Hi there Its probably been discussed before, but maybe time for a review. What F/R spring rates do folks use on race cars? On cars with road tyres and slicks. How much more when using slicks? How about complete removal of the front ARB when using higher spring rates? Lets have a recap... Cheers Rob
Great time for a review. Other than that, i think that we have never analyzed this subject before in detail. For start point, it will be very valuable to enrich this thread with opinions that are based on actual and specific parameters like motion ratios, suspension type used, deg/g, body frame stiffness, tire stiffness, damping coefficient, track surface, etc I used to race my OE track Mk2 on a 300lbs/300lbs F/R set up with matador slicks. No front arb, standard rear one. Ok for Greek circuits, mc pherson and torsion beam . Now, on wider set up (Berg Cup style) with true weld in roll cage, 400/400, no front arb, standard rear one with triangulated axle (which actually acts as having another arb) adjustable rear geometry and BTCC Dunlops. Seemed soft to me. I intend to run around 3.5Hz on my front suspension system and 3.8 on the rear. Will try 600lbs or even more.
Very interesting. Been running 500/228 (ratio 2.16 F:R) on mine and feels very nice and balanced, but recently on larger slicks get the impression the whole thing is leaning too much, loosing -ve camber and rolling onto the outside edge of the tyre, and also had the skirts at the back bottom out on the road recently also (65mm off the deck!). So are thinking more spring. Going to fit larger brakes also so want to minimise dive. KW racing dept suggested 750/350 to me a couple years back - almost same F:R ratio as I am running now - I thought at the time they were daft - but now I'm not so sure.... Hows the car with no front ARB? I am thinking at these high spring rates the ARB wont do much, and actually I might pick up some inside tyre grip. Very vocal chap in US Dick Shine used to say on a slick-shod VW racer, 500-800F, 250-350R, no front bar, loads -ve camber
Always worries me high spring rates. It literally bends/deflects the shell. A candid way to see it is to use a porta power type ram, and see how little hydraulic force is needed to change a shells shape. I know this after pushing my autocross mini door aperture and roof back into shape years ago after rolling it. Jon
Ok, just been out in the shed and taken a look at a Mk2 front Eibach bar and H+R rear bar 22mm Front Eibach for Mk2 narrow axle - 105 lb/in - probably same for VR6 give or take, their about the same length In 25mm this would be 175 lb/in Both of these might be a touch less if I measured carefully the full length of the midsection of the bar which is not completely straight, bit longer=softer rate 25mm rear bar - 220 lb/in (midpoint setting on H+R bar) In 28mm this would be 346 lb/in Question now is how does this affect the wheel spring rate - is it half the total bar strength per wheel, or all the bar strength per wheel????
Manufacturers use ARBars because they cannot go on high spring rates due to compromise in vehicle ride and comfort. Thus they try to give some extra springing and prevent roll with arbs. Even in a sport car. If someone selects high spring rates (higher than 300-350 lbs on Mk1/2/3) there is no reason to keep the arb on the front Mc Pherson system. No reason at all. Does very little after a point of stiffness. In a racing car we do not need long suspension travel (bump-rebound) in addition to rally cars where spring rates are much lower and arbs necessary to do what mentioned above. But we are talking about circuit racing. So, in the very beginning with OE track, always on 15" slicks and when i pulled front arb off my Mk2, car felt free on the front at once. I had better traction but a little more roll on high speed bends. What i did is chose higher spring rate for the front and went from 280lbs to 350. Did changes to the rear too. Now, this is a point that needs a little bit of discussion. From my experience and my point of view, when we race our cars all we need is two things: 1) front geometry as stable as possible for 4-5cm of bump and 2) necessary yaw from the rear. Depending on the driving style of each one of us, which is the most important parameter in the car's set up, the amount of yaw effect someone needs varies from person to person. As a starting point, i consider necessary for all Golf racers to know what is the motion ratio of the front and rear suspension system their vehicle operates. Knowing that, there is a general rule that indicates the ride frequency. 0.5 - 1.5 Hz for passenger cars 1.5 - 2.0 Hz for low downforce racecars 3.0 - 5.0+ Hz for high downforce racecars Knowing the tyre someone wants to race his car, i.e. slicks, he owes to chose the ride frequency of his suspension. We will talk about that in the next episode as time is limited lol .
From doing some more reading last night, it seems that ARB spring rate is shared between both wheels - so if you had a 500lb front spring and a 25mm arb, your wheel rate in lean would be 587.5lb. So if you went to a 650lb spring and removed the ARB, you should gain some roll resistance, gain some dive resistance, pick up some inside wheel traction, and loose some weight off the front of the car. Downside is that the ride might be firmer although I cannot say I noticed much effect going from 400 to 500lb springs in this regard. Did some wheel rate frequency calcs as well. Had to make a couple assumptions but should be fairly close. Front with a 500lb spring, 174CPM / 2.9Hz (assumes an unsprung weight of 40kg per corner). 600lb spring, 191CPM / 3.19Hz. 650lb spring 199CPM / 3.31 Hz. Rear with 230lb spring, 170CPM / 2.84Hz (assumes an unsprunf weight of 40kg/corner). 250lb spring, 179CPM / 2.98Hz. 300lb spring 195CPM / 3.26Hz. If unsprung weight is changed, the effect is illustrated for rear: 30kg with 228lb spring - 164CPM/2.73Hz 40kg with 228lb spring - 170CPM/2.84Hz 50Kg with 228lb spring - 178CPM/2.97Hz So if I have overestimated the unsprung weight, the frequencies will reduce. Mk2 Leon supercopa is specified at 3.3Hz. Runs slicks and some downforce. Mk1 Leon supercopa is specified at 3.3Hz front, 3.7Hz rear. 235 section slicks and not much downforce at all. Conventional wisdom is that for passenger cars, rear frequency wants to be 0.1-0.2Hz higher than front so front/rear oscillations dont develop in the chassis. On racecars apparently thats irrelevant as they are so highly damped anyhow and often front frequency is higher than rear to stop braking dive etc.
Rob, as I mentioned by email, now I`m running high rates, I keep meaning to try mine with the ARB disconnected. My intention is to do that at Donington at the end of October. Easy enough to do at lunchtime, I`ll keep it on in the morning and remove at lunch. Should give me good back to back feedback. I usually put Slicks on at Lunchtime, but I`ll do a couple of PM sessions on Cups first, then switch to slicks.
This an interesting thread, I think my springs are 400lbft front and 300lbft rear in a MK2 with H&R anti roll bars, I have found that I want to decrease the grip at the rear to aid turn in, when running cold tyres at Curby on the out lap the fronts would warm first and the rears would still be cool and the back would flick round before the front under steered, I would quite like to replicate this once the tyres are warm, ie have a setup that is more likely to oversteer than under steer and push wide. Leaving spring rates alone Gurd's has had success with a big thick rear anti role bar, meaning you can run lower rear rates which can take bumps better, too stiff and the rear will bounce around, alla MikeH and his rear suspension change when on track Now I have been thinking of upping the rear spring rate, but first I will change the rear arb to the hardest setting. I may also remove the front arb and test the effects too. To help achieve the setup I want I do run a wider front track a as much caster as I can but am finding the front end really has little or no more grip to offer, hence looking at the f/r balance.
on a touring car the FR ARB is good for 0,2 - 0,3 sec in laptime for only 3 -4 laps on new tires > qualifying running more laps results in losing traction In racetrim No FR-ARB is used to keep the tires more stable... Toe-Out at the rear (under bump) can bring 0,2 sec / corner ( in slow corners ) in fast corners you need a driver who keep his feet down at all times...
I run upwards of 800lb on my mk2 championship car. This conversation is very difficult to have without mentioning geometry and camber control,...
When I first got my car it was ex Euro saloons and came with 325lb F & 750lb R, ground down std F arb, Eibach R arb, dunlop slicks and toe out at the rear, quaife diff. Probably cornered as fast as it ever has on a circuit or sprint track, virtually undrivable on a hillclimb!! Now have 400lb F & 350lb R, no F arb, tubular R arb (probably less stiff than Eibach), semi slicks, parallel rear and plate diff. Both set ups were about 3.5 degrees of neg camber although I run much more castor now. Totally different but more of a compromise now. Interesting that you can change things that much and the difference is not really that great, neither were as different as the figure would suggest!! Relatively it's a bit slower on sprints now but much quicker on the hills. I'm planning on finishing off the front tubular arb as my plan in to connect it for the sprints and disconnect it for the hills (I'm too lazy to change springs every event), it's a compromise. Interesting what HPR says above, I'm not interested in keeping tyres stable, we don't run long enough to worry about that. So sounds like there may be some slight advantage to a front arb (plus the ability to fool the car in to thinking I've upped the front spring rate for the sprints). I'm probably going to go up to 450lb on the front as with stickier tyres I think it will be too soft for the speeds it gets up to now as it is much faster than when I started a couple of years ago. I've got a design here to modify the rear arb so I can can double the stiffness and simply adjust it back, again to adjust for the hills or sprints as I think it's too soft now. It does tend to understeer a little (relatively), it was better in it's Eurosaloon spec until I started developing the engine. Once we were up around 200bhp I had to re designed the whole front set up and geometry as you just couldn't get the power down reliably, that made a huge difference, probably one of the best mods I have done. I intend to do some testing early season next year to play with some of these items as there are so many variables and I need to test some of the above back to back.
Rob, have you come across and data to calculate what the relative rates are between a soild ARB and a tubular bar. I know that a tubular roll bar is far stiffer that a solid bar, area for area, but I would guess that the range of movement available is far less. I know most race ARB's are tubular for lightness and as long as you don't want a big range of 'twist' I see no problem. I've got 3 thickness of bars here to use but I've no real idea what poundage they would be or what they would do when connected. I've tested them by fixing one end and twisting the other and they obviously work but difficult to measure. Much lighter than a solid bar and when I made the back one I used the heaviest grade in 25mm and it seemed seem just as stiff as a solid 25mm Eibach when tested but it wasn't a very accurate test, I just wondered if there was some data available.
The mk2's standard geometry (when lower to the point of parallel wishbones) goes into Positive camber when it goes through it ark of movement. Thus necessitating the need for massively stiff spring to limit the roll to maintain a sensible contact patch.. Again, droop levels play a very important part of weight transfer and the overall balance of the car.
