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| mr_sperm1 |
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fordfreak ef wrote: FordFairmont wrote: fordfreak ef wrote: lets hope thats right as ive now 20's and up for my 1st dyno comp with them installed this weekend coming...  i would fit some stockies on for the comp. Theres prolly around 10 kg difference in weight between your 20" rims/tyres and a stockie with 195's and would affect intertia you would think considering 15's were stock on EF's, not 14's 
_________________ Maloo - Holden's word for ugly. |
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| 66 coupe |
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 dyno comps...
put it on the track, thats where the real numbers are |
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| sickd |
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it cant affect it they put info into the dyno wheel diameter and stuff otherwise eveyone would run 13' stockies cos they would get more kws
_________________ BA XR8 BOSS 260
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| ebxr82nv |
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depends how honest the operator is and i dont know if shoot out mode allows for this info
_________________ 9/98 AU1 XR6hp-about to retire from the road and be reborn on the race track. |
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| sickd |
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ebxr82nv wrote: depends how honest the operator is and i dont know if shoot out mode allows for this info
a true dyno allows for all these specs if you want a true reading you need it other wise the dyno read out is s**t and you pay for a lie
_________________ BA XR8 BOSS 260
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| fordfreak ef |
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66 coupe wrote: :roll: dyno comps... im a track hore.. well.. in tha past anyhows... so that cannot be directed my way!... put it on the track, thats where the real numbers are 
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| BigCav |
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4dlvr wrote: according to my physics teacher the torque curve will drop but the peak kw number should slightly increase
your teacher is sadly mistaken and should go back to uni i think. that theory is on motors revving harder, as power is a result of rpm and torque, if rpm increases so does power etc however at the treads where a dyno is reading the motors not physically making any more power at the motor because of big wheels is it. u can dyno tune your car in first gear or in 5th gear u will get the same rwkw, so what would changing the rolling circumfrence do, absoluty nothing as its the same thing as different gearing. u will lose power with those 20's, not because ratio's and speeds have changed but because you have greater rolling resistance due to the additional weight in the wheels. i ahve experiance with dyno's, i have been tought a little by the dynodynamic's trainer and he says the same. iv physically had experiance with running a vl on 14's then again on 19's if u wont the most power fit a set of stocko's on but you will lose very few kilowats with the rims. the vl went from 92 to 90 from memory |
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| Steady ED |
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BigCav wrote: u can dyno tune your car in first gear or in 5th gear u will get the same rwkw, so what would changing the rolling circumfrence do, absoluty nothing as its the same thing as different gearing.
In theory. In practice, and theres a thread where we tested it on FPV_GTps dyno with my Sprint, there was a slight variation between gears. Roughly 5kw spread from memory, testing 1st to 4th gears. 5th oversped the dyno so we had to abort the run.
_________________ ED XR8 Sprint - S-Trim, V500, 249rwkw |
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| Johnson stroker |
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just changing to 20's with no other variables being changes would not have a forseen effect, however, variables like the rotating mass, the quality of the rubber to width of the tyre will all effect the output.
a 20" rim would have a higher static mass than a 17" rim meaning the car has to work harder to spin that mass thus absorbing a small amount of power, the tyre width would have a similar effect as the traction footprint increases again the power required to rotate that footprint increases. As the overall rolling diameter is increased it will have a similar effect to changing diff ratios, though not as dramatic it will still have an affect. I have seen cars that normally run 235/45/17's pull figures around the 150kw mark, those same cars on little cheese cutter 14" steelies with smaller diameter wheels gain as much as 15rwkw's with nothing else being done. purely because the rotating mass is reduced.
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| BigCav |
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Steady ED wrote: BigCav wrote: u can dyno tune your car in first gear or in 5th gear u will get the same rwkw, so what would changing the rolling circumfrence do, absoluty nothing as its the same thing as different gearing. In theory. In practice, and theres a thread where we tested it on FPV_GTps dyno with my Sprint, there was a slight variation between gears. Roughly 5kw spread from memory, testing 1st to 4th gears. 5th oversped the dyno so we had to abort the run. yes there will be, i was tlaking more of a theoretical thing lol the reason there is a spread is because in lower gears there is more mechanical advantage in the gearbox and less resistance depending on your gears etc the slight difference in resistances and variables between gears at 4000rpm can make a big difference at your rear wheels |
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| fordfreak ef |
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i left my 20's on for yesterdays ford/holdne dyno day and i pulled my best ever figure's ... go figure!! 174.7 RWKW..
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| Tocchi |
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slightly different that power related. more tune
im getting the EF re-tuned this thursday, at the moment its got the 295/50/R15s on the rear. if i get it tuned with these on, and then switch to standard FTRs (for when i sell it, or other, etc) would the tune be affected. (even slightly) due to the fact when its tuned on the 295 it needs more effort to turn them, rather than 225/R16s which it would turn easier |
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| Nigel |
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You'll probably find that Larger wheels will affect your acceleration a bit, but not your overall power.
The problem is the inertia of the bigger wheel. It takes more to make it spin faster - keeping it at that speed though is no problem. I didnt notice 17's on my EB (not too much), but I did notice my little ford escape (3.0 V6) when I went from Factory 225*16's to 255*18*65's. Noticably less takeoff, but so much better traction. |
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| Steady ED |
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Tocchi wrote: slightly different that power related. more tune
im getting the EF re-tuned this thursday, at the moment its got the 295/50/R15s on the rear. if i get it tuned with these on, and then switch to standard FTRs (for when i sell it, or other, etc) would the tune be affected. (even slightly) due to the fact when its tuned on the 295 it needs more effort to turn them, rather than 225/R16s which it would turn easier Nah, the only way it could is if it brought up some weird load they hadn't tuned for. They'll load it up on the dyno anyway, I doubt the rim/tyre combo would be able to provide more load on the street then they can on the dyno.
_________________ ED XR8 Sprint - S-Trim, V500, 249rwkw |
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| Nigel |
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You would have more traction with bigger tyres....
would explain the power |
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