98 replies to this topic

[Arno]

That explains why you can buy about 8 or 9 different height shims for the steering rack..  

 

Lotus used to, but no longer do so.. Nowadays only the 6-notch original (A111H0017F) and 10-notch (A111H0021F) are available. Used to be the full range from a 1-notch to a 10-notch available.

 

Of course with some metal working skills it would still be fairly trivial to compare a 6 and 10 notch and create the remaining/additional ones.

 

Bye, Arno.

[alexb]

Don't forget that you have to use sprung weight only for ride frequecy calculations.

And your own weight too.

 

Used 930 kg for the car (SC) + 70 for me, 50/50 left/right, 40/60 front/back and 30 kg rear, 25 kg front unsprung weight. That's all more or less guesswork and especially the 50/50 L/R will not be correct. Good enough for government work I suppose

[2-20]

 

Don't forget that you have to use sprung weight only for ride frequecy calculations.

And your own weight too.

 

Used 930 kg for the car (SC) + 70 for me, 50/50 left/right, 40/60 front/back and 30 kg rear, 25 kg front unsprung weight. That's all more or less guesswork and especially the 50/50 L/R will not be correct. Good enough for government work I suppose

 

 

You can double the unsprung weights

[alexb]

I put helium in my tires. Tried vacuum, but didn't work. The tire patch was excellent, but ride height suffered for some reason

 

You're right. It all adds up, wheels, disks, uprights, half of the swing arms etc. I guess I was dreaming

[alexb]

As Arno mentioned the large selection of raiser plates that were available, I did some modelling of the changes in bumpsteer curve with vertical movement of the steering rack.

 

 

The offsets on the steering arm side are as measured and it's assumed that in the horizontal direction the steering rack pivot coincides with the pivot of the swing arm. Beware that y=0 here is upper swing arm horizontal. The different curves represent different vertical offsets, eg. -10 means steering rack 10mm lower than pivot point of swing arm. In the calculations I can move the steering arm in any position and a vertical offset at the rack is the same as a vertical offset at the steering arm. Too bad you can't move the rack up a bit more.

 

The swing arm length in the calculations is 230 mm. Not sure what that is in reality. I don't think it's far off. It made at least some sense to offer a range of raiser plates, but for most people it's just too much. So Marketing decided to only offer two, but compensated by offering them in different colours

Edited by techieboy, 31 January 2014 - 02:22 PM.
Fixed image embed

[alexb]

Put all the info I got out of measuring both front and back with and without riser plates/shims etc in a PDF, but can't upload as it's about 650Kb. Is there a way to share this?

[siztenboots]

if you email it to teamvxracing@gmail.com , I will host it

[alexb]

OK, thanks.

[siztenboots]

PDF file is here , https://dl.dropboxus...0 Bumpsteer.pdf

[DaveyC]

Thread resurrection...

 

Great work.

 

I've been measuring my front bump steer using your method and with a ride height of 100mm front I'm getting much less total toe change than you did. The only difference I can think of is that I didn't use the raiser plates on my rack, I just removed them completely and pushed it as far up as it would. Graph here:

 

https://drive.google...iew?usp=sharing

 

What settings did you go for on the front in the end?

 

I love how on this forum there are loads of people doing experiments, measuring stuff and working on that basis, rather than the typical box ticking exercises 'you need this part then this part and it'll just be better'.

[Arno]

I've been measuring my front bump steer using your method and with a ride height of 100mm front I'm getting much less total toe change than you did. The only difference I can think of is that I didn't use the raiser plates on my rack, I just removed them completely and pushed it as far up as it would. Graph here:

 

Leaving the plates out and pushing the rack up would gain you a little more height in most cases as the slots in the car are often taller than the corresonding hole positions on the plates max out to.

 

But just to be sure.. Are you using the standard steering rack or one of the (quick)racks from Eliseparts? The reason I ask is because the Eliseparts version of the steering racks are built different from the OEM one when it comes to the lenght of the sliding bar and the location of the pivot points and lenght of the steering arms. You'll notice when you want to rebuild one as the standard Titan parts won't fit This change in the rack layout would (should?) lessen the bumpsteer compared to an OEM setup. Bye, Arno.

[DaveyC]

I'm pretty sure it is a standard rack.

[alexb]

Curious that your measurements are different. Looks like a factor 2. First thought it might be the distance to the mirror, as that has to be taken times 2, but that would cause a reverse effect. I've measured the front bumpsteer three different ways on my car. And both left and right. Pretty sure about the results. But that doesn't mean that on your car it's the same. The rack to steering arm pivot point vertical distance is very critical. Just a couple of mm and you get a noticable diffference. It's only 6-7 mm less and you don't have bumpsteer at all. The one thing I noticed in your measurements is the big backswing at the top of the curve. When you measure, be sure to have a look that everything moves freely. In my case the rod coming from the steering rack came in contact with the steering arm and all you do is try to bend things.

 

I'm at 115 mm at the front and 125 at the back. I think. Found it very hard to find a place that is level and to measure with some consistency. But the ride height doesn't change the bumpsteer curve, you just change the origin. I've tried many things, like changing the steering arms and the joints. I'm now back to using the OEM arm with the joints that EP uses for their bumpsteer whatever kit. Because that lowers the pivot point a little (about 2 mm), I have less bumpsteer. But I also have higher rate springs, so less travel, also decreasing the amount of bumpsteer. TBH, looking back I think I concentrated a little too much on one thing. Many other things to consider, like spring rates, ARB etc.

[DaveyC]

Perhaps ignore the extremes of bump on the graph. There was a lot of resistance in the suspension arms at this point - probably the bushes.

 

For the scaling factor I used the exact measurement from the centre of the hub to the mirror and then back to the paper I used to plot the points / rim radius (220mm).

 

IIRC the slots in the tub for the steering rack seemed quite a lot longer than I expected them to be. I might put the old plates back on and measure again to see if this increases the total toe change so they're more in line with what you measured. Got to do something whilst I wait for the NSS group buy to turn up

[alexb]

You use mm change measured from center hub to rim. I use rim to rim. That's a factor 2 right there. I always interpret toe in mm as rim to rim. You can easily get rid of that confusion by using degrees (or better radians as for small angles arctan (x) = x), but that's not as intuitive as mm.

[DaveyC]

Not sure I understand what you mean when you said you measured rim to rim.

[Exmantaa]

He measured toe change as the mm difference measured on the rim @ front-of-wheel vs. @ backside-of-the -wheel.

So that is 2 x the wheel radius...

[DaveyC]

*ting* penny drops.

 

When I do all my toe settings I measure it that way: distance between rim at rear and reference line - distance between rim at front and reference line. I've effectively just been looking at the distance between the front and the reference line and completely forgetting the rear will also be moving away from the line in an equal manner. Something about only taking one measurement and doing loads of sketches and cad models made me completely forget how I actually measure toe.

 

Looks like the results are pretty similar once you add that factor in.

[DaveyC]

https://drive.google...iew?usp=sharing