irokin Posted August 2, 2011 Report Share Posted August 2, 2011 I know reducing unsprung weight can be a very good thing in motorsport but at what kind of threshold are you going to notice an improvement? 50g? 1kg? 5kg? I know the threshold for benefit is much lower when it comes to unsprung weight, but just how low is it? Save weight where at all possible whatever the cost? There is some background but I'll save it till some people reply so I don't taint your response with extra considerations. Talking about weight only at the moment. Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted August 2, 2011 Report Share Posted August 2, 2011 It won't make a speed performance difference, but you can notice the difference in brands of tyres by their weight on a sports car. I replaced Pirellis with Dunlops on my Lotus Europa and the suspension crashed and banged around very differently. That was probably 5Kg per wheel max. Say 20Kg per car of 1000Kg, that's only 2% and you won't feel it accelerate faster. Mind you, I could fiddle the handicapper by taking out the spare wheel, the jack, and the toolbox between handicap races, so maybe 20Kg makes half a second a lap. It didn't feel any faster but it kept me near the front!! So, if you can replace a tyre or a wheel with one of 5Kg lighter, go for it! The biggest gain would be the diff. That ugly great lump of cast iron bashing around in the rear end of the KE70 (and Escorts) is why IRS Datsuns were so good! I was given an alloy diff housing for my R31 Skyline one time, but never got around to fitting it. That was banjo style of course, so it wouldn't make such a difference as replacing the cast iron rubbish from Borg Warner. Quote Link to comment Share on other sites More sharing options...
irokin Posted August 2, 2011 Author Report Share Posted August 2, 2011 This is in the Silvia so I've got IRS and all that good stuff. The cars an unregistered track only car now so it's missing large portions of interior (but I've kept the electric windows :rolls:). The car was 1190kg and I've been aiming for 1100kg but I seriously doubt I've removed even half of that. I haven't gone silly with carbon fiber bonnet, doors and boot and polycarbonate windows yet, I just don't think that's worth the cost ($3000+) at the moment. I've just concentrated on removing useless shit that I don't need to be taking for a free ride around the track. I'm fiddling with my brake setup at the moment and I have the opportunity to save some weight in the calipers. There are other benefits but increased braking force isn't one of them. Its essentially the same type of caliper just lighter. I'm just not convinced that the other benefits make it cost effective, so I'm trying to figure if the weight difference will play into the decision. I just feel like I might be splitting hairs. The biggest gain I'm going to see is from the tyres which should give me something like 2-3 seconds a lap, that and MOAR POWAH!! Whats another tenth of a second on top of that? Quote Link to comment Share on other sites More sharing options...
Spencer[RL] Posted August 2, 2011 Report Share Posted August 2, 2011 If you reducing the weight of your calipers wouldn't that fall into the same area as carbon fibre fenders and polycarbonate windows ? :laff: Quote Link to comment Share on other sites More sharing options...
irokin Posted August 2, 2011 Author Report Share Posted August 2, 2011 Not really, as its unsprung weight thus has considerably more effect on the cars handling. IIRC for sprung weight its worth something like 0.5hp per 10kg removed equivalence. For unsprung weight removing 10kg would be an absolutely massive improvement to handling. The way I understand it, the reason it has such an effect is because it increases the momentum that the shock absorbers and springs have to handle when you hit a bump etc. Reducing the unsprung mass means they can keep the tyre in contact with the road more of the time. Remember I drive on the joke that is Queensland Raceway. Apparently they're going to resurface it this year, but they said they would do it last year... and the year before that.... and.......... yea you're probably safe putting your money on 'its not gonna happen'. Quote Link to comment Share on other sites More sharing options...
ke70dave Posted August 2, 2011 Report Share Posted August 2, 2011 The way I understand it, the reason it has such an effect is because it increases the momentum that the shock absorbers and springs have to handle when you hit a bump etc. Reducing the unsprung mass means they can keep the tyre in contact with the road more of the time. this is how i understand it too. which i think is the same reason why interved shocks are popular, all the shock weight is attached the chassis, not the wheel end. thus less un sprung weight. if you can get them, for cheap, id chuck them on. but i think the unsprung weight arguement is another one of those "it wont make much difference unless you save weight everywhere" so if you get those calipers, inverted shocks, light weight rims...it will all add up. this website gives a few different weights for nissan calipers: http://nissans15.com/brakes.htm it doesnt have the 13 caliper (i assume you are talking about s13?) but the alloy calipers are 3.3kg, and the cast iron ones are 4.8. (and i think all of those can bolt up to an s13 strut, with the right bits) 30% reduction in weight for the caliper combined with a light wheel has to be noticeable? just have to watch if you go to one of those massive calipers, that the disc you have to use (ie giant...) wont add more weight than you save with the caliper! Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted August 2, 2011 Report Share Posted August 2, 2011 just have to watch if you go to one of those massive calipers, that the disc you have to use (ie giant...) wont add more weight than you save with the caliper! true- I swear people fit giant brakes for looks when their brakes were quite adequate beforehand, and add more unsprung weight. Make it as light and as delicate as you can stand, although matching shocks to springs to car is a mission that will overwhelm any other differences you can make. Does it bottom out anywhere on the track, and if not does that mean it is too high or too stiff. If it does bottom out, does it mean that its too low or too soft.. but too soft in springs or too soft in shocks... and on it goes! Quote Link to comment Share on other sites More sharing options...
LittleRedSpirit Posted August 2, 2011 Report Share Posted August 2, 2011 When it comes to handling I think you need to consider the gyroscopic effect of the wheels and tyres spinning at different speeds as a varying directional force (thanks to the steering), and then also the static unsprung weight of fixed components as a secondary consideration. Potentially the momentum of a spinning wheel and tyre could be massive, and as such the gains would be greater if you consider that a 3 kg reduction in the spinning mass can result an a far lesser maximum momentum once its spinning fast and pointing in a certain direction. This would result in a more tactile response to the handling input and less work for the steering. So maybe its primarily more important to have lighter wheels and tyres and axles rather than worrying a whole bunch about the lightest static components such as calipers, stubs, housings etc. Just a thought... Quote Link to comment Share on other sites More sharing options...
ke70dave Posted August 2, 2011 Report Share Posted August 2, 2011 very good point Matt. Adding to what you said, adding massive brake discs adds to the rotarional mass- ie detrimental!! It's all a trade off!! Quote Link to comment Share on other sites More sharing options...
LittleRedSpirit Posted August 2, 2011 Report Share Posted August 2, 2011 Yeah, but it all depends on the hp available how far you go I guess, in a silvia, it could be a lot. Its all about optimising without too much overkill. Quote Link to comment Share on other sites More sharing options...
irokin Posted August 2, 2011 Author Report Share Posted August 2, 2011 I've got R33 GTSt brakes on the front currently and yes the disks are ridiculously heavy but the stopping power is fantastic. I can drop about 1.6kg out of them with 2 piece rotors but at $1500 a set, yea I'll pass for now. I run R33 GTR rims which are forged and relatively light and I've got Bilstein inverted monotubes on the front. I guess for the front, unless someone starts making billet alloy steering knuckles, the only two places I can take substantial weight out of now are the caliper and rotor. I just weighed my spare R32 GTR calipers at 3.13kg (dunno why that guy lists them as cast iron) which is surprising as they appear to be slightly bigger than the GTSt brakes. I can have the steel pistons replaced taking that weight down to something like 2.74kg which is why I'm wondering what kind of weights matter. Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted August 2, 2011 Report Share Posted August 2, 2011 Potentially the momentum of a spinning wheel and tyre could be massive, Sounds like an argument for smaller diameter tyres too! Quote Link to comment Share on other sites More sharing options...
oh what a nissan feeling! Posted August 2, 2011 Report Share Posted August 2, 2011 In a straight line perspective, i have seen a mid 11 sec car drop 0.2 of a secound purely because of removal of big ugly chromies on the fronts, relaced with standard wheels. In a situation where this amount of weight was removed from the body, the difference in time would have been measured in 0.0x instead. Will your braking improve with this new calliper package, or is it just weight? If you are going to full slick tyres, you will require more brakes than you have previously, will your existing setup be sufficient? I honestly think that there is more lap time to be gained in better brakes around qld raceway. As an example, i would gladly take on Xkg per wheel if i knew my braking ability was going to improve significantly. I spent a fair bit of time on QR with my zx10r. Quote Link to comment Share on other sites More sharing options...
Redwarf Posted August 2, 2011 Report Share Posted August 2, 2011 Ben, and you know that I mean this in the nicest possible way, don't worry about it and concentrate on driving faster. There's more in you to go faster than there is in things like this. :) Quote Link to comment Share on other sites More sharing options...
TRD ke70 Posted August 2, 2011 Report Share Posted August 2, 2011 IMO an weight out of the car is a good thing, whether it be sprung or unsprung. the less weight you have to drag around a race track the better. I have just gone through a weight reduction on a rally car, and removed about 50kg's, this was achieved by changing the sump guard to a lighter one, replacing the glass with lexan, and good use of a holesaw. The driver really noticed the difference in the way he could carry more speed through the corner. What we do, is to try and reduce as much of the unsprung weight as possible, IE tyres and wheels, but you get to the point where you just can't reduce it anymore. Every little bit of weight you can remove from the car helps, you might not feel 1 or 2kg's, but add that up over 3 or 4 items and you'll start to notice the difference. If you look closely at the car, there so much you can remove, from intrusion bars in the doors, to unused brackets and it's only going to cost you time with a grinder and hole saw. Other stuff will start to cost money, but the benefits are there. A change in battery saved us 7kg's!! My advice would be, look at the over all picture not just one thing!! Hope this helps!! Quote Link to comment Share on other sites More sharing options...
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