edmandsd Posted September 7, 2003 Share Posted September 7, 2003 I presume the answer to this question is when it's level ? I know a lot of Caterham racers run a 10-15mm rake down from the rear to the front. What is the primary purpose to this and how is this actually measured in practice ? In drag racing the primary purpose is traction but aerodynamics is also important when you're travelling at 130mph in a car with the shape of a Caterham. Question is therefore - Does keeping the car level or even lowering the rear in relation to the front assist weight transfer and hence traction ? Home of BDR700 Link to comment Share on other sites More sharing options...
westy Posted September 7, 2003 Share Posted September 7, 2003 Going backwards 😬 For me it's getting on the Gas, when everything you know say's get on the brake!!! Link to comment Share on other sites More sharing options...
Chelspeed Posted September 7, 2003 Share Posted September 7, 2003 In my understanding the rake is not so much a deliberate attempt to slope the whole car forward for any aerodynamic or other advantage but a comment from those that know that "the handling is best" when the ride height is 10 to 15mm higher at the back than the front. Could be aerodynamic but much more likely that this just sets the front and rear suspension at it's optimum geometry. Ride height is measured under the chassis rails at the front of the car and for the rear it's the ground clearance under the floor pan at the back of the cockpit. If the floor is the same height as the chassis rails (and it woud appear to be) then this will become a rake in the bottom of the chassis. Link to comment Share on other sites More sharing options...
gee_fin Posted September 7, 2003 Share Posted September 7, 2003 Flat flooring reduces drag, preferably flat-flooring all the way to the rear with some sort of diffuser/tray to finish things off. One that has always stuck in my mind is the drag created in and around the engine bay (with sealed floors) - I think it would be an interesting exercise to measure/calc the volume of air coming in through the nose cone and the volume of air that can escape from the scant few vents on the bonnet. Did anyone say parachute? If you're just running a 1/4 mile and temps aren't a huge issue I'd think about reducing the air going into the nosecone. Inboard shocks would fractionally reduce drag further too. Always run the half tonneau too.... ________________________________________________________ graeme finlayson / tyre warmer / fluke motorsport graeme@fluke-motorsport.co.uk / www.fluke-motorsport.co.uk Link to comment Share on other sites More sharing options...
normalbloke.29 Posted September 7, 2003 Share Posted September 7, 2003 Err, when parked? Link to comment Share on other sites More sharing options...
Michael Posted September 7, 2003 Share Posted September 7, 2003 Cover the front wheels as much as poss. Fill in the space under the diff and fuel tank. Use half doors and cover passenger space. Roll bar over driver only. Freestyle front end. No screen at all or mirrors. Link to comment Share on other sites More sharing options...
Bare Posted September 7, 2003 Share Posted September 7, 2003 As Above: only When Parked :-) Aero is all about Drag.. Sevens are Nothing But Drag. But, c'mon you can't be serious? Early on, as in the FIRST seven design the S1 had a Full under belly panel, not only did this aid structure but it was an Aero advantage. Cleverly deleted on al subsequent cars..as was the far superior rear axle location setup... cuz: 'These are built to a Price, you know'.. except of course the price is currently (actually always was) Horrific for what one is actually given possesion of in exchange for their rather largish Bucket of Money :-) Dicking with the Rake won't get you much, except perhaps the 'joy' of thinking yer acomplishing something. Suggest you add a full undertray and then a rigid tonneau cover (no windshield of course) then something monstrous at the rear of the car to ameliorate the 'blunt' tail (drag) OR.. just drive the thing, enjoying what is essentially unalterable. Link to comment Share on other sites More sharing options...
edmandsd Posted September 7, 2003 Author Share Posted September 7, 2003 Thanks for your comments. For those who are unaware my car does have the following to facilitate 'aero': Single rollbar Single aeroscreen Wrap around front arches Ali panelled underside with small relief at rear of engine compartment and at the rear of the vehicle to vent air passing through tunnel Arch alloy passenger tonneau No mirrors Driver's side panel It doesn't have In-board suspension but I can appreciate the marginal aero advantage this would give. I'm therefore really only interested in the effects of rake for these purposes. I suppose in practice on a 1/4 mile run the car's profile is changing through launch, gear changes and as a result of decreasing rates of acceleration and grip. Spring rates and suspension geometry will therefore play a part here. I suppose that if you start off with 10/15mm of rake from the rear down to the front (incl driver aboard) when the car's stationary, under acceleration the car's likely to move to a more horizontal position. That said does a nose down attitude at launch compromise weight transfer and hence initial traction ? Graham - Thanks for the measuring advice.....i'm popping out to the garage now ! If a bit of rake increases the car's stability then I'm all for it based upon recent events. Graeme - I agree with your 'aero' points but it looks like my new rear suspension set up's likely to mean i'd be better off removing the existing rear end pannelling ☹️ I'm sure I'll end up with a vented nosecone sooner or later. Home of BDR700 Link to comment Share on other sites More sharing options...
Smokin Joe Posted September 7, 2003 Share Posted September 7, 2003 IMHO horsepower can overcome aero, you have plenty of aero add ons, concentrate on getting your hp to the track... Softer rear springs, Spool the rear end, at least 15" rims with beadlocked (Inside and outside)Hoosier Dragslicks (as big as you can fit) maybe Tub the rears too. Skinny skinny minny front tyres This will give you a nose down stance any way. Inflate fronts to maxpsi for tyre 45lbs rears 8-9lbs should be plenty check temp after burnout. front of car should lift off the ground at least a foot if we are hooking up well on launch. Once we get your car to hook up and get rid of all that wheelspin times will come down and she will be much easier to control. Best wishes, Joe Link to comment Share on other sites More sharing options...
edmandsd Posted September 7, 2003 Author Share Posted September 7, 2003 I don't disagree Joe. I used a spool and big slicks but after I lost control at Santa Pod i've reverted back to hillclimb slicks and an LSD. I was going to sell them but Andy Robinson (of Pro Mod fame over here in the UK) has persuaded me to hang on to them until I get my confidance back. The 'off' was predominantly the result of having a 4 link with only 3 foot instantaneous centres, meaning I was hitting the tyres too hard with excessive anti squat, resulting in the car wheelspinning the length of the track ! Andy's now fabricated a new adjustable rear end set up for drag/sprint/circuit work. Cheers David. Home of BDR700 Link to comment Share on other sites More sharing options...
Smokin Joe Posted September 7, 2003 Share Posted September 7, 2003 Hi David, Glad Andy persuaded you! Yup the wheelspin is the cause of the uncontrollability-like driving on grease as the slicks overheat. The spool by locking your rear gives full time 2wd. The reason the lsd seems more comfortable is it is giving you one wheel drive decreasing the driven power hence decreasing the wheelspin....in turn higher et's. If we can get you hooked up with a locked rear and no spin I guarantee the best et you have seen by a mile as all the driven force is converted to fwd momentum. + if both rears are turning equally with no slip she will fly very straight! From a drivers point the launch will seem like a hard slam into the seat as the front rises rather than a shove with the nose flat. In addition to Andy's mods which sound spot on can you get a better gear for the rear to help with traction. Have you considered an automatic 2 speed tranny like a powerglide where the torque lockup can be adjusted? Maybe a launch rpm limiter? I make these suggestions as it sounds as if you are serious about the Dragging, once you lock that rear end street is out, so may as well go all the way! Wanting you to run faster than ever Joe Link to comment Share on other sites More sharing options...
se7enmad Posted September 8, 2003 Share Posted September 8, 2003 Hi! Your query and postings set me thinking (well rummagaing through my own thoughts and questions as I have obviously little technical background). I've done a few searches to try find photos of dragracing 7's to clarify what I meant but it's sad to confirm dragracing 7's are still extremely rare ☹️ Now, if one considers the 7 as another rwd vehicle for a moment - One would not need worry so much re: dropping the front or raising the rear. In fact most drag racing cars are indeed allowed to lift off, transfer weight onto the rear, and all too often use wheelie bars to contol the lift. How these cars steer is the question you may want to be answering! (You can get a bike to steer whilst doing wheelies by putting the correct amount of weight/traction through it - am I talking rubbish?) Also, as least down here, instead of stiffening front suspension to ensure the car is glued down to the track, the reverse attitude is taken with the car wobbling away under launch and again throwing weight back. Another serious consideration is that it will be difficult to control the car with real power, so in this section, there will always be some difficulties. I have noted, with the local rail cars, that all too often, in their runs they are correcting with the throttle when it suddenly goes wrong, and with tyre shake it seems to go wrong most times. I also noted that it may be that the launch/first 60ft is decisive in this power control, so maybe it is not so much of an aerodynamic consideration after all. Maybe you will want to revert to dragracing tyres in the end?! You may also want to consider lenghtening your se7en; might this reduce twitchiness? I think you may want to turn your car into a se7en bodied rail car in the end My ha' penny worth of ramblings ... Antonella 1998 Caterham Classic (Malta) .. still not spotted ! my site here more photos here Link to comment Share on other sites More sharing options...
Badger Bill Posted September 8, 2003 Share Posted September 8, 2003 edmandsd, It's clear that some people don't know of you... *smile* BB *smile*Vorsprung Dürch Leichtigkeit Link to comment Share on other sites More sharing options...
Peter Carmichael Posted September 8, 2003 Share Posted September 8, 2003 I carried out some definitive testing of aero mods at Aintree on Saturday. Removing all the bulky rollbar padding, removing the passenger aeroscreen and reversing the headlights resulted in... 111mph through the speed trap compared to 110mph on the previous run. On the final run I didn't change into 6th but held it on the limiter at 7900 in fifth to get 110mph again. So in other words it made no difference. I did manage a 2.35s 0-64 foot time on that final run which I think is a personal best. I will be examining the logs very thoroughly to find out exactly what I did! Link to comment Share on other sites More sharing options...
Peter Carmichael Posted September 8, 2003 Share Posted September 8, 2003 I'm going to try and stick to answering the original question. Question is therefore - Does keeping the car level or even lowering the rear in relation to the front assist weight transfer and hence traction ? Weight transfer under acceleration is a function of the height of CofG and nothing else, so both ends high gives the greatest weight transfer. As long as the front wheels aren't lifting off the ground, this gives maximum acceleration. That is just the steady state mechanics answer to the problem. The static condition of weight transfer is only part of the story. The grip of the car is developed by the microscopic making and breaking of grip between the tyre and the tarmac. We know a spinning tyre grips less effectively than a tyre showing say 8% slip (generally accepted optimum). When a tyre breaks traction we want it to regain traction as quickly as possible. When a tyre breaks traction acceleration drops and we want the suspension to push the tyre harder into the road to regain grip. i.e. low acceleration the rear of the car stands up vs. high acceleration the rear of the car squats. Hence for grip under acceleration you want a lot of pro-squat in the suspension - it acts as traction control. Aero is the next problem, but I am going to try and convince you it isn't a problem at all from a grip point of view in a drag race. First things first. Aero isn't going to do anything until you are at 100mph plus. If you sort out the mechanical grip problem for starting in the first couple of gears you are not going to have a grip problem in the higher gears. What you are interested in then is not a ratio of downforce to drag (efficiency in a traditional sense), but just minimising the drag. A flat undertray and rear diffuser are in theory good for reducing drag, but you will be dragging their weight all the way from the start line. A "time over distance" event is very sensitive to the start and initial acceleration and is very insensitive to the aero drag. If you try and reduce drag by adding mass, you will harm your ET as the price for getting a marginal improvement in terminal speed. Hope some of this is useful. The honest answer is that you *need* more power... Witnessed the Quantum Extreme at Aintree pop in reliable 2.25 0-64 foot times by letting the revs die and just using the grunt of the 5 litre engine to launch. It was making 140mph over the line where I was making 110mph (~160 bhp) and Simon Rogers was making 118mph (~200bhp). The 3500cc Formula 3000 Reynard 88D was making 169mph over the line and 2.05s 0-64ft Edited by - Peter Carmichael on 8 Sep 2003 15:20:10 Link to comment Share on other sites More sharing options...
Jason Plato Posted September 8, 2003 Share Posted September 8, 2003 I recorded 2.11 & 2.16 for 64foot at curborough . This was of course on wooden 32R's . Aintree is also downhill start ( slightly ) as for drag , shirley whatever rake or underbody panels you put on the car , you will still have a huge great hole in the front nose , and 2 large rear wings ?? I would try experimenting with minimising the nose cone hole or evacuating out of the top of the nose with a deflector , and making some side defletors - ala F1 for the rear wings ?? Dave Edited by - Dave Jackson on 8 Sep 2003 16:25:45 Link to comment Share on other sites More sharing options...
edmandsd Posted September 8, 2003 Author Share Posted September 8, 2003 Makes sense Peter as a lot of drag cars concentrate on grip not aero - a drag race is more often than not won in the first 60 feet. I'm also totally unsurprised by the negligible effects of you trying to reduce drag at Aintree...........Arnie will of course be very disappopinted to hear this Home of BDR700 Link to comment Share on other sites More sharing options...
andy couchman Posted September 8, 2003 Share Posted September 8, 2003 Have also tried reversing the headlamps. It looks faster but the clock showed otherwise. Someone told me that headlamps are closer to the theoretical teardrop shape if run facing forwards - make sense? I understood that the reason why many drag saloon cars run low at the front is to reduce frontal area (which is the area from the ground upwards not just the cross section of the car body?) and to prevent or reduce lift at speed. Also if there is less air to get under the car, then there is less air to slow it down. A soft back end would also presumably help to shift weight transfer to the rear and so aid traction, then returning to normal height as wheelspin becomes less important at higher speeds. Less weight at high speeds maybe also means that power can get to the wheels more easily giving maximum assistance to turning the wheels as friction is effectively less. Or am I talking bo**ocks? Andy Q831FDD #83 at Brighton on Saturday. Link to comment Share on other sites More sharing options...
Nemesis Posted September 8, 2003 Share Posted September 8, 2003 I have found that following a coach at 100mph really improves the aerodynamics, I hope this helps Nemesis Check out Will She Find Out.Com for the build of my car and SHHH don't tell the wife! Link to comment Share on other sites More sharing options...
edmandsd Posted September 8, 2003 Author Share Posted September 8, 2003 That's funny Nemesis - nice one Now all we need is a coach that accelerates like the Caterham and we've resolved this issue. See you at Brighton Andy. Home of BDR700 Link to comment Share on other sites More sharing options...
Tight fart Posted September 9, 2003 Share Posted September 9, 2003 I thought all coach's had 65mph speed limiters fitted as standard. Link to comment Share on other sites More sharing options...
moosetestbestanden Posted September 10, 2003 Share Posted September 10, 2003 The honest answer is that you *need* more power... And there ain't no replacement for displacement HALLELUJAH Brothers Praise the Lord and pass the Nitro Methane! ------- Chris A day you don't go a hundred is a day wasted Link to comment Share on other sites More sharing options...
moosetestbestanden Posted September 10, 2003 Share Posted September 10, 2003 The honest answer is that you *need* more power... And there ain't no replacement for displacement HALLELUJAH Brothers Praise the Lord and pass the Nitro Methane! ------- Chris A day you don't go a hundred is a day wasted Link to comment Share on other sites More sharing options...
moosetestbestanden Posted September 10, 2003 Share Posted September 10, 2003 The honest answer is that you *need* more power... And there ain't no replacement for displacement HALLELUJAH Brothers Praise the Lord and pass the Nitro Methane! ------- Chris A day you don't go a hundred is a day wasted Link to comment Share on other sites More sharing options...
Joe 90 Posted September 10, 2003 Share Posted September 10, 2003 Chris, judging by your sig, you might enjoy the story about a german owner of a Mclaren F1. He took it back to the factory for a service, where they checked on on board logs. The mechanics were slightly taken aback that the owner had exceeded 200 MPH on 6 out of 7 days. When questioned he said it was because he takes it easy on sunday ❗ 😬 Starting all over at 40. Link to comment Share on other sites More sharing options...
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