S batteries, it probably won't be quite as big a saving.
IMG_6966.jpg



So you can see I have not added any 'lightweight' parts, and I don't think I will. I'll focus now on setup, and practicing driving it at the track for fun.

Race weight is 5.4kg. That's not much lighter than a stocker with 2x 3S batteries, but this does have a much better (and heavier) motor and ESC compared to stock. If I'd got an ESC and motor just for 4S (hindsight), it'd be very close to 5kg ready to race. My gut feel is that it'd get down to 4.5kg with lots of carbon fibre and titanium parts, but that'd cost a fair bit and isn't worth it to me.

So back in the real world, this is still heavy compared to a race 1/8 GT car. I think the 1/8 GT class min weight is 3.5kg.
 
Argggg rain, rain go away, stopping me from my track day!

I guess it's time for me to do diff maintenance anyway.

Speaking of diffs, I've noticed that some on road race cars don't have a centre diff.

I wonder if the infraction centre diff is necessary for a track focused infraction?

Would a spool be better, or just a spur gear?

Thoughts?
 
Argggg rain, rain go away, stopping me from my track day!

I guess it's time for me to do diff maintenance anyway.

Speaking of diffs, I've noticed that some on road race cars don't have a centre diff.

I wonder if the infraction centre diff is necessary for a track focused infraction?

Would a spool be better, or just a spur gear?

Thoughts?
imo spool would be best, that said I've busted the grub screw pin on my lim from just "light" parking lot bashing. Because of that and wanting lower gearing I tossed in a diff.

spool is light and has no loss.

omg I think that answers why I feel my Lim's rear end is TOO planted and front too loose...it's the center diff doing that!!
 
The 6S setup has a XeRun plus ESC and G3 2250 motor combo, with the turbo timing cranked.
How does the turbo timing work? I’ve read about it but curious to hear firsthand experience on the change to driving experience.

And do you see more heat buildup?
 
Yea, traditionally, stiffer springs means heavier oil.

Here’s my thinking behind modding these specific cars for track use, rather than speed runs or drifting, vs a proper 1/8 scale touring car. I’m not saying I’m the expert at all, just what I’ve changed to make my cars turn:)

These cars are looong off-road buggies, with short shocks, and absolutely terrible tires out of the box. They have a laggy radio, with a gyro, ancient pillow ball front suspension, super flexy rear suspension arms, awful endlinks, an 18 degree caster angle, SLOW servo, an aluminum tower to tower brace, and bushing loaded steering components. Bashing buggies. Not race bred platforms. The rear ends are sooo stiff and don’t articulate at all in a turn, the only way to get them around a corner is to drift it.

Any 1/8 scale touring car platform will smoke these cars around a track. The challenge as I see it, is to find the changes in setup and components to have fast comer entry, a consistent, smooth transition to on power out of the apex, and creating grip through chassis dynamics in order not to trash your tyres in one pack. IMHO, caster angle needs to be changed from 18 deg to about 10-12deg, roll center raised at the rear, shocks need to be stood up, and the rear springs softened, we have to figure out how to create better geometry with sways and links, ackermann needs to be eliminated, anti-squat must be increased at the rear, rear toe has to be changed from -3 deg, rear arms need to be stiffer, weight needs to be reduced, and functional aero must be added.

When was the last time someone was like, holy poop bro, that (off-road) Arrma turns like crazy?

Never, lol…any Tekno will smoke an Arrma on a track. We have to re-think the engineering and goals of this platform to a certain extent:) Take some ideas/setups from 1/8 touring, but not all, as touring car platforms are vastly different than these cars.

After seeing the lightweight 4S ideas, that’s gotta be my next build. A Scorched R\C carbon fiber chassis is on the way:)
Great assessment of the Arrma 1/7 on road platform, everything you said about the car is true but that's all done on purpose by Arrma. These are meant to be bashers not precision racing instruments. Most people buy these and beat the crap out of them, and do little or no maintenance so they build it to survive that kind of use. If you want to take one of these big heavy cars on track then it will always be at a disadvantage to dedicated 1/8 track cars pretty much no matter what you do as far as upgrades. The fun is trying to get it as close as you can.
I would love to see a Limitless/infraction class at a on road RC track, would be very cool to see these cars banging wheels going into turns
 
I'm doing diff maintenance soon, so need to decide what weights to use.

Thoughts or recommendations on which weights for track use?
 
I went with approx 100k front (my own mix), 500k centre, and 60k rear. Haven't had a chance to drive the car yet.
 
I'm getting myself a 1/8 Serpent SRX8 GTE, in the long wheel base variant, and will be doing some racing against a few nitro 1/8 GT cars at my local club.

Here's some pics of someone else's with a Porsche body: https://www.facebook.com/groups/172179578324024/permalink/287374133471234/

I really love the scale look of these lwb GTE's. They are slightly off the pace than the usualy buggy based shorter wheel base, but they look soooooooo much better. Dam that car looks good!!

There's quite a few body options as well so the opportunity to have a track full of awesome proper scale looking, fast, 1/8 cars is really there, but not holding out any hope. Serpent is the only manufacturer doing 1/8 GT cars with a long wheel base.
 
Old Thread: Hello . There have been no replies in this thread for 90 days.
Content in this thread may no longer be relevant.
Perhaps it would be better to start a new thread instead.
Back
Top