equal length driveshaft - Interesting Math result!
Turbo Mini Forums

Just done the calc in excel to see what the difference is as far as the shaft windup is...

Made a few assumptions aswell (because i don't know the details!)
Shaft dia: 25mm
Length of longest shaft: 300mm
Length of shorter shaft: 250mm
hence difference: 50mm
Engine torque 150lb ft
1st gear ratio 2.54:1
FD 3.44:1

I correlated it against the mainshaft in one of our transmissions, and it works out, so must be doing something right!

So, by my calcs,
The long shaft will twist by 1.11 degrees at peak torque.
The short shaft will twist by 0.92 degrees at peak torque.

This is of course assuming that the whole engine torque is going through one wheel - eg a welded diff is used, and one wheel is in the air)...
More interestingly than the above results however, the twist along a shaft 50mm long (my guess at the difference between the two shaft lengths) is just 0.18 degrees!

Considering the above, I can't see any possible gain in fitting an 'equal length' driveshaft kit, especially with an open or slipper diff. A fully locked diff, maybe.

If your driveshafts are at mad angles, there is probably a minute gain, but minis aren't renowned for pitching and squatting under acceleration (like a moderate power swb car like a Nova for example). So, how much change in angle are you actually going to see, for the very small change the driveshafts move through?

I know some people fit these, and swear by them, but if I'd just spent ?300 on something, i'd propably convince myself it was worth the money also...



ps
For those slightly more technical, the max stress (again assuming all the torque is passing through just one shaft) is 570Mpa... Not particularly excessive for a semi-decent material... Hardly surprising that we don't see breakages in road cars...


Right, i'm off into my shell again!

And for the doubters, the max stress at the min dia (under the spline) is 112MPa at the surface (assuming 3/4" root dia) - but this is in a heat-treated area, so will have a higher potential stress limit anyway!

Edited by TurboDave16V on 28th Jun, 2004.

very good dave ,usb.

Everyone knows that instructions only have to be read if the thing doesn't work....

You buying one then?

Only you've been buying a lot of shite this year already...

Edited by TurboDave16V on 28th Jun, 2004.

hell dave very impressive as always, i think you really should now get and do some work.

I was also told about this and the general was that they don't really work, now we know why!

that's why i've never got one:(

Best 1/4 mile 13.2 seconds @116 mph
First 5 port miniturbo to make over 200 bhp on a carb?
First 5 port miniturbo to make over 200 bhp on Injection?

http://www.mattwoodsphotography.com

just been down the lockup and found two sets of equal length drive shafts , so i thought well why not try them ...fitted one side but the other was too short tried the others but one side was too long , might try cut`n` shut on them and se if that works.

Everyone knows that instructions only have to be read if the thing doesn't work....

stu told it would work

Everyone knows that instructions only have to be read if the thing doesn't work....

Dave,

Can't match your maths, I'm 'electrical' rather than 'mechanical' at the end of the day !! I guess you have access to some fairly sophisticated simulation software like ADAMS/Motorsport or something. Forgive me, for I am new here !! and I know not what everyone knows or does, so if I'm waaaay out of line feel free to ignore me !!

(Edited to add : OK, I'm a dumb-ass, I re-read your post and you did the calcs in excel, which trumps my ADAMS/Motorsport query because it means you know all the formulie as well !!)

I had a really good technical article about torque steer and I'm blow'd if I can find it now, but the thrust of the article was that if the shafts are level, like those on an open wheel race car, then there will be little difference in the torque reaction side to side. Unfortunately on an mini it's impossible to get level shafts, so the shafts are at an angle wrt to road surface.

In your model did you assume that the shafts were level, or at an angle, and as they are different lengths the angles described by the shafts wrt each other and the road surface is different ??

I think this is where the problem lies, as the difference in torque reaction will now be a vector not a scalar due to the angular difference.

Equal length shafts will cannot and will not eliminate torque steer unless they are dead level, but by equalising the angles of the shafts at least the reaction should be equal each side, not withstanding that the shafts are effectively rotating in opposite directions to each other ??

In my specific case an equal length drive shaft setup helped, it reduced the noticable torque steer in most circumstances, and improved traction out of corners. Yes the steering does still pull when you get a change in road surface or you go from light to full throttle, but I feel it's helped.

Wasted money ?? Well maybe, people said JKD straight cut 5 speeds were crap too, but I've not broken mine yet........ Now theres the kiss of death on it !!

Edited by Phil1380 on 29th Jun, 2004.

Hold on lads, I ve got an idea............

This is what i wanted to get going - some ideas banged off the wall so we can see if i'm right in my logic!

I assumed the shafts are level, because in my mini the shafts are level.... It is possible (!)

Even with level shafts though, if you had a significant variation in length (like you get on 16v Astras as an extreme example!) you would get this 'sensation' of torque steer if the shafts were to wind up to any extent - again, made even worse with a slipper or locked diff.
In the mini, this is simply not the case of course, as the differece between the two is so small...


I've also seen a good article on it in the past (why do we never properly document good articles!!!) and if i recall, the actual amount the shafts want to 'twist' about the neutral axis of the supported end (CV axis) is related to the size of the angle they are being driven through...
With such a small difference in length of the mini shafts, the variation of anglular deviation between the two (the difference being what is generating the torque steer) is all that can be left to promote the torque steer sensation...

Think i'll get some dims off my mini tomorrow, so we can attack the angular aspect in greater detail...

Anyone else want to add thoughts?

Edited by TurboDave16V on 29th Jun, 2004.

I've never had a problem with torque steer.

I guess this is due to either having a low powered Mini which wouldn't promote the phonomenon or having very sticky tyres on a high powered mini.

However, I think, as Dave points out that the twisting of the driveshafts is not the problem. More likely that the angle of the shafts is to blame.

So:

1) Dave how are your driveshafts level?
2) How does the efficency of the CV and pot joints change with change in driveshaft angle?

Do the joints 'bind' slightly with more accute angles?

Just some thoughts.

Wil

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

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http://www.sportcompactcarweb.com/editors/...c_technobabble/

http://autozine.kyul.net/technical_school/..._handling_6.htm

http://www.mscsoftware.com/support/library...UC_008_FORD.pdf

Maybe of interest!
Harry

Bimmer Twinky headed and turboed A-Series:
http://www.minifreunde.at/harry/projects.htm

Harry - as regards the 'first' link, with the 'Dave' point, this has been my opinion since i first started getting into minis all those years ago, having a very basic understanding of the need for the tyre footprint to be theoretically located centrally about the king-pin axis.

As an example, my good friend Graeme has a 16v vauxhall engine in his mini. With the 7x13 starmags, this torquesteered all over the place, eve worse with a slight road camber... I believed it was the wide offset of the footprint, so he borrowed a set of 12" rover minilights (which looked a little strange under grp 5 arches) but with these, despite the lower traction, he could actually accelerate quicker and under more control. To exercise the point further, two hands and arm muscles were needed to control it with the starmags, one hand loosley holding the wheel was sufficient for max acceleration on the rover wheels.
Graeme being Graeme decided to do things the hard way shortly after, making new 'thin' drive flanges to take alloy bells and 10.2" diameter discs. The offset is still there, but narrower than a std (non vented) mini hub by around 30mm / side! It now drives beutifully!

Edited by TurboDave16V on 30th Jun, 2004.

Dave

A good, if somewhat extream, example of correcting the wheel offset. This used to be a problem with those 6x10" Weller wheels from years back, and it's returned with the current fashion for fitting 13" rims. One of the worst culprits is those darn Rover Sportspack wheels.

You've got to consider the suspension as a whole, include wheel and tire offsets. The centre line of the tyre should be as close as possible to the theoretical point where the Kingpin centre line strikes the road, otherwise you will get kick-back and torque steer.

I've got 13" rims on my current car, with nothing like the offset of the Rover wheels, but perhaps that's were my torque steer problems were originating from. If your running 10's or even 12's the offset shouldn't be anything like so pronounced.

I still haven't found that article, it was in something like an early issue of "Racecar Engineering" or something like. I'll keep looking...........

Hold on lads, I ve got an idea............

6 x 10" wellers.... Now those did have a big offset didn't they!

Oh, the pictures shown in this page are of my mini in it's normal ride height.
http://www.netsnapshot.com/pcw/buildalbum-...=0&ACCOUNT=4541
At this point, the shafts are as near as dammit level...

Dave, I reduced the KPO on my car by 5mm each side, also did the corner weights right the same time. It reduced my torque steer troubles a lot, but did not cure it. (Did not look after bump steer yet) I will mount the equal kit next time I have the engine out - will keep you informed about the success/disappointment of this kit.

Bimmer Twinky headed and turboed A-Series:
http://www.minifreunde.at/harry/projects.htm

Bump!

Anyone else using these?
Harry - did you ever get it fitted and tried?

i beleiv ethe equal length shaft setup is a fashion accessory for people who know little except what they are told ,
as you and i have chated about in the past dave my car makes a lot of torque but i never get torque steer on a dry track. neither do i believe it to have anything to do with drive shaft angles ,after all a lot of talk is bandied about reguarding seriously lowered cars and shafts runnig uphill,and sugestion it causews bindup to a small degree, but what happens when you are applying full lock , you are getting very high angles going through the outer CVs and causing a lot more bind [if any] than the inners will ever see.
My shafts run up hill towardsa the hub at least 40mm and still no iffy steering .
if mark goes back to early last year he asked me for some advise re settings for the front end as he was having probs going in a straight line [as he does],
i'm sure he will be along to tell if they worked along with ridding the front end of the rubber bushes. enough for now..

carl

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

very true , carl , the car did go straight after our chat , not very fast but it went straight

Everyone knows that instructions only have to be read if the thing doesn't work....

Good response Carl.

Mark - was that around the time when carl had messed up your new rose-jointed bottom arms so badly they didn't fit onto the ball-joints?

D

Edited by TurboDave16V on 14th Apr, 2005.

thats right dave i sent them back the wrong way round ,lol.

dave ,heres one for you to try . if you up the dia of the long shaft by 2mm how does the twist work.
carl

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

For torque steer, the driveshaft angles are important as well as the roll centre and stiffness of suspension, I reckon the key factors are KPO and the compressibility of the suspension bushes, rose joints should see a lot of it controlled. I suppose tyre pressures as well.

Interesting point about the driveshaft twists relative to length, I just ignored that in my thoughts.

It's sort of like a pendulum effect, any unequal relationship between the front wheels under power will cause one wheel to grip more, that causes distortion of the distortables and results in a sideways drift, it can often result in a weave (like my bloody mini).

Key contributors.

1. Driveshaft angle
2. KPO
3. Sloppy suspension bushes
4. Softer tyres (radials) (crossplies are better)
4. Stiff suspension
5. Higher roll centre.

I expect that 10" wheels are worse for it considerably. Lowering the roll centre (ride height) sorts it out considerably. When I was mucking around with my suspension setup (REAL TESTING!!!!!!!!!!!!!) I managed to get it right under control by dropping it and adding a weeny bit more tow out to the steering. I reckon that if you are running non-rose joints, a bit of extra tow out helps lots. With a bit of testing, you might adjust it right out.

That's my bollocks.

Bugger off, I'm getting there.

Actually this was one of the bits on my wishlist - an equal length driveshaft conversion!

So, Dave, apart from the Maths, having one of the more powerful Minis around (and MiniWilliams could also contribute here) - how bad is the torque steer on a 150bhp Mini?

And what size of steering wheel do you use? The bigger, the more leverage you have to combat torque steer.

I'ld really like my project mini to be nice to drive (and scary for the passenger) as possible, so any plus in this aread would be a benefit.

I donated, but somehow didn't get the label! :(

My car with 13" wheels torquesteers as hell on an uneven road surface. I can tell you it's very scary for the passengers. Scary for me too :)

Carl - do you mean top ask " what diameter increase do you need on the longer shaft to make the twist equal"?

Torquesteer on my mini is minimal. I use 10x5" 100+ minilight rims which have a good amount of inset. I also use reasonably compliant (read: Soft) suspension as mine is a road car... I use a 13" mountey steering wheel.

Do you have any standard (steel) mini wheels? If so, I recommend you put a set of these on first - see if your problem is related to offset...