binliner 0 Posted February 24, 2004 Report Share Posted February 24, 2004 Been wondering why a few n/a cars broke the 200bhp mark while most with similar mods didnt... obviously there's lots of factors which mean theres bound to be some variation but why were some noticeably higher?Dubloke, Pete & sixappeal are all running slightly wider tyres (215 as opposed to 205) which would mean their rolling radius was slightly bigger than normal I'm just guessing but could this account for the higher figures?Dont get me wrong this isnt a competitive thing, Im well chuffed with my result and pleased to see them all perform so well, Id just be interested to know what you think? Link to post Share on other sites
Macca 1 Posted February 24, 2004 Report Share Posted February 24, 2004 Im not sure about the physics behind the theory, but my tyres are 215 and i 'only' got 187.7 bhp, corrected.Am i right in saying readings seemed to improve throughout the day?perhaps the longer you gave your car to cool down was an advantage, or maybe the rollers became looser and spun more easily throughout the day? (Ok this is clearly bullshit)But as you say binliner its not competitive: i was really pleased at my reading, and i guess there are hundreds of reasons why some cars run better than others: so long as theres nothing major wrong im perfectly happy..........but a 200bhp car would be nice [ Edited Tue Feb 24 2004, 04:40PM ] Link to post Share on other sites
nickbee 1 Posted February 24, 2004 Report Share Posted February 24, 2004 The 205/215 thing won't affect the rolling radius (that's the '40' bit) but I see where you're coming from. I'd be surprised if it was the case though, as some people had much smaller wheels and their results would be way off.Not sure about the 'loosening up' theory - surely they have to have thought of that when they made them (surely!).I think it's all a bit of luck personally, sometimes a car does well, sometimes it doesn't. I don't know about everyone else, but I had two runs on my graph and 1 whole bhp between them. I'm guessing if you do 40 or 50 runs in a day, then some people are going to get lucky, and some aren't. Link to post Share on other sites
dubloke 4 Posted February 24, 2004 Report Share Posted February 24, 2004 to be honest i think i am more or less on the right track by saying the rolling radius of your tyres does not effect how much power your engine produces! it takes more engine "effort" to spin up a bigger rolling radius, and on the road it equates to slightl slower acceleration and a slightly better top speed in a lot of cases. although obviously speedo discrepencies and road surface etc etc all have to be taken into account! i'm sure mina would have loved a bit more power by changing up a tyre size but i dont think it quite works like that! all the figures for the day were good because of the ambient temp and only those with problems had lower than expected figures! maybe we should have another when the weather improves to see the comparison![ Edited Tue Feb 24 2004, 04:33PM ] Link to post Share on other sites
VR6Pete 1,455 Posted February 24, 2004 Report Share Posted February 24, 2004 I would have to disagree with the idea of cars getting better marks throughout the afternoon... I was on fairly early in the day and I had had my car running for abit while i was there. I was on just after Claire and before mina.... I'm going to put it down to the cool weather and the fact that cars were operatring at the right temperature with the modifications they have... Link to post Share on other sites
dubloke 4 Posted February 24, 2004 Report Share Posted February 24, 2004 think i'd be inclined to go with that account of the day too pete. at the end of the day most were happy with what their cars did and of those that weren't most knew there was a problem before attending! Link to post Share on other sites
ukdub 0 Posted February 24, 2004 Report Share Posted February 24, 2004 i think you will find that most cars will be closer on the power at the wheels. I have a reason why some cars produced more power "at the flywheel" but it will take me to long to write. Link to post Share on other sites
1990 1 Posted February 24, 2004 Report Share Posted February 24, 2004 The 40 bit is 40% of the 205/215 so it would affect the roling radius a bit. Link to post Share on other sites
binliner 0 Posted February 24, 2004 Author Report Share Posted February 24, 2004 maccas result blows my theory!the 215 (ie width) does affect the rolling radius though because the 40 part is the sidewall height as a percentage of the tread width so a 215/40/17 tyre has a sidewall height 40% of 215mm so a slightly bigger rolling radius than a 205/40/17... but as to whether it would make any difference, like I said only really thinking out loud Link to post Share on other sites
binliner 0 Posted February 24, 2004 Author Report Share Posted February 24, 2004 damn beat me to it! Link to post Share on other sites
nickbee 1 Posted February 24, 2004 Report Share Posted February 24, 2004 Yeah, OK, but we're talking about 3mm in radius, the amount of wear would have more effect. Link to post Share on other sites
six appeal 53 Posted February 24, 2004 Report Share Posted February 24, 2004 LOL, if thats the theory too, what ever PSI your tyres are at may also come into question and how hard it was strapped down, ie. compressing the tyre!I think you are right though Justin as no 2 cars are exactly the same so many variables, but they all add up! I think the main one being the temp. of the day, as when i spoke to Vince thats we he put it all own too!There was a massive article about all this and what effects the rollers, in The Golf a few years back, but it was far too boring too read, and basically they all counted, but you'd have to have them all in the right combination to create a huge impact! Link to post Share on other sites
six appeal 53 Posted February 24, 2004 Report Share Posted February 24, 2004 LOL, if thats the theory too, what ever PSI your tyres are at may also come into question and how hard it was strapped down, ie. compressing the tyre!I think you are right though Justin as no 2 cars are exactly the same so many variables, but they all add up! I think the main one being the temp. of the day, as when i spoke to Vince thats we he put it all own too!There was a massive article about all this and what effects the rollers, in The Golf a few years back, but it was far too boring too read, and basically they all counted, but you'd have to have them all in the right combination to create a huge impact! Link to post Share on other sites
ukdub 0 Posted February 24, 2004 Report Share Posted February 24, 2004 am i guessing right by saying that the rollers work out the loss through transmission by timing how long it takes the car to slow down in neutral after the power run. If it does, thats where the difference could be coming from. For example if a good vw gearbox and driveshafts take 15 secs to slow down this may be a loss of 40 bhp. Now if your tracking was out or your tyres where a bit down on pressure this would increase friction on the rollers and say stop the rollers in 10 secs. Now the computer that is working out all the figures thinks that there is a bigger loss through the transmission than the good vw box so adds a bigger loss to the power at the wheels figure, therefore giving a bigger power at the flywheel. :? [ Edited Tue Feb 24 2004, 05:07PM ] Link to post Share on other sites
ukdub 0 Posted February 24, 2004 Report Share Posted February 24, 2004 i think &| %-6 [ Edited Tue Feb 24 2004, 05:09PM ] Link to post Share on other sites
dubloke 4 Posted February 25, 2004 Report Share Posted February 25, 2004 thats right, thats what vince told me about mine having such a big loss shown on the sheet, but in reality its not as bad as it looks! still gonna get my geometry re-checked by vw tho' the little turds. only did it two days b4 the rr and i did 6 miles back from them until the sat. Link to post Share on other sites
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