KugaWestie Posted October 9, 2018 Author Posted October 9, 2018 3 hours ago, corsechris said: Found this site, describes the laser method petty well.  https://www.svtperformance.com/threads/a-r-t-laser-bumpsteer-gauge-for-rent.468364/ A bump board is ever so easy to DIY though, loads of info out there, but briefly, you need a frame or board that sits on the floor, hinged to that is another frame or board that sits more or less vertically. You align the hinge axis along the length of the car. You also need a board or sheet of some non flexible material that bolts to the hub. Mark this with a series of horizontal lines, spaced as far apart as you feel neccesarily, but start at say 1cm. Attach a fixed pointer/rod/whatever to one vertical edge of the vertical board, this rests on the bit you bolted to the hub, at the other end of the hinged board, you put a DTI. Set the suspension at ride height, set the hub so the lines are horizontal, lock the hub, tweak the position of the whole bump board so your pointer hits one of the lines, zero your DTI about mid-range of it’s travel, then move the suspension up and down in increments, measuring the movement on the DTI. Plot this against vertical deflection from ride height.  As always, I make a simple process sound horribly complicated.....I have no doubt you’ll find much better descriptions out there I think I might just test drive it firstÂ
BenD Posted October 9, 2018 Posted October 9, 2018 15 hours ago, KugaWestie said: Chris, the whole reason for doing threads like this is other people sometimes see things that have not have been considered/could be done better etc, so keep on chipping in please  I am interested in the bump board you mention though, as I have no idea how to check what I have done whilst in the workshop also i get to see all the random bits i make for things
corsechris Posted October 9, 2018 Posted October 9, 2018 32 minutes ago, Ben (bunje) said: also i get to see all the random bits i make for things You do realise the danger in that though??  :D So many times I wish I had a decent lathe, plus the ability to use it of course...  I used to have access to one years ago at my old employer, but they got rid of the workshop bit by bit over the years. Also there, and very useful, 4 foot wide guillotine and sheet metal bender, fly press, large cutoff saw, pillar drill, linisher. The perfect kit car building workshop in fact.
corsechris Posted October 9, 2018 Posted October 9, 2018 1 hour ago, KugaWestie said: I think I might just test drive it first Honestly, it really is a LOT easier than I make it sound and very much worth doing, particularly given the situation you find yourself in here where you don't have a known starting point. I tend to bang on about it, but the Marcos Mantula we used to have had the most shocking bump steer. Somehow, they managed to copy the suspension geometry from the Triumph Herald and get it spectacularly wrong. There were a few solutions doing the rounds at the time, I opted for a modified rack initially, then changed uprights and wishbones entirely in the end. By the time I'd finished, it was almost perfect and a massive improvement over the original setup which had it so bad you needed to measure the error in 10s of degrees. Before I got it resolved, it was impossible to go round a corner in a smooth arc, and it jumped all over the road when you hit bumps.
Dave Eastwood (Gadgetman) - Club Chairman Posted October 9, 2018 Posted October 9, 2018 Oh the times I’ve wished for the guillotine and a box/sheet brake when I’ve been making car bits, let alone a lathe and mill! Oh and a water jet cutter would be neat. hmmm CNC...
B.RAD Posted October 9, 2018 Posted October 9, 2018 1 hour ago, KugaWestie said: I think I might just test drive it first Having driven a kit car with bump steer, I would actively discourage this approach (as much as I share your enthusiasm!! ). It really is horrific, completely random & violent response to road undulations and steering inputs. It's really very dangerous. While you're in the build stage, it'd be worth taking the time to do some measurements as suggested and just see where you are and what can be done, if anything.
AdamR Posted October 9, 2018 Posted October 9, 2018 IME bump steer can be beneficial but it depends on how much, which end of the car, which direction it steers in, and how the static geometry is set. I like slight toe out in bump up front with static toe out, and slight toe in in bump at the rear with static toe in.
BenD Posted October 9, 2018 Posted October 9, 2018 Cnc's are great for most things but we still have the good old trusty manual machines. The cnc lathe is probably the one that amazes people the most. The 5 axis vertical makes most people who don't usually watch them sick lol
KugaWestie Posted October 9, 2018 Author Posted October 9, 2018 I have been googling for a while tonight trying to understand how to measure bump steer diy style without much successÂ
AdamR Posted October 9, 2018 Posted October 9, 2018 Feel free to call me Gary if you think I may be able to help, number on CleaR Motorsport website busy until lunchtime ish tomorrow though.
KugaWestie Posted October 9, 2018 Author Posted October 9, 2018 5 minutes ago, AdamR said: Feel free to call me Gary if you think I may be able to help, number on CleaR Motorsport website busy until lunchtime ish tomorrow though. Cheers Adam. I have been trying to find a pictorial narrated guide to read to try and understand the process with no joy so far
AdamR Posted October 10, 2018 Posted October 10, 2018 Stick something on the hub that makes a mark out horizontally (eg. Laser pen), the bigger distance the better. Imagine you're extending the hub axle by a few feet. Move hub up and down in, say, 10mm increments and mark off where your 'pointer' is aiming. A bit of old scrap board and a marker pen will do it. If the line of dots is vertical and straight you have no bump steer. If it isn't then you do. The direction tells you which way, and the amount of lean / curve tells you how much.
B.RAD Posted October 10, 2018 Posted October 10, 2018 1 hour ago, AdamR said: Stick something on the hub that makes a mark out horizontally (eg. Laser pen), the bigger distance the better. Imagine you're extending the hub axle by a few feet. Move hub up and down in, say, 10mm increments and mark off where your 'pointer' is aiming. A bit of old scrap board and a marker pen will do it. If the line of dots is vertical and straight you have no bump steer. If it isn't then you do. The direction tells you which way, and the amount of lean / curve tells you how much. Do both axles!
Trevor Little (Trevturtle) - Treasurer Posted October 10, 2018 Posted October 10, 2018 12 hours ago, KugaWestie said: I have been googling for a while tonight trying to understand how to measure bump steer diy style without much success  The work through it on one of the binky episodes.. that may help?
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