It seems like I'm seeing this more and more these days. People using sport bike rear coilover shocks on cars. I wanted to get everyone's opinion on this. I'm curious if anyone has had experience doing it, and what they thought. It seems like you can pick up a pretty nice coilover shock for a bike a lot cheaper then a set of QA1's of AFCO's.
do they put 4 on a corner or something? what car is light enough that that works?
Stripped-out LBCs and Locosts from what I've seen.
Most of then are 700+lb/in springs some as high as 1300-1500. The biggest issue is low travel. 2.0-2.5". This causes issues as the motion ratios that give good travel can cause the wheel rates to be a bit low. If your using them on an low travel suspension you can get 3-4" of suspension travel with decent wheel rates. If your car has 350-500lb corner rates you can probably make them work OK.
Another issue is they are set up with preload. This will result in reduced or no droop travel and may require custom spring perches. Some have full threaded bodies so this isn't an issue.
They are all high quality with loads of adjustment and cheap. I'd like to tell you how great they work but mine this far only work in the garage as the car isn't running yet.
Thanks for the info guys. I was looking into them for the rear of my GT6. I'm limited on space and haven't decided on using a really short coilover or build a push rod type suspension. The motorcycle coilovers seem'd like a compact inexpensive choice.
What about snowmobiles and ATVs? They'd be a little heavier ...
It's not just about weight, the pivot link geometry is why bikes use such super high compared to the weight spring rates. Do snowmobiles / Atv's use pivot links? If so you would need to compare the dimension differences between them and a motorcycle to figure out comparable wheel rates.....
Here's another thing to ponder:
A common goof with motion ratios is forgetting to square the ratio to get the wheel rate from the spring rate. E.g. if you mount the shock halfway out the arm, the wheel rate is 1/4 the spring rate, because the force at the wheel is half the force at the spring, but also, the spring is only compressed half as far for a given movement.
So, that's a common one, but here's another that just dawned on me:
While a spring's that leverage is linear and works with displacement, dampers vary their force based on the velocity of the shaft, and it's not a linear relationship. Cartridge dampers make things considerably more complex, but in general a piston in fluid will have its force increase as the cube (? IIRC) of velocity.
So moving a shock designed to work at shaft velocities of 1:8 wheel velocity on a bike and putting it on a car where it'll be moving at more like 1:2, it'll be in a drastically steeper part of the damping curve, won't it?
I'm thinking out loud here, and I really don't know off the top of my head what leverage ratios bikes run (I think they're progressive via linkage, but what range?); I'm assuming that at 60mph going over bumps, vertical wheel velocity will be similar between bikes and cars; and this doesn't get into high/mid/low-speed damping ranges...
Just to sketch it out a bit further, if a bump generates a wheel speed of 5 m/s...
... and if a bike's leverage ratio is 1:8...
... and if the bike's force at the piston is X with the piston traveling 5/8 m/s...
... making the force at the wheel X/8 (1/8 of the piston force)...
... and if it does increase as the cube of velocity...
... and if the car's leverage ratio is 1:2...
... then the car's piston speed would be 5/2 m/s...
EDIT FOR POOR, POOR MATH SKILLS:
... and the car's piston force would be ((5/2)^3/(5/8)^3)X ~> 64X...
... making the force at the wheel (64/2)X or 32X...
I can see a car needing more damping than a bike, 32 times the wheel force for a given velocity? Perhaps rather than getting anywhere near that, it's just that a car would be operating in the "high speed damping" range of a bike shock virtually all the time, which really eliminates one of the advantages of the high-end bike dampers.
I use YZF-R1's on my MG Midget. They work fine. You can put any 7" 2.25 ID spring on them. I'm using 350lb on the front and the YZF stock 500lb on the back. With bumpstop, about 2" stroke, if removed, about 2.9".
When I had previously looked into do this, the Hayabusa was one of the best combination of availability, stroke length, and spring rate. This resulted in an adjustable coilover you could get on ebay for $25-$50 each with one of the highest total pounds of force required to fully compress it...Of course it has been a few years since I last looked into it, so I'm not sure what other shocks have come or gone that could also fit the bill.
The Hayabusa coilovers were listed as a 2.8" stroke, although I measured ~2.0" to the factory bumpstop, and either a 732lb/in (early) or 810lb/in (late) spring rate. The biggest drawback on the Busa shocks is probably the awkwardly located reservoir. If anybody is interested in procuring an early one, just let me know.
Damping and droop travel (preload) are both probably going to be less-than-ideal when installed into a car, but also might be able to work surprisingly well too.
Teh E36 M3 wrote: I use YZF-R1's on my MG Midget. They work fine. You can put any 7" 2.25 ID spring on them. I'm using 350lb on the front and the YZF stock 500lb on the back. With bumpstop, about 2" stroke, if removed, about 2.9".
Why such high spring rates on such a small car?
Ohlins sponsored our Formula SAE team and we used modified snowmobile shocks. FWIW
The Abomination has R1 rear shocks on it all the way around. I'm not sure of the spring rates. Shoot Curmudgeon a PM. He's the one that built the car.
MKI_GT6 wrote:Teh E36 M3 wrote: I use YZF-R1's on my MG Midget. They work fine. You can put any 7" 2.25 ID spring on them. I'm using 350lb on the front and the YZF stock 500lb on the back. With bumpstop, about 2" stroke, if removed, about 2.9".Why such high spring rates on such a small car?
To meet my requirements. Did a lot of suspension geometry design on this- it has a miata-based independent rear and completely redesigned dual a-arm front with Miata spindles all around. I guess I didn't mention that.
I am looking into this for an Insight that I will probably be bring home tonight. What about dirt bike shocks? Much longer stroke and softer springs
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