17 replies to this topic

[Northernpower]

 

 

just a comment here Torque steer is i believe the wrong word. what i think you are asking about is tram lining. how the car behaves over imperfections on the road surface.

 

and how the car behaves has much to do with the suspension set up also having an ET close to/or zero can help.

well tram lining too, but i did mean torque steer. like does it pull(turn) almost too much when going around corners fast?

 

Torque steer is very common in a straight line and very often this is induced by high engine torque through unequal length driveshafts. The effect of oversteer or understeer when cornering fast is more to do with suspension setup. You ask about pull(turn) through fast corners, this is more commonly associated with incorrect corner weighting, suspension set up, tyres far wider than the original design parameters for the original suspension set up, hence the understeer or oversteer. I know Nick can answer for himself but technically he was correct in saying its more about tramlining. This is something I have experience of and I'll say it's almost impossible to dial out if you want the look of wide tyres on a road Mini. I have the worst of all worlds, high torque and 175x13 tyres. If you fit wide tyres with a standard engine, the cornering, while not being great, won't be as bad as a high torque output engine.

 

 

 

un equal length drive shafts. torque steer sorry no. some great sales marketing.

It's interesting you say that, I thought with unequal length drive shafts the torsional stiffness had to be equalised; this is why some manufactures have a hollow shorter drive shaft and a solid longer one. If you don't equalise the torsional stiffness how do you stop more torque going through one shaft than the other?

[nicklouse]

have a read

http://www.theminifo...5-diff-shimming

[nicklouse]

and something interesting on Hardy Spicer UJs

https://youtu.be/gmV4qwLfOMY

[Northernpower]

have a read

http://www.theminifo...5-diff-shimming

 

 

and something interesting on Hardy Spicer UJs

https://youtu.be/gmV4qwLfOMY

Two interesting articles but neither of them disproves the laws of physics. If there are two shafts of equal torsional stiffness and equal length they will both have the same amount of distorted twist from one end to the other before the load is transmitted. If one shaft is longer than the other and they are made from the same material and specification the longer shaft will twist further around its axis before the load is transmitted, as Scotty said on the Enterprise, “you cannae change the laws of physics Jim”.

 

Torque steer is more notable in a straight line because the conditions are easy to replicate and the result is very easy to experience, the longer shaft takes longer to wind up and will take a split second longer to transmit the power to the wheel and providing the load keeps increasing it will generate torque steer.

 

When cornering it’s not so easy to measure because the parameters are subject to change, most notably, the torque input is normally not constantly increased, add to this, the load reducing on the inside wheel as it lifts, changes in the camber angle through hitting bumps and easing of the accelerator etc. Driving the corner at the same speed will not induce torque steer because the shaft distortion will be neutralised as the torque (and hence the twist in the shaft) is now stable rather than increasing.

 

None of this takes into account the load imposed by bearings and joints or unbalanced corner weighting and there is a school of thought that having a short intermediate shaft and equal length driveshafts is not always an ideal solution because the offset carrier bearing imposes its own variable.

 

The simple solution is two have two shafts of equal torsional stiffness regardless of length. But nothing in this world is rarely simple.

[Spider]

I'm sure I've piped up here in regards to this, but Torque Steer due to Un-equal Driveshaft lengths is a folly.

 

It comes about due to all the irregularities in the road, tyres, temperatures, build tolerances and variations in rubber hardness.

To highlight this and how sensitive steering is to these, adjust one of your caster rod (if you have adjustables) by 1/4 of a turn and see the difference. It's an amount that's difficult to measure, but makes a difference.

 

Also, Try it again, only this time lower the car on it's Hi Los all the way, then raise it all the way. That will put the drive shafts through all manner of angles.

 

If it did come down to Unequal Drive Shaft Lengths you'd have a hard time steering or generally controlling the car at all. The CV's aren't called CV's for a catchy title, they are just that.

No Mini can make enough power to tortionaly twist the drive shafts, it will spin wheels way before that happens. The proof of this is the older slip type Unijoint Drive Shafts. If they would get up any Twist, they couldn't slide, they'd only bind.

[Northernpower]

I'm sure I've piped up here in regards to this, but Torque Steer due to Un-equal Driveshaft lengths is a folly.

 

It comes about due to all the irregularities in the road, tyres, temperatures, build tolerances and variations in rubber hardness.

To highlight this and how sensitive steering is to these, adjust one of your caster rod (if you have adjustables) by 1/4 of a turn and see the difference. It's an amount that's difficult to measure, but makes a difference.

 

Also, Try it again, only this time lower the car on it's Hi Los all the way, then raise it all the way. That will put the drive shafts through all manner of angles.

 

If it did come down to Unequal Drive Shaft Lengths you'd have a hard time steering or generally controlling the car at all. The CV's aren't called CV's for a catchy title, they are just that.

No Mini can make enough power to tortionaly twist the drive shafts, it will spin wheels way before that happens. The proof of this is the older slip type Unijoint Drive Shafts. If they would get up any Twist, they couldn't slide, they'd only bind.

I fully agree with your comments and I tried to allude to this when I mentioned the variables in cornering. Torque steer is most noticeable when launching and changing up a gear in a straight line and also when accelerating hard out a corner in first gear.

 

Unless the car is set up correctly as you mention then it’s going to be subject to being pulled out of line quite easily when under hard acceleration and the minimal effect from driveshaft torque steer will be so small it’ll be almost unnoticeable if everything else is not correct.

 

The point I was making was unequal length driveshafts do transmit the power to the wheels at different times and this was confirmed by a study by the NHRA in the states in the early 2,000’s. They were trying to get the engine and drivetrain as low as possible and used an offset diff and worked out they were getting torque steer through unequal length driveshafts of the same torsional stiffness. From memory, in the tests they conducted they worked out the ratio of the driveshaft length increase per degree of yaw.

 

What has this to do with Mini’s with unequal length driveshafts, probably absolutely nothing, due to the torque from an A series through driveshafts that are not too dissimilar in length being insignificant when compared to the Top Fuel dragster used in the test, which had one drive shaft twice as long as the other. Given the Matco Fuels dragster produces 7,400 lbs of torque for 3.7 seconds it’s not a fair comparison. All it does is prove unequal length driveshafts do induce torque steer. All I have to do is find some way of measuring such an insignificant value when it's in relation to a Mini.   

[Ethel]

An open diff will turn until the torque's equal on both outputs. When that happens you effectively have one shaft between the wheels, both of which will divvy up the whole of the torsion equally. The system needs to be dynamic so that more work can be done by one side than the other creating unbalanced reaction forces from the tyre contact patches to feed back in to the steering. If unequal length driveshafts do contribute to that, it'll be the increased angles in the shorter shaft making the joints articulate and generate more friction.

[Spider]

Agree with all of that and Graham, at 7400 ft / lb of torque, yes, I'm sure there will be some torsional twisting along with tyre slip !!!!!

[xrocketengineer]

Here is how the Honda Civic Type R deals with torque steer:

 

[Spider]

Great clip Rocketman, many thanks for finding and posting it.

 

That does really illustrate where it comes from really well and Honda's great solution.

 

A quick google for Honda R type Drive Shafts and I came up with these

 

 

Hardly equal length,,,,,,,

 

A sneak peak on a project I've been working on

 

 

(only fits inside 13" wheels ) where in the design phase, I really did well see all these issues, and how they can come about, though, this is not just what this hub is all about,,,,,

[nicklouse]

i have to say that those are not like the ones that i find for the Type R

but again if there is a half shaft or not  they are still not Equal length.

what i did find interesting n the video and kinda expected was the info where torque steer was felt during corning when the axle inputs angles were not equal.

[Spider]

They were the first ones that cam up when I punched them in, hence why I said 'quick google', none the less,,,

 

  a half shaft or not  they are still not Equal length.

what i did find interesting n the video and kinda expected was the info where torque steer was felt during corning when the axle inputs angles were not equal.

 

yes.

 

I suspect the cornering torque steer is more from the load on the tyre gong from more or less central in the tread to the outside of the outer wheel and the inside of the inner wheel. There really is a lot to it, as I know full well that you do appreciate.

 

IMO, It's a bigger 'area' than engine modifications.

[nicklouse]

yep.

 

you will find just about every HOT version of a car has the driveshafts that connect to the hub of the same length so that the angles are the same in the HOT hatch drivers favourite position for booting it. IE straight ahead. but that is not the whole story as the scrub radii has a lot to do with it.

 

what Honda and Ford have done is very similar to each other.

 

a nice cut away of the Minis suspension as originally designed.

 

 suspension_cutaway.jpg   52.71K   2 downloads

[whistler]

I am not an engineer but after watching the video of the Civic R and looking at nicklouse's cutaway drawing it seems to me that if we return to reverse rims, where the extra width is on the inside of the wheel then the scrub radius would be reduced as the tyre centre is moved inboard slightly, or am I misunderstanding this?

[mini13]

thats pretty much it in basic term's but as soon as you put a tyre on thats much wider than about 155, then you run out of space and start having to move the wheel offset out to make room, the worst of these are 7x13's with their -7 offset which it totally not needed as you can run about an inch less than that without problems.

KAD have made some widetrack setups, most notably used on Lloyd Hutchensons 16v rally car, I dont know the details, but as far as I can tell they use longer arms, and much less offset to get the scrub angle sensible.

 

 

I am not an engineer but after watching the video of the Civic R and looking at nicklouse's cutaway drawing it seems to me that if we return to reverse rims, where the extra width is on the inside of the wheel then the scrub radius would be reduced as the tyre centre is moved inboard slightly, or am I misunderstanding this?