NoCoast Grant Hughes Junior Moderator Location: Whitefish, MT Join Date: 01/11/2006 Age: Midlife Crisis Posts: 6,818 Rally Car: BMW |
I "think" having lower ratio in the rear and higher ratio in the front reduces stresses on the gearbox gears, output shaft, drive shaft, and lesser extent the pinion gear. If the bulk of your torque multiplication is occurring in the rear end instead of the gearbox the stresses on everything between the gear and ring gear is lessened. I know I have never seen anything advertised as a rally gearbox with a first gear lower (numerically larger) than 2.4-2.5 or so. Not that that means anything... Grant Hughes |
Andrew_Frick Andrew Frick Ultra Moderator Location: Greenville, SC Join Date: 05/18/2007 Age: Midlife Crisis Posts: 684 Rally Car: Rally Spec Ford Focus |
|
DaveK Dave Kern Mod Moderator Location: Centennial Join Date: 07/11/2008 Age: Midlife Crisis Posts: 1,085 Rally Car: Compact M3 & Evo IX |
My take is that they're not up to the task. I ran JVAB fronts and Billy HDs in the back at a local hillclimb on the Coupe and it felt like I had two different cars under me - ready to run over anything up front, and ready to bottom out at the smallest dip in the road out back. I really like the JVABs all around that I've got on the Compact, so I'm on the hunt for a proper solution to beef up the rears. I'd prefer to do it without having to add taller shock towers out back. Regarding springs - if anyone tells you that the rear E30 325 convertible springs are beefier or taller than the E36 ones...they're full of crap. Still trying to find an OEM spring that's beefier than the 328 vert, but no luck so far. BMW pervs are so secretive with everything, it really sucks. Dave |
john vanlandingham John Vanlandingham Mega Moderator Location: Ford Asylum, Sleezattle, WA Join Date: 12/20/2005 Age: Fossilized Posts: 14,152 Rally Car: Saab 96 V4 |
Grant a "LOW" first is 4.2:1 ; a higher 1st is 2.95:1, a typical rally box 1st is 2.25 to maybe 2.35 just to remind everybody Low axle is 5.35:1 and "High" axle 2.85.. Disregarding what every kid on the intraweb says and reversing it and just sticking with the convention usage sure helps for clarity.. And short AXLE means you don't need the box the size of a 3.5 ton truck box Then its just a matter of finding a toof count that is good for the ratio and the strength you need. (Road car shit being selected for quietness) To see this in action look at mid/late 80s Saab 900 T16 gearboxes with the taller chain drive primary ratio to reduce torque to the box, then the replacement of the 3.73 final drive with 3.9 to make up for it. John Vanlandingham Sleezattle, WA, USA Vive le Prole-le-ralliat www.rallyrace.net/jvab CALL +1 206 431-9696 Remember! Pacific Standard Time is 3 hours behind Eastern Standard Time. |
NoCoast Grant Hughes Junior Moderator Location: Whitefish, MT Join Date: 01/11/2006 Age: Midlife Crisis Posts: 6,818 Rally Car: BMW |
Yeah, and that is exactly what I said. Here, I'll rephrase it...
Grant Hughes |
Cosworth Paulinho Ferreira Infallible Moderator Location: Charlotte, NC Join Date: 03/15/2007 Age: Midlife Crisis Posts: 721 Rally Car: Honda Civic |
That theory works for some applications but for example on a fwd, the shorter ratio ring and pinions get much weaker the higher the number gets. The pinion becomes too small and the teeth tend to break easier. But anyways, dogbox is a rally specific gearbox and has a 2.636 1st gear, and 1:1 6th with a 4.9 CWP. And of course the Evo and STI gearboxes have a 3.0 1st and 3.3 respectively. And the Super1600 cars were around 3.5 to 3.6 first gear and 3.9 to 4.7 CWP. But since this a RWD application, it is true to see more boxes setup between 2.4 and 1:1 with a CWP in the 5.1 range. Mucho spesive setups though. |
Pete Pete Remner Elite Moderator Location: Cleveland, Ohio Join Date: 01/11/2006 Age: Midlife Crisis Posts: 2,022 |
Lower gears are a higher ratio.
There's a big benefit, for solid axle cars, for putting most of the gear reduction in the rearend. Less torque on the driveshaft means the axle stays flatter instead of trying to pick one tire up. Easier on diffs, and handling stays more consistent left vs. right. Pete Remner Cleveland, Ohio 1984 RX-7 (rallycross thing) 1978 Silence is golden, but duct tape is silver. |
Cosworth Paulinho Ferreira Infallible Moderator Location: Charlotte, NC Join Date: 03/15/2007 Age: Midlife Crisis Posts: 721 Rally Car: Honda Civic |
|