Why is Torque Twist A Problem

[jdnoss]

I hear the concept of trying to eliminate torque twist thrown around in a ton of threads. My question is why do we care. What difference does a little torque twist make when you are crawling, and do you care if you are trailing or out just having fun. The engineer in me says no I don't, but I wanted to hear from the rest of you why its a problem.

[Waitwhatsthat?]

Well when trying to crawl it'll cause a front tire to lift and inhibits the suspension from working optimally. Causes traction loss and degrades performance. As for general trading or just having fun. Yeah you could live with it, but it's a lot more fun to be able to pull off the more challenging obstacles.

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[SPLATT]

Easy way to see what's happening is to climb a steep incline. The flatter the rig stays the better it can climb but with torque twist it will lift a front wheel changing the COG and usually ends in it flipping over backwards.

[fyrstormer]

It unevenly loads the tires when climbing over difficult obstacles, and it can tilt the chassis to the point that the vehicle loses its balance and falls over when side-hilling.

On high-speed vehicles it causes terrible torque-steer and makes the vehicle more likely to traction-roll when turning in one direction vs. the other direction.

[jdnoss]

I know what torque twist is I don't need that explained, but it sounds like a little anti-squat or stiffer rear springs could go a long way. That is what I have done, it helps in other ways as well. I don't run a big power brushless system in it either.

[fyrstormer]

It sounds like you're not actually asking a question, but saying "It's not a problem, people who say it is are wrong based on my experience."

[Reflektr]

It's bad because it can rotate your axle, thus changing your pinion angle, thus putting your driveline in a bind... It can cause premature failure of parts if it gets really out of control. Not only that, but if you run leaf-springs, it can eventually ruin them as well. Torque twist is nasty.

[WHITE-TRASH]

A bit of torque twist isn't a problem. A lot of torque twist sure is though.

Oddly enough 2 of my rigs (both high power brushless. 3s and 4s) run OG ax10 geometry with the rear uppers raised about 3/8" over stock and neither rig has enough torque twist to be a problem.

[Col_Sanders]

On steep climbs or sidehilling torque twist is a killer. Not being able to have all 4 tires on the ground really hurts and makes it easy to tip over.

There is a climb here the local guys call the great wall. It is very steep with small ledges and a small creek right in front of it. I know its featured on some of the Vegas area videos (ferndog, rivas). Its a tough climb. Torque twist on that climb will make you tumble down in a hurry.

[jdnoss]

Originally Posted by fyrstormer

It sounds like you're not actually asking a question, but saying "It's not a problem, people who say it is are wrong based on my experience."

Sorry, let me clarify where my question comes from. I do more reading on here than anything and I have recently read several builds where they complain about it and the solution is sway bar or worse. I wasn't meaning to come off as "my sh*t doesn't stink" even though reading it again. It kind of sounds like it. I also worded the problem rather poorly. It should read why is torque twist still a problem. From what I have read and seen, it is an old design flaw that has been around for years, with nothing saying here are the answers, this is how you fix it.

[josh6575]

Monster trucks have nearly eliminated toque twist by gearing down on the axle instead of the transmission. They have a separate planetary hub on each wheel. Losi axles have very little TT but create a huge power loss due to the inefficiency of worm gears. TT sucks because it forces the rig to mostly have traction on 3 instead of 4 raising the CG(Wheelie Rollover).

[JohnRobHolmes]

It isn't much problem on modern kits and rtr's. Considering the lack of axel reduction on the vaterra ascender, stock geometry has become quite amazing.

The first shafty chassis I built before crawlers were purchasable (stampede tranny, tlt axles, all thread arrow links) had abhorrant geometry and was practically incapable compared to other custom trucks I had the pleasure of driving in future years. Considering what it could be, even the ax10 handled pretty good.


Even with today's rigs, time spent tuning suspension will yield more stability. Nobody can guess the exact weight of your rig , what tires you will use, where the chassis cg will be. It's up to you to go the extra step.

[fyrstormer]

Originally Posted by jdnoss

Sorry, let me clarify where my question comes from. I do more reading on here than anything and I have recently read several builds where they complain about it and the solution is sway bar or worse. I wasn't meaning to come off as "my sh*t doesn't stink" even though reading it again. It kind of sounds like it. I also worded the problem rather poorly. It should read why is torque twist still a problem. From what I have read and seen, it is an old design flaw that has been around for years, with nothing saying here are the answers, this is how you fix it.

Two thoughts:

1) Probably everyone has their own approach to minimizing torque-twist, and each approach has its tradeoffs, hence there's no definitive how-to guide for dealing with it. The closest I've found is a guide for dealing with torque-twist on solid-axle drag cars, which says to slightly shorten one of the upper suspension links to preload the axle -- but again, there are tradeoffs to every approach.

2) It's impossible to completely eliminate torque-twist on a solid-axle vehicle without mounting the motor directly on the axle. When the motor applies torque to the drivetrain, the motor *housing* applies reverse torque to the chassis, and since the differentials aren't hard-mounted to the chassis, that reverse torque can't be cancelled-out. Torque-twist is almost un-heard-of on independent-suspension vehicles because the reverse torque applied to the chassis is cancelled-out by the torque applied to the diff housing, but that can't happen when the diff housing is only attached to the chassis via springs.

[Highmark]

On slow steep climbs a rig will transfer a good port of it's weight to the back axle. It's a battle between creating forward momentum to climb, and the rig pivoting on the back axle if the COG exceeds the point of stability (sort of like when a drag car wheelies - it's easier for the drive train to move the car upward than forward).

Thus, ideally it would be good have a low center of gravity that is shifted away from that axis (i.e long wheelbase).

Rigs that torque twist like crazy tend to have a lot of squat and compress one or both of the shocks in the back raising the center of gravity and shifting more of the rigs weight up and backwards. As mentioned earlier this can also upset the suspension on side hills and other precarious situations.

Another consideration is that your front tires provide your most stable grip - it's why clod stall and over / under gears work so well. You don't want one of your back tires providing 80% of your grip.

[C*H*U*D]

Originally Posted by jdnoss

I know what torque twist is I don't need that explained, but it sounds like a little anti-squat or stiffer rear springs could go a long way. That is what I have done, it helps in other ways as well. I don't run a big power brushless system in it either.

Are you running a scaler or comp rig? TT is a very different animal between the two.