Kissy
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| posted on 14/3/05 at 09:18 PM |
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CBR1000F Diff ratios
Apologies now if I'm treading old ground.
I was advised (incorrectly as it transpires) by S-T to use a 3.89:1 diff for my CBR1000FP (Damn me if he didn't have one to hand: lucky me).
Having now got it on the road it is way undergeared (I sort of guessed some reduction in gearing)Today I did the calcs, with a top bhp declared at
9,500rpm the bike is geared, long legged, to do 147.5mph.
This was assuming the bike wheel at 1921mm circumference, with final drive at 2.47:1 (17t:42t). My 185/60x13" tyres are 1694mm around. With
the 3.89 diff I'm looking at 83mph in top @ 9,500rpm!, and with the newly acquired 3.54 diff, 91mph. Feck. To get to 115mph @9,500rpm I'll
need a 2.80:1 diff. Unless someone knows of a Mk1 or 2 diesel escort I have a few serious decisions to make. I cannot be alone in this dilemma
(bloody feels like it). I've had a few thoughts (some a little less sensible than others).
1. Source a crown-wheel/pinion to give me the right ratio (could this be done by mix-n-match? - I think not). Therefore a custom jobby.
2. Any way sierra bits can be bastardised to fit (m/c gears?)
3. Go IRS/de-dion
4. Make an axle using a sierra, or other, diff (yes I'm serious!)
All comments welcome, those that are helpful and constructive even more so.
p.s. I'm sticking with 13" wheels
pps. 3.54 and 3.89 diffs anybody?
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zilspeed
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| posted on 14/3/05 at 09:20 PM |
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This is almost blindingly simple.
I think.
GTS De dion axle - fits your chassis and allows Sierra diff.
Gawd - I hope I'm right.
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chrism
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| posted on 14/3/05 at 10:04 PM |
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I got this excel spread sheet from Yahoo groups I think, It calculates speeds in gear for given bikes and diff ratios.
If the rev limit is 1100rpm then the top speed would be 95mph with 3.89 or 105mph with the 3.54.
It does seem to be the lowest gearing of the few bikes in there.
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A little hard work never killed anyone, but why take the risk!
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Kissy
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| posted on 14/3/05 at 10:28 PM |
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Chris, trust me, I've done the sums. The CBR has a low speed output at the sprocket, god knows why (somebody sowed this seed of doubt with me a
while back). Just did another check: taking the tyre circumference and diff/final drives cumulatively I am ~44% down on the bike ratios, therefore
147 becomes a theorectical 83.
Cheers Zil, Gawd, I hope you're right!
Just wonder how much welding I'll have to do to get the diff mounts in. Car weighed in at 430kg wet. How much will a de-dion add to it?
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tks
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| posted on 15/3/05 at 12:47 AM |
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clutch
did you already looked / thinked @ your clutch??
how do you know if it loses for 100%??
can you make/show some pics of the M/C used for it??
have same prob..
TKS
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Kissy
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| posted on 15/3/05 at 07:56 AM |
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tks: You have u2u
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locoboy
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| posted on 15/3/05 at 09:56 AM |
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Kissy,
Am i right in thinking that you are using a modded F27 Chassis?
If you are i have plans for the rear end IRS for a F27, a mate of mine is already looking at taking on the conversion next winter.
Might be worth a go, at least it will free up a lot more diff ratios for you. I estamlished early on that the CBR was one of the more poorly geared
engines available thats why im looking for a 3.38 to chop about the internals and make an LSD out of it. would still top out about 110 i think.
ATB
Locoboy
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Kissy
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| posted on 16/3/05 at 08:10 AM |
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It's more locost than F27. Mine is a 'ground up rebuild with updates'! Hence has trailing links to rear axle. Could never
understand why Steve Porter used forward facing links. His answer was "...Bugatti did it...", my reply was that even Etorre got it wrong
sometimes. What rpm did you calculate 110 being achieved at with a 3.38?
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locoboy
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| posted on 16/3/05 at 09:11 AM |
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cant remember the rpm but i seem to just remember the 110mph bit, maybe i was pissed at the time and it was nothing like 110?
ATB
Locoboy
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jambojeef
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| posted on 16/3/05 at 04:23 PM |
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HI there,
Yep - this is a problem for me too!
Heres the cure - as far as I can tell anyway...
According to the bike gear ratio calculator posted earlier on (which I have used to work out my ratios) I'll be getting around about 120-125mph
with a 3.38 rear diff and 195/50/15 wheels and tyres running at 10,000 rpm in 6th.
I can live with that as a top speed - its just the sligt buzziness on long journeys which might get to me after a while but it'll be worth it
for the low down acceleration - just get ear plugs!!
Jeef
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bike_power
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| posted on 16/3/05 at 07:10 PM |
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BMW diffs come down as low as 2.56:1, E36 325 TD, you can also get 2.9 something then 3.07, 3.15 etc. They're plentyful, cheapish and the case
can be modified by welding on a couple of bracks and grinding off a couple of others to make it compatible with Sierra chassis mounts.
Bit heavier than a Sierra diff though. Can get the LSD gubbins too for £200 extra.
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Kissy
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| posted on 16/3/05 at 09:14 PM |
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Nice one, I've also seen an X-Type Jag diff on ebay with suitably high ratio (diesel), but he was being a bit greedy (can't think where
he got a brand new diff from??). I can't believe someone has not, at some time, made a high ratio c/w & p for the english axle - what are
the chances of modifying those out of IRS diffs??
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Kissy
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| posted on 16/3/05 at 09:15 PM |
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Jambo, is that chart referring to the CBR1000F or RR? Just a thought.
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locoboy
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| posted on 17/3/05 at 09:04 AM |
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I recon its the 1000F , isnt the RR a fireblade?
ATB
Locoboy
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Kissy
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| posted on 17/3/05 at 11:32 AM |
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Yeah it's the latest 'blade - just waiting for one to pop up in a car! Somebody must have dropped their CBR1000RR by now.
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trikerneil
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 posted on 18/3/05 at 01:00 AM |
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Diff ratios
This diff ratio thing is a problem for Trike builders too. The best Diff I could come up with was a SIERRA 2.3 V6 Mk1 Ghia on a "Y" plate
it had a 3.14:1 diff. the same diff may be fitted to the Diesels. Look for a donor with a "M" on the VIN plate.
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Kissy
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| posted on 18/3/05 at 07:58 AM |
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I've just taken a flyer on a Mustang diff on ebay (internals only) 7.5", 2.46:1. It really is a flyer as I am hoping to get the bits into
either a Sierra or English diff, bought for 10 quid. I'm keeping my options open as I may do GTS de-dion. Whatever there has to be a way to
get high ratios into these diffs without making custom gears.
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jambojeef
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| posted on 18/3/05 at 02:11 PM |
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Yep - is the CBR1000F - I've got the Haynes if you want all the gear ratios and primary reduction onto the clutch basket if you want it?
Have you got it sorted now?
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Kissy
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| posted on 21/3/05 at 02:04 PM |
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Not sorted, but adamant my sums are good! Have just bought s/h GTS de-dion beam, so on lookout for the other bits now!
Disc-braked English axle 3.89 & 3.54 ratios, all brackets, and discs (no calipers I'm keeping them) - any takers??
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mattpilmoor
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| posted on 23/3/05 at 03:29 PM |
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Are bigger wheels and tyres not an option?
Measure twice - Cut once - Still f*!K it up!
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Kissy
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| posted on 24/3/05 at 09:03 AM |
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I want to stick with 13", partly aesthetics, partly weight/drag, partly clearances. Now have GTS de-dion beam. Am also looking at the
possibilities of getting other CWs & Ps into the english axle - just to be different, and for the challenge.
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Coose
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| posted on 24/3/05 at 09:50 AM |
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Bah.... You advertise your 3.54 now that I've got one! 
Spin 'er off Well...
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mattpilmoor
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| posted on 24/3/05 at 01:27 PM |
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Fair enough. I hope mine's OK i got 16" and a 3.54 to help resolve the gearing problem but the offsets are very large so i've just
ordered some spacers to stop them rubbing on the trailing arms, hopefully this'll solve the problem - if not they'll be going on Ebay!
Measure twice - Cut once - Still f*!K it up!
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Kissy
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| posted on 24/3/05 at 01:30 PM |
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That sounds a bit more serious if the offset is that profound. Are they intended for RWD application? Sure you can correct for the rear wheels, but
what about the fronts, and your geometry (KPI etc)?
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Shandylegs
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| posted on 24/3/05 at 05:06 PM |
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I'm currently stuck with the same CBR gearing problem and was considering going the bigger wheel route to get round this.
Matt - Is your wheel offet positive or negative. I thought most common wheels have a negative offet, meaning if your wheel are catching on the inside
a greater offset is required.
Is this correct or I have got things the wrong way round (Again!)?
Thanks.....
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