37 replies to this topic

[cnrandall]

You don't want to remove bump steer... Lotus aren't silly enough to put bump steer into the chassis by accident!  What you need is to have the correct bump steer curve, set based on your ride height.  There is some adjustment in the rack but that doesn't allow for very low ride heights, then you are into adjustable arms.  Be careful with the kits though as you often have to make up spacers additionally to the kit to find the right adjustment.  There are more ways of skinning the cat, you can bend the steering arms with heat or rose joint your rack ends and modify the arms to make them adjustable but you need to know what you're doing.

 

The VX is more tolerant to the wrong bump steer than an Elise due to the extra chassis length but its still a critical setting.  Too much bump steer can be quite unpleasant, no bump steer is horrible!

[Steve.i.am]

Really interesting input. Appreciate it. This is interesting if you haven't read it: http://www.vx220.org...-bumpsteer-wtf/ From this it does seem lowering the front more than 15mm or so does start to put you into much less linear toe changes. Alex also produced this http://www.speedster...e51b9b7363389d8 Which has measured curves with and without the 8mm rack raiser plates. Looking at these graphs it suggests to me it'll redress it upto a point. Maybe 10-15mm of lowered ride height. Beyond that other options are needed. Anyway I'm going to raise my rack up 8mm. Get all my ride heights and static toes rechecked. Will report outcome.

[Kieran McC]

Just fitted the rack riser plates for bump steer, Not the quickest of tasks to do, They seem to work ,most of the bump steer has now gone, They donot seem to have upset the Geo. I had no problems until I dropped the ride height to 130 r, 120 f.

[Steve.i.am]

Ah glad that worked for you Kieren. Yeah I have the riser plates on my car as well now. It's improved it on my mine but it's still there. I'm waiting till I fit my new shocks to revisit the ride height. I may run it a tad higher than it is at the moment. When my riser plates were put on it did affect the front toe slightly (introduced a tad of toe in) so that was readjusted.

[Zoobeef]

Looked at fitting the bump steer kit today but i think it's missing the shims so going to leave it to matt Bentley to do.

[ArticMonkey]

The Bump steer kit really has made a difference to the way my car handles. 

 

I second cnrandall comments on if being slightly out, the car is horrible to drive. I'd go as far as saying not drivable in the wet. I say this as just having my cars suspension rebuilt and going on track at Croft, the rear end was stepping out on the sighting lap! Every right hand bend it would over steer, which Scuffers kindly pointed out as we drifted round the second bend.

 

The wet condition of the track was highlighting this issue which would of been more controllable and less noticeable in the dry. In the end, Matt and Scuffers pin pointed it to be 2mm out on the front corner. Once adjusted it was a completely different car. 

 

The new suspension settling in and not having time for fine adjustment, was the cause of my miss hap. Without the track side crew, I would of had an early day. 

[Kieran McC]

The Bump steer kit really has made a difference to the way my car handles.    I second cnrandall comments on if being slightly out, the car is horrible to drive. I'd go as far as saying not drivable in the wet. I say this as just having my cars suspension rebuilt and going on track at Croft, the rear end was stepping out on the sighting lap! Every right hand bend it would over steer, which Scuffers kindly pointed out as we drifted round the second bend.   The wet condition of the track was highlighting this issue which would of been more controllable and less noticeable in the dry. In the end, Matt and Scuffers pin pointed it to be 2mm out on the front corner. Once adjusted it was a completely different car.    Nothing to do with driver error then LOL The new suspension settling in and not having time for fine adjustment, was the cause of my miss hap. Without the track side crew, I would of had an early day. 

Edited by kieranmcc, 22 June 2014 - 08:03 AM.

[ArticMonkey]

Learn how to quote you tit.

[Kieran McC]

Learn how to quote you tit.

Tablet being a pain

[ArticMonkey]

Excuses, excuses. Just like your track speed.

[Steve.i.am]

In the end, Matt and Scuffers pin pointed it to be 2mm out on the front corner. Once adjusted it was a completely different car.   

What was out by 2mm?

[ArticMonkey]

The bump steer arm I believe. Wasn't 100% lisserning if I'm honest. Just wantsed to get some of my track time back so jumped right in and off I went.

[Dave E]

That'll be the spacers between the steering arm and track rod end.

[Paulus H]

This is mystery to me. What is std ride height? I imagined 120/130 was std. Really is this low enough to cause instability issues? KIndly, Paul

[smiley]

This is mystery to me. What is std ride height?

 

145

[techieboy]

140 according to TIS (with driver, passenger and half tank of fuel).

[Steve.i.am]

This is mystery to me. What is std ride height? I imagined 120/130 was std. Really is this low enough to cause instability issues? KIndly, Paul

Standard is 140/140 I believe. So let's say you lower the front to 120 and running 17" wheels, you've altered the relationship of rack to steering arm on the hub by 20mm. This seems to push things onto an area of the bump steer curve which is quite different to that around the standard ride height. And going by arctic's experience above seemingly small changes can have a significant effect.

[TazN]

I'll have to double check my geo, I was only looking at it the other day to remind myself how the car was setup. Iirc I'm running 130/140 ride heights and have noticed a big difference, however went from old leaky bilsteins to new ntr. I think I might have a trip up to MB soon to see what is the cause of it all.